概率循环应力─应变曲线及其估计方法

PROBABILITY - BASED CYCLIC STRESS - STRAIN CURVES AND ESTIMATION METHOD

试验揭示了核工程材料１Ｃｒ１８Ｎｉ９Ｔｉ不锈钢管道焊缝金属的循环应力─应变响应存在很大分散性。意味着任何外载，即使恒幅条件，将产生随机应变加载史。为保证设计分析的安全性，引入了称为“概率循环应力─应变曲线”的表征方法。应用线性回归技术和极大似然法原理，给出了概率曲线及其置信限的估计方法。以经过验证的良好假设分布──正态分布模拟循环应力幅的随机性。概率曲线表征为均值和均方差循环应力─应变幅曲线的形式。任意可靠度下的分析可方便地根据正态分布函数完成。材料低周疲劳试验结果分析说明了方法的有效性。

A significant Scatter of cyclic stress - strain responses is observed for a nuclear engineering material, 1Cr18Ni9Ti stainless steel pipe - weld metal. This implies that a random fatigue strain applied history should be introduced under any of loading modes even a deterministic loading history. To assure safety of design evaluation, a modelling of so - called probability - bassed cyclic stress - strain curves is 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 appropriate assumed distribution, namely normal distribution, is introduced to describe the material random cyclic stress amplitude data. The curves are approximated by the mean value and standard deviation cyclic stress - strain curves of Ramberg - Osgood law. Then, analysis at an arbitrary given reliability should ie conveniently made according to the normal distribution function. Availability of the method has been indicated by an analysis to the test results of the present material.