Compressive Behavior And Energy Absorption Of Closed-cell Aluminum Foam

Aluminum foam has a range of properties that are desirable in many applications. These properties include light weight, sound damping, impact energy absorption, thermal insulation and non combustibility and so on. The most striking aspect of these properties is the Plateau region of compression stress-strain curve, resulting in a large amount of energy absorption.In the present work, the quasi-static, high strain ratio and axial impact mechanical response of closed-cell aluminum foam has been investigated, respectively. Al foam, AlSi foam, Al/fly ash and Al/carbon fiber foam manufactured via melt route and Al foam manufactured via powder route were used. The main research contents include the mechanical properties, failure mode and energy dissipation mechanisms of aluminum foam with different matrix materials and density.The Young’s modulus, plastic collapse stress and anisotropic properties of five foamed Al were studied in quasi-static compression. The deformation process of closed-cell aluminum foam was investigated in various scales. The object is to understand the generation of the deformation band, the deformation mode at the cell/membrane level and the effect of cell wall micro structure on the fracture of the cell wall. Results show that density is still the major factor to affect the compressive behavior of closed-cell aluminum foam. The interaction between cell structure, distribution and imperfection resulting from the various densities leads to different compressive stress-strain curves and energy absorption. Failure mode of plastic aluminum foam exhibits localized deformation band. The collapse of deformation bands causes the densification of foamed specimen. Failure mode of brittle aluminum foam exhibits progressive crashing. Single cell shows three deformation modes. Four failure modes and frictional effect were observed at cell/membrane level, which are the main energy dissipation mechanism.High strain ratio tests were conducted using a split-Hopkinson pressure bar (SHPB) at different strain ratio. The axial impact tests were carried out using drop-tower apparatus at different impact velocity but same impact kinetic energy. The factors affecting the strain-ratio effect and energy absorption mechanism were discussed. The velocity sensitivity and energy absorption of closed-cell aluminum foam were discussed by kinetic control and defects control experiments. It is evident that closed-cell aluminum foam exhibits strain-ratio sensitivity. The strain rate effect of fiber/aluminum foam is considered to be primarily related to the rate sensitivity of dense fiber/aluminum composite and foam structure including cell morphology, cell distribution and cell imperfection. Moreover, the micro-inertial effect, gas pressure effect and viscous flow of gas through cracks play little role in enhancing the strength of metallic foam. Two deformation modes, shear deformation and end localized deformation, were observed at high strain ratio. The energy absorption is related to the generation of new surface own to the smash of the cell wall. Axial impact displacement-load curves of closed-cell aluminum foam exhibits two regions-initial compression region and progressive crushing region. Three failure modes were observed as closed-cell aluminum foam sustains impact load. The steady state compression deformation includes four failure modes. Closed-cell aluminum foam absorbs more energy at dynamic load than at quasi-static load. The results of kinetic energy control experiment show that specific energy absorption is velocity sensitive. The specific energy absorption increases but the crushing length decreases with increasing impact velocity. Defects control experiment indicates that double-chamfer angle triggered specimen shows lower initial peak load and longer initiation length than single-chamfer angle triggered specimen. Moreover, it is more obvious that the hardening of the second half of the displacement-load curve increases own to the existence of chamfer angle.