Crashworthiness of Aluminium Extrusions with Aluminium Foam Filler

In order to asses the crashworthiness of square thin-walled extrusions subjected to axial impact, a research programme was established at the Department of Structural Engineering, NTNU, in collaboration with the aluminium industry in Norway [1]. The main objective with this programme was to study the energy absorption of aluminium extrusions under axial impact, and to give experimental data for validation of a numerical model. The primary variables during the tests were the hardening of the material, the slenderness of the sidewall of the extrusions as well as the impact velocity. However, in order to improve the energy absorption of aluminium extrusion subjected to axial impact, a research programme has recently been started in order to study the behaviour of aluminium extrusions with aluminium foam filler [2-6]. Based on quasi-static and dynamic tests, an experimental database was established to support the development of design formulas to predict the mean crushing force. The primary variables in the test programme were the strength of the aluminium alloy, the wall thickness of the tubes and the foam density. Then design formulas were developed as an extension of existing theories for non-filled extrusions. The models of the mean crushing force assumed additive decomposition of 1) the mean force of non-filled extrusions, 2) the axial crushing of the foam core and 3) an interaction effect. The design formulas were applied for the investigation of optimum design of foam filled extrusions, i.e. minimum weight design. It was found that weight savings are possible by utilising foam filler. However, this requires a reduction of the outer cross section dimensions compared to traditionally designed non-filled extrusions.