Mechanical properties of materials

Mechanical properties are most important in selecting materials for structural machine components. Any tool, or any power transmission device and wear member of the components, should include a number of the factors needed for serviceability which are given below.

  • Strength: Tensile, Yield, Shear, Creep, Flexural, Stress Rupture.
  • Formability: % elongation, %reduction in the area, bending radius.
  • Rigidity: Modulus of elasticity, Modulus of rigidity, Bulk modulus, Flexural Modulus.
  • Toughness: Impact strength, Notch sensitivity.
  • Durability: Hardness wears resistance, Fatigue strength.

For load-bearing applications, engineering materials are selected according to their mechanical properties to the design specifications and service conditions required of the component. The first step in the selection process requires an analysis of the materials applied to determine their most important characteristics.
The mechanical properties of material must also be understood so that we can process materials into useful shapes using material processing techniques. Material processing such as the use of steel and plastics to fabricate car bodies requires a detailed understanding of the mechanical properties of the material at different temperatures and conditions of loading.

Engineering stress or stress: The total intensity of all the elementary interatomic forces or the internal resistance that the body is exerting to counteract the applied load is called stress or engineering stress.

The resultant deformation expressed as a fractional change in dimension is termed strain or engineering strain.

Engineering stress = Load(pressure)/ original cross-sectional area.
Engineering strain = ratio of the change in length to the original length is called the strain

Different types of simple stress are

1) Tensile stress,
2) Compressive stress,
3) Shear which acts in the plane, parallel to the cross-sectional area,
4) Bending stress,
5) Torsional stress

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