ASTM C1337-96(2005)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:C1337–96 (Reapproved 2005)
Standard Test Method for
Creep and Creep Rupture of Continuous Fiber-Reinforced
Ceramic Composites under Tensile Loading at Elevated
Temperatures
This standard is issued under the fixed designation C1337; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope C1275 Test Method for Monotonic Tensile Behavior of
Continuous Fiber-Reinforced Advanced Ceramics with
1.1 This test method covers the determination of the time-
Solid Rectangular Cross-Section Test Specimens atAmbi-
dependent deformation and time-to-rupture of continuous
ent Temperature
fiber-reinforced ceramic composites under constant tensile
D3878 Terminology for Composite Materials
loading at elevated temperatures. This test method addresses,
E4 Practices for Force Verification of Testing Machines
but is not restricted to, various suggested test specimen
E6 TerminologyRelatingtoMethodsofMechanicalTesting
geometries. In addition, specimen fabrication methods, allow-
E83 Practice for Verification and Classification of Exten-
able bending, temperature measurements, temperature control,
someter Systems
data collection, and reporting procedures are addressed.
E139 Test Methods for Conducting Creep, Creep-Rupture,
1.2 This test method is intended primarily for use with all
and Stress-Rupture Tests of Metallic Materials
advanced ceramic matrix composites with continuous fiber
E220 Test Method for Calibration of Thermocouples By
reinforcement: unidirectional (1-D), bidirectional (2-D), and
Comparison Techniques
tridirectional (3-D). In addition, this test method may also be
E230 Specification and Temperature-Electromotive Force
used with glass matrix composites with 1-D, 2-D, and 3-D
(EMF) Tables for Standardized Thermocouples
continuous fiber reinforcement. This test method does not
E337 Test Method for Measuring Humidity with a Psy-
address directly discontinuous fiber-reinforced, whisker-
chrometer (the Measurement of Wet- and Dry-Bulb Tem-
reinforced,orparticulate-reinforcedceramics,althoughthetest
peratures)
methods detailed here may be equally applicable to these
E1012 PracticeforVerificationofTestFrameandSpecimen
composites.
Alignment Under Tensile and Compressive Axial Force
1.3 Values expressed in this test method are in accordance
Application
withtheInternationalSystemofUnits(SI)andIEEE/ASTMSI
IEEE/ASTM SI 10 American National Standard for Use of
10 .
the International System of Units (SI): The Modern Metric
1.4 This standard does not purport to address all of the
System
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
3. Terminology
priate safety and health practices and determine the applica-
3.1 Definitions—The definitions of terms relating to tensile
bility of regulatory limitations prior to use. Hazard statements
testing appearing inTerminology E6 apply to the terms used in
are noted in 7.1 and 7.2.
this test method. The definitions relating to advanced ceramics
2. Referenced Documents appearinginTerminologyC1145applytothetermsusedinthis
test method. The definitions of terms relating to fiber rein-
2.1 ASTM Standards:
forced composites appearing in Terminology D3878 apply to
C1145 Terminology of Advanced Ceramics
the terms used in this test method. Additional terms used in
conjunction with this test method are defined in the following:
This test method is under the jurisdiction of ASTM Committee C28 on
3.1.1 continuous fiber-reinforced ceramic matrix composite
Advanced Ceramics and is the direct responsibility of Subcommittee C28.07 on
(CFCC)—ceramic matrix composite in which the reinforcing
Ceramic Matrix Composites.
phase consists of a continuous fiber, continuous yarn, or a
Current edition approved June 1, 2005. Published June 2005. Originally
approved in 1996. Last previous edition approved in 2000 as C1337 – 96 (2000).
woven fabric.
DOI: 10.1520/C1337-96R05.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
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.
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C1337–96 (2005)
3.1.2 fracture strength—tensile stress which the material properties of the entire, full-size end product or its in-service
sustains at the instant of fracture. Fracture strength is calcu- behavior in different environments or at various elevated
lated from the load at fracture during a tension test carried to temperatures.
rupture and the original cross-sectional area of the specimen. 4.6 For quality control purposes, results derived from stan-
3.1.2.1 Discussion—In some cases, the fracture strength dardizedtensiletestspecimensmaybeconsideredindicativeof
may be identical to the tensile strength if the load at fracture is the response of the material from which they were taken for
the maximum for the test. Factors such as load train compli- given primary processing conditions and post-processing heat
ance and fiber pull-out behavior may influence the fracture treatments.
strength.
5. Interferences
3.1.3 proportional limit stress—greatest stress which a ma-
5.1 Test environment (vacuum, inert gas, ambient air, etc.)
terial is capable of sustaining without any deviation from
including moisture content (for example, relative humidity)
proportionality of stress to strain (Hooke’s law).
may have an influence on the creep and creep rupture behavior
3.1.3.1 Discussion—Many experiments have shown that
of CFCCs. In particular, the behavior of materials susceptible
values observed for the proportional limit vary greatly with the
to slow crack growth fracture and oxidation will be strongly
sensitivity and accuracy of the testing equipment, eccentricity
influenced by test environment and test temperature. Testing
of loading, the scale to which the stress-strain diagram is
can be conducted in environments representative of service
plotted, and other factors. When determination of proportional
conditions to evaluate material performance under these con-
limit is required, the procedure and sensitivity of the test
ditions.
equipment shall be specified.
5.2 Surface preparation of test specimens, although nor-
3.1.4 slow crack growth—subcritical crack growth (exten-
mally not considered a major concern with CFCCs, can
sion) which may result from, but is not restricted to, such
introducefabricationflawswhichmayhavepronouncedeffects
mechanisms as environmentally assisted stress corrosion or
on the mechanical properties and behavior (for example, shape
diffusive crack growth.
and level of the resulting stress-strain-time curve, etc.). Ma-
4. Significance and Use
chiningdamageintroducedduringspecimenpreparationcanbe
4.1 This test method may be used for material development, either a random interfering factor in the ultimate strength of
material comparison, quality assurance, characterization, and pristine material (that is, increased frequency of surface-
design data generation. initiated fractures compared to volumeinitiated fractures) or an
4.2 Continuous fiber-reinforced ceramic matrix composites inherent part of the strength characteristics to be measured.
are candidate materials for structural applications requiring Surfacepreparationcanalsoleadtotheintroductionofresidual
high degrees of wear and corrosion resistance and toughness at stresses. Universal or standardized test methods of surface
high temperatures. preparation do not exist. It should be understood that final
4.3 Creep tests measure the time-dependent deformation of machining steps may or may not negate machining damage
a material under constant load at a given temperature. Creep introduced during the initial machining. Thus, specimen fabri-
rupture tests provide a measure of the life of the material when cation history may play an important role in the measured
subjected to constant mechanical loading at elevated tempera- time-to-failure or deformation, and shall be reported. In addi-
tures. In selecting materials and designing parts for service at tion, the nature of fabrication used for certain composites (for
elevatedtemperatures,thetypeoftestdatausedwilldependon example, chemical vapor infiltration or hot pressing) may
the criteria for load carrying capability which best defines the require the testing of specimens in the as-processed condition
service usefulness of the material. (that is, it may not be possible to machine the specimen faces
4.4 Creepandcreeprupturetestsprovideinformationonthe without compromising the in-plane fiber architecture).
time-dependent deformation and on the time-of-failure of 5.3 Bending in uniaxial tests does induce nonuniform stress
materials subjected to uniaxial tensile stresses at elevated distributions. Bending may be introduced from several sources
temperatures. Uniform stress states are required to effectively including misaligned load trains, eccentric or misshaped speci-
evaluate any nonlinear stress-strain behavior which may de- mens, and nonuniformly heated specimens or grips. In addi-
velop as the result of cumulative damage processes (for tion, if deformations or strains are measured at surfaces where
example, matrix cracking, matrix/fiber debonding, fiber frac- maximum or minimum stresses occur, bending may introduce
ture, delamination, etc.) which may be influenced by testing over or under measurement of strains depending on the
mode, testing rate, processing or alloying effects, environmen- location of the strain measuring device on the specimen.
tal influences, or elevated temperatures. Some of these effects Similarly, fracture from surface flaws may be accentuated or
may be consequences of stress corrosion or subcritical (slow) suppressed by the presence of the nonuniform stresses caused
crack growth. It is noted that ceramic materials typically creep by bending.
more rapidly in tension than in compression. Therefore, creep 5.4 Fractures that initiate outside the uniformly stressed
data for design and life prediction should be obtained in both gage section of a specimen may be due to factors such as stress
tension and compression. concentrations or geometrical transitions, extraneous stresses
4.5 The results of tensile creep and tensile creep rupture introduced by gripping or thermal gradients, or strength limit-
tests of specimens fabricated to standardized dimensions from ing features in the microstructure of the specimen. Such
a particular material or selected portions of a part, or both, may non-gage section fractures will normally constitute invalid
not totally represent the creep deformation and creep rupture tests.Inaddition,forface-loadedgeometries,grippingpressure
C1337–96 (2005)
is a key variable in the initiation of fracture. Insufficient warm grips and generally reduce the thermal gradient in the
pressure can shear the outer plies in laminated CFCCs, while specimen but at the expense of using high-temperature alloy
too much pressure can cause local crushing of the CFCC and grips and increased degradation of the grips due to exposure to
lead to fracture in the vicinity of the grips. the elevated-temperature environment. Cooled grips located
5.5 The time-dependent stress redistribution that occurs at outside the heated zone are termed cold grips and generally
elevated temperatures among the CFCC constituents makes it induce a steep thermal gradient along the length of the
necessary that the precise loading history of a creep specimen specimen.
be specified. This is of particular importance since the rate at
NOTE 1—The expense of the cooling system for cold grips is balanced
which a creep load is initially applied can influence the
against maintaining alignment that remains consistent from test to test
subsequent creep behavior and damage modes. For example, (stable grip temperature) and decreased degradation of the grips due to
exposure to the elevated-temperature environment. When grip cooling is
whether matrix cracking would occur at the end of loading will
employed, provisions shall be provided to control the cooling medium to
depend on the magnitude of the loading rate, the test stress, the
maximum fluctuations of 5 K (less than 1 K preferred) about a setpoint
test temperature and the relative creep resistance of the matrix
temperature over the course of the test to minimize thermally induced
,
3 4
with respect to that of the fibers.
strain changes in the specimen. In addition, opposing grip temperatures
5.6 WhenCFCCsaremechanicallyunloadedeitherpartially
shouldbemaintainedatuniformandconsistenttemperaturesnottoexceed
or totally after a creep test during which the specimen
a difference 65 K (less than 61 K preferred) so as to avoid inducing
accumulated time-dependent deformation, the specimen may unequal thermal gradients and subsequent nonuniaxial stresses in the
specimen. Generally, the need for control of grip temperature fluctuations
exhibit creep recovery as manifested by a time-dependent
or differences may be indicated if specimen gage section temperatures
reductionofstrain.Therateofcreeprecoveryisusuallyslower
cannot be maintained within the limits prescribed in 9.2.2.
than the rate of creep deformation, and both creep and creep
6.2.1.1 Active Grip Interfaces—Active grip interfaces re-
recovery are in most cases thermally activated processes,
quire a continuous application of a mechanical, hydraulic, or
making them quite sensitive to temperature. Often it is desired
pneumatic force to transmit the load to the test specimen.
to determine the retained strength of a CFCC after being
Generally, these types of grip interfaces cause a load to be
subjected to creep for a prescribed period of time.Therefore, it
applied normal to the surface of the gripped section of the
is customary to unload the specimen from the creep stress and
specimen.Transmission of the uniaxial load applied by the test
then reload it monotonically until failure. Under these circum-
machine is then accomplished by friction between the speci-
stances, the time elapsed between the end of the creep test and
men and the grip faces. Thus, important aspects of active grip
the conduction of the monotonic fast fracture test to determine
interfaces are: (1) uniform contact between the gripped section
the retained strength as well as the loading and unloading rates
of the specimen and the grip faces, and (2) constant coefficient
will
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