Abstract: Ceramics have been used as armor materials because of their high effectiveness in absorbing kinetic energy under extreme loading conditions such as ballistic impacts. This is possible because they have very high compressive strengths. Ceramics exhibit significant compressive strength even when pulverized by a ballistic projectile. In addition, ceramic armors are lightweight, compared to conventional steel armors that are much heavier and more cumbersome. However, the brittleness of ceramics under tension has limited their use to applications that require little deformation such as the torso of war fighters.
A damage model for ceramic materials is developed and incorporated into the geometrically nonlinear solid shell element formulation for dynamic analyses of multi-layered ceramic armor panels under blast wave pressure loading. The damage model takes into account material behaviors observed from multi-axial dynamic tests on Aluminum Nitride (AlN) ceramic. The ceramic fails in a brittle or gradual fashion, depending upon the hydrostatic pressure and applied strain-rate. In the model, the gradual failure is represented by two states: the initial and final failure states. These states are described by two separate failure surfaces that are pressure-dependent and strain-rate-dependent. A scalar damage parameter is defined via using the two failure surfaces, based on the assumption that the local stress state determines material damage and its level. In addition, the damage model accounts for the effect of existing material damage on the new damage. The multi-layered armor panel of interest is comprised of an AlN-core sandwich with unidirectional composite skins and a woven composite back-plate. To accommodate the material damage effect of composite layers, a composite failure model in the open literature is adopted and modified into two separate failure models to address different failure mechanisms of the unidirectional and woven composites.
Keywords: Engineering, Aerospace, Engineering, Mechanical, Applied Mechanics.
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