Strength Degradation of Brittle Surfaces: Blunt Indenters.

Indentation fracture mechanics is used to develop a theoretical basis for pre-determining the strength properties of brittle surfaces in prospective contact situations. Indenters are classified as 'blunt' or 'sharp,' of which only the first is considered in the present work. The classical Hertzian cone crack conveniently models the fracture damage incurred by the surface in this class of indentation event. Bend tests on abraded glass slabs confirm the essential features of the theoretical predictions. The role of controlling variables in the degradation process, notably starting flaw size and indenter radius, is systematically investigated. An indication is also given as to optimization of material parameters. The analysis leads to some novel suggestions concerning surface preparation procedures that might be followed in order to minimize strength losses.