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Impact Response of Advanced Transparent Materials

PHILLIP A. JANNOTTI, GHATU SUBHASH

Abstract


The demand for improved visibility in hostile environments requires materials with high transparency and superior impact resistance. Numerous materials satisfy the above requirements including transparent polymers (PMMA), polycrystalline glass ceramics (e.g., AlON, spinels, transparent Al2O3), single crystals sapphire, hardened glass, etc. In this study, an investigation into fracture behavior and fragmentation characteristics of three different classes of transparent materials, namely, single crystal sapphire, polycrystalline magnesium aluminate spinel, and amorphous strengthened glass with high residual surface compressive stress exceeding 1 GPa. The materials were examined to better understand the operative damage mechanisms during quasistatic and dynamic loading. Due to their inherently different structural features, the mechanisms of deformation under static and dynamic loads are vastly different. While high hardness has been considered as a dominant property that contributes to superior performance of any armor material, it is now recognized that it is not the only property that determines the resistance against an incoming projectile. A range of mechanisms including the tendency for mixed mode fracture, grain boundary shielding, and pulverization characteristics etc., act in favor of spinel, whereas propensity for fracture along preferred crystallographic planes contributes to inferior performance of sapphire. In the case of strengthened glass, large residual compressive stresses (up to 1 GPa) enable increased impact resistance. Finally, the energy dissipated in each of these failure modes is quantified to gain further insight into the mechanics of failure in these materials.

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