Performance of aluminium/Terocore® hybrid structures in quasi-static three-point bending: Experimental and finite element analysis study

The structural epoxy foam Terocore® and round tubes of different aluminium alloys (AA6060 T5, AA6061 T6 and AA7075 T6) were used to make the hybrid (foam-filled) structure. Terocore® foam was sandwiched between two concentric tubes, where the inner tube was acted as a carrier for the foam. Quasi-static three-point bending was carried out on empty (hollow) and hybrid structures to characterise the performance. In addition, the lowest generator (bottom surface) displacement and lateral (side) displacement of the structures were measured using two linear potentiometers to investigate the differences in structural deformation. The performance and deformation of hybrid structures were changed with percentage volume of Terocore® foam relative to the total volume of the structure and tube wall thickness. In addition, material properties such as yield stress, elastic modulus and work hardening behaviour of the tubes are very important when optimising the performance of the hybrid structure. Two failure modes were observed in this study. Top surface failure (compression) from structures made of AA7075 T6 and bottom surface failure (tensile) from structures with higher percentage volume of foam. It was also found 55% as the optimum percentage volume of foam to prevent bottom surface failure, while maximizing the performance under current experimental conditions. Finite element analysis was carried out using LS-DYNA. A number of standard mechanical tests were performed to characterise the material properties. Input parameters for failure criterion based on effective strain and volumetric strain were determined from inverse finite element analysis of tube lateral compression and full section tube tensile testing. Simulations were in very good agreement with experimental findings including successful prediction of the failure. The verified model was then used to optimise the tube dimensions and percentage volume of foam filling in order to maximise the performance of hybrid structure. It was calculated that the tube dimensions and percentage volume of Terocore® foam could be optimised to match the required performance in terms of energy absorption, while reducing the weight.