Aluminium foams for energy absorbing structures under axial loading

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Aluminium foams for energy absorbing structures under axial loading

Haberling, C. / Haldenwanger, H.G. / Bernard, T. / Burzer, J. / Bergmann, H.W.

In the Audi A8 car the deformation energy for speeds up to 10 km/h is absorbed by the reversible deformation of an impact damper. For speeds between 10 and 20 km/h the sequential buckling of easily replaceable circular aluminium tubes works as energy absorbing mechanism in order to prevent damage to the frame body due to low speed impact. Besides increasing the wall thickness, utilising foam filled structures is one possibility for improving the energy absorbing properties of the tubes. When doing this two mechanisms have to be distinguished. One mechanism is a parallel action of foam body and tube, which means that the foam body does not influence the buckling process. The other mechanism involves an interaction between the foam and tube which can be attained by locating the foam as close to the tube wall as possible. Although the efficiency of structural foams based on aluminium or epoxy (EP) is significantly higher than that of an empty tube, the mass-related energy absorption of aluminium foam components is lower. Nevertheless, due to the interaction between the foam and the buckling process, the effectiveness of the structure can be improved. Besides the degree of filling the tube with foam, the applied joining technique affects the energy absorbing properties, too. Whereas gluing does not show much effect on the deformation process, laser beam welding leads to a lower peak load necessary for initiating the buckling process due to the reduced strength of the tube material in the area of the welding seam. However, comparative experiments show that Al-tubes lined with a 2 mm-thick EP-foam layer show better mass specific properties than those filled with an 8 mm-thick Al-foam layer.