含裂纹的双块式无砟轨道道床垂向振动特性分析

基于线弹性断裂力学理论和车辆-轨道耦合动力学理论,采用有限单元法,建立含道床裂纹的车辆-双块式无砟轨道垂向耦合动力学模型,模型中通过设置奇异等参元来反映三维裂尖应力场、位移场的奇异性,由节点位移外推法得到在列车动荷载作用下道床裂尖的应力强度因子,最后探讨裂纹对道床振动特性的影响。结果表明:在列车动荷载作用下,裂尖附近的应力场强度主要由Ⅰ型应力强度因子控制,裂纹出现张开与闭合的交替状态,裂纹在一次列车动荷载作用下不会发生失稳扩展,但应注意其疲劳扩展导致道床的断裂破坏;裂纹对道床的振动位移和振动加速度影响较小,但对道床的动弯应力和道床下层钢筋的动应力影响明显,会加速道床的疲劳损伤。

Analysis on Vertical Vibration Characteristics of Double-block Ballastless Roadbed with Cracks

On the basis of the theories of linear elastic fracture mechanics and vehicle-track coupled dynamics,the vertical dynamic coupled model of vehicle and double-block ballastless track with roadbed cracks was established with the finite element method.Singular elements for 3-D fracture models were placed near the crack tip to reflect the singularity of the stresses and displacements in the crack tip field,and the stress intensity factor varying with dynamic loads roadbed was obtained with the displacement extrapolation method.The influence of roadbed cracks on roadbed dynamic responses was also studied.The results show as follows:Under dynamic train loads,the intensity of stress field near the crack tip is controlled by Stress Intensity Factor Type-Ⅰ,the crack opens and closes alternately,and much attention should be paid to roadbed fracture caused by fatigue crack growth though crack instability propagation does not occur under one time dynamic loading;the influence of roadbed cracks on vibrating displacement and acceleration of roadbed is small,but it becomes remarkable when dynamic bending stresses of roadbed and dynamic stresses of the bottom bars,which will accelerate fatigue fracture in the roadbed.