随机超载下疲劳裂纹扩展的模拟计算

采用蒙特卡罗法对随机超载作用下的疲劳裂纹扩展进行模拟计算。载荷谱为在基本循环载荷基础上加入一以泊松流发生的随机超载序列．超载的大小为均匀分布。相邻两次超载发生的时间间隔通过一系列相互独立、服从指数分布的随机数进行模拟。采用Wheeler模型考虑超载的迟滞效应，计算出每一载荷循环的裂纹扩展量。由此模拟出裂纹从初始长度一直到疲劳破坏的扩展曲线。通过大量样本的模拟计算，获得随机超载作用下疲劳裂纹扩展寿命的平均值与标准差。最后研究超载发生强度和大小对疲劳裂纹扩展寿命的影响。

SIMULATION OF FATIGUE CRACK GROWTH UNDER RANDOM OVERLOADS

The analytical prediction of fatigue crack growth under random loading is complicated by the load interaction. In order to study the behavior of fatigue crack propagation under random overloads, a Monte Carlo simulation scheme is proposed. Overloads of Poisson flow with uniform distribution on base-line constant-amplitude cyclic loads are considered. A series of independent random number with exponential distribution are generated to simulate the interoverload times. The retardation effect of overload is taken into account using Wheeler' model and fatigue crack propagations are computed cycle by cycle. As the crack grows to some size, fatigue fracture will occur due to either overload or base-line loading peak and the fatigue crack propagation life is obtained. Through the large number of simulated samples, the mean and standard deviation of fatigue crack propagation life are calculated. Finally, the effects of overload intensity and magnitude on fatigue crack propagation life are studied.