Validation of the K and J Parameters in a Compact Tension Specimen Containing Intergranular and Straight Crack Paths

Methods have been examined to evaluate the fracture mechanics parameters J and K in finite element (FE) analyses on a compact tension, C(T), geometry using a mesh appropriate for the evaluation of both intergranular and transgranular microstructural damage processes. Realistic grain and grain boundary microstructures were modelled using ABAQUS. Both straight and deviating crack profiles were considered, representing transgranular and intergranular crack growth processes, respectively. Elastic and elastic-plastic finite element analyses were performed on a C(T) specimen model with a standard straight and deviating crack profile to derive and compare the stress intensity factor, K, and J parameter values under plane stress and plane strain conditions. Considerations as to the validity of the J domain integral calculations that ABAQUS computes are discussed. It has been found that the values of K and J obtained from FE simulations are consistent with theoretical solutions and the stress distribution ahead of the crack tip is very close to that of expected from analytical studies for the case of a straight fronted transgranular crack. Reasonable values of K and J parameters could also be achieved from the FE contour integral values of a deviating crack when the contours selected were adequately far from the crack tip. However, significant differences were found between the analytical and FE contour integral values of a deviating crack when the crack growth direction was considered to continue at the angle defined by its grain boundary. The values of J obtained by from the load line displacement measurements were uninfluenced by the crack profile and in good agreement with other analytical solutions.