Fracture Toughness Determination of A12O3 Using Four‐Point‐Bend Specimens with Straight‐Through and Chevron Notches

Abstract

Fracture toughness of a sintered A12O3 was determined with four‐point‐bend specimens having either straight‐through or chevron notches. For the straight‐through notched specimens, measured KIc decreased with decreasing notch width. For the smallest notch width (66 μm) KIc= 3.42±0.13 MN m−¾. For specimens with chevron notches, a crack initiates and extends from the tip of the notch under increasing load. KIc is calculated from the maximum load without measuring crack length, under the assumption that the derivative of the compliance is the same as that for a specimen with a straight‐through crack. A refined calculation accounts for the truncated chevron crack shape at maximum load using Bluhm's slice model. For the chevronnotch configuration, a value of KIc= 3.49±0.11 MN m−¾ was measured, which appears to be independent of the initial notch length a0 (distance from the crack mouth to the tip of the triangular notch). An effect of a1 (length of the chevron notch at the surface) on KIc was observed, independent of whether the calculation of KIc was based on the straight‐through crack assumption or on the slice model.