带保载平面应变塑性诱发裂纹闭合效应

用黏塑性有限元法模拟含中心裂纹试件在等幅循环拉伸加载和保载作用下的裂纹扩展规律.试件采用涡轮盘材料Udimet720 Li(low inclusion)、恒温700℃和平面应变假设,通过逐步释放裂纹尖端节点约束来模拟裂纹扩展.计算了在应力比R=0,不同最大循环载荷、不同保载时间对平面应变下无量纲裂纹张开应力强度因子的影响.平面应变情况下,无量纲裂纹张开应力强度因子随最大载荷的变化而趋于分散,并随着裂纹的扩展,会存在先上升后下降并趋于一个稳定值的趋势;载荷相同时,保载时间的增加使裂纹张开应力强度因子增加.高温保载情况下,蠕变会影响裂纹扩展速率. 

Plasticity-induced fatigue crack closure under plane strain condition with dwelling

Visco-plastic finite element method was used to simulate fatigue crack propagation under constant amplitude cyclic and dwelling tensile loading conditions for a middle-crack specimen made of turbine disc material Udimet720 Li(low inclusion).Node release was used to model the crack propagation at 700 ℃.The influences of different maximum cycle loads and dwelling time on crack open stress intensity factor were studied under plane strain and constant load stress ratio R=0 condition.The values of normalized crack open stress intensity factor were dispersed under different maximum cycle loads,increased at the beginning of the cycles,and then decreased slightly to a steady value after adequate cycles with the crack growth.The result shows that the increase of dwelling time will increase normalized crack open stress intensity factor.Creep may influence the crack growth rate at elevated temperature and under dwelling condition.