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.
The effect of slip degassing on the microstructure and mechanical properties of slip cast and reaction bonded Si3N4 was studied. The slip was prepared by aqueous ball milling of silicon (Si) powder. Hydrogen bubbles, a result of Si oxidation during milling, were degassed from the slip using a combination of vacuum and heat. The slip was then cast into a plaster mould to obtain rectangular green bodies. The Si green samples were sintered in a nitrogen atmosphere at 1500°C to convert the Si to Si3N4. After that the nitrided samples were polished to dimensions of 3 x 4 x 30 mm. The density, porosity, flexural strength, phase content and microstructure of the sintered samples were studied. The results showed that the degassing process increased the slip density. After casting and subsequent nitridation, it was found that the average apparent density of the samples increased from 2.89 to 2.95 g/cm3, the porosity decreased from 52.9 to 49.5 %, and the flexural strength increased from 8.1 to 9.3 MPa, when the degassed slip was used. A microstructural examination showed that the pores in the samples were filled with whiskers, which most likely resulted from a vapor phase growth mechanism. The samples produced from the degassed slip tended to have fewer whiskers, due to the reduced pore size and volume. A comparison of the XRD patterns showed no phase differences between the samples. The appearance of Si2N2O, and SiC likely resulted from the reactions between O2 and C impurities with Si3N4.
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