钢轨表面三维疲劳裂纹扩展数值分析

Numerical Analysis of 3D Fatigue Crack Propagation on Rail Surface

在车轮循环滚动接触载荷作用下,钢轨接触表面裂纹问题频发,严重威胁高速列车运行安全,开展钢轨表面三维滚动接触疲劳裂纹扩展分析意义重大.首先,考虑不同初始裂纹角度,建立钢轨轨头含初始裂纹的三维有限元模型,对钢轨表面施加循环滚动接触载荷,进行轮轨滚动接触计算;然后,基于相互作用积分法计算裂纹前缘的应力强度因子;最后,采用最大周向应力准则和Paris公式计算当前状态下裂纹扩展方向和扩展速率,进而更新下一时刻的裂纹形状和尺寸.通过对上述过程重复实现,从而预测钢轨表面三维裂纹的扩展路径.加载过程中裂纹前缘应力强度因子计算结果表明,随着初始裂纹角度增加,K_(Ⅰ)的峰值逐渐减小,K_(Ⅱ)的峰值逐渐增大,裂纹前缘各位置的等效应力强度因子逐渐减小;裂纹前缘节点的位置越靠近钢轨表面,等效应力强度因子越大.疲劳裂纹扩展计算结果表明,随着循环次数的增加,不同初始角度下的裂纹都发生了偏折,逐渐朝着钢轨深度方向扩展,且裂纹的初始角度越大,发生扩展时需要的循环次数越多.对比三种初始裂纹角度下裂纹长度随循环次数的演化曲线可以发现,初始裂纹角度越小,裂纹扩展速率越大.所开发的方法也适用于研究钢轨多个裂纹的交互作用和其他位置的裂纹扩展问题,可为在役钢轨的剩余寿命提供技术支持.

Under the action of cyclic rolling contact load,the problems of crack propagation on the rail surface occur frequently.Such problems seriously threaten the safety of trains.Therefore,it is significant to conduct the research of three-dimensional(3D)rolling contact fatigue crack propagation on the rail surface.Firstly,a 3Dfinite element model of rail with different initial crack angles is established.A cyclic rolling contact load is applied to the rail surface to substitute the contact between the wheel and the rail.Then,the stress intensity factor(SIF)of the crack front is calculated based on the interaction integral method.Finally,the maximum tangential stress criterion and Paris’s law are used to calculate the direction and rate of crack propagation in the current state.The shape and size of the crack at the next moment are updated consequently.By repeating the above procedures,the propagation path of the 3Dcrack on the rail surface can be predicted.The SIF at the crack front subjected to cyclic rolling loading is analyzed.With the increase of the initial crack angle,the peak values of K_(Ⅰ)and K_(Ⅱ)decrease and increase,respectively,and the equivalent SIF at each position of the crack front decreases gradually.The closer is the node at the crack front to the rail surface,the larger is the equivalent SIF.The calculation results of crack propagation show that,with increasing the number of cycles,the cracks with different initial angles deflect and gradually expand towards the depth direction of the rail.The larger is the initial crack angle,the more are the cycles required for propagation.The evolution curves of crack length with the number of cycles under different initial crack angles are calculated.It is found that the smaller is the initial crack angle,the higher is the crack growth rate.The method developed in this work is also suitable for investigating the interaction of multiple cracks and crack propagation at other positions of the rail,which can provide technical support for the residual life of the rail in service.