铁路钢轨裂纹萌生的键型近场动力学预测模型

为克服经典连续介质力学在解决不连续问题时的困难，采用近场动力学方法预测铁路钢轨的裂纹萌生，以避免数学构架在不连续处的失效问题；建立了考虑轨枕支承作用的钢轨形变分析模型，分析了模型参数合理取值及收敛性，计算了车轮滚动接触荷载下的钢轨位移；根据近场动力学损伤理论，以键伸长率为指标，分别研究了车轮全滑动、粘着-滑动及无摩擦状态对铁路钢轨裂纹萌生的影响规律。计算结果表明:近场动力学模型和经典连续介质力学模型的钢轨形变计算结果十分吻合，最大计算误差均在8%以内，验证了所建近场动力学模型的正确性；当裂纹萌生于钢轨轨头时，其启裂位置不在钢轨表面，而在钢轨表面以下约2 mm的位置，与现场观察结果一致，验证了近场动力学方法在模拟铁路钢轨疲劳裂纹萌生时的适用性；当车轮荷载位于钢轨跨中时，在车轮状态由全滑动向无摩擦转变的过程中，钢轨疲劳裂纹的萌生起点位置由轨头转移到轨底、由接触斑前端转移到接触斑中心，裂纹类型由局部滚动接触疲劳裂纹转变为整体结构疲劳裂纹，键最大伸长率由1.1×10-3降低到8.1×10-4，因此，增大切向接触应力会降低钢轨裂纹萌生寿命；当车轮荷载位于轨枕上方时，随车轮滚动状态的改变，钢轨裂纹的萌生位置始终位于轨头。 

Prediction model of rail crack initiation using bond-based peridynamics theory

The peridynamic method is used to predict the crack initiation of rails to overcome the difficulty of classical continuum mechanics in solving discontinuous problems and to prevent the failure of mathematical framework in discontinuities. The deformation analysis model of the rail was established by considering the support of the sleeper. The reliability of parameter values and the convergence of the model were analyzed, and the displacements of the rail under wheel-rolling contact loads were calculated. Based on the peridynamic damage theory, taking the bond stretch rate as index, the effects of wheel full sliding, adhesive-sliding, and frictionless state on the crack initiation of rails were investigated. Calculation results show that the rail deformations calculated using the peridynamic model and the classical continuum mechanics model are consistent. Moreover, the maximum calculation errors are within 8%, verifying the preciseness of the peridynamic model. When the fatigue crack is initiated on the rail head, the crack initiation position is approximately 2 mm below the surface of the rail instead of on the rail surface. This result is consistent with field observation, demonstrating the applicability of the peridynamic method in simulating the fatigue crack initiation of railway rails. When the wheel load is at the midspan of rails and the wheel transits from full sliding to frictionless state, the starting location of fatigue crack initiation of the rails is transferred from the rail head to the bottom and from the front end to the center of contact patch. The crack type changes from local rolling contact fatigue to integral structural fatigue, and the maximum bond stretch decreases from 1.1×10-3 to 8.1×10-4. Therefore, an increase of the tangential contact stress decreases the crack initiation life of the rail. When the wheel load is above the sleeper, the crack initiation position of the rail is always at the rail head. 11 figs, 30 refs.