6.4 Strain and Stress
The measure of deformation produced is called Strain. For the
type of deformation as in (B) above, these can be the following kinds of strains.
Longitudinal or Tensile Strain
The change in length (Dl) to the original length (l) is called
The change in area (DA) to the original area (A) is called
Note : For a small deformation angle of shear (q) is
also considered as Shear Strain.
The figure shows Shear deformation of the rectangular block
ABCDGEMN, due to displacement of face BCME to position B'C'M'E' when forces
applied on top & base as shown. The angle q by which the force
ABEG (or DCMN) is twisted to the position AB'E'G (or DC'M'N') is called angle