CONSTITUTIVE EQUATIONS FOR RIGID PLASTIC OR VISCOPLASTIC MATERIALS CONTAINING VOIDS

— A systematic numerical study is reported that uses a homogenization technique to consider the plastic and viscoplastic potential of a porous medium; the study also takes account of the interactions between cavities. Calculations are carried out in plane strain with cylindrical cavities for various stress states characterized by the ratio of the principal stresses and for various values of the porosity as well as of the strain hardening exponent of the matrix. It is shown that the cavity growth rate is a strong function of the porosity, of the strain hardening exponent of the matrix and that it is a linear function of the stress triaxiality ratio. It is demonstrated that the growth models in an infinite body of Rice and Tracey or of Budiansky et al. can underestimate the cavity growth rate for intermediate stress triaxiality ratios, even for porosities as low as 1%.