Stress-strain curves of polycrystals: Analysis of hardening and softening

The stress-plastic strain curve is regarded as a result of the simultaneous action of two processes: hardening occurring during instantaneous loading and softening which depends on temporal parameters. A physical interpretation of the piecewise-parabolic dependence for the stress—plastic strain curve is given. It was established experimentally that the instantaneous stress-plastic strain curve of a number of annealed polycrystals (copper, brass, duralumin, steel) regardless of the degree of plastic strain or type of deformation substructure can be described by a single parabolic function called the astructural stress-strain curve. The formation of the substructure provides realization of softening processes, the rate of which depends on the type of substructure. A criterion of transition from one parabolic segment of the stress-strain curve to another and, accordingly, change of the deformation substructures is formulated as the condition of maximum stress relaxation during deformation.Translated from Problemy Prochnosti, No. 10, pp. 18–33, October, 1995.