Strain

Strain:


The structural member and machine components undergo deformation as they are brought
under loads.
To ensure that the deformation is within the permissible limits and do not affect the
performance of the members, a detailed study on the deformation assumes significance.
A quantity called strain defines the deformation of the members and structures in a better
way than the deformation itself and is an indication on the state of the material.

Consider a rod of uniform cross section with initial length.
Application of a tensile load P at one end of the rod results in elongation of the rod by
L0


Application of a tensile load P at one end of the rod results in elongation of the rod by
L0
δ .
After elongation, the length of the rod is L. As the cross section of the rod is uniform, it is
appropriate to assume that the elongation is uniform throughout the volume of the rod. If
the tensile load is replaced by a compressive load, then the deformation of the rod will be a
contraction. The deformation per unit length of the rod along its axis is defined as the
normal strain. It is denoted by ε


                                               ε =   δ/L = L-L0/L




Though the strain is a dimensionless quantity, units are often given in mm/mm, μm/m.