2019 年 85 巻 876 号 p. 19-00141
This paper presents two numerical simulation methods for fatigue crack propagations with the plasticity-induced crack closure under arbitrary cyclic loading conditions. One of the methods is Direct Numerical Simulation (DNS) using S-version Finite Element Method (SFEM), which allows us to simulate the fatigue crack propagation by the combination of the global mesh representing whole structure and local meshes including cracks. Crack opening level due to the plasticity-induced crack closure is evaluated by the elastic-plastic analyses with the local mesh, which is used in the SFEM analyses and is rearranged to simulate the small size of plastic zone around crack tip. The crack growth rate affected by the plasticity-induced crack closure is calculated by a modified Paris ’law in which the stress intensity factor range is converted into an effective stress intensity factor range by multiplying the crack opening level. The crack shape is updated by the crack growth rate, and then, the local mesh is reconstructed in accordance with the updated crack shape. By repeating the processes, the developed method enables us simulating directly the fatigue crack propagation with the plasticity-induced crack closure effect. Another method is a simplified fatigue crack propagation analysis method, where the effective stress intensity factor range is approximately determined by the relationship between the maximum stress intensity factor and the crack opening level. The relationship is constructed in advance using a series of two-dimensional DNSs. The comparison with experimental results confirms that the developed methods have a capability to predict the propagation of surface cracks under bending and tensile loading conditions.