Quasi-Static Structural Optimization of an Automobile Roof Structure using the Enforced Displacement Method: A Preliminary Study

Abstract

Many people are seriously injured each year in automobile rollover accidents. Although the occurrence rate of the automobile rollover accident is low, the injury is fatal. When a car rolls over, the roof structure has to maintain occupant survival space. The National Highway Traffic Safety Administration (NHTSA) proposes a regulation of strength requirements of the roof structure, FMVSS 216. Recently, the Insurance Institute for Highway Safety (IIHS) proposed the reinforced strength requirements of the roof structure. Structural optimization has been performed based on the regulations for roof crush. Most previous studies have been using approximation methods such as the response surface method (RSM). However, the approximation method can give inaccurate solutions in highly nonlinear problems, and it has a limitation on the number of design variables. Therefore, the equivalent static loads method (ESLM) has been proposed to solve highly nonlinear problems. Nonlinear quasi-static response optimization using ESLM has been performed by considering the automobile rollover accident, however, the ideal force-displacement curve needs to be defined. In this research, a new nonlinear quasi-static response optimization method is proposed using the enforced displacement method. The proposed method consists of the analysis and design domains. The displacements from nonlinear quasi-static analysis are used as the enforced displacements in linear static response optimization as a loading condition. The roof strength requirement is considered as reaction force constraints by following the reinforced regulations of IIHS. An example of nonlinear quasi-static response optimization is solved by using the proposed method.