On the crashworthiness of foam-filled ultralight automotive structures

by Heyerman, Jeffrey Bernard

Recent developments in the manufacruring of economical closed-ce11 aluminium foam has led to increased interest in the use of that foarn as a filler in energy absorbing thinwalled ultraiight structures. Foarns are ideal energy absorbea because they can undergo large deformations at nearly constant stress. In addition to the energy that can be absorbed by the foam aione, its presence as a filler material leads to a modification of the mode of collapse of the composite structure, thereby increasing the energy absorption of that structure. In this thesis, a novel layered mode1 for simulating the quasi-static and dynarnic collapse of foam-filled ultraiight aluminium structures using three-dimensional elasto-plastic finite elernent analysis is pnsented. Specifically, the quasi-static and dynarnic axial collapse of foam-filled box columns is investigated. The column was modelled using shell elements, while the filler foam was modelled as a series of solid layers with a shear-stress failure criterion, which ties the layers together. This method enabled the simulation of the shear rupture of the foam, as observed in the extensive mechanical testing carried out in support of this study. The interface between the filler and the tube was modelled using an automatic contact algorithm, which incorporates the penalty method. The f~te element analysis consisteci of two investigations. In the fmt, aluminium columns of varying dimensions füled with aluminium foam of varying densities undergoing quasi-static axial cmshing were examined. The effect of foam density, wd thickness and width of the column on energy absorption was evaluated and discussed. In the second, the same geometry was explored under dynamic impact loading. The changes in coiiapse behaviour under different sniker masses and velocities were considered. The results nveal the influence of the presence of the ultralight aluminium foam upon the collapse mechanism and the energy absorbed during impact. The results of this work are valuable for enhancing the crashworthiness of a number of automotive cornponents and ultimately the car of the next century. iii