Compressive Strength, Hardness, and Identification Damage in Ceramic Materials.

Hardness and compressive strength of several strong ceramics are measured from room temperature to 1000 C. Similarities in behavior, and the results of microscopic examination, are interpreted in terms of the relative contributions of microplasticity and microfracture to material failure during compression testing and microhardness indentation. It is shown that microplasticity alone is an insufficient basis upon which to relate material response under the two test conditions, and that tensile microfracture is a significant contributor both to compressive failure and to subsurface indentation deformation, hence to hardness. Previous determinations of the strengths of several ceramics subject to impulsive loads were interpreted in terms of a theory based on material inertia. Recent experiments are described, which show that the dynamic strengthening mechanism is athermal, as required by the inertial theory, and that microcrack growth, rather than initiation, is suppressed by the inertial effect. Indentation microfracture measurements in the low load, near threshold regime were carried out using scanning electron microscopy. Results were interpreted in terms of existing theoretical treatments.