Cyclic Fatigue‐Crack Propagation in Magnesia‐Partially‐Stabilized Zirconia Ceramics

The subcritical growth of fatigue cracks under (tension‐tension) cyclic loading is demonstrated for ceramic materials, based on experiments using compact C(T) specimens of a MgO‐partially‐stabilized zirconia (PSZ), heat‐treated to vary the fracture toughness K c from ∼3 to 16 MPa·m 1/2 and tested in inert and moist environments. Analogous to behavior in metals, cyclic fatigue‐crack rates (over the range 10 −11 to 10 −5 m/cycle) are found to be a function of the stress‐intensity range, environment, fracture toughness, and load ratio, and to show evidence of fatigue crack closure. Unlike toughness behavior, growth rates are not dependent on through0‐thickness constraint. Under variable‐amplitude cyclic loading, crack‐growth rates show transient accelerations following low‐high block overloads and transient retardations following high‐low block overloads or single tensile overloads, again analogous to behavior commonly observed in ductile metals. Cyclic crack‐growth rates are observed at stress intensities as low as 50% of K c , and are typically some 7 orders of magnitude faster than corresponding stress‐corrosion crack‐growth rates under sustained‐loading conditions. Possible mechanisms for cyclic crack advance in ceramic materials are examined, and the practical implications of such “ceramic fatigue” are briefly discussed.