波磨激励下的地铁钢轨滚动接触疲劳裂纹瞬态扩展行为

Transient propagation behavior of rolling contact fatigue cracks on metro rails in the presence of rail corrugation

针对地铁曲线段钢轨波磨与滚动接触疲劳损伤共存现象,在ANSYS/LS-DYNA软件中建立了采用显式时间积分的瞬态有限元模型,分析钢轨短波波磨对其上滚动接触疲劳裂纹瞬态扩展行为的影响。以我国某地铁R450 m圆曲线段低轨损伤为例,考虑21条长度15 mm、深度3 mm、倾角30°且等间距分布的半椭圆形裂纹,波长30 mm、波深范围为0.03~0.09 mm的典型短波波磨,分析在速度67.6 km/h、摩擦因数0.5和牵引系数0.1等条件下,导向轮对通过时低轨侧瞬态滚动接触行为和裂纹群瞬态扩展行为。结果表明:裂纹群对轮轨接触产生持续周期性激励,且造成法、切向动态轮轨力波动幅值远低于典型短波波磨;处于波磨激励下动态加载时段内的裂纹,其最大裂尖动态应力强度因子较无波磨工况更大,而在减载时段内则相对更小,整个裂纹群的动态应力强度因子结果呈现出与波磨几何相对应的周期性波动;当波深增加时,最大裂尖动态应力强度因子也相应增大。在波长30 mm、波深0.09 mm的波磨激励下,裂纹群内的等效动态应力强度因子最大值较无波磨工况增加了34.4%,采用文献中报道的裂纹稳态扩展速率Paris公式发现,对应裂纹扩展速率增加了179.3%。这意味着波磨会显著加速钢轨滚动接触疲劳裂纹的扩展速率,增加断轨风险,现场必须对波磨区段内的钢轨滚动接触疲劳裂纹给予高度重视。

In view of the co-existence of rail corrugation and rolling contact fatigue(RCF)on metro curves,a transient finite element model using explicit time integration was established in the ANSYS/LS-DYNA software program,and the effect of short-wavelength corrugation on transient propagation of rail RCF cracks was analyzed.By taking the low rail damage in a certain metro R450 m circular curve segment in China as an example,a group of 21 identical semi-elliptical cracks distributed evenly along the rolling direction were simulated,and their length,depth,and angle were taken as 15 mm,3 mm,and 30°,respectively.The typical short wavelength corrugation with a wavelength of 30 mm and the depth varying from 0.03 to 0.09 mm was taken.The transient rolling contact behavior of the low rail side and the transient crack propagation behavior during the passage of the guiding wheelset were analyzed under the condition of a speed of 67.6 km/h,a friction coefficient of 0.5,and a traction coefficient of 0.1.The results show that the cracks excite the wheel-rail rolling contact periodically and continuously,but the resulting dynamic wheel-rail forces along normal and tangential directions are much lower than those resulting from the typical short wavelength corrugation.The maximum dynamic stress intensity factors(DSIFs)fluctuate periodically along the geometry of corrugation,so that it is larger during dynamic loading and lower when unloading,with respect to that in the case without corrugation.When the wave depth increases,the maximum DSIFs increases as expected.Under the excitation of a corrugation with a wavelength of 30 mm and a wave depth of 0.09 mm,the maximum equivalent DSIF among the considered crack group increases by 34.4%compared with that in the case without corrugation,corresponding to an increase of propagation rate by 179.3%when a Paris law of steady crack propagation reported in the literature was used.This means that corrugation can significantly accelerate the propagation of rail RCF cracks,leading to increased risks of rail breakage,and thus special attention has to be paid on rail RCF cracks occurring in corrugated sections.