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As an important impact energy absorber and a way to produce double-wall tubes, the inversion of the metal tube over a conical die is investigated in this study. Adopting the deformation profile inspired by FEM simulations, a theoretical model is proposed assuming the energy is dissipated by bending and compression in the meridional direction, and expansion in the circumferential direction. FEM simulations with a large range of geometrical parameters are used to validate the theoretical model, and results show that both the compressional force and the final circular radius of tube predicted by the theoretical model are quite accurate. Then, the energy dissipations along the axis of the tube by various mechanisms are analyzed in detail, and it is identified that the tube deformation in the thickness direction is the major reason of the current model’s deviation. Besides, the influence of the die radius, the friction between die and tube, as well as the dynamic effect are discussed. [ABSTRACT FROM AUTHOR]

An analytical model is proposed for global buckling circular tubes of low diameter-to-thickness ratio ( 25 < D / t < 40 ) and moderate length ( 7 < L / D < 8 ), based on experimental observations and numerical simulations. Compared with FEM simulations, the current model gives accurate predictions on the whole load-displacement curve, energy dissipation and peak force. Employing this model, the energy absorption properties of circular metal tubes are analyzed. For global buckling tubes of same geometry, fixed boundary can absorb more energy than free boundary due to the bending plastic mechanism at ends. For oblique compression (compression angle ≤ 30 ° ), the load-displacement curve of global buckling is similar to that of uniaxial compression. For tubes of different geometries under uniaxial compression, the total response and energy absorption ability are compared between global buckling and progressive buckling. If the effective stoke is small, the specific energy absorbing (SEA) of global buckling tube could be higher than progressive buckling tube. [ABSTRACT FROM AUTHOR]

The inversion of a metal tube over a circular die is an important energy absorption device. Taking into consideration the curvature change during inversion process, this study proposes a two-dimensional theoretical model. Using rigid-perfectly plastic (R-PP) material idealization, its steady inversion load, curling radius after the tube׳s separation from the die, and the optimization of the die radius are analytically obtained based on energy conservation. Compared with the FE simulations, the current model greatly improves the prediction accuracy of the steady inversion force, with the deviation smaller than 10%. The prediction of the tube radius after inversion agrees well with the FE simulation and experimental data. Out of our expectation, the optimized die radius is found to be different from that of free inversion radius of the same tube. In this study, a simple formula of the optimized die radius is given. [ABSTRACT FROM AUTHOR]

Inversion of tubes can be used in the design of energy absorbers. In this study, by comparing the initial state and the final state of the inverted tube, a deformation theory based theoretical analysis is proposed to predict the knuckle radius and the inversion load of a tube under an external free inversion. Employing the rigid, perfectly plastic (RPP) material idealization, three kinds of deformation mechanisms are compared. It is concluded that for tubes within a certain range of geometrical parameters, the analytical results based on a two-stage assumption about tube thickness agree well with those obtained from FE simulations as well as the experimental data. By re-visiting the existing theoretical models, the reasons of deviations in their predictions are discussed, indicating that neglecting the energy dissipation due to the axial stretching will lead to an overestimate of the knuckle radius. [ABSTRACT FROM AUTHOR]

Abstract: Comprised of cover ply, tensor ply and carrying ply, tensor skin is a kind of composite sandwich structure developed to improve the helicopter's crashworthiness in water impacts. In this study, a theoretical model is proposed to analyze the static and dynamic response of a kind of tensor skin. The whole response of tensor skin is divided into three stages: an elastic deformation stage of the whole beam; an unfolding stage of the tensor ply; and a stretching stage of the tensor ply. At the beginning of impact, the whole beam undergoes elastic deformation until the breakage of the cover and carrying plies; then the tensor ply left is unfolded and stretched to absorb more impact kinetic energy. In the unfolding stage, by adopting the rigid, perfectly plastic material idealization, a deformation mechanism with stationary plastic hinges is proposed. It is found that the static critical pressure first decreases then increases with the increasing central deflection. The static critical pressure varies with the geometric parameters, but the total energy dissipated in the unfolding stage is independent of the geometric parameters. The residual kinetic energy at the end of unfolding stage will be dissipated by the plastic stretching. The dynamic responses of the tensor skin are analyzed for step loaded pressure and rectangular pressure pulse. It is verified that the theoretical predictions display very good agreement with the corresponding finite element simulations. [Copyright &y& Elsevier]