FRACTURE-TOUGHNESS MEASUREMENTS ON SIC/AL2O3 COMPOSITE

Three test techniques are addressed for the measurements of plane strain critical stress intensity factors, K(IC), on monolithic Al2O3 and SiC-whisker/Al2O3 composite: a four-point test on chevron-notched bend bars; a four-point test on single edge-notched bend bars; and a fractometric test on chevron-notched short bars. The tests were performed on 99.80% Al2O3 and 30 vol % SiC whisker-reinforced Al2O3. Bend bar test techniques yielded more realistic stress intensity factors, K(IC), on the SiC-whisker/Al2O3 composite than the short-bar test results. Chevron-notched bend-bar tests yielded relatively higher critical stress intensity factors, on both Al2O3 and SiC/Al2O3, possibly due to R-curve effects, suggesting the use of stress intensity factor as a function of crack length instead of using the minimum value. Ambiguous results, K(IC), obtained from short-bar tests on SiC/Al2O3 composite, strongly suggests the need to run compliance calibration tests on ceramic composites to determine an appropriate K-factor.