AMIE Notes for All Subjects Diploma Stream

2009-02-23T21:47:00.000-08:00

Questions

2008-09-30T23:52:00.000-07:00

QUESTIONS
1. How can you explain the term design? Explain the process of mechanical design. Discuss the role of creativity in the design process (S’94, 8M)
2. The design of product is …..........customer expectations. (S’99, S’94)
3. .…………get first preference in design
Ans. Functional requirements (S’93)
4. Explain the meaning of
(i) Conceptual design
(ii) Functional design
(iii) Production design. Give suitable examples for each. (S’03)
Questions
1. What are the characteristics features of system design, assembly/sub-assembly design and component design? Explain briefly with the help of examples. [S'93, 5M]
2. Distinguish between functional design and industrial design. [W'93]
3. Discuss the meanings of conceptual design, creative design, adoptive design and variant design. [S'97]
4. What are the three main types of design? Give a comparative analysis. [W'00, W '97]
1. Explain the difference between creative design, adoptive design and variant design. [S'02 W'98]
2. Designing for function involves the use and knowledge of ……………..
Ans. Eng. Sciences [W '94]
8. Explain the meaning of
(i) Conceptual design, (ii) Functional design and (iii) production design. Give suitable example of each.[S0'3]
10. Explain layout design. [S0'2]
QUESTIONS
1. How can you explain the term design? Explain the process of mechanical design. Discuss the role of creativity in the designs process. (S94. 8M)
2. The mechanical design process normally has six stages and amongst them the three stage are ----- ------ -------(S99, S94, 1 M)
3. What is morphology of design? Explain the various steps with the help of block diagram (W.95)
4. The three stages of design are…………(W 96)
5. State the different phases that are involved in morphology of design (S.96)
6. Briefly discuss the concept of creativity as applicable for solving design problems (W 98. 6M)
7. What makes the design process tortuous?Explain (W99,6M)
8. The creative design process can be considered to be(S93)
9. Discuss creativity and creative design. Use examples to explain. (W 95)
10. What do you understand by intuition (S 01)
11. Draw a flow-chart showing different stages of engineering design. Explain why some stages are repeated several times.(S.93.5M)
12. What feedback loops provide information for the redesign of products and the productive systems. (W’93)
13. The process of design by evolution adopted by craftsman is a …………..
Ans. Slow process of design development(W’94)
14. With suitable examples, compare ‘Design by evolution’ and ‘Design by innovation’. (S 96)
15. Enumerate the steps in Engg. Design process and explain (W’96)
16. Justify the statement with reasons ‘Modern design problems cannot be handled by traditional methods’. (S’97, W’98)
17. Good design requires both------ --------.
Ans. Analysis and Synthesis. (S’93)
18. Define creative design routes. What are the stages of these routes, Explain these in brief. (S’00)
19. Explain the process involved in creativity. What are the various qualities of creative designer? Give the brief description of these. (S’00).
20. What do you mean by creative design routes. Write down the different statements about creativity and creative designers. (S’01)
21. Compare the design synthesis and design analysis. Explain the basics procedure of design synthesis giving suitable examples. (S ’02).
22. What are the common features and differences between creative design activities and Engg? Design activities. Explain briefly with the help of examples. (W’94)
23. Discuss the divergence, transformation, and convergence phases in the design of a new product. (S’97)
24. What are the three different stages in the design process? Explain with example. (W’99)
25. What are the most important steps involved in the design process? Explain? (W’00)
26. What are the methods currently being adopted for design process using advanced technology? (W’00)
27. Name various phases in design morphology. Explain these in brief. (S’01)
28. Explain Engg. Design (S’01)
29. What major steps are involved in design process? Briefly explain each one (W’01).
30. What do you understand by the design process? List out the various phases involved and explain them briefly. (S’02)
31. Give the checklist for an engg. Design problem. (W’98)
32. ___ is one of the most powerful aids to creativity in design.(Use of analogy) (W ’94).
33. What do you understand by the term “creativity”? What are its requirements? (’03).
34. Discuss the stages in engineering design process with the help of example. (S 05)
35. Explain ‘Design processes. Illustrate the steps followed with the help of a figure. Also explain the flow of work during the design process. (W 05, 8M)
What do you understand by ‘morphology of design’? Discuss the phases of feasibility study, preliminary design and detailed design.
Questions
1. List hierarchy of human needs that motivate individuals. [W’96]
2. Give one need statement for each of the following
Bicycle (ii) Voltage stabilizer (iii) Personnel Computer [S’93]
3. Explain the steps involved in identification of a problem by a designer [S’96]
4. Every product is made in response to……….of individual or society.
Ans. needs [S’97]
5. Enumerate and explain variety of needs which can generate ideas for the
Development of new product.
Questions
1. Market research is necessary before starting the production of any product.
(True) [S '97]
2. Write a short note on – Product planning and task classification. [S '01]

CHAPTER 5

2008-07-29T03:59:00.000-07:00

5.1 Introduction
Once the top management of an organisation recognized a need to develop a product, it will go for product design, only if,
- the purposed product will guarantee a handsome profit
- the market conditions are favorable in respect of competition.
- the necessary resources are available
- the purposed design is worthwhile.
5.2 Feasibility Study.
The starting point of a design project is a need. Once the need has been identified, the company has to ensure the worth of the project. Feasibility study is a preliminary analysis for making a decision regarding the design project, to be forwarded or not. If the feasibility study reveals that the proposed design project does not bring comfortable revenue, or the design demands huge investments beyond the capacity of the organisation, the project is dropped.
5.3 .Product Planning [S 01]
Planning is the process used to develop a scheme for scheduling and committing the resources of time, money and people. A plan shows how a project will be initiated, organized, co-coordinated and monitored. A product plan is a decision-making as regards to the design and manufacture of a product, by considering the revenues from different products. For example assume that a company already manufacturing 3 products, say P1, P2 and P3 identifies a need to design a new product ‘N’. Owing to the design and manufacture of the new product, the production volume, and hence revenue from products P1, P2,and P3 may be affected (due to re-allocation of company resources such as raw materials, machineries). In this situation, the company has to decide a time-schedule for the design and manufacture of the new product. Such plan made by the management is called the product plan. It must contain the time-as well as resource allocation for each of the products. More over it will result in optimum and efficient use of resources. After the product plan in made, the management begins a project for a new product design.
5.4. Organisation Of Design Group
The complexity of mechanical devices has grown rapidly over the last 200 years. For example Boeing 747 aircraft (which has over 50,000 components) required over 10 thousand persons’ years of design time. Thousands of designers worked over a three-year period on the project. These show that, design work is generally done by a team or group. A design team may include thousands of design and manufacturing engineers, material scientists, technicians, purchasing agents, drafters, and quality control specialists, all working over many years.
The first phase in any design process is identification of needs. Needs may be identified by market survey, the desire to improve an existing product or even by the development of a technology.
Since any design activity consumes company resources like money, people and equipments etc. –the planning of these resources is the next phase after need- identification. Planning means allocation of resources such as money, people etc. The first step in planning is to form a design team.
5.5. Members of Design Team
Following is a list of individuals needed in a design team. Their titles may vary from company to company.
1. Design Engineer.
This person is responsible for suggesting ideas for the proposed product. For that, he must clearly understand needs for the product as well as its engineering requirements. Hence, he must posses both creative and analytical skills. He must be an engineering graduate having vast experience in the particular product area.
2. Marketing Manager.
He is responsible for success of the product in the market. He is a link between the product and the customer. He always sees “whether the customer like this product?
3. Manufacturing Engineer.
He knows the best manufacturing process suitable for the production of the particular product. He can give advice on the various manufacturing processes available in the industry.
4. Detailer
In many companies the design engineer is responsible for specification development, planning, conceptual design and the early stages of product design. The project is then turned over to detailers who finishes the details, develops manufacturing and assembly documents.
5. Drafter
A drafter aids the design engineer and detailer by making drawing of the product. In many companies the detailer and the drafter are the same individual.
6. Technician.
The technicians aid the design engineer in developing test-apparatus, performing experiments etc.
7. Materials Specialist.
In some products, the choice of the material is based on availability. In some other cases, a certain material is to be chosen according to some features of the product. Material specialist can give advice on properties of different materials.
8. Quality Control Specialist.
A quality control specialist observes how well the product meets specifications. This inspection is done on finished products as well as raw materials purchased from vendors.
9. Industrial Engineer.
Industrial designers are responsible for how a product looks and how well it interacts with customers. They generally have background in fine arts and in human factor analysis.
10. Assembly Manager.
The assembly manager is responsible for putting the product together. Note that assembly process is an important aspect of product design.
11. Suppliers’ Representative.
As part of product development, the company may purchase components or sub-assemblies from out-sources. In that case, the representative of the supplier of the specified component must be included in the design team.

5.6 Organisational Structure of Design Teams
Since a design project requires individuals with different fields of expertise, they can be organised into different structures. Listed below are the five organisational structures. The number in the bracket shows the percentage of design projects that use that particular organisation structure.
1. Project matrix, (28%)
It is an organisation structure having the features of project and matrix organisations.
2. Functional matrix (26%)
It is another organisational structure obtained by combining functional as well as matrix organisations.
3. Balanced Matrix (16%)
Here the project manager and functional manager work together. A project manager is assigned to oversee the project, and the responsibility and authority for completing the project rests with functional managers.
4. Project Team (16%)
A project manager is put in charge of a project team composed of a core group of personnels from several functional areas or groups assigned on a full time basis.
5. Functional Organisation (13%)
Each project is assigned to a relevant functional area or group within a functional area. A functional area focuses on a single discipline.
5.7. Task Clarification [S 01]
A project plan is a document that defines the tasks necessary to be completed during a design process. A project plan is used to keep the project under control. It helps the design team and management to know how the project is actually progressing.
There are five steps to establish a plan. They are,
1. Identify the task
2. State the objective of each task
3. Estimate Personnel’s, time, resources required.
4. Develop a sequence for these tasks.
5. Estimate product development cost.

Step 1 Identify the tasks
In the first step of the planning of the design project, the different tasks needed to bring the problem from its initial state to the final products are identified. The tasks are the activities to be performed during the design process. Given below is a list of tasks drafted by a design team, for the development of a certain product.
a. Collect and evaluate customer requirements and competition scenario.
b. Establish two concepts for product development.
c. Develop final prototype.
d. Test prototype No1 and select one design for finalisation.
e. Redesign and produce proto type No2.
f. Field test prototype No2.
g. Complete production documentation.
h. Develop marketing plan.
i. Develop quality control procedures.
j. Prepare patent applications.
k. Establish product appearance.
l. Develop packaging.
Step .2. State the objective for each task.
Even though the tasks are initially identified, they need to be refined to ensure that the results of the activities are the stated objectives. For example, for the task No. (a) above, the objective is to collect information required for developing specification.
Step 3: Estimate the Personnel, Time & other Resources Required.
Completion of each of the tasks listed above will consume resources such as personnel, time etc. An estimate of the requirement of resources may look like:
Task Personnel/time
Collecting data Two market surveyors, two months
Concept generation Two designers, two week.
Step 4 Develop a Sequence for the tasks
The next step is scheduling of tasks-the purpose is to ensure that each task is completed, before its result is needed. CPM is the best method to accomplish this.
Step 5 Estimate Product Development Cost
On the basis of the above steps, the costs for developing the product can be estimated. Normally design cost is only about 5% of manufacturing cost.
The above plan developed in the early stage of the design has to be refined as the project progresses.
QUESTIONS
1. How can you explain the term design? Explain the process of mechanical design. Discuss the role of creativity in the design process (S’94, 8M)
2. The design of product is …..........customer expectations. (S’99, S’94)
3. .…………get first preference in design
Ans. Functional requirements (S’93)
4. Explain the meaning of
(i) Conceptual design
(ii) Functional design
(iii) Production design. Give suitable examples for each. (S’03)
Questions
1. What are the characteristics features of system design, assembly/sub-assembly design and component design? Explain briefly with the help of examples. [S'93, 5M]
2. Distinguish between functional design and industrial design. [W'93]
3. Discuss the meanings of conceptual design, creative design, adoptive design and variant design. [S'97]
4. What are the three main types of design? Give a comparative analysis. [W'00, W '97]
1. Explain the difference between creative design, adoptive design and variant design. [S'02 W'98]
2. Designing for function involves the use and knowledge of ……………..
Ans. Eng. Sciences [W '94]
8. Explain the meaning of
(i) Conceptual design, (ii) Functional design and (iii) production design. Give suitable example of each.[S0'3]
10. Explain layout design. [S0'2]
QUESTIONS
1. How can you explain the term design? Explain the process of mechanical design. Discuss the role of creativity in the designs process. (S94. 8M)
2. The mechanical design process normally has six stages and amongst them the three stage are ----- ------ -------(S99, S94, 1 M)
3. What is morphology of design? Explain the various steps with the help of block diagram (W.95)
4. The three stages of design are…………(W 96)
5. State the different phases that are involved in morphology of design (S.96)
6. Briefly discuss the concept of creativity as applicable for solving design problems (W 98. 6M)
7. What makes the design process tortuous?Explain (W99,6M)
8. The creative design process can be considered to be(S93)
9. Discuss creativity and creative design. Use examples to explain. (W 95)
10. What do you understand by intuition (S 01)
11. Draw a flow-chart showing different stages of engineering design. Explain why some stages are repeated several times.(S.93.5M)
12. What feedback loops provide information for the redesign of products and the productive systems. (W’93)
13. The process of design by evolution adopted by craftsman is a …………..
Ans. Slow process of design development(W’94)
14. With suitable examples, compare ‘Design by evolution’ and ‘Design by innovation’. (S 96)
15. Enumerate the steps in Engg. Design process and explain (W’96)
16. Justify the statement with reasons ‘Modern design problems cannot be handled by traditional methods’. (S’97, W’98)
17. Good design requires both------ --------.
Ans. Analysis and Synthesis. (S’93)
18. Define creative design routes. What are the stages of these routes, Explain these in brief. (S’00)
19. Explain the process involved in creativity. What are the various qualities of creative designer? Give the brief description of these. (S’00).
20. What do you mean by creative design routes. Write down the different statements about creativity and creative designers. (S’01)
21. Compare the design synthesis and design analysis. Explain the basics procedure of design synthesis giving suitable examples. (S ’02).
22. What are the common features and differences between creative design activities and Engg? Design activities. Explain briefly with the help of examples. (W’94)
23. Discuss the divergence, transformation, and convergence phases in the design of a new product. (S’97)
24. What are the three different stages in the design process? Explain with example. (W’99)
25. What are the most important steps involved in the design process? Explain? (W’00)
26. What are the methods currently being adopted for design process using advanced technology? (W’00)
27. Name various phases in design morphology. Explain these in brief. (S’01)
28. Explain Engg. Design (S’01)
29. What major steps are involved in design process? Briefly explain each one (W’01).
30. What do you understand by the design process? List out the various phases involved and explain them briefly. (S’02)
31. Give the checklist for an engg. Design problem. (W’98)
32. ___ is one of the most powerful aids to creativity in design.(Use of analogy) (W ’94).
33. What do you understand by the term “creativity”? What are its requirements? (’03).
34. Discuss the stages in engineering design process with the help of example. (S 05)
35. Explain ‘Design processes. Illustrate the steps followed with the help of a figure. Also explain the flow of work during the design process. (W 05, 8M)
What do you understand by ‘morphology of design’? Discuss the phases of feasibility study, preliminary design and detailed design.
Questions
1. List hierarchy of human needs that motivate individuals. [W’96]
2. Give one need statement for each of the following
Bicycle (ii) Voltage stabilizer (iii) Personnel Computer [S’93]
3. Explain the steps involved in identification of a problem by a designer [S’96]
4. Every product is made in response to……….of individual or society.
Ans. needs [S’97]
5. Enumerate and explain variety of needs which can generate ideas for the
Development of new product.
Questions
1. Market research is necessary before starting the production of any product.
(True) [S '97]
2. Write a short note on – Product planning and task classification. [S '01]

CHAPTER 4

2008-07-29T03:57:00.000-07:00

4.1. What is a need?
A need can be defined as a personnel unfulfilled vacancy which determines and organizes all psychological and behavioral activities in the direction of fulfilling the vacancy
A product can be product and marketed only if it is ‘needed’ by the customer. A person buys a pen because he ‘needs’ to write. A patient ‘needs’ something that can cure his illness. These examples show that needs are nothing but a scarcity or problem or wants felt by a person, device or a system. In fact a designer’s goal is to find solutions to such problems
4.2. Hierarchy of Human needs (W’ 96)
Maslow developed a hierarchy of human needs as given below
1. Physiological needs
- These are the basic needs of the body- For example, thirst, hunger, sex, sleep etc.
2. Safety and security needs
For a person whose physiological needs are met, the new emerging needs are safety needs. These include, protection against danger, threat etc.
3. Social needs
Once the physiological and safety needs are met, the next dominant need is social need. For example he/she want to love and be loved, he want to be “in group”, etc.
4. Psychological needs
These are the needs for self-respect and self- esteem, and for recognition.
5. Self-fulfillment needs
These are the needs for the realisation of one’s full potential through self-development, creativity, and self-expression.
4.3. Identification/Recognition of Needs (W 96)
The beginning of any design process is the recognition of need or problem. When a turner hears an awkward noise from some part of the lathe he identifies/ recognises a need. i.e. the lathe requires repair. When the sales personnel observes that their customers are always complaining of poor performance of the products, a need to develop a better product is identified. Similarly, when the customers are unsatisfied with the present ‘model’, a new need is recognised.
Needs can be identified from,
* Careful market analysis
* Statements made by politicians from their observations
* Interpretations of a community’s requirements
* Trends in other parts of the world
4.4. Variety of Needs [S’00]
Following are the needs, which can generate ideas for the development of new products.
(i). Variation of an existing product.
This could be a change in a single or a few parameters of an existing product.
Eg - Changing the length of a cylinder.
-Changing the power of a motor, etc.
(i) Improvements in the existing product.
This implies the need to redesign some of the features of an existing product. Such needs can arise, when
-Customers want a new feature or better performance than existing features
-A vendor can no longer supply components or materials that had been used so far
-Manufacturing or assembly departments identifies a quality improvement
-Invention of a new technology that can be incorporated in the existing design.
(iii) A change in production model
Whenever the production model changes from job-shop to mass, a corresponding change in product design may be demanded. For example, there is more tendency to buy off-the shelf components for short-run products.
Whatever may be the situation, a company has to identify or locate a need before the production of any device. This crucial step is called Recognition/ Identification of need.
Examples:
1. With the free-entry of Chinese products to Indian market, manufacturers in India recognize a need to sell their products at a lower price.
2. When a company observes that their products do not perform well, the company recognizes a need to re-design it.
4.5 Need Statement
Once the need has recognized, the next step is to prepare the need statement. It is a general statement specifying the problem for which a solution is required. In other words-It is the objective of design, expressed in the form of a statement.
Need Statement – Examples [S ‘93]
Give one need statement for each of the following
Bicycle
Voltage stabilizers
Personnel Computer
i). Bicycle: -
The need statement for a bicycle could be “A device for a common person to travel reasonable distance comfortably with least effort” –“The initial cost should be low- and be as light as possible, have adequate life, be easy to maintain etc “
(ii). Voltage stabilizer
“A solid state noiseless electrical device of adequate power rating to provide continuously an output at constant voltage, accepting the input power at varying voltage between the limits__and__volts “. The indications for input and output voltage levels may be provided.
iii). Personnel Computer “A computing device to accept input data, manipulate it according to a set of instructions and provide the desired output on CRT and printer”

Remaining part of chapter 3

2008-07-29T03:49:00.000-07:00

3.7 Detailed Morphology of Design
A design project goes through a number of time phases. Morphology of design refers to the collection of these time phases. The morphology of design as put forward by Morris Asimow can be elaborated as given below. It consists of seven phases.
Phase 1. Feasibility Study.
This stage is also called conceptual design. A design project always begins with a feasibility study. The purpose and activities during feasibility study are
¬ To ascertain there really exists a need [ie the existence of need must be supported by necessary evidences, rather than the outcome of one’s fancy]
¬ Search for a number of possible solutions
¬ Evaluate the solutions
i.e. is it physically realisable?
Is it economically worthwhile?
Is it within our financial capacity?
Phase 2 Preliminary (Embodiment) Design.
This is the stage art which the concept generated in the feasibility study is carefully developed. The important activities done at this stage are:
* Model building & testing
* Study the advantages and disadvantages of different solutions.
* Check for performance, quality strength, aesthetics etc.

Phase III: Detail Design
Its purpose is to furnish the complete engineering description of the tested product. The arrangement, from, dimensions, tolerances and surface properties of all individual parts are determined. Also, the materials to be used and the manufacturing process to be adopted etc. are decided. Finally, complete prototype is tested.
Phase IV: Planning for manufacture
This phase includes all the production planning and control activities necessary for the manufacture of the product. The main tasks at this phase are
* Preparation of process sheet, i.e. the document containing a sequential list of manufacturing processes.
* Specify the condition of row materials.
* Specify tools & machine requirements.
* Estimation of production cost.
* Specify the requirement in the plant.
* Planning QC systems.
* Planning for production control.
* Planning for information flow system etc.
Phase V: Planning for Distribution
The economic success of a design depends on the skill exercised in marketing. Hence, this phase aims at planning an effective distribution system. Different activities of this phase are
* Designing the packing of the product.
* Planning effective and economic warehousing systems.
* Planning advertisement techniques
* Designing the product for effective distribution in the prevailing conditions.
Phase VI Planning for Consumption/use
The purpose of this phase is to incorporate in the design all necessary user- oriented features. The various steps are
* Design for maintenance
* Design for reliability
* Design for convenience in use
* Design for aesthetic features
* Design for prolonged life
* Design for product improvement on the basis of service data.
Phase VII: Planning for Retirement.
This is the phase that takes into account when the product has reached the end of useful life. A product may retire when
* It does not function properly
* Another competitive design emerges
* Changes of taste or fashion
The various steps in this phase are
* Design for several levels of use
* Design to reduce the rate of obsolescence.
* Examine service-terminated products to obtain useful information

3.8. Methods of Innovative Design
As we know, innovative design is an organized, systematized and logical approach for solving a design problem. There are two design methods for innovative design.
(i) Design by creative design route
(ii) Engineering Design
(i) Design by creative routs [Creative Design]
This is a design method that demands maximum ‘creativity’ from the part of the designer. Hence this method is also called creative design. Here the designer finds solutions to problems by allowing his creativity aspects grow in a particular manner.
Creativity [S94, W95, W98, S03]
Majority of designs belong to variant design, where the designer simply modifies an existing system. But the success of engineering design depends on the modes of thinking and acting distinctively different from others. A creative designer is distinguished by his ability to synthesize new combinations of ideas and concepts into meaningful and useful forms. Design is commonly thought of as a creative process involving the use of imagination and lateral thinking to create new and different products.
Qualities of a creative designer [S96, S00, S03]
The creative designer is generally a person of average intelligence, a visualiser, a hard worker and a constructive non-conformist with average knowledge about the problem at hand.
Generally, a creative designer has the following qualities.
* Visualization ability.
Creative designers have good ability to visualize, to generate and manipulate visual images in their heads.
* Knowledge
All designers start their job with what they know. During designing, they make minor modifications of what they already know –or, creative designers create new ideas out of bits of old designs they had seen in the past. Hence, they must have knowledge of past designs.
* Ability to manipulate knowledge
The ability to use the same knowledge in a different way is also an important quality of a designer.
* Risk taking
A person who does not take the risk of making mistakes cannot become a good designer. For example, Edison tried hundreds of different light bulb designs before he found the carbon filament.
* Non-conformist
There are two types of non-conformists:-constructive and obstructive. Constructive non-conformists are those who take a firm stand, because they think they are right. Obstructive non-conformists are those who take a stand just to have an opposing view. The constructive non-conformists might generate a good idea. But the obstructive non-conformists will only slow down the design process. Creative designers are constructive non-conformists, and they want to do things in their own way.
* Technique
Creative designers have more than one approach to problem solving. They are prepared to try alternative techniques, till they reach a satisfactory solution.
* Motivation
They always motivate others in the design team. In such a favourable environment creativity is further enhanced.
* Willingness to practice
Creativity comes with practice. Creative designers are ready to practice for a long enough period.
Roadblocks to Creativity
* Fear of making a mistake
* Unwillingness to think and act in a way other than the accepted norm.
* Desire to conform to standard solutions.
* Unwillingness to try new approaches
* Fear of criticism
* Lack of knowledge
* Overconfidence due to past experience
* Unwillingness to reject old solutions
* Fear of authority
* Difficulty in visualization
* Inability to distinguish between cause and effect
* Inability to collect complete information
* Unwillingness to be different

Methods to enhance Creativity
* Use of analogy
* Asking question from different view points
* Memories of past designs
* Competitive products
* Deliberate day-dreaming
* Reading science fictions, etc.

Intuition [S’01]
Intuition means sudden ideas or flashes of inspiration and involves complex associations of ideas, elaborated in subconscious mind. Intuitive ideas lead to a large number of good and even excellent solutions.
Creative Design Route [W95, 94, 98, 9’00]
Creative design route is the procedure through which a creative design is born. The success of this design lies with the creativity of the designer. Creative design route can be practiced by following the sequences shown in figure.
During preparation period, the designer analyses the need and collect all the necessary information required at various stages.

Concentration is the period when the designer digests all the aspects of the problem situation and tries various possible combinations.
The next step is the incubation period. The designer relaxes away from the problem for some time.
Illumination is the sudden insight and throwing up with a solution.
The final step is the verification. Now, testing and inspection of the design is done and the details are completed.
For a designer using creative methods for design, habitual or familiar methods must be avoided.
(ii) ENGINEERING DESIGN (W 96)
Another procedure for obtaining innovative design is Engg. Design. Apart from creativity-approach, this is a logical and intellectual attempt to solve design problems. It largely depends on discoveries and laws of science.
The different steps in Engg. design process is given below: -

Since all design projects are meant for satisfying some need, any design work starts with Recognition of the need. The need for a design is initiated by either a market requirement, the development of a new technology or the desire to improve an existing product.
Once the need has identified, the next step is to define the design problem. This is the most critical step in the design process. The definition of the problem expresses as specifically as possible, what the design is intended to accomplish. It should include objectives and goals, definitions of any special technical terms, the constraints on the design and the criteria that will be used to evaluate the designs.
The success of a design project depends on the clarity in the definition of the problem. Need Analysis is the technique used to define the problem(Chapter 6).
The next step is collecting information. In many phases of deign process a large quantity of information may be required. The required information can be obtained from textbooks, journals, or other agencies (See Art. 6.4)
The conceptualization step involves, finding several design ideas to meet the given need. Inventiveness and creating is very important in this step.
The different ideas conceived are weighted and judged in the evaluation step. The advantages and disadvantages of each idea against its performance, cost aesthetics etc is valued.
After evaluation, the best design is emerged. This final design with every detail is furnished in last step-ie communicating the design.

Common features between Creative Design & Engg. Design (W.94)
(1) The preparation phase in creative design and need analysis in Engg. Design is more or less common. Both steps deal with analyzing the need.
(2) In both design methods brainstorming and Synetics can be applied.
(3) Reviewing is applicable in both design methods.
(4) For both deigns, the success depends on the clarity with which the need statement is prepared.
(5) Testing and inspection is applicable for both designs.
Difference between Creative Designs & Engg, Designs (W 94)
1. Intelligence is not a must for creative design-but the same is desirable in Engg. Design.
2. Creative design is based on use of analogy and synthesis of alternatives – but engineering design is based on proven laws and past experience.
3. Creative design involves phases like incubation, illumination – but no such philosophy is followed in engineering designs.
4. Creative person is highly intuitive and independent in thinking and usually resists working in group – but engineering designers like teamwork.
5. Customs, habits and traditions are enemies of creativity – but the same are required in engineering design.
3.9. Divergence, Transformation & Convergence (S’97 5M)
The entire design process can be said to have composed of three distinct phases Viz. Divergence, Transformation and Convergence phases.
The problem definition, need analysis and conceptualization etc. aims at generating as many ideas as possible to solve a given design problem. Thus, these activities belong to the Divergence phase.
That activity wherein the concept is converted into physical object is termed as transformation phase. The convergence is a narrowing process, where the best optimal solution is tried for, by eliminating unwanted ideas.
3.10. Design Process Using Advanced Technology (W”00)
Although Engineering is a major sector of the economy in a developing country. It has not been benefited greatly from advances in computer technology. Engineers still use computers only in peripheral tasks, such as drafting and analyzing, but not in making fundamental design decisions. Current computer tools such as ‘computer-aided drafting’ are restricted to the end of the design process and play no fundamental role in aiding design. It aids only in the final drafting of the specifications. Computer-aided Design, (CAD) means a class of tools for crating drawing, or the physical description of the object. CAD systems have been sophisticated and 2D and 3D models are available.
The CAD allows the designer to conceptualize objects more easily. The design process in CAD system consists of the following stages.
1) Geometric modeling
2) Analysis and optimization
3) Evaluation4) Documentation and drafting.

Chapter 3 DIGN PROCESS AND ITS STRUCTURES

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3.1. Introduction
Developing a manufacturable product is not an easy job। This chapter presents some methods that help achieve quality products. Rather than making a detailed study, only an overview of designing process is attempted here.

3.2. Features of design process
The following features can be observed in a design process.
* Iteration
* Decision-making
* Conversion of resources
* Satisfaction of need
Design is completed in many phases. In each phase, repeated attempts are required to accomplish the aim. A satisfactory conclusion can be reached on, only after a number of trials.
Decision-making is essential for a designer to select one out of several. A designer often comes across several equally acceptable alternatives to meet some end. In such conflicting situations, designer has to make the best decision.
In any design process, there is conversion of resources such as time, money, talent, materials and other natural resources.
All designs are aimed at satisfying some human need। Needs, whether important or unimportant is the starting point of design.

3.3. How a design is born?
In a broad sense there are two methods by which a design comes into existence.
a. Design by evolution (Traditional Design)
b. Design by innovation (Modern Design)
a. Design by evolution
This implies the traditional method of design in which the objects and articles that we see around has taken its present form by gradual change of time. If one looks at history it can be seen that most of the tools, equipments, implements, took a long time to acquire their present form. Things changed gradually with the passage of time. Each change was made to rectify some defects or difficulties faced by the users. Bicycles, calculators, computers, steam locomotives etc. all went through a process of evolution in which designers tried one concept after another. Even today this process is being used to some extent. However, this evolutionary process is very slow. i.e., it took a very long period of time to occur even a slight modification. The main reason for this slow evolutionary process of design was the absence of proper information and design data records.
In modern design situations the evolutionary methods are not adequate because of the following reasons.
1। The traditional designing did not consider the interdependence of products. They were concerned about only one component /product. But in the modern world, the existence of one product is dependent on another in some way or other.

2। In the past, production was on small scale. Thus the penalty of a wrong design was tolerable. But, in the present time, production is on large-scale basis. As a result, any penalty of a wrong design will cost great loss.

3। Requirements of the customers of today’s world changes so frequently. Traditional design lags behind the advanced product & process technologies available today.

4 Traditional design methods cannot cope with competitive requirements of the modern world.
Due to the above reasons modern design problem cannot be handled by traditional methods.
b. Design by Innovation
Since the traditional design method failed to cope with modern design requirements, nowadays almost all designs are made by innovation. i.e., developments of a product by following scientific and purposeful effort.
The innovative design is entirely different from the past practice of evolutionary design। Here the designer’s task is greatly magnified. He has to design and create something, which did not exist yet. Here he tries to solve the design problem in a systematic and orderly manner. This approach is similar to analytical problem solving.

However, an innovative designer faces the following difficulties.
1. He has to collect and evaluate information on a product, which is non-existing yet.
2. Necessity of analyzing complicated interaction of components.
3. He has to make predictions regarding its performance.
4। He has to ensure the technical and economical feasibility of the product.

Notwithstanding the above difficulties, there are eminent experts like Morris Asimow, J।E. Shigly, Dieter etc have attempted to systematize the design process. This systematized steps in design process is called Morphology of Design. The best way in which any problem can be solved is to break up the problem and to try for a solution in an analytical method. This approach of problem solving is also adopted in the Morphology of design.

3.4. Problem-solving Methodology
Knowingly or unknowingly we follow six basic actions when we try to find solution of any problem।

1. Establish or convince ourselves that there ‘is’ a problem. Or we understand that a solution is needed.
2. Plan how to solve this problem
3. By analyzing the problem we decide what is actually required from the problem-solver. Or we decide the requirements.
4. Generate alternative solutions.
5. Evaluate the alternatives.
6। Present the acceptable solution.

3.5. Morphology of Design.
Morphology means ‘a study of form or structure’। Morphology of design refers to the time based sequencing of design operations. It is a methodology of design by which ideas about things are converted into physical objects. The logical order of different activities or phases in a design project is called the morphology of design.

3.6. Design Process- Simplified ApproachA simplified approach to designing as outlined by Morris Asimow is given below। According to him the entire design process in its basic forms consists of five basic elements as given below

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(c) Parametric Design
Parametric design involves finding values for the features that characterize the object being studied.
Consider a simple example –
We want to design a cylindrical storage tank that must hold 4 m3 of liquid.
The volume is given by
V = r2 l
The tank is described by the parameters, radius 'r', and length l.
Given V = 4 m3 = r2 l
r2 l = 1.273
We can see a number of values for the radius and length, that will satisfy this equation। Each combination-values of r and l gives a possible solution for the design problem.

(d) Original Design
As described in an earlier section, an original design in the development of an assembly or component that did not exist before।

(e) Redesign
The redesign is a modification of an existing product to meet new requirements। It is same as adaptive design. Most design problems solved in industry are for the redesign of an existing product. Suppose a manufacturer of hydraulic cylinders makes a product that is 0.25m long. If the customer needs a cylinder 0.3m long, the manufacturer might lengthen the outer cylinder and the piston rod to meet this special need.

2.3. On the basis of the objective or strategy the designs are of following main types.
A. Production Design
B. Functional Design
C. Optimum डिजाईन

A. Production Design
In production design, the designer designs something in such a way that the cost of producing the product is minimum। That is, the first responsibility of the designer is reduction of production cost. Hence, a production designer is concerned with the ease with which something can be produced, and that at a minimum cost.

B. Functional Design W93
In functional design, the aim is at designing a part or member so as to meet the expected performance level.
Functional design is a way of achieving given requirements।- but the same may the unproducible or costly to produce. A good designer, then, has to consider the production aspects also. A product designed without keeping all these aspects into account, wastes time, money and efforts.

C। Optimum Design [W 95]
It is the best design for given objective function, under the specified constraints।

2.4 On the basis of the field/ area or the domain of design, the following types are important.
1. Mechanical Design
2. Machine Design
3. System Design
4. Assembly/sub-assembly design
5. Computer aided डिजाईन

1. Mechanical Design
It means use of scientific principles, technical information and imagination in the design of a structure,or machine to perform prescribed functions with maximum economy and efficiency।

2. Machine Design
It is the process of achieving a plan for the construction of a machine।

3. System Design
System Design is an iterative decision making process to conceive and implement optimum systems, to solve problems and needs of society।

4. Assembly/sub-assembly design [S 93]
In the design of Assembly/sub-assembly the major criterion is the fulfillment of functional requirements. The assembly has to be designed to meet broad technical parameters and purpose for which it was meant.
The characteristic features are:
¬ The total number of parts used in the design must be minimum.
¬ Sub-assemblies should be capable of being built separately in order to give maximum manufacturing flexibility.
¬ Standard parts may be used.
¬ Flexible parts should be avoided, as they are easily damaged during handling and assembly।

5. Computer aided design [CAD]
It is a design methodology in which the designs take the advantages of digital computer to draw concepts, analyze and evaluate data etc. Computers are largely used in a design office for simulation and prototype study. In modern design, computers have become an indispensable tool.
Other types of designs are
Probabilistic Design
Industrial Design
Probabilistic Design [S 96]
It is a design approach in which design decisions are made using statistical tools. Generally, the external load acting on a body, the properties of materials etc are liable to vary. In probabilistic design, the designer takes into account the variations of such parameters.
Industrial Design [W 93]It is the design made by considering aesthetes, ergonomics and production aspects

CHAPTER 2

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TYPES OF DESIGNS
2.1 The design can be classified in many ways. On the basis of knowledge, skill and creativity required in the designing process, the designs are broadly classified into three types
(i) Adaptive Design (W 95, 97, 98 ‘00)
(ii) Variant Design (S 97, 99)
(iii) Original Design

(i) Adaptive Design
In most design situations the designer’s job is to make a slight modification of the existing design। These are called adaptive designs. This type of design needs no special knowledge or skill. E.g. converting mechanical watches into a new shape.

(ii) Variant Design
This type of design demands considerable scientific training and design ability, in order to modify the existing designs into a new idea, by adopting a new material or a different method of manufacture. In this case, though the designer starts from the existing designs, the final product may be entirely different from the original product.
E।g. converting mechanical watches into quartz watches. Here a new technology is adopted.

(iii) Original Design
Here the designer designs something that did not exist previously। Thus, it is also called new design or innovative design. For making original designs, a lot of research work, knowledge and creativity are essential. A company thinks of new design when there is a new technology available or when there is enough market push. Since this type of design demands maximum creativity from the part of the designer, these are also called creative designs.

2.2 On the basis of the nature of design problem, design may be classified as
(a) Selection design
(b) Configuration design
(c) Parametric design
(d) Original design
(e) Re-design

(a) Selection Design.
It involves choosing one or more items from a list of similar items. We do this by using catalogues.
Eg. -Selection of a bearing from a bearing catalogue
-Selection of a fan for cooling equipment
-Selecting a shaft।

(b) Configuration / Layout / Packaging Design (W 97, S'02)
In this type of problem, all the components have been designed and the problem is how to assemble them into the completed product. This type of design is similar to arranging furniture in a living room.
Consider the packing of electronic components in a laptop computer. A laptop computer has a keyboard, power supply, a main circuit board, a hard disk drive, a floppy disk drive and room for two extension boards. Each component is of known design and has certain constraints on its position. For example, the extension slots must be adjacent to the main circuit board and the keyboard must be in front of the machine.

The different components are shown above. The designer’s aim is to find, how to fit all the components in a case? Where do we put what? One method for solving such problems is to – select a component randomly from the list and position it in the case so that all the constraints on that component are met.
Let's take keyboard first. It is placed in the front. Then we select and place a second component. This procedure is continued until we reach a conflict, or all the components are in the case. If a conflict arises, we back up and try again. Two potential configurations are shown above.

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1.4 Definition of Design: (S ‘94)
Designing is such a vast field that it is defined in several ways. Various definitions of designing as pronounced by well-known designers are
“Design is that which defines solutions to problem which have previously been solved in a different way”
“Design is the conscious human process of planning physical things that display a new form in response to some pre-determined need”.
“Design is an act of collecting all pertinent information for the production of goods and services to meet some human need”.
The design of any component includes two things,
(i) Product design
(ii) Process design
The product design involves the development of specification for a product that will be functionally sound, good in appearance, and will give satisfactory performance for an adequate life.
The process design involves developing methods of manufacture of the products so that the component can be produced at a reasonably low cost.

1.5 History of Design Process
(i) Design by Single Person
(ii) Over-the-wall design
(iii) Simultaneous Engineering
(iv) Concurrent Engineering
(v) Integrated design and Manufacture.
In olden times one person could design and manufacture an entire product. Even for a large project such as the design of a ship or a bridge, one person had sufficient knowledge of the Physics, Materials and manufacturing processes to manage all aspects of the design and construction of the project. This period is referred to as the period of design by single person in the history of design.

By the middle of the 20th century products and manufacturing processes became so complex that, one person could not handle all aspects of design and manufacturing. This situation led to over-the-wall design process.
In this method each functional departments were separated from others, as shown by wall. There was only one-way communications between Customer, Marketing, Engg. Design and production department. The customers ‘throw’ their needs to marketing department. The marketing department may throw the customer needs to the design department, in many instances, orally. The Engg. Design department may conceive a design and hands it over to the manufacturing sections. The manufacturing department interprets that design and makes the product according to what they think suitable. Unfortunately, often what is manufactured by a company using over-the-wall process is not what the customers had in mind. This is due to lack of interaction between the different departments. Thus, this single direction over-the-wall approach is inefficient and costly and may result in poor quality products.
By the early 1980’s the concept of simultaneous engineering emerged. This philosophy emphasized simultaneous development of the manufacturing process- the goal was the simultaneous development of the product and the manufacturing process. This was accomplished by assigning manufacturing representatives to be members of design team, so that they could interact with the design engineers throughout the designs process.
In the 1980’s the simultaneous design philosophy was broadened and called concurrent engineering. A short definition of concurrent engineering is the simultaneous progression of all aspects, at all stages of product development, product specification, design, process and equipment etc. In concurrent engineering the primary focus is on the integration of teams of people having a stake in the product, design tools, and techniques and information about the product and the processes used to develop and manufacture it. Tools and techniques connect the teams with the information. Although many of the tools are computer-based, much design work is still done with pencil and paper. In fact, concurrent engineering is 80% company culture and 20% computer support.
With the advent of computer technology, drastic changes have taken place in the field of design and manufacturing. The result was a completely integrated design and manufacturing system. This system makes a good use of technologies such as CAD/CAM, FMS etc. The computer integrated manufacturing systems (CIMS) moves towards the ‘Factory of the future’. CIMS is necessary for better quality, efficiency and productivity.

CHAPTER 1 DEFINITION OF ENGINEERING DESIGN

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Introduction:
The economic future of India depends on our ability to design, make and sell competitive products. Excellent design and effective manufacture are the pre-requisites of a successive industry. There is a general impression that the quality of Indian products can still be improved. The fact that consumers have lost their confidence on Indian-made products cannot be denied. This problem can be solved only by designing and manufacturing better products through improved methodology. Keeping this in view, the subject “Design and manufacturing” purpose to present the methods and procedures of design and manufacture.
Although engineers are not the only people who design things, the professional practice of engineering is largely concerned with design. It is usually said that design is the essence of engineering.
The ability to design is both a science and an art. The science can be learned through procedures developed by eminent scholars. But the art can be learned only by doing desi

Types of Products
A product is the tangible end result of a manufacturing process and is meant for satisfying human needs. The product can be classified as follows: -
1. Convenience goods
These are less expensive and are clustered around shops and restaurants.

These can be purchased at consumer’s convenience.
E.g. Cigarette, Candy, Magazines etc.

2. Shopping goods
These are expensive and people buy it less frequently.
E.g. Jewellary garments etc.

3. Specialty goods
These are purchased, taking extra pain.
E.g. Rare objects like stamps.

4. Industrial goods.
These are items used in the production of other items.
Eg. Raw materials.
Another way of classifying products is into,
(a) Continuous Products, and
(b) Discrete products
The continuous products are those which are produced in a continuous fashion. For example, plates, sheets, tubes and bars etc are produced in very long lengths, and then these are cut into desired lengths.
On the other hand, discrete products are produced one after another, each in separate units.
On the basis of the output product, the Industry is usually named as continuous industry and discrete industry.

1.3 Requirements in a good product
1. Customer Satisfaction
2. Profit
How to achieve customer satisfaction?
-The product should function properly.
-It must have desired accuracy
-It must have desired reliability
-It must be easy to operate
-It must be serviceable
-It must make minimum space utilization
-It must withstand rough handling
-Pleasant appearances.
-Reasonable price.
How can it be profitable?
-It must be easy to manufacture
-The raw material must be cheap and easily available
-The manufacturing process has to the decided on the basis of quantity to be produced
-It must use standard parts
-It must be easy to pack and distribute.

SYLLABUS OF FUNDAMENTALS OF DESIGN AND MANUFACTURING

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Group A
Engineering design process and its structure. Identification and analysis of need, product design specifications, standards of performance and constraints.

Searching for design concepts; morphological analysis, brainstorming. Evaluation of design concepts for physical reliability, economic feasibility and utility.

Detailed design; design for manufacture, assembly, shipping, maintenance, use, and recyclability.

Design checks for clarity, simplicity, modularity and safety. Standardization and size ranges.

Reliability and robust design. Design organisation and communication, . technical reports, drawings, presentations and models.

Concept of manufacturing; classification of manufacturing processes. Fundamentals of casting. Basic understanding of commonly used casting processes (sand casting, investment casting and permanent mould casting processes).

Fundamentals of metal forming; hot and cold working; basic understanding of primary metal forming processes (rolling, forging, extrusion and drawing processes, punching and blanking).

Fundamentals of metal cutting; tool-work interaction for production of machined surfaces. Classification of machining processes. Basic machining operations (turning, shaping, planning, drilling and milling processes).

Group B

Fundamentals of grinding and finishing; overview of unconventional machining processes; fundamentals of welding processes; introduction to primary welding and allied processes; selection of manufacturing processes. Design for manufacturability.

Need for integration-commercial, economic and technological perspective; basic tools of integration; concept of a system. introduction to information technology and its elements.
Introduction to group technology; introduction to simulation and database management systems.

Elements of integration:-eontrol1ers, sensors, robots, automated machines; AGVs, AS, RS, etc.

Product and process design- for integration; design for economic manufacturing; design for manufacturing integration.

Introduction to computer aided process planning; selection of machine tools.

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Group B
Heat treatment . Iron-carbon system. Annealing, normalising, hardening,. critical cooling rate, hardenability, age hardening, surface hardening, tempering.

Thermal properties . High temperature materials; materials for cryogenic application, thermally insulating materials. (Specific heat, thermal conductivity, thermal expansion).

Ceramic materials and polymers . Silicon structures, polymerism . in glass, electrical properties of ceramic phases, rocks, building stones, refractories.

Polymerisation mechanism , structural properties of polymer, thermoplastics, thermosets, elastomer, resins, composites, particles and fibre reinforced composite. Composite material including nano material.

Electronic properties . Magnetism, diamagnetism, paramagnetism, ferromagnetism, magnetic energy, zone theory of solids, zones in conductors and insulators.

Syllabus of Material Science And Engineering

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Group A
Introduction to materials . Metal and alloys, ceramics, polymers and semi conducting materials-introduction and application as engineering materials.

Defects in solids . Point, line and surface defects. Diffusion in solids.

Phase diagrams . Mono-component and binary systems, non-equilibrium system, phase diagram and. application in crystalline and non-crystalline solids.

Mechanical properties . Tensile strength, yield strength, elastic and viscoelastic properties, creep, stress relaxation and impact. Fracture behaviour. Ductile fracture, Griffith theory, effect of heat treatment and temperature on properties of metals.

Deformation of metals. Elastic and plastic deformation, slip, twin, dislocation theory, critical resolved shear stress, deformation in polycrystalline materials; season cracking, Bachinger's effect, strengthening mechanics; work hardening recovery, crystallization and grain growth, cold and hot working. .

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Dielectric Materials
Capacitors require dielectrics of high e that can function at high frequencies (small relaxation times). Many of the ceramics have these properties, like mica, glass, and porcelain). Polymers usually have lower .

Ferroelectricity
Ferroelectric materials are ceramics that exhibit permanent polarization in the absence of an electric field. This is due to the asymmetric location of positive and negative charges within the unit cell. Two possible arrangements of this asymmetry results in two distinct polarizations, which can be used to code "0" and "1" in ferroelectric memories. A typical ferroelectric is barium titanate, BaTiO3, where the Ti4+ is in the center of the unit cell and four O2- in the central plane can be displaced to one side or the other of this central ion

Piezoelectricity
In a piezolectric material, like quartz, an applied mechanical stress causes electric polarization by the relative displacement of anions and cations.

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Conduction in Ionic Materials
In ionic materials, the band gap is too large for thermal electron promotion. Cation vacancies allow ionic motion in the direction of an applied electric field, this is referred to as ionic conduction. High temperatures produce more vacancies and higher ionic conductivity.
At low temperatures, electrical conduction in insulators is usually along the surface, due to the deposition of moisture that contains impurity ions.

Electrical Properties of Polymers
Polymers are usually good insulators but can be made to conduct by doping. Teflon is an exceptionally good insulator.
Dielectric Behavior
A dielectric is an electrical insulator that can be made to exhibit an electric dipole structure (displace the negative and positive charge so that their center of gravity is different).

Capacitance
When two parallel plates of area A, separated by a small distance l, are charged by +Q, –Q, an electric field develops between the plates
E = D/ee0
where D = Q/A. e0 is called the vacuum permittivity and e the relative permittivity, or dielectric constant (e = 1 for vacuum). In terms of the voltage between the plates, V = E l,
V = Dl/ee0 = Q l/Aee0 = Q / C
The constant C= Aee0/l is called the capacitance of the plates.

Field Vectors and Polarization
The dipole moment of a pair of positive and negative charges (+q and –q) separated at a distance d is p = qd. If an electric field is applied, the dipole tends to align so that the positive charge points in the field direction. Dipoles between the plates of a capacitor will produce an electric field that opposes the applied field. For a given applied voltage V, there will be an increase in the charge in the plates by an amount Q' so that the total charge becomes Q = Q' + Q0, where Q0 is the charge of a vacuum capacitor with the same V. With Q' = PA, the charge density becomes D = D0 E + P, where the polarization P = e0 (e–1) E .

Types of Polarization
Three types of polarization can be caused by an electric field:
Electronic polarization: the electrons in atoms are displaced relative to the nucleus.
Ionic polarization: cations and anions in an ionic crystal are displaced with respect to each other.
Orientation polarization: permanent dipoles (like H2O) are aligned.

Frequency Dependence of the Dielectric Constant
Electrons have much smaller mass than ions, so they respond more rapidly to a changing electric field. For electric field that oscillates at very high frequencies (such as light) only electronic polarization can occur. At smaller frequencies, the relative displacement of positive and negative ions can occur. Orientation of permanent dipoles, which require the rotation of a molecule can occur only if the oscillation is relatively slow (MHz range or slower). The time needed by the specific polarization to occur is called the relaxation time.

Dielectric Strength
Very high electric fields (>108 V/m) can free electrons from atoms, and accelerate them to such high energies that they can, in turn, free other electrons, in an avalanche process (or electrical discharge). This is called dielectric breakdown, and the field necessary to start the is called the dielectric strength or breakdown strength.

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Electrical Characteristics of Commercial Alloys
The best material for electrical conduction (lower resistivity) is silver. Since it is very expensive, copper is preferred, at an only modest increase in r. To achieve low r it is necessary to remove gases occluded in the metal during fabrication. Copper is soft so, for applications where mechanical strength is important, the alloy CuBe is used, which has a nearly as good r. When weight is important one uses Al, which is half as good as Cu. Al is also more resistant to corrosion.
When high resistivity materials are needed, like in electrical heaters, especially those that operate at high temperature, nichrome (NiCr) or graphite are used.

Intrinsic Semiconduction
Semiconductors can be intrinsic or extrinsic. Intrinsic means that electrical conductivity does not depend on impurities, thus intrinsic means pure. In extrinsic semiconductors the conductivity depends on the concentration of impurities.
Conduction is by electrons and holes. In an electric field, electrons and holes move in opposite direction because they have opposite charges. The conductivity of an intrinsic semiconductor is:
s = n e me + p e mh
where p is the hole concentration and mh the hole mobility. One finds that electrons move much faster than holes:
me > mh
In an intrinsic semiconductor, a hole is produced by the promotion of each electron to the conduction band. Thus:
n = p
Thus, s = 2 n e (me + mh) (only for intrinsic semiconductors).

Extrinsic Semiconduction
Unlike intrinsic semiconductors, an extrinsic semiconductor may have different concentrations of holes and electrons. It is called p-type if p>n and n-type if n>p. They are made by doping, the addition of a very small concentration of impurity atoms. Two common methods of doping are diffusion and ion implantation.
Excess electron carriers are produced by substitutional impurities that have more valence electron per atom than the semiconductor matrix. For instance phosphorous, with 5 valence electrons, is an electron donor in Si since only 4 electrons are used to bond to the Si lattice when it substitutes for a Si atom. Thus, elements in columns V and VI of the periodic table are donors for semiconductors in the IV column, Si and Ge. The energy level of the donor state is close to the conduction band, so that the electron is promoted (ionized) easily at room temperature, leaving a hole (the ionized donor) behind. Since this hole is unlike a hole in the matrix, it does not move easily by capturing electrons from adjacent atoms. This means that the conduction occurs mainly by the donated electrons (thus n-type).
Excess holes are produced by substitutional impurities that have fewer valence electrons per atom than the matrix. This is the case of elements of group II and III in column IV semiconductors, like B in Si. The bond with the neighbors is incomplete and so they can capture or accept electrons from adjacent silicon atoms. They are called acceptors. The energy level of the acceptor is close to the valence band, so that an electron may easily hop from the valence band to complete the bond leaving a hole behind. This means that conduction occurs mainly by the holes (thus p-type).

The Temperature Variation of Conductivity and Carrier Concentration
Temperature causes electrons to be promoted to the conduction band and from donor levels, or holes to acceptor levels. The dependence of conductivity on temperature is like other thermally activated processes:
s = A exp(–Eg/2kT)
where A is a constant (the mobility varies much more slowly with temperature). Plotting ln s vs. 1/T produces a straight line of slope Eg/2k from which the band gap energy can be determined. Extrinsic semiconductors have, in addition to this dependence, one due to the thermal promotion of electrons from donor levels or holes from acceptor levels. The dependence on temperature is also exponential but it eventually saturates at high temperatures where all the donors are emptied or all the acceptors are filled.
This means that at low temperatures, extrinsic semiconductors have larger conductivity than intrinsic semiconductors. At high temperatures, both the impurity levels and valence electrons are ionized, but since the impurities are very low in number and they are exhausted, eventually the behavior is dominated by the intrinsic type of conductivity.

Semiconductor Devices
A semiconductor diode is made by the intimate junction of a p-type and an n-type semiconductor (an n-p junction). Unlike a metal, the intensity of the electrical current that passes through the material depends on the polarity of the applied voltage. If the positive side of a battery is connected to the p-side, a situation called forward bias, a large amount of current can flow since holes and electrons are pushed into the junction region, where they recombine (annihilate). If the polarity of the voltage is flipped, the diode operates under reverse bias. Holes and electrons are removed from the region of the junction, which therefore becomes depleted of carriers and behaves like an insulator. For this reason, the current is very small under reverse bias. The asymmetric current-voltage characteristics of diodes is used to convert alternating current into direct current. This is called rectification.
A p-n-p junction transistor contains two diodes back-to-back. The central region is very thin and is called the base. A small voltage applied to the base has a large effect on the current passing through the transistor, and this can be used to amplify electrical signals (Fig. 19.22). Another common device is the MOSFET transistor where a gate serves the function of the base in a junction transistor. Control of the current through the transistor is by means of the electric field induced by the gate, which is isolated electrically by an oxide layer.

remainig part of chapter 17

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Energy Band Structures in Solids
When atoms come together to form a solid, their valence electrons interact due to Coulomb forces, and they also feel the electric field produced by their own nucleus and that of the other atoms. In addition, two specific quantum mechanical effects happen. First, by Heisenberg's uncertainty principle, constraining the electrons to a small volume raises their energy, this is called promotion. The second effect, due to the Pauli exclusion principle, limits the number of electrons that can have the same property (which include the energy). As a result of all these effects, the valence electrons of atoms form wide valence bands when they form a solid. The bands are separated by gaps, where electrons cannot exist. The precise location of the bands and band gaps depends on the type of atom (e.g., Si vs. Al), the distance between atoms in the solid, and the atomic arrangement (e.g., carbon vs. diamond).
In semiconductors and insulators, the valence band is filled, and no more electrons can be added, following Pauli's principle. Electrical conduction requires that electrons be able to gain energy in an electric field; this is not possible in these materials because that would imply that the electrons are promoted into the forbidden band gap.
In metals, the electrons occupy states up to the Fermi level. Conduction occurs by promoting electrons into the conduction band, that starts at the Fermi level, separated by the valence band by an infinitesimal amount.

Conduction in Terms of Band and Atomic Bonding Models
Conduction in metals is by electrons in the conduction band. Conduction in insulators is by electrons in the conduction band and by holes in the valence band. Holes are vacant states in the valence band that are created when an electron is removed.
In metals there are empty states just above the Fermi levels, where electrons can be promoted. The promotion energy is negligibly small so that at any temperature electrons can be found in the conduction band. The number of electrons participating in electrical conduction is extremely small.
In insulators, there is an energy gap between the valence and conduction bands, so energy is needed to promote an electron to the conduction band. This energy may come from heat, or from energetic radiation, like light of sufficiently small wavelength.
A working definition for the difference between semiconductors and insulators is that in semiconductors, electrons can reach the conduction band at ordinary temperatures, where in insulators they cannot. The probability that an electron reaches the conduction band is about exp(-Eg/2kT) where Eg is the band gap and kT has the usual meaning. If this probability is, say, <> 55. At room temperature, 2kT = 0.05 eV; thus Eg > 2.8 eV can be used as the condition for an insulator.
Besides having relatively small Eg, semiconductors have covalent bond, whereas insulators usually are partially ionic bonded.

Electron Mobility
Electrons are accelerated in an electric field E, in the opposite direction to the field because of their negative charge. The force acting on the electron is -eE, where e is the electric charge. This force produces a constant acceleration so that, in the absence of obstacles (in vacuum, like inside a TV tube) the electron speeds up continuously in an electric field. In a solid, the situation is different. The electrons scatter by collisions with atoms and vacancies that change drastically their direction of motion. Thus electrons move randomly but with a net drift in the direction opposite to the electric field. The drift velocity is constant, equal to the electric field times a constant called the mobility m,
vd= – me E
which means that there is a friction force proportional to velocity. This friction translates into energy that goes into the lattice as heat. This is the way that electric heaters work.
The electrical conductivity is:
s = n e me
where n is the concentration of electrons (n is used to indicate that the carriers of electricity are negative particles).

Electrical Resistivity of Metals
The resistivity then depends on collisions. Quantum mechanics tells us that electrons behave like waves. One of the effects of this is that electrons do not scatter from a perfect lattice. They scatter by defects, which can be:
atoms displaced by lattice vibrations
vacancies and interstitials
dislocations, grain boundaries
impurities One can express the total resistivity rtot by the Matthiessen rule, as a sum of resistivities due to thermal vibrations, impurities and dislocations. illustrates how the resistivity increases with temperature, with deformation, and with alloying

Chapter 17. Electrical Properties

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Electrical Conduction
Ohm’s Law
When an electric potential V is applied across a material, a current of magnitude I flows. In most metals, at low values of V, the current is proportional to V, according to Ohm's law:
I = V/R
where R is the electrical resistance. R depends on the intrinsic resistivity r of the material and on the geometry (length l and area A through which the current passes).
R = rl/A

Electrical Conductivity
The electrical conductivity is the inverse of the resistivity: s = 1/r.
The electric field in the material is E=V/l, Ohm's law can then be expressed in terms of the current density j = I/A as:
j = s E
The conductivity is one of the properties of materials that varies most widely, from 107 (W-m) typical of metals to 10-20 (W-m) for good electrical insulators. Semiconductors have conductivities in the range 10-6 to 104 (W-m).

Electronic and Ionic Conduction
In metals, the current is carried by electrons, and hence the name electronic conduction. In ionic crystals, the charge carriers are ions, thus the name ionic conduction

Chapter 16. Composites

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16.1 Introduction
The idea is that by combining two or more distinct materials one can engineer a new material with the desired combination of properties (e.g., light, strong, corrosion resistant). The idea that a better combination of properties can be achieved is called the principle of combined action.
New - High-tech materials, engineered to specific applications
Old - brick-straw composites, paper, known for > 5000 years.
A type of composite that has been discussed is perlitic steel, which combines hard, brittle cementite with soft, ductile ferrite to get a superior material.
Natural composites: wood (polymer-polymer), bones (polymer-ceramics).
Usual composites have just two phases:
matrix (continuous)
dispersed phase (particulates, fibers)
Properties of composites depend on
properties of phases
geometry of dispersed phase (particle size, distribution, orientation)
amount of phase
Classification of composites: three main categories:
particle-reinforced (large-particle and dispersion-strengthened)
fiber-reinforced (continuous (aligned) and short fibers (aligned or random)
structural (laminates and sandwich panels)
Particle-reinforced composites
These are the cheapest and most widely used. They fall in two categories depending on the size of the particles:
large-particle composites, which act by restraining the movement of the matrix, if well bonded.
dispersion-strengthened composites, containing 10-100 nm particles, similar to what was discussed under precipitation hardening. The matrix bears the major portion of the applied load and the small particles hinder dislocation motion, limiting plastic deformation.

16.2 Large-Particle Composites
Properties are a combination of those of the components. The rule of mixtures predicts that an upper limit of the elastic modulus of the composite is given in terms of the elastic moduli of the matrix (Em) and the particulate (Ep) phases by:
Ec = EmVm + EpVp
where Vm and Vp are the volume fraction of the two phases. A lower bound is given by:
Ec = EmEp / (EpVm + EmVp)
modulus of composite of WC particles in Cu matrix vs. WC concentration.
Concrete
The most common large-particle composite is concrete, made of a cement matrix that bonds particles of different size (gravel and sand.) Cement was already known to the Egyptians and the Greek. Romans made cement by mixing lime (CaO) with volcanic ice.
In its general from, cement is a fine mixture of lime, alumina, silica, and water. Portland cement is a fine powder of chalk, clay and lime-bearing minerals fired to 1500o C (calcinated). It forms a paste when dissolved in water. It sets into a solid in minutes and hardens slowly (takes 4 months for full strength). Properties depend on how well it is mixed, and the amount of water: too little - incomplete bonding, too much - excessive porosity.
The advantage of cement is that it can be poured in place, it hardens at room temperature and even under water, and it is very cheap. The disadvantages are that it is weak and brittle, and that water in the pores can produce crack when it freezes in cold weather.
Concrete is cement strengthened by adding particulates. The use of different size (stone and sand) allows better packing factor than when using particles of similar size.
Concrete is improved by making the pores smaller (using finer powder, adding polymeric lubricants, and applying pressure during hardening.
Reinforced concrete is obtained by adding steel rods, wires, mesh. Steel has the advantage of a similar thermal expansion coefficient, so there is reduced danger of cracking due to thermal stresses. Pre-stressed concrete is obtained by applying tensile stress to the steel rods while the cement is setting and hardening. When the tensile stress is removed, the concrete is left under compressive stress, enabling it to sustain tensile loads without fracturing. Pre-stressed concrete shapes are usually prefabricated. A common use is in railroad or highway bridges.
Cermets
are composites of ceramic particles (strong, brittle) in a metal matrix (soft, ductile) that enhances toughness. For instance, tungsten carbide or titanium carbide ceramics in Co or Ni. They are used for cutting tools for hardened steels.
Reinforced rubber
is obtained by strengthening with 20-50 nm carbon-black particles. Used in auto tires.

16.3 Dispersion-Strengthened Composites
Use of very hard, small particles to strengthen metals and metal alloys. The effect is like precipitation hardening but not so strong. Particles like oxides do not react so the strengthening action is retained at high temperatures.
Fiber-reinforced composites
In many applications, like in aircraft parts, there is a need for high strength per unit weight (specific strength). This can be achieved by composites consisting of a low-density (and soft) matrix reinforced with stiff fibers.
The strength depends on the fiber length and its orientation with respect to the stress direction.
The efficiency of load transfer between matrix and fiber depends on the interfacial bond.

16.4 Influence of Fiber Length
Normally the matrix has a much lower modulus than the fiber so it strains more. This occurs at a distance from the fiber. Right next to the fiber, the strain is limited by the fiber. Thus, for a composite under tension, a shear stress appears in the matrix that pulls from the fiber. The pull is uniform over the area of the fiber. This makes the force on the fiber be minimum at the ends and maximum in the middle, like in the tug-of-war game.
To achieve effective strengthening and stiffening, the fibers must be larger than a critical length lc, defined as the minimum length at which the center of the fiber reaches the ultimate (tensile) strength sf, when the matrix achieves the maximum shear strength tm:
lc = sf d /2 tm
Since it is proportional to the diameter of the fiber d, a more unified condition for effective strengthening is that the aspect ratio of the fiber is l/d > sf /2 tm.
16.5 Influence of Fiber Orientation
The composite is stronger along the direction of orientation of the fibers and weakest in a direction perpendicular to the fiber. For discontinuous, random fibers, the properties are isotropic.

16.6 Polymer Matrix Composites
Largest and most diverse use of composites due to ease of fabrication, low cost and good properties.
Glass-fiber reinforced composites (GFRC) are strong, corrosion resistant and lightweight, but not very stiff and cannot be used at high temperatures. Applications include auto and boat bodies, aircraft components.
Carbon-fiber reinforced composites (CFRC) use carbon fibers, which have the highest specific module (module divided by weight). CFRC are strong, inert, allow high temperature use. Applications include fishing rods, golf clubs, aircraft components.
Kevlar, and aremid-fiber composite can be used as textile fibers. Applications include bullet-proof vests, tires, brake and clutch linings.
Wood:
This is one of the oldest and the most widely used structural material. It is a composite of strong and flexible cellulose fibers (linear polymer) surrounded and held together by a matrix of lignin and other polymers. The properties are anisotropic and vary widely among types of wood. Wood is ten times stronger in the axial direction than in the radial or tangential directions.

Chapter 15. Polymers. Characteristics, Applications and Processing

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Stress-Strain Behavior
The description of stress-strain behavior is similar to that of metals, but a very important consideration for polymers is that the mechanical properties depend on the strain rate, temperature, and environmental conditions.
The stress-strain behavior can be brittle, plastic and highly elastic (elastomeric or rubber-like), . 1. Tensile modulus (modulus) and tensile strengths are orders of magnitude smaller than those of metals, but elongation can be up to 1000 % in some cases. The tensile strength is defined at the fracture point and can be lower than the yield strength.
Mechanical properties change dramatically with temperature, going from glass-like brittle behavior at low temperatures (like in the liquid-nitrogen demonstration) to a rubber-like behavior at high temperatures.
In general, decreasing the strain rate has the same influence on the strain-strength characteristics as increasing the temperature: the material becomes softer and more ductile.

Deformation of Semicrystalline Polymers
Many semicrystalline polymers have the spherulitic structure and deform in the following steps :
· elongation of amorphous tie chains
· tilting of lamellar chain folds towards the tensile direction
· separation of crystalline block segments
· orientation of segments and tie chains in the tensile direction
The macroscopic deformation involves an upper and lower yield point and necking. Unlike the case of metals, the neck gets stronger since the deformation aligns the chains so increasing the tensile stress leads to the growth of the neck..

Factors that Influence the Mechanical Properties of Polymers
The tensile modulus decreases with increasing temperature or diminishing strain rate.
Obstacles to the steps mentioned in 16.4 strengthen the polymer. Examples are cross-linking (aligned chains have more van der Waals inter-chain bonds) and a large mass (longer molecules have more inter-chain bonds). Crystallinity increases strength as the secondary bonding is enhanced when the molecular chains are closely packed and parallel. Pre-deformation by drawing, analogous to strain hardening in metals, increases strength by orienting the molecular chains. For undrawn polymers, heating increases the tensile modulus and yield strength, and reduces the ductility - opposite of what happens in metals.

Crystallization, Melting, and Glass Transition Phenomena
Crystallization rates are governed by the same type of S-curves we saw in the case of metals. Nucleation becomes slower at higher temperatures.
The melting behavior of semicrystalline polymers is intermediate between that of crystalline materials (sharp density change at a melting temperature) and that of a pure amorphous material (slight change in slope of density at the glass-transition temperature). The glass transition temperature is between 0.5 and 0.8 of the melting temperature.
The melting temperature increases with the rate of heating, thickness of the lamellae, and depends on the temperature at which the polymer was crystallized.
Melting involves breaking of the inter-chain bonds, so the glass and melting temperatures depend on:
· chain stiffness (e.g., single vs. double bonds)
· size, shape of side groups
· size of molecule
· side branches, defects
· cross-linking
Rigid chains have higher melting temperatures.

Thermoplastic and Thermosetting Polymers
Thermoplastic polymers (thermoplasts) soften reversibly when heated (harden when cooled back)
Thermosetting polymers (thermosets) harden permanently when heated, as cross-linking hinder bending and rotations. Thermosets are harder, more dimensionally stable, and more brittle than thermoplasts.

Viscoelasticity
At low temperatures, amorphous polymers deform elastically, like glass, at small elongation. At high temperatures the behavior is viscous, like liquids. At intermediate temperatures, the behavior, like a rubbery solid, is termed viscoelastic.
Viscoelasticity is characterized by the viscoelastic relaxation modulus
Er = s(t)/e0.
If the material is strained to a value e0.it is found that the stress needs to be reduced with time to maintain this constant value of strain (see figs. 16.11 and 16.12).
In viscoelastic creep, the stress is kept constant at s0 and the change of deformation with time e(t) is measured. The time-dependent creep modulus is given by
Ec = s0/e(t).

Deformation and Elastomers
Elastomers can be deformed to very large strains and the spring back elastically to the original length, a behavior first observed in natural rubber. Elastic elongation is due to uncoiling, untwisting and straightening of chains in the stress direction.
To be elastomeric, the polymer needs to meet several criteria:
· must not crystallize easily
· have relatively free chain rotations
· delayed plastic deformation by cross-linking (achieved by vulcanization).
· be above the glass transition temperature

Fracture of Polymers
As other mechanical properties, the fracture strength of polymers is much lower than that of metals. Fracture also starts with cracks at flaws, scratches, etc. Fracture involves breaking of covalent bonds in the chains. Thermoplasts can have both brittle and ductile fracture behaviors. Glassy thermosets have brittle fracture at low temperatures and ductile fracture at high temperatures.
Glassy thremoplasts often suffer grazing before brittle fracture. Crazes are associated with regions of highly localized yielding which leads to the formation of interconnected microvoids . Crazing absorbs energy thus increasing the fracture strength of the polymer.

Miscellaneous Characteristics
Polymers are brittle at low temperatures and have low impact strengths (Izod or Charpy tests), and a brittle to ductile transition over a narrow temperature range.
Fatigue is similar to the case of metals but at reduced loads and is more sensitive to frequency due to heating which leads to softening.

Polymerization
Polymerization is the synthesis of high polymers from raw materials like oil or coal. It may occur by:
· addition (chain-reaction) polymerization, where monomer units are attached one at a time
· condensation polymerization, by stepwise intermolecular chemical reactions that produce the mer units.

Elastomers
In vulcanization, crosslinking of the elastomeric polymer is achieved by an irreversible chemical reaction usually at high temperatures (hence ‘vulcan’), and usually involving the addition of sulfur compounds. The S atoms are the ones that form the bridge cross-links. Elastomers are thermosetting due to the cross-linking.
Rubbers become harder and extend less with increasing sulfur content. For automobile applications, synthetic rubbers are strengthened by adding carbon black.
In silicone rubbers, the backbone C atoms are replaced by a chain of alternating silicon and oxygen atoms. These elastomers are also cross-linked and are stable to higher temperatures than C-based elastomers.

Chapter 14.Polymers

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14.1 Introduction
Polymers are common in nature, in the form of wood, rubber, cotton, leather, wood, silk, proteins, enzymes, starches, cellulose. Artificial polymers are made mostly from oil. Their use has grown exponentially, especially after WW2. The key factor is the very low production cost and useful properties (e.g., combination of transparency and flexibility, long elongation).

14.2 Hydrocarbon Molecules
Most polymers are organic, and formed from hydrocarbon molecules. These molecules can have single, double, or triple carbon bonds. A saturated hydrocarbon is one where all bonds are single, that is, the number of atoms is maximum (or saturated). Among this type are the paraffin compounds, CnH2n+2 . In contrast, non-saturated hydrocarbons contain some double and triple bonds.
Isomers are molecules that contain the same molecules but in a different arrangement. An example is butane and isobutane.

14.3 Polymer Molecules
Polymer molecules are huge, macromolecules that have internal covalent bonds. For most polymers, these molecules form very long chains. The backbone is a string of carbon atoms, often single bonded.
Polymers are composed of basic structures called mer units. A molecule with just one mer is a monomer.

14.4 The Chemistry of Polymer Molecules
Examples of polymers are polyvinyl chloride (PVC), poly-tetra-chloro-ethylene (PTFE or Teflon), polypropylene, nylon and polystyrene. Chains are represented straight but in practice they have a three-dimensional, zig-zag structure .
When all the mers are the same, the molecule is called a homopolymer. When there is more than one type of mer present, the molecule is a copolymer.

14.5 Molecular Weight
The mass of a polymer is not fixed, but is distributed around a mean value, since polymer molecules have different lengths. The average molecular weight can be obtained by averaging the masses with the fraction of times they appear (number-average) or with the mass fraction of the molecules (called, improperly, a weight fraction).
The degree of polymerization is the average number of mer units, and is obtained by dividing the average mass of the polymer by the mass of a mer unit.
Polymers of low mass are liquid or gases, those of very high mass (called high-polymers, are solid). Waxes, paraffins and resins have intermediate masses.

14.6 Molecular Shape
Polymers are usually not linear; bending and rotations can occur around single C-C bonds (double and triple bonds are very rigid) (Fig. 15.5). Random kings and coils lead to entanglement, like in the spaghetti structure.

14.7 Molecular Structure
Typical structures are :
linear (end-to-end, flexible, like PVC, nylon)
branched
cross-linked (due to radiation, vulcanization, etc.)
network (similar to highly cross-linked structures).

14.8 Molecular Configurations
The regularity and symmetry of the side-groups can affect strongly the properties of polymers. Side groups are atoms or molecules with free bonds, called free-radicals, like H, O, methyl, etc.
If the radicals are linked in the same order, the configuration is called isostatic
In a stereoisomer in a syndiotactic configuration, the radical groups alternative sides in the chain.
In the atactic configuration, the radical groups are positioned at random.

14.9 Copolymers
Copolymers, polymers with at least two different types of mers can differ in the way the mers are arranged. Shows different arrangements: random, alternating, block, and graft.

14.10 Polymer Crystallinity
Crystallinity in polymers is more complex than in metals . Polymer molecules are often partially crystalline (semicrystalline), with crystalline regions dispersed within amorphous material. .
Chain disorder or misalignment, which is common, leads to amorphous material since twisting, kinking and coiling prevent strict ordering required in the crystalline state. Thus, linear polymers with small side groups, which are not too long form crystalline regions easier than branched, network, atactic polymers, random copolymers, or polymers with bulky side groups.
Crystalline polymers are denser than amorphous polymers, so the degree of crystallinity can be obtained from the measurement of density.

14.11 Polymer Crystals
Different models have been proposed to describe the arrangement of molecules in semicrytalline polymers. In the fringed-micelle model, the crystallites (micelles) are embedded in an amorphous matrix . Polymer single crystals grown are shaped in regular platelets (lamellae) . Spherulites are chain-folded crystallites in an amorphous matrix that grow radially in spherical shape “grains”.

Chapter 13. Ceramics - Applications and Processing

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13.1 Introduction
Ceramics properties that are different from those of metals lead to different uses. In structures, designs must be done for compressive loads. The transparency to light of many ceramics leads to optical uses, like in windows, photographic cameras, telescopes and microscopes. Good thermal insulation leads to use in ovens, the exterior tiles of the Shuttle orbiter, etc. Good electrical isolation are used to support conductors in electrical and electronic applications. The good chemical inertness shows in the stability of the structures thousands of years old.

13.2 Glass Properties
A special characteristic of glasses is that solidification is gradual, through a viscous stage, without a clear melting temperature. The specific volume does not have an abrupt transition at a temperature but rather shows a change in slope at the glass-transition temperature (Fig. 14.3).
The melting point, working point, softening point and annealing point are defined in terms of viscosity, rather than temperature (Fig. 14.4), and depend on glass composition..

13.4 Heat Treating Glasses
Similar to the case of metals, annealing is used at elevated temperatures is used to remove stresses, like those caused by inhomogeneous temperatures during cooling. Strengthening by glass tempering is done by heating the glass above the glass transition temperature but below the softening point and then quenched in an air jet or oil bath. The interior, which cools later than the outside, tries to contract while in a plastic state after the exterior has become rigid. This causes residual compressive stresses on the surface and tensile stresses inside. To fracture, a crack has first to overcome the residual compressive stress, making tempered glass less susceptible to fracture. This improvement leads to use in automobile windshields, glass doors, eyeglass lenses, etc

remaining part of chapter-12

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12.5 Imperfections in Ceramics
Imperfections include point defects and impurities. Their formation is strongly affected by the condition of charge neutrality (creation of unbalanced charges requires the expenditure of a large amount of energy.
Non-stoichiometry refers to a change in composition so that the elements in the ceramic are not in the proportion appropriate for the compound (condition known as stoichiometry). To minimize energy, the effect of non-stoichiometry is a redistribution of the atomic charges Charge neutral defects include the Frenkel and Schottky defects. A Frenkel-defect is a vacancy- interstitial pair of cations (placing large anions in an interstitial position requires a lot of energy in lattice distortion). A Schottky-defect is the a pair of nearby cation and anion vacancies.
Introduction of impurity atoms in the lattice is likely in conditions where the charge is maintained. This is the case of electronegative impurities that substitute a lattice anions or electropositive substitutional impurities. This is more likely for similar ionic radii since this minimizes the energy required for lattice distortion. Defects will appear if the charge of the impurities is not balanced.

12.6 Ceramic Phase

to be prepare

12.7 Brittle Fracture of Ceramics
The brittle fracture of ceramics limits applications. It occurs due to the unavoidable presence of microscopic flaws (micro-cracks, internal pores, and atmospheric contaminants) that result during cooling from the melt. The flaws need to crack formation, and crack propagation (perpendicular to the applied stress) is usually transgranular, along cleavage planes. The flaws cannot be closely controlled in manufacturing; this leads to a large variability (scatter) in the fracture strength of ceramic materials.
The compressive strength is typically ten times the tensile strength. This makes ceramics good structural materials under compression (e.g., bricks in houses, stone blocks in the pyramids), but not in conditions of tensile stress, such as under flexure.
Plastic deformation in crystalline ceramics is by slip, which is difficult due to the structure and the strong local (electrostatic) potentials. There is very little plastic deformation before fracture.
Non-crystalline ceramics, like common glass deform by viscous flow (like very high-density liquids). Viscosity decreases strongly with increases temperature.

Chapter 12. Ceramics - Structures and Properties

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12.1 Introduction
Ceramics are inorganic and non-metallic materials that are commonly electrical and thermal insulators, brittle and composed of more than one element (e.g., two in Al2O3)
Ceramic Structures

12.2 Crystal Structures
Ceramic bonds are mixed, ionic and covalent, with a proportion that depends on the particular ceramics. The ionic character is given by the difference of electronegativity between the cations (+) and anions (-). Covalent bonds involve sharing of valence electrons. Very ionic crystals usually involve cations which are alkalis or alkaline-earths (first two columns of the periodic table) and oxygen or halogens as anions.
The building criteria for the crystal structure are two:
maintain neutrality
charge balance dictates chemical formula
achieve closest packing
the condition for minimum energy implies maximum attraction and minimum repulsion. This leads to contact, configurations where anions have the highest number of cation neighbors and viceversa.
The parameter that is important in determining contact is the ratio of cation to anion radii, rC/rA. Table 13.2 gives the coordination number and geometry as a function of rC/rA. For example, in the NaCl structure (Fig. 13.2), rC = rNa = 0.102 nm, rA =rCl.= 0.181 nm, so rC/rA.= 0.56. From table 13.2 this implies coordination number = 6, as observed for this rock-salt structure.
Other structures were shown in class, but will not be included in the test.

12.3 Silicate Ceramics
Oxygen and Silicon are the most abundant elements in Earth’s crust. Their combination (silicates) occur in rocks, soils, clays and sand. The bond is weekly ionic, with Si4+ as the cation and O2- as the anion. rSi = 0.04 nm, rO.= 0.14 nm, so rC/rA = 0.286. From table 13.2 this implies coordination number = 4, that is tetrahedral coordination (Fig. 13.9).
The tetrahedron is charged: Si4+ + 4 O2- Þ (Si O4)4-. Silicates differ on how the tetrahedra are arranged. In silica, (SiO2), every oxygen atom is shared by adjacent tetrahedra. Silica can be crystalline (e.g., quartz) or amorphous, as in glass.
Soda glasses melt at lower temperature than amorphous SiO2 because the addition of Na2O (soda) breaks the tetrahedral network. A lower melting point makes it easy to form glass to make, for instance, bottles.

12.4 Carbon
Carbon is not really a ceramic, but an allotropic form, diamond, may be thought as a type of ceramic. Diamond has very interesting and even unusual properties:
diamond-cubic structure (like Si, Ge)
covalent C-C bonds
highest hardness of any material known
very high thermal conductivity (unlike ceramics)
transparent in the visible and infrared, with high index of refraction
semiconductor (can be doped to make electronic devices)
metastable (transforms to carbon when heated)
Synthetic diamonds are made by application of high temperatures and pressures or by chemical vapor deposition. Future applications of this latter, cheaper production method include hard coatings for metal tools, ultra-low friction coatings for space applications, and microelectronics.
Graphite has a layered structure with very strong hexagonal bonding within the planar layers (using 3 of the 3 bonding electrons) and weak, van der Waals bonding between layers using the fourth electron. This leads to easy interplanar cleavage and applications as a lubricant and for writing (pencils). Graphite is a good electrical conductor and chemically stable even at high temperatures. Applications include furnaces, rocket nozzles, electrodes in batteries.
A recently (1985) discovered formed of carbon is the C60 molecule, also known as fullerene or bucky-ball (after the architect Buckminster Fuller who designed the geodesic structure that C60 resembles.) Fullerenes and related structures like bucky-onions amd nanotubes are exceptionally strong. Future applications are as a structural material and possibly in microelectronics, due to the unusual properties that result when fullerenes are doped with other atoms.

remaining part of chap-11

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11.6 Influence of Quenching Medium, Specimen Size, and Geometry
The cooling rate depends on the cooling medium. Cooling is fastest using water, then oil, and then air. Fast cooling brings the danger of warping and formation of cracks, since it is usually accompanied by large thermal gradients.
The shape and size of the piece, together with the heat capacity and heat conductivity are important in determining the cooling rate for different parts of the metal piece. Heat capacity is the energy content of a heated mass, which needs to be removed for cooling. Heat conductivity measures how fast this energy is transported to the colder regions of the piece.
Precipitation Hardening
Hardening can be enhanced by extremely small precipitates that hinder dislocation motion. The precipitates form when the solubility limit is exceeded. Precipitation hardening is also called age hardening because it involves the hardening of the material over a prolonged time.

11.7 Heat Treatments
Precipitation hardening is achieved by:
a) solution heat treatment where all the solute atoms are dissolved to form a single-phase solution.
b) rapid cooling across the solvus line to exceed the solubility limit. This leads to a supersaturated solid solution that remains stable (metastable) due to the low temperatures, which prevent diffusion.
c) precipitation heat treatment where the supersaturated solution is heated to an intermediate temperature to induce precipitation and kept there for some time (aging).
If the process is continued for a very long time, eventually the hardness decreases. This is called overaging.
The requirements for precipitation hardening are:
appreciable maximum solubility
solubility curve that falls fast with temperature composition of the alloy that is less than the maximum solubility

11.8 Mechanism of Hardening
Strengthening involves the formation of a large number of microscopic nuclei, called zones. It is accelerated at high temperatures. Hardening occurs because the deformation of the lattice around the precipitates hinder slip. Aging that occurs at room temperature is called natural aging, to distinguish from the artificial aging caused by premeditated heating.

11.9 Miscellaneous Considerations
Since forming, machining, etc. uses more energy when the material is hard, the steps in the processing of alloys are usually:
solution heat treat and quench
do needed cold working before hardening
do precipitation hardening
Exposure of precipitation-hardened alloys to high temperatures may lead to loss of strength by overaging.

Chapter 11. Thermal Processing of Metal Alloys

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Annealing Processes
11.1 Introduction
Annealing is a heat treatment where the material is taken to a high temperature, kept there for some time and then cooled. High temperatures allow diffusion processes to occur fast. The time at the high temperature (soaking time) is long enough to allow the desired transformation to occur. Cooling is done slowly to avoid the distortion (warping) of the metal piece, or even cracking, caused by stresses induced by differential contraction due to thermal inhomogeneities. Benefits of annealing are:
relieve stresses
increase softness, ductility and toughness
produce a specific microstructure

11.2 Process Annealing
Deforming a piece that has been strengthened by cold working requires a lot of energy. Reverting the effect of cold work by process annealing eases further deformation. Heating allows recovery and recrystallization but is usually limited to avoid excessive grain growth and oxidation.

11.3 Stress Relief
Stresses resulting from machining operations of non-uniform cooling can be eliminated by stress relief annealing at moderately low temperatures, such that the effect of cold working and other heat treatments is maintained.

11.4 Annealing of Ferrous Alloys
Normalizing (or austenitizing) consists in taking the Fe-C alloy to the austenitic phase which makes the grain size more uniform, followed by cooling in air.
Full anneal involves taking hypoeutectoid alloys to the austenite phase and hypereutectoid alloys over the eutectoid temperature (Fig. 11.1) to soften pieces which have been hardened by plastic deformation, and which need to be machined.
Spheroidizing consists in prolongued heating just below the eutectoid temperature, which results in the soft spheroidite structure discussed in Sect. 10.5. This achieves maximum softness that minimizes the energy needed in subsequent forming operations.
Heat Treatment of Steels
1.5 Hardenability
To achieve a full conversion of austenite into hard martensite, cooling needs to be fast enough to avoid partial conversion into perlite or bainite. If the piece is thick, the interior may cool too slowly so that full martensitic conversion is not achieved. Thus, the martensitic content, and the hardness, will drop from a high value at the surface to a lower value in the interior of the piece. Hardenability is the ability of the material to be hardened by forming martensite.
Hardenability is measured by the Jominy end-quench test (Fig. 11.2). Hardenability is then given as the dependence of hardness on distance from the quenched end. High hardenability means that the hardness curve is relatively flat.

Remaining part of chapter 10

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Microstructural and Property Changes in Fe-C Alloys
10.5 Isothermal Transformation Diagrams
We use as an example the cooling of an eutectoid alloy (0.76 wt% C) from the austenite (g- phase) to pearlite, that contains ferrite (a) plus cementite (Fe3C or iron carbide). When cooling proceeds below the eutectoid temperature (727 oC) nucleation of pearlite starts. The S-shaped curves (fraction of pearlite vs. log. time, fig. 10.3) are displaced to longer times at higher temperatures showing that the transformation is dominated by nucleation (the nucleation period is longer at higher temperatures) and not by diffusion (which occurs faster at higher temperatures).
The family of S-shaped curves at different temperatures can be used to construct the TTT (Time-Temperature-Transformation) diagrams (e.g., fig. 10.4.) For these diagrams to apply, one needs to cool the material quickly to a given temperature To before the transformation occurs, and keep it at that temperature over time. The horizontal line that indicates constant temperature To intercepts the TTT curves on the left (beginning of the transformation) and the right (end of the transformation); thus one can read from the diagrams when the transformation occurs. The formation of pearlite shown in fig. 10.4 also indicates that the transformation occurs sooner at low temperatures, which is an indication that it is controlled by the rate of nucleation. At low temperatures, nucleation occurs fast and grain growth is reduced (since it occurs by diffusion, which is hindered at low temperatures). This reduced grain growth leads to fine-grained microstructure (fine pearlite). At higher temperatures, diffusion allows for larger grain growth, thus leading to coarse pearlite.
At lower temperatures nucleation starts to become slower, and a new phase is formed, bainite. Since diffusion is low at low temperatures, this phase has a very fine (microscopic) microstructure.
Spheroidite is a coarse phase that forms at temperatures close to the eutectoid temperature. The relatively high temperatures caused a slow nucleation but enhances the growth of the nuclei leading to large grains.
A very important structure is martensite, which forms when cooling austenite very fast (quenching) to below a maximum temperature that is required for the transformation. It forms nearly instantaneously when the required low temperature is reached; since no thermal activation is needed, this is called an athermal transformation. Martensite is a different phase, a body-centered tetragonal (BCT) structure with interstitial C atoms. Martensite is metastable and decomposes into ferrite and pearlite but this is extremely slow (and not noticeable) at room temperature.
In the examples, we used an eutectoid composition. For hypo- and hypereutectoid alloys, the analysis is the same, but the proeutectoid phase that forms before cooling through the eutectoid temperature is also part of the final microstructure.

10.6 Continuous Cooling Transformation

10.7 Mechanical Behavior of Fe-C Alloys
The strength and hardness of the different microstructures is inversely related to the size of the microstructures. Thus, spheroidite is softest, fine pearlite is stronger than coarse pearlite, bainite is stronger than pearlite and martensite is the strongest of all. The stronger and harder the phase the more brittle it becomes.

10.8 Tempered Martensite
Martensite is so brittle that it needs to be modified in many practical cases. This is done by heating it to 250-650 oC for some time (tempering) which produces tempered martensite, an extremely fine-grained and well dispersed cementite grains in a ferrite matrix.

Chapter-10: Phase Transformations in Metals

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10.1 Introduction
The goal is to obtain specific microstructures that will improve the mechanical properties of a metal, in addition to grain-size refinement, solid-solution strengthening, and strain-hardening.

10.2 Basic Concepts
Phase transformations that involve a change in the microstructure can occur through:
Diffusion
Maintaining the type and number of phases (e.g., solidification of a pure metal, allotropic transformation, recrystallization, grain growth.
Alteration of phase composition (e.g., eutectoid reactions, see 10.5)
Diffusionless
Production of metastable phases (e.g., martensitic transformation, see 10.5)

10.3 The Kinetics of Solid-State Reactions
Change in composition implies atomic rearrangement, which requires diffusion. Atoms are displaced by random walk. The displacement of a given atom, d, is not linear in time t (as would be for a straight trajectory) but is proportional to the square root of time, due to the tortuous path: d = c(Dt) 1/2 where c is a constant and D the diffusion constant. This time-dependence of the rate at which the reaction (phase transformation) occurs is what is meant by the term reaction kinetics.
D is called a constant because it does not depend on time, but it depends on temperature as we have seen in Ch. 5. Diffusion occurs faster at high temperatures.
Phase transformation requires two processes: nucleation and growth. Nucleation involves the formation of very small particles, or nuclei (e.g., grain boundaries, defects). This is similar to rain happening when water molecules condensed around dust particles. During growth, the nuclei grow in size at the expense of the surrounding material.
The kinetic behavior often has the S-shape form of Fig. 10.1, when plotting percent of material transformed vs. the logarithm of time. The nucleation phase is seen as an incubation period, where nothing seems to happen. Usually the transformation rate has the form r = A e-Q/RT (similar to the temperature dependence of the diffusion constant), in which case it is said to be thermally activated.

10.4 Multiphase Transformations
To describe phase transformations that occur during cooling, equilibrium phase diagrams are inadequate if the transformation rate is slow compared to the cooling rate. This is usually the case in practice, so that equilibrium microstructures are seldom obtained. This means that the transformations are delayed (e.g., case of supercooling), and metastable states are formed. We then need to know the effect of time on phase transformations

Remainig part of chapter 9

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9.13 The Iron–Iron Carbide (Fe–Fe3C) Phase Diagram
This is one of the most important alloys for structural applications. The diagram Fe—C is simplified at low carbon concentrations by assuming it is the Fe—Fe3C diagram. Concentrations are usually given in weight percent. The possible phases are:
a-ferrite (BCC) Fe-C solution
g-austenite (FCC) Fe-C solution
d-ferrite (BCC) Fe-C solution
liquid Fe-C solution
Fe3C (iron carbide) or cementite. An intermetallic compound.
The maximum solubility of C in a- ferrite is 0.022 wt%. d-ferrite is only stable at high temperatures. It is not important in practice. Austenite has a maximum C concentration of 2.14 wt %. It is not stable below the eutectic temperature (727 C) unless cooled rapidly (Chapter 10). Cementite is in reality metastable, decomposing into a-Fe and C when heated for several years between 650 and 770 C.
For their role in mechanical properties of the alloy, it is important to note that:
Ferrite is soft and ductile
Cementite is hard and brittle
Thus, combining these two phases in solution an alloy can be obtained with intermediate properties. (Mechanical properties also depend on the microstructure, that is, how ferrite and cementite are mixed.)
9.14 Development of Microstructures in Iron—Carbon Alloys
The eutectoid composition of austenite is 0.76 wt %. When it cools slowly it forms perlite, a lamellar or layered structure of two phases: a-ferrite and cementite (Fe3C).
Hypoeutectoid alloys contain proeutectoid ferrite plus the eutectoid perlite. Hypereutectoid alloys contain proeutectoid cementite plus perlite.
Since reactions below the eutectoid temperature are in the solid phase, the equilibrium is not achieved by usual cooling from austenite. The new microstructures that form are discussed in Ch. 10.
9.15 The Influence of Other Alloying Elements
As mentioned in section 7.9, alloying strengthens metals by hindering the motion of dislocations. Thus, the strength of Fe–C alloys increase with C content and also with the addition of other elements.

Chapter-9: PHASE DIAGRAMS

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9.1 Introduction
Definitions
Component: pure metal or compound (e.g., Cu, Zn in Cu-Zn alloy, sugar, water, in a syrup.)
Solvent: host or major component in solution.
Solute: dissolved, minor component in solution.
System: set of possible alloys from same component (e.g., iron-carbon system.)
Solubility Limit: Maximum solute concentration that can be dissolved at a given temperature.
Phase: part with homogeneous physical and chemical characteristics

9.2 Solubility Limit
Effect of temperature on solubility limit. Maximum content: saturation. Exceeding maximum content (like when cooling) leads to precipitation.

9.3 Phases
One-phase systems are homogeneous. Systems with two or more phases are heterogeneous, or mixtures. This is the case of most metallic alloys, but also happens in ceramics and polymers.
A two-component alloy is called binary. One with three components, ternary.

9.4 Microstructure
The properties of an alloy do not depend only on concentration of the phases but how they are arranged structurally at the microscopy level. Thus, the microstructure is specified by the number of phases, their proportions, and their arrangement in space.
A binary alloy may be
a single solid solution
two separated, essentially pure components.
two separated solid solutions.
a chemical compound, together with a solid solution.
The way to tell is to cut the material, polish it to a mirror finish, etch it a weak acid (components etch at a different rate) and observe the surface under a microscope.

9.5 Phase Equilibria
Equilibrium is the state of minimum energy. It is achieved given sufficient time. But the time to achieve equilibrium may be so long (the kinetics is so slow) that a state that is not at an energy minimum may have a long life and appear to be stable. This is called a metastable state.
A less strict, operational, definition of equilibrium is that of a system that does not change with time during observation.
Equilibrium Phase Diagrams
Give the relationship of composition of a solution as a function of temperatures and the quantities of phases in equilibrium. These diagrams do not indicate the dynamics when one phase transforms into another. Sometimes diagrams are given with pressure as one of the variables. In the phase diagrams we will discuss, pressure is assumed to be constant at one atmosphere.

9.6 Binary Isomorphous Systems
This very simple case is one complete liquid and solid solubility, an isomorphous system. The example is the Cu-Ni alloy of Fig. 9.2a. The complete solubility occurs because both Cu and Ni have the same crystal structure (FCC), near the same radii, electronegativity and valence.
The liquidus line separates the liquid phase from solid or solid + liquid phases. That is, the solution is liquid above the liquidus line.
The solidus line is that below which the solution is completely solid (does not contain a liquid phase.)
Interpretation of phase diagrams
Concentrations: Tie-line method
locate composition and temperature in diagram
In two phase region draw tie line or isotherm
note intersection with phase boundaries. Read compositions.
Fractions: lever rule
construct tie line (isotherm)
obtain ratios of line segments lengths.
Note: the fractions are inversely proportional to the length to the boundary for the particular phase. If the point in the diagram is close to the phase line, the fraction of that phase is large.
Development of microstructure in isomorphous alloys
a) Equilibrium cooling
Solidification in the solid + liquid phase occurs gradually upon cooling from the liquidus line. The composition of the solid and the liquid change gradually during cooling (as can be determined by the tie-line method.) Nuclei of the solid phase form and they grow to consume all the liquid at the solidus line.
b) Non-equilibrium cooling
Solidification in the solid + liquid phase also occurs gradually. The composition of the liquid phase evolves by diffusion, following the equilibrium values that can be derived from the tie-line method. However, diffusion in the solid state is very slow. Hence, the new layers that solidify on top of the grains have the equilibrium composition at that temperature but once they are solid their composition does not change. This lead to the formation of layered (cored) grains (Fig. 9.14) and to the invalidity of the tie-line method to determine the composition of the solid phase (it still works for the liquid phase, where diffusion is fast.)

9.7 Binary Eutectic Systems
Interpretation: Obtain phases present, concentration of phases and their fraction (%).
Solvus line: limit of solubility
Eutectic or invariant point. Liquid and two solid phases exist in equilibrium at the eutectic composition and the eutectic temperature.
Note:
the melting point of the eutectic alloy is lower than that of the components (eutectic = easy to melt in Greek).
At most two phases can be in equilibrium within a phase field.
Single-phase regions are separated by 2-phase regions.
Development of microstructure in eutectic alloys
Case of lead-tin alloys, figures 9.9–9.14. A layered, eutectic structure develops when cooling below the eutectic temperature. Alloys which are to the left of the eutectic concentration (hipoeutectic) or to the right (hypereutectic) form a proeutectic phase before reaching the eutectic temperature, while in the solid + liquid region. The eutectic structure then adds when the remaining liquid is solidified when cooling further. The eutectic microstructure is lamellar (layered) due to the reduced diffusion distances in the solid state.
To obtain the concentration of the eutectic microstructure in the final solid solution, one draws a vertical line at the eutectic concentration and applies the lever rule treating the eutectic as a separate phase (Fig. 9.16).

9.8 Equilibrium Diagrams Having Intermediate Phases or Compounds
A terminal phase or terminal solution is one that exists in the extremes of concentration (0 and 100%) of the phase diagram. One that exists in the middle, separated from the extremes, is called an intermediate phase or solid solution.
An important phase is the intermetallic compound, that has a precise chemical compositions. When using the lever rules, intermetallic compounds are treated like any other phase, except they appear not as a wide region but as a vertical line.

9.9 Eutectoid and Peritectic Reactions
The eutectoid (eutectic-like) reaction is similar to the eutectic reaction but occurs from one solid phase to two new solid phases. It also shows as V on top of a horizontal line in the phase diagram. There are associated eutectoid temperature (or temperature), eutectoid phase, eutectoid and proeutectoid microstructures.
Solid Phase 1 à Solid Phase 2 + Solid Phase 3
The peritectic reaction also involves three solid in equilibrium, the transition is from a solid + liquid phase to a different solid phase when cooling. The inverse reaction occurs when heating.
Solid Phase 1 + liquid à Solid Phase 2

9.10 Congruent Phase Transformations
Another classification scheme. Congruent transformation is one where there is no change in composition, like allotropic transformations (e.g., a-Fe to g-Fe) or melting transitions in pure solids. 9.13 The Iron–Iron Carbide (Fe–Fe3C) Phase Diagram
This is one of the most important alloys for structural applications. The diagram Fe—C is simplified at low carbon concentrations by assuming it is the Fe—Fe3C diagram. Concentrations are usually given in weight percent. The possible phases are:
a-ferrite (BCC) Fe-C solution
g-austenite (FCC) Fe-C solution
d-ferrite (BCC) Fe-C solution
liquid Fe-C solution
Fe3C (iron carbide) or cementite. An intermetallic compound.
The maximum solubility of C in a- ferrite is 0.022 wt%. d-ferrite is only stable at high temperatures. It is not important in practice. Austenite has a maximum C concentration of 2.14 wt %. It is not stable below the eutectic temperature (727 C) unless cooled rapidly (Chapter 10). Cementite is in reality metastable, decomposing into a-Fe and C when heated for several years between 650 and 770 C.
For their role in mechanical properties of the alloy, it is important to note that:
Ferrite is soft and ductile
Cementite is hard and brittle
Thus, combining these two phases in solution an alloy can be obtained with intermediate properties. (Mechanical properties also depend on the microstructure, that is, how ferrite and cementite are mixed.)

Chapter 8. FAILURE

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Introduction
Failure of materials may have huge costs. Causes included improper materials selection or processing, the improper design of components, and improper use.

Fundamentals of Fracture
Fracture is a form of failure where the material separates in pieces due to stress, at temperatures below the melting point. The fracture is termed ductile or brittle depending on whether the elongation is large or small.
Steps in fracture (response to stress):
track formation
track propagation
Ductile vs. brittle fracture

Ductile/ Brittle

deformation extensive/ little

track propagation slow, /needs stress fast

type of materials most metals (not too cold) /ceramics, ice, cold metals

warning permanent elongation /none

strain energy higher /lower

fractured surface rough/ smoother

necking yes/ no

Ductile Fracture
Stages of ductile fracture
Initial necking
small cavity formation (microvoids)
void growth (elipsoid) by coalescence into a crack
fast crack propagation around neck. Shear strain at 45o
final shear fracture (cup and cone)
The interior surface is fibrous, irregular, which signify plastic deformation.

Brittle Fracture
There is no appreciable deformation, and crack propagation is very fast. In most brittle materials, crack propagation (by bond breaking) is along specific crystallographic planes (cleavage planes). This type of fracture is transgranular (through grains) producing grainy texture (or faceted texture) when cleavage direction changes from grain to grain. In some materials, fracture is intergranular. Principles of Fracture Mechanics

Fracture occurs due to stress concentration at flaws, like surface scratches, voids, etc. If a is the length of the void and r the radius of curvature, the enhanced stress near the flaw is:
sm » 2 s0 (a/r)1/2
where s0 is the applied macroscopic stress. Note that a is 1/2 the length of the flaw, not the full length for an internal flaw, but the full length for a surface flaw. The stress concentration factor is:
Kt = sm/s0 » 2 (a/r)1/2
Because of this enhancement, flaws with small radius of curvature are called stress raisers.

Impact Fracture Testing
Normalized tests, like the Charpy and Izod tests measure the impact energy required to fracture a notched specimen with a hammer mounted on a pendulum. The energy is measured by the change in potential energy (height) of the pendulum. This energy is called notch toughness.
Ductile to brittle transition occurs in materials when the temperature is dropped below a transition temperature. Alloying usually increases the ductile-brittle transition temperature (Fig. 8.19.) For ceramics, this type of transition occurs at much higher temperatures than for metals.

Fatigue
Fatigue is the catastrophic failure due to dynamic (fluctuating) stresses. It can happen in bridges, airplanes, machine components, etc. The characteristics are:
long period of cyclic strain
the most usual (90%) of metallic failures (happens also in ceramics and polymers)
is brittle-like even in ductile metals, with little plastic deformation
it occurs in stages involving the initiation and propagation of cracks.

Cyclic Stresses
These are characterized by maximum, minimum and mean stress, the stress amplitude, and the stress ratio

The S—N Curve
S—N curves (stress-number of cycles to failure) are obtained using apparatus like the one shown in Fig. 8.21. Different types of S—N curves are shown in Fig. 8.22.
Fatigue limit (endurance limit) occurs for some materials (like some ferrous and Ti allows). In this case, the S—N curve becomes horizontal at large N . This means that there is a maximum stress amplitude (the fatigue limit) below which the material never fails, no matter how large the number of cycles is.
For other materials (e.g., non-ferrous) the S—N curve continues to fall with N.
Failure by fatigue shows substantial variability (Fig. 8.23).
Failure at low loads is in the elastic strain regime, requires a large number of cycles (typ. 104 to 105). At high loads (plastic regime), one has low-cycle fatigue (N <>Crack Initiation and Propagation
Stages is fatigue failure:
I. crack initiation at high stress points (stress raisers)
II. propagation (incremental in each cycle)
III. final failure by fracture
Nfinal = Ninitiation + Npropagation
Stage I - propagation
slow
along crystallographic planes of high shear stress
flat and featureless fatigue surface
Stage II - propagation
crack propagates by repetive plastic blunting and sharpening of the crack tip. (Fig. 8.25.)
. Crack Propagation Rate (not covered)
. Factors That Affect Fatigue Life
Mean stress (lower fatigue life with increasing smean).
Surface defects (scratches, sharp transitions and edges). Solution:
polish to remove machining flaws
add residual compressive stress (e.g., by shot peening.)
case harden, by carburizing, nitriding (exposing to appropriate gas at high temperature)
. Environmental Effects
Thermal cycling causes expansion and contraction, hence thermal stress, if component is restrained. Solution:
eliminate restraint by design
use materials with low thermal expansion coefficients.
Corrosion fatigue. Chemical reactions induced pits which act as stress raisers. Corrosion also enhances crack propagation. Solutions:
decrease corrosiveness of medium, if possible.
add protective surface coating.
add residual compressive stresses.

Creep
Creep is the time-varying plastic deformation of a material stressed at high temperatures. Examples: turbine blades, steam generators. Keys are the time dependence of the strain and the high temperature.

. Generalized Creep Behavior

At a constant stress, the strain increases initially fast with time (primary or transient deformation), then increases more slowly in the secondary region at a steady rate (creep rate). Finally the strain increases fast and leads to failure in the tertiary region. Characteristics:
Creep rate: de/dt
Time to failure.
. Stress and Temperature Effects
Creep becomes more pronounced at higher temperatures (Fig. 8.37). There is essentially no creep at temperatures below 40% of the melting point.
Creep increases at higher applied stresses.
The behavior can be characterized by the following expression, where K, n and Qc are constants for a given material:
de/dt = K sn exp(-Qc/RT)
. Data Extrapolation Methods (not covered.)
. Alloys for High-Temperature Use
These are needed for turbines in jet engines, hypersonic airplanes, nuclear reactors, etc. The important factors are a high melting temperature, a high elastic modulus and large grain size (the latter is opposite to what is desirable in low-temperature materials).
Some creep resistant materials are stainless steels, refractory metal alloys (containing elements of high melting point, like Nb, Mo, W, Ta), and superalloys (based on Co, Ni, Fe.)

Chapter 7. DISLOCATIONS AND STRENGTHENING MECHANISM

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Introduction
The key idea of the chapter is that plastic deformation is due to the motion of a large number of dislocations. The motion is called slip. Thus, the strength (resistance to deformation) can be improved by putting obstacles to slip.

Basic Concepts
Dislocations can be edge dislocations, screw dislocations and exist in combination of the two (Ch. 4.4). Their motion (slip) occurs by sequential bond breaking and bond reforming (Fig. 7.1). The number of dislocations per unit volume is the dislocation density, in a plane they are measured per unit area.

Characteristics of Dislocations
There is strain around a dislocation which influences how they interact with other dislocations, impurities, etc. There is compression near the extra plane (higher atomic density) and tension following the dislocation line (Fig. 7.4)
Dislocations interact among themselves (Fig. 7.5). When they are in the same plane, they repel if they have the same sign and annihilate if they have opposite signs (leaving behind a perfect crystal). In general, when dislocations are close and their strain fields add to a larger value, they repel, because being close increases the potential energy (it takes energy to strain a region of the material).
The number of dislocations increases dramatically during plastic deformation. Dislocations spawn from existing dislocations, and from defects, grain boundaries and surface irregularities.

Slip Systems
In single crystals there are preferred planes where dislocations move (slip planes). There they do not move in any direction, but in preferred crystallographic directions (slip direction). The set of slip planes and directions constitute slip systems.
The slip planes are those of highest packing density. How do we explain this? Since the distance between atoms is shorter than the average, the distance perpendicular to the plane has to be longer than average. Being relatively far apart, the atoms can move more easily with respect to the atoms of the adjacent plane. (We did not discuss direction and plane nomenclature for slip systems.)
BCC and FCC crystals have more slip systems, that is more ways for dislocation to propagate. Thus, those crystals are more ductile than HCP crystals (HCP crystals are more brittle).

Slip in Single Crystals
A tensile stress s will have components in any plane that is not perpendicular to the stress. These components are resolved shear stresses. Their magnitude depends on orientation (see Fig. 7.7).
tR = s cos f cos l
If the shear stress reaches the critical resolved shear stress tCRSS, slip (plastic deformation) can start. The stress needed is:
sy = tCRSS / (cos f cos l)max
at the angles at which tCRSS is a maximum. The minimum stress needed for yielding is when f = l = 45 degrees: sy = 2tCRSS. Thus, dislocations will occur first at slip planes oriented close to this angle with respect to the applied stress

Chapter-6: Mechanical Properties of Metals

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1.Introduction

Often materials are subject to forces (loads) when they are used. Mechanical engineers calculate those forces and material scientists how materials deform (elongate, compress, twist) or break as a function of applied load, time, temperature, and other conditions.
Materials scientists learn about these mechanical properties by testing materials. Results from the tests depend on the size and shape of material to be tested (specimen), how it is held, and the way of performing the test. That is why we use common procedures, or standards, which are published by the ASTM.

Concepts of Stress and Strain

To compare specimens of different sizes, the load is calculated per unit area, also called normalization to the area. Force divided by area is called stress. In tension and compression tests, the relevant area is that perpendicular to the force. In shear or torsion tests, the area is perpendicular to the axis of rotation.
s = F/A0 tensile or compressive stress
t = F/A0 shear stress
The unit is the Megapascal = 106 Newtons/m2.
There is a change in dimensions, or deformation elongation, DL as a result of a tensile or compressive stress. To enable comparison with specimens of different length, the elongation is also normalized, this time to the length L. This is called strain, e.
e = DL/L
The change in dimensions is the reason we use A0 to indicate the initial area since it changes during deformation. One could divide force by the actual area, this is called true stress (see Sec. 6.7).
For torsional or shear stresses, the deformation is the angle of twist, q (Fig. 6.1) and the shear strain is given by:
g = tg q

Stress—Strain Behavior

Elastic deformation. When the stress is removed, the material returns to the dimension it had before the load was applied. Valid for small strains (except the case of rubbers).
Deformation is reversible, non permanent
Plastic deformation. When the stress is removed, the material does not return to its previous dimension but there is a permanent, irreversible deformation.
In tensile tests, if the deformation is elastic, the stress-strain relationship is called Hooke's law:
s = E e
That is, E is the slope of the stress-strain curve. E is Young's modulus or modulus of elasticity. In some cases, the relationship is not linear so that E can be defined alternatively as the local slope:
E = ds/de
Shear stresses produce strains according to:
t = G g
where G is the shear modulus.
Elastic moduli measure the stiffness of the material. They are related to the second derivative of the interatomic potential, or the first derivative of the force vs. internuclear distance (Fig. 6.6). By examining these curves we can tell which material has a higher modulus. Due to thermal vibrations the elastic modulus decreases with temperature. E is large for ceramics (stronger ionic bond) and small for polymers (weak covalent bond). Since the interatomic distances depend on direction in the crystal, E depends on direction (i.e., it is anisotropic) for single crystals. For randomly oriented policrystals, E is isotropic. .

Anelasticity

Here the behavior is elastic but not the stress-strain curve is not immediately reversible. It takes a while for the strain to return to zero. The effect is normally small for metals but can be significant for polymers.

Elastic Properties of Materials

Materials subject to tension shrink laterally. Those subject to compression, bulge. The ratio of lateral and axial strains is called the Poisson's ratio n.
n = elateral/eaxial
The elastic modulus, shear modulus and Poisson's ratio are related by E = 2G(1+n)

Tensile Properties

Yield point. If the stress is too large, the strain deviates from being proportional to the stress. The point at which this happens is the yield point because there the material yields, deforming permanently (plastically).
Yield stress. Hooke's law is not valid beyond the yield point. The stress at the yield point is called yield stress, and is an important measure of the mechanical properties of materials. In practice, the yield stress is chosen as that causing a permanent strain of 0.002 (strain offset, Fig. 6.9.)
The yield stress measures the resistance to plastic deformation.
The reason for plastic deformation, in normal materials, is not that the atomic bond is stretched beyond repair, but the motion of dislocations, which involves breaking and reforming bonds.
Plastic deformation is caused by the motion of dislocations.
Tensile strength. When stress continues in the plastic regime, the stress-strain passes through a maximum, called the tensile strength (sTS) , and then falls as the material starts to develop a neck and it finally breaks at the fracture point (Fig. 6.10).
Note that it is called strength, not stress, but the units are the same, MPa.
For structural applications, the yield stress is usually a more important property than the tensile strength, since once the it is passed, the structure has deformed beyond acceptable limits.
Ductility. The ability to deform before braking. It is the opposite of brittleness. Ductility can be given either as percent maximum elongation emax or maximum area reduction.
%EL = emax x 100 %
%AR = (A0 - Af)/A0
These are measured after fracture (repositioning the two pieces back together).
Resilience. Capacity to absorb energy elastically. The energy per unit volume is the
area under the strain-stress curve in the elastic region.
Toughness. Ability to absorb energy up to fracture. The energy per unit volume is the total area under the strain-stress curve. It is measured by an impact test (Ch. 8)

True Stress and Strain
When one applies a constant tensile force the material will break after reaching the tensile strength. The material starts necking (the transverse area decreases) but the stress cannot increase beyond sTS. The ratio of the force to the initial area, what we normally do, is called the engineering stress. If the ratio is to the actual area (that changes with stress) one obtains the true stress.
Elastic Recovery During Plastic Deformation
If a material is taken beyond the yield point (it is deformed plastically) and the stress is then released, the material ends up with a permanent strain. If the stress is reapplied, the material again responds elastically at the beginning up to a new yield point that is higher than the original yield point (strain hardening, Ch. 7.10). The amount of elastic strain that it will take before reaching the yield point is called elastic strain recovery (Fig. 6. 16).

Compressive, Shear, and Torsional Deformation
Compressive and shear stresses give similar behavior to tensile stresses, but in the case of compressive stresses there is no maximum in the s-e curve, since no necking occurs.

Hardness
Hardness is the resistance to plastic deformation (e.g., a local dent or scratch). Thus, it is a measure of plastic deformation, as is the tensile strength, so they are well correlated. Historically, it was measured on an empirically scale, determined by the ability of a material to scratch another, diamond being the hardest and talc the softer. Now we use standard tests, where a ball, or point is pressed into a material and the size of the dent is measured. There are a few different hardness tests: Rockwell, Brinell, Vickers, etc. They are popular because they are easy and non-destructive (except for the small dent).

Variability of Material Properties
Tests do not produce exactly the same result because of variations in the test equipment, procedures, operator bias, specimen fabrication, etc. But, even if all those parameters are controlled within strict limits, a variation remains in the materials, due to uncontrolled variations during fabrication, non homogenous composition and structure, etc. The measured mechanical properties will show scatter, which is often distributed in a Gaussian curve (bell-shaped), that is characterized by the mean value and the standard deviation (width).

Design/Safety Factors
To take into account variability of properties, designers use, instead of an average value of, say, the tensile strength, the probability that the yield strength is above the minimum value tolerable. This leads to the use of a safety factor N > 1 (typ. 1.2 - 4). Thus, a working value for the tensile strength would be sW = sTS / N.
Not tested: true stress-true stain relationships, details of the different types of hardness tests, but should know that hardness for a given material correlates with tensile strength. Varia

Chapter-5: DIFUSSION

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5.1 Introduction

Many important reactions and processes in materials occur by the motion of atoms in the solid (transport), which happens by diffusion.
Inhomogeneous materials can become homogeneous by diffusion, if the temperature is high enough (temperature is needed to overcome energy barriers to atomic motion.

5.2 Diffusion Mechanisms

Atom diffusion can occur by the motion of vacancies (vacancy diffusion) or impurities (impurity diffusion). The energy barrier is that due to nearby atoms which need to move to let the atoms go by. This is more easily achieved when the atoms vibrate strongly, that is, at high temperatures.
There is a difference between diffusion and net diffusion. In a homogeneous material, atoms also diffuse but this motion is hard to detect. This is because atoms move randomly and there will be an equal number of atoms moving in one direction than in another. In inhomogeneous materials, the effect of diffusion is readily seen by a change in concentration with time. In this case there is a net diffusion. Net diffusion occurs because, although all atoms are moving randomly, there are more atoms moving in regions where their concentration is higher.

5.3 Steady-State Diffusion

The flux of diffusing atoms, J, is expressed either in number of atoms per unit area and per unit time (e.g., atoms/m2-second) or in terms of mass flux (e.g., kg/m2-second).
Steady state diffusion means that J does not depend on time. In this case, Fick’s first law holds that the flux along direction x is:
J = – D dC/dx
Where dC/dx is the gradient of the concentration C, and D is the diffusion constant. The concentration gradient is often called the driving force in diffusion (but it is not a force in the mechanistic sense). The minus sign in the equation means that diffusion is down the concentration gradient.

5.4 Nonsteady-State Diffusion

This is the case when the diffusion flux depends on time, which means that a type of atoms accumulates in a region or that it is depleted from a region (which may cause them to accumulate in another region).

5.5 Factors That Influence Diffusion

As stated above, there is a barrier to diffusion created by neighboring atoms that need to move to let the diffusing atom pass. Thus, atomic vibrations created by temperature assist diffusion. Also, smaller atoms diffuse more readily than big ones, and diffusion is faster in open lattices or in open directions. Similar to the case of vacancy formation, the effect of temperature in diffusion is given by a Boltzmann factor: D = D0 × exp(–Qd/kT).

5.6 Other Diffusion Paths

Diffusion occurs more easily along surfaces, and voids in the material (short circuits like dislocations and grain boundaries) because less atoms need to move to let the diffusing atom pass. Short circuits are often unimportant because they constitute a negligible part of the total area of the material normal to the diffusion flux. .

Chapter-4: IMPERFECTIONS

2008-01-29T02:55:00.000-08:00

Imperfections in Solids

4.1 Introduction

Materials are often stronger when they have defects. The study of defects is divided according to their dimension:
0D (zero dimension) – point defects: vacancies and interstitials. Impurities.
1D – linear defects: dislocations (edge, screw, mixed)
2D – grain boundaries, surfaces.
3D – extended defects: pores, cracks.
Point Defects

4.2 Vacancies and Self-Interstitials

A vacancy is a lattice position that is vacant because the atom is missing. It is created when the solid is formed. There are other ways of making a vacancy, but they also occur naturally as a result of thermal vibrations.
An interstitial is an atom that occupies a place outside the normal lattice position. It may be the same type of atom as the others (self interstitial) or an impurity atom.
In the case of vacancies and interstitials, there is a change in the coordination of atoms around the defect. This means that the forces are not balanced in the same way as for other atoms in the solid, which results in lattice distortion around the defect.
The number of vacancies formed by thermal agitation follows the law:
NV = NA × exp(-QV/kT)
where NA is the total number of atoms in the solid, QV is the energy required to form a vacancy, k is Boltzmann constant, and T the temperature in Kelvin (note, not in oC or oF).
When QV is given in joules, k = 1.38 × 10-23 J/atom-K. When using eV as the unit of energy, k = 8.62 × 10-5 eV/atom-K.
Note that kT(300 K) = 0.025 eV (room temperature) is much smaller than typical vacancy formation energies. For instance, QV(Cu) = 0.9 eV/atom. This means that NV/NA at room temperature is exp(-36) = 2.3 × 10-16, an insignificant number. Thus, a high temperature is needed to have a high thermal concentration of vacancies. Even so, NV/NA is typically only about 0.0001 at the melting point.
stalline SiO2 (quartz) is still apparent in amorphous SiO2 (silica glass.)

4.3 Impurities in Solids

All real solids are impure. A very high purity material, say 99.9999% pure (called 6N – six nines) contains ~ 6 × 1016 impurities per cm3.
Impurities are often added to materials to improve the properties. For instance, carbon added in small amounts to iron makes steel, which is stronger than iron. Boron impurities added to silicon drastically change its electrical properties.
Solid solutions are made of a host, the solvent or matrix) which dissolves the solute (minor component). The ability to dissolve is called solubility. Solid solutions are:
homogeneous
maintain crystal structure
contain randomly dispersed impurities (substitutional or interstitial)
Factors for high solubility
Similar atomic size (to within 15%)
Similar crystal structure
Similar electronegativity (otherwise a compound is formed)
Similar valence
Composition can be expressed in weight percent, useful when making the solution, and in atomic percent, useful when trying to understand the material at the atomic level.
Miscellaneous Imperfections

4.4 Dislocations—Linear Defects

Dislocations are abrupt changes in the regular ordering of atoms, along a line (dislocation line) in the solid. They occur in high density and are very important in mechanical properties of material. They are characterized by the Burgers vector, found by doing a loop around the dislocation line and noticing the extra interatomic spacing needed to close the loop. The Burgers vector in metals points in a close packed direction.
Edge dislocations occur when an extra plane is inserted. The dislocation line is at the end of the plane. In an edge dislocation, the Burgers vector is perpendicular to the dislocation line.
Screw dislocations result when displacing planes relative to each other through shear. In this case, the Burgers vector is parallel to the dislocation line.

4.5 Interfacial Defects

The environment of an atom at a surface differs from that of an atom in the bulk, in that the number of neighbors (coordination) decreases. This introduces unbalanced forces which result in relaxation (the lattice spacing is decreased) or reconstruction (the crystal structure changes).
The density of atoms in the region including the grain boundary is smaller than the bulk value, since void space occurs in the interface.
Surfaces and interfaces are very reactive and it is usual that impurities segregate there. Since energy is required to form a surface, grains tend to grow in size at the expense of smaller grains to minimize energy. This occurs by diffusion, which is accelerated at high temperatures.
Twin boundaries: not covered

4.6 Bulk or Volume Defects

A typical volume defect is porosity, often introduced in the solid during processing. A common example is snow, which is highly porous ice.

4.7 Atomic Vibrations

Atomic vibrations occur, even at zero temperature (a quantum mechanical effect) and increase in amplitude with temperature. Vibrations displace transiently atoms from their regular lattice site, which destroys the perfect periodicity we discussed in Chapter 3.

Chapter-3: STRUCTURE OF CRYSTALS

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3.2 Fundamental Concepts

Atoms self-organize in crystals, most of the time. The crystalline lattice, is a periodic array of the atoms. When the solid is not crystalline, it is called amorphous. Examples of crystalline solids are metals, diamond and other precious stones, ice, graphite. Examples of amorphous solids are glass, amorphous carbon (a-C), amorphous Si, most plastics
To discuss crystalline structures it is useful to consider atoms as being hard spheres, with well-defined radii. In this scheme, the shortest distance between two like atoms is one diameter.

3.3 Unit Cells

The unit cell is the smallest structure that repeats itself by translation through the crystal. We construct these symmetrical units with the hard spheres. The most common types of unit cells are the faced-centered cubic (FCC), the body-centered cubic (FCC) and the hexagonal close-packed (HCP). Other types exist, particularly among minerals. The simple cube (SC) is often used for didactical purpose, no material has this structure.

3.4 Metallic Crystal Structures

Important properties of the unit cells are
· The type of atoms and their radii R.
· cell dimensions (side a in cubic cells, side of base a and height c in HCP) in terms of R.
· n, number of atoms per unit cell. For an atom that is shared with m adjacent unit cells, we only count a fraction of the atom, 1/m.
· CN, the coordination number, which is the number of closest neighbors to which an atom is bonded.
· APF, the atomic packing factor, which is the fraction of the volume of the cell actually occupied by the hard spheres. APF = Sum of atomic volumes/Volume of cell.
Unit Cell n CN a/R APF
SC 1 6 2 0.52
BCC 2 8 4Ö 3 0.68
FCC 4 12 2Ö 2 0.74
HCP 6 12 0.74
The closest packed direction in a BCC cell is along the diagonal of the cube; in a FCC cell is along the diagonal of a face of the cube.

3.5 Density Computations

The density of a solid is that of the unit cell, obtained by dividing the mass of the atoms (n atoms x Matom) and dividing by Vc the volume of the cell (a3 in the case of a cube). If the mass of the atom is given in amu (A), then we have to divide it by the Avogadro number to get Matom. Thus, the formula for the density is:

3.6 Polymorphism and Allotropy

Some materials may exist in more than one crystal structure, this is called polymorphism. If the material is an elemental solid, it is called allotropy. An example of allotropy is carbon, which can exist as diamond, graphite, and amorphous carbon.

3.11 Close-Packed Crystal Structures
The FCC and HCP are related, and have the same APF. They are built by packing spheres on top of each other, in the hollow sites (Fig. 3.12 of book). The packing is alternate between two types of sites, ABABAB.. in the HCP structure, and alternates between three types of positions, ABCABC… in the FCC crystals.
Crystalline and Non-Crystalline Materials

3.12 Single Crystals
Crystals can be single crystals where the whole solid is one crystal. Then it has a regular geometric structure with flat faces.

3.13 Polycrystalline Materials
A solid can be composed of many crystalline grains, not aligned with each other. It is called polycrystalline. The grains can be more or less aligned with respect to each other. Where they meet is called a grain boundary.

3.14 Anisotropy
Different directions in the crystal have a different packing. For instance, atoms along the edge FCC crystals are more separated than along the face diagonal. This causes anisotropy in the properties of crystals; for instance, the deformation depends on the direction in which a stress is applied.

3.15 X-Ray Diffraction Determination of Crystalline Structure – not covered

3.16 Non-Crystalline Solids
In amorphous solids, there is no long-range order. But amorphous does not mean random, since the distance between atoms cannot be smaller than the size of the hard spheres. Also, in many cases there is some form of short-range order. For instance, the tetragonal order of cry

Chapter 2. ATOMIC STRUCTURE AND BONDING

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2.2 Fundamental Concepts

Atoms are composed of electrons, protons, and neutrons. Electron and protons are negative and positive charges of the same magnitude, 1.6 × 10-19 Coulombs.
The mass of the electron is negligible with respect to those of the proton and the neutron, which form the nucleus of the atom. The unit of mass is an atomic mass unit (amu) = 1.66 × 10-27 kg, and equals 1/12 the mass of a carbon atom. The Carbon nucleus has Z=6, and A=6, where Z is the number of protons, and A the number of neutrons. Neutrons and protons have very similar masses, roughly equal to 1 amu. A neutral atom has the same number of electrons and protons, Z.
A mole is the amount of matter that has a mass in grams equal to the atomic mass in amu of the atoms. Thus, a mole of carbon has a mass of 12 grams. The number of atoms in a mole is called the Avogadro number, Nav = 6.023 × 1023. Note that Nav = 1 gram/1 amu.
Calculating n, the number of atoms per cm3 in a piece of material of density d (g/cm3).
n = Nav × d / M
where M is the atomic mass in amu (grams per mol). Thus, for graphite (carbon) with a density d = 1.8 g/cm3, M =12, we get 6 × 1023 atoms/mol × 1.8 g/cm3 / 12 g/mol) = 9 × 1022 C/cm3.
For a molecular solid like ice, one uses the molecular mass, M(H2O) = 18. With a density of 1 g/cm3, one obtains n = 3.3 × 1022 H2O/cm3. Note that since the water molecule contains 3 atoms, this is equivalent to 9.9 × 1022 atoms/cm3.
Most solids have atomic densities around 6 × 1022 atoms/cm3. The cube root of that number gives the number of atoms per centimeter, about 39 million. The mean distance between atoms is the inverse of that, or 0.25 nm. This is an important number that gives the scale of atomic structures in solids.

2.3 Electrons in Atoms

The forces in the atom are repulsions between electrons and attraction between electrons and protons. The neutrons play no significant role. Thus, Z is what characterizes the atom.
The electrons form a cloud around the neutron, of radius of 0.05 – 2 nanometers. Electrons do not move in circular orbits, as in popular drawings, but in 'fuzzy' orbits. We cannot tell how it moves, but only say what is the probability of finding it at some distance from the nucleus. According to quantum mechanics, only certain orbits are allowed (thus, the idea of a mini planetary system is not correct). The orbits are identified by a principal quantum number n, which can be related to the size, n = 0 is the smallest; n = 1, 2 .. are larger. (They are "quantized" or discrete, being specified by integers). The angular momentum l is quantized, and so is the projection in a specific direction m. The structure of the atom is determined by the Pauli exclusion principle, only two electrons can be placed in an orbit with a given n, l, m – one for each spin. Table 2.1 in the textbook gives the number of electrons in each shell (given by n) and subshells (given by l).

2.4 The Periodic Table

Elements are categorized by placing them in the periodic table. Elements in a column share similar properties. The noble gases have closed shells, and so they do not gain or lose electrons near another atom. Alkalis can easily lose an electron and become a closed shell; halogens can easily gain one to form a negative ion, again with a closed shell. The propensity to form closed shells occurs in molecules, when they share electrons to close a molecular shell. Examples are H2, N2, and NaCl.
The ability to gain or lose electrons is termed electronegativity or electropositivity, an important factor in ionic bonds.

2.5 Bonding Forces and Energies

The Coulomb forces are simple: attractive between electrons and nuclei, repulsive between electrons and between nuclei. The force between atoms is given by a sum of all the individual forces, and the fact that the electrons are located outside the atom and the nucleus in the center.
When two atoms come very close, the force between them is always repulsive, because the electrons stay outside and the nuclei repel each other. Unless both atoms are ions of the same charge (e.g., both negative) the forces between atoms is always attractive at large internuclear distances r. Since the force is repulsive at small r, and attractive at small r, there is a distance at which the force is zero. This is the equilibrium distance at which the atoms prefer to stay.
The interaction energy is the potential energy between the atoms. It is negative if the atoms are bound and positive if they can move away from each other. The interaction energy is the integral of the force over the separation distance, so these two quantities are directly related. The interaction energy is a minimum at the equilibrium position. This value of the energy is called the bond energy, and is the energy needed to separate completely to infinity (the work that needs to be done to overcome the attractive force.) The strongest the bond energy, the hardest is to move the atoms, for instance the hardest it is to melt the solid, or to evaporate its atoms.

2.6 Primary Interatomic Bonds

Ionic Bonding
This is the bond when one of the atoms is negative (has an extra electron) and another is positive (has lost an electron). Then there is a strong, direct Coulomb attraction. An example is NaCl. In the molecule, there are more electrons around Cl, forming Cl- and less around Na, forming Na+. Ionic bonds are the strongest bonds. In real solids, ionic bonding is usually combined with covalent bonding. In this case, the fractional ionic bonding is defined as %ionic = 100 × [1 – exp(-0.25 (XA – XB)2], where XA and XB are the electronegativities of the two atoms, A and B, forming the molecule.
Covalent Bonding
In covalent bonding, electrons are shared between the molecules, to saturate the valency. The simplest example is the H2 molecule, where the electrons spend more time in between the nuclei than outside, thus producing bonding.
Metallic Bonding
In metals, the atoms are ionized, loosing some electrons from the valence band. Those electrons form a electron sea, which binds the charged nuclei in place, in a similar way that the electrons in between the H atoms in the H2 molecule bind the protons.

2.7 Secondary Bonding (Van der Waals)

Fluctuating Induced Dipole Bonds
Since the electrons may be on one side of the atom or the other, a dipole is formed: the + nucleus at the center, and the electron outside. Since the electron moves, the dipole fluctuates. This fluctuation in atom A produces a fluctuating electric field that is felt by the electrons of an adjacent atom, B. Atom B then polarizes so that its outer electrons are on the side of the atom closest to the + side (or opposite to the – side) of the dipole in A. This bond is called van der Waals bonding.
Polar Molecule-Induced Dipole Bonds
A polar molecule like H2O (Hs are partially +, O is partially – ), will induce a dipole in a nearby atom, leading to bonding.
Permanent Dipole Bonds
This is the case of the hydrogen bond in ice. The H end of the molecule is positively charged and can bond to the negative side of another dipolar molecule, like the O side of the H2O dipole.

2.8 Molecules

If molecules formed a closed shell due to covalent bonding (like H2, N2) then the interaction between molecules is weak, of the van der Waals type. Thus, molecular solids usually have very low melting points

Chapter-9: PHASE DIAGRAMS

2008-01-12T02:09:00.005-08:00

9.1 Introduction

Definitions
Component: pure metal or compound (e.g., Cu, Zn in Cu-Zn alloy, sugar, water, in a syrup.)
Solvent: host or major component in solution.
Solute: dissolved, minor component in solution.
System: set of possible alloys from same component (e.g., iron-carbon system.)
Solubility Limit: Maximum solute concentration that can be dissolved at a given temperature.
Phase: part with homogeneous physical and chemical characteristics

9.2 Solubility Limit
Effect of temperature on solubility limit. Maximum content: saturation. Exceeding maximum content (like when cooling) leads to precipitation.

9.3 Phases
One-phase systems are homogeneous. Systems with two or more phases are heterogeneous, or mixtures. This is the case of most metallic alloys, but also happens in ceramics and polymers.
A two-component alloy is called binary. One with three components, ternary.

9.4 Microstructure
The properties of an alloy do not depend only on concentration of the phases but how they are arranged structurally at the microscopy level. Thus, the microstructure is specified by the number of phases, their proportions, and their arrangement in space.
A binary alloy may be
a. a single solid solution
b. two separated, essentially pure components.
c. two separated solid solutions.
d. a chemical compound, together with a solid solution.
The way to tell is to cut the material, polish it to a mirror finish, etch it a weak acid (components etch at a different rate) and observe the surface under a microscope.

9.5 Phase Equilibria
Equilibrium is the state of minimum energy. It is achieved given sufficient time. But the time to achieve equilibrium may be so long (the kinetics is so slow) that a state that is not at an energy minimum may have a long life and appear to be stable. This is called a metastable state.
A less strict, operational, definition of equilibrium is that of a system that does not change with time during observation.
Equilibrium Phase Diagrams
Give the relationship of composition of a solution as a function of temperatures and the quantities of phases in equilibrium. These diagrams do not indicate the dynamics when one phase transforms into another. Sometimes diagrams are given with pressure as one of the variables. In the phase diagrams we will discuss, pressure is assumed to be constant at one atmosphere.

9.6 Binary Isomorphous Systems
This very simple case is one complete liquid and solid solubility, an isomorphous system. The example is the Cu-Ni alloy of Fig. 9.2a. The complete solubility occurs because both Cu and Ni have the same crystal structure (FCC), near the same radii, electronegativity and valence.
The liquidus line separates the liquid phase from solid or solid + liquid phases. That is, the solution is liquid above the liquidus line.
The solidus line is that below which the solution is completely solid (does not contain a liquid phase.)
Interpretation of phase diagrams
Concentrations: Tie-line method
a. locate composition and temperature in diagram
b. In two phase region draw tie line or isotherm
c. note intersection with phase boundaries. Read compositions.
Fractions: lever rule
a. construct tie line (isotherm)
b. obtain ratios of line segments lengths.
Note: the fractions are inversely proportional to the length to the boundary for the particular phase. If the point in the diagram is close to the phase line, the fraction of that phase is large.
Development of microstructure in isomorphous alloys
a) Equilibrium cooling
Solidification in the solid + liquid phase occurs gradually upon cooling from the liquidus line. The composition of the solid and the liquid change gradually during cooling (as can be determined by the tie-line method.) Nuclei of the solid phase form and they grow to consume all the liquid at the solidus line.
b) Non-equilibrium cooling
Solidification in the solid + liquid phase also occurs gradually. The composition of the liquid phase evolves by diffusion, following the equilibrium values that can be derived from the tie-line method. However, diffusion in the solid state is very slow. Hence, the new layers that solidify on top of the grains have the equilibrium composition at that temperature but once they are solid their composition does not change. This lead to the formation of layered (cored) grains (Fig. 9.14) and to the invalidity of the tie-line method to determine the composition of the solid phase (it still works for the liquid phase, where diffusion is fast.)

9.7 Binary Eutectic Systems
Interpretation: Obtain phases present, concentration of phases and their fraction (%).
Solvus line: limit of solubility
Eutectic or invariant point. Liquid and two solid phases exist in equilibrium at the eutectic composition and the eutectic temperature.
Note:
· the melting point of the eutectic alloy is lower than that of the components (eutectic = easy to melt in Greek).
· At most two phases can be in equilibrium within a phase field.
· Single-phase regions are separated by 2-phase regions.
Development of microstructure in eutectic alloys
Case of lead-tin alloys, figures 9.9–9.14. A layered, eutectic structure develops when cooling below the eutectic temperature. Alloys which are to the left of the eutectic concentration (hipoeutectic) or to the right (hypereutectic) form a proeutectic phase before reaching the eutectic temperature, while in the solid + liquid region. The eutectic structure then adds when the remaining liquid is solidified when cooling further. The eutectic microstructure is lamellar (layered) due to the reduced diffusion distances in the solid state.
To obtain the concentration of the eutectic microstructure in the final solid solution, one draws a vertical line at the eutectic concentration and applies the lever rule treating the eutectic as a separate phase

9.8 Equilibrium Diagrams Having Intermediate Phases or Compounds
A terminal phase or terminal solution is one that exists in the extremes of concentration (0 and 100%) of the phase diagram. One that exists in the middle, separated from the extremes, is called an intermediate phase or solid solution.
An important phase is the intermetallic compound, that has a precise chemical compositions. When using the lever rules, intermetallic compounds are treated like any other phase, except they appear not as a wide region but as a vertical line.

9.9 Eutectoid and Peritectic Reactions
The eutectoid (eutectic-like) reaction is similar to the eutectic reaction but occurs from one solid phase to two new solid phases. It also shows as V on top of a horizontal line in the phase diagram. There are associated eutectoid temperature (or temperature), eutectoid phase, eutectoid and proeutectoid microstructures.
Solid Phase 1 à Solid Phase 2 + Solid Phase 3
The peritectic reaction also involves three solid in equilibrium, the transition is from a solid + liquid phase to a different solid phase when cooling. The inverse reaction occurs when heating.
Solid Phase 1 + liquid à Solid Phase 2

9.10 Congruent Phase Transformations
Another classification scheme. Congruent transformation is one where there is no change in composition, like allotropic transformations (e.g., a-Fe to g-Fe) or melting transitions in pure solids.

9.13 The Iron–Iron Carbide (Fe–Fe3C) Phase Diagram
This is one of the most important alloys for structural applications. The diagram Fe—C is simplified at low carbon concentrations by assuming it is the Fe—Fe3C diagram. Concentrations are usually given in weight percent. The possible phases are:
· a-ferrite (BCC) Fe-C solution
· g-austenite (FCC) Fe-C solution
· d-ferrite (BCC) Fe-C solution
· liquid Fe-C solution
· Fe3C (iron carbide) or cementite. An intermetallic compound.
The maximum solubility of C in a- ferrite is 0.022 wt%. d-ferrite is only stable at high temperatures. It is not important in practice. Austenite has a maximum C concentration of 2.14 wt %. It is not stable below the eutectic temperature (727 C) unless cooled rapidly (Chapter 10). Cementite is in reality metastable, decomposing into a-Fe and C when heated for several years between 650 and 770 C.
For their role in mechanical properties of the alloy, it is important to note that:
Ferrite is soft and ductile
Cementite is hard and brittle
Thus, combining these two phases in solution an alloy can be obtained with intermediate properties. (Mechanical properties also depend on the microstructure, that is, how ferrite and cementite are mixed.)

9.14 Development of Microstructures in Iron—Carbon Alloys
The eutectoid composition of austenite is 0.76 wt %. When it cools slowly it forms perlite, a lamellar or layered structure of two phases: a-ferrite and cementite (Fe3C).
Hypoeutectoid alloys contain proeutectoid ferrite plus the eutectoid perlite. Hypereutectoid alloys contain proeutectoid cementite plus perlite.
Since reactions below the eutectoid temperature are in the solid phase, the equilibrium is not achieved by usual cooling from austenite. The new microstructures that form are discussed in Ch. 10.

9.15 The Influence of Other Alloying Elements
As mentioned in section 7.9, alloying strengthens metals by hindering the motion of dislocations. Thus, the strength of Fe–C alloys increase with C content and also with the addition of other elements.

Chapter 2. ATOMIC STRUCTURE AND BONDING

2008-01-12T02:09:00.004-08:00

2.2 Fundamental Concepts
Atoms are composed of electrons, protons, and neutrons. Electron and protons are negative and positive charges of the same magnitude, 1.6 × 10-19 Coulombs.
The mass of the electron is negligible with respect to those of the proton and the neutron, which form the nucleus of the atom. The unit of mass is an atomic mass unit (amu) = 1.66 × 10-27 kg, and equals 1/12 the mass of a carbon atom. The Carbon nucleus has Z=6, and A=6, where Z is the number of protons, and A the number of neutrons. Neutrons and protons have very similar masses, roughly equal to 1 amu. A neutral atom has the same number of electrons and protons, Z.
A mole is the amount of matter that has a mass in grams equal to the atomic mass in amu of the atoms. Thus, a mole of carbon has a mass of 12 grams. The number of atoms in a mole is called the Avogadro number, Nav = 6.023 × 1023. Note that Nav = 1 gram/1 amu.
Calculating n, the number of atoms per cm3 in a piece of material of density d (g/cm3).
n = Nav × d / M
where M is the atomic mass in amu (grams per mol). Thus, for graphite (carbon) with a density d = 1.8 g/cm3, M =12, we get 6 × 1023 atoms/mol × 1.8 g/cm3 / 12 g/mol) = 9 × 1022 C/cm3.
For a molecular solid like ice, one uses the molecular mass, M(H2O) = 18. With a density of 1 g/cm3, one obtains n = 3.3 × 1022 H2O/cm3. Note that since the water molecule contains 3 atoms, this is equivalent to 9.9 × 1022 atoms/cm3.
Most solids have atomic densities around 6 × 1022 atoms/cm3. The cube root of that number gives the number of atoms per centimeter, about 39 million. The mean distance between atoms is the inverse of that, or 0.25 nm. This is an important number that gives the scale of atomic structures in solids.

2.3 Electrons in Atoms
The forces in the atom are repulsions between electrons and attraction between electrons and protons. The neutrons play no significant role. Thus, Z is what characterizes the atom.
The electrons form a cloud around the neutron, of radius of 0.05 – 2 nanometers. Electrons do not move in circular orbits, as in popular drawings, but in 'fuzzy' orbits. We cannot tell how it moves, but only say what is the probability of finding it at some distance from the nucleus. According to quantum mechanics, only certain orbits are allowed (thus, the idea of a mini planetary system is not correct). The orbits are identified by a principal quantum number n, which can be related to the size, n = 0 is the smallest; n = 1, 2 .. are larger. (They are "quantized" or discrete, being specified by integers). The angular momentum l is quantized, and so is the projection in a specific direction m. The structure of the atom is determined by the Pauli exclusion principle, only two electrons can be placed in an orbit with a given n, l, m – one for each spin. Table 2.1 in the textbook gives the number of electrons in each shell (given by n) and subshells (given by l).

2.4 The Periodic Table
Elements are categorized by placing them in the periodic table. Elements in a column share similar properties. The noble gases have closed shells, and so they do not gain or lose electrons near another atom. Alkalis can easily lose an electron and become a closed shell; halogens can easily gain one to form a negative ion, again with a closed shell. The propensity to form closed shells occurs in molecules, when they share electrons to close a molecular shell. Examples are H2, N2, and NaCl.
The ability to gain or lose electrons is termed electronegativity or electropositivity, an important factor in ionic bonds.

2.5 Bonding Forces and Energies
The Coulomb forces are simple: attractive between electrons and nuclei, repulsive between electrons and between nuclei. The force between atoms is given by a sum of all the individual forces, and the fact that the electrons are located outside the atom and the nucleus in the center.
When two atoms come very close, the force between them is always repulsive, because the electrons stay outside and the nuclei repel each other. Unless both atoms are ions of the same charge (e.g., both negative) the forces between atoms is always attractive at large internuclear distances r. Since the force is repulsive at small r, and attractive at small r, there is a distance at which the force is zero. This is the equilibrium distance at which the atoms prefer to stay.
The interaction energy is the potential energy between the atoms. It is negative if the atoms are bound and positive if they can move away from each other. The interaction energy is the integral of the force over the separation distance, so these two quantities are directly related. The interaction energy is a minimum at the equilibrium position. This value of the energy is called the bond energy, and is the energy needed to separate completely to infinity (the work that needs to be done to overcome the attractive force.) The strongest the bond energy, the hardest is to move the atoms, for instance the hardest it is to melt the solid, or to evaporate its atoms.

2.6 Primary Interatomic Bonds

Ionic Bonding
This is the bond when one of the atoms is negative (has an extra electron) and another is positive (has lost an electron). Then there is a strong, direct Coulomb attraction. An example is NaCl. In the molecule, there are more electrons around Cl, forming Cl- and less around Na, forming Na+. Ionic bonds are the strongest bonds. In real solids, ionic bonding is usually combined with covalent bonding. In this case, the fractional ionic bonding is defined as %ionic = 100 × [1 – exp(-0.25 (XA – XB)2], where XA and XB are the electronegativities of the two atoms, A and B, forming the molecule.

Covalent Bonding
In covalent bonding, electrons are shared between the molecules, to saturate the valency. The simplest example is the H2 molecule, where the electrons spend more time in between the nuclei than outside, thus producing bonding.

Metallic Bonding
In metals, the atoms are ionized, loosing some electrons from the valence band. Those electrons form a electron sea, which binds the charged nuclei in place, in a similar way that the electrons in between the H atoms in the H2 molecule bind the protons.
2.7 Secondary Bonding (Van der Waals)

Fluctuating Induced Dipole Bonds
Since the electrons may be on one side of the atom or the other, a dipole is formed: the + nucleus at the center, and the electron outside. Since the electron moves, the dipole fluctuates. This fluctuation in atom A produces a fluctuating electric field that is felt by the electrons of an adjacent atom, B. Atom B then polarizes so that its outer electrons are on the side of the atom closest to the + side (or opposite to the – side) of the dipole in A. This bond is called van der Waals bonding.

Polar Molecule-Induced Dipole Bonds
A polar molecule like H2O (Hs are partially +, O is partially – ), will induce a dipole in a nearby atom, leading to bonding.
Permanent Dipole Bonds
This is the case of the hydrogen bond in ice. The H end of the molecule is positively charged and can bond to the negative side of another dipolar molecule, like the O side of the H2O dipole.

2.8 Molecules
If molecules formed a closed shell due to covalent bonding (like H2, N2) then the interaction between molecules is weak, of the van der Waals type. Thus, molecular solids usually have very low melting points

Chapter 1. INRODUCTION

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1 .1 Historical Perspective
Materials are so important in the development of civilization that we associate Ages with them. In the origin of human life on Earth, the Stone Age, people used only natural materials, like stone, clay, skins, and wood. When people found copper and how to make it harder by alloying, the Bronze Age started about 3000 BC. The use of iron and steel, a stronger material that gave advantage in wars started at about 1200 BC. The next big step was the discovery of a cheap process to make steel around 1850, which enabled the railroads and the building of the modern infrastructure of the industrial world.

1.2 Materials Science and Engineering
Understanding of how materials behave like they do, and why they differ in properties was only possible with the atomistic understanding allowed by quantum mechanics, that first explained atoms and then solids starting in the 1930s. The combination of physics, chemistry, and the focus on the relationship between the properties of a material and its microstructure is the domain of Materials Science. The development of this science allowed designing materials and provided a knowledge base for the engineering applications (Materials Engineering).
Structure:
· At the atomic level: arrangement of atoms in different ways. (Gives different properties for graphite than diamond both forms of carbon.)
· At the microscopic level: arrangement of small grains of material that can be identified by microscopy. (Gives different optical properties to transparent vs. frosted glass.)
Properties are the way the material responds to the environment. For instance, the mechanical, electrical and magnetic properties are the responses to mechanical, electrical and magnetic forces, respectively. Other important properties are thermal (transmission of heat, heat capacity), optical (absorption, transmission and scattering of light), and the chemical stability in contact with the environment (like corrosion resistance).
Processing of materials is the application of heat (heat treatment), mechanical forces, etc. to affect their microstructure and, therefore, their properties.
1.3 Why Study Materials Science and Engineering?
· To be able to select a material for a given use based on considerations of cost and performance.
· To understand the limits of materials and the change of their properties with use.
· To be able to create a new material that will have some desirable properties.
All engineering disciplines need to know about materials. Even the most "immaterial", like software or system engineering depend on the development of new materials, which in turn alter the economics, like software-hardware trade-offs. Increasing applications of system engineering are in materials manufacturing (industrial engineering) and complex environmental systems.
1.4 Classification of Materials
Like many other things, materials are classified in groups, so that our brain can handle the complexity. One could classify them according to structure, or properties, or use. The one that we will use is according to the way the atoms are bound together:
Metals: valence electrons are detached from atoms, and spread in an 'electron sea' that "glues" the ions together. Metals are usually strong, conduct electricity and heat well and are opaque to light (shiny if polished). Examples: aluminum, steel, brass, gold.
Semiconductors: the bonding is covalent (electrons are shared between atoms). Their electrical properties depend extremely strongly on minute proportions of contaminants. They are opaque to visible light but transparent to the infrared. Examples: Si, Ge, GaAs.
Ceramics: atoms behave mostly like either positive or negative ions, and are bound by Coulomb forces between them. They are usually combinations of metals or semiconductors with oxygen, nitrogen or carbon (oxides, nitrides, and carbides). Examples: glass, porcelain, many minerals.
Polymers: are bound by covalent forces and also by weak van der Waals forces, and usually based on H, C and other non-metallic elements. They decompose at moderate temperatures (100 – 400 C), and are lightweight. Other properties vary greatly. Examples: plastics (nylon, Teflon, polyester) and rubber.
Other categories are not based on bonding. A particular microstructure identifies composites, made of different materials in intimate contact (example: fiberglass, concrete, wood) to achieve specific properties. Biomaterials can be any type of material that is biocompatible and used, for instance, to replace human body parts.

1.5 Advanced Materials
Materials used in "High-Tec" applications, usually designed for maximum performance, and normally expensive. Examples are titanium alloys for supersonic airplanes, magnetic alloys for computer disks, special ceramics for the heat shield of the space shuttle, etc.
1.6 Modern Material's Needs
· Engine efficiency increases at high temperatures: requires high temperature structural materials
· Use of nuclear energy requires solving problem with residues, or advances in nuclear waste processing.
· Hypersonic flight requires materials that are light, strong and resist high temperatures.
· Optical communications require optical fibers that absorb light negligibly.
· Civil construction – materials for unbreakable windows.
· Structures: materials that are strong like metals and resist corrosion like plastics.

Syllabus of Material Science

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MATERIAL SCIENCE AND ENGINEERING
Group A
Introduction to materials . Metal and alloys, ceramics, polymers and semi conducting materials-introduction and application as engineering materials.
Defects in solids . Point, line and surface defects. Diffusion in solids.
Phase diagrams . Mono-component and binary systems, non-equilibrium system, phase diagram and. application in crystalline and non-crystalline solids.
Mechanical properties . Tensile strength, yield strength, elastic and viscoelastic properties, creep, stress relaxation and impact. Fracture behaviour. Ductile fracture, Griffith theory, effect of heat treatment and temperature on properties of metals.
Deformation of metals. Elastic and plastic deformation, slip, twin, dislocation theory, critical resolved shear stress, deformation in polycrystalline materials; season cracking, Bachinger's effect, strengthening mechanics; work hardening recovery, crystallization and grain growth, cold and hot working. .

Group B
Heat treatment . Iron-carbon system. Annealing, normalising, hardening,. critical cooling rate, hardenability, age hardening, surface hardening, tempering.
Thermal properties . High temperature materials; materials for cryogenic application, thermally insulating materials. (Specific heat, thermal conductivity, thermal expansion).
Ceramic materials and polymers . Silicon structures, polymerism . in glass, electrical properties of ceramic phases, rocks, building stones, refractories.
Polymerisation mechanism , structural properties of polymer, thermoplastics, thermosets, elastomer, resins, composites, particles and fibre reinforced composite. Composite material including nano material.
Electronic properties . Magnetism, diamagnetism, paramagnetism, ferromagnetism, magnetic energy, zone theory of solids, zones in conductors and insulators.

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SECTION 'B' EXAMINATION ( CODE 4 )

CHEMICAL ENGINEERING (Branch Code 4)

Compulsory Subjects
IC 402 Engineering Management
CH 403 Chemical Reaction Engineering
CH 404 Transport Phenomena
CH 405 Chemical Engineering Thermodynamics
CH 406 Chemical Process Principles
CH 407 Chemical Engineering Equipment Design

Optional Subjects (Any three from any one Group)
Group I Transfer Process

CH 411 Mass Transfer Operations
CH 412 Heat Transfer Operations
CH 413 Mechanical Operations
CH 414 Fluid Mechanics
CH 415 Instrumentation and Control

Group II Process Technology

CH 421 Fuels and Combustion
CH 422 Biochemical Engineering
CH 423 Mechanical Operations
CH 424 Chemical Process Technology
CH 425 Instrumentation and Control

Group III Process Industries

CH 431 Polymer Materials and Technology
CH 432 Petrochemical Engineering
CH 433 Industrial Pollution and Control
CH 434 Fertilizer Technology
CH 435 Instrumentation and Control

CIVIL ENGINEERING (Branch Code 05)

Compulsory Subjects
IC 402 Engineering Management
CV 403 Civil Engineering Materials and Construction Practices
CV 404 Geo-technical and Foundation Engineering
CV 405 Water Resources Systems
CV 406 Principles of Geo-informatics
CV 407 Analysis and Design of Structures

Optional Subjects (Any three from any one Group)

Group I Structural Engineering
CV 411 Advanced Structural Analysis
CV 412 Design of RCC and Pre-stressed Concrete Structures
CV 413 Design of Steel Structures
CV 414 Structural Dynamics
CV 415 Seismic Design of Structures

Group II Environmental Engineering
CV 421 Principles of Environmental Engineering
CV 422 Environmental Engineering — Processes and Management
CV 423 Air Pollution and Its Control
CV 424 Design of Water and Wastewater Treatment Systems
CV 425 Waste Management and Environmental Impact Assessment

Group III Infrastructure and Urban Development
CV 431 Transportation Engineering
CV 432 Traffic and Transportation Systems
CV 433 Town Planning and Urban Development
CV 434 Design of Water and Wastewater Treatment Systems
CV 435 Construction Management Systems

COMPUTER SCIENCE AND ENGINEERING (Branch Code 06)

Compulsory Subjects
IC 402 Engineering Management
CP 403 Data Structures
CP 404 Programming Languages
CP 405 Pulse and Digital Circuits
CP 406 Computer Architecture
CP 407 Systems Analysis and Design

Optional Subjects (Any three from any one Group)

Group I Computer Applications
CP 411 Graph Theory and Combinatorics
CP 412 Computer Networks
CP 413 Operating Systems
CP 414 Artificial Intelligence
CP 415 Database Management Systems

Group II Hardware Engineering
CP 421 Parallel Processing
CP 422 Computer Networks
CP 423 Operating Systems
CP 424 Computer Graphics
CP 425 Micro-processors and Micro-controllers

Group III Information Technology
CP 431 Pattern Recognition and Image Processing
CP 432 Theory of Computation
CP 433 Operating Systems
CP 434 Computer Graphics
CP 435 Software Engineering

ELECTRICAL ENGINEERING (Branch Code 07)

Compulsory Subjects
IC 402 Engineering Management
EL 403 Power Systems
EL 404 Circuit and Field Theory
EL 405 Electrical Machines
EL 406 Measurements and Control
EL 407 Design of Electrical Systems

Optional Subjects (Any three from any one Group)

Group I Power Systems
EL 411 Energy Systems
EL 412 Power Electronics
EL 413 High Voltage Engineering and Power Apparatus
EL 414 Power System Performance
EL 415 Micro-processors and Micro-controllers

Group II Electrical Machines and Drives
EL 421 Advanced Aspects of Electrical Machines
EL 422 Power Electronics
EL 423 Electrical Drives
EL 424 Electrical Power Utilization
EL 425 Micro-processors and Micro-controllers

Group III Control and Instrumentation
EL 431 Control Theory
EL 432 Power Electronics
EL 433 Process Control Systems
EL 434 Instrumentation Systems
EL 435 Micro-processors and Micro-controllers

ELECTRONICS AND COMMUNICATION ENGINEERING (Branch Code 08)

Compulsory Subjects
IC 402 Engineering Management
EC 403 Communication Engineering
EC 404 Circuit Theory and Control
EC 405 Micro-processors and Micro-controllers
EC 406 Electronic Circuits
EC 407 Design of Electronic Devices and Circuits

Optional Subjects (Any three from any one Group)

Group I Telecommunication Engineering
EC 411 Broadcast and Television Engineering
EC 412 Radar and Antenna Engineering
EC 413 Microwave Engineering
EC 414 Optical and Satellite Communication
EC 415 Computer Networks and Communication

Group II Integrated Circuits & Systems Engineering
EC 421 Digital Hardware Design
EC 422 Pulse and Digital Circuits
EC 423 IC Design Techniques
EC 424 Solid State Physics and Semiconductor Devices
EC 425 Software Engineering

Group III Control and Instrumentation
EC 431 Sensors and Transducers
EC 432 Industrial Instrumentation and Computer Control
EC 433 Biomedical Electronics
EC 434 Signal Processing
EC 435 Control Systems

syllabus of section A

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SECTION 'A' EXAMINATION ( DIPLOMA SCHEME )

AD 301 Fundamentals of Design and Manufacturing
AD 302 Material Science and Engineering
AD 303 Computing and Informatics
AD 304 Society and Environment