Instrumented Indentation Contact with Sharp Probes of Varying Acuity

Abstract

AbstractWhile elastic and plastic material property extraction from instrumented indentation tests has been well-studied, similarly-based fracture property measurement remains difficult. Furthermore, estimation of the fracture toughness requires measurement of the crack lengths from a micrograph, which makes nano-scale indentation toughness measurement expensive and difficult. Initiation and propagation of cracks on the nano-scale requires a more acute indenter than a Berkovich or sphere, such as the cube-corner pyramid. Experiments described here were performed on a range of elastic, plastic and brittle materials with diamond indenters of acuity varying between the Berkovich and the cube-corner. These experiments reveal some of what is changed and what remains the same, when the acuity of the probe is changed, when fracture is initiated at the contact, or both. A preliminary model for the physical origin of the extra crack-driving power of acute probes is presented in light of these, and complementary macro-scale in-situ indentation experiments. This work provides the basis for development of instrumented indentation-based nano-scale toughness measurement.