On the gas pressure forming of aluminium foam sandwich panels: Experiments and numerical simulations Hani Nassar, Mohammad Albakri, Hao Pan, Marwan Khraisheh (2)* Masdar Institute of Science and Technology, Masdar City, Abu Dhabi, United Arab Emirates 1. Introduction Aluminium foam sandwich (AFS) panels are novel materials consisting of porous aluminium cores bonded between stiff aluminium sheets. AFS panels are characterized by their high stiffness to weight ratio, sound and vibration damping, thermal insulation, impact absorption and buoyancy. Potential applications of AFS panels include aircraft interior and wing panels, car body panels, ship hulls and many more [1]. Many applications require sandwich panels to be formed into three-dimensional shells rather than flat two-dimensional sheets. In automotive vehicles for example, it would be desirable to form a metal sheet bonded to a metal foam component to yield a compactable structure that would deform at predetermined levels when subjected to impact. A number of studies discussed the forming of sandwiched foamable precursors, which comprise metal cores containing a blowing agent, usually TiH 2 , bonded to metal face sheets [2,3]. After the sandwich is formed, e.g. by bending or deep drawing, the core is expanded by heating to the foaming temperature of the blowing agent. These methods however pose limitations on the choice of alloys, since TiH 2 decomposes at relatively low temperatures. Also, only closed pore foams can be achieved with these methods. Direct forming of metal foams has been addressed in very few studies. This is partly attributed to the high compressibility and frequent damage in the foam, limiting predictive capabilities for the forming process. In their work on aluminium alloy foams, Merklein and Geiger [4] achieved significant deformations in bending experiments at temperatures near the solidus. Recent studies include the work by Contorno et al. [5], where stamping of relatively thick AFS panels was investi- gated. Mohr [6] performed deep drawing of U-shaped parts by draw-bending of an initially flat thin sandwich sheet. More recently, incremental forming of AFS panels was investigated by Jackson et al. [7]. Gas pressure forming is a metal forming technique used to form sheet metal into complex three-dimensional shapes, and is usually carried out at elevated temperatures. Applying such method to shape flat AFS panels into complex three-dimensional shells would mark a development in the manufacturing of these materials. In this work, gas pressure forming of AFS panels is investigated experimentally and using finite element (FE) simulations. Hot uniaxial tensile and compressive tests at variable strain rates are performed on samples prepared from finished AFS panels and foam core material. Results of these tests are used to calibrate material deformation models for the solid skins and the porous core. The models are then incorporated into the FE code, ABAQUS, to simulate the deformation of AFS panels during gas pressure forming. Simulation results of dome height, panel thickness and forming time are validated by actual gas pressure forming experiments. 2. Experimental procedure The study was conducted on 3 mm-thick AFS panels. The panel consist of two 0.4 mm-thick aluminium alloy AA6101-T6 sheets bonded using 0.1 mm-thick adhesive epoxy layers to opposite sides of a 2 mm-thick open-cell AA6101-T6 foam plate. The foam core has a relative density of 7% and a nominal pore size of 40 pores per inch. 2.1. Uniaxial tension and compression Dog-bone tensile testing specimens (Fig. 1a) with a gauge length of 10 mm and a cross-sectional area of 3 mm  6 mm were machined from the AFS panels using water jet cutting. The tensile tests were performed on an Instron 5982 universal testing CIRP Annals - Manufacturing Technology 61 (2012) 243–246 A R T I C L E I N F O Keywords: Hot deformation Simulation Aluminium foam sandwich panel A B S T R A C T Forming of light-weight highly stiff aluminium foam sandwich (AFS) panels into complex 3D components would mark a development in the manufacturing of these materials. In this work, gas pressure forming of AFS panels is investigated experimentally and using numerical simulations. Deformation behaviour of AFS panels is studied during high-temperature uniaxial tension and compression, and constitutive models are developed and incorporated into FE simulations of the gas pressure forming process. Simulation results and experimental observations show reasonable agreement and demonstrate the possibility of forming AFS panels to significant deformations while maintaining considerable core porosity. ß 2012 CIRP. * Corresponding author. Contents lists available at SciVerse ScienceDirect CIRP Annals - Manufacturing Technology journal homepage: http://ees.elsevier.com/cirp/default.asp 0007-8506/$ – see front matter ß 2012 CIRP. http://dx.doi.org/10.1016/j.cirp.2012.03.116