Preforms made from porous salt beads with different diameters (0.5-1.0, 1.4-2.0 and 2.5-3.1 mm) have been infiltrated with molten Al to produce porous structures using pressure-assisted vacuum investment casting. Infiltration was incomplete for preforms with high densities. At higher infiltration pressures, penetration of molten Al occurred into beads of all sizes and was predicted using a simple model. The yield strength of the porous structures increased with increasing density and decreasing pore (bead) size. Despite the non-optimum distribution of metal in the porous structure, due to partial infiltration within the beads, the magnitude and density dependence of the yield stress were comparable with those for pure Al foams reported in similar studies. The structural efficiency was improved for structures produced at lower infiltration pressure, where the metal is predominantly distributed in the cell walls. The rate of salt dissolution from the preforms was high, in particular for high density preforms, large beads and preforms infiltrated at low pressures, owing to the ability of the porous beads to collapse as well as dissolve.
The purpose of this study is to investigate the effectiveness of composite armor against 7.62 mm ballistic threats. A sandwich panel construction consisting of a 96% alumina ceramic strike face, an annealed aluminum alloy 7075 cubic lattice sandwich panel, and a thin aluminum backing plate were used to create hard armor. The ballistic test based on NIJ standard level III was performed using 7.62 mm × 51 mm NATO projectiles at an impact velocity of 847 ± 9.1 m∙s-1. The influences of the alumina strike face panel with thicknesses of 7, 10, and 14 mm on the ballistic performance were investigated. The results of the ballistic test suggest that hard armor designs can resist a ballistic impact of 7.62 mm × 51 mm NATO projectiles without penetrating them. With the increase in thickness of alumina ceramic tile, the deformation of the aluminum backing plate decreased. Furthermore, the annealed aluminum alloy 7075 cubic lattice sandwich panel could be able to absorb the residual kinetic energy of the projectile after it was eroded by the ceramic strike panel. The damaged targets after ballistic impact were presented. Collectively, these results indicate that the armor composites in this study may be used in military vehicle applications.
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