Developing lightweight vehicle structures

The work presented here involves the study of aluminium foam-filled tubular structures under three-point bending. Alloy AA 6060 T5 was used for the tube. Commercially available closed-cell aluminium alloy foam, Alporas foam, was used for the filling. Although the aluminium alloy tube selected is not used in the automobile industry, the aim of the research work was to look generically at the effect of the Alporas foam filling on the overall energy and deformation profile of tubular structures under three-point bending. Both experimental and corresponding numerical simulations have been carried out. Tests with indentation speed of up to 50mm/s were carried out using an MTS universal testing machine, while dynamic tests were carried out using a drop hammer test (DHT) system where the experiments are referred to as MTS and DHT experiments, respectively. Focus was placed on the energy absorption of the structure with respect to the travel of the lowest surface, referred to as the intrusion depth'. The index of the energy absorption effciency with respect to the weight and intrusion depth, referred to as performance index', have been introduced and the comparison of the various structures has also been made using this index. Corresponding finite element (FE) models were produced and analysed using the explicit FE analysis software package LS-DYNA. Verification of the model was carried out for both the MTS and DHT experiments. The FE analyses (FEA) were carried out to obtain greater understanding of the experimental results and for parametric studies looking at the effect of foam density, tube wall thickness, foam insert length, foam insert cross-sectional diameter and the tube geometry. Comparison of the behaviour against pseudo-steel tube models was also made. It was found that the strain-rate behaviour of the foam has a beneficial effect of increasing the energy absorption of the overall structure with an increasing indentation speed. However, this effect was found to diminish with increase in the wall thickness of the tube. It was also observed from the FEA that the foam-insert was able to reduce the rate of drop in the performance index allowing the foam-filled tube to perform better than the empty tube counter part at larger bending. Comparison of the foam-filled aluminium tube against the pseudo-boron steel tube using FEA showed that the aluminium foam-filled tube did not experience structural failure, hence showed the possibility of outperforming the higher strength steel at large deformation.