It is defined as the force applied on unit area to produce change in the shape,volume or length of a body.Mathematically it is expressed as:
The SI unit of stress (σ) is newton per square meter (Nm-2),which is given the name pascal (pa).
Stress may cause a change in length,volume and shape.
When a stress changes the length,it is called tensile stress.
When a stress changes its volume, it is called compressional stress.
When stress changes the shape, it is called shear stress.
Strain is a measure of the deformation of a solid when stress is applied to it.In the case of deformation in one dimensional strain is defined as the frictional change in length.If Δl is the change in length and l is the original length,then strain is given by:
Since strain is ratio of lengths,it is dimensionless,and therefore,has no units.
If strain is ε is due to tensile stress σ,it is called tensile strain.
If strain is produced as a result of compressive stress,it is called compressive strain.
When the applied stress changes the volume,the change in volume per unit volume is known as volumetric strain.
When the opposite faces of a rigid cube are subjected to shear stress.