铁路碎石道砟静态压碎行为数值模拟

为揭示碎石道砟静态受压力学行为与破碎机理,用激光扫描仪获得道砟的真实几何形态,采用球形单元构建了道砟的离散元模型;通过定义单元间接触与黏结行为,模拟了30~60 mm粒径道砟的静态压碎过程,分析了压碎过程中载荷-位移响应以及内部力链和黏结断裂的分布与演化.结果表明:道砟静态压碎特征强度的离散性大且服从Weibull分布,这与已有试验结果一致;初始加载时,尖锐棱角和表面不平整导致道砟表面接触点应力集中与局部压碎,引起道砟翻转及接触状态变化,内部力链分布随之变化,载荷出现短暂回落;道砟稳定弹性变形阶段,部分单元间的接触力随载荷增大逐渐超过黏接强度,出现黏结断裂和局部微裂纹;当黏结断裂数量急剧增加到一定规模时,内部裂纹快速扩展,道砟最终劈裂破碎. 

Numerical Analysis of Static Crushed Behavior of Railway Ballast

In order to reveal the static compressive behavior and breakage mechanism of railway ballast, the discrete element method was applied to simulate its crushed behavior under statically loading between two flat platens. A laser scanner was used to obtain the three dimensional morphology of a ballast. Discrete element models for the ballast with a realistic shape were constructed using hexagonal close packed agglomerates. Contact and bond behaviors between particles were defined in these models. History of load-displacement, distribution evolution of force chain and broken bonds in the ballast during the crush process were analyzed. The numerical results show that the characteristic strength of railway ballast follows a Weibull distribution, being consistent with the existing experimental results. Stress concentration at ballast surface and local crush due to sharp corner and surface irregularity induce the initial rotation of ballast and the change of its contact state, resulting in variation of force chain distribution in the ballast and a short drop of load. During the stable elastic response phase, contact forces between some parts of elements gradually increase with the enlargement of load and then exceed the bond strength, thus broken bonds exist in the ballast. When the number of broken bonds dramatically increases and reaches a certain scale, the ballast is crushed due to the rapid propagation of internal micro cracks.