Q. Define the concept of strain hardening.
Ans. Strain hardening or work hardening in metal occurs because of interaction between the this location and some of obstruction. During the plastic deformation in metals the required shear stress to produce slip is continuously increase with shear strain. This increase in shear stress in known as work hardening or strain hardening. The principle of work hardening can be explained by stress strain diagram.
When loaded strain cases with stress and reaches P in the plastic range. At this stage when the specimen is unloaded the curve move along the forward downward path of PS, if the specimen is again reloaded the curve again rises from S and P and reaches the point Q and follows the curvature path.
But if the specimen is loaded itially is not unloaded and process of increase in loading is continued, the stress strain curves take the path PN. The path PQR and PN clearly reveals that cold working has increased the yield strength, tensile strength and ultimate strength of metal or alloy.