【作者】 王冰；

【导师】 杨宇祥； 高瑞鹏； 尹宏飞；

【作者基本信息】 西安理工大学 ， 仪器仪表工程（专业学位）， 2019， 硕士

【摘要】 在铁路运输行业中,钢轨踏面由于受到循环载荷的作用极易产生疲劳微裂纹,随着疲劳作用的积累,钢轨表面会产生剥离、掉块,甚至断轨。因此,针对钢轨踏面疲劳裂纹扩展特性的研究能够预测其形成及扩展,为合理维护钢轨、制定检修周期提供理论依据,从而延长钢轨的服役期限。本文利用ANSYS软件建立三维轮轨接触模型,从而对钢轨踏面裂纹进行研究。首先,对钢轨疲劳扩展的基础理论进行了介绍,重点介绍了用来评估轮轨接触疲劳裂纹扩展特性的应力强度因子。其次,分别采用赫兹理论与有限元分析法对轮轨接触问题进行了分析研究,对比了两种方法在求解接触问题时的差异。结果表明:在轮轨接触疲劳分析过程中,以赫兹理论为基础的求解法计算结果偏差较大,且应用范围窄;而有限元法的计算结果精度高,且适用范围比较广泛,因此本文采用有限元法分析钢轨踏面疲劳裂纹的扩展特性。随后,本文研究了钢轨疲劳裂纹扩展过程中的几个主要因素如钢轨裂纹长度、轴重、摩擦力、裂纹角度以及循环载荷次数的影响。主要得出以下结论:(1)随着钢轨裂纹长度的增加,裂纹产生张开型(Ⅰ)扩展的位置由轮轨接触斑的内缘向外缘移动,当裂纹扩展至0.3～0.5mm时,裂纹会向钢轨表面扩展,将会导致钢轨表面材料产生剥离、掉块等破坏。(2)钢轨踏面的疲劳裂纹为张开型-滑开型(Ⅰ-Ⅱ)的复合型。无摩擦时,随钢轨踏面垂直轴重的增大,应力强度因子(KⅠ)随之显著增加,而应力强度因子(KⅡ)的变化规律较凌乱;考虑摩擦时,KⅠ、KⅡ随垂直轴重的增大而增加,其峰值较无摩擦时显著增加,因此摩擦力、垂直轴重加剧了钢轨踏面疲劳裂纹的扩展。(3)当裂纹角度小于30°时,以滑开型裂纹为主;当裂纹角度为30°～70°,此时裂纹属于Ⅰ-Ⅱ型复合型;当裂纹角度大于70°时,以张开型裂纹为主;当裂纹角度等于60°时,等效应力强度因子值最大,此时钢轨裂纹扩展的速率最快。(4)随着垂直、切向循环载荷次数的增加,钢轨裂纹长度随之增加,与Paris扩展曲线结论基本一致。最后,在实验室的条件下,对循环载荷次数与钢轨裂纹扩展长度间的规律进行验证,具体采用疲劳试验机对钢轨材料进行垂直、切向疲劳载荷加载。结果显示裂纹扩展的规律与前述仿真结果、Paris扩展曲线结论基本一致,从而验证了仿真结果的准确性。更多还原

【Abstract】 In the railway transportation industry,the surface of the rail is prone to fatigue cracks due to the cyclic load.With the accumulation of fatigue,the rail surface is peeled off,and even broken.Therefore,the research on the fatigue crack growth mechanism of the rail tread can predict the formation and expansion of the rail fatigue crack,which provides a basis for effective maintenance of the rail,thus extending the safe service life of the rail.In this thesis,the model of wheel-rail contact is established by ANSYS software,and the rails with cracks on the surface are analyzed.Firstly,the basic theory of rail fatigue expansion is introduced.It can be seen that the stress intensity factor K value can be used to evaluate the expansion of wheel-rail contact fatigue crack.Secondly,the three-dimensional wheel-rail contact model is established by using the method,and the wheel-rail contact problem is analyzed by Hertz theory and finite element analysis method.The difference between the two methods is compared.In the process of wheel-rail contact fatigue analysis,the calculation results based on Hertz theory have large deviations and narrow application range.The finite element method has higher calculation accuracy and can solve the complicated wheel-rail fatigue contact problem.And a wide range of applications.Subsequently,the influences of several main factors in the process of fatigue crack propagation of the rail were studied,including the factors such as the crack length,axle weight,friction and crack angle of the rail.The following conclusions were drawn.(1)As the length of the crack increases,the most dangerous position of the crack-induced open-type failure is moved from the inner edge to the outer edge of the wheel-rail contact spot.When the crack length is 0.3～0.5mm,the crack will expand toward the surface of the rail.Causes the destruction of the stripped off.(2)The fatigue crack on the surface of the rail is basically a typeⅠ-Ⅱ composite crack.When there is no friction,with the increase of the vertical axis weight of the rail tread,KI will increase significantly,and the variation of KII is more messy.When considering friction,KI and KII increase with the increase of vertical axis weight,and the peak value is less.The friction increases remarkably,so the friction and vertical axle weight increase the expansion of the fatigue crack of the rail tread.(3)when the crack angle is less than 30°,the type Ⅱ crack is dominant;when the crack is 300°and 700°At this time,the crack belongs to the I-II type composite.When it is greater than 70°,the type I crack is dominant.When the crack angle is 60°,the rate of crack propagation of the rail is the fastest.(5)With the increase of vertical and tangential load loading times,the crack length of the rail increases,which is basically consistent with the pairing expansion curve.Finally,under the conditions of th e laboratory,the variation law between the number of cyclic loads and the crack length is verified.The fatigue tester is used to load the rail material with vertical and tangential fatigue loads.The results show that the law of crack propagation is basically consistent with the above simulation results and pairs expansion curve,which verifies the reliability of the simulation results.更多还原