Static and dynamic fracture of transparent nanograined alumina

Transparent nanograined alumina has a great technological potential for highly demanding applications which take advantage of its superior mechanical properties like hardness, wear resistance, and strength, in addition to its optical performance in the infrared and visible domain. Accurate fracture properties (toughness) of this material are rather scarce in the quasi-static regime, and almost non-existent in the dynamic regime. Therefore, the present work investigates the static and dynamic fracture toughness of polycrystalline, nanograined alumina. The results show a marked increase in the dynamic initiation toughness when compared with the quasi-static regime, a phenomenon that was previously observed for other quasi-brittle materials. A combined fractographic and numerical study is carried out in order to identify the underlying mechanism(s) for the observed high dynamic initiation toughness. It is proposed that the latter results from the combined effect of a geometrical crack-front perturbation along with the contribution of the kinetic energy of the specimen. A discussion of the dynamic fracture toughness as a material property concludes this work.