Preparation and Evaluation of Fracture Resistance for Glass-Ceramic/Metal Composites
Mitsuhiro TOYODA, Takeshi SHIONO and Toshihiko NISHIDA
Abstract:-spodumene glass-ceramics containing 30vol% Ni or 30vol% Co were prepared. Their mechanical properties were studied in comparison with the glass and monolithic glass-ceramics with different mean grain size. The R-curve behavior and the COD (Crack Opening Displacement) profiles for these composites were evaluated and the mechanism for fracture resistance was examined. For the composite containing Co, fracture resistance showed remarkable R-curve behavior from KT0=1.6MPa~m1/2 to KR=4.0MPa~m1/2 within short crack extension of 1.0mm. The composite was notably toughened. This result was discussed in terms of the microstructure. The COD measurements in glass showed that the interaction between fracture surfaces was not observed. In the COD profiles of glass-ceramic/metal composites and monolithic glass-ceramics, on the other hand, the experimental values were found to be lower than the theoretical values (Irwin parabola) near the crack tip because the interaction enhanced. Especially, it was obvious that external stress shielding effects acted more strongly near the crack tip in glass-ceramic/metal composites. The increase in the grain size and addition of metal were found to enhance the interaction between fracture surfaces. The relationship between the applied stress intensity (Kappl) and the stress intensity at the tip of crack (Ktip) as a function of Kappl/KTC indicated that metal particles acted as elastic bridging elements in glass-ceramic/metal composites. The size of bridging zone in COD profile for each specimen was clarified to correspond to that of rising extension in R-curve. Key Words:Glass-ceramics, Composites, COD, Fracture resistance, R-curve behavior, Stress shielding,@Elastic bridging