HIGH STRAIN RATE MECHANICAL BEHAVIOR OF CLOSED-CELL ALUMINIUM FOAM

Abstract

Aluminum foams have the potential to be used as structural material for the impact energy absorption applications due to their extended constant stress region during compression. The compression behavior of closed-cell aluminum foams synthesized by liquid melt route using TiH2 as a blowing agent is studied in the present work. Both, quasi-static and dynamic compression tests were carried out on foam specimen having relative density ranging from 0.062 to 0.395 and average pore diameter in the range of 1.696 mm to 5.18 mm. The dynamic tests were conducted using a Split Hopkinson Pressure Bar (SHPB) apparatus with a hollow aluminum transmitted bar. The results of the study indicated that the plateau stress of aluminum foam increases with relative density and strain rate. The dynamic tests were carried out using SHPB, assembled with ultra high speed camera to explain and understand the mechanism of deformation of cell wall material and pores at dynamic condition. The deformation of cell walls and collapse of pores propagate from one loading end to other throughout the foam in dynamic compression condition, while the deformation is concentrated in a localized zone near the moving crosshead at quasi-static compression. The high variability in the foam cell structure and complex relationship between structural and plateau stress makes, analytical modeling highly involved. The multi-linear regression and ANN models developed to predict the mechanical properties of foam on the basis of known, easily quantifiable structural parameters such as density, pore diameter, anisotropy and strain rate as the independent variables normalized as relative density (p*/p), cell diameter (d/D), anisotropy (L1/L2), and strain rate.