基于应力分布模型的随机疲劳加速试验设计

将两段式S-N曲线应用于Dirlik随机振动疲劳寿命预测模型，分段计算各自的疲劳损伤并进行叠加。基于该模型所模拟的应力幅值分布，推导了在两段式S-N曲线的情况下激励放大倍数同疲劳寿命之间的等效关系，并提出了基于该等效关系的加速试验寿命换算方法，为加速试验应力等级的确定提供了参考。针对随机振动中小应力幅占比较大的情况，该方法优化了这一部分的损伤计算方式，同时该方法还可以推广至超高周疲劳等需要使用多段式S-N曲线表达疲劳性能的情况中去，得到更加贴近实际的理论疲劳寿命与加速寿命间的等效关系。通过分析算例表明，在两段式S-N曲线下，应力与寿命也大体呈现出了两段式的对数线性关系，并使用文献中的试验数据进行了验证。

Accelerated random fatigue test design based on stress distribution model

The two-stage S-N curve is applied to the Dirlik random vibration fatigue life prediction model. The fatigue damage of each stress interval is calculated in segments and superimposed together. Based on the stress amplitude distribution estimated by the Dirlik model, the equivalent relationship between the magnification of excitation and fatigue life under the two-stage S-N curve is deduced. A life conversion method of accelerated life test based on the equivalent relationship is proposed, which provides a reference for the determination of stress level for accelerated life tests. The method can be generalized to the multi-stage S-N curve, like the very high cycle fatigue. For the large ratio of small stress amplitude in the random vibration fatigue, the damage computing method of this part is optimized, and the more realistic equivalent relationship between theoretical fatigue life and accelerated life is obtained. The analysis of an example shows that under the two-stage S-N curve, the relationship between stress and life also shows a logarithmic linear relationship of two-stage, which is verified by using the experimental data in the literature.