The influence of triaxiality on stable crack growth

Variations in the J resistance curves obtained for the same material with different specimen geometries are usually attributed to local differences in the state of stress in the vicinity of the crack front. From elastic-plastic finite element evaluations of two post yield fracture experiments the variation along the crack front of the local J and of a constraint factor h for the smooth and side-grooved compact specimen are obtained and correlated with experimental observation. While initiation occurs in both specimens at identical local J and local h the different resistance curve slopes correspond to differences in the average h in both specimens. With that information a simple linear relationship between average h and the slope of the resistance curve was postulated. Applications of this model to the case of a part-through crack in a plate under tension yielded improved prediction of the crack front development due to stable crack extension especially at the specimen surface. (orig.)