Fracture Toughness Determination of A1 ₂ O ₃ Using Four‐Point‐Bend Specimens with Straight‐Through and Chevron Notches

Abstract

Fracture toughness of a sintered A1 2 O 3 was determined with four‐point‐bend specimens having either straight‐through or chevron notches. For the straight‐through notched specimens, measured K Ic decreased with decreasing notch width. For the smallest notch width (66 μm) K Ic = 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. K Ic 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 K Ic = 3.49±0.11 MN m −¾ was measured, which appears to be independent of the initial notch length a 0 (distance from the crack mouth to the tip of the triangular notch). An effect of a 1 (length of the chevron notch at the surface) on K Ic was observed, independent of whether the calculation of K Ic was based on the straight‐through crack assumption or on the slice model.