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Crack-Tip Toughness from Vickers Crack-Tip Opening Displacements for Materials with Strongly Rising R-Curves


  • J. Rödel—contributing editor

  • This work was financially supported by the National Science Foundation CAREER award #0547394 and the Deutsche Forschungsgemeinschaft DFG for financing parts of this work within the SFB 483.

†Author to whom correspondence should be addressed. e-mail:


Accurate measurements of the intrinsic crack-tip toughness, KI0, are essential to understanding the strength and toughness of bridging ceramics. Furthermore, even the most carefully made R-curve measurements cannot accurately assess this initial toughness point. In this manuscript, both rigorous and approximate methods are proposed for determining KI0 from crack-tip opening displacement (COD) measurements on Vickers indent cracks for materials with steeply rising R-curves. Such approaches are attractive because of the relative ease of producing indentation cracks and analyzing the CODs; further, the latter method is of particular interest because it saves considerable computational effort. Both the advantages and limitations of the proposed methods are discussed. Finally, based on applying the above methods to three Si3N4 ceramics, it was concluded that there is a common crack-tip toughness of KI0≈2.2±0.3 MPa·√m.