Comparison of Experimental and Numerically Simulated Fatigue Crack Propagation

The objective of this study is to present a methodology that can properly simulate three-dimensional fatigue crack propagation with consideration of the crack closure effect. To simulate fatigue crack growth in three-dimensional elastic structures, the superposition finite element method (S-FEM) is employed. A local model is used to represent the near crack area to overcome difficulties that appear in the process of re-meshing the FE model during crack propagation; therefore, many complex crack geometries that may be generated under mixed mode conditions can be easily modeled. Considering the plasticity-induced crack closure effect, elastic-plastic analysis was first conducted to study the behavior of the crack closure effect along the crack tip. Normalized crack opening level along the direction of thickness was obtained and applied to simulations. Experiments on single edge notch specimens under Mode I, Mode I+II or Mode I+II+III loading conditions were conducted to verify the method. Experimental results related to crack growth direction, crack shape and fatigue life were compared with simulation results. Better predictions on crack path were shown. Significant improvement of crack shape evolution in the simulation model was obtained considering the crack closure effect.