Abstract Impact damage are critical for damage tolerance assessment of high-speed train axles. Flying ballast impact damage on railway axles produce geometry discontinuities, which become preferential sites for fatigue crack initiation and usually lead to premature failure. According to this, the formation of surface impact damage and its influence on structural integrity of induction hardened S38C axles are herein explored. In particular, the morphology of impact damage on induction hardened S38C axles were analyzed as well as fatigue properties of specimens with artificial defects, electronic discharge machine (EDM) defects and impact defects fabricated by shooting metallic balls to the surface with compressed-gas gun. Results show that surface impact damage of the axles include two types, namely scratches and notches. Fatigue strength of the specimens with EDM defects are larger than the Murakami’s model predictions due to existence of compressive residual stresses. The influence of shallower impact damage (less than 200 μm) on the fatigue strength is negligible. With a larger depth, the rim is extracted out of the original surface and fatigue crack starts from this point with a decline of fatigue strength. Microcracks and loss of materials appear at the rim of impact damage, and microcracks along adiabatic shear bands lies beneath the surface when the impact depth is about 300 μm resulting in 50% reduction of fatigue strength. Fatigue strength of impacted specimens are larger than that of EDM specimens by 200 MPa with the equivalent area due to the local residual stresses.

中文翻译：

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人工缺陷对感应淬火S38C车桥疲劳强度的影响

摘要 冲击损伤是高速列车车轴损伤容限评估的关键。铁路车轴上的飞行道碴撞击损坏会产生几何不连续性，这成为疲劳裂纹萌生的首选位置，通常会导致过早失效。据此，本文探讨了表面冲击损伤的形成及其对感应淬火S38C车桥结构完整性的影响。特别是分析了感应淬火S38C车轴的冲击损伤形态，以及具有人工缺陷、电子放电加工(EDM)缺陷和用压缩气枪将金属球射向表面的冲击缺陷试样的疲劳性能。结果表明，车轴的表面冲击损伤包括划痕和缺口两种类型。由于残余压应力的存在，电火花加工缺陷试样的疲劳强度大于村上隆模型的预测值。较浅的冲击损伤（小于 200 μm）对疲劳强度的影响可以忽略不计。随着深度的增加，轮辋被从原始表面提取出来，疲劳裂纹从该点开始，疲劳强度下降。冲击损伤边缘出现微裂纹和材料损失，当冲击深度约300 μm时，沿绝热剪切带的微裂纹位于表面下方，导致疲劳强度降低50%。由于局部残余应力，冲击试样的疲劳强度比电火花试样的疲劳强度大 200 MPa，等效面积。