FRACTURE-MECHANICS OF HIGH-TOUGHNESS MAGNESIA-PARTIALLY-STABILIZED ZIRCONIA

Crack growth resistance in MgO‐partially‐stabilized ZrO2 (Mg‐PSZ) has been studied using notched double‐cantilever beams (DCB's). High‐toughness Mg‐PSZ exhibited nonlinear mechanical behavior in the form of residual displacements, related to the transformation of tetragonal (t) ZrO2 precipitates to monoclinic (m) symmetry. The influence of this residual displacement on crack resistance behavior (“R‐curve” behavior) was analyzed using several different fracture mechanics approaches. Specifically, the “global” resistance WR(Δa), a J‐integral type parameter WJ(Δa), were determined as a function of crack extension (Δa). Some of these parameters displayed a geometry dependence; their form depended on the initial notch depth and the size of the unbroken ligament. The early stages of crack growth were best described by WJ(δa). The residual strains building up in the wake during crack growth and their effect on specimen displacement made the WR curves (and to some extent the WJ curves) dependent on the ratio between initial notch depth and crack extension. The only curves independent of geometry were the G(δa) curves, but only in a restricted range of geometry. However, the material resistance of Mg‐PSZ is clearly under‐estimated with such a linear elastic approach. Copyright © 1990, Wiley Blackwell. All rights reserved