The influence of seat structure and passenger weight on the rollover crashworthiness of an intercity coach

Abstract

A rollover event is one of the most crucial hazards for the safety of passengers and the crew riding in a bus. In past years it was observed that the deforming body structure seriously threatens the lives of the passengers after the accident, and thus the rollover strength has become an important issue for bus and coach manufacturers. Today the European regulation "ECE-R66" is in force to prevent catastrophic consequences of such rollover accidents, thereby ensuring the safety of bus and coach passengers. According to the said regulation the certification can be gained either by full-scale vehicle testing, or by analysis techniques based on advanced numerical methods (i.e., nonlinear explicit dynamic finite element analysis). The quantity of interest at the end is the bending deformation enabling engineers to investigate whether there is any intrusion in the passenger survival space along the entire vehicle. In this paper, explicit dynamic ECE-R66 rollover crash analyses of a stainless-steel bus under development were performed and the strength of the vehicle is assessed with respect to the requirements of the official regulation. Subsequently, starting from a baseline design, different considerations which are not currently mentioned in the regulation (i.e., passenger and luggage weight) and some worst case assumptions, such as the influence of the seat structure, were investigated. The nonlinear explicit dynamics code LS-DYNA as a solver and ANSA and LS-PREPOST softwares as FEA pre/post-processors were utilized throughout the bus rollover analysis project. The FEA model was generated by using PCs running on Linux Suse operating system, whereas the LS-DYNA solutions were performed on a multiple-processor workstation running on an AIX UNIX operating system. During the first stage, a verification of the analysis procedure following regulation ECE-R66 was performed. The verification of analysis is a compulsory requirement of the regulation, as it is the technical service's responsibility (TUV Suddeutschland in this case) to verify the assumptions used in the finite element analysis. The investigations indicated that the introduction of belted passengers increases the energy to be absorbed during rollover significantly (37% greater than the baseline), which severely impacts the rollover behavior of the pillars. When the vehicle is fully loaded (including passenger weight and luggage mass) the situation gets even worse. Even the tough center of gravity of the vehicle is lowered, and the total mass increases, which in turn gives the maximum intrusion.