Investigation of compression mechanical behaviour of aluminum foam filled metal tubes
Novel crash element designs, composing of packing of foam-filled multi tubes, were investigated through compression testing at quasi-static deformation rates. Multi-tube designs involved the hexagonal and cubic packing of Al foam-filled deep drawn Al tubes inside rigid cylindrical and rectangular dies. For comparison purposes, empty Al tubes, Al and polystyrene foam-filled single tubes, Al and polystyrene foam-filled bitubular tubes and empty multi-tube designs of hexagonal and cubic packing were also tested under the similar test conditions. The Al-closed cell foams used for the filling of tubes were prepared in house using a patented foaming process. For each tube geometry investigated the average crushing load and specific energy absorption was calculated and the results were compared.It was shown that although foam filling resulted in higher energy absorption than the sum of the energy absorptions of the tube alone and foam alone, it was not more effective in increasing the specific energy than simply thickening the tube walls. The lower specific energy absorptions of the Al-foam filled single tubes based on the equal mass criterion were due to the relatively lower plateau stresses of the filler material used. The experimental results have further shown that both multi-tube and bitubular geometries exhibited higher specific energy absorption capabilities than those of foam-filled single tubes. The increased strengthening coefficients of the multi-tube geometries with foam filling were solely due to the frictional loads between the adjacent tube walls, tube walls and die wall and constraint effect of die itself. The frictional loads were also found to increase the specific energy absorption of empty multi-tube geometries. The effect of Al foam density was found to increase the specific energy absorption in multi-tube geometries.