ASTM C1291-00a(2010)
(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). 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 an...
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 ).
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 2010)
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 2. Referenced Documents
2.1 ASTM Standards:
1.1 This test method covers the determination of tensile
E4Practices for Force Verification of Testing Machines
creep strain, creep strain rate, and creep time-to-failure for
E6Terminology Relating to Methods of Mechanical Testing
advanced monolithic ceramics at elevated temperatures, typi-
E83Practice for Verification and Classification of Exten-
cally between 1073 and 2073 K. A variety of specimen
someter Systems
geometriesareincluded.Thecreepstrainatafixedtemperature
E139Test Methods for Conducting Creep, Creep-Rupture,
is evaluated from direct measurements of the gage length
and Stress-Rupture Tests of Metallic Materials
extension over the time of the test. The minimum creep strain
E177Practice for Use of the Terms Precision and Bias in
rate, which may be invariant with time, is evaluated as a
ASTM Test Methods
function of temperature and applied stress. Creep time-to-
E220Test Method for Calibration of Thermocouples By
failure is also included in this test method.
Comparison Techniques
E230Specification and Temperature-Electromotive Force
1.2 This test method is for use with advanced ceramics that
(EMF) Tables for Standardized Thermocouples
behave as macroscopically isotropic, homogeneous, continu-
E639Test Method for Measuring Total-Radiance Tempera-
ous materials. While this test method is intended for use on
ture of Heated Surfaces Using a Radiation Pyrometer
monolithicceramics,whisker-orparticle-reinforcedcomposite
(Withdrawn 2011)
ceramics as well as low-volume-fraction discontinuous fiber-
E691Practice for Conducting an Interlaboratory Study to
reinforced composite ceramics may also meet these macro-
Determine the Precision of a Test Method
scopic behavior assumptions. Continuous fiber-reinforced ce-
E1012Practice for Verification of Testing Frame and Speci-
ramic composites (CFCCs) do not behave as macroscopically
men Alignment Under Tensile and Compressive Axial
isotropic, homogeneous, continuous materials, and application
Force Application
of this test method to these materials is not recommended.
IEEE/ASTM SI 10 American National Standard for Use of
1.3 The values in SI units are to be regarded as the standard theInternationalSystemofUnits(SI):TheModernMetric
System
(see IEEE/ASTM SI 10 ).
1.4 This standard does not purport to address all of the
3. Terminology
safety concerns, if any, associated with its use. It is the
3.1 Definitions—The definitions of terms relating to creep
responsibility of the user of this standard to establish appro-
testing, which appear in Section E of Terminology E6 shall
priate safety and health practices and determine the applica-
apply to the terms used in this test method. For the purpose of
bility of regulatory limitations prior to use.
this test method only, some of the more general terms are used
with the restricted meanings given as follows.
3.2 Definitions of Terms Specific to This Standard:
1 2
This test method is under the jurisdiction of ASTM Committee C28 on For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Advanced Ceramics and is the direct responsibility of Subcommittee C28.01 on contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Mechanical Properties and Performance. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved June 1, 2010. Published November 2010. Originally the ASTM website.
approved in 1995. Last previous edition approved in 2005 as C1291– 00a (2005). The last approved version of this historical standard is referenced on
DOI: 10.1520/C1291-00AR10. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1291 − 00a (2010)
3.2.1 axial strain, ε , [nd], n—average of the strain mea- function of time and temperature. The two tests compliment
a
sured on diametrically opposed sides and equally distant from eachotherindefiningtheload-carryingcapabilityofamaterial
the specimen axis. foragivenperiodoftime.Inselectingmaterialsanddesigning
parts for service at elevated temperatures, the type of test data
3.2.2 bending strain, ε [nd], n—difference between the
b
used will depend on the criteria for load-carrying capability
strain at the surface and the axial strain.
that best defines the service usefulness of the material.
3.2.2.1 Discussion—In general, it varies from point to point
around and along the gage length of the specimen. [E1012] 4.2 Thistestmethodmaybeusedformaterialdevelopment,
qualityassurance,characterization,anddesigndatageneration.
3.2.3 creep-rupture test, n—test in which progressive speci-
men deformation and the time-to-failure are measured. In
4.3 High-strength, monolithic ceramic materials, generally
general, deformation is greater than that developed during a
characterized by small grain sizes (<50 µm) and bulk densities
creep test.
near their theoretical density, are candidates for load-bearing
structural applications at elevated temperatures. These appli-
3.2.4 creep strain, ε, [nd], n—time dependent strain that
cations involve components such as turbine blades which are
occurs after the application of load which is thereafter main-
subjected to stress gradients and multiaxial stresses.
tained constant. Also known as engineering creep strain.
4.4 Dataobtainedfordesignandpredictivepurposesshould
3.2.5 creep test, n—test that has as its objective the mea-
beobtainedusinganyappropriatecombinationoftestmethods
surement of creep and creep rates occurring at stresses usually
that provide the most relevant information for the applications
well below those that would result in fast fracture.
beingconsidered.Itisnotedherethatceramicmaterialstendto
3.2.5.1 Discussion—Since the maximum deformation is
creep more rapidly in tension than in compression (1, 2, 3).
only a few percent, a sensitive extensometer is required.
This difference results in time-dependent changes in the stress
3.2.6 creep time-to-failure, t, [s], n—time required for a
f
distribution and the position of the neutral axis when tests are
specimen to fracture under constant load as a result of creep.
conducted in flexure. As a consequence, deconvolution of
3.2.6.1 Discussion—This is also known as creep rupture
flexural creep data to obtain the constitutive equations needed
time.
for design cannot be achieved without some degree of uncer-
3.2.7 gage length, l, [m], n—original distance between
tainty concerning the form of the creep equations, and the
fiducialmarkersonorattachedtothespecimenfordetermining
magnitude of the creep rate in tension vis-a-vis the creep rate
elongation.
in compression. Therefore, creep data for design and life
3.2.8 maximum bending strain, ε , [nd], n—largestvalue predictionshouldbeobtainedinbothtensionandcompression,
bmax
of bending strain along the gage length. It can be calculated
as well as the expected service stress state.
from measurements of strain at three circumferential positions
at each of two different longitudinal positions. 5. Interferences
−1
3.2.9 minimum creep strain rate, ε ,[s ], n—minimum 5.1 Time-Dependent Phenomena—Other time-dependent
min
value of the strain rate prior to specimen failure as measured
phenomena, such as stress corrosion and slow crack growth,
fromthestrain-timecurve.Theminimumcreepstrainratemay can interfere with determination of the creep behavior.
not necessarily correspond to the steady-state creep strain rate.
5.2 Chemical Interactions with the Testing Environment—
3.2.10 slow crack growth, ν, [m/s], n—subcritical crack
The test environment (vacuum, inert gas, ambient air, etc.)
growth (extension) which may result from, but is not restricted
including moisture content (for example, % relative humidity
to, such mechanisms as environmentally assisted stress
(RH))mayhaveastronginfluenceonbothcreepstrainrateand
corrosion, diffusive crack growth, or other mechanisms.
creep rupture life. In particular, materials susceptible to slow
crack growth failure will be strongly influenced by the test
3.2.11 steady-state creep, ε , [nd], n—stage of creep
ss
environment.Surfaceoxidationmaybeeitheractiveorpassive
wherein the creep rate is constant with time.
and thus will have a direct effect on creep behavior by
3.2.11.1 Discussion—Also known as secondary creep.
changing the material’s properties. Testing must be conducted
3.2.12 stress corrosion, n—environmentally induced degra-
in environments that are either representative of service con-
dation that initiates from the exposed surface.
ditions or inert to the materials being tested depending on the
3.2.12.1 Discussion—Such environmental effects com-
performance being evaluated. A controlled gas environment
monlyincludetheactionofmoisture,aswellasothercorrosive
with suitable effluent controls must be provided for any
species, often with a strong temperature dependence.
material that evolves toxic vapors.
3.2.13 tensile creep strain, ε, [nd], n—creep strain that
t
5.3 Specimen Surfaces—Surface preparation of test speci-
occurs as a result of a uniaxial tensile-applied stress.
mens can introduce machining flaws that may affect the test
results. Machining damage imposed during specimen prepara-
4. Significance and Use
tionwillmostlikelyresultinprematurefailureofthespecimen
4.1 Creep tests measure the time-dependent deformation
but may also introduce flaws that can grow by slow crack
under load at a given temperature, and, by implication, the
load-carrying capability of the material for limited deforma-
tions. Creep-rupture tests, properly interpreted, provide a
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
measure of the load-carrying capability of the material as a this test method.
C1291 − 00a (2010)
growth. Surface preparation can also lead to residual stresses beginning and the end of each test series. An additional
which can be released during the test. Universal or standard- verification of alignment is recommended, although not
ized methods of surface preparation do not exist. It should be required, at the middle of the test series. Either a dummy or
understood that final machining steps may or may not negate actual test specimen may be used. Tensile specimens used for
machiningdamageintroducedduringearlierphasesofmachin- alignment verification should be equipped with a recom-
ing which tend to be rougher. mended eight separate longitudinal strain gages to determine
bending contributions from both eccentric and angular mis-
5.4 Specimen/Extensometer Chemical Incompatibility—The
alignment of the grip heads. (Although it is possible to use a
strain measurement techniques described herein generally rely
minimum of six separate longitudinal strain gages for speci-
on physical contact between extensometer components (con-
mens with circular cross sections, eight strain gages are
tacting probes or optical method flags) and the specimen so as
recommendedhereforsimplicityandconsistencyindescribing
to measure changes in the gage section as a function of time.
the technique for both circular and rectangular cross sections.)
Flag attachment methods and extensometer contact materials
If dummy specimens are used for alignment verification, they
must be chosen with care to ensure that no adverse chemical
should have the same geometry and dimensions as the actual
reactions occur during testing. Normally, this is not a problem
test specimens as well as an elastic modulus that closely
if specimen/probe materials that are mutually chemically inert
matches that of the test material to ensure similar axial and
are employed (for example, SiC probes on Si N specimens).
3 4
bending stiffness characteristics.
The user must be aware that impurities or second phases in the
flags or specimens may be mutually chemically reactive and 6.2 Gripping Devices:
could influence the results.
6.2.1 Various types of gripping devices may be used to
transmit the measured load applied by the testing machine to
5.5 Specimen Bending—Bending in uniaxial tensile tests
the test specimens. The brittle nature of advanced ceramics
can cause extraneous strains or promote accelerated rupture
requires a uniform interface between the grip components and
times. Since maximum or minimum stresses will occur at the
thegrippedsectionofthespecimen.Lineorpointcontactsand
surface where strain measurements are made, bending may
nonuniform pressure can produce Hertzian-type stresses lead-
introduce either an over or under measurement of axial strain,
ing to crack initiation and fracture of the specimen in the
if the measurement is made only on one side of the tensile
gripped section. Gripping devices can be classed generally as
specimen. Similarly, bending stresses may accentuate surface
those employing active and those employing passive grip
oxidation and may also accentuate the severity of surface
interfaces as discussed in the following sections. Regardless of
flaws.
the type of gripping device chosen, it must be consistent with
5.6 Temperature Variations—Creep strain is often related to
the thermal requirements imposed on it by the elevated
temperaturethroughanexponentialfunction.Thusfluctuations
temperature nature of creep testing. This requirement may
in test temperature or change in temperature profile along the
preclude the use of some material combinations and gripping
length of the specimen in real time can cause fluctuations in
designs.
strain measurements or changes in creep rate.
6.2.1.1 Active Grip Interfaces—Active grip interfaces re-
quire a continuous application of a mechanical, hydraulic, or
6. Apparatus
pneumatic force to transmit the load applied by the test
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
...
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