ASTM C1465-08(2013)e1
(Test Method)Standard Test Method for Determination of Slow Crack Growth Parameters of Advanced Ceramics by Constant Stress-Rate Flexural Testing at Elevated Temperatures
Standard Test Method for Determination of Slow Crack Growth Parameters of Advanced Ceramics by Constant Stress-Rate Flexural Testing at Elevated Temperatures
SIGNIFICANCE AND USE
4.1 For many structural ceramic components in service, their use is often limited by lifetimes that are controlled by a process of slow crack growth. This test method provides the empirical parameters for appraising the relative slow crack growth susceptibility of ceramic materials under specified environments at elevated temperatures. This test method is similar to Test Method C1368 with the exception that provisions for testing at elevated temperatures are given. Furthermore, this test method may establish the influences of processing variables and composition on slow crack growth as well as on strength behavior of newly developed or existing materials, thus allowing tailoring and optimizing material processing for further modification. In summary, this test method may be used for material development, quality control, characterization, and limited design data generation purposes.Note 3—Data generated by this test method do not necessarily correspond to crack velocities that may be encountered in service conditions. The use of data generated by this test method for design purposes may entail considerable extrapolation and loss of accuracy.
4.2 In this test method, the flexural stress computation is based on simple beam theory, with the assumptions that the material is isotropic and homogeneous, the moduli of elasticity in tension and compression are identical, and the material is linearly elastic. The average grain size should be no greater than one fiftieth (1/50) of the beam thickness.
4.3 In this test method, the test specimen sizes and test fixtures were chosen in accordance with Test Method C1211, which provides a balance between practical configurations and resulting errors, as discussed in Refs (5, 6). Only the four-point test configuration is used in this test method.
4.4 In this test method, the slow crack growth parameters (n and D) are determined based on the mathematical relationship between flexural strength and applied stress rate, log σf =...
SCOPE
1.1 This test method covers the determination of slow crack growth (SCG) parameters of advanced ceramics by using constant stress-rate flexural testing in which flexural strength is determined as a function of applied stress rate in a given environment at elevated temperatures. The strength degradation exhibited with decreasing applied stress rate in a specified environment is the basis of this test method which enables the evaluation of slow crack growth parameters of a material.Note 1—This test method is frequently referred to as “dynamic fatigue” testing (Refs (1-3))2 in which the term “fatigue” is used interchangeably with the term “slow crack growth.” To avoid possible confusion with the “fatigue” phenomenon of a material which occurs exclusively under cyclic loading, as defined in Terminology E1823, this test method uses the term “constant stress-rate testing” rather than “dynamic fatigue” testing.Note 2—In glass and ceramics technology, static tests of considerable duration are called “static fatigue” tests, a type of test designated as stress-rupture (Terminology E1823).
1.2 This test method is intended primarily to be used for negligible creep of test specimens, with specific limits on creep imposed in this test method.
1.3 This test method applies primarily to advanced ceramics that are macroscopically homogeneous and isotropic. This test method may also be applied to certain whisker- or particle-reinforced ceramics that exhibit macroscopically homogeneous behavior.
1.4 This test method is intended for use with various test environments such as air, vacuum, inert, and any other gaseous environments.
1.5 Values expressed in this standard test are in accordance with the International System of Units (SI) and IEEE/ASTM SI 10.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish ap...
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Designation: C1465 − 08 (Reapproved 2013)
Standard Test Method for
Determination of Slow Crack Growth Parameters of
Advanced Ceramics by Constant Stress-Rate Flexural
Testing at Elevated Temperatures
This standard is issued under the fixed designation C1465; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—Fig. 4 was reinserted editorially in March 2014.
1. Scope 1.5 Values expressed in this standard test are in accordance
with the International System of Units (SI) and IEEE/
1.1 Thistestmethodcoversthedeterminationofslowcrack
ASTMSI10.
growth (SCG) parameters of advanced ceramics by using
constantstress-rateflexuraltestinginwhichflexuralstrengthis 1.6 This standard does not purport to address all of the
determined as a function of applied stress rate in a given safety concerns, if any, associated with its use. It is the
environment at elevated temperatures. The strength degrada- responsibility of the user of this standard to establish appro-
tion exhibited with decreasing applied stress rate in a specified priate safety and health practices and determine the applica-
environment is the basis of this test method which enables the bility of regulatory limitations prior to use.
evaluation of slow crack growth parameters of a material.
2. Referenced Documents
NOTE 1—This test method is frequently referred to as “dynamic
fatigue” testing (Refs (1-3)) in which the term “fatigue” is used
2.1 ASTM Standards:
interchangeably with the term “slow crack growth.” To avoid possible
C1145Terminology of Advanced Ceramics
confusion with the “fatigue” phenomenon of a material which occurs
C1211Test Method for Flexural Strength of Advanced
exclusively under cyclic loading, as defined in Terminology E1823, this
Ceramics at Elevated Temperatures
test method uses the term “constant stress-rate testing” rather than
“dynamic fatigue” testing.
C1239Practice for Reporting Uniaxial Strength Data and
NOTE 2—In glass and ceramics technology, static tests of considerable
Estimating Weibull Distribution Parameters forAdvanced
duration are called “static fatigue” tests, a type of test designated as
Ceramics
stress-rupture (Terminology E1823).
C1322Practice for Fractography and Characterization of
1.2 This test method is intended primarily to be used for
Fracture Origins in Advanced Ceramics
negligiblecreepoftestspecimens,withspecificlimitsoncreep
C1368 Test Method for Determination of Slow Crack
imposed in this test method.
Growth Parameters of Advanced Ceramics by Constant
Stress-Rate Strength Testing at Ambient Temperature
1.3 Thistestmethodappliesprimarilytoadvancedceramics
D1239Test Method for Resistance of Plastic Films to
that are macroscopically homogeneous and isotropic. This test
Extraction by Chemicals
method may also be applied to certain whisker- or particle-
E4Practices for Force Verification of Testing Machines
reinforcedceramicsthatexhibitmacroscopicallyhomogeneous
E6Terminology Relating to Methods of Mechanical Testing
behavior.
E220Test Method for Calibration of Thermocouples By
1.4 This test method is intended for use with various test
Comparison Techniques
environmentssuchasair,vacuum,inert,andanyothergaseous
E230Specification and Temperature-Electromotive Force
environments.
(EMF) Tables for Standardized Thermocouples
E337Test Method for Measuring Humidity with a Psy-
chrometer (the Measurement of Wet- and Dry-Bulb Tem-
peratures)
This test method is under the jurisdiction of ASTM Committee C28 on
Advanced Ceramics and is the direct responsibility of Subcommittee C28.01 on
Mechanical Properties and Performance.
Current edition approved Aug. 1, 2013. Published September 2013. Originally
approved in 2000. Last previous edition approved in 2008 as C1465– 08. DOI: For referenced ASTM standards, visit the ASTM website, www.astm.org, or
10.1520/C1465-08R13. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof Standards volume information, refer to the standard’s Document Summary page on
this standard. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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C1465 − 08 (2013)
E616Terminology Relating to Fracture Testing (Discontin- MPa/s, where the time for slow crack growth would be
ued 1996) (Withdrawn 1996) minimized or eliminated (4).
E1150Definitions of Terms Relating to Fatigue (Withdrawn
3.1.11 slow crack growth (SCG),n—subcritical crack
1996)
growth (extension) which may result from, but is not restricted
IEEE/ASTMSI10American National Standard for Use of
to, such mechanisms as environmentally assisted stress corro-
theInternationalSystemofUnits(SI):TheModernMetric
sion or diffusive crack growth.
System
−3/2
3.1.12 stress intensity factor, K [FL ],n—the magnitude
I
E1823TerminologyRelatingtoFatigueandFractureTesting
of the ideal-crack-tip stress field (stress-field singularly) sub-
jectedtoModeIloadinginahomogeneous,linearelasticbody.
3. Terminology
(E616)
3.1 Definitions:
3.1.13 R-curve, n—a plot of crack-extension resistance as a
3.1.1 The terms described inTerminologies C1145, E6, and
function of stable crack extension. (E616)
E1823 are applicable to this test method. Specific terms
relevant to this test method are as follows:
3.2 Definitions of Terms Specific to This Standard:
3.1.2 advanced ceramic, n—a highly engineered, high-
3.2.1 slow crack growth parameters, n and D, n—the
performance, predominately, nonmetallic, inorganic, ceramic
parameters estimated as constants in the flexural strength (in
material having specific functional attributes. (C1145)
megapascals)-stressrate(inmegapascalspersecond)equation,
−2 −1
which represent a measure of susceptibility to slow crack
3.1.3 constant stress rate, σ˙[FL t ],n—a constant rate of
growthofamaterial(seeAppendixX1).Fortheunitsof D,see
increase of maximum flexural stress applied to a specified
9.3.1.
beam by using either a constant load or constant displacement
rate of a testing machine.
4. Significance and Use
3.1.4 environment, n—the aggregate of chemical species
and energy that surrounds a test specimen. (E1150)
4.1 For many structural ceramic components in service,
their use is often limited by lifetimes that are controlled by a
3.1.5 environmental chamber, n—a container surrounding
process of slow crack growth. This test method provides the
the test specimen and capable of providing controlled local
empirical parameters for appraising the relative slow crack
environmental condition.
−2 growth susceptibility of ceramic materials under specified
3.1.6 flexural strength, σ [FL ],n—a measure of the
f
environments at elevated temperatures. This test method is
ultimate strength of a specified beam specimen in bending
similar to Test Method C1368 with the exception that provi-
determined at a given stress rate in a particular environment.
sions for testing at elevated temperatures are given.
3.1.7 flexural strength-stress rate diagram—a plot of flex-
Furthermore, this test method may establish the influences of
ural strength as a function of stress rate. Flexural strength and
processing variables and composition on slow crack growth as
stress rate are both plotted on logarithmic scales.
well as on strength behavior of newly developed or existing
3.1.8 flexural strength-stress rate curve—a curve fitted to materials, thus allowing tailoring and optimizing material
the values of flexural strength at each of several stress rates, processing for further modification. In summary, this test
based on the relationship between flexural strength and stress methodmaybeusedformaterialdevelopment,qualitycontrol,
rate: characterization, and limited design data generation purposes.
log σ = [1/(n + 1)] log σ˙ + log D (see Appendix X1)
f
NOTE 3—Data generated by this test method do not necessarily
3.1.8.1 Discussion—In the ceramics literature, this is often
correspond to crack velocities that may be encountered in service
called a “dynamic fatigue” curve.
conditions. The use of data generated by this test method for design
−3/2
purposes may entail considerable extrapolation and loss of accuracy.
3.1.9 fracture toughness, K [FL ],n—agenerictermfor
IC
measures of resistance to extension of a crack. (E616)
4.2 In this test method, the flexural stress computation is
−2
based on simple beam theory, with the assumptions that the
3.1.10 inert flexural strength [FL ],n—a measure of the
materialisisotropicandhomogeneous,themoduliofelasticity
strength of a specified beam specimen in bending as deter-
in tension and compression are identical, and the material is
minedinanappropriateinertconditionwherebynoslowcrack
linearly elastic. The average grain size should be no greater
growth occurs.
than one fiftieth (1/50) of the beam thickness.
3.1.10.1 Discussion—An inert condition at near room tem-
perature may be obtained by using vacuum, low temperatures,
4.3 In this test method, the test specimen sizes and test
very fast test rates, or any inert media. However, at elevated
fixtures were chosen in accordance with Test Method C1211,
temperatures, the definition or concept of an inert condition is
which provides a balance between practical configurations and
unclear since temperature itself acts as a degrading environ-
resultingerrors,asdiscussedinRefs (5, 6).Onlythefour-point
ment. It has been shown that for some ceramics one approach
test configuration is used in this test method.
to obtain an inert condition (thus, inert strength) at elevated
4.4 Inthistestmethod,theslowcrackgrowthparameters(n
temperatures is to use very fast (ultra-fast) test rates ≥3×10
and D) are determined based on the mathematical relationship
between flexural strength and applied stress rate, log σ = [1/(n
f
+ 1)] log σ˙ + log D, together with the measured experimental
The last approved version of this historical standard is referenced on
www.astm.org. data.Thebasicunderlyingassumptiononthederivationofthis
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C1465 − 08 (2013)
relationship is that slow crack growth is governed by an complete testing of a typical, advanced ceramic. Because of
n
empirical power-law crack velocity, v= A[K /K ] (see this long test time, the chemical variables of the test environ-
I IC
Appendix X1). ment must be prevented from changing throughout the tests.
Inadequate control of these chemical variables may result in
NOTE 4—There are various other forms of crack velocity laws which
inaccurate strength data and SCG parameters, especially for
are usually more complex or less convenient mathematically, or both, but
materials that are sensitive to the environment.
maybephysicallymorerealistic (7).Themathematicalanalysisinthistest
method does not cover such alternative crack velocity formulations.
5.2 Significant creep at both higher temperatures and lower
4.5 In this test method, the mathematical relationship be-
testratesresultsinnonlinearityinstress-strainrelationsaswell
tweenflexuralstrengthandstressratewasderivedbasedonthe
as accumulated tensile damage in flexure (9). This, depending
assumption that the slow crack growth parameter is at least n
on the degree of nonlinearity, may limit the applicability of
≥ 5 (1, 8). Therefore, if a material exhibits a very high
linear elastic fracture mechanics (LEFM), since the resulting
susceptibility to slow crack growth, that is, n < 5, special care
relationship between strength and stress rate derived under
should be taken when interpreting the results.
constant stress-rate testing condition is based on an LEFM
approach with negligible creep (creep strain less than 0.1%).
4.6 The mathematical analysis of test results according to
Therefore, creep should be kept as minimal as possible, as
the method in 4.4 assumes that the material displays no rising
compared to the total strain at failure (see 8.11.2).
R-curve behavior, that is, no increasing fracture resistance (or
crack-extension resistance) with increasing crack length. It
5.3 Depending on the degree of SCG susceptibility of a
should be noted that the existence of such behavior cannot be
material, the linear relationship between log (flexural strength)
determinedfromthistestmethod.Theanalysisfurtherassumes
and log (applied stress rate) (see Appendix X1) may start to
that the same flaw types control strength over the entire test
deviateatacertainhighstressrate,atwhichslowcrackgrowth
range. That is, no new flaws are created, and the flaws that
diminishes or is minimized due to the extremely short test
control the strength at the highest stress rate control the
duration. Strengths obtained at higher stress rates (>1000
strength at the lowest stress rate.
MPa/s) may remain unchanged so that a plateau is observed in
4.7 Slow crack growth behavior of ceramic materials can the plot of strength versus stress rate, see Fig. 1a (4).Ifthe
strength data determined in this plateau region are included in
vary as a function of mechanical, material, thermal, and
environmental variables. Therefore, it is essential that test the analysis, a misleading estimate of the SCG parameters will
beobtained.Therefore,thestrengthdataintheplateaushallbe
results accurately reflect the effects of specific variables under
study. Only then can data be compared from one investigation excluded as data points in estimating the SCG parameters of
the material. This test method addresses this issue by recom-
to another on a valid basis, or serve as a valid basis for
characterizing materials and assessing structural behavior. mending that the highest stress rate be ≤1000 MPa/s.
4.8 The strength of advanced ceramics is probabilistic in 5.4 Aconsiderable strength degradation may be observed at
nature. Therefore, slow crack growth that is determined from lower stress rates and higher temperatures for some materials.
the flexural strengths of a ceramic material is also a probabi- In these cases, excessive creep damage in the form of creep
listic phenomenon. Hence, a proper range and number of test
cavities,micro-ormacro-cracks,orboth,developinthetensile
rates in conjunction with an appropriate number of specimens surface (10-13). This results in a nonlinearity in the relation-
at each test rate are required for statistical reproducibility and
ship between log (flexural strength) and log (applied stress
design (2). Guidance is provided in this test method. rate), see Fig. 1b. It has been reported that the strength
degradation with respect to the expected normal strength (at
NOTE 5—For a given ceramic material/environment system, the
...
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