表面裂纹疲劳扩展的数值模拟(Ⅱ)

根据Paris疲劳裂纹扩展规律,对拉伸和纯弯曲疲劳载荷下表面裂纹扩展进行了数值模拟。数值模型中,用三次样条函数曲线拟合裂纹尖端,在裂纹扩展增量计算中考虑了裂纹闭合影响。裂纹形状演化的模拟结果与Newman和Raju经验公式预测结果进行了比较,表明了所采用的数值模拟方法的实用性。研究发现,裂纹闭合对疲劳裂纹扩展过程中的裂纹形状演化以及裂纹尖端的应力强度因子(SIF)分布都有明显影响。同裂纹形状演化一样,疲劳裂纹扩展过程中裂纹尖端的SIF分布表现出明显的特征。最后,建议了一个简单函数来统一描述表面裂纹尖端的SIF分布。

Numerical simulation to surface crack fatigue growth(Ⅱ)

Fatigue crack growth of surface cracks in tension and bending plates is investigated with numerical simulation technique based on the Paris law of fatigue crack growth rate.The cubic splines are chosen to represent the crack front and the effect of crack closure on the estimation of crack extension is taken into account.The aspect-ratio variation of surface cracks under fatigue loading is predicted and compared with the predictions of the empirical equations proposed by Newman and Raju.A close agreement between them demonstrates the applicability of the simulation technique.It is found that the crack closure exerts evident effect on both the aspect-ratio variation of surface cracks and SIF-distribution along crack front.Similar to the shape evolution of surface cracks,the SIF-distribution along crack front shows a clear characteristic during the process of crack growth.Finally a simple function is suggested to describe the SIF-distribution along crack front.