Abstract
A method of plastic analogy is proposed to construct a constitutive model describing the viscoplastic behavior of materials. By using the method, the knowledge obtained through the study of the plastic constitutive model can be utilized to construct the viscoplastic model. The plastic analogy is drawn because most of the viscoplastic models proposed previously can be written in the form of 3/2(Sij-αij)(Sij-αij)-κ2=0 and this is the same formula describing the yield surface of the plastic model except that the size κ of the surface is a function of the inelastic strain rate. The function κ can be determined from the data of the rate dependence of the yield stress obtained by constant strain rate tensile tests. As a demonstration of the method, a two-surface plastic model with a nonhardening strain region by Ohno is extended to a viscoplastic model. The viscoplastic model obtained here can be shown qualitatively to represent the plastic, creep and plastic-creep interaction behavior of materials with nonlinear strain hardening and cyclic strain hardening.
