Dynamic axial and oblique crushing of foam-filled aluminium conical tubes

Abstract

The aim of this study was to investigate the response of conical aluminium tubes subjected to dynamic axial and oblique loading. The effect of foam filling on the energy absorption for variation in geometry, tube material and filler density was evaluated and discussed. This study employs a nonlinear finite element model which was validated against experimental data. Main trends in the experimental results are well captured by the FE results under dynamic axial and oblique loading. Nevertheless, the differences observed under oblique loading between experimental and FE results are as high as 35.4 % particularly for energy absorption. These differences may due to uneven thickness and inability to constraint the movement of the tube at the fixed end (as per simulation) during experiment. The validated model was subsequently used to assess the beneficial of foam filling with respect to the variation of geometry, tube material and filler density. The identification of critical effective point which signifies the critical total tube mass and critical filler density with the approach taken in varying the semi apical angle and by keeping the bottom diameter constant proved to enhance the Specific Energy Absorption ( SEA) of foam-filled tube over that of empty tube. However, these approaches apply to only particular combination of geometrical parameters. Moreover, SEA of foam-filled tubes is found to loss its performance at a bottom diameter of 240 mm. On top of this, the maximum SEA is not necessarily obtained with achieving higher SEA of foam-filled tube over that of empty tube. These findings highlight the importance of appropriate selection of these parameters thus showing that these parameters can be controlled and hence permits an efficient dissipation of energy absorber which is beneficial for impact applications. With the intention of achieving enhanced performance foam-filled conical aluminium tube, multi-objective optimization is explored to search for multiple objective functions namely SEA and initial peak force under various loading. It is found that foam-filled straight aluminium tube is favoured in achieving optimum design under dynamic axial loading whilst empty conical tube is preferable under dynamic oblique loading. The information gained serves as a basis for future enhancement of aluminium tube energy absorber.