Analytical and Numerical Study of Foam-Filled Corrugated Core Sandwich Panels under Low Velocity Impact 17

Content Provider	Semantic Scholar
Author	Damghani, Mohammad Nouri Gonabadi, Arash Mohammadzadeh
Copyright Year	2017
Abstract	Analytical and finite element simulations are used to predict the effect of core density on the energy absorption of composite sandwich panels under low-velocity impact. The composite sandwich panel contains two facesheets and a foam-filled corrugated core. Analytical model is defined as a two degree-of-freedom system based on equivalent mass, spring, and dashpot to predict the local and global deformation response of a simply supported panel. The results signify a good agreement between analytical and numerical predictions. Introduction. Sandwich panels have been widely used for constructing bridge decks, temporary landing mats and thermal insulation wall boards due to better performance in comparison to other structural materials in terms of enhanced stability, higher strength to weight ratios, better energy absorbing capacity and ease of manufacture and repair. In sandwich panels, low density material, known as core, is usually adopted in combination with high stiffness face sheets to resist high loads. The main functions of core materials are to absorb energy and provide resistance to face sheets to avoid local buckling [1]. For sandwich panels having corrugated cores, it has been envisioned that this may be achieved if proper lateral support to core members against plastic yielding and buckling is supplied. To this end, recently, Yan et al. [2] inserted high porosity close-celled aluminium foams into the interstices of corrugated sandwich panels made of 304 stainless steel. A combined experimental and numerical study of the hybrid-cored sandwich was carried out under quasi-static compressive loading. It was found that the foam filling into the core of an empty corrugated sandwich could increase the compressive strength and energy absorption capacity of the hybrid sandwich by as much as 211% and 300%, respectively, and the specific energy absorption by 157%. Yan et al. [3] made theoretically and experimental studies on the behavior of sandwich beams with aluminum foam-filled corrugated cores under three-point bending. The bending stiffness, initial failure load and peak load of the sandwich structure were predicted by theoretical analysis. They concluded that the filling of aluminum foams led to dramatically increased bending stiffness, initial failure load, peak load, and sustained load-carrying capacity relative to an unfilled corrugated sandwich panel. Yu et al. [4] investigated the crushing response and collapse modes of metallic corrugate-cored sandwich panels filled with close-celled aluminum foams using Finite Elements Method. They show that at low compression velocities, the foam-filled panel was more efficient in energy absorption The Authors. Published by Magnolithe GmbH. This is an open access article under the CC BY-NC-ND license http://creativecommons.org/licenses/by-nc-nd/4.0/ Mechanics, Materials Science & Engineering, December 2016 ISSN 2412-5954 MMSE Journal. Open Access www.mmse.xyz 176 compared to the empty panel due to the lateral support provided by the filling foam against strut buckling if the foam relative density was sufficiently large. Yazici et al. [5] investigated experimentally the influence of foam infill on the blast resistivity of corrugated steel core sandwich panels and numerically through Finite Elements Method. After verifying the finite element model, numerical studies were conducted to investigate the effect of face sheet thickness, corrugated sheet thickness, and boundary conditions on the blast performance. Experimental and numerical results were found to be in good agreement with R2 values greater than 0.95. The greatest impact on blast performance came from the addition of foam infill, which reduced both the back-face and front-face deflections by more than 50% at 3 ms after blast loading at a weight expense of only 2.3%. Foam infill benefits were more prominent for Simple Supported edge case than Encastre Supported edge case. Han et al. [6] explored the physical mechanisms underlying the beneficial effect of filling aluminum foams into the interstices of corrugated plates made of stainless steel with finite element simulations. Relative to unfilled corrugated plates of equal mass, this effect was assessed on the basis of elevated peak stress and enhanced energy absorption under quasi-static out-of-plane compression. Upon validating the FE predictions against existing measurements, the influence of key geometrical and material parameters on the compressive response of foam-filled corrugated plates was investigated. Four new buckling modes were identified for foam-filled corrugations. Based upon these deformation modes of post-buckling, collapse mechanism maps were constructed. Due to the additional resistance provided by foam filling against buckling of the corrugated plate and the strengthening of foam insertions due to complex stressing, both the load bearing capacity and energy absorption of foamfilled sandwiches were greatly enhanced. In this paper, the effect of core geometry on the energy absorption of foam-filled corrugated core sandwich panels is investigated through analytical and numerical simulations. 1. Analytical study of composite sandwich panels 1.1. Static indentation Local deformation. Rigidly supported sandwich panels experience only local deformation of top facesheet. Many of the analytical methods for determining the local deformation involve Hertzian contact methods [7]. Since the local deformation causes transverse deflections of the entire top facesheet and core crushing, that Hertzian contact laws are inappropriate for finding local indentation response. Other methods for determining local deformation and core compression include modeling the top facesheet on a deformable foundation [8,9]. Turk and Hoo Fatt [10] presented an analytical solution for the local indentation of a rigidly supported composite sandwich panel by a rigid, hemispherical nose cylinder. They modelled the sandwich composite as an orthotropic membrane resting on a rigid-plastic foundation model. The solution was found to be within 15% of experimental results that involved facesheet indentations that were several times the facesheet thickness [11]. In this paper, local indentation of a sandwich panel is found by considering the elastic, perfectly plastic core as a deformable foundation for the top facesheet. Fig. 1 shows three possible regimes of top facesheet indentation: (I) plate on an elastic foundation; (II) plate on a rigid-plastic foundation; (III) membrane in a rigid-plastic foundation. When the indentation is very small and core crushing is elastic the local indentation response is found by considering a plate on an elastic foundation. As the facesheet indentation becomes larger but still less than about half of the plate thickness, local indentation response is found using a plate on a plate on a rigid-plastic foundation. If the facesheet indentation is larger than the facesheet thickness, the local indentation response is found by considering a thin membrane on a rigid-plastic foundation. Mechanics, Materials Science & Engineering, December 2016 ISSN 2412-5954 MMSE Journal. Open Access www.mmse.xyz 177 Fig. 1. Regimes of local indentation of top facesheet. Abrate [12] gives the following expression for the local indentation of a simply supported plate on the elastic foundation (1) where is the bending stiffness of the laminate face-sheet; is the transverse elastic stiffness of the core. Plate on rigid-plastic foundation. Fatt and Park [13] obtained the load-indentation by using the principle of minimum potential energy. The total potential energy is given by (2) where is the strain energy due to bending; is the work due to core crushing; is the work done by the indentation force. Assume that the local indentation is only due to bending and has the form
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