二级加载下疲劳可靠性分析

FATIGUE RELIABILITY ANALYSIS UNDER TWO STAGE LOADING

基于二维概率Miner准则，建立了在二级变幅加载下进行疲劳可靠性分析的系统方法并采用八组较大子样的二级低高和高低加载下的试验数据进行了验证、结果表明；本文方法初步实现了对第一级加载后的剩余疲劳寿命和二级加载下的疲劳总寿命进行较为准确的可靠性预测。

Based on two-dimensional probabilistic Miner's rule, a new method of fatigue reliabilityanalysis under two-stage loading is established, and a very successful experimental verification is made in terms of eight large samples of low-high as well as high-low two-stage fatigue experimental data given by Tanaka, et al.For a two-stage cyclic loading, let the first loading level be denoted by (Sa1, Sm1), and the second level by (Sa2, Sm2). Each individual in the specimen population is first subjected to n1 cycles at (Sa1, Sm1), and then run to failure after n2 cycles at (Sa2, Sm2).Let the constant amplitude fatigue life corresponding to (Sa1, Sm1) be denoted by Nc1=Nc(Sa1 , Sm1). Likewise, Nc2= Nc(Sa2 5 Sm2). For any given value of n1, one can obtain po=Pr{Nc1＞n1}, po is the survival probability of the specimen population at the first loading level (Sa1,Sm1). If po=1, that means all the specimen individuals survive at the first loading level,then two-dimensional probabilistic Miner's rule can be directly applied perform reliability-based prediction of the residual fatigue life n2 and the total fatigue life, denoted as Nv, under two-stage loading. If po＜1, that means some specimen individuals will fail in advance at the first loading level,hence n2p=0(p 2 po) for those individuals. Consequently, the specimen population is divided into two parts of (p 2 po) and (p＜po). Now let Nvp, Nc1p and Nc2p denote percentiles of p per cent survival of random variables Nv, Nc1 and Nc2，respectively, and define n2p=Nvp-n1, based on two-dimensional probabilistic Anner's rule it follows that Except the fifth case of high-low two-stage loading with n1=13300 cycles, experimental verification of this new method shows that the prediction agrees very well with the experimental result of the residual fatigue life as well as of the total fatigue life under two-stage loading. Nevertheless, the retardation effect of high loading applied firstly in the two-stage loadings is worth further studding.