On the effect of anisotropy on the performance and simulation of shrinking tubes used as energy absorbers for railway vehicles

Abstract

The standard BS EN 15227 requires accurate numerical modelling of railway vehicle energy absorbers that must be correlated against experimental data. Although thin-walled tubes can exhibit anisotropy, such numerical models have traditionally included isotropic material properties. Thus, this work investigates whether anisotropic material models may increase the accuracy of numerical models of shrinking tube energy absorbers.Tensile testing of extruded AW-6082 aluminium alloy shrinking tubes showed the yield strength of the tubes was 10% lower in the hoop direction than in the longitudinal direction. Further, to assess the effect of incorporating anisotropic material behaviour in the numerical model, the tubes were compressed under quasi-static conditions.Numerical models of the shrinking tubes, including isotropic (von Mises yield function) and anisotropic (Hill’s quadratic yield function) material properties, were compared to the experimental data. The isotropic numerical models overestimated the steady-state reaction force, even without the inclusion of friction, indicating that such models do not fulfil the requirements of the standard. Conversely, incorporating anisotropic material models predicted a lower reaction force and enabled the inclusion of energy dissipation by friction, by means of a coefficient of friction μ ​= ​0.03. Although these results demonstrate the need to include anisotropy in the numerical simulation, the friction value was lower than expected due to the methodology of the material characterization and the accuracy of the anisotropic model implemented.