HERTZIAN CONTACT DAMAGE IN POROUS ALUMINA CERAMICS

A study has been made of Hertzian contact damage in porous and dense l iquid-phase-sintered aluminas. Indentation stress-strain curves show i ncreasing nonlinearity as the materials become more porous, illustrati ng an increasing component of ''quasi-plasticity'' in the contact dama ge. Observations of the surface and subsurface damage patterns using a bonded-interface sectioning technique reveal a transition in the Hert zian damage process, from classical tension-driven cone cracks in the high-density material, to distributed shear- and compression-driven su bsurface damage and deformation in the porous materials. Strength test s on specimens subjected to cyclic indentations reveal a substantially higher susceptibility to fatigue in the most porous structure.