表面粗糙度对动车组车轮钢弯曲疲劳性能的影响

Effects of Surface Roughness on Bending Fatigue Properties of Motor Train Unit Wheel Steel

目的分析不同程度的表面损伤对车轮钢疲劳性能的影响程度,为车轮疲劳的预测提供有效指导。方法采用X射线衍射仪测量不同程度表面损伤试样的表面残余应力分布,通过弯曲疲劳试验机对不同表面损伤的试样进行疲劳测试,并采用扫描电镜对断口形貌进行分析。结果 Ra4.1试样表面残余压应力大约为Ra0.7试样的2~3倍。Ra0.7试样疲劳极限为287.5 MPa,Ra4.1试样疲劳极限为280 MPa,前者比后者提高了2.6%。在相同应力下,Ra0.7试样的疲劳寿命至少高出Ra4.1试样一个数量级。Ra0.7试样的疲劳裂纹起裂于表面机加工刀痕,深度约为20?m;Ra4.1试样的疲劳裂纹起裂于表面凹坑,深度约为40?m,直径约为100?m。结论试样表面粗糙度越大,表面损伤越严重,表面残余压应力越大。表面粗糙度等级提高,表面应力集中严重,材料的疲劳性能下降。所有试样均起裂于表面损伤宏观缺陷处,裂纹易于在表面粗糙度大的试样表面形成,向内部扩展速度更快。

The work aims to provide effective guidance for predicting wheel fatigue by analyzing impact of varying degrees of surface damage on fatigue property of wheel steel. Surface residual stress distribution of varying degrees of surface damage samples was measured by using X-ray diffractometer. Fatigue test of varying degrees of surface damage samples was performed by using a bending fatigue test machine. The fracture morphology of samples were analyzed by using SEM. Surface roughness of sample Ra4.1 was about 2-3 times that of sample RaO.7. Fatigue limit of sample RaO.7 was 287.5 MPa, and Ra4.1 280 MPa, the former was 2.6% higher. Under the same stress, fatigue life of sample Ra0.7 was at least an order of magnitude higher than that of Ra4.1. The fatigue cracks of Ra0.7 caused by surface machining mark was about 20 μm in depth; while fatigue cracks of Ra4.1 caused by surface pit was about 100 μm in diameter and 40 microns in depth. The larger the surface roughness is, the more serious the surface damage is, and the higher surface residual stress will be. The greater the surface roughness is, the more serious the surface stress concentration is, and the greater the material fatigue property decrease will be. All samples crack due to the surface macroscopic defects of surface damage. The cracks may be present on surface of large surface roughness easily and expand inward rapidly.