Ceramic toughness assessment through edge chipping measurements—Influence of interfacial friction

In this paper, a comparative study between two techniques to determine material toughness through edge chipping measurements, is presented. The first technique relies on static Rockwell indentations, performed at well-defined distances from the edge with an increasing load until chipping occurs. The second technique keeps the applied load constant but drives the Rockwell indenter towards the edge at constant speed until a chip is formed (scratch testing). In most studied cases, our experimental results on ceramics are shown to conform with the predictions of previous models in the literature expressing the toughness KIc as a function of chip size lc and critical chipping load P   through KIc≅P/lc3/2KIc≅P/lc3/2. However, for silicon carbide, the toughness values obtained by both variants of the method are mutually incompatible. The discrepancy is shown to be related to the tangential loading occurring during scratch testing. A new equation for toughness assessment is derived that takes into account the influence of friction. This equation is demonstrated to match well the experimental results both for static and sliding indentation.