Effect of low cycle fatigue loading on the crack tip plastic zone of high cycle fatigue crack

To ascertain the loading interaction mechanism of the crack growth under high and low combined cycle fatigue loading, the elastic-plastic finite element numerical simulation method was used to determine the plastic zone of crack tip of the specimens with center crack under high and low combined cycle fatigue loading. It was proven that the unloading of low cycle fatigue loading contributed to the reduction of reversed plastic zone of crack tip corresponding to high cycle fatigue loading. This resulted in the decrease of crack closure level and the increase of crack growth rate, as well as the reduction of crack growth life under high and low combined cycle fatigue loading. The effects of the stress ratio of low cycle fatigue loading, the stress ratio of high cycle fatigue loading, the high cycle fatigue loading number per low cycle fatigue loading on the reversed plastic zone of crack tip were also investigated in contrast. The unloading of low cycle fatigue loading gradually increased along with the decrease of low cycle fatigue loading stress ratios, the increase of high cycle fatigue loading stress ratios, and the decrease of high cycle fatigue loading numbers per low cycle fatigue loading.