Coach crashworthiness and failure analysis during a frontal impact

Abstract

Accidents involving coaches may endanger the physical integrity of their occupants, since the driver stands very close to the collision region. In the event of a frontal impact, there is a violation of the driver's residual operational space, which depends on the energy of the crash, and this may jeopardize the driver's safety. The most decisive factors in achieving a successful design of structural vehicles is to design innovative solutions that safely control the high energy released as a consequence of the high accelerations involved during impacts. Long-course coaches currently lack design techniques and technologies to absorb in a controlled way the kinetic energy released in the collision. Thus, to fulfill this gap in the passive safety of these vehicles, it is necessary to conduct structural optimization research, to improve the passive safety in the eventual event of a frontal collision. The main goal of this research is to develop new solutions for passive safety used in coaches. To this end, a feasibility study involving experimental and numerical techniques was conducted to assess the improvement of driver safety in case of a frontal impact. This study addresses the need for improved experimental validation and fills a literature gap by developing a realistic testing system and incorporating advanced monitoring techniques for evaluating frontal collisions in vehicles, so a M3 Class III coach was used to conduct this study. Experimentally, the vehicle was subjected to a frontal crash test, whereby the ECE Regulation R29 was considered as the baseline, despite focusing on the certification of heavy vehicles with separate driver's cab. Since no standards are available focusing on coaches, the ECE R29 was used and adapted to the studied model. The experimental testing setup comprises a 2500kg pendulum supported by two steel bars was used. When released it collides with the structure, anchored to the ground, with an energy of 55kJ. Monitoring techniques were employed to track the structure, namely Digital Image Correlation (DIC), strain gauges, and accelerometers. These were placed at specific points to accurately assess the damage evolution of the structure. The experimental results were used to validate the numerical results, obtained using VPS/PamCrash® by FEM techniques. The frontal crash simulation was performed using the Finite Element Method, with an explicit dynamic analysis. Strain evolution, accelerations, and displacements were obtained and compared with the experimental results. Furthermore, the evolution of the kinetic energy is plotted and compared with the reference value of the standard. Through the different obtained outcomes, a determination could be made whether the current models meet the safety criteria or whether a proposed solution is required to enhance its performance. According to the standard guidelines, the present structure has no potential to meet the essential safety requirements. In the future, new alternatives should be explored, leading to a structure that can efficiently absorb all the energy released in the experiment under controlled conditions.