研究目的:车辆在运行过程中受到多种载荷的相互作用。在多种因素作用下，如车轮本身有不圆度;车 辆在通过曲线段、轨缝、岔道时对钢轨产生冲击，不可避免车轮会对钢轨产生法向载荷，从而使得弯矩对疲劳 裂纹的萌生和扩展产生影响。为研究弯矩对不同材料钢轨疲劳性能的影响，本文在NENE -2型微动实验机 上，对U71Mn,PD3 2种材料钢轨在弯矩作用下的疲劳裂纹扩展性能进行试验研究，据此提出减缓钢轨疲劳损 伤的措施。
研究结果:分析研究和试验表明，疲劳裂纹从应力集中点首先开始萌生，其中主剪切应力占有重要影响; 静载作用时裂纹扩展方向会发生大角度改向，而动态加载过程中疲劳裂纹扩展方向稳定;相同加载速率条件 下，PD3钢轨疲劳裂纹较U71 Mn钢轨更易萌生与扩展。为了防止和减缓钢轨的疲劳损伤，应根据线路的类型 和钢轨的实际工作环境选择适合材料的钢轨，货运重载线路，选择较高机械强度的PD3钢轨;高速线路，选择U71Mn钢轨。
Research purposes: There have various combined loads on vehicles in the moving process. Because of variety factors,such as ovality of wheel,attack of vehicle at curve rail,rail slot,turnoff,fatigue crack's initiation and growth~ influenced by the moment of flexure which was induce by the normal force existing between wheel and rail in the course of vehicles running. The growth behavior of fatigue carck of U71 Mn and PD3 rail steel under moment of flexure condition was investigated using NENE-2 fretting test machine. Based on the results, measures are proposed to avoid fatigue damage.
Research results: The results indicate that the crack initiate in the stress focus position , and the impact of main shear stress is very important. The growth of crack under static load is different from dynamic load condition. Under the same loading rate, the crack of PD3 rail is easier to initiate and grow than U71Mn's. To prevent and mitigate fatigue damage, suitable materials must be chosen based on the type of the rail line and work environment. PD3 rail steel would be used at heavy haul railway. U71 Mn rail steel would be used at high-speed railway.
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