THE APPLICATION OF FRACTURE MECHANICS TO CEMENTED TUNGSTEN CARBIDES

The difficulties encountered in the measurement of the toughness of cemented tungsten carbides are discussed and the benefits that might be expected from an application of fracture mechanics to the problem are described. A simple method for the measurement of the fracture-toughness parameter, KIC, for the more brittle grades of carbide is considered. The method involves indenting a beam-shaped specimen with a Knoop diamond to produce a crack, and loading the pre-cracked specimen to failure in four-point bending. Results from two grades of cemented carbide are presented and show that a standard error of the mean KIC of ∼3% can be obtained from a set of 10 measurements, with a minimum of specimen preparation and no special testing equipment. The results show also that the toughness of the cemented carbide can be affected by grain-size variations within the same batch of material and by the pressing direction during manufacture.