Microscratch of copper by a Rockwell C diamond indenter under a constant load

The scratch test is used for quality control mostly in phenomenological ways, and whether fracture toughness can be obtained from this test is still a matter of debate requiring further elucidation. In this paper, values of the fracture toughness of copper obtained by different scratch-based approaches are compared in order to examine the applicability of scratch-based methodologies to characterize the fracture toughness of soft metals. The scratch response of copper to a Rockwell C diamond indenter is studied under a constant normal load condition. The variations of penetration depth, residual depth, and residual scratch width with applied normal load are quantified from spherical to sphero-conical contact regimes by piecewise functions. A newly proposed size effect law is found to be the most suitable for scratch-based approaches to characterizing the fracture toughness of soft metallic materials with significant plasticity. A simple expression relating the nominal stress to the penetration depth is proposed for the spherical contact regime and gives almost the same value of fracture toughness. The residual scratch width provides useful information on pile-up of material and on the spherical tip radius of the indenter. It is found that the values of the fracture toughness obtained from the microscratch test are influenced by the data range for analysis.