Materials Selection

Introduction to Materials Selection

A. Material Selection

When we talk about choosing materials for a component, we take into account many different factors. These factors can be broken down into the following areas.

1. Material Properties

The expected level of performance from the material

2. Material Cost and Availability

a. Material must be priced appropriately (not cheap but right)

b. Material must be available (better to have multiple sources)

3. Processing

a. Must consider how to make the part, for example:

  • Casting
  • Machining
  • Welding

4. Environment


    1. The effect that the service environment has on the part
    2. The effect the part has on the environment
    3. The effect that processing has on the environment
  1. Kinds of Materials
    1. Metals
      • Iron
      • Aluminum
      • Copper
      • Magnesium
      • Composites
      • Ceramics
        1. Glass
        2. Semi-conductors
        3. Structural ceramics (SiN, SiC)
        4. Refractory Composites
        5. Polymers
          1. Rubber
          2. Plastics
        6. Liquids
        7. Gases
  1. Material Properties

As mechanical engineers we are most concerned with characteristics such as:

  1. Mechanical Properties
    1. Strength

1)     Yield Strength

2)     Ultimate Tensile Strength

3)     Shear Strength

  1. Ductility
  2. Young’s Modulus
  3. Poisson’s ratio
  4. Hardness
  5. Creep
  6. High or low temperature behavior
  7. Density
  8. Anisotropy
  9. Fatigue strength
  10. Fracture Toughness
  11. Thermal Properties
    1. Thermal expansion coefficient Thermal conductivity
    2. Specific heat capacity
    3. Magnetic Properties
    4. Fabrication Properties
      1. Ease of machining
      2. Ease of welding, casting, etc
      3. Hardening ability
      4. Formability
      5. Availability
      6. Joining techniques
      7. Environmental Properties
        1. Corrosion properties
        2. Toxic effects
        3. Out-gassing properties
        4. Gas and Liquids
          1. Viscosity



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