Numerical simulation of fatigue crack initiation in thin-walled high strength steel as modeled by voronoi-polygons

The fatigue endurance of TS 590 MPa grade low-alloy precipitation strengthened steel was numerically and experimentally examined. The microstructure was modeled using two-dimensional Voronoi polygons. Heterogeneous stress distributions were calculated using the finite element method, taking elastic anisotropy into consideration. The number of cycles before crack initiation was estimated based on the Tanaka-Mura model. By taking into account the effects of the cyclic strain of the preceding cracks, a definable macroscopic crack initiation cycle was obtained. An actual tensile and compression fatigue test was conducted on the same steel. The stress amplitude decreased as the cycle number increased. Distinct dislocation cell structure was not observed by TEM analysis. The experimental strain fatigue limit was, to some extent, lower than that of the simulation. Surface effects, specimen homogeneity, selection of slip system, and dislocation reversibility are mentioned as the probable causes for the difference.