mechanical strength of different zirconia thin films in relation with their thickness

Zirconia layers with different fractions of tetragonal phase and thicknesses were subjected to multi-cracking tests. Cracks perpendicular to the tensile direction appeared. Cross sections showed that cracks blunt into the substrate. The ratio of crack spacing at saturation to layer thickness decreases when the layer thickness increases. Unit cell modelling has been used to establish a relationship between the crack spacing and the strength of the layer. The relation falls within both bounds of Hu and Evans model. The relation is insensitive to the tetragonal zirconia fraction.