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Aluminum for an automotive has greater potential benefits than steel, from the viewpoint of conservation of natural resources and the market for recycling. Aluminum has a good energy absorption property as well as has contributed to weight-reduction and recycling. These advantages have been utilized on electric vehicles that consist of aluminum space frames and other aluminum components. From the viewpoint of the crashworthiness, the side members of an aluminum space frame play an important role in frontal crash. Occupant analyses are accomplished for the aluminum space frame vehicle and the results are verified by comparison with real experiment. The experiment is a barrier test that is carried out by frontal impact. With the model validated by test results, modifications have been made to improve the crashworthiness and to minimize the injury of passenger by modifying the side members of die aluminum space frame.

An aluminum space frame is the main structure of our recently developed electric vehicle. The frame consists of extruded members. As each extrusion has the same cross section, it is possible to accomplish an optimal design of the whole space frame by setting up design variables for each extruded member. Size optimization was completed to minimize the weight of the space frame at the desired overall stiffnesses, service loads, and desired natural frequencies. A tray structure was proposed for the batteries of the electric vehicle, and as a result, the overall stiffness was improved. In addtion, it became easier to install the batteries. A method to reduce the weight of tray was tried within the design constraints. Special reinforcements were used for weak parts between each member. The space frame was modeled as shell elements for the numerical analysis.

The difference of strain energy is concentrated on joint area between beam and shell modeling of box channel structures. Therefore, the analysis errors from the beam modeling are basically due to this strain energy difference. At concept design stage of automotive body we usually use the beam model. However, this kind of error at joint area is so dominant on the analysis that a correct beam modeling technique is necessary. There are some conventional beam modeling techniques in this problem. The most widely used one is using spring elements at the joint area. But the spring element has some problems in application to sensitivity analysis because it is a zero dimension element which does not have material properties and section properties such as mass, area, etc.

This paper describes the development of joint design approach for aluminum space frame. The space frame consists of thin-walled closed extrusions joined by welding. A welded joint cannot be treated by the rigid joint assumption for the effect of the weld line. The continuous fillet parts are modelled as interface elements using detailed finite element model. The study presents the equivalent effective Young's modulus and the effective zone with equivalent modulus. The structural joint stiffnesses of several pillars are calculated by the present joint design method and examined by stiffness test. The effects of fillet size, wall thickness and pillar geometry are considered. The results provide a useful and general method to predict the stiffness of joints with various configurations, and practical guidelines to analyze the stiffness of aluminum space frame.