Combined mode-I and mode-II fracture of ceramics with crack-face grain and/or whisker bridging

Crack-face grain and/or whisker bridging in ceramics was investigated under combined mode-I and mode-II loading. A novel technique for analysing the stress shielding at the crack tip caused by the bridging was proposed, in which the critical values of the local mode-I and mode-II stress intensity factors were numerically derived from an azimuthal angle at the onset of noncoplanar crack extension using the mixed-mode failure criteria. The wedging effect, which induced local mode-I crack opening at the tip, was identified under the combined-mode loading on polycrystalline alumina as well as an alumina matrix composite reinforced with silicon carbide whiskers. The effect was accelerated with the increase in the mode-II component of nominally applied loading and the decrease in the bridging zone length. It was also found that the stress shielding due to the whisker bridging was not only effective for mode-I but also for mode-II crack opening.