ASTM C1576-05
(Test Method)Standard Test Method for Determination of Slow Crack Growth Parameters of Advanced Ceramics by Constant Stress Flexural Testing (Stress Rupture) at Ambient Temperature
Standard Test Method for Determination of Slow Crack Growth Parameters of Advanced Ceramics by Constant Stress Flexural Testing (Stress Rupture) at Ambient Temperature
SCOPE
1.1 This test method covers the determination of slow crack growth (SCG) parameters of advanced ceramics by using constant stress flexural testing in which time to failure of flexure test specimens is determined in four-point flexure as a function of constant applied stress in a given environment at ambient temperature. In addition, test specimen fabrication methods, test stress levels, data collection and analysis, and reporting procedures are addressed. The decrease in time to failure with increasing applied stress in a specified environment is the basis of this test method that enables the evaluation of slow crack growth parameters of a material. The preferred analysis in the present method is based on a power law relationship between crack velocity and applied stress intensity; alternative analysis approaches are also discussed for situations where the power law relationship is not applicable.
Note 1—The method in this test method is frequently referred to as static fatigue or stress-rupture testing (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 that occurs exclusively under cyclic loading, as defined in Terminology E 1823, this test method uses the term constant stress testing rather than static fatigue testing.
1.2 This test method applies primarily to monolithic advanced ceramics that are macroscopically homogeneous and isotropic. This test method may also be applied to certain whisker- or particle-reinforced ceramics as well as certain discontinuous fiber-reinforced composite ceramics that exhibit macroscopically homogeneous behavior. Generally, continuous fiber ceramic composites do not exhibit macroscopically isotropic, homogeneous, continuous behavior, and the application of this test method to these materials is not recommended.
1.3 This test method is intended for use with various test environments such as air, other gaseous environments and liquids.
1.4 The values stated in SI units are to be regarded as the standard and in accordance with IEEE/ASTM SI 10 Standard.
1.5 This test method may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety concerns associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:C1576–05
Standard Test Method for
Determination of Slow Crack Growth Parameters of
Advanced Ceramics by Constant Stress Flexural Testing
(Stress Rupture) at Ambient Temperature
This standard is issued under the fixed designation C1576; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 1.3 This test method is intended for use with various test
environments such as air, other gaseous environments and
1.1 This test method covers the determination of slow crack
liquids.
growth (SCG) parameters of advanced ceramics by using
1.4 The values stated in SI units are to be regarded as the
constant stress flexural testing in which time to failure of
standard and in accordance with SI10-02 IEEE/ASTM SI 10 .
flexure test specimens is determined in four-point flexure as a
1.5 This test method may involve hazardous materials,
function of constant applied stress in a given environment at
operations, and equipment. This standard does not purport to
ambient temperature. In addition, test specimen fabrication
address all of the safety concerns associated with its use. It is
methods, test stress levels, data collection and analysis, and
the responsibility of the user of this standard to establish
reporting procedures are addressed. The decrease in time to
appropriate safety and health practices and determine the
failure with increasing applied stress in a specified environ-
applicability of regulatory limitations prior to use.
ment is the basis of this test method that enables the evaluation
of slow crack growth parameters of a material. The preferred
2. Referenced Documents
analysis in the present method is based on a power law
2.1 ASTM Standards:
relationship between crack velocity and applied stress inten-
C1145 Terminology of Advanced Ceramics
sity; alternative analysis approaches are also discussed for
C1161 Test Method for Flexural Strength of Advanced
situations where the power law relationship is not applicable.
Ceramics at Ambient Temperature
NOTE 1—The method in this test method is frequently referred to as
C1322 Practice for Fractography and Characterization of
static fatigue or stress-rupture testing (1-3) in which the term fatigue is
Fracture Origins in Advanced Ceramics
used interchangeably with the term slow crack growth. To avoid possible
C1368 Test Method for Determination of Slow Crack
confusion with the fatigue phenomenon of a material that occurs exclu-
Growth Parameters of Advanced Ceramics by Constant
sively under cyclic loading, as defined in Terminology E1823, this test
Stress-Rate Flexural Testing at Ambient Temperature
method uses the term constant stress testing rather than static fatigue
testing.
C1465 Test Method for Determination of Slow Crack
Growth Parameters of Advanced Ceramics by Constant
1.2 This test method applies primarily to monolithic ad-
Stress-Rate Flexural Testing at Elevated Temperatures
vanced ceramics that are macroscopically homogeneous and
E4 Practices for Force Verification of Testing Machines
isotropic. This test method may also be applied to certain
E6 TerminologyRelatingtoMethodsofMechanicalTesting
whisker- or particle-reinforced ceramics as well as certain
E112 Test Methods for Determining Average Grain Size
discontinuous fiber-reinforced composite ceramics that exhibit
E337 Test Method for Measuring Humidity with a Psy-
macroscopicallyhomogeneousbehavior.Generally,continuous
chrometer (the Measurement of Wet- and Dry-Bulb Tem-
fiber ceramic composites do not exhibit macroscopically iso-
peratures)
tropic, homogeneous, continuous behavior, and the application
E399 Test Method for Linear-Elastic Plane-Strain Fracture
of this test method to these materials is not recommended.
Toughness K of Metallic Materials
Ic
E1823 Terminology Relating to Fatigue and Fracture Test-
ing
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 June 1, 2005. Published June 2005 DOI: 10.1520/ For referenced ASTM standards, visit the ASTM website, www.astm.org, or
C1576-05. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
The boldface numbers in parentheses refer to the list of references at the end of 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.
C1576–05
SI10-02 IEEE/ASTM SI 10 American National Standard 3.1.15 time to failure, t [t], n—total elapsed time from test
f
for Use of the International System of Units (SI): The initiation to test specimen failure.
Modern Metric System
4. Significance and Use
3. Terminology
4.1 The service life of many structural ceramic components
3.1 Definitions: The terms described in Terminologies
is often limited by the subcritical growth of cracks. This test
C1145, E6, and E1823 are applicable to this test method.
method provides an approach for appraising the relative slow
Specific terms relevant to this test method are as follows:
crack growth susceptibility of ceramic materials under speci-
3.1.1 advanced ceramic, n—highly engineered, high perfor-
fied environments at ambient temperature. Furthermore, this
mance, predominately non-metallic, inorganic, ceramic mate-
test method may establish the influences of processing vari-
rial having specific functional attributes. C1145
ables and composition on slow crack growth as well as on
-2
3.1.2 constant applied stress, s[FL ], n—constant maxi-
strength behavior of newly developed or existing materials,
mum flexural stress applied to a specified beam test specimen
thus allowing tailoring and optimizing material processing for
by using a constant static force with a test machine or a test
furthermodification.Insummary,thistestmethodmaybeused
fixture.
for material development, quality control, characterization,
3.1.3 constant applied stress-time to failure diagram—plot
design code or model verification, and limited design data
of constant applied stress against time to failure. Constant
generation purposes.
applied stress and time to failure are both plotted on logarith-
mic scales.
NOTE 4—Data generated by this test method do not necessarily corre-
3.1.4 constant applied stress-time to failure curve—curve spond to crack velocities that may be encountered in service conditions.
The use of data generated by this test method for design purposes,
fitted to the values of time to failure at each of several applied
dependingontherangeandmagnitudeofappliedstressesused,mayentail
stresses.
extrapolation and uncertainty.
NOTE 2—In the ceramics literature, this is often called a static fatigue
4.2 This test method is related to Test Method C1368
curve.
(constant stress-rate flexural testing); however, Test Method
3.1.5 test environment, n—aggregate of chemical species
C1368 uses constant stress rates to determine corresponding
and energy that surrounds a test specimen. E1823
flexural strengths whereas this test method employs constant
3.1.6 test environmental chamber, n—container surround-
stress to determine corresponding times to failure. In general,
ing the test specimen that is capable of providing controlled
the data generated by this test method may be more represen-
local environmental condition. C1368, C1465
tative of actual service conditions as compared with those by
-2
3.1.7 flexural strength, s [FL ], n—measure of the ulti-
f
constant stress-rate testing. However, in terms of test time,
mate strength of a specified beam test specimen in flexure
constant stress testing is inherently and significantly more
determined at a given stress rate in a particular environment.
time-consuming than constant stress rate testing.
3.1.8 fracture toughness (critical stress intensity factor)
4.3 The flexural stress computation in this test method is
-3/2
K [FL ], n— generic term for measures of resistance to
IC
based on simple elastic beam theory, with the assumptions that
extension of a crack. E1823, E399
the material is isotropic and homogeneous, the moduli of
-2
3.1.9 inert flexural strength [FL ], n—flexuralstrengthofa
elasticity in tension and compression are identical, and the
specified beam as determined in an inert condition whereby no
material is linearly elastic. The grain size should be no greater
slow crack growth occurs.
than one-fiftieth ( ⁄50) of the beam depth as measured by the
NOTE 3—An inert condition may be obtained by using vacuum, low
mean linear intercept method (Test Methods E112). In cases
temperature,veryfasttestrate,oraninertenvironmentsuchassiliconeoil
where the material grain size is bimodal or the grain size
or high purity dry N .
distribution is wide, the limit should apply to the larger grains.
3.1.10 R-curve, n—plot of crack-extension resistance as a
4.4 The test specimen sizes and test fixtures have been
function of stable crack extension. C1145
selected in accordance with Test Methods C1161 and C1368,
3.1.11 run-out, n—test specimen that does not fail before a
which provides a balance between practical configurations and
prescribed test time.
resulting errors, as discussed in Refs (4,5).
3.1.12 slow crack growth (SCG), n—subcritical crack
4.5 The data are evaluated by regression of log applied
growth (extension) which may result from, but is not restricted
stress vs. log time to failure to the experimental data. The
to, such mechanisms as environmentally-assisted stress corro-
recommendation is to determine the slow crack growth param-
sion or diffusive crack growth. C1368, C1465
eters by applying the power law crack velocity function. For
3.1.13 slow crack growth (SCG) parameters—parameters
derivation of this, and for alternative crack velocity functions,
estimated as constants in the log (time to failure) versus log
see Appendix X1.
(constant applied stress), which represent a measure of sus-
NOTE 5—Avariety of crack velocity functions exist in the literature.A
ceptibility to slow crack growth of a material (see Appendix
comparison of the functions for the prediction of long-term static fatigue
X1).
data from short-term dynamic fatigue data (6) indicates that the exponen-
-3/2
3.1.14 stress intensity factor, K [FL ], n—magnitude of
I
tial forms better predict the data than the power-law form. Further, the
the ideal-crack-tip stress field stress field singularity) subjected
exponential form has a theoretical basis (7-10); however, the power law
to mode I loading in a homogeneous, linear elastic body.
form is simpler mathematically. Both have been shown to fit short-term
E1823 test data well.
C1576–05
4.6 The approach used in this test method assumes that the
material displays no rising R-curve behavior, that is, no
increasing fracture resistance (or crack-extension resistance)
with increasing crack length. The existence of such behavior
cannot be determined from this test method. The analysis
further assumes that the same flaw type controls all times-to-
failure.
4.7 Slow crack growth behavior of ceramic materials can
vary as a function of mechanical, material, thermal, and
environmental variables. Therefore, it is essential that test
results accurately reflect the effects of specific variables under
study. Only then can data be compared from one investigation
to another on a valid basis, or serve as a valid basis for
characterizing materials and assessing structural behavior.
4.8 Like strength, time to failure of advanced ceramics
subjected to slow crack growth is probabilistic in nature.
Therefore, slow crack growth that is determined from times to
failure under given constant applied stresses is also a probabi-
listic phenomenon. The scatter in time to failure in constant
FIG. 1 Schematic Diagram Showing Unacceptable (Average) Data
stress testing is much greater than the scatter in strength in
Points (With an “Open” Symbol) in the Plateau Region in
constant stress-rate (or any strength) testing (1, 11-13) (see
Determining Slow Crack Growth (SCG) Parameters
Appendix X2). Hence, a proper range and number of constant
applied stresses, in conjunction with an appropriate number of
data determined in this plateau region are included in the
test specimens, are required for statistical reproducibility and
analysis, a misleading estimate of the SCG parameters will be
reliabledesigndatageneration(1-3).Thistestmethodprovides
obtained (17). Therefore, the strength data in the plateau shall
guidance in this regard.
beexcludedasdatapointsinestimatingtheSCGparametersof
4.9 The time to failure of a ceramic material for a given test
the material. Similarly, a plateau can also exist at the fatigue
specimen and test fixture configuration is dependent on its
limit end of the curve, and these data points shall also be
inherent resistance to fracture, the presence of flaws, applied
excluded in estimating the SCG parameters.
stress, and environmental effects. Fractographic analysis to
verify the failure mechanisms has proven to be a valuable tool NOTE 6—There are no simple guidelines in determining whether a
plateau region is reached; however, with knowledge of the inert strength
in the analysis of SCG data to verify that the same flaw type is
and the fracture toughness of the test material, the slow crack growth rate
dominantovertheentiretestrange(14,15),anditistobeused
– applied stress intensity (v-K) curve may be determined. Evaluating this
in this test method (see Practice C1322).
will help determine where the experimental conditions fall.
5. Interferences
5.3 When testing a material exhibiting a high SCG resis-
5.1 Slowcrackgrowthmaybetheproductofbothmechani- tance(typicallySCGparameter n>70),anunrealisticallylarge
calandchemicaldrivingforces.Thechemicaldrivingforcefor number of test specimens may be required in a small range of
a given material can vary strongly with the composition and applied stresses since a significant number of test specimens
temperature of a test environment. Testing is conducted in may be expected to fail while loading. Furthermore, if lower
environments representative of service conditions so as to stresses are to be used, unrealistically long test times are to be
evaluate material performance under use conditions. Note that expected. As a result, practical, specific, and quantitative
slow crack growth testing, particularly constant stress testing, values of SCG parameters required for life prediction can only
is very tim
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