Determination of elastic modulus, tensile strength and fracture toughness of bioceramics using the flattened Brazilian disc specimen: analytical and numerical results

Ceramics and bioceramic composites are materials characterized with strong but quite low crack-resistance properties. Indeed, their application is hindered by their brittleness and low ability to deform, and the accurate measurement of their fracture toughness can often be challenging. This measurement along with that of tensile strength and elastic modulus were conducted using a novel configuration of the Brazilian test. The flattened Brazilian specimens, which are in the shape of discs having parallel flat ends, are subjected to compression for the determination of opening mode I fracture toughness KIC. The experiments were conducted using tricalcium phosphate–fluorapatite composites which were tested by compressive loading on the parallel flat ends. The loading angle corresponding to the flat end width is about 2α=20° to guarantee crack initiation at the specimen center according to the Griffith criteria. Finite element program, called ABAQUS, is used for the numerical modeling for finding stress intensity factors. The effects of fluorapatite additives and fracture toughness were studied. The fracture toughness values of tricalcium phosphate–fluorapatite composites were found to increase with the increase in fluorapatite addition until an appropriate value. It is shown that there is a good agreement between the experimental, analytical and numerical results.