Cyclic Fatigue-Crack Propagation Behavior in Advanced Ceramics

Contrary to traditional notions, recent studies in several engineering ceramics have provided persuasive evidence of degradation and premature failure under cyclic loading. In the present study, such cyclic fatigue-crack propagation behavior is investigated in a range of advanced ceramic materials, including monolithic alumina, partially-stabilized zirconia (PSZ), zirconia-toughened alumina (ZTA), graphite, and silicon nitride. Cyclic crack-growth is unequivocally demonstrated for tension-tension loading; growth rates over the range 10−10-10−6 m/cycle are found to be power-law dependent on the stress intensity range, and to exhibit mean-stress, crack-closure, frequency, and environmental effects, analogous to behavior in metals. In addition, transient growth rate behavior following block loading sequences, anomalous growth rate behavior of small fatigue cracks, and comparisons of stress-corrosion crack growth under monotonic loads with cyclic crack velocities are reported. Mechanisms for such cyclic fatigue behavior are described.