MATERIAL SELECTION ByDr. R. PANNEERDESIGN FOR MANUFACTURE

UNIT: II MATERIAL SELECTION TOPIC 1: Factors determining choice of materials, TOPIC 2: Performance characteristics of materials, TOPIC 3: Material selection process. TOPIC 4: Evaluation methods for material selection. TOPIC 5: Principal materials used in manufacturing.

Topic 1: Factors determining choice of materials Materials science and engineering plays a vital role in this modern age of science and technology.Various kinds of materials are used in industry, housing, agriculture, transportation, etc. to meet the plant and individual requirements. The rapid developments in the field of quantum theory of solids have opened vast opportunities for better understanding and utilization of various materials.

Topic 1: Factors determining choice of materials The spectacular success in the field of space is primarily due to the rapid advances in high-temperature and high-strength materials. The selection of a specific material for a particular use is a very complex process. However, one can simplify the choice if the details about (i) operating parameters, (ii) manufacturing processes, (iii) functional requirements and (iv) cost considerations are known. Factors affecting the selection of materials are summarized in Table 1 & 2

Topic 1: Factors determining choice of materials Table 1 Factors determining choice of materials: (Manufacturing Processes and Functional Requirements)

Topic 1: Factors determining choice of materials Table 2 Factors determining choice of materials: (Cost Considerations and Operating Parameters)

Topic 1: Factors determining choice of materials Table 2 Factors determining choice of materials: (Cost Considerations and Operating Parameters)

TOPIC 2: Performance characteristics of materials The table below provides fairly complete listing of material performance characteristics.1. Physical Properties:i. Crystal Structure ii. Density iii. Melting Point iv. Vapor Pressurev. Viscosity vi. Porosity vii. Permeability viii. Reflectivity ix. Transparency x. Optical Properties xi. Dimensional Stability2. Electrical Properties:i. Conductivity ii. Dielectric Constant iii. Coercive Force iv. Hysteresis3 Mechanical Properties:i. Hardnessii. Modulus of Elasticity-Tension & Compression iii. Poison Ratioiv. Stress Strain curve

TOPIC 2: Performance characteristics of materials The table below provides fairly complete listing of material performance characteristics.3 Mechanical Properties:v. Yield strength-Tension & Compression -Shear vi. Ultimate strength-Tension & CompressionBearing vii. Fatigue properties- Smooth- Notched- Corrosion Fatigue- Rolling Fatigue- Fretting3 Mechanical Properties:viii. Charpy Transition Temp.ix. Fracture Toughnessx. High Temp.- Creep -Stress Rupture xi. Damping Propertyxii. Wear Property- Galling, Abrasion, & Erosion xiii. Cavitationsxiv. Spalling xv. Ballistic Impact

TOPIC 2: Performance characteristics of materials The table below provides fairly complete listing of material performance characteristics.4 Thermal Properties:i. Conductivityii. Specific Heatiii. Coeff. of Expansioniv. Emissivityv. Absorbtivityvi. Ablation Ratevii. Fire Resistance

5 Chemical Properties:i. Position in electromotive series5 Chemical Properties:ii. Corrosion & Degradation- Atmosphere- Salt water- Acids- Hot gases- Ultra-violetiii. Oxidationiv. Thermal Stabilityv. Biological Stability.vi. Stress Corrosionvii. Hydrogen Embrittlementviii. Hydraulic Permeability

TOPIC 2: Performance characteristics of materials The table below provides fairly complete listing of material performance characteristics.6 Nuclear Properties:i. Half-lifeii. Cross-sectioniii. Stability

7 Fabrication Properties:i. Castability ii. Heat Treatability iii. Hardenability iv. Formability v. Machinability vi. Weldability

There are thousands and thousands of materials available and it is very difficult for an engineer to possess a detailed knowledge of all the materials.

However, a good grasp of the fundamental principles which control the properties of various materials help one to make the optimum selection of material.

MATERIAL SELECTION PROCESS The selection of materials on purely rational basis is far from easy. The problem is not only often made difficult by insufficient or in accurate property data but is typically one of decision making in the face of multiple constraints without a clear cut objective function.Material selection usually involves one of two different situations.1. Selection of Materials for new product or design2. Revaluation of existing product or design to reduce cost, increase reliability, improve performance etc.