Mechanical properties and energy absorption of aluminium foam and sandwich panels

Aluminium foams and aluminium sandwich structures with metal foam cores are novel materials and structures that have a great application potential in the automobile, marine, aircraft and building industries. They have the capability of absorbing considerable impact energy by large plastic deformation under quasi-static or dynamic loading, making them ideal structure protectors and energy absorbers. The microstructures of metal foams give them the ability to undergo large plastic deformation at nearly constant stress, thus absorbing a large amount of kinetic energy before collapsing to a more stable configuration or fracture. Studies on the mechanical properties of aluminium foam were presented by previous studies on the tensile, compressive loadings. The shear behaviour of aluminium foam is critical when it works as the core of sandwich structures. However, there has been very limited literature reporting on or addressing this aspect. Recent research on the performance of sandwich structures, especially on those made of various fibre-reinforced plastic laminates with polymer foam cores, has been focused on their behaviours under quasi-static loading and impact at a wide range of velocities. Work on the structural deformation and energy absorption of circular aluminium sandwich structures with metal foam cores is still limited. In this research, experimental investigations were conducted on the shearing strength and energy absorption of aluminium foams. Variation of the ultimate shear stress against geometrical dimension and relative density as well as impact velocity is discussed and empirical formulae are obtained for the ultimate shear stress and shear energy in terms of the relative density. Finite element method (FEM) simulation corresponding to the shearing experiment has been undertaken using commercial software LS-DYNA 970 to analyse the energy dissipation during the shearing process. Further experiments were carried out to study the structural performance of circular aluminium sandwich structures with metal foam cores under quasi-static and low-velocity indentation loading. Deformations of specimens in the tests were observed and analysed; quantitative results from different loading conditions were recorded and discussed; different failure modes were proposed and failure maps were constructed according to the geometrical configurations of the panels. A finite element simulation has been performed to validate an analytical model of sandwich panels under indentation loading with large deflection. Comparative studies have been conducted for the analytical solutions of monolithic plates and circular sandwich panels with the identical mass per unit area, but with different face-core thickness ratios. The analytical model has been proposed for the elastic and post-yield behaviours of the circular sandwich panels. Experiments were also conducted on circular metallic sandwich panels with aluminium foam cores to investigate the energy absorption and plastic deformation of the structures under ballistic impact loading. A parametric study was carried out to examine the effect of the face sheets, the foam core, the shapes of projectiles and the impact velocities on the performance and behaviour of the sandwich structures. An empirical equation was suggested to approximately estimate the energy enhancement during dynamic perforation. Finally, LS-DYNA 970 was used to construct numerical models of sandwich structures to simulate the deformation and energy absorption of sandwich structure under ballistic impact loading. The progress of damage and deformation was illustrated. The energy dissipation of the sandwich structure was analysed. The simulated perforation energy absorption by the sandwich structure will increase when the impact velocity increases, which agrees with the findings from previous impact experiments.