测定概率疲劳长裂纹扩展门槛值的新方法

New Method for Measuring the Random Thresholds of Long Fatigue Crack Propagation

提出了合理测定随机疲劳长裂纹扩展门槛值的"局部概率Paris关系法"· 揭示了常规法不能保证各试样门槛值数据处于相同扩展率水平,测定结果不尽合理的缺陷· 以Paris_Erdogan方程描述门槛值附近局部试验数据,考虑数据分散性规律和试样数量两方面的影响,在应力强度因子服从对数正态分布下建立了包含存活概率和置信度的局部概率关系模型。

A so_called 'local probabilistic Paris relation method' was presented for measuring the random thresholds of long fatigue crack propagation. A check was made to the conventional method, in which the thresholds were measured statistically and directly by the test data. It was revealed that this method was not reasonable because the test data have seldom a unified level of crack growth rates. Differently,in the presented method the Paris_Erdogan equation was applied to model the local test data around the thresholds. Local probabilistic relations with both the survival probability and the confidence were established on a lognormal distribution of the stress density factors. And then, the probabilistic thresholds were derived from the probabilistic factors with a given critical level of growth rate. An analysis on the test data of LZ50 axle steel for the Chinese railway vehicles verifies that the present method is feasible and available.