ASTM C1291-00
(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
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 Practice E380).
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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Designation: C 1291 – 00
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 C 1291; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope E 139 Practice for Conducting Creep, Creep-Rupture, and
Stress-Rupture Tests of Metallic Materials
1.1 This test method covers the determination of tensile
E 177 Practice for Use of the Terms Precision and Bias in
creep strain, creep strain rate, and creep time-to-failure for
ASTM Test Methods
advanced monolithic ceramics at elevated temperatures, typi-
E 220 Test Method for Calibration of Thermocouples by
cally between 1073 and 2073 K. A variety of specimen
Comparison Techniques
geometries are included. The creep strain at a fixed temperature
E 230 Temperature-Electromotive Force (EMF) Tables for
is evaluated from direct measurements of the gage length
Standardized Thermocouples
extension over the time of the test. The minimum creep strain
E 380 Practice for Use of the International System of Units
rate, which may be invariant with time, is evaluated as a
(SI)
function of temperature and applied stress. Creep time-to-
E 639 Test Method for Measuring Total-Radiance Tempera-
failure is also included in this test method.
ture of Heated Surfaces Using a Radiation Pyrometer
1.2 This test method is for use with advanced ceramics that
E 691 Practice for Conducting an Interlaboratory Study to
behave as macroscopically isotropic, homogeneous, continu-
Determine the Precision of a Test Method
ous materials. While this test method is intended for use on
E 1012 Practice for Verification of Specimen Alignment
monolithic ceramics, whisker- or particle-reinforced composite
Under Tensile Loading
ceramics as well as low-volume-fraction discontinuous fiber-
reinforced composite ceramics may also meet these macro-
3. Terminology
scopic behavior assumptions. Continuous fiber-reinforced ce-
3.1 Definitions—The definitions of terms relating to creep
ramic composites (CFCCs) do not behave as macroscopically
testing, which appear in Section E of Terminology E 6 shall
isotropic, homogeneous, continuous materials, and application
apply to the terms used in this test method. For the purpose of
of this test method to these materials is not recommended.
this test method only, some of the more general terms are used
1.3 The values in SI units are to be regarded as the standard
with the restricted meanings given as follows.
(see Practice E 380).
3.2 Definitions of Terms Specific to This Standard:
1.4 This standard does not purport to address all of the
3.2.1 axial strain, e , [nd], n—the average of the strain
a
safety concerns, if any, associated with its use. It is the
measured on diametrically opposed sides and equally distant
responsibility of the user of this standard to establish appro-
from the specimen axis.
priate safety and health practices and determine the applica-
3.2.2 bending strain, e [nd], n—the difference between the
b
bility of regulatory limitations prior to use.
strain at the surface and the axial strain.
2. Referenced Documents 3.2.2.1 Discussion—In general, it varies from point to point
around and along the gage length of the specimen. [E 1012]
2.1 ASTM Standards:
2 3.2.3 creep-rupture test, n— a test in which progressive
E 4 Practices for Force Verification of Testing Machines
specimen deformation and the time-to-failure are measured. In
E 6 Terminology Relating to Methods of Mechanical Test-
2 general, deformation is greater than that developed during a
ing
creep test.
E 83 Practice for Verification and Classification of Exten-
2 3.2.4 creep strain, e, [nd], n— the time dependent strain
someters
that occurs after the application of load which is thereafter
maintained constant. Also known as engineering creep strain.
This test method is under the jurisdiction of ASTM Committee C-28 on
Advanced Ceramics and is the direct responsibility of Subcommittee C28.01 on
Properties and Performance. Annual Book of ASTM Standards, Vol 14.02.
Current edition approved June 10, 2000. Published October 2000. Originally Annual Book of ASTM Standards, Vol 14.03.
e1 5
published as C 1291 – 95. Last previous edition 1291 – 95 Discontinued 1997; Replaced by IEEE/ASTM SI-10.
2 6
Annual Book of ASTM Standards, Vol 03.01. Annual Book of ASTM Standards, Vol 15.03.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
C 1291
3.2.5 creep test, n—a test that has as its objective the creep more rapidly in tension than in compression (1, 2, 3).
measurement of creep and creep rates occurring at stresses This difference results in time-dependent changes in the stress
usually well below those that would result in fast fracture. distribution and the position of the neutral axis when tests are
3.2.5.1 Discussion—Since the maximum deformation is conducted in flexure. As a consequence, deconvolution of
only a few percent, a sensitive extensometer is required. flexural creep data to obtain the constitutive equations needed
3.2.6 creep time-to-failure, t , [s], n—the time required for for design cannot be achieved without some degree of uncer-
f
a 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—the original distance between prediction should be obtained in both tension and compression,
fiducial markers on or attached to the specimen for determining as well as the expected service stress state.
elongation.
5. Interferences
3.2.8 maximum bending strain, e , [nd], n—the largest
bmax
5.1 Time-Dependent Phenomena—Other time-dependent
value of bending strain along the gage length. It can be
phenomena, such as stress corrosion and slow crack growth,
calculated from measurements of strain at three circumferential
can interfere with determination of the creep behavior.
positions at each of two different longitudinal positions.
−1
5.2 Chemical Interactions with the Testing Environment—
3.2.9 minimum creep strain rate, e ,[s ], n—minimum
min
The test environment (vacuum, inert gas, ambient air, etc.)
value of the strain rate prior to specimen failure as measured
including moisture content (for example, % relative humidity
from the strain-time curve. The minimum creep strain rate may
(RH)) may have a strong influence on both creep strain rate and
not necessarily correspond to the steady-state creep strain rate.
creep rupture life. In particular, materials susceptible to slow
3.2.10 slow crack growth, n, [m/s], n—subcritical crack
crack growth failure will be strongly influenced by the test
growth (extension) which may result from, but is not restricted
environment. Surface oxidation may be either active or passive
to, such mechanisms as environmentally assisted stress corro-
and thus will have a direct effect on creep behavior by
sion, diffusive crack growth, or other mechanisms.
changing the material’s properties. Testing must be conducted
3.2.11 steady-state creep, e , [nd], n—a stage of creep
ss
in environments that are either representative of service con-
wherein the creep rate is constant with time.
ditions or inert to the materials being tested depending on the
3.2.11.1 Discussion—Also known as secondary creep.
performance being evaluated. A controlled gas environment
3.2.12 stress corrosion, n—environmentally induced degra-
with suitable effluent controls must be provided for any
dation that initiates from the exposed surface.
material that evolves toxic vapors.
3.2.12.1 Discussion—Such environmental effects com-
5.3 Specimen Surfaces—Surface preparation of test speci-
monly include the action of moisture, as well as other corrosive
mens can introduce machining flaws that may affect the test
species, often with a strong temperature dependence.
results. Machining damage imposed during specimen prepara-
3.2.13 tensile creep strain, e , [nd], n—creep strain that
t
tion will most likely result in premature failure of the specimen
occurs as a result of a uniaxial tensile-applied stress.
but may also introduce flaws that can grow by slow crack
4. Significance and Use
growth. Surface preparation can also lead to residual stresses
which can be released during the test. Universal or standard-
4.1 Creep tests measure the time-dependent deformation
ized methods of surface preparation do not exist. It should be
under load at a given temperature, and, by implication, the
understood that final machining steps may or may not negate
load-carrying capability of the material for limited deforma-
machining damage introduced during earlier phases of machin-
tions. Creep-rupture tests, properly interpreted, provide a
ing which tend to be rougher.
measure of the load-carrying capability of the material as a
5.4 Specimen/Extensometer Chemical Incompatibility—The
function of time and temperature. The two tests compliment
strain measurement techniques described herein generally rely
each other in defining the load-carrying capability of a material
on physical contact between extensometer components (con-
for a given period of time. In selecting materials and designing
tacting probes or optical method flags) and the specimen so as
parts for service at elevated temperatures, the type of test data
to measure changes in the gage section as a function of time.
used will depend on the criteria for load-carrying capability
Flag attachment methods and extensometer contact materials
that best defines the service usefulness of the material.
must be chosen with care to ensure that no adverse chemical
4.2 This test method may be used for material development,
reactions occur during testing. Normally, this is not a problem
quality assurance, characterization, and design data generation.
if specimen/probe materials that are mutually chemically inert
4.3 High-strength, monolithic ceramic materials, generally
are employed (for example, SiC probes on Si N specimens).
characterized by small grain sizes (<50 μm) and bulk densities
3 4
The user must be aware that impurities or second phases in the
near their theoretical density, are candidates for load-bearing
flags or specimens may be mutually chemically reactive and
structural applications at elevated temperatures. These appli-
could influence the results.
cations involve components such as turbine blades which are
5.5 Specimen Bending—Bending in uniaxial tensile tests
subjected to stress gradients and multiaxial stresses.
can cause extraneous strains or promote accelerated rupture
4.4 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
The boldface numbers in parentheses refer to the list of references at the end of
being considered. It is noted here that ceramic materials tend to this test method.
C 1291
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—Creep strain is often related to temperature nature of creep testing. This requirement may
temperature through an exponential function. Thus fluctuations 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. The testing machine must maintain the desired constant
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, either through dead-weight loading or through active load
between the gripped section of the specimen and the grip faces,
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 Practice E 4.
rangement acts as the grip interface (4, 5). Generally, close
6.1.2 Allowable Bending—Allowable bending, as defined in
tolerances are required for concentricity of both the grip and
Practice E 1012, 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 has been reached,
promote uniform contact at the specimen/grip interface. Toler-
there will be no record of percent bending for each specimen.
ances will vary depending on the exact configuration used.
The testing system alignment including the test machine,
(
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