As a type of novel sandwich structure, porous material filled thin-walled structure has turned to be an important solution to the confliction between lightness and crashworthiness. Conventional aircrafts are fabricated with spars, ribs and skins connected using fasteners. A more efficient design could be achieved with elimination of the ribs by inserting a porous filler such as a foam into the wingbox which is light, but could sustain enough load to maintain the wing shape. Impact safety and crashworthiness of a vehicle could be greatly enhanced by filling porous foams into the front rail or other hollow structures, with only slight alteration in its weight and volume.

    Significant increase in crushing force and energy absorption was found in the foam-filled structures, and this phenomenon is now known as the “interaction effect”. However, up to now little work has been carried out to quantitatively determine this effect, therefore its mechanism is still unrevealed. Dr. Hong-Wei Song in the institute of Mechanics of CAS, closely collaborated with researchers in Tsinghua University and Wrocław University of Technology, Poland, carried out systemic investigation into the crushing behavior and energy absorption capacity of aluminum foam filled thin-walled structures. They propose a “coupling method” to partition the energy absorption of the hybrid structure. They found that the increase in energy absorption is mainly due to the formation of “extremely densified region” in the foam filler, a phenomenon not observed by previous researchers. The morphology of cells is directly related to the loading condition, and the stress of the foam filler increases in an exponential function when subjected to both axial and side loadings. Combined the superfolding element model with the current model according to the coupling method, they found that when filled with porous foams, there is 5% increase in energy absorption for the thin-walled structure, whereas about 40% increase in the foam filler. Numerical simulation was also carried out to partition the energy absorption of the hybrid structure, and similar results were obtained.

    This results would be helpful to design the hybrid crashworthy members in the meso-microscopic level, and could tremendously simplify the design, improve efficiency and reduce operating costs. All of the benefits would propel the real application of this hybrid structure into aeronautical, astronautical and automotive engineering.

    Part of this work has been published in the International Journal of Solids and Structures(2005, 42(10):2575-2600) and International Journal of Crashworthiness(in press).