Researches On Structural Reliability Analysis Methods Under Fatigue Loads

It is possible that lots of failure modes have emergenced during the structural service period. Fatigue failure is one of the important failure modes in these failure modes. Fatigure failure phenomena often occur in our life.So,the reliability research of fatigure failure phenomena is gived a important attention more and more than ever.The methods of fatigure failure research of structural system are not many now. The normal method is that using the method of dead load strength failure of structural system calculates the life of the element under the different fatigue loads respectively, determines element failure sequence and gains safety margin expressions. Because of fatigue damage being cumulative,the former failure element have an impact on the later failure element,the former series life of the element is needed to consider when the element's life in different failure series is calculated . When there is lots of elements in structural system,the calculating process will be very complex and it is not convenient for the large structural system to calculate. The paper does some try on mending analytical method of fatigue reliability of structural system. Using the concept of equivalent fatigue life ,the effect of fatigue damage cumulative of the former element to the later element is considered fully,and element failure sequence is distinguished by using the method of risk value. Due to only considering equivalent fatigue life of the current failure series , the calculating process is abridged. At the same time ,according to the theory of damage mechanics,the formula of stiffness fatigue damage is deduced and it is showed by an example that it is necessary that fatigue strength and stiffness reliability of structural system are considered simultaneously. Main content of this paper is as following:1.Some main methods are expounded: the method of Monte-carlo, the method of FOSM, the method of AFOSM. The random sample Monte-carlo formula of planar normal distribution is deduced, AFOSM caculating software is produced.2.The main method that failure probability of structural system is expounded: Branch-and-Bound-method, PNET method, Taylor series stochastic finite element method and Sequential Response Surface Method.3.The basic theory of structural fatigue failure is expounded. The reliability of fatigue life of obeying logarithm normal distribution is solved by using the method of equivalent fatigue life and risk value,it is quite convenient for the large structural system to solve its fatigue reliability.4.The method that damage mechanics combines the residual strength model is used to analyse stiffness reliability ,and a general formula of calculating stiffness reliability is deduced. It is quite necessary that fatigue strength and stiffness reliability of structural system are considered simultaneously by means of an example..