Determination of True Fracture Toughness of Polycrystalline Advanced Ceramics at a Range of Loading Rates
Polycrystalline advanced ceramics represent synthetic product constituted of hard carbide or other tough material particles bonded together by a metallic binder. Superior wear and corrosion resistance, high temperature stability, low thermal expansion and many more extreme properties give significance to these materials for their use in ferrous materials machining and industrial applications such as construction and mining, automotive and agriculture, oil and gas drilling etc. Behaviour of these materials is of extreme importance considering the nature and costs of these materials, in order to be able to prevent their fracture in operation. At present, their fracture properties data are quite scarce in the literature. Fracture of polycrystalline advanced ceramics in mode I loading across the range of loading rates was studied using notched three point bending specimens with two different average grain size and the predictions of the linear elastic fracture mechanics theory. Dependency on the notch root radius was analysed experimentally obtaining apparent and true fracture toughness as well as their interdependence. This dependency was confirmed analytically using predictions by the theory of critical distances. The resulting true fracture toughness showed certain deviation to apparent fracture toughness, which is more pronounced for smaller grain size compacts.
Index Terms - Fracture toughness, Notch root radius dependency, Polycrystalline advanced ceramics, Theory of critical distances