Abstract
Dynamic collapse behavior for a bus body structure in rollover was studied. Since the purpose of this study is to make a well-established development process of a bus body structure for rollover safety, the suitable development method for each design stage from a component to complete body structure were considered in this study. For the efficient approach of the concept design stage, a beam-spring hybrid FE model combined with plastic hinge theory was used instead of detailed shell models. After setting up the concept design for the component size and geometry, the shell model was used to confirm and optimize the whole structure composition, and also to examine the influence of rollover environment like body contact ground condition and friction force. First of all, the plastic hinge theory for bending collapsed rectangular and top-hat section tubular beams was studied. The theoretical bending collapse mechanism for the beams was established based on the quasi-static and rigid-plastic method of analysis, and the theoretical load-deflection and energy-deflection relationships were obtained using the principle of virtual velocity. The dynamic effect such as strain rate sensitivity was applied to the theoretical formula with coupling of the material strain hardening effect. Since these tubular beams form key components of the body structure of a bus body structure, an understanding of the energy absorbing characteristics of thin-walled structures under impact loads is an essential prerequisite for the rollover protection of the vehicle. Second, framework-type vehicle model including main ring structure of bus upper body was made using beam-spring hybrid FE. The moment-rotation angle characteristics of spring elements for each component section were obtained from the plastic hinge theory. For applying the theoretical predictions to the hybrid model with reliability, they were compared with the experimental results. Some simulations were conducted to get the most compatible component size and geometry for various component sections. Finally, a detailed shell model was used to examine the component joint collapse phenomena and energy absorbing characteristics of whole bus body structure. In this stage, the maximum deflection of developed superstructure was calculated to confirm if the result satisfy the bus rollover regulation ECE R66. The influence of contact condition between bus upper body and test ground is also verified. In current rollover tests and simulations, it is observed that the friction force is very important role to determine the collapse behavior and deflection of the impacted bus structure. In this stage, therefore, the influence of the friction force on the body deflection was quantitatively analyzed by means of non-linear FEM for the variation of energy corresponds to friction coefficient. The theoretical prediction of collapse behavior on the whole body as well as component was good agreement with the experimental results. The process developed in this study was practically used as an effective method to predict the rollover behavior of a new bus body structure.
KEYWORDS – Bus Rollover, ECE R66, Hybrid(beam-spring) Element, Bending Collapse Behaviour, Plastic Hinge