Structural response of hybrid sandwich panels with aluminium foam

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					                            Structural response of hybrid sandwich panels with
                              aluminium foam core and thin Aluminium face
                                       sheets under bending loading
                                                   Kaveh R.Kabir, TaniaVodenitcharova and Mark Hoffman
                                                         School of Materials Science and Engineering, University of New South Wales
                                                                                       Sydney, NSW 2052, Australia

Aim                                                                                                     Failure modes and deformation behaviour
Develop a set of design parameters to manufacture aluminium-skinned metal                                 Deformation behaviour
foam sandwich panels which can resist three-point bending loading                                      Failed in two different mode
                                                                                                         Symmetric deformation
                                                                                                         Observed in both thicknesses but only in 100 mm span
Why metallic foams?                                                                                        Four hinges, indentation mark and shearing between
                                                                                                         supports observed
     Characteristics:                  Applications:
                                                                                                         Asymmetric deformation
   Low density                        Light-weigh structures
   High energy absorption             Energy absorbers                                                     Observed in beams with 50 mm span                                                    Hinges

   Low thermal conductivity           Sound absorbers                                                      Five hinges observed - three on top skin and two on
   High acoustic absorption           Heat exchangers                                                    back face
   Mechanical damping                 Multi-functional structures                                          Indentation mark observed, specially in thicker panels
                                                                                                           Smaller span length    higher shear force

                                                                                                       Two plastic hinges in both skins above one support
Materials                                                                                              developed and the foam core shears there; only one hinge
                                                                               Skin                    above the other support                                                    Indentation
  Foam core                                                                                                                           Asymmetric deformation
                                                                              Thin aluminium sheet
  Closed cell aluminium foam
                                                                              AA 3104- H19
 (Trade name ALPORAS)                                                                                     Failure load
                                                                              Thickness 0.32 mm
  Density=0.2-0.3 g/cm3
  Relative density= 7-11%                                                     Thin aluminium sheet       Increasing by increasing core
  Pore size= 2.5 mm                                                                                    thickness
  Modulus of elasticity1= 1.1 GPa                                              Adhesive                  Higher in thinner panels and
  Yield strength1= 1.4-1.6 MPa                                               Epoxy adhesive film       larger span
  Bending strength1= 2.5-3.1 MPa                                           (Redux 322)                   Higher in thicker panels and
1 Alporas data sheet                                                                                   smaller span, due to indentatio

Materials characterization                                             Indentation                      Bending Strength                                             Sandwich panels

  Vickers hardness test                                                                                                   My
                                                   96 MPa                                                             E             Fully elastic material
                                       y , solid                                                                        ( EI ) eq
On cell walls of the foam                                                                                  max

                                                                                                                           max L    One hinge failure mechanism
                                                                                                                           bc 2
  Tension test                                           70 GPa                                                           btd 2
                                                                                                          ( EI )eq   Ef
On dog-bone samples of the skin                    y ( skin) 230 MPa                                                        2

                                                                                                          Foam panels

Sample preparation and test method
   Sample preparation                                                    Test method
  Cutting foam panels and Al sheet                                       Three-point bending
  Degreasing and Abrading of foam                                        Foam only & sandwich
core and skins                                                         panels
  Assembling sandwich panels                                             ASTM C 393-06
  Employing hot press machine to                                         50 and 100 mm span lengths                                                                  Higher in larger span
cure the adhesive                                                        Foam thickness 6 and 12 mm                                                                  Lower in thicker panel

                                                                                                        Dissipated energy
Failure modes and failure load of foam panels                                                           Calculated by the area under load vs. displacement
                                                                                                          Foam panels
   Deformation behaviour                                                                                 Calculated up to failure load
  Similar deformation behaviour observed in both                             Crack
                                                                                                         Higher for thicker panels
thicknesses and span lengths                                                                             Higher for larger span
   Crack observed in all samples at mid-span; initiated at                                                Sandwich panels
the tensile side of the beam and propagated by further
loading                                                                                                   Calculated up to 1 mm of crosshead
                                                                                                          Higher for smaller span length
                                                                                                          Higher for thicker panels
  Failure load
  Increased with panel thickness
  Higher for smaller span length                                                                         Conclusions:
                                                                                                        . Bending strength, failure load and dissipated energy increased dramatically by laminating foam
                                                                                                        . The failure mode depends on span length

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