Proposal and verification of novel fatigue crack propagation simulation method by finite element method.

Abstract

In this paper, we propose and verify a novel method to simulate crack propagation without propagating a crack by finite element method. We propose this method for elastoplastic analysis coupled with convection-diffusion. In the previous study, we succeeded in performing elastoplastic analysis coupled with convection-diffusion of hydrogen for a material with a crack under tensile loading. This research extends the successful method to fatigue crack propagation. In convection-diffusion analysis, in order to simulate the invasion and release of elements through the free surface, the crack tip is expressed by using a notch with a sufficiently small radius. Therefore, the node release method conventionally used to simulate crack propagation cannot be applied. Hence, instead of crack propagation based on an analytical model, we propose a novel method that can reproduce the influence of the vicinity of the crack tip on a crack. We moved the stress field near the crack tip in the direction opposite to that of crack propagation by an amount corresponding to the crack propagation length. When we extend the previous method to fatigue crack propagation simulation, we must consider the difference in strain due to loading and unloading. This problem was solved by considering the strain due to loading as a displacement. Instead of moving the strain due to loading, we moved the displacement. First, we performed a simple tensile load analysis on the model and output the displacement of all the nodes of the model at maximum load. Then, the displacement was moved in the direction opposite to that of crack propagation. Finally, the stress field was reproduced by forcibly moving all the nodes by the displacement amount. The strain due to unloading was reproduced by removing the displacement. Furthermore, we verified the equivalence of the crack propagation simulation and the proposed method.