The influence of the indenter tip-radius on indentation testing of brittle materials

Indentation testing of a brittle material using a notionally 'sharp' indenter may reveal several important physical properties, including fracture toughness, surface finish information-and the residual stress state. In the case of shallow cone indenters, the contact and fracture mechanics is well defined and closed-form solutions exist in elasticity theory. However, no real indenter is atomically sharp, and the scope of the present article is to quantify how a finite apex radius may modify the stress state induced by a conical indenter. In particular, implications for the load-displacement relation, occurrence of yielding and maximum contact pressure induced are found. A brief discussion of the influence of edge radius on the flat-ended indenter, once used to induce Hertzian type ring cracks, is also included, as this may be treated by a similar procedure