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本文要解决的是平面复合型疲劳裂纹扩展方向以及疲劳寿命的预测问题。主要内容如下: 1.提出“等双剪应力线上δθmax平面复合型裂纹开裂判据”。与其它判据相比较;本判据所预测的裂纹开裂方向更接近于疲劳裂纹扩展试验的结果。 2.文中指出:是Z形裂纹的分支方向,而不是其主裂纹方向,在Z形裂纹的K_Ⅰ,K_Ⅱ值中起着支配性的作用。接着提出二个计算Z形裂纹应力强度因子的近似方法。 3.为预测复合型疲劳裂纹扩展的寿命,文中提出了一个新的裂纹扩展速率表达式,即折合张应力强度因子指数公式。此式所预测的寿命较接近于实验值。 最后,还讨论了应用主应力强度因子K~*,应变能释放率G,应变能密度因子S,预测复合型疲劳裂纹扩展的寿命问题。
This article is to solve the plane composite fatigue crack growth direction and fatigue life prediction problem. The main contents are as follows: 1. Put forward the “double shear stress line δθmax plane composite crack cracking criteria.” Compared with other criteria, the predicted crack direction in this criterion is closer to the result of fatigue crack propagation test. The paper points out that it is the branching direction of the Z-shaped crack, not the main crack direction, which plays a dominant role in the K_I and K_II values of the Z-shaped crack. Then two approximate methods for calculating the stress intensity factor of Z-shaped crack are proposed. In order to predict the life span of compound fatigue crack growth, a new expression of crack propagation rate is proposed, which is equivalent to the formula of tensile stress intensity factor index. The life expectancy predicted by this formula is closer to the experimental value. Finally, the application of the main stress intensity factor K *, the strain energy release rate G, the strain energy density factor S, and the prediction of the life span of composite fatigue crack growth are also discussed.