Pressure-shear plate impact studies of alumina ceramics and the influence of an intergranular glassy phase

Under impact loading conditions, monolithic brittle materials display several mechanisms of failure including comminution and flow of rubble, grain fragmentation and failure at grain boundaries where a secondary glassy phase may be present. The strength of the ceramic thus depends on how well it resists failure as well as on the shear flow strength of the failed material at high strain rates under high compressive stresses. In this work we have undertaken pressure-shear plate impact studies of three kinds of alumina ceramics--a high purity alumina powder, a high purity, high porosity monolithic ceramic, and an alumina ceramic with 15 wt% of an added oxide glass phase (Coors AD85). The addition of the glassy phase is found to reduce the shear strength of the ceramic considerably. Recognizing a need to have a clearer understanding of the failure processes in oxide glasses under conditions of high compressive and shear stresses, a pressure-shear plate impact study on thin layers of vapor-deposited soda-lime glass has been performed. These experiments show a dramatic loss of shear strength in soda-lime glass occurring at nominal shear strains of the order of 2 and provide valuable insight into the failure mechanisms in these oxide glasses. An attempt is also made to explain the origin and nature of failure waves that have been reported in soda-lime glass.