introduction to materials science and engineering · pdf file© 2011 cengage learning...

© 2011 Cengage Learning Engineering. All Rights Reserved.© 2011 Cengage Learning Engineering. All Rights Reserved.

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Chapter 1:Chapter 1:

Introduction to Introduction to Materials Materials

Science and Science and EngineeringEngineering

Chapter 1: Introduction to Materials Science and Engineering


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Learning Objectives

1. What is materials science and engineering?

2. Classification of materials.

3. Functional classification of materials.

4. Classification of materials based on structure.

5. Environmental and other effects.

6. Materials design and selection.



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Composition Chemical makeup of a material

Structure Description of the arrangement of atoms, as seen at different levels of detail

Materials science Underlines the relationships between the synthesis and processing, structure, and properties of materials

Materials engineering

Focuses on how to translate or transform materials into useful devices or structures

Microstructure Structure of the material at the microscopic scale

What is Materials Science and Engineering?



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Figure 1.1 - Application of the Tetrahedron of Materials Science and Engineering to Sheet Steels for Automotive

Chassis



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Figure 1.2 - Application of the Tetrahedron of Materials Science and Engineering to Semiconducting Polymers for

Microelectronics



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Table 1.1 - Representative Examples, Applications, and Properties for Each Category of Materials



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Polymers

Polymerization Process by which polymers are produced

Strength-to-weight ratio

Is high for polymers

Thermoplastic polymers

Contain long polymer chains that are not rigidly connected, have good ductility and formability

Thermosettingpolymers

Strong polymers but more brittle because the molecular chains are tightly linked

Plastics Contain additives that enhance the properties of polymers

Composites Formed from two or more materials, producing properties not found in any single material



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Figure 1.3 - Representative strengths of various categories of materials



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Figure 1.6 - Functional Classification of Materials



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Classification of Materials Basedon Structure

Crystalline The material’s atoms are arranged in a periodic fashion

Amorphous The arrangement of the material’s atoms does not have a long-range order

Single crystals Crystalline materials in the form of one crystal

Polycrystalline Crystalline materials with many crystals or grains

Grain boundaries Regions between individual crystals in a

polycrystalline material



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Figure 1.7 - Increasing Temperature NormallyReduces the Strength of a Material



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Figure 1.8 - Skin Operating Temperatures for Aircraft Have Increased With the Development of Improved Materials



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Environmental and Other Effects

Corrosion Metals and polymers react with oxygen or other gases,

particularly at elevated temperatures. Metals and ceramics — Disintegrate. Polymers and non-oxide ceramics — Oxidize. Materials are attacked by corrosive liquids which leads to

premature failure.



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Environmental and Other Effects

Fatigue Components must be designed such that the load on the

material may not be enough to cause permanent deformation.

Fatigue failure: When the material is loaded and unloaded thousands of times small cracks may begin to develop and materials fail as these cracks grow.

Strain rate Metallic materials:

Can be stretched significantly if pulled slowly — Small rate of strain.

Can snap if pulled fast — High rate of strain.



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Materials Design and Selection

The material must: Acquire the desired physical and mechanical properties. Be capable of being processed or manufactured into the

desired shape. Provide an economical solution to the design problem.

Material cost is calculated on a cost-per-kilogram basis. Density of the material or its weight per unit volume

should be considered.



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Table 1.2 - Strength-to-Weight Ratios of Various Materials



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Key Terms

Composition Composites Crystalline Density Fatigue failure Grains Grain boundaries Materials science and engineering Materials science



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Key Terms

Mechanical properties Materials engineering Microstructure Materials science and engineering tetrahedron Polymerization Plastics Polycrystalline Physical properties Processing



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Key Terms

Structure Synthesis Strength-to-weight ratio Semiconductors Smart material Single crystals Thermoplastic Thermosetting


introduction to materials science and engineering · pdf file© 2011 cengage learning...

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