Keywords: expanded metal, finite element methods, energy absorption.

Expanded metal sheets have been employed in the construction industry mainly as furniture, safety fences and sidewalks among other uses. These sheets are manufactured by cutting and stretching flat metal plates forming a diamond-like pattern, which is characterized by both out and in plane deformation. This particular feature is an asset when designing structures requiring controlled plastic deformation when collapsing. Such structures are potentially used in energy absorbing application.

Energy absorbers are devices designed to absorb/dissipate the impact energy in a controlled manner and hence protect the structure under consideration [1]. Consequently, an energy absorber should be capable of absorbing kinetic energy upon impact and dissipate it in some other energy form, ideally in an irreversible manner. Inelastic energy can exist in various forms such a plastic deformation, viscous energy and friction or fracture energy [2].

In this paper, the structural behavior of expanded metal tubes is investigated using computational modeling. Expanded metal tubes are subjected to axial compression; thereafter the influence of the orientation of the cells is also analyzed. The explicit finite element code ANSYS-LS-DYNA is used to simulate the axial compression of expanded metal tubes of both cylindrical and square cross sections. Numerical results are compared with experimental results obtained by Smith [3].

A quasi-static numerical analysis, using the finite element method, of cylindrical expanded metal tubes is conducted. Geometries and boundary conditions are similarly to those used by Smith [3], i.e. the tube is clamped at both ends. This similarity remained in order to compare numerical and experimental results. For the numerical analysis the following geometries were developed: (a) cylindrical geometry, horizontal orientation of the pattern (G_00); and (b) cylindrical geometry, vertical orientation of the pattern (G_90).

It is observed that the failure for Model G_90 is caused by buckling of the expanded metal cells at mid-length of the tube. Afterwards, a plastic collapse mechanism occurs in the walls caused by the closure of the cells. The load-displacement response consists of an initial peak at mean load; subsequently the load decreases rapidly until reaching a steady value. For Model G_00, the failure is caused by progressive plastic collapse of the expanded metal cells until fully closure of the cells. This mechanism is characterized by the formation of plastic hinges at each cell junction, and the load-displacement response shows a gradual increase of the load until a plateau is reached. This behavior is desirable for energy absorbing systems, where energy should be dissipated in a controlled way. When comparing the energy absorbed and the mean load obtained by the two models, G_90 and G_00, there is a reduction of 45%. Nevertheless, the structural behavior is more stable in the latter.

From the results, it can be concluded that when the long axis of the cell is perpendicular to the applied load the response (Model G_00) is more stable and controlled. This orientation is more suitable for applications requiring energy dissipation.

1

G.M. Nagel, D.P. Thambiratnam, "Computer simulation and energy absorption of tapered thin-walled rectangular tubes", Thin-Walled Structures, 45(8): 1225-1242, 2005. doi:10.1016/j.tws.2005.03.008

2

A.G. Olabi, E. Morris, M.S.J. Hashmi, "Metallic tube type energy absorbers: A synopsis", Thin-Walled Structures, 45(7-8): 706-726, 2007. doi:10.1016/j.tws.2007.05.003

3

D. Smith, "Estudio Experimental de Estructuras Fabricadas con Láminas de Metal Expandido Sometidas a Compresión Axial", Tesis de Maestría, Universidad Simón Bolívar, Caracas, Venezuela, 2008. (In Spanish).

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