Both of the fatigue origins existed on the failed gear shaft of the pulling motor revolving shaft assembly of the HXD1 locomotive often nucleated at the interact zone of the oil groove and the oil hole with a characteristic of asymmetry with respect to the diameter plane of the oil groove valley but rather exactly at the oil groove valley. In order to study the roles of the stress played in the fatigue cracking procedure, a detailed stress analysis model was built based on the finite element method, and especially the detailed stress characteristic of the gear shaft was attracted more attention. The calculation results showed that there were two stress concentration locations formed at the interact zone of the oil groove and the oil hole, and both of the sites were asymmetric with respect to the diameter plane of the oil groove valley which agreed well with the characteristic of fatigue origins locations. Observed from the cone side to the gear side, the first principle stress of the left stress concentration site was larger than that of the right with a value of 26 MPa, and this difference resulted an improvement of the rate of the fatigue cracking at the left stress concentration site, which also agreed well with the statistic analysis result of the failed gear shafts. It confirmed that the asymmetric stress concentration played a critical role in the fatigue cracking procedure. As a result, it was proposed to introduce a proper compressive residual stress in the both of the stress concentration zones through surface mechanical enhancement technique to improve the fatigue resistance of gear shaft.%HXD1机车牵引电机小齿轮轴的两个疲劳源位于齿轮轴大端油槽－油孔交界处，相对于油槽谷底直径平面呈反对称分布，且不在油槽谷底。为深入研究应力在疲劳裂纹源萌生位置和裂纹萌生过程中的作用，本文基于有限元法建立了HXD1机车牵引电机转轴组件有限元细节应力分析模型，分析了在齿轮副啮合力作用下小齿轮轴的细节应力及分布状态。计算结果表明：小齿轮轴大端油孔两侧的两个应力集中点关于油槽谷底直径平面呈现反对称分布，这与裂纹源的实际位置吻合；从小齿轮轴锥端向齿端观察，油孔左侧应力集中点第一主应力值较右侧大（约26 MPa），这一区别导致左侧首先萌生疲劳裂纹的概率增大，该分析结果与失效小齿轮轴失效样本统计分析结果吻合。计算结果证实，油槽－油孔交界处呈反对称分布的应力集中在小齿轮轴的疲劳裂纹萌生过程中起决定性作用，建议采用表面机械强化的方法在两个疲劳危险点引入适当的残余压应力，以改善小齿轮轴的抗疲劳性能。
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