Discrete element modeling of sleeper-ballast interaction under impact loading

Generally, track structure experience impact load (also called “shock load”) due to the irregularities of either wheel or rail. The impact load, that may greatly exceed the static wheel load, are mainly caused by wheel/rail abnormalities such as poor weld geometry, rail corrugation, and rail defects like spalling, wheel burns and squats. Impact load is transient by nature which occurs over a short period with a high magnitude. This corresponds to the frequency range from 0 to 2000 Hz. In fact, ballast is a nonhomogeneous and discontinuities by nature. Based on literature, the conventional method, continuum modelling, cannot provide insight into the interaction of ballast particles. Hence, continuum modelling should be replaced by discrete element modelling (DEM) which has a finite number of ballast particles. The discrete element modelling is an approach to present the discontinuity of material. The ballast particles with various radii are modelled in LS-DYNA. The spherical shapes are modelled instead of polyhedral due to the lower cost of computational time and memory consumption. Even though the spherical model has limitation on the contact interlocking, this can be compensated by adopting the contact model. One bay ballasted track modelling has been conducted. The impact load associated with actual train load is applied on the rail. The interaction between sleeper and ballast are highlighted. Moreover, sleeper and ballast particle movement are presented. This study will provide greater insight into the ballast particle and the sleeper motion induced by impact load associated with actual train load.