Fluctuation of J-integral due to grain arrangement of Ni-based directionally solidified superalloy

The effect of local anisotropy due to the arrangement of anisotropic and arbitrary shaped grains of a directionally solidified superalloy on the J-integral is investigated by means of finite element analyses, where the models simulate the grain shape, its orientation, and the crack path of real material. The magnitudes of Janiso, obtained by a detailed model, where most of grains are simulated, shows a stepwise change against the crack length a. This is mainly caused by the anisotropy of the grain at the crack tip. JCV, obtained by a simplified model, where only the grains in the vicinity of the crack path are simulated, shows the same stepwise change as Janiso. It elucidates that the anisotropy in the vicinity of the crack path is the dominant factor for the fluctuation of Janiso. The magnitude of Janiso and JCV, however, are different from each other in detail. A large inhomogeneous area such as a cluster of grains and a large grain has a far-field influence and is mainly responsible for the differences between Janiso and JCV.