Effect of Rate of Change of Strain Rate on Deformation Behavior in Ductile Materials.

Abstract

In an analysis of the deformation of rate-dependent sheet materials, the rate of change of strain rate is a significant factor, as well as the strain rate sensitivity m value. The extended theories of plastic instability combined with the rate of change of strain rate are presented, and reveal a significant role of accelerated strain rate on increasing instability strain in uniaxial and biaxial tension. This prediction was verified experimentally on three kinds of ductile sheet materials which indicate different rate dependencies. In order to arbitrarily change strain rate, a computer-controlled system was introduced into uniaxial tension tests and stretch flange forming tests. The effect of accelerated strain rate was recognized on the instability strain in the experimental results. By the comparison of the experimental results with calculated results, it was suggested that instability strain increases as work hardening during deformation increases with accelerating strain rate.