钢轨表面疲劳裂纹扩展机制

Analysis of propagation mechanism of fatigue crack on rail surface

针对轮轨接触疲劳问题,基于Hertz接触理论与库伦摩擦定律,建立含表面裂纹的轮轨接触疲劳计算模型,并对加载位置、轴重、摩擦因数等因素对裂纹扩展速率的影响进行研究。结果表明,轮轨滚动接触的表面裂纹为Ⅰ-Ⅱ型裂纹,且以Ⅱ型扩展为主,其最容易发生断裂的位置在接触斑边缘。轴重和摩擦力是影响轮轨接触疲劳的两个重要因素;随着轴重的增加,应力强度因子K_Ⅰ、K_Ⅱ均呈增加趋势,20 t相对于10 t分别增加359%和185%;随着摩擦因数的增加,应力强度因子K_Ⅰ、K_Ⅱ均呈增加趋势,0.3的摩擦因数相对于无摩擦分别增加了108.7%和119.3%,表明摩擦力的存在明显加剧了裂纹扩展速率。在钢轨涂油养护时,应优先选用固体润滑剂。

The contact fatigue of wheel and rail was studied. Based on the Hertz contact theory and the coulomb law of friction, the calculation model of wheel/rail contact fatigue with rail surface crack was established, and the influence of loading position, axle load, friction coefficient on the crack propagation rate was analyzed, respectively. The results show that, the surface crack of wheel/rail contact includes sliding mode and opening mode, the major damage of crack is the sliding mode, and the most dangerous position for crack leading to fracture is the edge of contact area. The axle load and friction are two important factors affecting the fatigue of rail. As the axle load increases, the KI and KII of stress intensity increase. The KI and KII under the axle load of 20 t increase by 359% and 185%, respectively, compared to that under the axle of 10 t, With the increase of the coefficient friction, the KI and KII increase. The KI and KII under the state of friction coefficient 0.3 increase by 108.7% and 119.3%, respectively, compared to that under no friction. It is clear that the friction force can accelerate the crack growth obviously. Reducing the friction coefficient is an effective method to retard the fatigue of wheel/rail contact, and the solid lubricant should be used firstly when curing the rail.