Katsunori Hanakawa

Development of a Technique to Strengthen Body Frame with Structural Foam

A technique to strengthen body frame with a polymeric structural foam has been developed with benefits of reducing vehicle weight and improving drivability and fuel economy. The idea of this new technology was evolved from the concept that body frame strength will increase drastically if the body frames are prevented from folding on collision. The energy of a collision impact would be effectively absorbed if weak portions of body frames are reinforced by a high strength structural foam. The new technology composed of the high strength structural foam and a light-weight frame structure with partial foam filling is reported here. INTRODUCTION The objectives of achieving collision performance and light-weight body structure are co-existed with the advanced development of body structure, materials, and manufacturing . Up until now, steel bodies have been lightened mainly by applying high strength steel sheets, devising frame structures and applying new manufacturing technologies such as the tailored welded blank. However, the weight increase is sometime inevitable from the demand of further collision performance improvement. We have developed a body frame strengthening technology that uses a polymeric structural foam to enhance the collision performance with a minimum weight increase. Deformation modes of body frames have both an axial collapse and a bending collapse during crash. The entire frame is distorted during the axial collapse. However, during the bending collapse, the deformation area does not extend and the energy absorption is relatively small because the frame is only partially distorted . Our developed technology spreads the crash energy by preventing the bending collapse by filling a structural foam in the body frame which controls local buckling deformation of the frame. This newly developed structural foam which expands and cures at painting process with outstanding strength, and the partial filled frame structure with just a small amount of foam to improve the frame strength are reported in this paper. REQUIREMENT OF STRUCTURAL FOAM To increase the energy absorption during the frame bending deformation, it is essential to prevent the local buckling deformation and to broaden the deformation area. To investigate the material properties of structural foam to prevent buckling deformation effectively, three-point bending tests were used to simulate the hat section frame with various structural foams. The test configurations and the relationship between the compression strength of the structural foam and the energy absorption of the frame are shown in Figure 1. Compressive strength of material (MPa) A bs or be d en er gy (K J) Wood (0.4) Aluminum (2.7) Aluminum foam (0.3) Epoxy (0.5)