ON YIELDING AND DEFORMATION OF POROUS PLASTIC MATERIALS

A non-associated flow rule is introduced in this paper to characterize the yield and subsequent plastic deformation of porous solids. The pr essure sensitive yield function has the form of that suggested by Gurs on and Tvergaard. A macroscopic plastic potential is assumed to exist for porous plastic materials, and plastic strain increment is along th e normal to the macroscopic plastic potential. The yielding function, the flow rule and the evaluation of the void volume fraction compose t he non-associated constitutive model for porous plastic materials. Det ailed finite element analysis on an axisymmetric unit cell is performe d; the unit cell is a representative volume element of porous material s. The results show that the yield and deformation of the cell with th e aspect ratio of pi/4 is isotropic, and the yield can be described we ll by the Gurson-Tvergaard yield function with the parameters q(1) = 1 .35, and q(2) = 0.95, The post-yield response of the unit cell is in g ood agreement with the prediction of the non-associated constitutive m odel. (C) 1998 Elsevier Science Ltd. All rights reserved.