Stress and strain curve for metal is as shown in fig. When a metal Wire is stretched, for small value of load the elongation produced Is proportional to the load. Hence stress is directly proportional to the strain upto point A , obeying Hooke’s law. Stress corresponding to the point A is called proportional
When stress increased beyond A, for a small stress change, there is a large strain up to point B so that stress is directly proportional to strain. But on removal of load the body is still regain its original shape and size , when applied load is less than certain limit. This limit is called elasticity limit.(point B). Metals shows elasticity behavior . If stress is increased beyond B strain further increase rapidly and if load is removed wire does not regain its original length i.e. the stain produced in the wire is permanent and it is said to have permanent set. Such a deformation is called is plastic deformation.
