Both of the applied criteria provided reasonable estimates for possible sites of maximum fretting damage that are also consistent with the experimental results.Considering critical defect size, both criteria have provided results comparable to the crack size mea- surements obtained by fractographic analysis of tested F1 and F4 axles. Fractographic investigation of broken axles proved the pres- ence of propagated cracks starting from multiple-site surface dam- age or from defects with a length of 350–400 lm. The predicted range is found to be in agreement with the permissible defect size predictions made by the applied  criteria.

In addition, a great number of non-propagating cracks originat- ing from surface defects were observed both on broken and run-

S. Foletti et al. / International Journal of Fatigue 86 (2016)  34–43 43

out axles. Size of non-propagating cracks are measured to reach 100–150 lms in length, which also justifies the critical size estima- tion made by the  criteria.

The critical plane estimations made by Dang Van criterion were comparable with the experimental results. For this reason, modi- fied Dang Van criterion can be concluded to be the most suitable approach for identification of susceptible  regions.

In conclusion, the proposed method is able to establish a crite- rion for the acceptability of defect at press-fit in railway axles. The run-out conditions described by the mathematical method were verified by the failure analysis data collected from full-scale axle tests. The achieved acceptance  criteria,  which  allows  defects up to 500 lm in length and 200 lm in depth, is found to be compat- ible with the practical application presented in the   literature.

Acknowledgement

Part of this research (analysis with modified Dang Van crite- rion) has been developed within the EU-FP7 Project EURAXLES ‘‘Minimizing the risk of fatigue failure of railway axles” – Grant agreement no: 265706.

G. Gurer participated in this research activity during the period he spent at PoliMi with a research assistant fellowship supported by the Department of Mechanical Engineering at Politecnico di Milano.

摘要铁路车轴是关乎于铁路安全关键性元器件，它们结构的完整性需要针对潜在的灾难性故障进行适当的监测。本文提出了一种通过测量轮轴在役弯曲振动以及诊断并监视铁路轮轴基于对应谐波分量来判断裂纹轴转周期（nxRev）的整分倍数的周期性连续状态的检查。

本文分析了这个方法的可行性，并全面测量和破获执行铁路车轴来进行实验，运用被定义数学有限元（FE）模型来再现该实验室实验，上述也能用来分析在一铁路轨道裂化滚动的铁路轮轴的情况。实验和数值研究的结果表明，该1xRev，2xRev和3xRev车轴弯曲振动的组件可以用于检测车轴所有裂纹面积在轮轴横截面或更大的16％的范围内的裂缝的情况。因此，该方法不能取代周期性非破坏性检查，但可以作为一个附加的安全措施以避免在服务故障。

毕业论文关键词：轴损耗标准  缺陷可接受性  铁路计轴

1引言

在铁路列车上车轮经常被连接成对使用，该组件被称为轴。它是在车辆非常重要的子系统，因为它们提供的接口与轨道，支持静态和动态载荷，提供牵引力，制动和指导使车辆跟随轨道前进。由于它们的使用寿命很长（30年甚至以上），所以很容易出现机械损伤从而导致材料缺陷或服务相关的触发损伤如腐蚀或镇流器受影响。这种破坏在一铁路发生的后果可能是灾难性的，因为一个车轴的故障很可能产生整个车辆的脱轨，其可以反过来导致以机车车辆严重损坏，基础设施损坏，乘客损伤，在最坏的情况下甚至导致死亡。