Crashworthiness design optimization using equivalent static loads

Crashworthiness is an issue that should be considered when designing a passenger vehicle to ensure the occupants' safety in a vehicle accident. Many governments and insurance companies around the world suggest conditions relating to passenger safety in designing vehicles, and regulations that include the conditions have been utilized. The suggested regulations reflect the crashworthiness of structures in order to consider passenger safety. Therefore, these conditions should be used as objective functions or constraints when optimizing a vehicle structure. However, it is difficult to apply gradient-based optimization methods to crash optimization problems because of the large non-linearities of the problems which should be considered in the time domain. The non-linearities and oscillation of the responses make it difficult to calculate the sensitivity information. Therefore, a design method regarding the crash optimization problem needs to be developed. A crash problem should consider the crashworthiness of the vehicle. That is, a design problem should be solved regarding the crash energy conveyed from the outside and injuries to the human body. In the present research, a crashworthiness design optimization method using equivalent static loads that considers the strain energy and injuries of the human body is proposed. The equivalent static loads method for non-linear static response structural optimization (ESLSO) is modified to handle responses imposed on the strain energy and the head injury criterion (HIC) responses. The proposed ESLSO is verified through three practical examples. Design optimization of a crash box and a knee bolster are carried out to maximize absorbed impact energy, and size optimization of a frontal structure of a simplified vehicle is performed to reduce head injury. In verifying the proposed method, traditional optimization methods such as the response surface method are used. The excellence and usefulness of the proposed crashworthiness optimization method are proved by successfully applying it to a crash problem and improving the crashworthiness of the vehicle.