Fabrication and simulation of random and periodic composites for reduced stress wave propagation

During a ballistic impact event between a monolithic ceramic target and a projectile, a shock wave precedes the projectile penetration and propagates through the target. Shock wave induced damage, fundamentally caused by the creation of tensile stress, can reduce the, expected performance of the target material. If the shock wave could be prevented from propagating it would be possible to improve ballistic performance of the target material. Recent research on phononic band gap structures has shown that it is possible to design and fabricate biphasic structures that forbid propagation of low amplitude acoustic waves. The goal of this dissertation was to determine the feasibility of creating a structure that is capable of limiting and or defeating large amplitude shock wave propagation by applying the concepts of phononic band gap research.; A model system of Al2O3 and WC-Co was selected based on processing, acoustic and ballistic criteria. Al2O 3/WC-Co composites were fabricated by die pressing and vacuum sintering. The WC-Co was added as discrete inclusions 0.5 to 1.5 mm in diameter up to 50 vol. %. The interfacial bonding between Al2O3 and WC-Co was characterized by indentation and microscopy to determine optimal sintering conditions. A tape casting and lamination technique was developed to fabricate large dimension Al2O3 samples with periodically placed WC-Co inclusions. Through transmission acoustic characterization of green tape cast and laminated samples showed acoustic velocity could be reduced significantly by proper WC-Co inclusion arrangement.; Two dimensional finite element simulations were performed on a series of designed Al2O3 structures containing both random and periodically arrayed WC-Co inclusions. For a fixed loading scheme, the effects of WC-Co inclusion diameter, area fraction and stacking arrangement were studied. Structures were found to respond either homogenously, heterogeneously or in a mixed mode fashion to the propagating stress wave. The response was determined to be primarily controlled by the WC-Co inclusion size and further reinforced by the inclusion content. The arrangement of the WC-Co was less of a factor due to the two-dimensional nature of the simulations.