弯扭组合载荷下圆轴表面裂纹应力强度因子计算

Stress intensity factors of surface cracks in round bars under combined bending and torsion loadings

传动轴往往承受弯扭组合载荷的作用,准确计算弯扭组合载荷下轴上半椭圆表面裂纹的应力强度因子对于传动轴的疲劳寿命预报来说十分重要。本文讨论了扭转载荷下裂纹前缘各点的Ⅱ、Ⅲ型应力强度因子计算和网格质量之间的关系,对扭转载荷下Ⅱ、Ⅲ型应力强度因子沿裂缝前缘的分布情况进行研究;并对弯扭组合载荷下轴上半椭圆表面裂纹的应力强度因子进行分析。结果显示在扭转载荷下裂纹最深点仅有Ⅲ型应力强度因子存在,沿裂纹前缘其他各点不仅存在Ⅲ型应力强度因子,还存在着不可忽视的Ⅱ型应力强度因子。弯扭组合载荷下的裂纹是Ⅰ-Ⅱ-Ⅲ型复合裂纹,且弯扭组合载荷下的表面裂纹各型应力强度因子可以视作分别施加弯曲和扭转载荷下同型应力强度因子的叠加。所得结论可为传动轴类构件疲劳寿命预报提供参考。

Transmission shaft usually subjected to combined bending and torsion loads. To predict fatigue life of the shaft,it is necessary to get the stress intensity factors（ SIFs） accurately. In this paper,the stress intensity factors of surface cracks in a round bar under bending are calculated and the results are compared with the results taken from the previous literature to validate the proposed FE model firstly. Then the stress intensity factors under torsion and combined loading are calculated,the relationship between mesh quality and SIFs are discussed. Results shows that only the KIIIexists at the deepest point of crack in torsion case,whereas at other points of the crack front,both KIIand KIIIexist. In the case of combined bending and torsion loadings,KI,KIIand KIIIexist and the superposition principle is applicable when calculate the SIFs under combined bending and torsion loads. The conclusions can be a reference to predict crack propagation life of semi-elliptical surface cracks in transmission shaft.