Simulation of the high velocity impact of railway ballast on thermoplastic train underbody structures

Abstract

Railway transportation represents an environmentally friendly alternative to automotive transportation for long distance travel. In the project Next Generation Train of the DLR, new railway solutions are developed for passenger and freight transportation for a broad range of applications (intercity, cargo, long distance). Specifically, the high-speed train NGT HST aims at reducing travel times and specific energy consumption with new technologies. At the maximal operating speed of 400 km/h, the coupling of mechanical and aerodynamical forces leads to increasing risks of ballast stone impact on the train structures (in particular underbody structures), thus threatening primary components underneath [1]. Through the repetition of stone impacts during the entire lifetime of a structure, critical damage can occur and reparation or replacement concepts are required. The present work aims at investigating an impact-resistant underbody structure made out thermoplastic composite materials for the HST train on numerical and experimental basis. By considering multiple impact scenario in the structure sizing process, the project intends to reduce the interval at which the structure has to be replaced. Starting with two combinations of thermoplastics and preforms, an experimental test campaign is performed on specimen scale to investigate their impact resistance at low velocities. The most promising material is then tested on component level under high-velocity impact at the gas gun DLR facility. Tests on single ballast stones are performed as well for validation of the numerical methodology. As support to time and material expensive test methods, a numerical framework is developed within LS-DYNA at all levels from low to high impact velocities. The composite parts are automatically modelled with stacked TSHELL and cohesive-element interfaces via *PART_STACKED_ELEMENTS. Composite materials and interface use the state-of-the-art material models *MAT_262 and *MAT_240 respectively. Random ballast stones geometries are automatically generated with the Voronoi tessellation and simulated with DEM particles. The present paper illustrates key aspect of the modelling techniques and their influence on the numerical impact behaviour. Furthermore, achieved results along the test pyramid are presented.