ASTM C1291-00a(2005)
(Test Method)Standard Test Method for Elevated Temperature Tensile Creep Strain, Creep Strain Rate, and Creep Time-to-Failure for Advanced Monolithic Ceramics
Standard Test Method for Elevated Temperature Tensile Creep Strain, Creep Strain Rate, and Creep Time-to-Failure for Advanced Monolithic Ceramics
SIGNIFICANCE AND USE
Creep tests measure the time-dependent deformation under load at a given temperature, and, by implication, the load-carrying capability of the material for limited deformations. Creep-rupture tests, properly interpreted, provide a measure of the load-carrying capability of the material as a function of time and temperature. The two tests compliment each other in defining the load-carrying capability of a material for a given period of time. In selecting materials and designing parts for service at elevated temperatures, the type of test data used will depend on the criteria for load-carrying capability that best defines the service usefulness of the material.
This test method may be used for material development, quality assurance, characterization, and design data generation.
High-strength, monolithic ceramic materials, generally characterized by small grain sizes (50 μm) and bulk densities near their theoretical density, are candidates for load-bearing structural applications at elevated temperatures. These applications involve components such as turbine blades which are subjected to stress gradients and multiaxial stresses.
Data obtained for design and predictive purposes should be obtained using any appropriate combination of test methods that provide the most relevant information for the applications being considered. It is noted here that ceramic materials tend to creep more rapidly in tension than in compression (1, 2, 3).3 This difference results in time-dependent changes in the stress distribution and the position of the neutral axis when tests are conducted in flexure. As a consequence, deconvolution of flexural creep data to obtain the constitutive equations needed for design cannot be achieved without some degree of uncertainty concerning the form of the creep equations, and the magnitude of the creep rate in tension vis-a-vis the creep rate in compression. Therefore, creep data for design and life prediction should be obtained in both tension a...
SCOPE
1.1 This test method covers the determination of tensile creep strain, creep strain rate, and creep time-to-failure for advanced monolithic ceramics at elevated temperatures, typically between 1073 and 2073 K. A variety of specimen geometries are included. The creep strain at a fixed temperature is evaluated from direct measurements of the gage length extension over the time of the test. The minimum creep strain rate, which may be invariant with time, is evaluated as a function of temperature and applied stress. Creep time-to-failure is also included in this test method.
1.2 This test method is for use with advanced ceramics that behave as macroscopically isotropic, homogeneous, continuous materials. While this test method is intended for use on monolithic ceramics, whisker- or particle-reinforced composite ceramics as well as low-volume-fraction discontinuous fiber-reinforced composite ceramics may also meet these macroscopic behavior assumptions. Continuous fiber-reinforced ceramic composites (CFCCs) do not behave as macroscopically isotropic, homogeneous, continuous materials, and application of this test method to these materials is not recommended.
1.3 The values in SI units are to be regarded as the standard (see IEEE/ASTM SI 10).
1.4 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 appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Standards Content (Sample)
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Designation: C1291 – 00a (Reapproved 2005)
Standard Test Method for
Elevated Temperature Tensile Creep Strain, Creep Strain
Rate, and Creep Time-to-Failure for Advanced Monolithic
Ceramics
This standard is issued under the fixed designation C1291; 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 E6 TerminologyRelatingtoMethodsofMechanicalTesting
E83 Practice for Verification and Classification of Exten-
1.1 This test method covers the determination of tensile
someter Systems
creep strain, creep strain rate, and creep time-to-failure for
E139 Test Methods for Conducting Creep, Creep-Rupture,
advanced monolithic ceramics at elevated temperatures, typi-
and Stress-Rupture Tests of Metallic Materials
cally between 1073 and 2073 K. A variety of specimen
E177 Practice for Use of the Terms Precision and Bias in
geometriesareincluded.Thecreepstrainatafixedtemperature
ASTM Test Methods
is evaluated from direct measurements of the gage length
E220 Test Method for Calibration of Thermocouples By
extension over the time of the test. The minimum creep strain
Comparison Techniques
rate, which may be invariant with time, is evaluated as a
E230 Specification and Temperature-Electromotive Force
function of temperature and applied stress. Creep time-to-
(EMF) Tables for Standardized Thermocouples
failure is also included in this test method.
E639 Test Method for Measuring Total-Radiance Tempera-
1.2 This test method is for use with advanced ceramics that
ture of Heated Surfaces Using a Radiation Pyrometer
behave as macroscopically isotropic, homogeneous, continu-
E691 Practice for Conducting an Interlaboratory Study to
ous materials. While this test method is intended for use on
Determine the Precision of a Test Method
monolithicceramics,whisker-orparticle-reinforcedcomposite
E1012 PracticeforVerificationofTestFrameandSpecimen
ceramics as well as low-volume-fraction discontinuous fiber-
Alignment Under Tensile and Compressive Axial Force
reinforced composite ceramics may also meet these macro-
Application
scopic behavior assumptions. Continuous fiber-reinforced ce-
IEEE/ASTM SI 10 American National Standard for Use of
ramic composites (CFCCs) do not behave as macroscopically
the International System of Units (SI): The Modern Metric
isotropic, homogeneous, continuous materials, and application
System
of this test method to these materials is not recommended.
1.3 The values in SI units are to be regarded as the standard
3. Terminology
(see IEEE/ASTM SI 10 ).
3.1 Definitions—The definitions of terms relating to creep
1.4 This standard does not purport to address all of the
testing, which appear in Section E of Terminology E6 shall
safety concerns, if any, associated with its use. It is the
apply to the terms used in this test method. For the purpose of
responsibility of the user of this standard to establish appro-
this test method only, some of the more general terms are used
priate safety and health practices and determine the applica-
with the restricted meanings given as follows.
bility of regulatory limitations prior to use.
3.2 Definitions of Terms Specific to This Standard:
2. Referenced Documents 3.2.1 axial strain, ´ , [nd], n—average of the strain mea-
a
sured on diametrically opposed sides and equally distant from
2.1 ASTM Standards:
the specimen axis.
E4 Practices for Force Verification of Testing Machines
3.2.2 bending strain, ´ [nd], n—difference between the
b
strain at the surface and the axial strain.
This test method is under the jurisdiction of ASTM Committee C28 on
3.2.2.1 Discussion—In general, it varies from point to point
Advanced Ceramics and is the direct responsibility of Subcommittee C28.01 on
around and along the gage length of the specimen. [E1012]
Mechanical Properties and Performance.
3.2.3 creep-rupture test, n—testinwhichprogressivespeci-
Current edition approved June 1, 2005. Published June 2005. Originally
approved in 1995. Last previous edition approved in 2000 as C1291–00a. DOI:
men deformation and the time-to-failure are measured. In
10.1520/C1291-00AR05.
general, deformation is greater than that developed during a
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
creep test.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
C1291 – 00a (2005)
3.2.4 creep strain, ´, [nd], n—time dependent strain that 4.4 Dataobtainedfordesignandpredictivepurposesshould
occurs after the application of load which is thereafter main- beobtainedusinganyappropriatecombinationoftestmethods
tained constant. Also known as engineering creep strain. that provide the most relevant information for the applications
3.2.5 creep test, n—test that has as its objective the mea- beingconsidered.Itisnotedherethatceramicmaterialstendto
creep more rapidly in tension than in compression (1, 2, 3).
surement of creep and creep rates occurring at stresses usually
well below those that would result in fast fracture. This difference results in time-dependent changes in the stress
distribution and the position of the neutral axis when tests are
3.2.5.1 Discussion—Since the maximum deformation is
only a few percent, a sensitive extensometer is required. conducted in flexure. As a consequence, deconvolution of
flexural creep data to obtain the constitutive equations needed
3.2.6 creep time-to-failure, t , [s], n—time required for a
f
for design cannot be achieved without some degree of uncer-
specimen to fracture under constant load as a result of creep.
tainty concerning the form of the creep equations, and the
3.2.6.1 Discussion—This is also known as creep rupture
magnitude of the creep rate in tension vis-a-vis the creep rate
time.
in compression. Therefore, creep data for design and life
3.2.7 gage length, l, [m], n—original distance between
predictionshouldbeobtainedinbothtensionandcompression,
fiducialmarkersonorattachedtothespecimenfordetermining
as well as the expected service stress state.
elongation.
3.2.8 maximum bending strain, ´ , [nd], n—largest
bmax
5. Interferences
value of bending strain along the gage length. It can be
5.1 Time-Dependent Phenomena—Other time-dependent
calculatedfrommeasurementsofstrainatthreecircumferential
phenomena, such as stress corrosion and slow crack growth,
positions at each of two different longitudinal positions.
−1
can interfere with determination of the creep behavior.
3.2.9 minimum creep strain rate, ´ ,[s ], n—minimum
min
5.2 Chemical Interactions with the Testing Environment—
value of the strain rate prior to specimen failure as measured
The test environment (vacuum, inert gas, ambient air, etc.)
fromthestrain-timecurve.Theminimumcreepstrainratemay
including moisture content (for example, % relative humidity
not necessarily correspond to the steady-state creep strain rate.
(RH))mayhaveastronginfluenceonbothcreepstrainrateand
3.2.10 slow crack growth, n, [m/s], n—subcritical crack
creep rupture life. In particular, materials susceptible to slow
growth (extension) which may result from, but is not restricted
crack growth failure will be strongly influenced by the test
to, such mechanisms as environmentally assisted stress corro-
environment.Surfaceoxidationmaybeeitheractiveorpassive
sion, diffusive crack growth, or other mechanisms.
and thus will have a direct effect on creep behavior by
3.2.11 steady-state creep, ´ , [nd], n—stage of creep
ss
changing the material’s properties. Testing must be conducted
wherein the creep rate is constant with time.
in environments that are either representative of service con-
3.2.11.1 Discussion—Also known as secondary creep.
ditions or inert to the materials being tested depending on the
3.2.12 stress corrosion, n—environmentally induced degra-
performance being evaluated. A controlled gas environment
dation that initiates from the exposed surface.
with suitable effluent controls must be provided for any
3.2.12.1 Discussion—Such environmental effects com-
material that evolves toxic vapors.
monlyincludetheactionofmoisture,aswellasothercorrosive
5.3 Specimen Surfaces—Surface preparation of test speci-
species, often with a strong temperature dependence.
mens can introduce machining flaws that may affect the test
3.2.13 tensile creep strain, ´, [nd], n—creep strain that
t
results. Machining damage imposed during specimen prepara-
occurs as a result of a uniaxial tensile-applied stress.
tionwillmostlikelyresultinprematurefailureofthespecimen
but may also introduce flaws that can grow by slow crack
4. Significance and Use
growth. Surface preparation can also lead to residual stresses
4.1 Creep tests measure the time-dependent deformation
which can be released during the test. Universal or standard-
under load at a given temperature, and, by implication, the
ized methods of surface preparation do not exist. It should be
load-carrying capability of the material for limited deforma-
understood that final machining steps may or may not negate
tions. Creep-rupture tests, properly interpreted, provide a
machiningdamageintroducedduringearlierphasesofmachin-
measure of the load-carrying capability of the material as a
ing which tend to be rougher.
function of time and temperature. The two tests compliment
5.4 Specimen/ExtensometerChemicalIncompatibility—The
eachotherindefiningtheload-carryingcapabilityofamaterial
strain measurement techniques described herein generally rely
foragivenperiodoftime.Inselectingmaterialsanddesigning
on physical contact between extensometer components (con-
parts for service at elevated temperatures, the type of test data
tacting probes or optical method flags) and the specimen so as
used will depend on the criteria for load-carrying capability
to measure changes in the gage section as a function of time.
that best defines the service usefulness of the material.
Flag attachment methods and extensometer contact materials
4.2 Thistestmethodmaybeusedformaterialdevelopment,
must be chosen with care to ensure that no adverse chemical
qualityassurance,characterization,anddesigndatageneration.
reactions occur during testing. Normally, this is not a problem
4.3 High-strength, monolithic ceramic materials, generally
if specimen/probe materials that are mutually chemically inert
characterized by small grain sizes (<50 µm) and bulk densities
are employed (for example, SiC probes on Si N specimens).
3 4
near their theoretical density, are candidates for load-bearing
structural applications at elevated temperatures. These appli-
cations involve components such as turbine blades which are
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
subjected to stress gradients and multiaxial stresses. this test method.
C1291 – 00a (2005)
The user must be aware that impurities or second phases in the 6.2.1 Various types of gripping devices may be used to
flags or specimens may be mutually chemically reactive and transmit the measured load applied by the testing machine to
could influence the results. the test specimens. The brittle nature of advanced ceramics
5.5 Specimen Bending—Bending in uniaxial tensile tests requires a uniform interface between the grip components and
can cause extraneous strains or promote accelerated rupture thegrippedsectionofthespecimen.Lineorpointcontactsand
times. Since maximum or minimum stresses will occur at the nonuniform pressure can produce Hertzian-type stresses lead-
surface where strain measurements are made, bending may ing to crack initiation and fracture of the specimen in the
introduce either an over or under measurement of axial strain, gripped section. Gripping devices can be classed generally as
if the measurement is made only on one side of the tensile those employing active and those employing passive grip
specimen. Similarly, bending stresses may accentuate surface interfaces as discussed in the following sections. Regardless of
oxidation and may also accentuate the severity of surface the type of gripping device chosen, it must be consistent with
flaws. the thermal requirements imposed on it by the elevated
5.6 Temperature Variations—Creepstrainisoftenrelatedto temperature nature of creep testing. This requirement may
temperaturethroughanexponentialfunction.Thusfluctuations preclude the use of some material combinations and gripping
in test temperature or change in temperature profile along the designs.
length of the specimen in real time can cause fluctuations in
6.2.1.1 Active Grip Interfaces—Active grip interfaces re-
strain measurements or changes in creep rate.
quire a continuous application of a mechanical, hydraulic, or
pneumatic force to transmit the load applied by the test
6. Apparatus
machine to the test specimen. Generally, these types of grip
6.1 Load Testing Machine:
interfaces cause a load to be applied normal to the surface of
6.1.1 Specimens may be loaded in any suitable testing
the gripped section of the specimen. Transmission of the
machine provided that uniform, direct loading can be main-
uniaxial load applied by the test machine is then accomplished
tained.Thetestingmachinemustmaintainthedesiredconstant
by friction between the specimen and the grip faces. Thus,
load on the specimen regardless of specimen deformation with
important aspects of active grip interfaces are uniform contact
time,eitherthroughdead-weightloadingorthroughactiveload
betweenthegrippedsectionofthespecimenandthegripfaces,
control. The force measuring system can be equipped with a
and constant coefficient of friction over the grip/specimen
means for retaining readout of the force, or the force can be
interface.
recorded manually. The accuracy of the testing machine must
(1) For cylindrical specimens, a one-piece split collet ar-
be in accordance with Practices E4.
rangement acts as the grip interface (4, 5). Generally, close
6.1.2 AllowableBending—Allowablebending,asdefinedin
tolerances are required for concentricity of both the grip and
Practice E1012, should not exceed 5%. This is based on the
specimen diameters. In addition, the diameter of the gripped
same assumptions as those for tensile strength testing (see Ref
section of the specimen and the unclamped, open diameter of
4, for example). It should be noted that unless percent bending
the grip faces must be within similarly close tolerances to
is monitored until the end-of-test condition
...
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