Computer modeling and analysis of foam-ﬁlled conical tube under axial loading Z. Ahmad, D.P. Thambiratnam, A.C.C. Tan Faculty of Built Environment & Engineering, Queensland University of Technology, Australia Keywords: conical tube, foam-ﬁlled, energy absorption, impact loading, ﬁnite element ABSTRACT: Foam-ﬁlled thin-walled tubes have been considered to be desirable energy absorbers under axial loading due to their relatively high energy absorption and crush force efﬁciency compared with an empty tube. In particular, the combination of a tapered tube and foam ﬁller is preferable to a straight tube for energy absorption purposes as a tapered tube can withstand impact load in a stable manner. This paper investigates and compares the energy absorption response of empty and foam-ﬁlled conical tubes under quasi static axial loading, in terms of variation in their wall thickness, semi-apical angle and foam density. A parametric study has been performed using a ﬁnite element model validated using existing theoretical and numerical models. The numerical model was developed using explicit ﬁnite element code LS-DYNA. Overall, the results show that energy absorption capacity is signiﬁcantly enhanced and a more stable crush response can be obtained by ﬁlling the conical tube with metallic foam ﬁller. In addition, the advantages of using a foam-ﬁlled conical tube as an energy absorber are highlighted. As a practical outcome of this study, an empirical formula and design information will be developed for the use of foam-ﬁlled conical tubes as energy absorbers. 1 INTRODUCTION During an impact, some or most of the energy needs to be absorbed by well designed energy absorbing devices in order to protect the structure under con- sideration. Energy-absorbing systems consisting of various cross-sectional shapes are frequently used to mitigate the adverse impact as such tubes have been known as excellent impact energy absorbers because of their progressive axial folding. Over recent years, light weight material has also become increasingly attractive in impact applications due to the relatively high energy absorption efﬁciency under compressive deformation. Recently increasing focus has been paid to the use of a foam-ﬁlled thin-walled tube as an impact energy absorber to dissipate energy during an impact event. Such combination is very effective in impact and energy absorption application such as in automo- tive structures, aircraft sub-ﬂoor structure and energy absorbing barriers. Tremendous beneﬁts have been found in addition to the primary one of increasing the energy absorbing capacity. It is evident that the crush- ing loads of foam-ﬁlled tubes are higher than the sum of the separate crushing loads of foam and tube due to the interaction effect between the foam and tube wall (Guden & Kavi 2006). Numerous studies investigated the energy absorp- tion response of foam-ﬁlled circular and square tubes under axial loading. In most of the existing numerical and theoretical studies, energy absorption capacity is signiﬁcantly increased by introducing the foam ﬁller to the tubular components and it is a function of foam density (Lu & Yu 2003). However, low density foam is almost ineffective in increasing speciﬁc energy absorption. Therefore high density foam needs to be used if high energy absorbing capacity and speciﬁc energy absorption is desirable. Although high foam density enhances the energy absorption performance, it can cause global Euler buckling which represents a considerable loss of energy absorbing capacity (Seitzberger et al. 1997). Obviously there are some limitations in designing foam-ﬁlled tubular tubes. In comparison to an empty straight tube, a tapered tube either with circular or square cross sections is more preferable as it has a stable load-deﬂection response and minimizes the chances of collapse by buckling in the Euler mode (Mamalis et al. 2005). Since circular cross section is more effective com- pared to a square or rectangle (Mamalis & Johnson 1983), a conical tube will has greater advantages than other tapered tubes. It is envisaged that by ﬁlling a metallic conical tube with aluminum foam, the energy 670 Structural Engineering, Mechanics and Computation 3, A. Zingoni (ed.)