ABSTRACT
The term fatigue as applied to ceramics and glasses traditionally covers the phenomena of cyclic fatigue, static fatigue, and dynamic fatigue. Cyclic fatigue (referred to solely as “ fatigue” in the metallurgy community) in volves cyclic loading of a component or specimen until failure occurs, and can include various minimum-to-maximum stress ratios (e.g. tension-com pression [stress ratio less than 0 ], tension-tension [stress ratio greater than 0]) and numerous different wave forms. Static fatigue describes the stable growth of a crack under a static (tensile) loading at a stress level less than that required to cause sudden fracture, and dynamic fatigue is the term used for subcritical stable crack growth under a monotonically increasing stress or load. The terms environmentally enhanced crack growth, delayed failure, and slow crack growth (SCG) are also frequently used. Time-dependent failures are found in almost all structural ceramics and glasses, in some cases in humid air and water at room temperature (e.g., glass and A120 3) and in other cases at elevated temperatures in ambient air or an oxidizing environ ment (e.g., Si3N4) [1,2].
