Design and analysis of rear underrun protection devices composed of auxetic structures for heavy vehicles

Highway transportation systems in the world are constantly developing as a result of the increase of demand due to the growing population and urbanization, as well as the rise in trade and commerce. In addition, increase in the number of vehicles leads to an increase in the number of accidents inherently. Considering the distribution of these accidents, underrun accidents occur when a passenger vehicle collides with the rear of a heavy vehicle. This collision causes sliding of passenger vehicle underneath of heavy vehicle and results in fatal results and poses a severe threat to road safety. One of the most effective safety measures for preventing underrun accidents involves the installation of rear underrun protection devices (RUPDs) on heavy vehicles. In this study, the use of auxetic structures was proposed to improve performance of RUPDs. Auxetic structures are characterized by a negative Poisson's ratio and this unique mechanical behavior can improve the energy-absorbing capacity of RUPDs and provide better protection to the occupants of the colliding vehicles. For this purposes, a traditional RUPD design was modelled with SpaceClaim software according to UNECE Regulation No. 58 firstly. Later, empty crash box crash box filled with honeycomb and auxetics were added to RUPD design and finite element analyses were carried out using Abaqus/Explicit software to evaluate their capabilities. In addition, effect of different material usage in RUPD, impact velocity, core structure thickness and overlap positions were also investigated and obtained energy, acceleration and reaction force results compared to each other. As a result of simulations; RUPD with empty crash box was found more effective than the conventional RUPD, RUPD with honeycomb filled model was more effective than empty crash box model and RUPD with auxetic core structure-filled modeel was more effective than honeycomb filled model in mitigating the effects of underrun accidents.