Strength Degradation of Brittle Surfaces: Sharp Indenters.
Interim rept. 1 Jul 74-30 Jun 75,
NATIONAL BUREAU OF STANDARDS WASHINGTON D C INST FOR MATERIALS RESEARCH
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A theory of strength loss for brittle surfaces in contact situations, developed in a previous paper for blunt indenters, is here extended to the case of sharp indenters. A prior fracture mechanics analysis of crack growth beneath ideal cone indenters serves as the basis for predetermining the prospective surface degradation of ceramic components in service. Compared to blunt indenters, severe degradation can occur at the lower contact loads. However, at high loads the extent of degradation becomes remarkably insensitive to indenter geometry. Essential theoretical predictions are verified by bend tests on glass slabs. The effect of indenter sharpness and initial specimen surface flaw state are investigated systematically, along with some secondary rate effects in the contact process. The possibility of minimizing degradation via adjustment of material parameters including hardness or surface condition e.g., residual stresses, frictional properties is briefly discussed.
- Ceramics, Refractories and Glass