ASTM C1834-16

Standard Test Method for Determination of Slow Crack Growth Parameters of Advanced Ceramics by Constant Stress Flexural Testing (Stress Rupture) at Elevated Temperatures

SIGNIFICANCE AND USE
4.1 The service life of many structural ceramic components is often limited by the subcritical growth of cracks over time, under stress at a defined temperature, and in a defined chemical environment (Refs 1-3). When one or more cracks grow to a critical size, brittle catastrophic failure may occur in the component. Slow crack growth in ceramics is commonly accelerated at elevated temperatures. This test method provides a procedure for measuring the long term load-carrying ability and appraising the relative slow crack growth susceptibility of ceramic materials at elevated temperatures as a function of time, temperature, and environment. This test method is based on Test Method C1576 with the addition of provisions for elevated temperature testing.  
4.2 This test method is also used to determine the influences of processing variables and composition on slow crack growth at elevated temperatures, as well as on strength behavior of newly developed or existing materials, thus allowing tailoring and optimizing material processing for further modification.  
4.3 This test method may be used for material development, quality control, characterization, design code or model verification, time-to-failure, and limited design data generation purposes.
Note 2: 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, depending on the range and magnitude of applied stresses used, may entail extrapolation and uncertainty.  
4.4 This test method and Test Method C1576 are similar and related to Test Methods C1368 and C1465; however, C1368 and C1465 use constant stress-rates (linearly increasing stress over time) to determine corresponding flexural strengths, whereas this test method and C1576 employ a constant stress (fixed stress levels over time) to determine corresponding times-to-failure. In general, the data generated by this test m...
SCOPE
1.1 This test method covers the determination of the slow crack growth (SCG) parameters of advanced ceramics in a given test environment at elevated temperatures in which the time-to-failure of four-point-1/4 point flexural test specimens (see Fig. 1) is determined as a function of different levels of constant applied stress. This SCG constant stress test procedure is also called a slow crack growth (SCG) stress rupture test. The test method addresses the test equipment, test specimen fabrication, test stress levels and experimental procedures, data collection and analysis, and reporting requirements.  
1.2 In this test method the decrease in time-to-failure with increasing levels of applied stress in specified test conditions and temperatures is measured and used to analyze the slow crack growth parameters of the ceramic. The preferred analysis 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: This test method is historically referred to in earlier technical literature as static 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 that occurs exclusively under cyclic stress loading, as defined in E1823, this test method uses the term constant stress testing rather than static fatigue testing.  
1.3 This test method uses a 4-point-1/4 point flexural test mode and 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 ...

General Information

• Status: Published
• Publication Date: 31-Jan-2016
• ICS: 81.060.30 - Advanced ceramics
• Technical Committee: C28 - Advanced Ceramics
• Drafting Committee: C28.01 - Mechanical Properties and Performance

Relations

• 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 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
• 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 C1145-19 - Standard Terminology of 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 C1291-18 - Standard Test Method for Elevated Temperature Tensile Creep Strain, Creep Strain Rate, and Creep Time to Failure for Monolithic Advanced Ceramics
• Effective Date: 01-Jan-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 C1576-05(2017) - Standard Test Method for Determination of Slow Crack Growth Parameters of Advanced Ceramics by Constant Stress Flexural Testing (Stress Rupture) at Ambient Temperature
• Effective Date: 01-Feb-2017
• Refers: ASTM C1291-16 - Standard Test Method for Elevated Temperature Tensile Creep Strain, Creep Strain Rate, and Creep Time-to-Failure for Monolithic Advanced Ceramics
• Effective Date: 01-Sep-2016
• 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

Overview

ASTM C1834-16 is an internationally recognized standard test method developed by ASTM for the determination of slow crack growth (SCG) parameters of advanced ceramics. It specifies procedures for constant stress flexural testing, also known as stress rupture testing, at elevated temperatures. This method is vital for evaluating the long-term mechanical reliability of advanced ceramics commonly used in structural applications where their performance can be compromised by slow crack growth under sustained loads and high temperatures.

The standard guides laboratories, manufacturers, and engineers in assessing the susceptibility of ceramic materials to subcritical crack growth and provides data that supports material development, quality control, and design validation.

Key Topics

• Slow Crack Growth (SCG): The standard addresses the subcritical propagation of cracks in ceramics over time under constant stress, which is accelerated at elevated temperatures and can result in catastrophic, brittle failure.
• Test Procedure: Utilizes a four-point-1/4 point flexural configuration where specimens are subjected to defined levels of constant stress at elevated temperatures, and time-to-failure is recorded.
• Material Applicability: Primarily intended for monolithic advanced ceramics that are macroscopically homogeneous and isotropic, but can also apply to certain reinforced ceramics exhibiting similar behavior.
• Data Analysis: Emphasizes the power law relationship between crack velocity and applied stress intensity, while also providing alternative analysis methods.
• Environmental and Testing Variables: Considers the effects of temperature, test environment (air, vacuum, inert gas, steam), and chemical interactions on crack growth.
• Probabilistic Nature: Recognizes the statistical scatter in time-to-failure data, reinforcing the need for a sufficient number of specimens and stress levels for reproducibility.
• Comparison with Other Methods: Unlike related standards using increasing stress rates, this method applies constant loads, providing data more representative of prolonged service conditions.

Applications

ASTM C1834-16 is utilized across a range of industries where advanced ceramics are deployed in demanding environments. Key practical applications include:

• Material Development and Optimization: Enables researchers and manufacturers to evaluate how processing variables and compositional changes affect the slow crack growth and reliability of novel or existing ceramic materials, assisting in material tailoring for specific applications.
• Quality Control and Assurance: Factories use this method to ensure material batches meet specified slow crack growth performance criteria, helping maintain high product quality.
• Design and Reliability Assessment: Engineers analyze SCG parameters to predict the service life and safety margins of ceramic components, supporting the validation of design codes and modeling efforts.
• Limited Design Data Generation: Provides critical input for estimating the long-term durability of ceramic parts, especially for components subjected to harsh thermal and chemical environments (e.g., turbine blades, heat exchangers, electronic substrates).
• Verification and Characterization: Supports verification of material models and offers standardized comparison across different ceramic formulations and production lots.

Related Standards

To provide a comprehensive approach to ceramic testing, ASTM C1834-16 references and complements several other ASTM standards, including:

• ASTM C1211 - Flexural Strength of Advanced Ceramics at Elevated Temperatures
• ASTM C1161 - Flexural Strength of Advanced Ceramics at Ambient Temperature
• ASTM C1368 / C1465 - Determination of Slow Crack Growth Parameters using Constant Stress-Rate Testing
• ASTM C1576 - Stress Rupture Testing at Ambient Temperature
• ASTM C1239 - Reporting Strength Data and Weibull Distribution Analysis
• ASTM E112 - Determining Average Grain Size
• ASTM C1322 - Fractography and Fracture Origin Characterization

These related standards provide additional protocols for flexural strength testing, test specimen preparation, data analysis, and fractographic examination, ensuring a thorough evaluation of ceramic materials' performance under service-like conditions.

---

By following ASTM C1834-16, organizations can reliably assess the long-term structural integrity of advanced ceramics, enhance quality control, improve material formulations, and ensure the safe and effective application of ceramics in critical high-temperature environments.

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: C1834 −16
Standard Test Method for
Determination of Slow Crack Growth Parameters of
Advanced Ceramics by Constant Stress Flexural Testing
(Stress Rupture) at Elevated Temperatures
This standard is issued under the fixed designation C1834; 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 homogeneous, elastic continuous behavior, and the application
of this test method to these materials is not recommended.
1.1 This test method covers the determination of the slow
1.4 This test method is intended for use at elevated tem-
crack growth (SCG) parameters of advanced ceramics in a
peratures with various test environments such as air, vacuum,
given test environment at elevated temperatures in which the
inertgas,andsteam.ThistestmethodissimilartoTestMethod
time-to-failure of four-point- ⁄4 point flexural test specimens
C1576 with the addition of provisions for testing at elevated
(see Fig. 1) is determined as a function of different levels of
temperatures to establish the effects of those temperatures on
constantappliedstress.ThisSCGconstantstresstestprocedure
slowcrackgrowth.Theelevatedtemperaturetestingprovisions
is also called a slow crack growth (SCG) stress rupture test.
are derived from Test Methods C1211 and C1465.
The test method addresses the test equipment, test specimen
fabrication,teststresslevelsandexperimentalprocedures,data
1.5 Creepdeformationatelevatedtemperaturescanoccurin
collection and analysis, and reporting requirements.
some ceramics as a competitive mechanism with slow crack
growth.Those creep effects may interact and interfere with the
1.2 In this test method the decrease in time-to-failure with
slow crack growth effects (see 5.5). This test method is
increasing levels of applied stress in specified test conditions
intended to be used primarily for ceramic test specimens with
and temperatures is measured and used to analyze the slow
negligible creep. This test method imposes specific upper-
crackgrowthparametersoftheceramic.Thepreferredanalysis
bound limits on measured maximum creep strain at fracture or
method is based on a power law relationship between crack
run-out (no more than 0.1%, in accordance with 5.5).
velocity and applied stress intensity; alternative analysis ap-
proaches are also discussed for situations where the power law
1.6 The values stated in SI units are to be regarded as the
relationship is not applicable.
standard and in accordance with IEEE/ASTM SI 10.
NOTE 1—This test method is historically referred to in earlier technical
1.7 This standard does not purport to address all of the
literature as static fatigue testing (Refs 1-3) in which the term fatigue is
safety concerns, if any, associated with its use. It is the
used interchangeably with the term slow crack growth. To avoid possible
responsibility of the user of this standard to establish appro-
confusion with the fatigue phenomenon of a material that occurs exclu-
sively under cyclic stress loading, as defined in E1823, this test method priate safety and health practices and determine the applica-
uses the term constant stress testing rather than static fatigue testing.
bility of regulatory limitations prior to use.
1.3 This test method uses a 4-point- ⁄4 point flexural test
2. Referenced Documents
mode and applies primarily to monolithic advanced ceramics
that are macroscopically homogeneous and isotropic. This test 2.1 ASTM Standards:
method may also be applied to certain whisker- or particle- C1145Terminology of Advanced Ceramics
reinforced ceramics as well as certain discontinuous fiber- C1161Test Method for Flexural Strength of Advanced
reinforced composite ceramics that exhibit macroscopically
Ceramics at Ambient Temperature
homogeneous behavior. Generally, continuous fiber ceramic C1211Test Method for Flexural Strength of Advanced
composites do not exhibit macroscopically isotropic,
Ceramics at Elevated Temperatures
C1239Practice for Reporting Uniaxial Strength Data and
Estimating Weibull Distribution Parameters forAdvanced
Ceramics
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 Feb. 1, 2016. Published April 2016. DOI: 10.1520/ For referenced ASTM standards, visit the ASTM website, www.astm.org, or
C1834-16. 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
C1834 − 16
FIG. 1 Four-point- ⁄4 Point Flexural Test Schematic
C1291Test Method for ElevatedTemperatureTensile Creep IEEE/ASTM SI 10American National Standard for Use of
Strain, Creep Strain Rate, and Creep Time-to-Failure for theInternationalSystemofUnits(SI):TheModernMetric
Advanced Monolithic Ceramics System
C1322Practice for Fractography and Characterization of
3. Terminology
Fracture Origins in Advanced Ceramics
C1368 Test Method for Determination of Slow Crack
3.1 Definitions:
Growth Parameters of Advanced Ceramics by Constant
3.1.1 The terms described in Terminology C1145 and Ter-
Stress-Rate Strength Testing at Ambient Temperature
minology E1823 are applicable to this test method. Specific
C1465 Test Method for Determination of Slow Crack
terms relevant to this test method are as follows:
Growth Parameters of Advanced Ceramics by Constant
3.1.2 advanced ceramic, n—a highly engineered, high
Stress-Rate Flexural Testing at Elevated Temperatures
performance, predominately non-metallic, inorganic, ceramic
C1576 Test Method for Determination of Slow Crack
material having specific functional attributes. C1145
Growth Parameters of Advanced Ceramics by Constant
-2
3.1.3 constant applied stress, σ[FL ], n—a constant maxi-
Stress Flexural Testing (Stress Rupture) atAmbient Tem-
mum flexural stress applied to a specified beam test specimen
perature
by using a constant static force with a test machine and a test
E4Practices for Force Verification of Testing Machines
fixture. C1576
E112Test Methods for Determining Average Grain Size
3.1.4 constant applied stress versus time-to-failure diagram,
E220Test Method for Calibration of Thermocouples By
n—a plot of constant applied stress against time-to-failure for
Comparison Techniques
experimental test data. (See Fig. 2)
E230Specification and Temperature-Electromotive Force
3.1.4.1 Discussion—Constant applied stress and time-to-
(EMF) Tables for Standardized Thermocouples
failure are both plotted on logarithmic scales. Data may be
E337Test Method for Measuring Humidity with a Psy-
organized and plotted by experimental test temperature. Also
chrometer (the Measurement of Wet- and Dry-Bulb Tem-
called an SCG stress rupture diagram. (See Fig. 2) C1576
peratures)
E399Test Method for Linear-Elastic Plane-Strain Fracture 3.1.5 constant applied stress versus time-to-failure curve,
Toughness K of Metallic Materials n—a curve fitted to the values of time-to-failure at each of
Ic
E1823TerminologyRelatingtoFatigueandFractureTesting several applied stresses. (See Fig. 2)
FIG. 2 Examples of Applied Stress versus Time-to-Failure Diagrams [NC132 Silicon Nitride at 1100°C in Air (Ref 28) and NCX34 Silicon
Nitride at 1200°C and 1300°C in Air (Ref 29)]
C1834 − 16
3.1.5.1 Discussion—In the historical ceramics literature, the 3.1.18 test environment, n—the aggregate of chemical spe-
constant applied stress versus time-to-failure curve is often cies and energy that surrounds a test specimen. E1823
called a static fatigue curve.Amore accurate descriptive name
3.1.19 test environmental chamber, n—a container sur-
is a slow crack growth (SCG) stress rupture curve. C1576
rounding the test specimen that is capable of providing a
-3/2 -1
3.1.6 crack-extension resistance, K [FL ], G [FL ]or controlled local environmental condition. C1368, C1465
R R
-1
J [FL ], n—ameasureoftheresistanceofamaterialtocrack
R
3.1.20 time-to-failure, t [t], n—total elapsed time from test
f
extension expressed in terms of the stress-intensity factor, K;
initiation to test specimen failure/rupture for a defined test
crack-extension force, G; or values of J derived using the
condition.
J-integral concept. E1823
3.1.6.1 Discussion—The J-integral concept in this E1823
4. Significance and Use
definition is a metal fracture concept and is not applicable to
4.1 The service life of many structural ceramic components
brittle ceramics.
is often limited by the subcritical growth of cracks over time,
3.1.7 creep strain, n—the time-dependent strain that occurs
understressatadefinedtemperature,andinadefinedchemical
after the application of a force which is thereafter maintained
environment (Refs 1-3). When one or more cracks grow to a
constant. C1291
critical size, brittle catastrophic failure may occur in the
3.1.8 dead weight test machine, n—a mechanical testing
component. Slow crack growth in ceramics is commonly
machine which uses a load frame, lever-arms, and an adjust-
acceleratedatelevatedtemperatures.Thistestmethodprovides
able weight train (with calibrated dead weights) to apply a
a procedure for measuring the long term load-carrying ability
constant known force to the test specimen over an extended
and appraising the relative slow crack growth susceptibility of
period of time.
ceramic materials at elevated temperatures as a function of
-2
time, temperature, and environment. This test method is based
3.1.9 flexural strength, σ [FL ], n—a measure of the
f
on Test Method C1576 with the addition of provisions for
ultimate strength of a specified beam test specimen in flexure
elevated temperature testing.
determinedatagivenstressinaparticularenvironment. C1576
4.2 Thistestmethodisalsousedtodeterminetheinfluences
3.1.10 fracture toughness, n—a generic term for measures
of processing variables and composition on slow crack growth
of resistance to extension of a crack. E399, E1823
at elevated temperatures, as well as on strength behavior of
-2
3.1.11 inert flexural strength [FL ], n—theflexuralstrength
newly developed or existing materials, thus allowing tailoring
of a specified beam as determined in an inert test condition
and optimizing material processing for further modification.
whereby no slow crack growth occurs.
4.3 Thistestmethodmaybeusedformaterialdevelopment,
3.1.11.1 Discussion—Aninertconditionmaybeobtainedby
quality control, characterization, design code or model
testing at a low temperature, at a very fast test rate, or in an
verification,time-to-failure,andlimiteddesigndatageneration
inerttestenvironmentsuchasvacuum,siliconeoil,highpurity
purposes.
dry N , or liquid nitrogen. C1465
NOTE 2—Data generated by this test method do not necessarily
3.1.12 plane-strain fracture toughness, (critical stress inten-
correspond to crack velocities that may be encountered in service
-3/2
sity factor) K [FL ], n—the crack extension resistance
IC conditions. The use of data generated by this test method for design
under conditions of crack-tip plane strain in Mode I for slow purposes, depending on the range and magnitude of applied stresses used,
may entail extrapolation and uncertainty.
rates of loading under predominantly linear-elastic conditions
and negligible plastic-zone adjustment. E1823
4.4 ThistestmethodandTestMethodC1576aresimilarand
related to Test Methods C1368 and C1465; however, C1368
3.1.13 R-curve, n—a plot of crack-extension resistance as a
and C1465 use constant stress-rates (linearly increasing stress
function of stable crack extension. C1145
over time) to determine corresponding flexural strengths,
Also defined as a K-R curve. E1823
whereas this test method and C1576 employ a constant stress
3.1.14 run-out, n—a test specimen that does not fail before
(fixed stress levels over time) to determine corresponding
a prescribed test time limit. C1576
times-to-failure. In general, the data generated by this test
3.1.15 slow crack growth (SCG), n—subcritical crack
method may be more representative of actual service condi-
growth (extension) which may result from, but is not restricted
tions as compared with data from constant stress-rate testing.
to, such mechanisms as environmentally-assisted stress corro-
However, in terms of test time, constant stress testing is
sion or diffusive crack growth. C1368, C1465, C1576
inherently and significantly more time consuming than con-
stant stress-rate testing.
3.1.16 slow crack growth (SCG) parameters, n—the param-
eters estimated as constants in the log (time-to-failure) versus
4.5 The flexural stress computation in this test method is
log (constant applied stress), which represent a measure of the
based on simple elastic beam theory, with the following
susceptibilitytoslowcrackgrowthofamaterial(seeAppendix
assumptions: the material is isotropic and homogeneous; the
X1). C1465
moduli of elasticity in tension and compression are identical;
-3/2
3.1.17 stress intensity factor, K [FL ], n—the magnitude and the material is linearly elastic. These assumptions are
I
of the ideal-crack-tip stress field stress field singularity) sub- based on small grain size in the ceramic specimens. The grain
jectedtoModeIloadinginahomogeneous,linearelasticbody. size should be no greater than ⁄50 of the beam depth as
E1823 measuredbythemeanlinearinterceptmethod(E112).Incases
C1834 − 16
where the material grain size is bimodal or the grain size 5. Interferences
distribution is wide, the limit should apply to the larger grains.
5.1 Slow crack growth (SCG) may be the product of both
4.6 The test specimen sizes and test fixtures have been
mechanical stress and chemical driving forces. The chemical
selected in accordance with Test Method C1211 which pro- driving force for a given material may vary strongly with the
vides a balance between practical configurations and resulting
chemistry and temperature of the test environment. SCG
errors, as discussed in Refs 4 and 5. Test Method C1211 also testing is conducted at temperatures and in environments
specifies fixture material requirements for elevated test tem- representative of service conditions, so as to evaluate material
perature stability and functionality. performance under service conditions. Note that slow crack
growth testing, particularly constant stress testing, is very time
4.7 The SCG data are evaluated by regression of log
consuming. The overall test time is considerably greater in
applied-stress vs. log time-to-failure to the experimental data.
constant stress testing than in constant stress-rate testing.
The recommendation is to determine the slow crack growth
Because of this longer test time, the temperature and chemical
parameters by applying the power law crack velocity function.
variables of the test environment shall be controlled to mini-
For derivation of this, and for alternative crack velocity
mize changes during the test. Inadequate control of tempera-
functions, see Appendix X1.
ture and environmental conditions may result in inaccurate
NOTE 3—Avariety of crack velocity functions exist in the literature.A
comparisonofthefunctionsforthepredictionoflong-termconstantstress time-to-failure data, especially for materials that are more
(static fatigue) data from short-term constant stress rate (dynamic fatigue)
sensitive to elevated temperatures and reactive environments.
data (Ref 6) indicates that the exponential forms better predict the data
5.2 Awide range of different interference effects can occur
than the power-law form. Further, the exponential form has a theoretical
basis(Refs 7-10);however,thepowerlawformissimplermathematically. in slow crack growth testing at elevated temperatures (Refs
Both forms have been shown to fit short-term test data well.
16-27).
4.8 The approach used in this test method assumes that the 5.2.1 Creep damage (cavitation and micro-cracks) on or
near the tensile surface of the test specimen.
ceramic material displays no rising R-curve behavior, that is,
no increasing fracture resistance (or crack-extension resis- 5.2.2 Creep-induced non-linear stress-strain effects on the
tensile surface of the test specimen.
tance) with increasing crack length for a given test tempera-
ture. The existence of such R-curve behavior cannot be 5.2.3 Differences in creep strain on the tensile surface
determinedfromthistestmethod.Theanalysisfurtherassumes versus the compressive surface of the test specimen introduc-
that the same flaw type controls all times-to-failure for a given ing non-linear stress-strain effects through the thickness of the
test temperature. test specimen.
5.2.4 Deviations in the linear relationship between log
4.9 Slow crack growth behavior of ceramic materials can
(constant applied stress) and log (time-to-failure) at high stress
vary as a function of material properties, thermal conditions,
levels.
and environmental variables. Therefore, it is essential that test
5.2.5 Oxidation induced crack healing and crack tip blunt-
results accurately reflect the effects of the specific variables
ing.
under study. Only then can data be compared from one
5.2.6 Chemical reactions, oxidation, phase changes, and
investigation to another on a valid basis, or serve as a valid
devitrification of grain boundary layers in the ceramics.
basis for characterizing materials and assessing structural
behavior.
5.3 Variations in the test specimens and the experimental
conditions can also act as interferences.
4.10 Like mechanical strength, the SCG time-to-failure of
5.3.1 Differentflawpopulationsbetweenthesurfaceandthe
advanced ceramics is probabilistic in nature. Therefore, slow
interior of the test specimen.
crack growth that is determined from times-to-failure under
5.3.2 Surface condition effects and anomalous surface flaws
given constant applied stresses is also a probabilistic phenom-
from specimen machining and grinding.
enon. The scatter in time-to-failure in constant stress testing is
5.3.3 Non-uniform test specimen dimensions (dimensional
much greater than the scatter in strength in constant stress-rate
variations, warp, twist, and bowing).
(or any strength) testing (Refs 1, 11-13; see Appendix X2).
5.3.4 Localizedfracturefromcontactandfrictionstressesat
Hence, a proper range and number of constant applied stress
load points.
levels, in conjunction with an appropriate number of test
NOTE 4—These issues are discussed in detail in AnnexA1 and in Test
specimens, are required for statistical reproducibility and
Methods C1211 and C1291.
reliable design data generation (Ref 1-3). This test method
5.4 Alloftheseeffectsmaychangethestressconditions,the
provides guidance in this regard.
flaw populations, and the crack growth mechanisms in the test
4.11 The time-to-failure of a ceramic material for a given
specimens.These factors need to be considered, accounted for,
testspecimenandtestfixtureconfigurationisdependentonthe
and controlled for each given test material and set of test
ceramic material’s inherent resistance to fracture, the presence
conditions.
of flaws, the applied stress, and the temperature and environ-
mental effects. Fractographic analysis to verify the failure 5.5 Creep deformation and effects may be a primary inter-
mechanisms has proven to be a valuable tool in the analysis of ference in high temperature SCG testing. Significant creep at
SCGdatatoverifythatthesameflawtypeisdominantoverthe both higher temperatures and longer test times may produce
entire test range (Refs 14, 15), and fractography is recom- nonlinearity in stress-strain relations as well as accumulated
mended in this test method (refer to Practice C1322). tensile damage in flexure (Ref 11). This, depending on the
C1834 − 16
degree of nonlinearity, may limit the applicability of linear bearing cylinders shall be free to roll in order to relieve
elasticfracturemechanics(LEFM),sincetheresultingrelation- frictional constraints, as described in Test Method C1211.
ship between strength and stress derived under constant stress
6.2.3 Semiarticulating Four-Point Fixture—Thesemiarticu-
testing condition is based on an LEFM approach with negli-
lating four-point fixture is described in Test Method C1211.
gible creep (maximum creep strain less than 0.1 %).Therefore
Use the semiarticulating test fixture for test specimens that
creepstrainshouldminimizedasmuchaspossible(tonomore
meet the parallelism requirements of Test Method C1211.
than 0.1%), as compared to the total elastic strain at failure
6.2.4 Fully Articulating Four-Point Fixture—The fully ar-
(see Fig. 3 and 8.9.2).
ticulatingfour-pointfixtureisdescribedinTestMethodC1211.
Use the fully articulating test fixture for test specimens that do
6. Apparatus
not meet the parallelism requirements in Test Method C1211,
6.1 Test Machine—Dead weight test machines or universal
due to the ceramic fabrication process (as-fired, heat-treated or
test machines capable of maintaining a constant applied force oxidized).
shallbeusedforconstantstresstesting.Testmachinesusedfor
6.3 Heating Apparatus—The heating system (such as fur-
this test method shall conform to the requirements of Practice
nace enclosure, heating elements, thermal control, temperature
E4.Theappliedforceshallbemonitoredduringthetestandthe
measuring device, or thermocouple, or combinations thereof)
variations in the applied force shall not exceed 6 1.0% of the
shall conform to the requirements in Test Method C1211,
nominal value at any given time during the test.
section 6.11.
6.1.1 Universal test machines shall meet the system com-
6.3.1 Test Furnace and Temperature Readout Device—The
pliance requirements as cited in Annex A2 and Test Method
furnace shall be capable of maintaining the test specimen
C1211, section 6.9. Dead-weight machines do not have any
temperature within 62°C during each testing period. The
compliance requirements.
temperature readout device shall have a resolution of 1°C or
6.2 Test Fixtures—The configurations and mechanical prop-
smaller. The furnace system shall be such that thermal gradi-
erties of test fixtures shall be in accordance with Test Method
ents are minimal along the length of the test specimen with no
C1211. The materials from which the test fixtures, including
more than a 5°C differential from end-to-end in the test
bearingcylinders,arefabricatedshallbeeffectivelyinerttothe
specimen.
test environment at the test temperatures, so that they do not
NOTE 6—Tests are sometimes conducted in furnaces that have thermal
significantly react with or contaminate either the test specimen
gradients. Test specimens of smaller sizes will reduce thermal gradient
or the test environment. In addition, the test fixtures shall
problems,butitisessentialtomonitorthetemperaturealongthelengthof
remain elastic under test temperatures and loading conditions.
the test specimen.
NOTE 5—Various grades of silicon carbide (such as hot-pressed or
6.3.2 Thermocouples:
sintered) and high-purity aluminas are candidate materials for test fixtures
6.3.2.1 The specimen temperature shall be monitored by a
as well as load train components in the hot zone. The load-train material
thermocouplewithitstipsituatednomorethan1mmfromthe
should also be effectively inert to the test environment. For more specific
midpoint of the test specimen. Either a fully sheathed or
information regarding use of appropriate materials for fixtures and load
train with respect to test temperatures, refer to Section 6 of Test Method
exposed bead junction may be used. If a sheathed tip is used,
C1211.
verifythatthereisnegligibleerrorassociatedwiththecovering
6.2.1 Four-Point Flexure—The four-point- ⁄4 point fixture sheath.
described in Test Method C1211, Section 6.2, shall be used in (1)Thermocouple integrity and stability are significant
thistestmethod(seeFig.1).Thenominalouter(support)spans concerns at elevated temperatures and long exposure times.
(L)fortheA,B,andCtestfixturesare L=20mm,40mm,and Exposed thermocouple beads have greater sensitivity, but they
80 mm, respectively. Three-point flexure shall not be used. may be exposed to vapors that may react with the thermo-
6.2.2 Bearing Cylinders—The requirements of dimensions couple materials. (For example, silica vapors will react with
and mechanical properties of bearing cylinders as described in platinum.) Beware of the use of heavy-gage thermocouple
Test Method C1211 shall be used in this test method. The wire, thermal gradients along the thermocouple length, or
FIG. 3 Creep Deformation and Deflection at Constant Force Conditions
C1834 − 16
excessively heavy-walled insulators, all of which may lead to 6.5.2 Deflection-measuring equipment shall be capable of
-3
erroneous temperature readings. resolutionandaccuracyof2×10 mm.SeeA2.2fordetailson
(2)The thermocouple tip may contact the test specimen, deflection measurement and creep strain calculation.
but only if there is certainty that the thermocouple tip or
6.6 Data Acquisition—Accurate determination of the time-
sheathing material will not interact chemically with the test
to-failure (or maximum test time in case of run-out) is
specimen.Thermocouplesmaybepronetobreakageiftheyare
important, since time-to-failure is the only dependent variable
in contact with the test specimen.
in this test method.Applied force versus elapsed time shall be
6.3.2.2 Aseparate thermocouple may be used to control the
measured and recorded during testing to ensure constant stress
furnace,ifnecessary,butthetestspecimentemperatureshallbe
conditions.
the reported temperature of the test.
6.6.1 Accurate time determination is particularly important
6.3.2.3 The thermocouple(s) shall be calibrated in accor- when time-to-failure may be relatively short (<10 s). Devices
dance with Test Method E220 and Specification and Tables
to measure time-to-failure may be either digital or analog and
E230. The thermocouples shall be periodically checked since incorporate a switching mechanism to mark the time of test
calibration may drift with usage or contamination.
specimen failure. Either analog chart recorders or digital data
acquisition systems may be used for this purpose.
6.3.2.4 Themeasurementoftemperatureshallbeaccurateto
6.6.2 Time recording devices shall be accurate to 1.0% of
within 65°C. The accuracy shall include the error inherent to
therecordingrangeandshallhaveaminimumdataacquisition
the thermocouple as well as any errors in the measuring
rate sufficient to adequately describe the whole test data series.
instruments.
The appropriate data acquisition rate depends on the actual
NOTE 7—Resolution should not be confused with accuracy. Beware of
time-to-failure but should preferably be in the 0.2 to 50 Hz
recording instruments that read out to 1°C (resolution) but have an
range (50 Hz for times less than 5 s, 10 Hz for times between
1 1
accuracy of only 610°C or 6 ⁄2 % of full-scale (for example, ⁄2%of
5sand10min,1Hzfortimesbetween10minand5h,and0.2
1200°C is 6°C).
Hz for times over 5 h).
NOTE8—Temperaturemeasuringinstrumentstypicallyapproximatethe
temperature-electromotive force (EMF, in millivolt) tables, and may have
6.7 Dimension Measuring Devices—Micrometers and other
an error of a few degrees.
devices used for measuring test specimen dimensions shall
6.3.2.5 The appropriate thermocouple extension wire shall have a resolution of 0.002 mm or smaller. To avoid damage in
beusedtoconnectathermocoupletothefurnacecontrollerand
the inner span section, thickness/depth measurements should
temperature readout device, which shall have either a cold
be made using a flat, anvil type micrometer. Ball-tipped or
junction or a room-temperature compensation circuit. Special
sharp anvil micrometers should not be used because localized
care should be directed toward connecting the extension wire
surface damage (e.g., cracking) may be induced.
with the correct polarity.
7. Test Specimen
6.4 Furnace Environmental Chamber—The furnace may
7.1 Specimen Size—The types/configurations, dimensions,
have an air, inert, vacuum, or any other gaseous environment,
and tolerances of rectangular flexure beam specimens de-
asrequired.Iftestingisconductedinanygaseousenvironment
scribedinTestMethodC1211shallbeusedinthistestmethod.
other than ambient air, an appropriate environmental chamber
The nominal dimensions [width (b), depth (d), and length (l)]
shall be constructed to facilitate handling, control, and moni-
for each type of test specimen are given in Table 1.
toringofthetestenvironmentsothatconstanttestenvironment
conditionscanbemaintained.Thechambershallbeeffectively 7.2 Specimen Preparation—Specimen fabrication and fin-
ishing methods as described in Test Method C1211, Section
corrosion-resistant to the test environment so that it does not
react with or change the environment. If the load train acts 7.2, shall be used in this test method. These methods are
defined as application-matched machining, customary
through bellows, fittings, or seals, verify that force losses or
errors do not exceed 1% of the prospective failure forces. procedures, and standard procedures.
7.3 Specimen Measurement—It is common practice to mea-
6.5 Deflection Measurement—Beam deflection and outer
sure the specimen dimensions post-test to prevent surface
fiber strain (strain at the outer face of the flexure beam)
damage in the critical area (inner span section). If there is a
measurements are not needed to calculate a slow crack growth
concern about dimensional changes in test specimens from
parameter. However, deflection measurements may be neces-
sary for determining if significant creep deformation is occur-
A,B
ring. Deflection measurement of test specimens for creep is
TABLE 1 Test Specimen Dimensions (per Test Method C1211)
particularly important for certain ceramic materials at higher
Type/ Width (b), Depth/Thickness Length (l) mm,
Configuration mm (d), mm minimum
test temperatures and longer test times and is highly recom-
A 2.0 1.5 25
mended to ensure that maximum creep strain of those ceramic
B 4.0 3.0 45
specimens is within the allowable limit (see 8.9.2).
C 8.0 6.0 90
6.5.1 Creepdeformationcanbemeasuredbythreemethods:
A
Cross-sectional dimensional tolerances are ±0.05 mm for A specimens and
real-timein-situdeflectionofthemidpointorloadpointsofthe ±0.13 mm for B and C specimens.
B
The parallelism tolerances on the four longitudinal faces are 0.015 mm forAand
test specimen, crosshead displacement, and post-test measure-
B specimens and 0.03 mm for C specimens. The two end faces need not be
ment of the permanent deformation of the midpoint of the test
precision machined.
specimen.
C1834 − 16
oxidation/reaction layers on the surface over long test times, ization may not be appropriate if the specimens are taken from
measure the test specimen dimensions prior to testing. different billets. Trace and record the source of the test
specimens and use an appropriate statistical blocking scheme
7.3.1 Formeasurementspriortoandaftertesting,determine
for distributing the specimens.
the width (b) and depth (d) at three points along the inner span
of each test specimen as described in Test Method C1211,
7.7 Valid Tests—Avalidindividualtestisonethatmeetsthe
either optically or mechanically using a flat, anvil-type mi-
following three requirements: (1) all the experimental require-
crometer. Exercise extreme care in pretest measurements to
ments of this test method are met, (2) fracture occurs in the
prevent damage to the critical area (the inner span section) of
uniformly stressed section (that is, in the inner span; see
the test specimen. Record and report the measured dimensions
8.10.2), and (3) the maximum creep strain does not exceed the
and locations of the measurements. Use the average of the
selected creep strain limit.
multiple measurements (width and depth) in the stress calcu-
lation.
8. Procedure
7.3.2 Measurement of surface finish is not required,
however, such information may be helpful in assessing surface 8.1 Test Preparation:
flaws. Methods such as contact profilometry may be used to
8.1.1 Range and Number of Applied Stress Levels—The
determine the surface roughness of the test specimen faces.
choice of range and number of applied stress levels (or applied
When measured, report the measured surface roughness
force levels) not only depends on test material but also affects
(RMS),testmethod,andthedirectionofthemeasurementwith
the statistical reproducibility of SCG parameters. A minimum
respect to the long axis of the test specimen.
of ten specimens per each applied stress level is recommended
in this test method with at least four different applied stress
7.4 Handling, Cleaning, and Storage—Exercise care in
levels (4 stresses × 10 specimens = 40 specimens).
handling and storing specimens in order to avoid introducing
8.1.2 In general, choose an upper limit of applied stress that
random and severe flaws, which might occur if the specimens
were allowed to impact or scratch each other. Clean the test would result in a corresponding time-to-failure of ~10 s. The
choiceofthelowerlimitofappliedstressesdependsonrun-out
specimens with an appropriate medium such as methanol or
high-purity (> 99%) isopropyl alcohol to avoid contamination times, where some of the test specimens would not fail within
a prescribed length of test time. Determine an appropriate
of the test environment by residual machining or processing
fluids.After cleaning and drying, store the test specimens in a run-outtimeforeachparticulartestprogram,dependingonthe
controlled environment such as a vacuum or a dessicator in SCG mechanisms of the ceramic and the material service and
order to minimize exposure to moisture.Adsorbed moisture on temperature requirements. Reported laboratory tests of high
the test specimen surfaces may change slow crack growth strength, high temperature ceramics have used a range of
6 7 8
rates. run-out times: 10,10 , and 10 seconds. Choose at least four
applied stresses covering at least four orders of magnitude in
7.5 Number of Test Specimens—Therequirednumberoftest
time.
specimens depends on the desired level of statistical reproduc-
ibility of the calculated SCG parameters (n and D). The
NOTE10—Time-to-failureofadvancedmonolithicceramicsinconstant
statistical reproducibility is a function of the strength scatter
stress testing is probabilistic. Furthermore, the scatter in time-to-failure is
significantly greater than the scatter in strengths (Refs 11-13), typically
number (Weibull modulus), the range of applied stress levels,
(n+1) times the Weibull modulus of strength distribution (see Appendix
and the SCG parameter (n). Because of these different
X2). Hence, unlike metallic or polymeric materials, a considerable
variables, there is no absolute rule as to the determination of
increase in the scatter of time-to-failure is expected for advanced
the appropriate number of test specimens.
monolithic ceramics, attributed to both a large strength scatter (Weibull
modulus of about 10 to 15) and a typically high SCG parameter n ≥ 20.
7.5.1 A minimum of ten specimens per each applied stress
Asaconsequence,testingafewtestspecimensateachappliedstressusing
level is recommended in this test method with at least four
a few stress levels may not be sufficient to produce statistically reliable
different applied stress levels (4 stresses × 10 specimens = 40
design data. On the other side of the equation, the use of many test
specimens). The recommended number of test specimens (and
specimenswithmanyappliedstressesisquitetimeconsumingandmaybe
applied stress levels) has been established with the intent of
unrealistic in time and cost.
determining reasonable confidence limits on both time-to-
NOTE 11—If SCG parameters are available from constant stress-rate
testing (Test Method C1368 and Test Method C1465), time-to-failure in
failure distribution and SCG parameters. (See 8.1.1.)
constantstresstestingcanbeestimatedasafunctionofappliedstressfrom
NOTE 9—Refer to Ref 1 when a specific purpose is sought for the
a prediction shown in Appendix X3. This approach, although theoretical,
statistical reproducibility of SCG parameters.
allows one to quickly find the range and magnitude of stresses and the
run-out time to be applied. There might be some discrepancies in the
7.6 Randomization of Test Specimens—Since a large num-
prediction; however, use of this prediction may significantly reduce many
beroftestspecimens(arecommendedminimumof40)withat
uncertainties and trial-and-errors associated with selecting stresses and
least four different applied stresses is used in this test method,
run-out time. If no SCG data for the test material is available, run
it is highly recommended that all the test specimens be simplified constant stress-rate testing using both high (around 10 MPa/s)
and low (around 0.01 MPa/s) stress rates with at least five test specimens
randomized prior to testing in order to reduce any systematic
at each stress rate to determine fracture strengths. Then determine the
error associated with material fabrication or specimen
corresponding SCG parameters (n and D ) based on the procedure inTest
d
preparation, or both. Randomize the test specimens (using, for
Method C1368. Use these simplified SCG data to select applied stresses
example, a random number generator) in groups equal to the
and run-out time to be used in constant stress testing by following the
number of applied stresses to be employed. Complete random- prediction described in Appendix X3.
C1834 − 16
8.1.3 For each selected stress level, calculate the necessary 8.4.2 Loading the Test Fixture/Specimen Assembly into Test
applied force for the dimensions of the selected test specimen Machine—Mountandalignthetestspecimen/fixtureassembly
andloadingconfiguration,usingthestresscalculationequation in the load train of the test machine. If necessary, slowly apply
(Eq 1)in 9.1.1. a preload of no more than 25% of the test force to maintain
8.1.4 Defineaheatingrateforthefurnacethatwillminimize system alignment during deflection probe positioning and
temperature overshoot and thermal shock to the test specimen. specimen heat up.
8.4.3 If test specimen deflection is to be measured (see 6.5)
8.2 Test Specimen Inspection and Measurement—Conduct
using a contact type of equipment, position the deflection-
100% inspection of the test specimens to assure compliance
measurement probe(s) with its rounded tip in contact with the
with the specifications in this test method. Specimen dimen-
midpoint and/or the inner load points (tension side) of the test
sions (width, b, and depth, d) are commonly measured post-
specimen. Exercise care to apply an appropriate contact force
test, to prevent pretest damage to the surfaces of the test
(see 6.5.2 and Annex A2).
specimen (see 7.3.1 and 8.10.2). If there is a concern about a
dimensionalchangesintestspecimensfromoxidation/reaction
8.5 An appropriate containment shield should be furnished
layers on the surface over long test times, measure the test
for keeping test fragments from scattering in the furnace after
specimen dimensions prior to testing.
fracture. If possible, retrieve the test specimens from the
furnace as soon as possible after fracture in order to preserve
8.3 Test Fixture and System Assembly:
the primary fracture surfaces for subsequent fractographic
8.3.1 Test Fixtures—Choose the appropriate fixture for the
analysis.
specific test configurations, as described in 6.2. Use the
four-point “A” fixture for the SizeAspecimens. Similarly, use
8.6 Environment—Choosethetestenvironmentasappropri-
the four-point “B” fixture for Size B specimens, and the
ate to the test program. If the test environment is other than
four-point “C” fixture for Size C specimens. Use a fully
ambient air, supply the environmental chamber with the test
articulating fixture if the specimen parallelism requirements
atmosphere so that the test specimen is completely exposed to
cannot be met.
the test atmosphere. Consistent conditions (composition, sup-
8.3.2 Inspecting and Assembling the Test Fixture—Examine
ply rate, etc.) of the test environment should be maintained
the bearing cylinders to make sure that they are undamaged,
throughout the test series (see 6.4). If the tests are carried out
and that there are no reaction products (corrosion products or
in a humid atmosphere, the relative humidity should not vary
oxidation) that could result in uneven line loading of the test
more than 10% (absolute) during the entire test series. At
specimen or could prevent the bearing cylinders from rolling.
ambient temperatures, determine the relative humidity in
Remove and clean, or replace, the bearing cylinders, if neces-
accordance with Test Method E337. Allow a sufficient period
sary.Avoidanyundesirabledimensionalchangesinthebearing
for equilibration of the test specimen in the test environment.
cylinders, for example, the inadvertent forming a small flat on
8.7 Heating to the Test Temperature—Initiate the tempera-
the cylinder surface when abrasion (e.g., abrasive paper) is
ture data acquisition. Heat the test specimen to the test
used to remove the reaction products from the cylinders. The
temperatureattheselectedheatingrate.Temperatureovershoot
samecareshouldbedirectedtowardthecontactsurfacesofthe
over the test temperature shall be strictly controlled and shall
loading and support members of the test fixture that are in
be no more than 5°C. Maintain the temperature within 6 5°C
contactwiththebearingcylinders.Assemblethetestfixture,so
(soak time) to allow the entire system to reach thermal
thatitisproperlyalignedandcanarticulatewithoutrestraintor
equilibrium. Prior to testing, the soak time should be deter-
significant friction.
mined experimentally at the test temperature. The soak time
8.3.3 Furnace and Environmental Chamber Set Up—Install
shall be stated in the test report.
and assemble the heating/furnace system (and environmental
8.8 Hot-Furnace Loading and Heating (Optional)—Insome
chamber, if used) so that it is properly aligned and functioning
cases,testspecimensmaybeloadeddirectlyintoahotfurnace,
for test specimen heating, environmental control, and testing.
as described in section 8.4 of Test Method C1211. The fixture
8.3.4 Load System Set-Up—Set up and check the load-
may be either left in the furnace for the entire time or removed
control and force measurement devices in the test system. For
partially or completely, depending on the details of the system.
dead weight systems, select and mount the required weights
Exercise care to ensure that the bearing cylinders and test
into the load train. For universal test machines, set the test
specimen are positioned accurately. Furthermore, exercise
mode to load-control.
extreme care to ensure that possible damage associated with
8.4 Test Specimen Loading and Heating:
thermal shock shall not have any effect on strength or slow
8.4.1 Carefully place the test specimen into the test fixture
crack growth, or both, of test specimens. If needed and
to avoid possible damage and contamination and to ensure
possible, place the deflection-measurement probe in contact
alignmentofthetestspecimenrelativetothetestfixture.There
with the midpoint of specimens between the two inner bearing
should be an equal amount of overhang of the test specimen
cylinders, in accordance with 8.4.3. Determine the equilibra-
beyond the outer bearing cylinders and the test specimen shall
tion time of the test specimen at the test temperature experi-
be directly centered below the axis of the applied force.
mentally prior to testing.
Provide a method (e.g., pencil marking in the test specimen or
known positioning of the test specimen relative to a reference 8.9 Conducting the Test—Initiate the data acquisition for
point or surface of the test fixture) to determine the fracture force,temperature,time,anddeflection(ifmeasured).Startthe
location of the test specimen upon fracture. testbyapplyingtheselectedappliedforce(appliedstress)with
C1834 − 16
an accuracy of
...