ELASTIC-PLASTIC FRACTURE-ANALYSIS OF FINITE BODIES .2. CONDITIONS OF FRACTURE INITIATION

The normal and triaxial stresses on uncracked ligament for different s pecimens were analyzed by large deformation plane strain finite elemen t analysis (FEM) at their fracture loads, and the critical characteris tic parameters (J, Q, k) of the stress field established in Part I [Fa shang Ma and Zhen-Bang Kuang, Engng Fracture Mech. 48, 727-737 (1994)] were determined by fitting. Using several continuum damage mechanics (CDM) models and the present stress field, the conditions of the initi ation of elastic-plastic fracture growth for different specimens were discussed in detail, and it was verified by experimental data that the critical conditions suggested in this paper are independent of specim en geometry and of the ratios of crack depth a to specimen width w whe n an appropriate microscopic model for fracture initiation is adopted. When characteristic parameters of the stress field k = 1 and Q = 0, t he present conditions will reduce to the well-known elastic-plastic si ngle parameter fracture criteria.