NEW EVALUATION METHODS FOR MICRO-R-CURVE OF ADVANCED CERAMIC COMPOSITES

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A new evaluation method for micro-R-curve of advanced ceramic composites was proposed based on controlled surface flaw method (CSF method). A fracture mechanical model was developed to theoretically discuss the influence of interaction force between crack faces, residual stress around a Vickers indent, initial crack length and shape of a surface crack on micro-R-curveby CSF method. This model was verified with experimental results of glass, polycrystalline alumna, polycrystalline silicon nitride and tetragonal zirconia polycrystals. In case of polycrystalline silicon nitride, a rising micro-R-curve was measured and a bridging stress betwen crack faces was also estimated. In case of tetragonal zirconia polycrystals, micro-r-curve was not measured because residual stress was not eliminated by polishing larger than three times depth of the Vickersindent. We conclude that the new evaluation method can provide micro-R-curve for the materials that residual stress around a Vickers indent can be eliminated by polishind larger than three times depth of the indent.