1999 Volume 42 Issue 3 Pages 321-327
This paper is aimed at the construction of a lower bound rigid plastic constitutive model for the plastic deformation and micro void evolution process of porous materials. In this model a lower bound yield loci for porous materials is taken as one of the pillars of the theoretical system. To overcome the obstacles to the establishment of rigid plastic theory, a few concepts such as the effective stress, effective strain rate, nominal effective stress, nominal effective strain rate, generalized triaxiality ratio and generalized triaxiality function are defined from the lower bound meaning. The physical meanings of these concepts are systematically annotated. The potentialities to predict and control the strength and ductility of porous materials under forming by applying respectively the effective stress and generalized triaxiality function are discussed. The lower bound model together with the upper bound model in previous research will form a perfect and complete theoretical system that may enable us to simulate the real plastic deformation and damage evolution much more accurately by rigid plastic analysis.