随机疲劳长裂纹扩展率的新概率模型

Probabilistic model of random-long fatigue crack propagation rates

为实现在全应力强度因子范围合理进行结构安全性分析,提出了概全门槛值和断裂韧度的随机疲劳长裂纹扩展率的新概率模型。考虑了平均应力效应,以给定应力强度因子下裂纹扩展率服从对数正态分布为基础,考虑数据分散性规律和试样数量对概率评价的影响,将存活概率和置信度相融合,由线性回归结合极大似然原理确定概率模型的参数。通过对铁道车辆LZ50车轴钢试验数据的分析表明,模型从数学上良好描述了疲劳长裂纹从裂纹启裂到瞬时断裂的整个随机过程,比较Paris、Elber和Forman模型拟合试验数据表明,该模型相关系数最大,拟合效果最好。

For the reasonable-probabilistic safety assessment in entire stress intensity factor range, a probabilistic model was presented for characterizing the random-long fatigue crack propagation rates covering the factor range from threshold to fracture roughness. Based on the rates following lognormal distribution, the effects of the scattering regularity of test data and sampling size on the probabilistic assessment were taken into account, and the survival probability and the confidence were coupled in the model. The parameters of the model were measured by linear regression technique and maximum likelihood method. The model was applied to analyze the test data of LZ50 axle steel about Chinese railway vehicles. The result indicates that the entire random process of long fatigue crack growth from crack initiation to fracture can be mathematically described by the model, the compared to Paris, Elber and Forman models. correlation coefficient of the model is maximum 1 tab, 7 figs, 7 refs.