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The use of structural optimization in the design of automotive structures is increasingly common. However, it is often challenging to apply these methods simultaneously for different requirements or model configurations. Multi-model optimization (MMO) aims to simplify the iterative design process associated with optimizing multiple parts or configurations with common design variables especially when conflicting requirements exist. In this paper, the use of MMO is demonstrated to evaluate the feasibility of an automotive door concept using an alternative material.

A demonstration structure was cast in AM60. The structure, known as the Generic Frame Casting or GFC, was designed specifically to mimic features seen in castings for closure applications. Excised samples were subsequently removed from different areas of the casting and tested under axial loading conditions. Component level tests were also conducted. Comparison of the excised sample results and the component level testing indicated the influence of local properties on the component level deformation. It was shown that varying the casting processing conditions could change the local ductility and yield strength in different areas of casting with the same geometry. Lowering the local ductility decreased the total displacement in a component level test and lowered the amount of energy absorption. Therefore, understanding the processing conditions and their influence on the local properties is important for predicting behavior in a component level test.

Racecar safety has received an increased amount of attention in the motorsports industry. Along these lines, the use of composites in racecars has improved structural stiffness and crashworthiness, while reducing weight. Besides having high stiffness and low weight, composites are recognized to be very good materials for absorbing impact energy. However, the use of aerospace grade carbon fiber composites in passenger vehicles faces the issues of high cost and long manufacturing cycle times. The design cycle for developing composite impact structures has traditionally been based on experiments with guidance from some simplified empirical models. Recently, a new composite material model has been developed by Mechalog in the Radioss™ crash analysis code. This model takes into account the orthotropic material properties of the composite as well as the failure strains.

The crush performance of lightweight composite automotive structures varies significantly between static and dynamic test conditions. This paper discusses the development of a new dynamic testing facility that can be used to characterize crash performance at high loads and constant speed. Previous research results from the Energy Management Working Group (EMWG) of the Automotive Composites Consortium (ACC) showed that the static crush resistance of composite tubes can be significantly greater than dynamic crush results at speeds greater than 2 m/s. The new testing facility will provide the unique capability to crush structures at high loads in the intermediate velocity range. A novel machine control system was designed and projections of the machine performance indicate its compliance with the desired test tolerances. The test machine will be part of a national user facility at the Oak Ridge National Laboratory (ORNL) and will be available for use in the summer of 2002.

In this paper, the impact energy absorption behavior of carbon and glass fiber composite materials will be discussed. In particular, the crush behavior of cylindrical and conical structures will be evaluated based on micromechanical failure modes. Studies show that stiffness and strength of the constituent materials alone cannot be used to design impact structures. Experimental results also show that by controlling the mode of micromechanical damage, crush efficiency can be maximized. Moreover, crushed structures which form many microcracks in the fiber and resin have increased energy absorption. Based on these results, some generic design guidelines for improving the energy absorption capacity of composite structures will be shown.