Probabilistic model of random-long fatigue crack propagation rates

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 correlation coefficient of the model is maximum compared to Paris, Elber and Forman models.