1991 Volume 40 Issue 458 Pages 1479-1484
Fatigue crack growth in polycrystalline magnesia has been investigated at room temperature using a combined loading technique, in which compression load is applied to the ligament of the compact specimen in order to stabilize the crack growth. Measurement of the crack length was performed continuously by the surface film technique, in which the change in crack length was monitored by a thin layer of carbon on the surface which encompasses the region of fracture. The propagation of a crack leads to a break in the carbon film which is atomically bonded to the surface of specimen. Crack grew stably under cyclic tension loading with the maximum stress intensity factor Kmax lower than fracture toughness. Initially, the growth occurred in each cycle, but it became discontinuous in the following cycles. The continuous monitoring of crack length revealed that the crack grew quickly in a single cycle at Kmax over several tens of microns and arrested until the next growth occurred. The crack growth mechanism is discussed in terms of a wake effect of the fatigue crack, and the role of cyclic loading in the crack growth of ceramics is suggested.
