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The characteristic features of many armor-related ceramic materials are the anisotropy on the micro-scale level and the very limited, though non-vanishing, plasticity due to limited number of the planes for plastic slip. This work in progress is targeted toward revising phenomenological models of such materials with limited number of slip planes. In order to emphasize the key ideas of our approach, we illustrate the approach using the simplest possible model, the so-called deck-of-cards model., The original document contains color images.

When a high-speed projectile impacts a brittle material, such as glass or polycrystalline ceramic, severe damage and fragmentation is normally observed before projectile penetrates. AlON is a material being considered for a variety of transparent armor, sensor window, and radome applications. It is a polycrystalline ceramic that fulfills the requirements of transparency and requisite mechanical properties for transparent armor against armor piercing ammunition. AlON has a cubic, spinel crystal structure (Fd3m) that can be processed to transparency in a polycrystalline microstructure. It differs from glasses which do not have any periodic crystalline order, but it is akin to polycrystalline opaque ceramics, such as aluminum oxide. AlON was recently investigated by Strassburger, Patel, McCauley, and Templeton (2006) using EOI test in two different optical configurations. In the first, a regular transmitted-light shadowgraph set-up was used to observe wave and damage propagation. In the second, a modified configuration was used, where the specimens were placed between crossed polarizers, and the photoelastic effect was utilized to visualize the stress waves. Pairs of impact tests at approximately equivalent velocities were carried out in transmitted plane light (shadowgraphs) and crossed polarized light. AlON and fused silica specimens were impacted using solid cylinder steel projectiles with velocities ranging from 270 to 925 m/s., Presented at the International Symposium on Ballistics (23rd) held in Tarragona, Spain on 16-20 April 2007. Published in the Proceedings of the International Symposium on Ballistics (23rd), p953-963, April 2007. The original document contains color images.

A simple and accurate approach to modeling deformation processes that are highly constrained by boundary conditions is presented. The method involves a detailed finite element analysis of the most controlling aspects of the process. Additional analysis of the material states of texture and anisotropy are calculated as deemed necessary. The method is applied to the rolling process with a detailed analysis of the rolling of aluminum sheet. Particular attention is paid to the analysis of the roll-gap geometry and the transfer of tractions from the roll to the workpiece. The calculated deformation state is then applied to a more detailed calculation of material texture, which tracks the motion of individual crystalites due to macroscopic boundary conditions. The method not only allows a detailed analysis of through-thickness texture gradients, but also a detailed description of the boundary conditions and deformation states that cause such textures. The macroscopic anisotropy resulting from such textures is investigated, and the use of the method as a process design tool is discussed. Finally, results are compared to experimentally determined through-thickness texture gradients in rolled aluminum alloys, and details concerning the general roll-gap deformation field are discussed.

A description for the strain-rate and temperature-dependent behavior of pure tantalum (Ta) at large strains is developed. An integral part of the model incorporates the kinematics of crystallographic slip, and thus, the rotation of single crystals within the material, so as to reflect the evolution of anisotropy resulting from applied mechanical deformation. Such deformation is accommodated via bulk dislocation motion and governed by interactions that may or may not be thermally assisted. The model represents each discrete slip system as a single facet in a multisurface plasticity theory, which is well suited to high-rate numerical methods (explicit integration schemes). A formulation of this type allows for the complete kinematic decomposition of macroscopic material rotations and the rotations of single crystals due to motion through the lattice. Applications to high-rate deformation in polycrystals is conducted within a finite element implementation by invoking a Taylor criterion for interaction between the macroscopic and the mesoscopic (single-crystal) length scales. The model behavior is examined in application to high-rate problems with increasingly complex geometries (homogeneous uniaxial compression, the impact of a textured cylindrical bar into a rigid anvil, and the explosive deep-drawing of a Ta disk).