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This paper describes the shape optimization analysis of solid structures such as chassis components of a car, where the shape optimization problems of linearly elastic structures are treated to improve strength or to reduce weight of solid structures. The optimization method used here is the growth-strain method, and the shape optimization system is developed based on this method. The growth-strain method, which modifies a shape by generating bulk strain, was previously proposed for analysis of the uniform-strength shape. The generation law of the bulk strain is given as a function of a distributed parameter to be uniformed, such as von Mises stress. Two improved generation laws are presented. The first law makes the distributed parameter uniform while controlling the structural volume to a target value. The second law makes the distributed parameter uniform while controlling the maximum value of the distributed parameter to a target value.

It is important to predict the crashworthiness of a body frame in order to design the structure which absorbs the impact energy effectively at the front or rear structure member of the body. We have been analyzing the crashworthiness with the following methods to establish a fundamental concept on the buckling characteristics of the frame at the initial design stage of vehicle development. 1) The method to introduce the empirical formulas considered with the effective width theory 2) The finite element method (FEM) based on the plastic joint method 3) The buckling analysis considered with the initial strain and the inertia force of engine Nowadays, it is possible to conduct a large deformation analysis of a crashworthiness by using the Super Computer.

It has become possible to calculate impact phenomena of comlex body structures by utilzing of a supercomputer and recent progress of computational mechanics including the Finite Element Method (FEM). However there are some problems to rely heavily on these methods for the analysis of crashworthiness from the view of time and cost in modeling or in calculation. It is important to develop each specific say of calculation for corresponding to various crashworthiness in early design stages. This papaer describes some FEM analyses for the various crashworthiness in statics and/or dynamics, regarding the body structure as resultant of components such as a side frame and subassembly such as a frontal structure. As a result, it is important to select optimum methods from FEM analysis for static and/or dynamic crash. It is also discussed that the difference between static and dynamic calculations is observed in deformation mode of body structure in collision.

An analysis of the static behavior of T-shaped joint is presented. Advanced testings by laser holography and infrared ray stress wave analyzers verified the surface deformation and the stress concentration of joint area, which are very important factors of thin-walled joint stiffness. The definition of structural joint stiffness is attempted, and the relationship between structural joint stiffness and sizes(dimension) of the constructing members is obtained in case of a thin-walled T-shaped member with rectangular cross section. The parametric study to accomplish weight reduction, while maintaining the necessary structural joint stiffness, is described in case of Rocker to Center pillar. The numerical analysis of body structure considering the structural joint stiffness shows better accuracy as compared with the analysis with the joint assumed rigid.

The objective of this paper is to present one of the application of the finite element method (FEM) in early stages of vehicle development to calculate larger deflections of body sheet panel. The stiffness of sheet metal shells is defined in conjunction with the local elastic buckling instability under concentrated loads. Considerable amount of weight reduction of outer panels could be obtained by optimizing metal gauges, radii, peripheral conditions and reinforcing manner of the panel. Among several outer panels of an automobile, a roof panel is picked up as an example and its stiffness is calculated by FEM analysis. The results shows satisfactory coincidence with the experimental ones. Regarding the calculation procedure, Central Processor Unit (CPU) time of finite elements was found to be reduced by varying and optimizing supporting conditions of the panel. Furthermore, the stiffness analysis program during the initial design stages of vehicle development is described.