A Study Of Structural Crashworthiness Of Car Sub-frame

In recent years, with the rapid growth of car ownership, people pay more attention to vehicle safety performance. Especially, after the C-NCAP evaluation system introduced, many manufacturers make effort to improve safety performance of their productions. In this situation, there is increasing needs for improvement of the safety performance of small models via research during new car development.This thesis aims to study how to use the whole box-type sub-frame to improve the crashworthiness of a small car. The collision influence mechanism between sub-frame and vehicle safety performance is investigated. An optimization design for the side rails of the box-type sub-frame was carried out to meet the requirement of crashworthiness in front impact.First, the relationship between occupant injury characteristics and vehicle collision response was identified. Furthermore the relationship between the characteristics of vehicle collision response and the structure design of car body was analyzed. So, the requirements of occupant protection from car collision can be transferred into the demand for crashworthiness of car body in structure design.Then, it’s found that simply improving material and thickness of vehicle front rails structure can not improve the crashworthiness performance via analysis of the front longitudinal beam of a small car. It is necessary to have other structures to help the front rails by sharing of the collision force and energy. Therefore, a whole box-type sub-frame is put forward to take on the collision force and energy.And then, in order to improve the crashworthiness of sub-frame, an optimization design for the side rails of whole box-type sub-frame was carried out in terms of structural parameters to meet the requirement for light weight and crashworthiness in front impact. The optimized sub-frame side rails can improve crashworthiness performance while maintain a good light-weight level.Finally, the designed whole box-type sub-frame is applied to the vehicle. For the sake of improvement of vehicle crashworthiness, A RBF approximation model was built to optimize the front vehicle structures by by varying of the thickness and materials.The results show that the whole box-type sub-frame can help to share the front collision force and energy and to induce partial impact energy and force transmission to the threshold beam, the longitudinal beam through the sub-frame side rails under the floor. So, it helpful to reduce the firewall intrusion pressure, improve the energy absorbing of front component and optimize the acceleration curve. The designed whole box-type sub-frame was apply to the vehicle. After the optimization of the side rails of sub-frame, the acceleration on the left side decreases by13.23%, and acceleration on the right side decreases by19.59%, firewall intrusion decreases by30.93%.