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Cyclic Fatigue from Frictional Degradation at Bridging Grains in Alumina

Authors

  • Srinivasarao Lathabai,

    1. Ceramics Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899
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    • *

      Member, American Ceramic Society.

    • Guest scientist from the Department of Materials Science and Engineering, Lehigh University, Bethlehem, PA.

    • Now in the Division of Materials Science, CSIRO, Clayton, Victoria 3168, Australia.

  • Jürgen Rödel,

    1. Ceramics Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899
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    • Guest scientist from the Department of Materials Science and Engineering, Lehigh University, Bethlehem, PA.

  • Brian R. Lawn

    1. Ceramics Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899
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      Member, American Ceramic Society.


  • K. Faber—contributing editor

  • Presented at the 92nd Annual Meeting of the American Ceramic Society, Dallas, TX, April 25, 1990 (Paper No. J-XX-90).

  • Supported by the U. S. Air Force Office of Scientific Research.

Abstract

Tension—tension cyclic loading tests have been conducted on a coarse-grained alumina ceramic that exhibits toughnesscurve behavior by grain-interlock bridging. Fatigue effects are observed in the regions of both short cracks, using indentation flaws, and long cracks, using compact-tension specimens. A true mechanical fatigue effect is demonstrated by running the tests below the static fatigue limit. A custom-made device for in situ observation of crack propagation in the scanning electron microscope enables us to identify bridge degradation as a cause of the fatigue process. “Wear” debris cumulates at the sliding intergranular frictional contact points, indicating a loss of traction at the junction. The basis of a fracture mechanics model describing the effect of this frictional degradation in reducing crack-tip shielding is outlined and fitted to the data. It is suggested that the bridge degradation fatigue mechanism may be widespread in polycrystalline ceramics with pronounced toughness curves.

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