ASTM C1337-17

Standard Test Method for Creep and Creep Rupture of Continuous Fiber-Reinforced Advanced Ceramics Under Tensile Loading at Elevated Temperatures

SIGNIFICANCE AND USE
4.1 This test method may be used for material development, material comparison, quality assurance, characterization, and design data generation.  
4.2 Continuous fiber-reinforced ceramic matrix composites are candidate materials for structural applications requiring high degrees of wear and corrosion resistance and toughness at high temperatures.  
4.3 Creep tests measure the time-dependent deformation of a material under constant load at a given temperature. Creep rupture tests provide a measure of the life of the material when subjected to constant mechanical loading at elevated temperatures. 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 which best defines the service usefulness of the material.  
4.4 Creep and creep rupture tests provide information on the time-dependent deformation and on the time-of-failure of materials subjected to uniaxial tensile stresses at elevated temperatures. Uniform stress states are required to effectively evaluate any nonlinear stress-strain behavior which may develop as the result of cumulative damage processes (for example, matrix cracking, matrix/fiber debonding, fiber fracture, delamination, etc.) which may be influenced by test mode, test rate, processing or alloying effects, environmental influences, or elevated temperatures. Some of these effects may be consequences of stress corrosion or subcritical (slow) crack growth. It is noted that ceramic materials typically creep more rapidly in tension than in compression. Therefore, creep data for design and life prediction should be obtained in both tension and compression.  
4.5 The results of tensile creep and tensile creep rupture tests of specimens fabricated to standardized dimensions from a particular material or selected portions of a part, or both, may not totally represent the creep deformation and creep rupture properties of the entire, full-size end p...
SCOPE
1.1 This test method covers the determination of the time-dependent deformation and time-to-rupture of continuous fiber-reinforced ceramic composites under constant tensile loading at elevated temperatures. This test method addresses, but is not restricted to, various suggested test specimen geometries. In addition, test specimen fabrication methods, allowable bending, temperature measurements, temperature control, data collection, and reporting procedures are addressed.  
1.2 This test method is intended primarily for use with all advanced ceramic matrix composites with continuous fiber reinforcement: unidirectional (1-D), bidirectional (2-D), and tridirectional (3-D). In addition, this test method may also be used with glass matrix composites with 1-D, 2-D, and 3-D continuous fiber reinforcement. This test method does not address directly discontinuous fiber-reinforced, whisker-reinforced, or particulate-reinforced ceramics, although the test methods detailed here may be equally applicable to these composites.  
1.3 Values expressed in this test method are in accordance with the International System of Units (SI) and 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. Hazard statements are noted in 7.1 and 7.2.

General Information

• Status: Published
• Publication Date: 31-Jan-2017
• ICS: 19.060 - Mechanical testing
• ICS: 81.060.30 - Advanced ceramics
• ICS: 81.060.99 - Other standards related to ceramics
• Technical Committee: C28 - Advanced Ceramics
• Drafting Committee: C28.07 - Ceramic Matrix Composites

Relations

• Replaces: ASTM C1337-10(2015) - Standard Test Method for Creep and Creep Rupture of Continuous Fiber-Reinforced Advanced Ceramics Under Tensile Loading at Elevated Temperatures
• Effective Date: 01-Feb-2017
• Refers: ASTM D3878-19a - Standard Terminology for Composite Materials
• Effective Date: 15-Oct-2019
• Refers: ASTM C1145-19 - Standard Terminology of Advanced Ceramics
• Effective Date: 01-Jul-2019
• Refers: ASTM D3878-19 - Standard Terminology for Composite Materials
• Effective Date: 15-Apr-2019
• Refers: ASTM D3878-18 - Standard Terminology for Composite Materials
• Effective Date: 01-Apr-2018
• Refers: ASTM C1275-18 - Standard Test Method for Monotonic Tensile Behavior of Continuous Fiber-Reinforced Advanced Ceramics with Solid Rectangular Cross-Section Test Specimens at Ambient Temperature
• Effective Date: 01-Jan-2018
• Refers: ASTM C1275-16 - Standard Test Method for Monotonic Tensile Behavior of Continuous Fiber-Reinforced Advanced Ceramics with Solid Rectangular Cross-Section Test Specimens at Ambient Temperature
• Effective Date: 01-Dec-2016
• Refers: ASTM D3878-16 - Standard Terminology for Composite Materials
• Effective Date: 01-Aug-2016
• Refers: ASTM C1275-15 - Standard Test Method for Monotonic Tensile Behavior of Continuous Fiber-Reinforced Advanced Ceramics with Solid Rectangular Cross-Section Test Specimens at Ambient Temperature
• Effective Date: 01-Jul-2015
• Refers: ASTM D3878-15 - Standard Terminology for Composite Materials
• 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
• Refers: ASTM D3878-07(2013) - Standard Terminology for Composite Materials
• Effective Date: 01-May-2013
• Refers: ASTM C1145-06(2013)e1 - Standard Terminology of Advanced Ceramics
• Effective Date: 01-Feb-2013
• Refers: ASTM C1145-06(2013) - Standard Terminology of Advanced Ceramics
• Effective Date: 01-Feb-2013

Overview

ASTM C1337-17 is the Standard Test Method for Creep and Creep Rupture of Continuous Fiber-Reinforced Advanced Ceramics Under Tensile Loading at Elevated Temperatures. This standard provides a comprehensive procedure for determining the time-dependent deformation (creep) and the time-to-rupture (creep rupture) characteristics of continuous fiber-reinforced ceramic matrix composites (CFCCs) and glass matrix composites subjected to tensile loading at high temperatures.

The method is vital for material development, quality assurance, characterization, and generating reliable design data essential for structural applications where wear resistance, corrosion resistance, and toughness at elevated temperatures are required. The test method outlines specifics on test specimen preparation, acceptable specimen geometries, test environment considerations, measurement protocols, and data reporting.

Key Topics

• Creep and Creep Rupture Testing: The method details procedures for exposing CFCC specimens to constant uniaxial tensile stress at elevated temperatures to evaluate both the rate of deformation over time and ultimate rupture behavior.
• Test Specimen Preparation: Recommended geometries include unidirectional (1-D), bidirectional (2-D), and tridirectional (3-D) continuous fiber-reinforced composites. The method applies to glass matrix composites with similar reinforcements but is not directly intended for discontinuous or particulate-reinforced ceramics.
• Test Environments: The testing considers the influences of various environments such as vacuum, inert gas, or ambient air, as environmental factors, humidity, and oxidation can impact creep and rupture behavior.
• Measurement Techniques: The standard specifies requirements for temperature measurement, strain measurement using extensometers, data acquisition systems, and dimensional measurement devices, with particular attention to calibration and precision.
• Analysis of Results: Creep and creep rupture data provide insights into deformation rates, time-to-failure, failure processes (such as matrix cracking or fiber fracture), and the effects of nonlinear stress-strain behavior. This data is critical for predicting material lifespan under operational conditions.

Applications

• Material Development and Comparison: Enables researchers and manufacturers to evaluate new CFCCs and compare their high-temperature performance, particularly in aerospace, energy, automotive, and industrial sectors.
• Design Data Generation: Produces essential mechanical data for engineers to make informed decisions in the design and reliability assessment of high-temperature structural components.
• Quality Assurance: Facilitates standardized quality control by enabling routine testing of batch-to-batch consistency for advanced ceramics and composites.
• Structural Applications: Supports the selection and design of materials for components such as turbine blades, heat exchangers, braking systems, and chemical process equipment where long-term performance under high stress and temperature is crucial.

Related Standards

ASTM C1337-17 references and aligns with several other important testing and terminology standards, including:

• ASTM C1145: Terminology of Advanced Ceramics
• ASTM C1275: Monotonic Tensile Behavior of Continuous Fiber-Reinforced Advanced Ceramics
• ASTM D3878: Terminology for Composite Materials
• ASTM E83: Practice for Verification and Classification of Extensometer Systems
• ASTM E139: Methods for Creep, Creep-Rupture, and Stress-Rupture Tests of Metallic Materials
• ASTM E220/E230: Calibration of Thermocouples and Temperature-EMF Tables
• ASTM E1012: Verification of Testing Frame and Specimen Alignment

Using ASTM C1337-17 ensures consistent, reliable, and repeatable results for the creep and creep rupture testing of continuous fiber-reinforced ceramic composites at elevated temperatures. This contributes directly to safer, more effective product development and structural performance in demanding applications.

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: C1337 − 17
Standard Test Method for
Creep and Creep Rupture of Continuous Fiber-Reinforced
Advanced Ceramics 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 2. Referenced Documents
2.1 ASTM Standards:
1.1 This test method covers the determination of the time-
C1145 Terminology of Advanced Ceramics
dependent deformation and time-to-rupture of continuous
C1275 Test Method for Monotonic Tensile Behavior of
fiber-reinforced ceramic composites under constant tensile
Continuous Fiber-Reinforced Advanced Ceramics with
loading at elevated temperatures. This test method addresses,
Solid Rectangular Cross-Section Test Specimens at Am-
but is not restricted to, various suggested test specimen
bient Temperature
geometries. In addition, test specimen fabrication methods,
D3878 Terminology for Composite Materials
allowable bending, temperature measurements, temperature
E4 Practices for Force Verification of Testing Machines
control, data collection, and reporting procedures are ad-
E6 Terminology Relating to Methods of Mechanical Testing
dressed.
E83 Practice for Verification and Classification of Exten-
1.2 This test method is intended primarily for use with all
someter Systems
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-
peratures)
reinforced,orparticulate-reinforcedceramics,althoughthetest
methods detailed here may be equally applicable to these E1012 Practice for Verification of Testing Frame and Speci-
men Alignment Under Tensile and Compressive Axial
composites.
Force Application
1.3 Values expressed in this test method are in accordance
IEEE/ASTM SI 10 American National Standard for Use of
withtheInternationalSystemofUnits(SI)andIEEE/ASTMSI
theInternationalSystemofUnits(SI):TheModernMetric
10.
System
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:
responsibility of the user of this standard to establish appro-
3.1.1 The definitions of terms relating to tensile testing
priate safety and health practices and determine the applica-
appearing in Terminology E6 apply to the terms used in this
bility of regulatory limitations prior to use. Hazard statements
test method. The definitions relating to advanced ceramics
are noted in 7.1 and 7.2.
appearinginTerminologyC1145applytothetermsusedinthis
test method. The definitions of terms relating to fiber rein-
forced composites appearing in Terminology D3878 apply to
This test method is under the jurisdiction of ASTM Committee C28 on
Advanced Ceramics and is the direct responsibility of Subcommittee C28.07 on
Ceramic Matrix Composites. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Feb. 1, 2017. Published February 2017. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 1996. Last previous edition approved in 2015 as C1337 – 10 (2015). Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/C1337-17. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1337 − 17
the terms used in this test method. Additional terms used in 4.4 Creepandcreeprupturetestsprovideinformationonthe
conjunction with this test method are defined in the following: time-dependent deformation and on the time-of-failure of
materials subjected to uniaxial tensile stresses at elevated
3.1.2 ceramic matrix composite—material consisting of two
temperatures. Uniform stress states are required to effectively
or more materials (insoluble in one another), in which the
evaluate any nonlinear stress-strain behavior which may de-
major,continuouscomponent(matrixcomponent)isaceramic,
velop as the result of cumulative damage processes (for
whilethesecondarycomponent/s(reinforcingcomponent)may
example, matrix cracking, matrix/fiber debonding, fiber
be ceramic, glass-ceramic, glass, metal, or organic in nature.
fracture, delamination, etc.) which may be influenced by test
These components are combined on a macroscale to form a
mode, test rate, processing or alloying effects, environmental
useful engineering material possessing certain properties or
influences,orelevatedtemperatures.Someoftheseeffectsmay
behavior not possessed by the individual constituents. C1145
be consequences of stress corrosion or subcritical (slow) crack
3.1.3 continuous fiber-reinforced ceramic matrix composite
growth. It is noted that ceramic materials typically creep more
(CFCC)—ceramic matrix composite in which the reinforcing
rapidly in tension than in compression. Therefore, creep data
phase consists of a continuous fiber, continuous yarn, or a
for design and life prediction should be obtained in both
woven fabric.
tension and compression.
3.1.4 fracture strength (F/L )—tensile stress that the mate-
4.5 The results of tensile creep and tensile creep rupture
rial sustains at the instant of fracture. Fracture strength is
tests of specimens fabricated to standardized dimensions from
calculated from the force at fracture during a tension test
a particular material or selected portions of a part, or both, may
carried to rupture and the original cross-sectional area of the
not totally represent the creep deformation and creep rupture
test specimen.
properties of the entire, full-size end product or its in-service
3.1.4.1 Discussion—In some cases, the fracture strength
behavior in different environments or at various elevated
may be identical to the tensile strength if the load at fracture is
temperatures.
the maximum for the test. Factors such as load train compli-
4.6 For quality control purposes, results derived from stan-
ance and fiber pull-out behavior may influence the fracture
dardizedtensiletestspecimensmaybeconsideredindicativeof
strength.
the response of the material from which they were taken for
3.1.5 proportional limit stress—greatest stress which a ma-
given primary processing conditions and post-processing heat
terial is capable of sustaining without any deviation from
treatments.
proportionality of stress to strain (Hooke’s law).
3.1.5.1 Discussion—Many experiments have shown that
5. Interferences
values observed for the proportional limit vary greatly with the
5.1 Test environment (vacuum, inert gas, ambient air, etc.)
sensitivity and accuracy of the test equipment, eccentricity of
including moisture content (for example, relative humidity)
loading, the scale to which the stress-strain diagram is plotted,
may have an influence on the creep and creep rupture behavior
and other factors. When determination of proportional limit is
of CFCCs. In particular, the behavior of materials susceptible
required, the procedure and sensitivity of the test equipment
to slow crack growth fracture and oxidation will be strongly
shall be specified.
influenced by test environment and test temperature. Testing
3.1.6 slow crack growth—subcritical crack growth (exten-
can be conducted in environments representative of service
sion) which may result from, but is not restricted to, such
conditions to evaluate material performance under these con-
mechanisms as environmentally assisted stress corrosion or
ditions.
diffusive crack growth. C1145
5.2 Surface preparation of test specimens, although nor-
mally not considered a major concern with CFCCs, can
4. Significance and Use
introducefabricationflawswhichmayhavepronouncedeffects
4.1 This test method may be used for material development,
on the mechanical properties and behavior (for example, shape
material comparison, quality assurance, characterization, and and level of the resulting stress-strain-time curve, etc.). Ma-
design data generation.
chining damage introduced during test specimen preparation
can be either a random interfering factor in the ultimate
4.2 Continuous fiber-reinforced ceramic matrix composites
strength of pristine material (that is, increased frequency of
are candidate materials for structural applications requiring
surface-initiated fractures compared to volume-initiated frac-
high degrees of wear and corrosion resistance and toughness at
tures) or an inherent part of the strength characteristics to be
high temperatures.
measured. Surface preparation can also lead to the introduction
4.3 Creep tests measure the time-dependent deformation of of residual stresses. Universal or standardized test methods of
a material under constant load at a given temperature. Creep surface preparation do not exist. It should be understood that
rupture tests provide a measure of the life of the material when final machining steps may or may not negate machining
subjected to constant mechanical loading at elevated tempera- damage introduced during the initial machining. Thus, test
tures. In selecting materials and designing parts for service at specimen fabrication history may play an important role in the
elevatedtemperatures,thetypeoftestdatausedwilldependon measured time-to-failure or deformation, and shall be reported.
the criteria for load-carrying capability which best defines the In addition, the nature of fabrication used for certain compos-
service usefulness of the material. ites (for example, chemical vapor infiltration or hot pressing)
C1337 − 17
may require the testing of specimens in the as-processed determine the retained strength as well as the loading and
condition (that is, it may not be possible to machine the test unloading rates will influence the rate of internal stress
specimen faces without compromising the in-plane fiber archi- redistribution among the phases and hence the CFCC strength.
tecture).
6. Apparatus
5.3 Bending in uniaxial tests does induce nonuniform stress
6.1 Test Machines—Machines used for tensile testing shall
distributions. Bending may be introduced from several sources
conform to the requirements of Practices E4. The forces used
including misaligned load trains, eccentric or misshaped
shall be accurate within 61 % at any force within the selected
specimens, and nonuniformly heated specimens or grips. In
force range of the test machine as defined in Practices E4.
addition, if deformations or strains are measured at surfaces
where maximum or minimum stresses occur, bending may 6.2 Gripping Devices:
introduce over or under measurement of strains depending on
6.2.1 General—Various types of gripping devices may be
the location of the strain-measuring device on the test speci- usedtotransmitthemeasuredforceappliedbythetestmachine
men.Similarly,fracturefromsurfaceflawsmaybeaccentuated
to the test specimens. The brittle nature of the matrices of
or suppressed by the presence of the nonuniform stresses CFCCs requires that a uniform interface exists between the
caused by bending.
grip components and the gripped section of the specimen. Line
or point contacts and nonuniform pressure can produce
5.4 Fractures that initiate outside the uniformly stressed
Hertzian-typestressesleadingtocrackinitiationandfractureof
gage section of a specimen may be due to factors such as stress
the test specimen in the gripped section. Gripping devices can
concentrations or geometrical transitions, extraneous stresses
be classified generally as those employing active and those
introduced by gripping or thermal gradients, or strength limit-
employing passive grip interfaces as discussed in the following
ing features in the microstructure of the test specimen. Such
sections. Grips located outside the heated zone surrounding the
non-gage section fractures will normally constitute invalid
specimen may or may not employ cooling. Uncooled grips
tests. In addition, for face-loaded test specimen geometries,
located outside the heated zone are termed “warm” grips and
gripping pressure is a key variable in the initiation of fracture.
generally reduce the thermal gradient in the test specimen but
Insufficient pressure can shear the outer plies in laminated
at the expense of using high-temperature alloy grips and
CFCCs, while too much pressure can cause local crushing of
increased degradation of the grips due to exposure to the
the CFCC and lead to fracture in the vicinity of the grips.
elevated-temperature environment. Cooled grips located out-
5.5 The time-dependent stress redistribution that occurs at
side 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 test
specimen.
specimen be specified. This is of particular importance since
NOTE 1—The expense of the cooling system for cold grips is balanced
the rate at which a creep load is initially applied can influence
against maintaining alignment that remains consistent from test to test
the subsequent creep behavior and damage modes. For
(stable grip temperature) and decreased degradation of the grips due to
example, whether matrix cracking would occur at the end of
exposure to the elevated-temperature environment. When grip cooling is
loading will depend on the magnitude of the test rate, the test
employed, provisions shall be provided to control the cooling medium to
stress, the test temperature and the relative creep resistance of maximum fluctuations of 5 K (less than 1 K preferred) about a setpoint
3,4
temperature over the course of the test to minimize thermally induced
the matrix with respect to that of the fibers.
strain changes in the test specimen. In addition, opposing grip tempera-
5.6 WhenCFCCsaremechanicallyunloadedeitherpartially
tures should be maintained at uniform and consistent temperatures not to
exceed a difference 65 K (less than 61 K preferred) so as to avoid
or totally after a creep test during which the test specimen
inducingunequalthermalgradientsandsubsequentnonuniaxialstressesin
accumulated time-dependent deformation, the specimen may
the specimen. Generally, the need for control of grip temperature
exhibit creep recovery as manifested by a time-dependent
fluctuations or differences may be indicated if test specimen gage section
reductionofstrain.Therateofcreeprecoveryisusuallyslower
temperatures 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 force to the test specimen.
to determine the retained strength of a CFCC after being
Generally, these types of grip interfaces cause a force to be
subjected to creep for a prescribed period of time.Therefore, it
applied normal to the surface of the gripped section of the test
is customary to unload the test specimen from the creep stress
specimen.Transmission of the uniaxial load applied by the test
and then reload it monotonically until failure. Under these
machine is then accomplished by friction between the test
circumstances, the time elapsed between the end of the creep
specimen and the grip faces. Thus, important aspects of active
test and the conduction of the monotonic fast fracture test to
grip interfaces are: (1) uniform contact between the gripped
sectionofthetestspecimenandthegripfaces,and(2)constant
3 coefficient of friction over the grip/test specimen interface. In
Holmes, J. W., and Wu, X., “Elevated Temperature Creep Behavior of
addition, note that fixed-displacement active grips set at
Continuous Fiber-reinforced Ceramics,” Elevated Temperature Mechanical Behav-
ior of Ceramic Matrix Composites, S. V. Nair and K. Jakus, eds., Butterworth-
ambient temperatures may introduce excessive gripping
Heinneman, 1994.
stresses due to thermal expansion of the test material when the
Lara-Curzio, E., and Ferber, M. K., “Redistribution of Internal Stresses in
test specimen is heated to the test temperature. Therefore,
Composite Materials During Creep,” Ceram. Eng. Sci., Vol 16, No. 5, 1995, pp.
791–800. provisions shall be made to avoid such excessive stresses prior
C1337 − 17
to the test by heating the test specimen while maintaining a loading by means of mechanically actuated wedge grip faces.
constant force in the load train (for example, force control). Proper tightening of the wedge grip faces against the test
specimen to prevent slipping while avoiding compressive
Hydraulic grips are usually water cooled, and special provi-
sions shall be made to ensure that these grips are continuously fracture of the test specimen gripped section must be deter-
mined for each material and test specimen type.
cooled since loss of cooling may result in rupture of the
(4) Note that passive grips employing single pins in each
hydraulic lines and hydraulic chamber creating a potentially
gripped section of the test specimen as the primary load
dangerous situation.
transfer mechanism are not recommended. Relatively low
(1) For flat test specimens, face-loaded grips, either by
interfacial shear strengths compared to longitudinal tensile
direct lateral pressure grip faces or by indirect wedge-type grip
strengths in CFCCs (particularly for 1-D reinforced materials
faces, act as the grip interface. Generally, close tolerances are
loadedalongthefiberdirection)maypromotenon-gagesection
required for the flatness and parallelism as well as for the
fractures along interfaces particularly at geometric transitions
wedgeangleofthewedgegripfaces.Inaddition,thethickness,
or at discontinuities such as holes.
flatness, and parallelism of the gripped section of the test
specimen must be within similarly close tolerances to promote
6.3 Load Train Couplers:
uniform contact at the test specimen/grip interface. Tolerances
6.3.1 General—Various types of devices (load train cou-
will vary depending on the exact test specimen configuration.
plers) may be used to attach the active or passive grip interface
For examples of tensile test specimen geometries, the user of
assemblies to the test machine. The load train couplers in
this test method is referred to Test Method C1275.
conjunction with the type of gripping device play major roles
(2) Sufficient lateral pressure must be applied to prevent
in the alignment of the load train and thus subsequent bending
slippage between the grip face and the test specimen. Grip
imposed in the test specimen. Load train couplers can be
surfacesthatarescoredorserratedwithapatternsimilartothat
classified generally as fixed and nonfixed as discussed in the
of a single-cut file have been found satisfactory. A fine
following sections. Note that use of well-aligned fixed or
serration appears to be the most satisfactory. The serrations
self-aligning nonfixed couplers does not automatically guaran-
shall be kept clean and well-defined but not overly sharp. The
teelowbendinginthegagesectionofthetensiletestspecimen.
length and width of the grip faces shall be equal to or greater
Generally, well-aligned fixed or self-aligning nonfixed cou-
than the respective length and width of the gripped sections of
plers provide for well-aligned load trains, but the type and
the test specimen.
operation of grip interfaces as well as the as-fabricated
6.2.1.2 Passive Grip Interfaces—Passive grip interfaces
dimensions of the tensile test specimen can add significantly to
transmit the force applied by the test machine to the test
the final bending imposed in the gage section of the test
specimen through a direct mechanical link. Generally, these
specimen.
mechanical links transmit the test force to the test specimen by
6.3.1.1 Regardless of which type of coupler is used, align-
means of geometrical features of the test specimens such as
ment of the load train must be verified as a minimum at the
shank shoulders or holes in the gripped head. Thus, the
beginning and end of a test series unless the conditions for
important aspect of passive grip interfaces is uniform contact
verifyingalignmentasdetailedinAppendixX1ofTestMethod
between the gripped section of the test specimen and the grip
C1275 are otherwise met.Atest series is interpreted to mean a
faces.
discrete group of tests on individual test specimens conducted
(1) For flat test specimens, passive grips may act either
within a discrete period of time on a particular material
through edge-loading by means of grip interfaces at the
configuration, test specimen geometry, test condition, or other
shoulders of the test specimen shank or by combinations of
uniquely definable qualifier. An additional verification of
face-loading and pin loading by means of pins at holes in the
alignment is recommended, although not required, at the
gripped head of the test specimen. Generally, close tolerances
middle of the test series. Either a dummy or actual test
of linear and angular dimensions of shoulder and grip inter-
specimen and the alignment verification procedures detailed in
faces are required to promote uniform contact along the entire
Appendix X1 of Test Method C1275 and Practice E1012 shall
test specimen/grip interface as well as to provide for nonec-
be used.Allowable bending requirements are discussed in 6.5.
centric loading. In addition, moderately close tolerances are
Tensile test specimens used for alignment verification shall be
required for center-line coincidence and diameters of the pins
equipped with eight separate longitudinal strain gages to
and hole. Examples of test specimen geometries adequate for
determine bending contributions from both eccentric and
passive grips are presented in Test Method C1275.
angular misalignment. Ideally the verification specimen shall
(2) When using edge-loaded test specimens, lateral center-
be of identical material to that being tested. However, in the
ing of the test specimen within the grip attachments is case of CFCCs the type of reinforcement or degree of residual
accomplished by use of wedge-type inserts machined to fit
porosity may complicate the consistent and accurate measure-
within the grip cavity. Examples of successfully used edge- ment of strain. Therefore, it is recommended that an alternate
loaded test specimens are presented in Figs. X2.1 and X2.2 of
material (isotropic and homogeneous) with similar elastic
Test Method C1275. modulus, elastic strain capability, and hardness to the test
(3) The pins in face/pin loaded grips (for such test speci-
material be used. In addition, dummy specimens used for
mens as those illustrated in Figs. X2.6, X2.7, and X2.8 of Test alignment verification shall have the same geometry and
Method C1275) are primarily for alignment purposes and force dimensions of the actual test specimens as well as similar
transmission. Secondary force transmission is through face- mechanical properties as the test material to ensure similar
C1337 − 17
axial and bending stiffness characteristics as the actual test 6.6 Heating Apparatus—The apparatus for and method of
specimen and material. heating the test specimens shall provide the temperature
control necessary to satisfy the requirement of 9.2.
6.3.2 Fixed Load Train Couplers—Fixed couplers may
6.6.1 Heating can be by indirect electrical resistance (heat-
incorporate devices which require either a one-time, pretest
ingelements),indirectinductionthroughasusceptor,orradiant
alignment adjustment of the load train which remains constant
lamp with the test specimen in ambient air at atmospheric
for all subsequent tests or an in situ, pretest alignment of the
pressure unless other environments are specifically applied and
load train which is conducted separately for each test specimen
reported. Note that direct resistance heating is not recom-
and each test. Such devices usually employ angularity and
mended for heating CFCCs due to possible differences of the
concentricity adjusters to accommodate inherent load train
electrical resistances of the constituent materials which may
misalignments. Regardless of which method is used, alignment
produce nonuniform heating of the test specimen.
verification must be performed as discussed in 6.3.1.1.
6.7 Temperature-Measuring Apparatus—The method of
6.3.3 Nonfixed Load Train Couplers—Nonfixed couplers
temperature measurement shall be sufficiently sensitive and
may incorporate devices which promote self-alignment of the
reliable to ensure that the temperature of the test specimen is
load train during the movement of the cross-head or actuator.
within the limits specified in 9.2.
Generally such devices rely upon freely moving linkages to
6.7.1 Primary temperature measurement shall be made with
eliminate applied moments as the load train components are
thermocouples in conjunction with potentiometers,
loaded. Knife edges, universal joints, hydraulic couplers, or air
millivoltmeters, or electronic temperature controllers or read-
bearings are examples of such devices.Although nonfixed load
out units, or both. Such measurements are subject to two types
train couplers are intended to be self-aligning and thus elimi-
of error. Thermocouple calibration and instrument measuring
nate the need to evaluate the bending in the test specimen for
errors initially produce uncertainty as to the exact temperature.
each test, the operation of the couplers must be verified as
Secondly, both thermocouples and measuring instruments may
discussed in 6.3.1.1.
be subject to variations over time. Common errors encountered
6.3.3.1 Nonfixed load train couplers are useful in rapid test
in the use of thermocouples to measure temperatures include
rate or constant load testing of CFCCs where the “graceful”
calibration error, drift in calibration due to contamination or
fracture process is not as apparent. If the material exhibits
deterioration with use, lead-wire error, error arising from
graceful fracture the self-aligning feature of the nonfixed
method of attachment to the test specimen, direct radiation of
coupler will allow rotation of the gripped section of the
heat to the bead, heat conduction along thermocouple wires,
specimen,thuspromotinganonuniformstressintheremaining
etc.
ligament of the gage section.
6.7.2 Temperature measurements shall be made with ther-
mocouples of known calibration. Representative thermo-
NOTE 2—Graceful fracture refers to the progressive process of matrix
couples shall be calibrated from each lot of wires used for
cracking and debonding and sliding of fibers that bridge those cracks and
making noble-metal (for example, platinum (Pt) or rhodium
prevent the otherwise catastrophic mode of failure associated with brittle
fracture.
(Rh))thermocouples.Exceptforrelativelylowtemperaturesof
exposure, noble-metal thermocouples are eventually subject to
6.4 Strain Measurement—Strain at elevated temperatures
error upon reuse. Oxidized noble-metal thermocouples shall
shall be determined by means of a suitable extensometer.
not be reused without clipping back to remove wire exposed to
6.4.1 Extensometers used for tensile creep testing of CFCC
the hot zone, re-welding, and annealing. Any reuse of noble-
test specimens shall satisfy Practice E83, Class B-1 require-
metalthermocouplesafterrelativelylow-temperatureusewith-
ments. Extensometers shall be calibrated periodically in accor-
out this precaution shall be accompanied by re-calibration data
dance with Practice E83. For extensometers which mechani-
demonstrating that calibration was not unduly affected by the
cally contact the test specimen, the contact shall not cause
conditions of exposure.
damage to the test specimen surface. In addition, extensometer
6.7.3 Measurement of the drift in calibration of thermo-
contact probes must be chosen to be chemically compatible
couples during use is difficult. When drift is a problem during
with the test material. In addition, the weight of the extensom-
tests, a method shall be devised to check the readings of the
eter shall be supported so as not to introduce bending greater
thermocouples monitoring the test specimen temperature dur-
than that allowed in 6.5. Finally, the tips of the probes of
ing the test. For reliable calibration of thermocouples after use,
contacting extensometers and the magnitude of the contact
thetemperaturegradientofthetestfurnacemustbereproduced
force shall be configured (for example, sharp knife edges or
during the re-calibration.
chisel tips) so as to minimize slippage.
6.7.4 Temperature measuring, controlling, and recording
instruments shall be calibrated against a secondary standard,
6.5 Allowable Bending—Studiesoftheeffectsofbendingon
such as precision potentiometer, optical pyrometer, or black-
the tensile creep and tensile creep rupture behavior of CFCCs
body thyristor. Lead-wire error shall be checked with the lead
do not exist. Until such information is forthcoming for CFCCs,
wires in place as they normally are used. For thermocouple
this test method adopts the recommendations for tensile testing
calibration procedures, refer to Test Method E220 and Speci-
ofmonolithicadvancedceramics.Therefore,therecommended
fication E230.
maximum allowable percent for test specimens tested under
this test method is 5 %. For verification of test specimen
6.8 Data Acquisition—At the minimum, gage section elon-
alignment, refer to Practice E1012. gation or strain versus time shall be obtained. Either analog
C1337 − 17
chart recorders or digital data acquisition systems can be used test method. Deviations from the recommended geometries
for this purpose, although a digital record is recommended for may be necessary depending upon the particular CFCC being
ease of later data analysis. Ideally, an analog chart recorder or evaluated. Stress analyses of untried test specimens shall be
plotter should be used in conjunction with the digital data conducted to ensure that stress concentrations which can lead
acquisitionsystemtoprovideanimmediaterecordofthetestas
to undesired fractures outside the gage sections do not exist. It
a supplement to the digital record. Recording devices shall be should be noted that contoured test specimens by their nature
accurate within 61 % of the selected range for the test system
contain inherent stress concentrations due to geometric transi-
including readout unit, as specified in Practices E4. tions. Stress analyses can indicate the magnitude of such stress
6.8.1 Cross-head displacement of the test machine may also
concentrations while revealing the success of producing a
be recorded but shall not be used to define displacement or uniform tensile stress state in the gage section of the test
strain in the gage section, especially when self-aligning cou-
specimen.Additionally, the success of an elevated-temperature
plers are used in the load train.
creep test will depend on the type of heating system, extent of
6.8.2 Temperature shall be recorded at the initiation and
test specimen heating, and test specimen geometry since these
completionoftheactualtest.However,temperaturecanalsobe
factors are all interrelated. For example, thermal gradients may
recorded parallel to the strain record in addition to temperature
introduce additional stress gradients in test specimens which
recordings at the start of the heating of the furnace (including
may already exhibit stress gradients at ambient temperatures
ramp-up to test temperature) and ending at the completion of
due to geometric transitions. Therefore, untried test configura-
the test.
tions should be simultaneously analyzed for both loading-
induced stress gradients and thermally induced temperature
6.9 Dimension-Measuring Devices—Micrometers and other
gradients to ascertain any adverse interactions.
devices used for measuring linear dimensions shall be accurate
and precise to at least one-half of the smallest unit to which the 8.1.1.2 Generally, test specimens with contoured gage sec-
individual dimension is required to be measured. For the tions (transition radii of >50 mm) are preferred to promote the
purposes of this test method, cross-sectional dimensions shall tensile stresses with the greatest values in the uniformly
be measured to within 0.02 mm, requiring dimension-
stressedgagesectionwhileminimizingthestressconcentration
measuring devices with accuracies of 0.01 mm. due to the geometrical transition of the radius. However, in
certain instances, (for example, 1-D CFCCs tested along the
7. Hazard Statements
direction of the fibers) low interfacial shear strength relative to
7.1 Duringtheconductofthistestmethod,thepossibilityof the tensile strength in the fiber direction will cause splitting of
flying fragments of broken test material may be high. The the test specimen initiating at the transition region between the
brittle nature of advanced ceramics and the release of strain gage section and the gripped section of the test specimen with
energy contribute to the potential release of uncontrolled
the split propagating along the fiber direction leading to
fragments upon fracture. Means for containment and retention fracture of the test specimen. In these cases, straight-sided test
of these fragments for later fractographic reconstruction and
specimens may be required for determining the tensile creep
analysis is highly recommended. and creep rupture behavior of the CFCC. Figure 7 in Test
Method C1275 shows an example of a straight-sided test
7.2 Exposed fibers at the edges of CFCC test specimens
specimen. In other instances, a particular fiber weave or
present a hazard due to the sharpness and brittleness of the
processing route will preclude fabrication of test specimens
ceramic fiber. All persons required to handle these materials
with reduced gage sections, thus requiring implementation of
shall be well informed of such conditions and the proper
straight-sided test specimens. Straight-sided test specimens
handling techniques.
may be gripped by any of the methods discussed herein,
8. Test Specimens although active gripping systems are recommended for mini-
mizing non-gage section fractures.
8.1 Test Specimen Geometry:
8.1.2 Edge-Loaded Flat Tensile Test Specimens—This type
8.1.1 General—The geometry of tensile creep test speci-
of geometry has been successfully employed for the evaluation
mens is dependent on the ultimate use of the tensile creep data.
of 2-D and 3-D CFCCs. Of particular concern with this
For example, if the tensile creep of an as-fabricated component
geometry is the proper and consistent angle of the edge-loaded
is required, the dimensions of the resulting tensile test speci-
shank. However, the preparation of this type of test specimen
men may reflect the thickness, width, and length restrictions of
with the stringent tolerances required is routine with
the component. If it is desired to evaluate the effects of
numerical-controlled machines. Furthermore, this test speci-
interactions of various constituent materials for a particular
men is ideal when using “warm” or “hot” grips to minimize
CFCCmanufacturedbymeansofaparticularprocessingroute,
thermal gradients along the length of the specimen. Figures
then the size of the test specimen and resulting gage section
X2.1 and X2.2 in Test Method C1275 show examples of
will reflect the desired volume to be sampled. In addition, grip
contoured edge-loaded test specimens.
interfaces and load train couplers as discussed in Section 6 will
influence the final design of the test specimen geometry. 8.1.3 Face-Loaded Flat Tensile Test Specimens—This con-
8.1.1.1 The following sections discuss the more common figuration exploits the friction at the test specimen/grip inter-
and, thus, proven test specimen geometries, although any face to transmit the uniaxial force applied by the test machine.
geometry is acceptable if it meets the gripping, fracture Important tolerances for the face-loaded geometry include
location, temperature profile, and bending requirements of this parallelism and flatness of faces, all of which will vary
C1337 − 17
depending on the exact configuration as shown in the appro- application where no machining is used, for example, as-cast,
priate test specimen drawings. sintered, or injection-molded part. No additional machining
specifications are relevant. As-processed test specimens might
8.1.3.1 For face-loaded test specimens, especially for
possess rough surface textures and nonparallel edges and as
straight-sided (for example, noncontoured) test specimens, end
such may cause excessive misalignment or proneness to
tabs may be required to provide a compliant layer for gripping.
non-gage section fractures, or both.
For CFCCs, fiberglass reinforced epoxy, PMR, and carbon
8.2.3 Application-Matched Machining—The tensile test
fiber-reinforced resins, tab materials have been used success-
specimen should have as close to the same surface/edge
fully. However, metallic tabs (for example, aluminum alloys)
preparation as that given to the component. Unless the process
may be satisfactory (or desirable for elevated temperature use)
is proprietary, the report shall be specific about the stages of
as long as the tabs are strain compatible (that is, having an
material removal, wheel grits, wheel bonding, amount of
elastic modulus of magnitude comparable to the bulk elastic
modulus of the CFCC) with the CFCC material being tested. material removed per pass, and type of coolant used.
8.2.4 Customary Practices—Ininstanceswhereacustomary
Each beveled tab (bevel angle ≤15°) shall be a minimum of
30 mm long, the same width of the specimen, and have the machining procedure has been developed that is completely
satisfactory for a class of materials (that is, it induces no
total thickness of the tabs on the order of the thickness of the
unwanted surface/subsurface damage or residual stresses), this
test specimen. Any high-elongation (tough) adhesive system
procedure shall be used.
maybeusedwiththelengthofthetabsdeterminedbytheshear
8.2.5 Standard Procedure—In instances where 8.2.2 – 8.2.4
strength of the adhesive, size of the test specimen, and
are not appropriate, 8.2.5 shall apply. Studies to evaluate the
estimated strength of the composite. In any case, a significant
machinability of CFCCs have not been completed. Therefore,
fraction (>10 to 20 %) of fractures within one test specimen
the standard procedure of 8.2.5 can be viewed as starting-point
width of the tab shall be cause to reexamine the tab materials
guidelines, and a more stringent procedure may be necessary.
and configuration, gripping method, and adhesive, and to make
8.2.5.1 All grinding or cutting shall be done with ample
necessary adjustments to promote fracture within the gage
supply of appropriate filtered coolant to keep the workpiece
section. Note that care should be taken to ensure that both the
and grinding wheel constantly flooded and particles flushed.
adhesive and tab material are capable of use at the temperature
Grinding can be done in at least two stages, ranging from
which might occur in the grip region. Figure 8 in Test Method
coarse to fine rate of material removal.All cutting can be done
C1275 shows an example of a bevelled tab.
in one stage appropriate for the depth of cut.
8.1.4 Pin/Face-Loaded Flat Tensile Test Specimens—These
8.2.5.2 Stock removal rate shall be on the order of 0.03 mm
test specimens employ combinations of pin and face loading to
per pass using diamond tools that have between 320 and 600
transmit the uniaxial force of the test machine to the test
grit. Remove equal stock from each face where applicable.
specimen. Close tolerances of hole/pin diameters and center
lines are required to ensure proper specimen alignment in the
8.3 Handling Precaution—Care should be exercised in stor-
grips and transmission of the forces, since the face-loaded part
age and handling of finished test specimens to avoid the
of the geometry provides a secondary force transmission
introduction of random and severe flaws. In addition, attention
mechanism in these test specimens. Important tolerances for
shallbegiventopre-teststorageoftestspecimensincontrolled
the face-loaded part of the geometry include parallelism and
environments or desiccators to avoid unquantifiable environ-
flatness of faces, both of which will vary depending on the
mental degradation of test specimens prior to testing.
exact configuration as shown in the appropriate test specimen
8.4 Test Specimen Sampling and Number—Samples of the
drawings. Thus, the pin/face-loaded geometry may require
material to provide test specimens must be taken from such
somewhat intensive fabrication procedures. Figures 14 through
locations so as to be representative of the billet or lot from
16 in Test Method C1275 show examples of contoured,
which it is taken. Although each test scenario will vary, a
pin/face-loaded test specimens.
typical designed experiment may include creep tests at stresses
8.1.4.1 Note that test specimens requiring single pins in
below, about, and above the monotonic matrix-cracking stress
each gripped section of the test specimen as the primary load
level and at least for one stress level, tests across a range of
transfer mechanism are not recommended. Relatively low
four temperatures. It is recommended that at least 20 % of the
interfacial shear strengths compared to longitudinal tensile
tests in the designed experiment be replicated (duplicated or
strengths in CFCCs (particularly for 1-D reinforced materials
triplicated) to determine levels of repeatability.
loadedalongthefiberdirection)maypromotenon-gagesection
fractures along interfaces particularly at geometric transitions
9. Procedure
or at discontinuities such as holes.
9.1 Test Specimen Dimensions—Determine the thickness
8.2 Specimen Preparation:
and width of the gage section of each test specimen to within
8.2.1 Dependingupontheintendedapplicationofthetensile
0.02 mm. Make measurements on at least three different
creep data, use one of the following test specimen preparation
cross-sectional planes in the gage section. To avoid damage in
procedures. Regardless of the preparation procedure used,
the gage section area, these measurements shall be made either
sufficient details regarding the procedure must be reported to
optically (for example, an optical comparator) or mechanically
allow replication.
using a flat, anvil-type micrometer. In either case, the resolu-
8.2.2 As-Fabricated—The tensile test specimen should tion of the instrument shall be as specified in 6.9. Exercise
simulatethesurface/edgeconditionsandprocessingrouteofan caution to prevent damage to the test specimen gage section.
C1337 − 17
Ball-tipped or sharp-anvil micrometers are not recommended for the final image processing. Typically, an image is recorded
because localized cracking can be induced. The measured before deformation at a particular brightness distribution and
dimensions and locations of the measurements shall be re- then a similar brightness distribution is searched for in the
corded and reported for use in the calculation of the tensile image after deformation.The gage section of the test specimen
stress. The average of multiple measurements shall be used in should be defined for the strain measurement. The displace-
the stress calculations. ment components of a pixel located at the center of the subset
aredetermined,andthedisplacementdistributionsareobtained
9.1.1 Alternatively, to avoid damage to the gage section,
by repeating this procedure for corresponding pixels. To
make post-fracture measurements of the gage section dimen-
determ
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: C1337 − 10 (Reapproved 2015) C1337 − 17
Standard Test Method for
Creep and Creep Rupture of Continuous Fiber-Reinforced
Advanced Ceramics 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
1.1 This test method covers the determination of the time-dependent deformation and time-to-rupture of continuous
fiber-reinforced ceramic composites under constant tensile loading at elevated temperatures. This test method addresses, but is not
restricted to, various suggested test specimen geometries. In addition, test specimen fabrication methods, allowable bending,
temperature measurements, temperature control, data collection, and reporting procedures are addressed.
1.2 This test method is intended primarily for use with all advanced ceramic matrix composites with continuous fiber
reinforcement: unidirectional (1-D), bidirectional (2-D), and tridirectional (3-D). In addition, this test method may also be used
with glass matrix composites with 1-D, 2-D, and 3-D continuous fiber reinforcement. This test method does not address directly
discontinuous fiber-reinforced, whisker-reinforced, or particulate-reinforced ceramics, although the test methods detailed here may
be equally applicable to these composites.
1.3 Values expressed in this test method are in accordance with the International System of Units (SI) and 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. Hazard statements are noted in 7.1 and 7.2.
2. Referenced Documents
2.1 ASTM Standards:
C1145 Terminology of Advanced Ceramics
C1275 Test Method for Monotonic Tensile Behavior of Continuous Fiber-Reinforced Advanced Ceramics with Solid
Rectangular Cross-Section Test Specimens at Ambient Temperature
D3878 Terminology for Composite Materials
E4 Practices for Force Verification of Testing Machines
E6 Terminology Relating to Methods of Mechanical Testing
E83 Practice for Verification and Classification of Extensometer Systems
E139 Test Methods for Conducting Creep, Creep-Rupture, and Stress-Rupture Tests of Metallic Materials
E220 Test Method for Calibration of Thermocouples By Comparison Techniques
E230 Specification and Temperature-Electromotive Force (EMF) Tables for Standardized Thermocouples
E337 Test Method for Measuring Humidity with a Psychrometer (the Measurement of Wet- and Dry-Bulb Temperatures)
E1012 Practice for Verification of Testing Frame and Specimen Alignment Under Tensile and Compressive Axial Force
Application
IEEE/ASTM SI 10 American National Standard for Use of the International System of Units (SI): The Modern Metric System
3. Terminology
3.1 Definitions:
This test method is under the jurisdiction of ASTM Committee C28 on Advanced Ceramics and is the direct responsibility of Subcommittee C28.07 on Ceramic Matrix
Composites.
Current edition approved July 1, 2015Feb. 1, 2017. Published September 2015February 2017. Originally approved in 1996. Last previous edition approved in 20102015
as C1337 – 10.C1337 – 10 (2015). DOI: 10.1520/C1337-10R15.10.1520/C1337-17.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. 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
C1337 − 17
3.1.1 The definitions of terms relating to tensile testing appearing in Terminology E6 apply to the terms used in this test method.
The definitions relating to advanced ceramics appearing in Terminology C1145 apply to the terms used in this test method. The
definitions of terms relating to fiber reinforced composites appearing in Terminology D3878 apply to the terms used in this test
method. Additional terms used in conjunction with this test method are defined in the following:
3.1.2 ceramic matrix composite—material consisting of two or more materials (insoluble in one another), in which the major,
continuous component (matrix component) is a ceramic, while the secondary component/s (reinforcing component) may be
ceramic, glass-ceramic, glass, metal, or organic in nature. These components are combined on a macroscale to form a useful
engineering material possessing certain properties or behavior not possessed by the individual constituents. C1145
3.1.3 continuous fiber-reinforced ceramic matrix composite (CFCC)—ceramic matrix composite in which the reinforcing phase
consists of a continuous fiber, continuous yarn, or a woven fabric.
3.1.4 fracture strength (F/L )—tensile stress that the material sustains at the instant of fracture. Fracture strength is calculated
from the force at fracture during a tension test carried to rupture and the original cross-sectional area of the test specimen.
3.1.4.1 Discussion—
In some cases, the fracture strength may be identical to the tensile strength if the load at fracture is the maximum for the test.
Factors such as load train compliance and fiber pull-out behavior may influence the fracture strength.
3.1.5 proportional limit stress—greatest stress which a material is capable of sustaining without any deviation from
proportionality of stress to strain (Hooke’s law).
3.1.5.1 Discussion—
Many experiments have shown that values observed for the proportional limit vary greatly with the sensitivity and accuracy of the
testingtest equipment, eccentricity of loading, the scale to which the stress-strain diagram is plotted, and other factors. When
determination of proportional limit is required, the procedure and sensitivity of the test equipment shall be specified.
3.1.6 slow crack growth—subcritical crack growth (extension) which may result from, but is not restricted to, such mechanisms
as environmentally assisted stress corrosion or diffusive crack growth. C1145
4. Significance and Use
4.1 This test method may be used for material development, material comparison, quality assurance, characterization, and
design data generation.
4.2 Continuous fiber-reinforced ceramic matrix composites are candidate materials for structural applications requiring high
degrees of wear and corrosion resistance and toughness at high temperatures.
4.3 Creep tests measure the time-dependent deformation of a material under constant load at a given temperature. Creep rupture
tests provide a measure of the life of the material when subjected to constant mechanical loading at elevated temperatures. 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 which best defines the service usefulness of the material.
4.4 Creep and creep rupture tests provide information on the time-dependent deformation and on the time-of-failure of materials
subjected to uniaxial tensile stresses at elevated temperatures. Uniform stress states are required to effectively evaluate any
nonlinear stress-strain behavior which may develop as the result of cumulative damage processes (for example, matrix cracking,
matrix/fiber debonding, fiber fracture, delamination, etc.) which may be influenced by testingtest mode, testingtest rate, processing
or alloying effects, environmental influences, or elevated temperatures. Some of these effects may be consequences of stress
corrosion or subcritical (slow) crack growth. It is noted that ceramic materials typically creep more rapidly in tension than in
compression. Therefore, creep data for design and life prediction should be obtained in both tension and compression.
4.5 The results of tensile creep and tensile creep rupture tests of specimens fabricated to standardized dimensions from a
particular material or selected portions of a part, or both, may not totally represent the creep deformation and creep rupture
properties of the entire, full-size end product or its in-service behavior in different environments or at various elevated
temperatures.
4.6 For quality control purposes, results derived from standardized tensile test specimens may be considered indicative of the
response of the material from which they were taken for given primary processing conditions and post-processing heat treatments.
5. Interferences
5.1 Test environment (vacuum, inert gas, ambient air, etc.) including moisture content (for example, relative humidity) may
have an influence on the creep and creep rupture behavior of CFCCs. In particular, the behavior of materials susceptible to slow
C1337 − 17
crack growth fracture and oxidation will be strongly influenced by test environment and test temperature. Testing can be conducted
in environments representative of service conditions to evaluate material performance under these conditions.
5.2 Surface preparation of test specimens, although normally not considered a major concern with CFCCs, can introduce
fabrication flaws which may have pronounced effects on the mechanical properties and behavior (for example, shape and level of
the resulting stress-strain-time curve, etc.). Machining damage introduced during test specimen preparation can be either a random
interfering factor in the ultimate strength of pristine material (that is, increased frequency of surface-initiated fractures compared
to volumeinitiatedvolume-initiated fractures) or an inherent part of the strength characteristics to be measured. Surface preparation
can also lead to the introduction of residual stresses. Universal or standardized test methods of surface preparation do not exist.
It should be understood that final machining steps may or may not negate machining damage introduced during the initial
machining. Thus, test specimen fabrication history may play an important role in the measured time-to-failure or deformation, and
shall be reported. In addition, the nature of fabrication used for certain composites (for example, chemical vapor infiltration or hot
pressing) may require the testing of specimens in the as-processed condition (that is, it may not be possible to machine the test
specimen faces without compromising the in-plane fiber architecture).
5.3 Bending in uniaxial tests does induce nonuniform stress distributions. Bending may be introduced from several sources
including misaligned load trains, eccentric or misshaped specimens, and nonuniformly heated specimens or grips. In addition, if
deformations or strains are measured at surfaces where maximum or minimum stresses occur, bending may introduce over or under
measurement of strains depending on the location of the strain measuring strain-measuring device on the test specimen. Similarly,
fracture from surface flaws may be accentuated or suppressed by the presence of the nonuniform stresses caused by bending.
5.4 Fractures that initiate outside the uniformly stressed gage section of a specimen may be due to factors such as stress
concentrations or geometrical transitions, extraneous stresses introduced by gripping or thermal gradients, or strength limiting
features in the microstructure of the test specimen. Such non-gage section fractures will normally constitute invalid tests. In
addition, for face-loaded test specimen geometries, gripping pressure is a key variable in the initiation of fracture. Insufficient
pressure can shear the outer plies in laminated CFCCs, while too much pressure can cause local crushing of the CFCC and lead
to fracture in the vicinity of the grips.
5.5 The time-dependent stress redistribution that occurs at elevated temperatures among the CFCC constituents makes it
necessary that the precise loading history of a creep test specimen be specified. This is of particular importance since the rate at
which a creep load is initially applied can influence the subsequent creep behavior and damage modes. For example, whether
matrix cracking would occur at the end of loading will depend on the magnitude of the loadingtest rate, the test stress, the test
3,4
temperature and the relative creep resistance of the matrix with respect to that of the fibers.
5.6 When CFCCs are mechanically unloaded either partially or totally after a creep test during which the test specimen
accumulated time-dependent deformation, the specimen may exhibit creep recovery as manifested by a time-dependent reduction
of strain. The rate of creep recovery is usually slower than the rate of creep deformation, and both creep and creep recovery are
in most cases thermally activated processes, making them quite sensitive to temperature. Often it is desired to determine the
retained strength of a CFCC after being subjected to creep for a prescribed period of time. Therefore, it is customary to unload
the test specimen from the creep stress and then reload it monotonically until failure. Under these circumstances, the time elapsed
between the end of the creep test and the conduction of the monotonic fast fracture test to determine the retained strength as well
as the loading and unloading rates will influence the rate of internal stress redistribution among the phases and hence the CFCC
strength.
6. Apparatus
6.1 TestingTest Machines—Machines used for tensile testing shall conform to the requirements of Practices E4. The forces used
shall be accurate within 61 % at any force within the selected force range of the testingtest machine as defined in Practices E4.
6.2 Gripping Devices:
6.2.1 General—Various types of gripping devices may be used to transmit the measured force applied by the testingtest machine
to the test specimens. The brittle nature of the matrices of CFCCs requires that a uniform interface exists between the grip
components and the gripped section of the specimen. Line or point contacts and nonuniform pressure can produce Hertzian-type
stresses leading to crack initiation and fracture of the test specimen in the gripped section. Gripping devices can be classified
generally as those employing active and those employing passive grip interfaces as discussed in the following sections. Grips
located outside the heated zone surrounding the specimen may or may not employ cooling. Uncooled grips located outside the
heated zone are termed warm“warm” grips and generally reduce the thermal gradient in the test specimen but at the expense of
using high-temperature alloy grips and increased degradation of the grips due to exposure to the elevated-temperature environment.
Cooled grips located outside the heated zone are termed cold“cold” grips and generally induce a steep thermal gradient along the
length of the specimen.
Holmes, J. W., and Wu, X., “Elevated Temperature Creep Behavior of Continuous Fiber-reinforced Ceramics,” Elevated Temperature Mechanical Behavior of Ceramic
Matrix Composites, S. V. Nair and K. Jakus, eds., Butterworth-Heinneman, 1994.
Lara-Curzio, E., and Ferber, M. K., “Redistribution of Internal Stresses in Composite Materials During Creep,” Ceram. Eng. Sci., Vol 16, No. 5, 1995, pp. 791–800.
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NOTE 1—The expense of the cooling system for cold grips is balanced against maintaining alignment that remains consistent from test to test (stable
grip temperature) and decreased degradation of the grips due to exposure to the elevated-temperature environment. When grip cooling is employed,
provisions shall be provided to control the cooling medium to maximum fluctuations of 5 K (less than 1 K preferred) about a setpoint temperature over
the course of the test to minimize thermally induced strain changes in the test specimen. In addition, opposing grip temperatures should be maintained
at uniform and consistent temperatures not to exceed a difference 65 K (less than 61 K preferred) so as to avoid inducing unequal thermal gradients
and subsequent nonuniaxial stresses in the specimen. Generally, the need for control of grip temperature fluctuations or differences may be indicated if
test specimen gage section temperatures cannot be maintained within the limits prescribed in 9.2.2.
6.2.1.1 Active Grip Interfaces—Active grip interfaces require a continuous application of a mechanical, hydraulic, or pneumatic
force to transmit the force to the test specimen. Generally, these types of grip interfaces cause a force to be applied normal to the
surface of the gripped section of the test specimen. Transmission of the uniaxial load applied by the test machine is then
accomplished by friction between the test specimen and the grip faces. Thus, important aspects of active grip interfaces are: (1)
uniform contact between the gripped section of the test specimen and the grip faces, and (2) constant coefficient of friction over
the grip/test specimen interface. In addition, note that fixed-displacement active grips set at ambient temperatures may introduce
excessive gripping stresses due to thermal expansion of the test material when the test specimen is heated to the test temperature.
Therefore, provisions shall be made to avoid such excessive stresses prior to the test by heating the test specimen while maintaining
a constant force in the load train (for example, force control). Hydraulic grips are usually water cooled, and special provisions shall
be made to ensure that these grips are continuously cooled since loss of cooling may result in rupture of the hydraulic lines and
hydraulic chamber creating a potentially dangerous situation.
(1) For flat test specimens, face-loaded grips, either by direct lateral pressure grip faces or by indirect wedge-type grip faces,
act as the grip interface. Generally, close tolerances are required for the flatness and parallelism as well as for the wedge angle of
the wedge grip faces. In addition, the thickness, flatness, and parallelism of the gripped section of the test specimen must be within
similarly close tolerances to promote uniform contact at the test specimen/grip interface. Tolerances will vary depending on the
exact test specimen configuration. For examples of tensile test specimen geometries, the user of this test method is referred to Test
Method C1275.
(2) Sufficient lateral pressure must be applied to prevent slippage between the grip face and the test specimen. Grip surfaces
that are scored or serrated with a pattern similar to that of a single-cut file have been found satisfactory. A fine serration appears
to be the most satisfactory. The serrations shall be kept clean and well-defined but not overly sharp. The length and width of the
grip faces shall be equal to or greater than the respective length and width of the gripped sections of the test specimen.
6.2.1.2 Passive Grip Interfaces—Passive grip interfaces transmit the force applied by the test machine to the test specimen
through a direct mechanical link. Generally, these mechanical links transmit the test force to the test specimen by means of
geometrical features of the test specimens such as shank shoulders or holes in the gripped head. Thus, the important aspect of
passive grip interfaces is uniform contact between the gripped section of the test specimen and the grip faces.
(1) For flat test specimens, passive grips may act either through edge-loading by means of grip interfaces at the shoulders of
the test specimen shank or by combinations of face-loading and pin loading by means of pins at holes in the gripped head of the
test specimen. Generally, close tolerances of linear and angular dimensions of shoulder and grip interfaces are required to promote
uniform contact along the entire test specimen/grip interface as well as to provide for noneccentric loading. In addition, moderately
close tolerances are required for center-line coincidence and diameters of the pins and hole. Examples of test specimen geometries
adequate for passive grips are presented in Test Method C1275.
(2) When using edge-loaded test specimens, lateral centering of the test specimen within the grip attachments is accomplished
by use of wedge-type inserts machined to fit within the grip cavity. Examples of successfully used edge-loaded test specimens are
presented in Figs. 8X2.1 and Figs. 9 X2.2 of Test Method C1275.
(3) The pins in face/pin loaded grips (for such test specimens as those illustrated in Figs. 14 through 16 X2.6, X2.7, and X2.8
of Test Method C1275) are primarily for alignment purposes and force transmission. Secondary force transmission is through
face-loading by means of mechanically actuated wedge grip faces. Proper tightening of the wedge grip faces against the test
specimen to prevent slipping while avoiding compressive fracture of the test specimen gripped section must be determined for each
material and test specimen type.
(4) Note that passive grips employing single pins in each gripped section of the test specimen as the primary load transfer
mechanism are not recommended. Relatively low interfacial shear strengths compared to longitudinal tensile strengths in CFCCs
(particularly for 1-D reinforced materials loaded along the fiber direction) may promote non-gage section fractures along interfaces
particularly at geometric transitions or at discontinuities such as holes.
6.3 Load Train Couplers:
6.3.1 General—Various types of devices (load train couplers) may be used to attach the active or passive grip interface
assemblies to the testingtest machine. The load train couplers in conjunction with the type of gripping device play major roles in
the alignment of the load train and thus subsequent bending imposed in the test specimen. Load train couplers can be classified
generally as fixed and nonfixed as discussed in the following sections. Note that use of well-aligned fixed or self-aligning nonfixed
couplers does not automatically guarantee low bending in the gage section of the tensile test specimen. Generally, well-aligned
fixed or self-aligning nonfixed couplers provide for well-aligned load trains, but the type and operation of grip interfaces as well
as the as-fabricated dimensions of the tensile test specimen can add significantly to the final bending imposed in the gage section
of the test specimen.
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6.3.1.1 Regardless of which type of coupler is used, alignment of the load train must be verified as a minimum at the beginning
and end of a test series unless the conditions for verifying alignment as detailed in Section 11Appendix X1 of Test Method C1275
are otherwise met. A test series is interpreted to mean a discrete group of tests on individual test specimens conducted within a
discrete period of time on a particular material configuration, test specimen geometry, test condition, or other uniquely definable
qualifier. An additional verification of alignment is recommended, although not required, at the middle of the test series. Either a
dummy or actual test specimen and the alignment verification procedures detailed in Section 11Appendix X1 of Test Method
C1275 and Practice E1012 shall be used. Allowable bending requirements are discussed in 6.56.5. Tensile test specimens used for
alignment verification shall be equipped with eight separate longitudinal strain gages to determine bending contributions from both
eccentric and angular misalignment. Ideally the verification specimen shall be of identical material to that being tested. However,
in the case of CFCCs the type of reinforcement or degree of residual porosity may complicate the consistent and accurate
measurement of strain. Therefore, it is recommended that an alternate material (isotropic and homogeneous) with similar elastic
modulus, elastic strain capability, and hardness to the test material be used. In addition, dummy specimens used for alignment
verification shall have the same geometry and dimensions of the actual test specimens as well as similar mechanical properties as
the test material to ensure similar axial and bending stiffness characteristics as the actual test specimen and material.
6.3.2 Fixed Load Train Couplers—Fixed couplers may incorporate devices which require either a one-time, pretest alignment
adjustment of the load train which remains constant for all subsequent tests or an in situ, pretest alignment of the load train which
is conducted separately for each test specimen and each test. Such devices usually employ angularity and concentricity adjusters
to accommodate inherent load train misalignments. Regardless of which method is used, alignment verification must be performed
as discussed in 6.3.1.1.
6.3.3 Nonfixed Load Train Couplers—Nonfixed couplers may incorporate devices which promote self-alignment of the load
train during the movement of the cross-head or actuator. Generally such devices rely upon freely moving linkages to eliminate
applied moments as the load train components are loaded. Knife edges, universal joints, hydraulic couplers, or air bearings are
examples of such devices. Although nonfixed load train couplers are intended to be self-aligning and thus eliminate the need to
evaluate the bending in the test specimen for each test, the operation of the couplers must be verified as discussed in 6.3.1.1.
6.3.3.1 Nonfixed load train couplers are useful in rapid test rate or constant load testing of CFCCs where the “graceful” fracture
process is not as apparent. If the material exhibits graceful fracture the self-aligning feature of the nonfixed coupler will allow
rotation of the gripped section of the specimen, thus promoting a nonuniform stress in the remaining ligament of the gage section.
NOTE 2—Graceful fracture refers to the progressive process of matrix cracking and debonding and sliding of fibers that bridge those cracks and prevent
the otherwise catastrophic mode of failure associated with brittle fracture.
6.4 Strain Measurement—Strain at elevated temperatures shall be determined by means of a suitable extensometer.
6.4.1 Extensometers used for tensile creep testing of CFCC test specimens shall satisfy Practice E83, Class B-1 requirements.
Extensometers shall be calibrated periodically in accordance with Practice E83. For extensometers which mechanically contact the
test specimen, the contact shall not cause damage to the test specimen surface. In addition, extensometer contact probes must be
chosen to be chemically compatible with the test material. In addition, the weight of the extensometer shall be supported so as not
to introduce bending greater than that allowed in 6.5. Finally, the tips of the probes of contacting extensometers and the magnitude
of the contact force shall be configured (for example, sharp knife edges or chisel tips) so as to minimize slippage.
6.5 Allowable Bending—Studies of the effects of bending on the tensile creep and tensile creep rupture behavior of CFCCs do
not exist. Until such information is forthcoming for CFCCs, this test method adopts the recommendations for tensile testing of
monolithic advanced ceramics. Therefore, the recommended maximum allowable percent for test specimens tested under this test
method is 5 %. For verification of test specimen alignment, refer to Practice E1012.
6.6 Heating Apparatus—The apparatus for and method of heating the test specimens shall provide the temperature control
necessary to satisfy the requirement of 9.2.
6.6.1 Heating can be by indirect electrical resistance (heating elements), indirect induction through a susceptor, or radiant lamp
with the test specimen in ambient air at atmospheric pressure unless other environments are specifically applied and reported. Note
that direct resistance heating is not recommended for heating CFCCs due to possible differences of the electrical resistances of the
constituent materials which may produce nonuniform heating of the test specimen.
6.7 Temperature-Measuring Apparatus—The method of temperature measurement shall be sufficiently sensitive and reliable to
ensure that the temperature of the test specimen is within the limits specified in 9.2.
6.7.1 Primary temperature measurement shall be made with thermocouples in conjunction with potentiometers, millivoltmeters,
or electronic temperature controllers or readout units, or both. Such measurements are subject to two types of error. Thermocouple
calibration and instrument measuring errors initially produce uncertainty as to the exact temperature. Secondly, both thermocouples
and measuring instruments may be subject to variations over time. Common errors encountered in the use of thermocouples to
measure temperatures include calibration error, drift in calibration due to contamination or deterioration with use, lead-wire error,
error arising from method of attachment to the test specimen, direct radiation of heat to the bead, heat-conduction heat conduction
along thermocouple wires, etc.
6.7.2 Temperature measurements shall be made with thermocouples of known calibration. Representative thermocouples shall
be calibrated from each lot of wires used for making noble-metal (for example, platinum (Pt) or rhodium (Rh)) thermocouples.
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Except for relatively low temperatures of exposure, noble-metal thermocouples are eventually subject to error upon reuse.
Oxidized noble-metal thermocouples shall not be reused without clipping back to remove wire exposed to the hot zone, re-welding,
and annealing. Any reuse of noble-metal thermocouples after relatively low-temperature use without this precaution shall be
accompanied by re-calibration data demonstrating that calibration was not unduly affected by the conditions of exposure.
6.7.3 Measurement of the drift in calibration of thermocouples during use is difficult. When drift is a problem during tests, a
method shall be devised to check the readings of the thermocouples monitoring the test specimen temperature during the test. For
reliable calibration of thermocouples after use, the temperature gradient of the test furnace must be reproduced during the
re-calibration.
6.7.4 Temperature measuring, controlling, and recording instruments shall be calibrated against a secondary standard, such as
precision potentiometer, optical pyrometer, or black-body thyristor. Lead-wire error shall be checked with the lead wires in place
as they normally are used. For thermocouple calibration procedures, refer to Test Method E220 and Specification E230.
6.8 Data Acquisition—At the minimum, gage section elongation or strain versus time shall be obtained. Either analog chart
recorders or digital data acquisition systems can be used for this purpose, although a digital record is recommended for ease of
later data analysis. Ideally, an analog chart recorder or plotter should be used in conjunction with the digital data acquisition system
to provide an immediate record of the test as a supplement to the digital record. Recording devices shall be accurate within 61 %
of the selected range for the testingtest system including readout unit, as specified in Practices E4.
6.8.1 Cross-head displacement of the test machine may also be recorded but shall not be used to define displacement or strain
in the gage section, especially when self-aligning couplers are used in the load train.
6.8.2 Temperature shall be recorded at the initiation and completion of the actual test. However, temperature can also be
recorded parallel to the strain record in addition to temperature recordings at the start of the heating of the furnace (including
ramp-up to test temperature) and ending at the completion of the test.
6.9 Dimension-Measuring Devices—Micrometers and other devices used for measuring linear dimensions shall be accurate and
precise to at least one half one-half of the smallest unit to which the individual dimension is required to be measured. For the
purposes of this test method, cross-sectional dimensions shall be measured to within 0.02 mm, requiring dimension measuring
dimension-measuring devices with accuracies of 0.01 mm.
7. Hazard Statements
7.1 During the conduct of this test method, the possibility of flying fragments of broken test material may be high. The brittle
nature of advanced ceramics and the release of strain energy contribute to the potential release of uncontrolled fragments upon
fracture. Means for containment and retention of these fragments for later fractographic reconstruction and analysis is highly
recommended.
7.2 Exposed fibers at the edges of CFCC test specimens present a hazard due to the sharpness and brittleness of the ceramic
fiber. All persons required to handle these materials shall be well-informed well informed of such conditions and the proper
handling techniques.
8. Test Specimens
8.1 Test Specimen Geometry:
8.1.1 General—The geometry of tensile creep test specimens is dependent on the ultimate use of the tensile creep data. For
example, if the tensile creep of an as-fabricated component is required, the dimensions of the resulting tensile test specimen may
reflect the thickness, width, and length restrictions of the component. If it is desired to evaluate the effects of interactions of various
constituent materials for a particular CFCC manufactured by means of a particular processing route, then the size of the test
specimen and resulting gage section will reflect the desired volume to be sampled. In addition, grip interfaces and load train
couplers as discussed in Section 6 will influence the final design of the test specimen geometry.
8.1.1.1 The following sections discuss the more common and, thus, proven test specimen geometries, although any geometry
is acceptable if it meets the gripping, fracture location, temperature profile, and bending requirements of this test method.
Deviations from the recommended geometries may be necessary depending upon the particular CFCC being evaluated. Stress
analyses of untried test specimens shall be conducted to ensure that stress concentrations which can lead to undesired fractures
outside the gage sections do not exist. It should be noted that contoured test specimens by their nature contain inherent stress
concentrations due to geometric transitions. Stress analyses can indicate the magnitude of such stress concentrations while
revealing the success of producing a uniform tensile stress state in the gage section of the test specimen. Additionally, the success
of an elevated-temperature creep test will depend on the type of heating system, extent of test specimen heating, and test specimen
geometry since these factors are all interrelated. For example, thermal gradients may introduce additional stress gradients in test
specimens which may already exhibit stress gradients at ambient temperatures due to geometric transitions. Therefore, untried test
configurations should be simultaneously analyzed for both loading-induced stress gradients and thermally induced temperature
gradients to ascertain any adverse interactions.
8.1.1.2 Generally, test specimens with contoured gage sections (transition radii of >50 mm) are preferred to promote the tensile
stresses with the greatest values in the uniformly stressed gage section while minimizing the stress concentration due to the
geometrical transition of the radius. However, in certain instances, (for example, 1-D CFCCs tested along the direction of the
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fibers) low interfacial shear strength relative to the tensile strength in the fiber direction will cause splitting of the test specimen
initiating at the transition region between the gage section and the gripped section of the test specimen with the split propagating
along the fiber direction leading to fracture of the test specimen. In these cases, straight-sided test specimens may be required for
determining the tensile creep and creep rupture behavior of the CFCC. Figure 7 in Test Method C1275 shows an example of a
straight-sided test specimen. In other instances, a particular fiber weave or processing route will preclude fabrication of test
specimens with reduced gage sections, thus requiring implementation of straight-sided test specimens. Straight-sided test
specimens may be gripped by any of the methods discussed herein, although active gripping systems are recommended for
minimizing non-gage section fractures.
8.1.2 Edge-Loaded Flat Tensile Test Specimens—This type of geometry has been successfully employed for the evaluation of
2-D and 3-D CFCCs. Of particular concern with this geometry is the proper and consistent angle of the edge-loaded shank.
However, the preparation of this type of test specimen with the stringent tolerances required is routine with numerical-controlled
machines. Furthermore, this test specimen is ideal when using “warm” or “hot” grips to minimize thermal gradients along the
length of the specimen. Figures 8X2.1 and Figures 9 X2.2 in Test Method C1275 show examples of contoured edge-loaded test
specimens.
8.1.3 Face-Loaded Flat Tensile Test Specimens—This configuration exploits the friction at the test specimen/grip interface to
transmit the uniaxial force applied by the test machine. Important tolerances for the face-loaded geometry include parallelism and
flatness of faces, all of which will vary depending on the exact configuration as shown in the appropriate test specimen drawings.
8.1.3.1 For face-loaded test specimens, especially for straight-sided (for example, noncontoured) test specimens, end tabs may
be required to provide a compliant layer for gripping. For CFCCs, fiberglass reinforced epoxy, PMR, and carbon fiber-reinforced
resins, tab materials have been used successfully. However, metallic tabs (for example, aluminum alloys) may be satisfactory (or
desirable for elevated temperature use) as long as the tabs are strain compatible (that is, having an elastic modulus of magnitude
comparable to the bulk elastic modulus of the CFCC) with the CFCC material being tested. Each beveled tab (bevel angle ≤15°)
shall be a minimum of 30 mm 30 mm long, the same width of the specimen, and have the total thickness of the tabs on the order
of the thickness of the test specimen. Any high-elongation (tough) adhesive system may be used with the length of the tabs
determined by the shear strength of the adhesive, size of the test specimen, and estimated strength of the composite. In any case,
a significant fraction (>10 to 20 %) of fractures within one test specimen width of the tab shall be cause to reexamine the tab
materials and configuration, gripping method, and adhesive, and to make necessary adjustments to promote fracture within the gage
section. Note that care should be taken to ensure that both the adhesive and tab material are capable of use at the temperature which
might occur in the grip region. Figure 138 in Test Method C1275 shows an example of a bevelled tab.
8.1.4 Pin/Face-Loaded Flat Tensile Test Specimens—These test specimens employ combinations of pin and face loading to
transmit the uniaxial force of the test machine to the test specimen. Close tolerances of hole/pin diameters and center lines are
required to ensure proper specimen alignment in the grips and transmission of the forces, since the face-loaded part of the geometry
provides a secondary force transmission mechanism in these test specimens. Important tolerances for the face-loaded part of the
geometry include parallelism and flatness of faces, both of which will vary depending on the exact configuration as shown in the
appropriate test specimen drawings. Thus, the pin/face-loaded geometry may require somewhat intensive fabrication procedures.
Figures 14 through 16 in Test Method C1275 show examples of contoured, pin/face-loaded test specimens.
8.1.4.1 Note that test specimens requiring single pins in each gripped section of the test specimen as the primary load transfer
mechanism are not recommended. Relatively low interfacial shear strengths compared to longitudinal tensile strengths in CFCCs
(particularly for 1-D reinforced materials loaded along the fiber direction) may promote non-gage section fractures along interfaces
particularly at geometric transitions or at discontinuities such as holes.
8.2 Specimen Preparation:
8.2.1 Depending upon the intended application of the tensile creep data, use one of the following test specimen preparation
procedures. Regardless of the preparation procedure used, sufficient details regarding the procedure must be reported to allow
replication.
8.2.2 As-Fabricated—The tensile test specimen should simulate the surface/edge conditions and processing route of an
application where no machining is used, for example, as-cast, sintered, or injection-molded part. No additional machining
specifications are relevant. As-processed test specimens might possess rough surface textures and nonparallel edges and as such
may cause excessive misalignment or proneness to non-gage section fractures, or both.
8.2.3 Application-Matched Machining—The tensile test specimen should have as close to the same surface/edge preparation as
that given to the component. Unless the process is proprietary, the report shall be specific about the stages of material removal,
wheel grits, wheel bonding, amount of material removed per pass, and type of coolant used.
8.2.4 Customary Practices—In instances where a customary machining procedure has been developed that is completely
satisfactory for a class of materials (that is, it induces no unwanted surface/subsurface damage or residual stresses), this procedure
shall be used.
8.2.5 Standard Procedure—In instances where 8.2.28.2.2 – 8.2.4 through 8.2.4are not appropriate, 8.2.5 shall apply. Studies to
evaluate the machinability of CFCCs have not been completed. Therefore, the standard procedure of 8.2.5 can be viewed as
starting-point guidelines, and a more stringent procedure may be necessary.
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8.2.5.1 All grinding or cutting shall be done with ample supply of appropriate filtered coolant to keep the workpiece and
grinding wheel constantly flooded and particles flushed. Grinding can be done in at least two stages, ranging from coarse to fine
rate of material removal. All cutting can be done in one stage appropriate for the depth of cut.
8.2.5.2 Stock removal rate shall be on the order of 0.03 mm per pass using diamond tools that have between 320 and 600 grit.
Remove equal stock from each face where applicable.
8.3 Handling Precaution—Care should be exercised in storage and handling of finished test specimens to avoid the introduction
of random and severe flaws. In addition, attention shall be given to pre-test storage of test specimens in controlled environments
or desiccators to avoid unquantifiable environmental degradation of test specimens prior to testing.
8.4 Test Specimen Sampling and Number—Samples of the material to provide test specimens must be taken from such locations
so as to be representative of the billet or lot from which it is taken. Although each testingtest scenario will vary, a typical designed
experiment may include creep tests at stresses below, about, and above the monotonic matrix-cracking stress level and at least for
one stress level, tests across a range of four temperatures. It is recommended that at least 20 % of the tests in the designed
experiment be replicated (duplicated or triplicated) to determine levels of repeatability.
9. Procedure
9.1 Test Specimen Dimensions—Determine the thickness and width of the gage section of each test specimen to within 0.02 mm.
Make measurements on at least three different cross-sectional planes in the gage section. To avoid damage in the gage section area,
these measurements shall be made either optically (for example, an optical comparator) or mechanically using a flat, anvil-type
micrometer. In either case, the resolution of the instrument shall be as specified in 6.9. Exercise caution to prevent damage to the
test specimen gage section. Ball-tipped or sharp-anvil micrometers are not recommended because localized cracking can be
induced. The measured dimensions and locations of the measurements sh
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