THE MEASUREMENT OF FRACTURE-TOUGHNESS AND WORK-OF-FRACTURE OF CERAMICS USING THE JIS-TYPE BENDING BEAM WITH A CHEVRON-NOTCH

Problems in the chevron notch method for fracture toughness and work-o f-fracture measurement were pointed out, The authors proposed three in dependent conditions to achieve stable fracture in the chevron notch m ethod, It was possible to realize the stable fracture when a JIS-type bending beam with a narrow chevron notch (0.2 mm) at the center was fr actured in three-point bending (span = 30 mm) with a rigid testing mac hine ( > 2 x 10(-7) m/N) at a crosshead transfer speed of 0.005 mm/min , The fracture toughness and the work-of-fracture of float glass, poly crystalline Al2O3 and SiC-whisker/Al2O3 composite were evaluated by th ree-point bending test with five kinds of chevron notched beam. The fr acture toughness obtained by the chevron notch method almost agreed wi th that estimated by SEPB and IF methods according to JIS R 1607 in th e case of the glass and the Al2O3 in which R-curve behavior did not af fect the measured fracture toughness appreciably, On the contrary, in the case of the composite, the former fracture toughness was larger th an the latter one and varied depending on the chevron geometry, which was caused by the R-curve behavior of the crack in the composite, Frac ture toughness derived from work-of-fracture with the Irwin similarity relationship corresponded to the measured fracture toughness in the g lass and the Al2O3, but was larger than the evaluated fracture toughne ss in the composite, That was also explained by the R-curve behavior, Therefore, the effect of the R-curve on fracture resistance was recogn ized by comparing the fracture toughness and the work-of-fracture usin g the Irwin similarity relationship.