概率循环应变—寿命曲线及其估计方法

Probability based cyclic-strain life curves and estimation method

引入了概率循环应变—寿命曲线描述低周疲劳循环应变—寿命试验数据的分散性。应用线性回归方法和极大似然法原理 ,发展了曲线及其置信限的估计方法。方法采用经验证的良好假设分布即对数正态分布模拟疲劳寿命的分散性。基于Coffin Manson律 ,将曲线近似表征均值和均方差循环应变—寿命曲线的形式。任意可靠度下的疲劳分析可方便地根据正态分布进行。与现有独立随机变量观点不同 ,材料常数视为关联随机变量。1Cr18Ni9Ti不锈钢管道焊接头试验数据分析验证了方法的有效性。

To model the random cyclic strain life relations during low cycle fatigue,probability based cyclic strain life curves are suggested.A method for estimating the curves and their confidence bounds is developed by a linear regression technique and a maximum likelihood principle.In the method,a verified disirbution,i.e.lognormal distribution,is used as an appropriate assumed distribution of the fatigue crack initial lives.The curves are approximated by the mean value and standard deviation cyclic strain life curves of the logarithm of fatigue life of Coffin Manson law.Then,fatigue analysis at an arbitrary given reliability can be made conveniently according to the normal distribution function.Different from the existent work that the material constants in the strain life relation are independent random variables,these constants are now dependent on the fit of the test data.Availability of the method has been indicated by an analysis of the test data of 1Cr18Ni9Ti stainless steel pipe welded joint.