The Defination And Probability Model Of Low Cycle Fatigue Crack Initial Life For 16MnR Pressure Vessel Steel

The low-cycle fatigue failures are always happened to pressure vessels. So initial life of low-cycle fatigue cracks of pressure vessels steel is one of the most important aspects The methods of initial life of low-cycle fatigue cracks are summed up in the paper. These methods have some deficiencies. They have no specific physics signification. And the definitions of initial life of cracks have some artificial ingredient. So lots of random errors are introduced.Using three points bending specimens with nick, low cycle fatigue tests were performed. The turning point from the linear propagation to non-linear propagation period in the a-N curve was pointed out by corresponding to the initial point of fatigue crack. The crack size and the cycle number at this point correspond to the initial size and initial life respectively. A new fatigue crack initial life is defined based on the stochastic propagation. The distribution of initial life of low-cycle fatigue cracks is the key in analyzing reliability of pressure vessels. The experimentation-data statistics of the above definition of initial life are collected in the paper. The results show that initial life of low-cycle fatigue cracks for 16MnR pressure vessel steel obeys logarithm normal school.