ASTM C1465-08(2019)

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 σ...
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 (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 a...

General Information

• Status: Published
• Publication Date: 30-Jun-2019
• ICS: 81.060.30 - Advanced ceramics
• Technical Committee: C28 - Advanced Ceramics
• Drafting Committee: C28.01 - Mechanical Properties and Performance

Relations

• Replaces: ASTM C1465-08(2013)e1 - Standard Test Method for Determination of Slow Crack Growth Parameters of Advanced Ceramics by Constant Stress-Rate Flexural Testing at Elevated Temperatures
• Effective Date: 01-Jul-2019
• Refers: ASTM E1823-24a - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 15-Feb-2024
• Refers: ASTM E1823-24 - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 01-Feb-2024
• Refers: ASTM E1823-20 - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 01-Feb-2020
• Refers: ASTM C1145-19 - Standard Terminology of Advanced Ceramics
• Effective Date: 01-Jul-2019
• Refers: ASTM C1322-15(2019) - Standard Practice for Fractography and Characterization of Fracture Origins in Advanced Ceramics
• Effective Date: 01-Jul-2019
• Refers: ASTM C1239-13(2018) - Standard Practice for Reporting Uniaxial Strength Data and Estimating Weibull Distribution Parameters for Advanced Ceramics
• Effective Date: 01-Jul-2018
• Refers: ASTM C1368-18 - Standard Test Method for Determination of Slow Crack Growth Parameters of Advanced Ceramics by Constant Stress Rate Strength Testing at Ambient Temperature
• Effective Date: 01-Jan-2018
• Refers: ASTM C1368-10(2017) - Standard Test Method for Determination of Slow Crack Growth Parameters of Advanced Ceramics by Constant Stress-Rate Strength Testing at Ambient Temperature
• Effective Date: 01-Feb-2017
• Refers: ASTM C1322-15 - Standard Practice for Fractography and Characterization of Fracture Origins in Advanced Ceramics
• Effective Date: 01-Jul-2015
• Refers: ASTM E4-14 - Standard Practices for Force Verification of Testing Machines
• Effective Date: 01-Jun-2014
• Refers: ASTM E220-13 - Standard Test Method for Calibration of Thermocouples By Comparison Techniques
• Effective Date: 01-Nov-2013
• Refers: ASTM C1211-13 - Standard Test Method for Flexural Strength of Advanced Ceramics at Elevated Temperatures
• Effective Date: 01-Aug-2013
• Refers: ASTM C1239-13 - Standard Practice for Reporting Uniaxial Strength Data and Estimating Weibull Distribution Parameters for Advanced Ceramics
• Effective Date: 01-Aug-2013
• Refers: ASTM C1145-06(2013) - Standard Terminology of Advanced Ceramics
• Effective Date: 01-Feb-2013

Overview

ASTM C1465-08(2019), titled Standard Test Method for Determination of Slow Crack Growth Parameters of Advanced Ceramics by Constant Stress-Rate Flexural Testing at Elevated Temperatures, provides a robust method to assess the susceptibility of advanced ceramics to slow crack growth (SCG) under various environments at high temperatures. Developed by ASTM, this standard is essential for materials engineers and quality control professionals working with advanced ceramics in structural applications. The method measures how the flexural strength of ceramics degrades as a function of the applied stress rate, enabling the evaluation of material reliability and long-term performance.

Key Topics

• Slow Crack Growth (SCG) Parameters: The standard describes how to empirically determine SCG parameters, focusing on the relationship between flexural strength and applied stress rate at elevated temperatures.
• Constant Stress-Rate Flexural Testing: Detailed procedures guide users in applying a constant rate of flexural stress to ceramic specimens to analyze strength loss over time.
• Importance of Environment: The impact of various environments-such as air, vacuum, inert, and other gases-on crack growth rates is addressed.
• Applicability: Intended for advanced ceramics that are macroscopically homogeneous and isotropic, with potential use on some whisker- or particle-reinforced ceramics.
• Specimen Preparation and Testing Configuration: Outlines requirements for specimen size, preparation, and the exclusive use of the four-point flexural test configuration.
• Data Interpretation: Emphasizes the significance of proper data selection and the exclusion of anomalous data points, particularly those affected by excessive creep or crack healing at certain stress rates.
• Statistical Reproducibility: Specifies the need for adequate sample sizes and test rates to ensure reliable, statistically meaningful results.

Applications

• Material Development: Aids in characterizing and optimizing new or existing ceramic materials by evaluating how processing variables and composition affect slow crack growth and overall strength.
• Quality Control: Provides consistent, quantifiable benchmarks for comparing the crack growth susceptibility of production batches and ensuring material performance in service.
• Characterization and Design Data Generation: Supplies critical parameters that help predict the long-term reliability of ceramics in demanding environments, supporting limited design data generation.
• Testing in Various Environments: Suitable for simulating realistic service conditions, including high temperatures and aggressive chemical exposures.
• Identification of Material Behavior: Enables identification of processing or environmental factors influencing ceramic strength, supporting process improvement and failure analysis.

Related Standards

For best practices and comprehensive understanding, refer to these related ASTM standards:

• ASTM C1368 – Determination of Slow Crack Growth Parameters of Advanced Ceramics by Constant Stress Rate Strength Testing at Ambient Temperature.
• ASTM C1211 – Flexural Strength of Advanced Ceramics at Elevated Temperatures.
• ASTM C1322 – Fractography and Characterization of Fracture Origins in Advanced Ceramics.
• ASTM C1239 – Reporting Uniaxial Strength Data and Estimating Weibull Distribution Parameters.
• ASTM E1823 – Terminology Relating to Fatigue and Fracture Testing.
• IEEE/ASTM SI 10 – American National Standard for Metric Practice.

Practical Value

Implementing ASTM C1465 enables engineers and materials scientists to:

• Assess Ceramic Durability: Understand the material’s resistance to subcritical crack growth in high-stress, high-temperature service.
• Enhance Product Reliability: Detect potential issues early in the development cycle or during quality assurance, leading to safer and more durable products.
• Optimize Manufacturing Processes: Tailor processing techniques to reduce SCG susceptibility and improve long-term strength.
• Support Regulatory Compliance: Use internationally recognized test methods in line with industry requirements and trade standards.

By adhering to this standard, organizations ensure their advanced ceramics meet demanding operational requirements and maintain competitiveness in high-performance markets.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: C1465 − 08 (Reapproved 2019)
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.
1. Scope 1.6 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 Thistestmethodcoversthedeterminationofslowcrack
responsibility of the user of this standard to establish appro-
growth (SCG) parameters of advanced ceramics by using
priate safety, health, and environmental practices and deter-
constantstress-rateflexuraltestinginwhichflexuralstrengthis
mine the applicability of regulatory limitations prior to use.
determined as a function of applied stress rate in a given
1.7 This international standard was developed in accor-
environment at elevated temperatures. The strength degrada-
dance with internationally recognized principles on standard-
tion exhibited with decreasing applied stress rate in a specified
ization established in the Decision on Principles for the
environment is the basis of this test method which enables the
Development of International Standards, Guides and Recom-
evaluation of slow crack growth parameters of a material.
mendations issued by the World Trade Organization Technical
NOTE 1—This test method is frequently referred to as “dynamic
Barriers to Trade (TBT) Committee.
fatigue”testing (1-3) inwhichtheterm“fatigue”isusedinterchangeably
with the term “slow crack growth.” To avoid possible confusion with the
2. Referenced Documents
“fatigue”phenomenonofamaterialwhichoccursexclusivelyundercyclic
loading, as defined in Terminology E1823, this test method uses the term
2.1 ASTM Standards:
“constant stress-rate testing” rather than “dynamic fatigue” testing.
C1145Terminology of Advanced Ceramics
NOTE 2—In glass and ceramics technology, static tests of considerable
C1211Test Method for Flexural Strength of Advanced
duration are called “static fatigue” tests, a type of test designated as
Ceramics at Elevated Temperatures
stress-rupture (Terminology E1823).
C1239Practice for Reporting Uniaxial Strength Data and
1.2 This test method is intended primarily to be used for
Estimating Weibull Distribution Parameters forAdvanced
negligiblecreepoftestspecimens,withspecificlimitsoncreep
Ceramics
imposed in this test method.
C1322Practice for Fractography and Characterization of
1.3 Thistestmethodappliesprimarilytoadvancedceramics
Fracture Origins in Advanced Ceramics
that are macroscopically homogeneous and isotropic. This test
C1368 Test Method for Determination of Slow Crack
method may also be applied to certain whisker- or particle-
Growth Parameters of Advanced Ceramics by Constant
reinforcedceramicsthatexhibitmacroscopicallyhomogeneous
Stress Rate Strength Testing at Ambient Temperature
behavior.
D1239Test Method for Resistance of Plastic Films to
Extraction by Chemicals
1.4 This test method is intended for use with various test
E4Practices for Force Verification of Testing Machines
environmentssuchasair,vacuum,inert,andanyothergaseous
E6Terminology Relating to Methods of Mechanical Testing
environments.
E220Test Method for Calibration of Thermocouples By
1.5 Values expressed in this standard test are in accordance
Comparison Techniques
with the International System of Units (SI) and IEEE/
E230Specification for Temperature-Electromotive Force
ASTMSI10.
(emf) Tables for Standardized Thermocouples
E337Test Method for Measuring Humidity with a Psy-
chrometer (the Measurement of Wet- and Dry-Bulb Tem-
This test method is under the jurisdiction of ASTM Committee C28 on
peratures)
Advanced Ceramics and is the direct responsibility of Subcommittee C28.01 on
Mechanical Properties and Performance.
CurrenteditionapprovedJuly1,2019.PublishedJuly2019.Originallyapproved
ɛ1
in 2000. Last previous edition approved in 2014 as C1465–08 (2013) . DOI: For referenced ASTM standards, visit the ASTM website, www.astm.org, or
10.1520/C1465-08R19. contact ASTM Customer Service at [e-mail]. 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
C1465 − 08 (2019)
E616Terminology Relating to Fracture Testing (Discontin- 3.1.11 slow crack growth (SCG),n—subcritical crack
ued 1996) (Withdrawn 1996) growth (extension) which may result from, but is not restricted
E1150Definitions of Terms Relating to Fatigue (Withdrawn to, such mechanisms as environmentally assisted stress corro-
1996) sion or diffusive crack growth.
−3/2
E1823TerminologyRelatingtoFatigueandFractureTesting
3.1.12 stress intensity factor, K [FL ],n—the magnitude
I
IEEE/ASTMSI10American National Standard for Metric
of the ideal-crack-tip stress field (stress-field singularly) sub-
Practice
jectedtoModeIloadinginahomogeneous,linearelasticbody.
(E616)
3. Terminology
3.1.13 R-curve, n—a plot of crack-extension resistance as a
3.1 Definitions:
function of stable crack extension. (E616)
3.1.1 The terms described inTerminologies C1145, E6, and
3.2 Definitions of Terms Specific to This Standard:
E1823 are applicable to this test method. Specific terms
relevant to this test method are as follows: 3.2.1 slow crack growth parameters, n and D, n—the
parameters estimated as constants in the flexural strength (in
3.1.2 advanced ceramic, n—a highly engineered, high-
megapascals)-stressrate(inmegapascalspersecond)equation,
performance, predominately nonmetallic, inorganic, ceramic
material having specific functional attributes. (C1145) which represent a measure of susceptibility to slow crack
−2 −1 growthofamaterial(seeAppendixX1).Fortheunitsof D,see
3.1.3 constant stress rate, σ˙[FL t ],n—a constant rate of
9.3.1.
increase of maximum flexural stress applied to a specified
beam by using either a constant load or constant displacement
4. Significance and Use
rate of a testing machine.
4.1 For many structural ceramic components in service,
3.1.4 environment, n—the aggregate of chemical species
their use is often limited by lifetimes that are controlled by a
and energy that surrounds a test specimen. (E1150)
process of slow crack growth. This test method provides the
3.1.5 environmental chamber, n—a container surrounding
empirical parameters for appraising the relative slow crack
the test specimen and capable of providing controlled local
growth susceptibility of ceramic materials under specified
environmental condition.
environments at elevated temperatures. This test method is
−2
3.1.6 flexural strength, σ [FL ],n—a measure of the similar to Test Method C1368 with the exception that provi-
f
ultimate strength of a specified beam specimen in bending sions for testing at elevated temperatures are given.
determined at a given stress rate in a particular environment. Furthermore, this test method may establish the influences of
processing variables and composition on slow crack growth as
3.1.7 flexural strength-stress rate curve—a curve fitted to
well as on strength behavior of newly developed or existing
the values of flexural strength at each of several stress rates,
materials, thus allowing tailoring and optimizing material
based on the relationship between flexural strength and stress
processing for further modification. In summary, this test
rate:
methodmaybeusedformaterialdevelopment,qualitycontrol,
log σ = [1/(n + 1)] log σ˙ + log D (see Appendix X1)
f
characterization, and limited design data generation purposes.
3.1.7.1 Discussion—In the ceramics literature, this is often
called a “dynamic fatigue” curve.
NOTE 3—Data generated by this test method do not necessarily
correspond to crack velocities that may be encountered in service
3.1.8 flexural strength-stress rate diagram—a plot of flex-
conditions. The use of data generated by this test method for design
ural strength as a function of stress rate. Flexural strength and
purposes may entail considerable extrapolation and loss of accuracy.
stress rate are both plotted on logarithmic scales.
4.2 In this test method, the flexural stress computation is
−3/2
3.1.9 fracture toughness, K [FL ],n—agenerictermfor
IC
based on simple beam theory, with the assumptions that the
measures of resistance to extension of a crack. (E616)
materialisisotropicandhomogeneous,themoduliofelasticity
−2
3.1.10 inert flexural strength [FL ],n—a measure of the
in tension and compression are identical, and the material is
strength of a specified beam specimen in bending as deter-
linearly elastic. The average grain size should be no greater
minedinanappropriateinertconditionwherebynoslowcrack
than one fiftieth (1/50) of the beam thickness.
growth occurs.
4.3 In this test method, the test specimen sizes and test
3.1.10.1 Discussion—An inert condition at near room tem-
fixtures were chosen in accordance with Test Method C1211,
perature may be obtained by using vacuum, low temperatures,
which provides a balance between practical configurations and
very fast test rates, or any inert media. However, at elevated
resultingerrors,asdiscussedinRefs (5, 6).Onlythefour-point
temperatures, the definition or concept of an inert condition is
test configuration is used in this test method.
unclear since temperature itself acts as a degrading environ-
4.4 Inthistestmethod,theslowcrackgrowthparameters(n
ment. It has been shown that for some ceramics, one approach
and D) are determined based on the mathematical relationship
to obtain an inert condition (thus, inert strength) at elevated
between flexural strength and applied stress rate, log σ = [1/(n
temperatures is to use very fast (ultra-fast) test rates ≥3×10 f
+ 1)] log σ˙ + log D, together with the measured experimental
MPa/s, where the time for slow crack growth would be
data.Thebasicunderlyingassumptiononthederivationofthis
minimized or eliminated (4).
relationship is that slow crack growth is governed by an
n
empirical power-law crack velocity, v= A[K /K ] (see
The last approved version of this historical standard is referenced on I IC
www.astm.org. Appendix X1).
C1465 − 08 (2019)
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
testratesresultsinnonlinearityinstress-strainrelationsaswell
4.5 In this test method, the mathematical relationship be-
as accumulated tensile damage in flexure (9). This, depending
tweenflexuralstrengthandstressratewasderivedbasedonthe
on the degree of nonlinearity, may limit the applicability of
assumption that the slow crack growth parameter is at least n
linear elastic fracture mechanics (LEFM), since the resulting
≥ 5 (1, 8). Therefore, if a material exhibits a very high
relationship between strength and stress rate derived under
susceptibility to slow crack growth, that is, n < 5, special care
constant stress-rate testing condition is based on an LEFM
should be taken when interpreting the results.
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
5.3 Depending on the degree of SCG susceptibility of a
crack-extension resistance) with increasing crack length. It
material, the linear relationship between log (flexural strength)
should be noted that the existence of such behavior cannot be
and log (applied stress rate) (see Appendix X1) may start to
determinedfromthistestmethod.Theanalysisfurtherassumes
deviateatacertainhighstressrate,atwhichslowcrackgrowth
that the same flaw types control strength over the entire test
diminishes or is minimized due to the extremely short test
range. That is, no new flaws are created, and the flaws that
duration. Strengths obtained at higher stress rates (>1000
control the strength at the highest stress rate control the
MPa/s) may remain unchanged so that a plateau is observed in
strength at the lowest stress rate.
the plot of strength versus stress rate; see Fig. 1a (4).Ifthe
4.7 Slow crack growth behavior of ceramic materials can
strength data determined in this plateau region are included in
vary as a function of mechanical, material, thermal, and
the analysis, a misleading estimate of the SCG parameters will
environmental variables. Therefore, it is essential that test
beobtained.Therefore,thestrengthdataintheplateaushallbe
results accurately reflect the effects of specific variables under
excluded as data points in estimating the SCG parameters of
study. Only then can data be compared from one investigation
the material. This test method addresses this issue by recom-
to another on a valid basis, or serve as a valid basis for
mending that the highest stress rate be ≤1000 MPa/s.
characterizing materials and assessing structural behavior.
5.4 Aconsiderable strength degradation may be observed at
4.8 The strength of advanced ceramics is probabilistic in
lower stress rates and higher temperatures for some materials.
nature. Therefore, slow crack growth that is determined from
In these cases, excessive creep damage in the form of creep
the flexural strengths of a ceramic material is also a probabi-
cavities,micro-ormacro-cracks,orboth,developinthetensile
listic phenomenon. Hence, a proper range and number of test
surface (10-13). This results in a nonlinearity in the relation-
rates in conjunction with an appropriate number of specimens
ship between log (flexural strength) and log (applied stress
at each test rate are required for statistical reproducibility and
rate); see Fig. 1b. It has been reported that the strength
design (2). Guidance is provided in this test method.
degradation with respect to the expected normal strength (at
NOTE 5—For a given ceramic material/environment system, the SCG
Point N in Fig. 1b) ranged from 15 to 50% (10-12). If these
parameter n is independent of specimen size, although its reproducibility
data points are used in the analysis, then an underestimate of
is dependent on the variables previously mentioned. By contrast, the SCG
the SCG parameters will be obtained. Hence, the strength data
parameter D depends significantly on strength, and thus on specimen size
exhibiting such a significant strength degradation occurring at
(see Eq X1.7).
lower stress rates shall be excluded as data points in obtaining
4.9 The elevated-temperature strength of a ceramic material
the SCG parameters of the material.
for a given test specimen and test fixture configuration is
dependentonitsinherentresistancetofracture,thepresenceof
5.5 Contrary to the case of significant strength degradation,
flaws, test rate, and environmental effects. Analysis of a
an appreciable strength increase may occur for some ceramics
fracture surface, fractography, though beyond the scope of this
atlowerstressrates(seeFig.1c),duetocrackhealingorcrack
test method, is highly recommended for all purposes, espe-
tipbluntingwhichdominatesslowcrackgrowth (10, 14).Ithas
cially to verify the mechanism(s) associated with failure (refer
been reported that the strength increase with respect to the
to Practice C1322).
expectednormalstrength(atpointNinFig.1c)rangedfrom15
to 60% (10, 14). Since the phenomenon results in a deviation
5. Interferences
fromthelinearrelationshipbetweenlog(flexural strength)and
5.1 Slowcrackgrowthmaybetheproductofbothmechani- log (applied stress rate), an overestimate of SCG parameters
may be obtained if such strength data are included in the
calandchemicaldrivingforces.Thechemicaldrivingforcefor
a given material can strongly vary with the composition and analysis.Therefore,anydataexhibitingasignificantorobvious
increase in strength at lower stress rates shall be excluded as
temperatureofatestenvironment.Notethatslowcrackgrowth
testing is time consuming. It may take several weeks to data points in estimating the SCG parameters of the material.
completetestingofatypicaladvancedceramic.Becauseofthis
NOTE 6—It has been shown that some preloading (up to 80% of
long test time, the chemical variables of the test environment
fracture load) prior to testing may be used to minimize or eliminate the
must be prevented from changing throughout the tests. Inad-
strength-increase phenomenon by minimizing or eliminating a chance for
equate control of these chemical variables may result in crack healing (or blunting) through shortening test time, as verified on
C1465 − 08 (2019)
mens need to be tested in the as-processed condition to
simulate a specific service condition. Therefore, specimen
fabrication history may play an important role in strength
behavior,whichconsequentlymayaffectthevaluesoftheSCG
parameters to be determined.
6. Apparatus
6.1 Test Machine—Test machines used for this test method
shall conform to the requirements of Practices E4. Test
specimensmaybeloadedinanysuitabletestmachineprovided
that uniform test rates, either using load-control or
displacement-controlmode,canbemaintained.Theloadsused
in determining flexural strength shall be accurate within
61.0% at any load within the selected test rate and load range
ofthetestmachineasdefinedinPracticesE4.Thetestmachine
shall have a minimum capability of applying at least four test
−1
rateswithatleastthreeordersofmagnitude,rangingfrom10
−2 −7 −4
to 10 N/s for load-control mode, and from 10 to 10 m/s
for displacement-control mode.
6.2 Test Fixtures—The configurations and mechanical prop-
erties of test fixtures shall be in accordance with Test Method
C1211. The materials from which the test fixtures, including
bearingcylinders,arefabricatedshallbeeffectivelyinerttothe
test environment so that they do not significantly react with or
contaminateeitherthetestspecimenorthetestenvironment.In
addition, the test fixtures must remain elastic under test
conditions (load and temperature).
NOTE 7—Various grades of silicon carbide (such as hot-pressed or
sintered)andhigh-purityaluminasarecandidatematerialsfortestfixtures
as well as load train. The load-train material should also be effectively
inert to the test environment and remain elastic under test conditions. For
more specific information regarding use of appropriate materials for
fixtures and load train with respect to test temperatures, refer to Section 6
of Test Method C1211.
6.2.1 Four-Point Flexure—The four-point- ⁄4-point fixture
configuration (see Fig. 2) as described in Test Method C1211
shall be used in this test method. The nominal outer (support)
span(L)foreachtestfixtureis L=20mm,40mm,and80mm,
NOTE 1—The arrows indicate unacceptable data points. The data point
marked with ‘N,’ in which a significant nonlinearity occurs, indicates a
strength value estimated by extrapolation of the linear regression line
represented by the rest of the strength data.
FIG. 1 Schematic Diagrams Showing Unacceptable Data Points in
Constant Stress-Rate Testing at Elevated Temperatures
some advanced ceramics such as alumina and silicon nitride (10, 15).In
general, preloading may be effective to reduce overall creep deformation
of test specimens due to reduced test time. Refer to 8.10 for more
information regarding preloading and its application.
5.6 Surface preparation of test specimens can introduce
fabrication flaws that may have pronounced effects on flexural
strength. Machining damage imposed during specimen prepa-
ration can be either a random interfering factor, or an inherent
part of the strength characteristics to be measured. Surface
preparation can also lead to residual stress. Universal or
standardizedtestmethodsofsurfacepreparationdonotexist.It
should be understood that the final machining steps may or
may not negate machining damage introduced during the early
coarse or intermediate machining steps. In some cases, speci- FIG. 2 Four-Point- ⁄4-Point Flexural Test Fixture Configuration
C1465 − 08 (2019)
couple length, or excessively heavy-walled insulators, all of which can
respectively, for A, B, and C test fixtures. The use of three-
lead to erroneous temperature readings.
point flexure is excluded from this test method.
NOTE 10—The thermocouple tip may contact the test specimen, but
6.2.2 Bearing Cylinders—The requirements of dimensions
only if there is certainty that thermocouple tip or sheathing material will
and mechanical properties of bearing cylinders as described in
not interact chemically with the test specimen. Thermocouples may be
Test Method C1211 shall be used in this test method. The
prone to breakage if they are in contact with the test specimen.
bearing cylinders shall be free to rotate in order to relieve
6.4.2.2 Aseparate thermocouple may be used to control the
frictional constraints, as described in Test Method C1211.
furnaceifnecessary,butthetestspecimentemperatureshallbe
6.2.3 Semiarticulating Four-Point Fixture—Thesemiarticu-
the reported temperature of the test.
lating four-point fixture as described in Test Method C1211
NOTE11—Testsaresometimesconductedinfurnacesthathavethermal
maybeusedinthistestmethod.Thisfixtureshallbeusedwhen
gradients. The small size of test specimens will alleviate thermal gradient
the parallelism requirements of test specimens are met in
problems, but it is essential to monitor the temperature at the test
accordance with Test Method C1211.
specimen.
6.2.4 Fully Articulating Four-Point Fixture—The fully ar-
6.4.2.3 The thermocouple(s) shall be calibrated in accor-
ticulatingfour-pointfixtureasdescribedinTestMethodC1211
dance with Test Method E220 and Specification and Tables
may be used in this test method. Specimens that do not meet
E230. The thermocouples shall be periodically checked since
the parallelism requirements inTest Method C1211, due to the
calibration may drift with usage or contamination.
nature of fabrication process (as-fired, heat-treated, or
6.4.2.4 Themeasurementoftemperatureshallbeaccurateto
oxidized), shall be tested in this fully articulating fixture.
within 65°C. The accuracy shall include the error inherent to
6.3 SystemCompliance—Thetestfixtureandloadtrainshall
the thermocouple as well as any errors in the measuring
be sufficiently stiff so that at least 80% of the crosshead or
instruments.
actuatormovementofthetestmachineisimposedontothetest
NOTE12—Resolutionshouldnotbeconfusedwithaccuracy.Bewareof
specimen up to the point of fracture. The test fixture and load
recording instruments that read out to 1°C (resolution) but have an
train shall not undergo creep or nonlinear deformation under
1 1
accuracy of only 610°C or 6 ⁄2% of full scale (for example, ⁄2%of
either load or displacement control.
1200°C is 6°C).
NOTE 13—Temperature-measuring instruments typically approximate
NOTE 8—Compliance of the test fixture and load train at the test
the temperature-electromotive force (EMF, in millivolt) tables, and may
temperature can be estimated by inserting a rigid block of a ceramic
have an error of a few degrees.
material onto the test fixture with the loading bearing cylinders in place,
and loading it to the maximum anticipated fracture load while recording
6.4.2.5 Theappropriatethermocoupleextensionwireshould
a load-deflection curve. The compliance corresponds to the inverse of the
beusedtoconnectathermocoupletothefurnacecontrollerand
slope of the load-deflection curve. It is recommended that the block be at
temperature readout device, which shall have either a cold
least five times thicker than the test specimen depth and one to two times
widerthanthetestspecimenwidth.Anyotherblockwhoserigidity(equal junction or a room-temperature compensation circuit. Special
to the inverse of compliance) is greater than at least 120 times that of the
care should be directed toward connecting the extension wire
testspecimencanbeused,providedthatitcanfitthetestfixture.Atypical
with the correct polarity.
testmachineequippedwithcommonloadtrainandtestfixturesshowsthat
more than 90% of the total compliance stems from the test specimen
6.5 Environmental Facility—The furnace may have an air,
itself, so that more than 90% of crosshead or actuator movement of test
inert, vacuum, or any other gaseous environment, as required.
machine can be imposed on the test specimen.
If testing is conducted in any gaseous environment other than
6.4 Heating Apparatus—The heating systems such as
ambient air, an appropriate environmental chamber shall be
furnace, temperature-measuring device, and thermocouple
constructed to facilitate handling and monitoring of the test
shall conform to the requirements as described in Test Method
environmentsothatconstanttestconditionscanbemaintained.
C1211.
The chamber shall be effectively corrosion resistant to the test
6.4.1 Furnace and Temperature Readout Device—The fur-
environment so that it does not react with or change the
nace shall be capable of maintaining the test specimen tem-
environment. If it is necessary to direct load through bellows,
perature within 62°C during each testing period. The tem-
fittings, or seal, it shall be verified that load losses or errors do
perature readout device shall have a resolution of 1°C or
not exceed 1% of the prospective failure loads.
lower. The furnace system shall be such that thermal gradients
6.6 Deflection Measurement—When determined, measure
are minimal in the test specimen so that no more than a 5°C
deflection of the test specimen close to the midpoint or inner
differential exists from end to end in the test specimen.
load point(s) (tension side). The method to measure the
6.4.2 Thermocouples:
deflection of the midpoint relative to the two inner load points
6.4.2.1 The specimen temperature shall be monitored by a
(forexample,three-probeextensometer)canalsobeutilized,if
thermocouplewithitstipsituatednomorethan1mmfromthe
determined. The deflection-measuring equipment shall be ca-
midpoint of the test specimen. Either a fully sheathed or
−3
pable of resolving1×10 mm. Deflection measurement of
exposed bead junction may be used. If a sheathed tip is used,
testspecimensisparticularlyimportantatthetestconditionsof
it must be verified that there is negligible error associated with
lower test rates or higher test temperatures, or both, and is
the covering.
highly recommended to ensure that creep strain of test speci-
NOTE9—Exposedthermocouplebeadshavegreatersensitivity,butthey
mens is within the allowable limit (see 8.11.2).
may be exposed to vapors that can react with the thermocouple materials.
(For example, silica vapors will react with platinum.) Beware of the use NOTE 14—Alternatively, crosshead or actuator displacement may be
of heavy-gage thermocouple wire, thermal gradients along the thermo- used to infer deflection of the test specimen. However, care should be
C1465 − 08 (2019)
taken in interpreting the result since crosshead or actuator displacement
growth for certain test environments. Also, residue from the
generally may not be as sensitive as measurements taken on the specimen
cleaning medium, if any, shall not have any undesirable effect
itself.
on slow crack growth (strength) of test specimens.
NOTE 15—When a contact-type deflection-measuring equipment such
as LVDT is employed, it is important not to damage the contact area of
7.5 Number of Test Specimens—Therequirednumberoftest
specimens due to prolonged contact with the deflection-measuring probe,
specimens depends on the statistical reproducibility of SCG
particularly at lower test rates and higher test temperatures.Any spurious
parameters (n and D) to be determined. The statistical repro-
damagemayactasafailure-originatingsourcesothatthecontactingforce
ducibility is a function of strength scatter (Weibull modulus),
should be kept minimal, in the range from 0.5 to 2 N.Ageneral guideline
is that the maximum contacting force is dependent on specimen size such number of test rates, range of test rates, and SCG parameter
that 0.5 N for SizeA, 1 N for Size B, and 2 N for Size C specimen. The
(n). Because of these various variables, there is no single
probewithitstiproundedmaybefabricatedwiththesamematerialastest
guideline as to the determination of the appropriate number of
specimens or with sintered silicon carbide.
test specimens. A minimum of ten specimens per test rate is
6.7 Data Acquisition—Accurate determination of both frac-
recommended in this test method. The total number of test
ture load and test time is important since they affect not only
specimens shall be at least 40, with at least four different test
fracture strength but applied stress rate. At the minimum, an
rates (see
8.2.2).The number of test specimens (and test rates)
autographic record of applied load versus time should be
recommendedinthistestmethodhasbeenestablishedwiththe
determined during testing. Either analog chart recorders or
intent of determining reasonable confidence limits on both
digital data acquisition systems can be used for this purpose.
strength distribution and SCG parameters.
An analog chart recorder should be used in conjunction with
NOTE 16—Refer to Ref (2) when a specific purpose is sought for the
the digital data acquisition system to provide an immediate
statistical reproducibility of SCG parameters.
record of the test as a supplement to the digital record.
7.6 Valid Tests—A valid individual test is one which meets
Recording devices shall be accurate to 1.0% of the recording
all the following requirements: (1) all the test requirements of
range and should have a minimum data acquisition rate of
this test method, and (2) fracture occurring in the uniformly
1kHz, with a response of 5 kHz or greater deemed more than
stressed section (that is, in the inner span) (see 8.12.3).
sufficient.The appropriate data acquisition rate depends on the
test rate; the greater the test rate, the greater the acquisition 7.7 Randomization of Test Specimens—Since a somewhat
rate, and vice versa.
largenumberoftestspecimens(aminimumof40)withatleast
four different test rates is used in this test method, it is highly
7. Test Specimen recommended that all the test specimens provided be random-
ized prior to testing in order to reduce any systematic error
7.1 Specimen Size—The types and dimensions of rectangu-
associated with material fabrication or specimen preparation,
lar beam specimens as described in Test Method C1211 shall
or both. Randomize the test specimens (using, for example, a
be used in this test method. The nominal dimensions of each
random number generator) in groups equal to the number of
type of test specimens are 2.0 by 1.5 by 25 mm (minimum),
test rates to be employed, if desired.
respectively, in width (b), depth (d), and length for SizeAtest
specimens; 4.0 by 3.0 by 45 mm (minimum) for Size B test
8. Procedure
specimens;and8.0by6.0by90mm(minimum)forSizeCtest
8.1 Test Fixtures—Choose the appropriate fixture in the
specimens.
specific test configurations, as described in 6.2. Use the
7.2 Specimen Preparation—Specimen fabrication and
four-pointAfixturefortheSizeAspecimens.Similarly,usethe
preparation methods as described in Test Method C1211 shall
four-pointBfixtureforSizeBspecimens,andthefour-pointC
be used in this test method.
fixture for Size C specimens. A fully articulating fixture is
7.3 Specimen Dimensions—If there is a concern about a
required if the specimen parallelism requirements cannot be
dimensional change in test specimens by possible reaction/ met.
reaction products due to a prolonged test duration, particularly
8.2 Test Rates:
at very low test rates, measure test specimen dimensions prior
8.2.1 The choice of range and number of test rates not only
to testing. Determine the thickness and width of each test
affects the statistical reproducibility of SCG parameters but
specimen to within 0.002 mm either optically or mechanically
depends on the capability of a test machine. Since various
usingaflat,anvil-typemicrometer.Exerciseextremecautionto
types of test machines are currently available, no simple
prevent damage to the critical area of the test specimen.
guideline regarding the range of test rates can be made.
Otherwise, measure the test specimen dimensions after testing
However, when the lower limits of the test rates of most
(see 8.12.2)
commercial test machines are considered (often attributed to
7.4 Handling and Cleaning—Exercise care in handling and insufficient resolution of crosshead or actuator movement
storing specimens in order to avoid introducing random and control), it is generally recommended that the lowest test rates
−2 −8
severeflaws,whichmightoccurifthespecimenswereallowed be ≥10 N/s and 10 m/s, respectively, for load- and
to impact or scratch each other. If desired or necessary, clean displacement-controlled modes. Choice of the upper limits of
test specimens with an appropriate cleaning medium such as the test rates of test machines is dependent on several factors
methanol, high-purity (>99%) isopropyl alcohol, or any other associated with the dynamic response of the crosshead or
cleaning agent, since surface contamination of test specimens actuator, the load cell, and the data acquisition system (includ-
by lubricant, residues, rust, or dirt might affect slow crack ing the chart recorder, if used). Since these factors vary widely
C1465 − 08 (2019)
from one test machine to another, depending on their test specimen beyond the outer bearing cylinders, and the test
capability,nospecificupperlimitcanbeestablished.However, specimen should be directly centered below the axis of the
based on the factors common to many test machines and in applied load. In some cases, depending on the fixture design,
order to avoid data generation in a plateau region (see 5.2), it the test fixture/test specimen assembly is not securely in
is generally recommended that the upper test rates be ≤10 N/s position but movable while being loaded into the load train of
−3
and 10 m/s, respectively, for load- and displacement-control the test machine. In this case, a room-temperature adhesive
modes. may be used to hold the test specimen firmly in place relative
to the bearing cylinders and the fixture members. However,
8.2.2 For a test machine equipped with load-control mode,
care must be exercised to ensure that use of an adhesive shall
choose at least four load rates (evenly spaced in a logarithmic
−1
nothaveanyundesirableeffectonslowcrackgrowth(strength)
scale) covering three orders of magnitude (for example, 10 ,
0 1 2
of the test specimen through contamination and/or reaction by
10,10 , and 10 N/s). Similarly, for a test machine equipped
with displacement-control mode, choose at least four displace- organic residue.
ment rates (evenly spaced in a logarithmic scale) covering
NOTE 18—Various room-temperature adhesives, such as an acetate
−7 −6 −5
three orders of magnitude (for example, 10 ,10 ,10 , and
household cement or a cyanoacrylate adhesive, may be utilized for this
−4
10 m/s). The use of five or more test rates (evenly spaced in purpose if the adequacy of an adhesive (see 8.3.2), evaluated prior to
testing, is met.
alogarithmicscale)coveringfourormoreordersofmagnitude
is also allowed if the testing machine is capable and the test 8.4 Loading the Test Fixture/Specimen Assembly into
specimens are available. In general, the load-control mode
Furnace—Mount the test fixture/test specimen assembly in the
provides a better output wave-form than the displacement- load train of the test machine prior to heating the furnace. If
control mode, particularly at low test rates. In addition, the
necessary, use a preload of no more than 25% of the fracture
specified applied load rate can be directly related to stress rate, load to maintain system alignment. If uneven line loading of
regardless of compliance of test frame, load train, fixture and
the test specimen occurs, use fully articulating fixtures.
specimen, thus simplifying data analysis. In the displacement-
NOTE 19—The temperature of the furnace during loading of the test
control mode, however, the load rate to be determined is a
fixture/testspecimenassemblyisnotnecessarilyatroomtemperature.The
function of both applied displacement rate and system compli-
furnace could be preheated or remain hot from the previous testing, with
temperatures not affecting any undesirable thermal shock damage to test
ancesothattheactualloadrateshouldalwaysbemeasuredand
fixtures and test specimens. Appropriate precautions should be taken to
used to calculate a corresponding stress rate, thus making data
ensure operator safety from the hazards of thermal or electrical burns.
analysis complex. Therefore, use of load-control mode is
Safety gloves, safety glasses, or other safety tools, or a combination
highly recommended.
thereof, are essential.
NOTE 17—When using faster test rates, care must be exercised 8.5 If test specimen deflection is to be measured (see 6.6)
particularly for the conventional, older electromechanical testing ma-
using a contact type of equipment, position the deflection-
chines equipped with slow-response load cells and chart recorders. In
measurement probe(s) with its rounded tip in contact with the
general, such systems have an upper limit stress rate of about 100 MPa/s
midpoint or the inner load points (tension side), or both, of the
since the chart recorder and/or the load cell cannot follow load rate and,
test specimen. Exercise care to apply an appropriate contact
hence, cannot correctly monitor the fracture load (16, 17). This factor
should be taken into account when the fast crosshead speeds are selected load (see Note 15).
onoldertestingmachines.Theminimumtimetofailureinthiscaseshould
8.6 Some appropriate means should be furnished for keep-
be within a few seconds (≥3 s). However, the use of a better load cell (for
ing test fragments from flying about the furnace after fracture.
example, piezoelectric load cell) or a fast-response chart recorder or a
digital data acquisition system, or both, can improve the existing perfor- Ifpossible,retrievethetestspecimensfromthefurnaceassoon
mance so that higher test rates (up to 2000 MPa/s (16) can be achieved. It
as possible after fracture in order to preserve the primary
has been shown that digitally controlled, modern testing machine is
fracture surfaces for subsequent fractographic analysis.
capable of applying stress rates up to1×10 MPa/s (4).
8.7 Environment—Choosethetestenvironmentasappropri-
8.3 Assembling Test Fixture/Specimen:
ate to the test program. If the test environment is other than
8.3.1 Examine the bearing cylinders to make sure that they
ambientairorvacuum,supplytheenvironmentalchamberwith
are undamaged, and that there are no reaction products or
the test medium so that the test specimen is completely
oxidation that could result in uneven line loading of the test
exposed by the test environment. The consistent conditions
specimen or prevent the bearing cylinders from rolling. Re-
(composition,supplyrate,andsoforth)ofthetestenvironment
move and clean, or replace the bearing cylinders, if necessary.
should be maintained throughout the tests (also refer to 6.5).
Avoid any undesirable dimensional changes in the bearing
8.8 Heating to the Test Temperature—Heat the test speci-
cylinders,forexample,byinadvertentlyformingasmallflaton
men to the test temperature at the prescribed heating rate.
the cylinder surface when certain abrasion (for example,
Temperature overshoot over the test temperature shall be
abrasive paper) is used to remove the reaction products from
strictlycontrolledandshallbenomorethan5°C.Maintainthe
the cylinders. The same care should be directed toward the
temperature within 65°C (soak time) to allow the entire
contactsurfacesintheloadingandsupportmembersofthetest
system to reach thermal equilibrium. Prior to testing, the soak
fixture that are in contact with the bearing cylinders.
time should be determined experimentally at the test tempera-
8.3.2 Carefully place each test specimen into the test fixture
ture.
to avoid possible damage and contamination and to ensure
alignment of the test specimen relative to the test fixture. In 8.9 Hot-Furnace Loading and Heating (Optional)—Insome
particular, there should be an equal amount of overhang of the cases,testspecimensmaybeloadeddirectlyintoahotfurnace,
C1465 − 08 (2019)
as described in 8.4 of Test Method C1211. The fixture may be
eitherleftinthefurnacefortheentiretimeorremovedpartially
or completely, depending on the details of the systems.
Exercise care to ensure that the bearing cylinders and test
specimen are positioned accurately. Furthermore, exercise
extreme care to ensure that possible damage associated with
thermal shock shall not have any effect on strength or slow
crack growth, or both, of test specimens. If needed and
possible, place the deflection-measurement probe in contact
with the midpoint of specimens between the two inner bearing
cylinders, in accordance with 8.5. Determine the soak time of
thetestspecimenatthetesttemperatureexperimentallypriorto
testing.
8.10 Preloading:
8.10.1 The time required for any strength testing can be
minimized by applying some preload to a test specimen prior
to testing, provided that the strength determined with preload-
ing does not differ from that determined without preloading.
NOTE 20—Preloads truncate the slow crack curve and can result in
FIG. 3 Normalized Strength as a Function of Preloading for Dif-
errorsintheestimatedslowcrackgrowthparameters (18).Whenindoubt,
ferent Slow Crack Growth Parameters n’s (15)
it is recommended that preloads greater than those required for setup not
be used (see section 8.4).
It has been shown that in constant stress-rate testing,
one may use Eq 1 or Fig. 3 as a guideline to apply an
considerable preloads can be applied to ceramic specimens
appropriate amount of preload to save test time, if desired.
with no change in the strength obtained, resulting in a
Preloading can be applied more accurately and quickly by
significant reduction of test time (15). The relationship be-
using the load-control mode than the displacement-control
tween strength and preloading is as follows:
mode.
n11
σ* 5 ~11α !n11 (1)
p
8.10.2 Applythepredeterminedpreloadtothetestspecimen
within 20 s.
where:
σ* = normalized strength = σ /σ , 8.11 Conducting the Test—Initiatethedataacquisition.Start
fp fn
α = preloading factor (0≤α < 1.0) = σ /σ ,
the test mode.
p p o fn
σ = strength with preloading,
8.11.1 Recording—For either load-control or displacement-
fp
σ = strength without preloading,
fn control mode, record a load-versus-time curve for each test in
σ = preload stress, and
o
ordertodeterminetheactualloadingrate,andthustocalculate
n = slow crack growth parameter.
the corresponding stress rate (see also 6.7 and 9.2). Determine
The strength with preloading is dependent both on the the actual load rate in units of newtons per second from the
magnitude of preloading and on the SCG parameter n. The slopeoftheload-versus-timecurveforeachtestspecimen.The
plots of the normalized strength as a function of preloading for initial nonlinear portion of the curve should not be used in
different n’s, Eq 1, are depicted in Fig. 3. This figure shows determining the slope. The slope should be the tangent to the
that, for example, a preload corresponding to 80% (= α)of load-time data using an analog chart recorder when a high test
p
strength for n ≥ 20 (common to most ceramic materials at rateisemployed.Considerthecurveincludingtheportionator
elevated temperatures) results in a maximum strength increase near the point of fracture. Exercise care in recording adequate
by 0.04% (α = 1.0004). And a preload of 70% gives the response
...