Shear banding and crack initiation in Zirconia ceramics

Experimental results obtained by Chen and Reyes Morel show that the behavior of Zirconia ceramics is highly pressure-sensitive and, in particular, fits coherently with the Drucker-Prager plasticity model. This is the macroscopic counterpart of shear banding into grains, interaction of shear bands with grain boundaries and subsequent microcracking. These results have strong implications in the design of Zirconia structural elements. In fact, design philosophy based on yield strength is much different from that based on flaw strength. Moreover, the DruckerPrager yield criterion predicts a material behavior substantially different from the von Mises based plasticity. In particular, the Drucker-Prager criterion allows for the introduction of a nonassociated flow rule, so giving the possibility of material instabilities (cavitation, surface exfoliations and macro shear banding) in the hardening range. Moreover, material pressure-sensitivity and nonassociativity have strong effects on crack growth, which may be significant to develop sound design criteria.