The Mechanical Behavior Of The Double Tube Structure With Aluminum Foam Core

Thin-walled tube structures used as energy absorbers have broad potential applications in traffic tools and aero areas. As an improved structure, the load carrying capacity of the foam-filled single tube is higher than the empty tube and the light weight character of this foam-filled structure is very important for reducing the fuel dissipation and the pollution to the atmosphere. But the critical problem is that the energy absorption efficiency of the foam-filled single tube structure is lower than the empty tube under the axial crushing. And the foam-filled single tube fails much earlier under the three point bending condition which limits the energy absorption ability of this structure at some extent. In the most possible situations when the impact happens, structures are subjected to not only the axial crushing but also the bending loads. But the study of foam-filled structures under combined loads is so little by now. So a new topology structure, foam-filled double tube structure, was given by improving the traditional foam-filled single tube in this paper. And the experimental and numerical investigations about the performances of this new structure under the pure axial crushing, three point bending and the combined loading condition were carried out. The detailed contents are as follows:1) The pure axial crushing behavior of the foam-filled double square aluminum alloy tube structure was studied experimentally. Compared with the empty tube and the traditional foam-filled single tube structure, the different deformation modes of these structures including the new structure were obtained. The deformation stabilization character of this new structure is much better than the traditional foam-filled single tube. The energy absorption efficiency of this new structure under the axial crushing is much higher than the foam-filled single tube and empty tube structures. Furthermore, the energy absorption efficiency of this new structure with the deformation mode of tearing in corners is higher than that with the axisymmetric mode. The effect of the inner tube thickness to the axial crushing behavior of this new structure was also investigated. According to the axial crushing behavior of the foam-filled double tube, a new improved structure, double tube structure filled with aluminum foams in corners, was given out by cutting off parts of aluminum foams with lower efficiency in the structure. The deformation modes and the axial crushing behavior of this improved structure were studied. The results show that this new improved structure stabilizes the deformation and increases the energy absorption efficiency of the foam-filled double tube structure.2) The quasi-static three point bending behavior of the foam-filled double square tube structure was studied experimentally. The load carrying capacity, crashworthiness and the energy absorption of this new structure under the three point bending condition were investigated. Compared with empty and foam-filled single tubes, the crashworthiness of this new structure is enhanced and the energy absorption efficiency is increased. The deformation of this new structure was studied and the results show that the inner tube thickness is so important. The effect of the span and the inner tube thickness to the new structure was also investigated. The adhesion effect between aluminum foam core and the profiles to the new structure was analyzed. The results show that the adhesion effect increases the load carrying capacity but weakens the crashworthiness and the energy absorption ability of the structure before failure. The study of the profile materials was also performed. The bending behavior comparisons between different profile materials were carried out.3) The detailed quasi-static experimental studies of the foam-filled double cylindrical tube structures under the pure axial and the oblique loading condition were carried out. The deformation modes of profiles in the foam-filled double tube structure under the pure axial crushing were studied. The inner tube deforms with the diamond mode much easier. But the inner and outer tubes influence the deformation mode of profiles together. Compared with the empty and foam-filled single tube, the deformation mechanism of this new structure was given. The energy absorption efficiency of the optimized foam-filled double tube structure is much higher than the traditional foam-filled single tube structure and comes close to or even higher than the empty tube structure. The effect of profiles to the new structure was also investigated in the experiments. An instrument used for quasi-static oblique loading was designed and the experimental studies of the foam-filled double cylindrical tube under the oblique loading condition were carried out. The deformation modes of empty tube, foam-filled single tube and the foam-filled double tube structures under the oblique loading conditions differs from those under the pure axial crushing. Under the small angle oblique loading condition, a special deformation mode, mixed mode with symmetric half folding up and down, appears in foam-filled cylindrical tubes. And this special deformation mode makes the load carrying capacity of foam-filled cylindrical tubes much steadier and comes close to the ideal structure for loading. Under small angle oblique loading conditions, the load carrying capacity nearly keeps the same as the results under the pure axial crushing. The experimental results show that, the energy absorption efficiency of this new structure under different angle oblique loading conditions is much higher than the traditional foam-filled single tube and the most important point is that this new structure surpasses the empty tube on the energy absorption efficiency. So, this foam-filled double tube structure with two fixed boundary condition achieves the combined goal of increasing the load carrying capacity, enhancing the load steadiness and improving the energy absorption efficiency of structures at the same time. And the effect of the oblique loading angle to these structures was studied experimentally.4) The quasi-static three point bending behavior of foam-filled double cylindrical tube structures was studied experimentally and numerically. Differing from the single crack failure mode of the traditional foam-filled single tube, two obvious cracks appear symmetrically about the center of the foam-filled double tube. The crashworthiness and the energy absorption efficiency of this new structure are much enhanced compared with the traditional foam-filled single tube. With the proper assembling of the inner and outer tube, the load carrying capacity of this new structure is much steadier, which is much suitable for the energy absorbers. The effect of the span, the inner and outer tube to this new structure was also investigated experimentally. An effective model of this new structure under the three point bending condition was created with the finite element code in ABAQUS. The failure mechanism was analyzed by studying the stress distributing of the foam in the foam-filled double tube structure. According to the analysis of the equivalent plastic strain and the maximum tension strain, the maximum tension strain could be as the critical parameter for the failure of these structures. Some explanations have been given for the experimental results that the crashworthiness of this new structure is higher than the traditional foam-filled single tube. At last, considering the combined performances of the structure, some optimizations for this new structure have been performed and the proper assembling of the inner and outer tube diameter was given.5) The dynamic three point bending behavior of the foam-filled double cylindrical tube structure was studied experimentally and numerically. Differing from the failure mode under the quasi-static condition, there are several cracks located symmetrically about the center of the foam in the foam-filled double tube structure, which is much suitable for the much more energy absorption of the structure. Although the load carrying capacity of the foam-filled structures remains the same level of the quasi-static results, but the crashworthiness of these structures is much higher than the quasi-static ones. So, under the impact condition, foam-filled structures could absorb much more energy than the static results. Compared with the traditional foam-filled single tube, the load carrying capacity of this new structure is much higher and steadier, the crashworthiness and the energy absorption efficiency of this new structure is much higher, which shows that this new structure is much suitable as an energy absorber under the three point bending load. The effect of the span and the outer tube thickness to the new structure was also studied. The dynamic failure mechanism of this new structure was analyzed using the finite element code in ABAQUS. The difference of the crashworthiness between static and dynamic results is also investigated.