Radial fracture during indentation by acute probes: I, description by an indentation wedging model

Extension of the indentation fracture toughness estimation method to very small length scales often requires the use of an indenting punch much more acute than the oft-used Vickers probe. Experimental results for very acute, sharp probes have motivated a new approach to the indentation fracture mechanics of radial crack development. An extension of the standard two-component (residual elastic-plastic+elastic contact) stress-field model of radial fracture is proposed, based on the concept that a sufficiently acute indenter can also act as a ‘wedge,’ prying open the surface-located radial cracks. In this, the first of a two-part series, a three-component wedging indentation model is constructed, and some general characteristics of the model are explored. In particular, the implications of the three-component stress field of the model for the description of radial crack development during load-unload indentation cycles of acute probes are considered. Explicit predictions of crack development are compared with the qualitative features of experimental observations, providing a basis for the quantitative comparisons in Part II.