Size dependence of the plane-strain response of single-crystal Al to indentation by diamond wedges

A single-crystal Al specimen was indented at room temperature with a series of prismatic diamond indenters. The indenters had triangular or wedge-shaped cross-sections and were relatively long, thus inducing a two-dimensional (2-D) plane-strain response. Different included wedge angles were used. For each wedge indenter, instrumented indentations were carried out at varying loads. Analysis of the response from each wedge indentation experiment clearly revealed the presence of a size effect, manifested in an increasing projected contact pressure as the contact dimensions decreased from micron to submicron scales. When indentation responses from 2-D wedge indenters with different included angles were compared, the data showed evidence that this indentation size effect depended on the included wedge angle. This dependence was analyzed and compared to existing models of indentation based on the concept of geometrically necessary dislocations. While the model prediction of the dependence of the characteristic length on the included wedge angle appears to be consistent with current experiments, the model estimate of the magnitude of the characteristic length significantly exceeds the value deduced from experimentation. The present results offer new experimental evidence of size-dependent indentation response in plane-strain geometries.