Modal Stiffness reduction method의 개념을 적용한 보행자 보호용 Hood Structure의 Passive Design

There have been many studies of passive systems in an effort to decrease the worst fatal head injuries in pedestrians from car accidents. A passive system of structural improvements in vehicles has been a major focus in the motor industry in an attempt to reduce the number road deaths and injuries. The HIC (head injury criterion) is a quantity for head injuries that was obtained by integrating the acceleration that is measured by a head-form impactor for a fixed amount of time. In general, the hood should be designed with lower stiffness to decrease the HIC value. This study introduced a method for decreasing the hood stiffness by making a hole on the inner hood panel. To determine the most effective hole position on the inner hood panel, the concept of modal stiffness was considered. The FRF (frequency response function) results for vehicle model on head-form impact simulation were obtained. In addition, modal analysis of the entire vehicle model was carried out simultaneously. Subsequently, using the results of these two analyses, adequate hole positions at each modal frequency were selected and the inner hood panel was improved by making a hole on these positions. Finally, through head-form impact simulations on the improved vehicle model with the hole, it was demonstrated that the new method applied in this study is acceptable and useful. In conclusion, the improved vehicle model with a 40㎜ diameter hole on the inner hood panel showed a significant reduction in the HIC; approximately 12.2% compared to the original vehicle model. A significant reduction in the HIC can be achieved by making only a single hole on the inner hood panel. In addition, this new method is incredibly effective and simple, and can be applied immediately to currently produced vehicles as well as to various impact studies including head-form impacts.