Design of negative Poisson’s ratio metamaterial filling structure for train energy absorber under complex boundary conditions

Abstract

Train collisions often cause severe casualties, however, the existing hexagonal honeycomb-filled energy absorbers with unpredictable deformation patterns are highly susceptible to bending under the complex boundary conditions, resulting in a substantial decrease in energy absorption and the accompanying risk of climbing and derailment. In order to solve these problems, this paper proposes a negative Poisson’s ratio metamaterial filled structure based on topology optimization. Firstly, a functional cell element topology optimization method is proposed, and the effects of complex parameters on the optimization results are considered. 50 optimization results are obtained by using design of experiments. Subsequently, the optimal structure with the higher specific energy absorption and the more stable deformation mode is determined by selective laser melting and simulation; finally, the optimal structure is applied to the energy absorber, and six kinds of working conditions, including centricity, wide range of offset, and angle, are designed on the basis of considering the complex and uncertain boundary conditions. The results show that the proposed lateral compressed negative Poisson’s ratio structure has a more stable deformation pattern and lower initial collision force than the conventional axially compressed hexagonal honeycomb-filled structure, and the degree of bending is significantly less than that of the conventional structure under complex boundary conditions. It is worth pointing out that, due to the extensive bending of the hexagonal honeycomb-filled absorber, the specific energy absorption of the proposed lateral compression absorber is instead higher by about 10.8%, while the degradation rate of the specific energy absorption is lower in the case of offset and angular collisions.