SYMPOSIA PAPER Published: 01 January 1992

Small-Crack Behavior and Safety-Critical-Design Criteria for Cyclic Fatigue in Mg-PSZ Ceramics


Cyclic fatigue-crack behavior is studied in a Mg-PSZ ceramic heat treated by sub-eutectoid aging to K1c toughnesses in the range 2.9 MPa√m(overaged) to 16 MPa√m (TS grade). S/N data, derived from unnotched cantilever-beam specimens, show markedly lower lives under tension-compression compared to tension-tension loading; “fatigue limits” (108 cycles) for tension-compression loading approach 50% of the tensile strength of the material. When “long” (>3 mm) fatigue crack propagation is examined, crack growth rates are found to be power-law dependent on the stress intensity range, ΔK, and to show evidence of a threshold stress intensity range, ΔKTH, approximately equal to 50% K1c. Conversely, for naturally occurring “small” (<100 μm) surface cracks, fatigue crack growth is seen to occur at applied ΔK levels some two to three times smaller than the long crack threshold, ΔKTH. The implications of such small crack growth behavior on safety-critical-design criteria for ceramic components is discussed.

Author Information

Steffen, AA
Failure Analysis Associates, Menlo Park, CA
Dauskardt, RH
Failure Analysis Associates, Menlo Park, CA
Ritchie, RO
Failure Analysis Associates, Menlo Park, CA
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Developed by Committee: E08
Pages: 69–81
DOI: 10.1520/STP15341S
ISBN-EB: 978-0-8031-5212-0
ISBN-13: 978-0-8031-1444-9