Design method of a hood structure adopting modal analysis for preventing pedestrian’s head injury

This study introduces a new 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 method of modal stiffness was employed, in an attempt to reduce the HIC from a collision between a vehicle and a head-form impactor. FRF (frequency response function) results for the reference vehicle model on head-form impact simulation were obtained. In addition, modal analysis of the entire vehicle model was simultaneously carried out. Subsequently, using the results of these two analyses, dominant frequencies (41.7 Hz and 83.3 Hz) were obtained, which related to deformation of the inner hood panel. Then, adequate hole positions at each modal frequency were selected, and the inner hood panel was improved, by making a hole at 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 the case of the improved vehicle model with a 40 mm diameter hole on the inner hood panel, this showed a significant reduction in the HIC of approximately 12.2%, compared to the original vehicle model.