NUMERICAL SIMULATION OF THE EFFECT OF LOADING HISTORY AND CRACK CLOSURE ON CRACK PROPAGATION BEHAVIOUR

Three kinds of finite element models were used to study the fatigue crack growth behavior of 16MnR steel under different stress ratios. The stationary crack propagation model considers only the effect of a crack closure, and the fake dynamic crack propagation model considers only the effect of loading history. However, the loading history and crack closure were considered in the dynamic crack propagation model. Based on the outputted elastic-plastic stress-strain results from the FE analysis, the crack closure process, the stress-strain hysteresis loop, the fatigue damage distribution and the fatigue crack growth rate were studied. The interactive mechanism between the crack closure and loading history for the fatigue crack growth behavior was discussed further. For an identical finite element model, it is difficult to find the appearance of a crack closure for the loading condition with a higher stress ratio. On the other hand, the residual compressive stress induced by loading history can promote the crack closure obviously for the identical stress ratio. The crack closure slows down the mean stress relaxation and decreases the stress-strain magnitude, which leads to the reduction of a fatigue crack growth rate. The residual compressive stress induced by loading history speeds up the mean stress relaxation and brings down the strain ratcheting. The predicted fatigue crack growth rate by the dynamic crack propagation model, in which the interactive influence of loading history and a crack closure was incorporated, agrees with the benchmark experimental data very well.