The Research Of Metallic Welded Structure Fatigue Split Based On Randomicity

Fatigue damage is the main destroy mode for the machinery parts and engineering structures under alternate loading over a long period of time. The fatigue life is determinate when determination methods are used to analyze fatigue. But the fatigue of structure is a much complicated phenomenon affected by many uncertainties. So it is necessary to analyze the structural fatigue from the point of view of probability and statistics.Firstly, metallic structural randomness analysis under cycle loading is of important theoretical significance and practical significance. The analysis of randomness of stress and strain in strain-based fatigue was studied, the approximate polynomial method was proposed. The approximate polynomial method was based on Neuber's method, By comparing to Nuobo, the error is very little. And polynomial function form is simply. So it is fit for application in engineering. The fatigue life for crack initiation can be predicted under any reliability by the stress and strain method.Secondly, the establishment principle and the applicability of the three improved Miner's rules were analyzed. The rules were examined by a constant amplitude loading. The results proved the rationality of the statistic Miner's rule. The approximate method was established to calculate the block number of cyclic loading. The mean value and variance of the fatigue life were obtained through the one-order approximate polynomial. By comparing to Daolin, the error is very little. And polynomial function form is simply. It is fit for application in engineering. If the distributing of the fatigue life was known, the reliability can be analyzed relative to any service life.The last to analyze the metallic fatigue strength and fatigue damage lifetime, and establish the fatigue crack initiation equation, fatigue crack extend equation about the metallic welded joint, and analyze the new model application in the fatigue crack extend.