VOID GROWTH IN CYCLIC LOADED POROUS PLASTIC SOLID

In low-cycle fatigue, where plastic strains are of great importance, f inal ductile fracture depends upon the mechanisms of void growth and c oalescence of voids. A cell model is used to simulate a periodic array of initial spherical voids and this model is subjected to different l oads that include cyclic loading. Three different types of matrix mate rial are simulated: elastic-perfectly plastic, isotropic hardening and kinematic hardening. The cell model results are compared with the app roximate constitutive equations for a voided material suggested by Gur son. The simulations show that the unspecified parameters introduced b y Tvergaard in the Gurson yield function depend on the hardening behav ior of the matrix material. For a perfectly plastic matrix material, t he parameters q(1) = 1.5 and q(2) = 1.02 provide very close prediction s for a variety of loadings. However, for isotropic or kinematic harde ning matrix materials these parameters result in an inferior agreement and a much closer accuracy is obtained by adopting q(1) = 1.5 and q(2 ) = 0.82. This suggests that the parameter q(2) depends on the hardeni ng behavior of the matrix material. For kinematic hardening of the Gur son model, it is shown that Ziegler's hardening rule is superior to Pr ager's hardening rule. Finally, the void shape change due to loading i s studied and it is found that this change has an insignificant effect on the response. (C) 1997 Elsevier Science Ltd.