Fracture mechanisms of sapphire under bending

The fracture mechanisms of a rapidly advancing crack in a single crystal are under investigation. Thin sapphire plates parallel to the basal plane were used as a model material for this purpose. Tests in three point bending (3PB) were carried out with smooth and with notched thin strip-shaped specimens having three different orientations with respect to the (101̄0) plane. The effect of the orientation on the fracture mechanisms is discussed and explained. Unique behavior was observed in the 3PB loading configuration, resulted from the typical state of stress in bending, i.e., tension in the lower, and compression in the upper region of the beam, which affected tho fracture mechanisms. The continual changes of the crack direction and energy revealed a large spectrum of fracture phenomena. The major phenomena are explained. The effect of the mechanical energy on fracture mechanisms and topology is discussed.