Measurement of the Fracture Toughness of Ceramic Materials Using a Miniaturized Disk‐Bend Test

Abstract

The fracture toughness of several ceramic materials has been measured using a miniaturized disk‐bend test apparatus and methodology based on small disk‐shaped samples 3 mm in diameter. The method involves the Vickers indentation of specimens ranging in thickness from 300 to 700 μm, and testing them in a ring‐on‐ring bending mode. New experiments on a glass‐ceramic (GC) and Si3N4 have been performed to demonstrate the validity of the technique, supplementing the original work on ZnS. The fracture resistances of these materials increase with increasing crack length (R‐curve behavior). The data are analyzed using a specific model for the relationship between fracture resistance and crack length; this model enables the R‐curve behavior to be treated analytically, and the fracture resistance at “infinite” crack length to be evaluated using a straightforward graphical procedure. The resulting values of the fracture toughness for ZnS, GC, and Si3N4 are 0.74 ± 0.02, 2.18 ± 0.09, and 4.97 ± 0.07 MPa‐m1/2, respectively, which are all in very good agreement with values obtained from conventional fracture toughness tests on large specimens. The results verify the utility of the miniaturized diskbend method for measuring the fracture toughness of brittle materials.