Additive effect of micro-damage zones from nano-scale crack tip and nano-grains for fracture toughness measurements of 3Y-TZP zirconia ceramics

A nano-scale crack tip around 500 nm wide introduced by femtosecond laser still affects the accuracy of fracture toughness K-IC measurements of 3Y-TZP zirconia ceramics with average grain size G from 200 to 500 nm. A simple formula was proposed to estimate the additive effect of crack-tip damage zones from an infinitely sharp crack to a nano-scale blunt notch. The error in fracture toughness measurements is less than 8 % if the nano-scale crack-tip width < 0.5.G. The intrinsic K-IC can be deduced from the simple formula if the nano-scale crack tip > 0.5.G. This study shows the same K-IC was deduced from two different sets of 3Y-TZP measurements with nano-and micro-scale notches of 500 nm and 18 um wide. Furthermore, the simple formula specifies the relation between the fracture toughness K-IC and intrinsic strength f(t) via grain size G, which means Kic can also be estimated from f(t) and G without testing pre-cracked specimens. K-IC, values of 3Y-TZP from specimens with and without pre-cracks were compared.