高速滚滑下轮轨表层材料的应变率水平估计

ESTIMATION OF STRAIN RATES FOR WHEEL-RAIL SURFACE MATERIALS UNDER HIGH-SPEED ROLLING-SLIDING CONTACT

基于显式有限元法建立了三维轮轨高速瞬态滚动接触模型,详细分析了车轮以300 km/h速度滚过平顺钢轨表面、钢轨波磨(波长30 mm～170 mm)和宏观粗糙度(波长4 mm～30 mm)时钢轨表层0.25 mm～0.5 mm厚材料的平均应变率水平。结果显示:1)空间上,表层单元的应变率最大,时间上,表层材料的最高应变率发生于其进出接触斑的加、减载过程,且法向应变分量的应变率最大,其最值是Von Mises(V-M)等效应变率最值的1.50倍～1.86倍;2)网格大小和时间步长对应变率估计有不可忽略的影响;3)采用0.5 mm网格和0.32μs步长,平顺轮轨表层单元的最大V-M等效应变率为64.1 s^(-1),材料弹塑性无影响,波磨和宏观粗糙度使弹性下的最大V-M等效应变率分别增至92.5 s^(-1)和79.4 s^(-1);采用0.25 mm网格和0.042μs步长的结果约为上述值的1.65倍～1.88倍;4)最大V-M等效应变率随速度线性增加,随摩擦系数的增加而单调递增,牵引系数的影响可忽略。

A 3D wheel-rail transient rolling contact model has been developed using the explicit finite element method to calculate the average strain rates of rail surface material of 0.25 mm^0.5 mm deep at 300 km/h, for which smooth rail, rail corrugation (wavelength of 30 mm^170 mm) and macro-roughness (wavelength of 4 mm^30 mm) are considered. Obtained results have shown: 1) the highest strain rate occurs on the surface layer spatially, and during the loading or unloading processes of a material particle passing the contact patch;the rate of the normal strain is the largest among all strain components, being 1.50~1.86 times of Von Mises (V-M) strain rate;2) element size and time step have important effects on strain rate results;3) the V-M strain rate of smooth surfaces reaches the maximum of 64.1 s^-1 when the element size is 0.5 mm and the time step is 0.32 μs, the material elasto-plasticity has no effects, the rail corrugation and macro-roughness result in the maximum V-M strain rate of 92.5 s^-1 and 79.4 s^-1 in elasticity respectively;the results are 1.65~1.88 times higher when an element size of 0.25 mm and a time step of 0.042 μs are used;4) the maximum strain rate increases linearly with speed, monotonically with increasing friction coefficient, while the influence of traction coefficient is negligible.