低周载荷对高周裂纹裂尖塑性区的影响

为探明高低周复合疲劳裂纹扩展中高低周载荷交互作用机理，采用弹塑性有限元模型模拟了含中心裂纹试件在高低周载荷交互作用下裂尖塑性区的变化.结果表明:低周载荷的卸载作用导致高周载荷对应的裂尖反向塑性区明显减小，裂纹闭合水平也因此降低，进而加速裂纹扩展，致使高低周复合疲劳裂纹扩展寿命降低.在此基础上，对比研究了低周载荷应力比、高周载荷应力比、高低周载荷循环比对裂尖反向塑性区的影响.结果表明:随着低周载荷应力比降低、高周载荷应力比增加，循环比的减少，均导致低周载荷的卸载作用增加. 

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.