YIELD CRITERIA FOR DUCTILE POROUS SOLIDS

Several investigators have suggested modifications to the form of Gurson's yield function for isotropic porous solids. The present article reexamines the form of Gurson's criterion, and attempts to interpret the various terms in the yield function in either geometric or physical terms. Yielding was examined under deviatoric and hydrostatic stress loading, and resulted in a proposal of a modified isotropic yield function. Two types of periodic spherical void spacings were considered, namely, cubical and hexagonal. The latter provided a more isotropic response, and the predicted loci agreed well with loci calculated from a three-dimensional finite-element model. In the second part of the paper anisotropy is considered by assuming a cubical array of ellipsoidal voids, and the isotropic yield function is modified accordingly. The resulting analytical model illustrates that the void geometry does not have a very strong effect on the shape of the yield loci. The finite-element calculations are in general agreement with the model, but the numerical results show a greater influence of void geometry.