基于最弱环理论的缺口件概率疲劳寿命预测方法

Probabilistic Fatigue Life Prediction Method for Notched Specimens Based on the Weakest-link theory

基于最弱环理论和光滑试样疲劳寿命的Weibull分布,建立了一种缺口件概率疲劳寿命预测方法。该方法首先基于最弱环理论和光滑试样的疲劳强度分布,通过定义缺口件的Weibull有效应力,建立了缺口件在给定循环载荷下的疲劳失效概率计算公式。基于Weibull有效应力和光滑试样的疲劳应力-特征寿命方程,可计算得到给定循环载荷时缺口件的特征疲劳寿命,进一步根据光滑试样的Weibull疲劳寿命分布可最终获得缺口件在给定循环载荷下的疲劳寿命分布。采用上述方法对TC4缺口试样进行了概率疲劳寿命预测,并与局部应力应变法预测结果进行了对比。结果表明:局部应力应变法预测结果过于保守,本文方法预测精度较高,50%失效概率时的疲劳寿命预测结果与缺口试样试验均值寿命吻合很好,10%和90%失效概率时的疲劳寿命预测结果基本分布在试验均值寿命的两倍分散带之内。

A probabilistic fatigue life prediction method for notched specimens was established based on the wea- kest-link theory and Weibull fatigue life distribution of smooth specimen. A Weibull equivalent stress was derived and fatigue failure probability for notched specimen was formulated based on the weakest-link theory and fatigue strength distribution of smooth specimen. According to the relationship between the Walker equivalent stress and the characteristic fatigue life, the characteristic life of notched specimen can be calculated based on the Weibull e- quivalent stress. Finally the life distribution of notched specimens can be obtained based on the fatigue life distribu- tion of smooth specimen. This method was evaluated by the probabilistic fatigue life prediction of TC4 alloy notched specimens and the prediction result was compared with the local stress-strain method. The result shows that the lo- cal stress-strain method was very conservative, the method presented in this paper can predict more accurately. The predicted life with 50% failure rate agrees well with the test mean tested life of TC4 alloy notched specimens. The predicted life with 10% and 90% failure rate are mostly within the scatter band of 2 compared to the test mean life.