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Mechanical Properties of Metals, Stress and Strain








Stress






When a material is subjected to an external force, a resisting force induced. The internal resistance force per unit area is called stress.
Stress Formula

Unit:    N/m2








Type of stress

  • Normal Stress
Normal Stress
Normal Stress Formula








  • Shear Stress
Shear Stress
Shear Stress Formula
          




  • Bulk Stress
Bulk Stress
Bulk Stress Formula
      









Strain


Deformation per unit length in the direction of deformation is known as strain. It is a dimensionless quantity.








Strain Formula

Types of Strain

  • Normal Strain
Normal Strain
Normal Strain Formula
    





  • Shear Strain
Shear Strain
Shear Strain Formula









  • Bulk Strain
Bulk Strain
Bulk Strain Formula
    






True Stress and True Strain


True stress is defined as the ratio of load to the instantaneous area. 

True Stress


Where σ and ε are the engineering stress and engineering strain respectively.








The true strain is defined as

True Strain

Stress-Strain Curve






Stress-Strain Curve



NOTE:

  • Limit of Proportionality: It is the stress at which the stress-strain curve is a straight line(OA).
  • Hook's law is valid up to the proportionality limit.
  • Elastic limit: point in the stress-strain curve up to which the material remains elastic. There is no permanent deformation up to this point.
  • Plastic Range: Region between elastic limit and point of fracture.
  • Yield Point: The point just beyond the elastic limit, at which material goes increase in length without further increase in the load.







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