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.