Numerical simulation of fatigue crack propagation with plasticity-induced crack closure under different loading conditions; Development of direct numerical simulation using S-version FEM and simplified method

Shintaku, Yuichi*; Shinozaki, Yuto*; Fujiwara, Takaki*; Takahashi, Akiyuki*; Kikuchi, Masanori

The contribution of this paper is to develop two kinds of numerical simulation method for fatigue crack propagation with plastic-induced crack closure under different cyclic loading conditions. One of the developed methods is Direct Numerical Simulation (DNS) using S-version FEM that allow us to simulate by combining with global mesh only representing whole structure and local mesh including crack. After stress intensity factor is calculated by S-version FEM, crack opening level due to plastic-induced crack closure is determined by elastic-plastic analysis using local mesh which is enough subdivided to realize small plastic zone around crack tip. The crack growth rate considering effect of plastic-induced crack closure is predicted by modified Paris' law in which the stress intensity factor range under cyclic loading is converted into the effective value by the crack opening level. Then, the local mesh is updated by new crack shape determined from crack growth rate. By repeating these processes, our developed method can provide us to simulate fatigue crack propagation with plastic-induced crack closure directly. Another method is simplified one that the effective stress intensity factor range is approximately determined by the relationship between the maximum stress intensity factor and crack opening level as a result of preanalysis using two-dimensional DNS. By comparison of experimental results, it can be confirmed that our developed methods predict propagation of surface crack in specimen under bending and tensile loading conditions.