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-of-fracture measurement were pointed out. The authors proposed three independent conditions to achieve stable fracture in the chevron notch method. It was possible to realize the stable fracture when a JIS-type bending beam with a narrow chevron notch (0.2mm) at the center was fractured in three-point bending (span=30mm) with a rigid testing machine (>2×10-7m/N) at a crosshead transfer speed of 0.005mm/min. The fracture toughness and the work-of-fracture of float glass, polycrystalline Al2O3 and SiC-whisker/Al2O3 composite were evaluated by three-point bending test with five kinds of chevron notched beam. The fracture toughness obtained by the chevron notch method almost agreed with that estimated by SEPB and IF methods according to JIS R 1607 in the case of the glass and the Al2O3 in which R-curve behavior did not affect the measured fracture toughness appreciably. On the contrary, in the case of the composite, the former fracture toughness was larger than the latter one and varied depending on the chevron geometry, which was caused by the R-curve behavior of the crack in the composite. Fracture toughness derived from work-of-fracture with the Irwin similarity relationship corresponded to the measured fracture toughness in the glass and the Al2O3, but was larger than the evaluated fracture toughness in the composite. That was also explained by the R-curve behavior. Therefore, the effect of the R-curve on fracture resistance was recognized by comparing the fracture toughness and the work-of-fracture using the Irwin similarity relationship.