Evaluation of Fracture Toughness on Porcelain for Metal-ceramics with Chevron Notches

Abstract

The chevron notched beam(CNB)method was used to evaluate the fracture toughness(K_<IC>)of porcelain for metal ceramics.Compliances were calculated using Bluhm's slice model, and the effects of notched shapes, span ratios and cross head speeds were examined by four point bending mode in Ar gas.Results indicated that K_<IC> was only slightly affected by these factors.In particular, the absence of dependence on cross head speeds supports that, in Ar gas, stable crack growth did not occur near the maximum load.The averaged K_<IC> was 1.11±0.08MPam^<1/2>, although slight increase, as considered due to R-curve behavior, was observed with increase of crack length at the maximum load.The fracture energy calculated from both K_<IC> and Young's modulus was about 8.9±0.7J/m^2.These measurements suggest that the CNB method is a simple technique than the SEPB method and useful for evaluating the K_<IC> of dental ceramics such as porcelain.