CALCULATION OF THE 2ND FRACTURE PARAMETER FOR FINITE CRACKED BODIES USING A 3-TERM ELASTIC-PLASTIC ASYMPTOTIC-EXPANSION

A three-term asymptotic expansion which is controlled by two amplitude parameters is used to describe the stress field in the vicinity of th e crack tip in a power-hardening material. The first parameter is the well-known J-integral. The second parameter (amplitude A)characterizes the following terms. A least squares procedure is developed for the d etermination of the amplitude parameter A by fitting of finite element data. The convergence of computed A values is investigated for a smal l scale yielding modified boundary layer problem. It is shown that the three-term expansion has certain advantages over the Q-stress approac h. Values of the amplitude parameter A are determined for an edge crac ked plate, center cracked plate, three-point bend specimen and compact tension specimen.