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 
Type of stress

Normal Stress 

Normal Stress Formula 

Shear Stress 

Shear Stress Formula 

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 Formula 

Shear Strain 

Shear Strain Formula 

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 Ïƒ and Îµ are the engineering stress and engineering strain respectively.
The true strain is defined as

True Strain 
StressStrain Curve

StressStrain Curve 
NOTE:
 Limit of Proportionality: It is the stress at which the stressstrain curve is a straight line(OA).
 Hook's law is valid up to the proportionality limit.
 Elastic limit: point in the stressstrain 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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