一种考虑应力梯度的疲劳寿命预测方法

针对临界距离法及应力场强法在疲劳寿命预测过程中存在的问题，结合临界距离法计算量小、应力场强法能够反映构件所处应力状态的优点，提出了以缺口附近球形区域内的等效应力均值作为控制疲劳行为的当量应力的方法。参照一组疲劳试验对当量应力与球形区域半径的关系进行了研究，结果表明可用线性和指数函数的形式表示两者间的关系。通过定义应力梯度、相对应力梯度，构建了一种能够考虑应力梯度的疲劳寿命预测模型。对模型中参数的确定方法进行研究，提出了以光滑试件、缺口试件在各自相同载荷条件的疲劳极限作用下，两者当量应力相等时的球形区域半径作为损伤区域大小的方法，该方法不再需要通过试验获得半径参数，具有较强的实用性。疲劳试验结果表明，模型预测结果均在2倍分散带内，证明模型具有较好的预测精度，同时模型可准确预测疲劳破坏位置。

Predicting Method for Fatigue Life with Stress Gradient

Aiming at the problems that existed in the predicting the fatigue life processes by the critical distance method and the stress field intensity method, taking advantages of the two methods, an equivalent stress approach was proposed, where the effective stress average in spherical regions near the notch was taken as fatigue behavior control parameters. According to a set of fatigue tests, the relationship between the equivalent stress and spherical radius was studied, results show the relationship is well represented in the form of linear and exponential functions, by defining the stress gradient and relative stress gradient, a fatigue life prediction model was constructed considering the stress gradient. Determination of parameters in the model was studied,The spherical radius with the same equivalent stress of the smooth specimen and the notched specimen was taken as the damage region size under action of fatigue limit in the same load condition.  The spherical radius was obtained without test, so this method had a strong practicality. Validation of the fatigue test results indicates that the model prediction results are within 2 fold of the dispersion bands, show that the model has good prediction accuracy; the model may also predict the fatigue damage location.