Simulation of fatigue initiation and non-self-similar fatigue crack growth under mixed mode I/II loading

The fatigue initiation and non-self-similar fatigue crack growth behavior of three notched compact tension and shear specimens of 16MnR steel under mixed mode I/II loading were investigated. The plane-stress finite element model with the implemented Armstrong-Frederick type cyclic plasticity model was used to calculate the elastic-plastic stress-strain responses. A recently developed dynamic crack growth model was used to simulate the effects of loading history on the successive crack growth. With the outputted numerical results, a multiaxial fatigue damage criterion based on the critical plane was used to determine the location of fatigue initiation. A formula of fatigue crack growth rate, which is based on the postulation that the fatigue initiation and crack growth have the same damage mechanism, was then used to calculate the transient crack growth rate and determine the non-self-similar crack growth path. The predicted fatigue initiation position, crack path and crack growth rate are in excellent agreement with the experimental data.