A method to evaluate critical J-integral value: Locus method

A method which evaluates the critical J-integral value (J_c) by utilizing the locus of crack initiation points on load-displacement records is presented. This method partitions the fracture energy along the locus line based on an energy rate interpretation. The shape of the locus line depends on both the material and the configuration of the specimen. Since the fracture energy can be partitioned even along a nonlinear locus line, the method is also suitable for highly deformable materials, which usually exhibit a nonlinear locus line. In order to validate this point, a thermoplastic rubber was used for experimental study. The experimental results show that J_c can be evaluated by this method without restricting the ratio of the initial crack length to the specimen width (a/w) or the specimen length provided that the locus line can be located on the load-displacement record.