Utilization of fractography in the evaluation of high temperature dynamic fatigue experiments Page: 1 of 14
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DEC f 8 1995
UTILIZATION OF FRACTOGRAPHY IN THE EVALUATION OFiIH
TEMPERATURE DYNAMIC FATIGUE EXPERIMENTS*
Kristin Breder, Metals and Ceramics Division, Oak Ridge National Laboratory,
Oak Ridge TN 37831-6069, Thomas J. Mroz, Advanced Refractory
Technologies, Inc. Buffalo NY 14207, Andrew A. Wereszczak, and
Victor J. Tennery, Metals and Ceramics Division, Oak Ridg 6iPgf G is
Laboratory, Oak Ridge TN 37831-6069.
DEC 28 I-5
ABSTRACT 08-T I
The slow crack growth properties of six structural ceramics were
measured by dynamic fatigue in air and inert atmospheres over a range of
elevated temperatures. The material response varied from no strength
degradation as a function of stress and environment to significant strength
degradation by slow crack growth (SCG) and by a combination of SCG and
creep. The fractographic investigation showed that SCG was evidenced by
growth of isolated cracks and often by an intergranular fracture mode, while
creep was evidenced by accumulated damage such as void formation and opening
of the microstructure at grain boundaries and triple junctions. For the materials in
which the strength was unaffected by the stress and environment, the fracture
surfaces were essentially indistinguishable from the inert fracture surfaces.
The dynamic fatigue method, in which strength is measured as a function
of stressing or loading rate, is well suited to the measurement of the slow crack
growth (SCG) properties of ceramics.1-4 Knowledge of the fast fracture, creep
and SCG parameters are necessary for design and life-time prediction of ceramic
components. The regimes of stress, temperature, and environment in which
SCG exists vary from material to material, and SCG may exist simultaneously
with other strength-degradation mechanisms such as creep and cyclic fatigue. In
* Research sponsored by the U.S. Department of Energy, Office of Fossil Energy, Pittsburgh
Energy Technology Center, Advanced Combustion Technology Program, DOE/FE AA
2010 000, under contract DE-AC05-840R21400 with Lockheed Martin Energy Systems.
TThe submitted ma EacrCt has beEn
auth'ored by a contractor of the U.S.
Govermttnt ,tder contract No. 0E-
ACOS-84082 1400. AoorndA*. ta U.S.
Government retain a nonexdusme.
royalty-free kcerue to publish or reproduce
the publihed form of this contrb~to. or
alow others to do so, for U.S. Govermerat
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Breder, K.; Wereszczak, A.A.; Tennery, V.J. & Mroz, T.J. Utilization of fractography in the evaluation of high temperature dynamic fatigue experiments, article, December 31, 1995; Tennessee. (https://digital.library.unt.edu/ark:/67531/metadc670054/m1/1/: accessed April 23, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.