基于裂纹扩展的两级加载下的疲劳-蠕变寿命预测

取加载一个周期内拉应力作用下的应变能密度增量为材料的损伤变量,由迟滞回线所围面积导出了该损伤变量的计算式;依据材料被损伤会使裂纹扩展,裂纹的扩展会导致试件发生断裂的事实,以J积分为裂纹扩展的控制参量,将裂纹扩展看作纯疲劳损伤与蠕变损伤二者共同的贡献,考虑疲劳-蠕变的交互作用,导出了在两级应力加载下的疲劳-蠕变寿命的表达式;该表达式与加载的波形、材料的疲劳-蠕变速率相关.应用该表达式对316L钢在550℃两级应力梯形波加载下的疲劳-蠕变寿命进行了预测,预测值在1.5倍误差因子以内,预测精度较高.

Prediction of Fatigue-Creep Life Based on Crack Propagation Under 2-step Load

By taking the increment of strain energy density under tensile stress within a cycle as the damage variable of the material, and according the positive acreage enclosed by hysteresis loops, the equation of the damage variable can be educed. In view of the fact that the damage of material would result in fatigue crack propagation and fatigue crack propagation would cause the crack of specimens, J-integral is considered as the control parameter during crack growth process, crack growth is regarded as the contribution of fatigue damages as well as creep damage, the interaction of the two factors is consid- ered, then the equation of Fatigue-Creep Life under 2-step stress load is educed ; the equation is relative to loading waveform and fatigue-creep rate. The equation is applied to predict fatigue-creep life of 316L steel, at 550 ℃ under 2-step load of strain trapezoidal wave. The prediction is proved to be satisfactory with an error factor of ±1.50 times.