Evaluation Of New Technique To Estimate Yield Stress In Brittle Materials Via Spherical Indentation Testing

Instrumented indentation testing provides the means to measure many mechanical properties and characteristics of materials. One such mechanical property that can be ascertained from indentation testing is a material's yield stress, the stress corresponding to the onset of permanent deformation. In brittle materials such as ceramics and glasses, traditional testing methods fall short of precisely establishing the yield stress. A new technique to estimate the yield stress is under development and described here. It utilizes the sensing and interpreting of the initiation of a residual surface impression through the change of the instantaneous contactstiffness(3)/load (S-3/P) as measured by load and depth-sensing indentation with spherical indenters. Several brittle materials (borosilicate, soda-lime silicate, and bulk metallic glass) are evaluated, and the test method and manner of interpreting the yield-like response through S-3/P are described.