考虑材料温度相关性的二维轮轨弹塑性滑动接触温升分析
FRICTIONAL TEMPERATURE ANALYSIS OF TWO-DIMENSIONAL ELASTO-PLASTIC WHEEL-RAIL SLIDING CONTACT WITH TEMPERATURE-DEPENDENT MATERIAL PROPERTIES
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摘要: 轮轨滑动接触温升的准确预测对于轮轨的磨耗和疲劳研究均具有重要意义. 目前的轮轨温升解析或半解析模型通常考虑Hertz弹性接触压力分布和单一材料属性的温度相关性, 与实际的轮轨传热状态尚有一定偏差, 因此在轮轨滑动温升计算模型中考虑接触压力的塑性修正和多种材料属性的温度相关性, 有望提高温升预测结果的准确性. 基于弹塑性接触理论, 同时考虑热导率、比热容和摩擦系数的温度相关性, 通过基尔霍夫变换方法以热导率温度相关性函数的积分作为待求量, 将复杂的非线性Fourier导热方程转化成含单个变系数的简单偏微分方程形式, 从而构建了一种不限制材料温度相关性函数形式的统一隐式差分求解格式, 分别讨论了对流换热系数、法向载荷、蠕滑率以及行车速度对钢轨表面滑动温升的影响. 结果表明, 当列车高速行驶时, 对流换热系数对轮轨滑动温升的影响甚微; 蠕滑率和行车速度的增大, 均会引起摩擦功率的增大, 进而导致钢轨表面温度的升高; 钢轨表面滑动温升的峰值随法向载荷的增大而近似线性上升. 此外, 在轮轨滑动温升计算模型中考虑材料属性的温度相关性可有效避免对滑动温升的过分高估, 且摩擦系数的温度相关性对温升的影响要显著强于热导率和比热容.Abstract: The accurate prediction of frictional temperature during wheel-rail sliding contact is of great significance to the studies for wear and fatigue performance of wheel-rail system. Current analytical or semi-analytical models of wheel-rail frictional temperature usually employ the elliptical distribution of contact pressure in the Hertz elastic contact theory and a single temperature-dependent material property, which differs from the actual heat-transfer state in many wheel-rail sliding contact conditions. Therefore, introducing the plastic correction of contact pressure and the temperature dependence of various properties in the calculation model of wheel-rail sliding temperature rise simultaneously could be great helpful to improve the accuracy of prediction result. Based on the elasto-plastic contact theory, considering the temperature dependence of thermal conductivity, specific heat capacity and friction coefficient simultaneously, the integration of thermal conductivity with respect to temperature is set as the quantity that needs to be solved by applying the Kirchhoff transformation method, and the nonlinear Fourier heat conduction equation is transformed into a corresponding simple partial differential equation with single variable coefficient, a unified implicit difference scheme with arbitrary form of temperature dependence is derived, and the influences of convection coefficient, vertical load, creepage and train speed on the temperature rise over rail surface are discussed, respectively. Results show that the convection coefficient has little effect on the temperature rise in the high-speed condition; the increase of creepage and train speed can enhance the friction power, and thus causes the increase of frictional temperature; and the maximum temperature rise also increases approximately linearly with the increasing vertical load. In addition, considering the temperature dependence of various thermophysical properties in the calculation model of temperature rise induced by the wheel-rail sliding contact can effectively avoid the overestimation of temperature rise, and the temperature-dependent friction coefficient has a more remarkable effect on the prediction result than thermal conductivity and specific heat capacity.