Particle Impact Damage in Ceramics

Abstract

Abstract : A brief summary is given of the research performed during the first four years of a program investigating particle impact damage in ceramics; a detailed count is given of the research performed during the fifth and final year. In the first four years, hot-pressed and reaction-bonded silicon nitride, chemical-vapor-deposited zinc sulfide, and a microstructurally toughened ceramic (Si3N4-20%ZrO2) were impacted with tungsten carbide spheres 0.4 mm to 2.4 mm in diameter at various velocities. Damage morphologies were ascertained and the fracture damage was assessed quantitatively. Plate impact experiments were performed on ZnS to investigate crack nucleation and growth under uniform dynamic stress fields. Effects of temperature on fracture damage in hot-pressed Si3N4 were examined. A finite difference code was used to compute the stress field history in the vicinity of an impact, a computational fracture model was outlined, and development of a predictive capability for particle impact damage was begun. In the fifth and final year, effects of chemical and phase composition on particle impact damage in Al2O3.xZrO2 ceramics were investigated. Results of quantitative assessment of the fracture damage suggest that retention of the tetragonal phase improves the impact resistance of sintered Al2O3.xZrO2 ceramics and that the improvement is attributable to surface compressive residual stresses.