ASTM E2714-13(2020)

Standard Test Method for Creep-Fatigue Testing

SIGNIFICANCE AND USE
4.1 Creep-fatigue testing is typically performed at elevated temperatures and involves the sequential or simultaneous application of the loading conditions necessary to generate cyclic deformation/damage enhanced by creep deformation/damage or vice versa. Unless such tests are performed in vacuum or an inert environment, oxidation can also be responsible for important interaction effects relating to damage accumulation. The purpose of creep-fatigue tests can be to determine material property data for (a) assessment input data for the deformation and damage condition analysis of engineering structures operating at elevated temperatures (b) the verification of constitutive deformation and damage model effectiveness (c) material characterization, or (d) development and verification of rules for new construction and life assessment of high-temperature components subject to cyclic service with low frequencies or with periods of steady operation, or both.  
4.2 In every case, it is advisable to have complementary continuous cycling fatigue data (gathered at the same strain/loading rate) and creep data determined from test conducted as per Practice E139 for the same material and test temperature(s). The procedure is primarily concerned with the testing of round bar test specimens subjected (at least remotely) to uniaxial loading in either force or strain control. The focus of the procedure is on tests in which creep and fatigue deformation and damage is generated simultaneously within a given cycle. Data which may be determined from creep-fatigue tests performed under such conditions may characterize  (a) cyclic stress-strain deformation response (b) cyclic creep (or relaxation) deformation response (c) cyclic hardening, cyclic softening response or (d) cycles to crack formation, or both.  
4.3 While there are a number of testing Standards and Codes of Practice that cover the determination of low cycle fatigue deformation and cycles to crack initiation properties (See Pr...
SCOPE
1.1 This test method covers the determination of mechanical properties pertaining to creep-fatigue deformation or crack formation in nominally homogeneous materials, or both by the use of test specimens subjected to uniaxial forces under isothermal conditions. It concerns fatigue testing at strain rates or with cycles involving sufficiently long hold times to be responsible for the cyclic deformation response and cycles to crack formation to be affected by creep (and oxidation). It is intended as a test method for fatigue testing performed in support of such activities as materials research and development, mechanical design, process and quality control, product performance, and failure analysis. The cyclic conditions responsible for creep-fatigue deformation and cracking vary with material and with temperature for a given material.  
1.2 The use of this test method is limited to specimens and does not cover testing of full-scale components, structures, or consumer products.  
1.3 This test method is primarily aimed at providing the material properties required for assessment of defect-free engineering structures containing features that are subject to cyclic loading at temperatures that are sufficiently high to cause creep deformation.  
1.4 This test method is applicable to the determination of deformation and crack formation or nucleation properties as a consequence of either constant-amplitude strain-controlled tests or constant-amplitude force-controlled tests. It is primarily concerned with the testing of round bar test specimens subjected to uniaxial loading in either force or strain control. The focus of the procedure is on tests in which creep and fatigue deformation and damage is generated simultaneously within a given cycle. It does not cover block cycle testing in which creep and fatigue damage is generated sequentially. Data that may be determined from creep-fatigue tests performed under conditions in whi...

General Information

• Status: Published
• Publication Date: 30-Apr-2020
• ICS: 19.060 - Mechanical testing
• Technical Committee: E08 - Fatigue and Fracture
• Drafting Committee: E08.05 - Cyclic Deformation and Fatigue Crack Formation

Relations

• Replaces: ASTM E2714-13 - Standard Test Method for Creep-Fatigue Testing
• Effective Date: 01-May-2020
• Refers: ASTM E1823-24a - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 15-Feb-2024
• Refers: ASTM E1823-24 - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 01-Feb-2024
• Refers: ASTM E8/E8M-24 - Standard Test Methods for Tension Testing of Metallic Materials
• Effective Date: 01-Jan-2024
• Refers: ASTM E647-23b - Standard Test Method for Measurement of Fatigue Crack Growth Rates
• Effective Date: 15-Nov-2023
• Refers: ASTM E1823-20 - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 01-Feb-2020
• Refers: ASTM E8/E8M-16 - Standard Test Methods for Tension Testing of Metallic Materials
• Effective Date: 15-Jul-2016
• Refers: ASTM E8/E8M-15 - Standard Test Methods for Tension Testing of Metallic Materials
• Effective Date: 01-Feb-2015
• Refers: ASTM E4-14 - Standard Practices for Force Verification of Testing Machines
• Effective Date: 01-Jun-2014
• Refers: ASTM E177-14 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-May-2014
• Refers: ASTM E220-13 - Standard Test Method for Calibration of Thermocouples By Comparison Techniques
• Effective Date: 01-Nov-2013
• Refers: ASTM E647-13a - Standard Test Method for Measurement of Fatigue Crack Growth Rates
• Effective Date: 15-Oct-2013
• Refers: ASTM E647-13ae1 - Standard Test Method for Measurement of Fatigue Crack Growth Rates
• Effective Date: 15-Oct-2013
• Refers: ASTM E8/E8M-13 - Standard Test Methods for Tension Testing of Metallic Materials
• Effective Date: 01-Jun-2013
• Refers: ASTM E177-13 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-May-2013

Overview

ASTM E2714-13(2020), the "Standard Test Method for Creep-Fatigue Testing," defines procedures for determining the mechanical properties of nominally homogeneous materials subjected to uniaxial forces under isothermal conditions where both creep and fatigue contribute to deformation and crack formation. This standard is essential for high-temperature material testing and is widely used in materials research, engineering design, quality control, product performance evaluation, and failure analysis. By simulating cyclic loading and conditions present in real-world service environments, ASTM E2714-13(2020) provides critical data for the assessment and life prediction of engineering structures operating under creep-fatigue conditions.

Key Topics

• Creep-Fatigue Test Methodology
  Focuses on determining how materials deform and form cracks under the simultaneous action of cyclic (fatigue) and time-dependent (creep) loading at elevated temperatures.

• Specimen and Test Conditions
  Testing is conducted on round bar specimens using uniaxial force or strain control, under isothermal conditions. The standard specifically addresses tests where fatigue and creep deformation develop concurrently within each cycle.

• Test Environment Considerations
  Recognizes the influence of oxidation (unless testing in vacuum or inert atmospheres), which can accelerate damage accumulation and alter failure mechanisms.

• Data and Measurements
  Key measurements include cyclic stress-strain response, cyclic creep (or relaxation), cyclic hardening or softening, and the number of cycles to crack initiation. Complementary fatigue and creep data collected under consistent conditions are advised to provide a comprehensive material characterization.

• Equipment and Calibration
  Calls for properly aligned, servo-controlled testing machines, high-accuracy force transducers, extensometers, and reliable temperature measurement systems. Calibration and alignment according to referenced standards ensure result accuracy.

Applications

• Materials Characterization and Development
  Used for generating foundational material property data required in the design and assessment of components and structures subjected to high-temperature, cyclic loading.

• Model Verification
  Assists in validating constitutive deformation and damage models for predicting the behavior of materials under service conditions involving creep-fatigue.

• Mechanical Design and Life Assessment
  Supports development of rules for the design, new construction, and remaining life estimation of high-temperature components in power plants, aerospace, and industrial equipment.

• Process and Quality Control
  Provides standardized testing approaches for assessing material suitability during procurement, manufacturing, and before component deployment.

• Failure Analysis
  Enables the investigation of component performance and the root causes of unexpected failures in high-temperature, cyclic service environments.

Related Standards

Several established international and national standards support or complement ASTM E2714-13(2020):

• ASTM E139: Creep, Creep-Rupture, and Stress-Rupture Tests of Metallic Materials
• ASTM E606: Strain-Controlled Fatigue Testing
• ASTM E647: Measurement of Fatigue Crack Growth Rates
• ISO 12106: Metallic materials - Fatigue testing - Axial strain-controlled method
• ISO 7500-1: Verification of static uniaxial testing machines
• BS 7270: Constant amplitude strain-controlled fatigue testing

These referenced standards provide detailed procedures for specific aspects such as calibration, fatigue, and creep testing, ensuring comprehensive material evaluation and consistency in results across laboratories.

---

By adhering to ASTM E2714-13(2020), laboratories and engineering teams can produce reliable, comparable data on creep-fatigue behavior essential for high-temperature application industries, enhancing structural integrity and operational longevity. This test method is a foundational tool for advancing materials performance in demanding environments.

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: E2714 − 13 (Reapproved 2020)
Standard Test Method for
Creep-Fatigue Testing
This standard is issued under the fixed designation E2714; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope strain deformation response (b) cyclic creep (or relaxation)
deformation response (c) cyclic hardening, cyclic softening
1.1 Thistestmethodcoversthedeterminationofmechanical
response (d) cycles to formation of a single crack or multiple
properties pertaining to creep-fatigue deformation or crack
cracks in test specimens.
formation in nominally homogeneous materials, or both by the
use of test specimens subjected to uniaxial forces under
NOTE 1—Acrack is believed to have formed when it has nucleated and
propagated in a specimen that was initially uncracked to a specific size
isothermal conditions. It concerns fatigue testing at strain rates
that is detectable by a stated technique. For the purpose of this standard,
or with cycles involving sufficiently long hold times to be
the formation of a crack is evidenced by a measurable increase in
responsible for the cyclic deformation response and cycles to
compliance of the specimen or by a size detectable by potential drop
crack formation to be affected by creep (and oxidation). It is
technique. Specific details of how to measure cycles to crack formation
intended as a test method for fatigue testing performed in
are described in 9.5.1.
support of such activities as materials research and
1.5 Thistestmethodisapplicabletotemperaturesandstrain
development, mechanical design, process and quality control,
rates for which the magnitudes of time-dependent inelastic
product performance, and failure analysis. The cyclic condi-
strains (creep) are on the same order or larger than time-
tions responsible for creep-fatigue deformation and cracking
independent inelastic strain.
vary with material and with temperature for a given material.
NOTE 2—The term inelastic is used herein to refer to all nonelastic
1.2 The use of this test method is limited to specimens and
strains. The term plastic is used herein to refer only to time independent
does not cover testing of full-scale components, structures, or (that is, non-creep) component of inelastic strain. A useful engineering
estimate of time-independent strain can be obtained when the strain rate
consumer products.
-3 -1
exceeds some value. For example, a strain rate of 1×10 sec is often
1.3 This test method is primarily aimed at providing the
used for this purpose. This value should increase with increasing test
material properties required for assessment of defect-free temperature.
engineering structures containing features that are subject to
1.6 The values stated in SI units are to be regarded as
cyclicloadingattemperaturesthataresufficientlyhightocause
standard. No other units of measurement are included in this
creep deformation.
standard.
1.4 This test method is applicable to the determination of
1.7 This standard does not purport to address all of the
deformation and crack formation or nucleation properties as a
safety concerns, if any, associated with its use. It is the
consequence of either constant-amplitude strain-controlled
responsibility of the user of this standard to establish appro-
tests or constant-amplitude force-controlled tests. It is primar-
priate safety, health, and environmental practices and deter-
ily concerned with the testing of round bar test specimens
mine the applicability of regulatory limitations prior to use.
subjected to uniaxial loading in either force or strain control.
1.8 This international standard was developed in accor-
The focus of the procedure is on tests in which creep and
dance with internationally recognized principles on standard-
fatigue deformation and damage is generated simultaneously
ization established in the Decision on Principles for the
within a given cycle. It does not cover block cycle testing in
Development of International Standards, Guides and Recom-
whichcreepandfatiguedamageisgeneratedsequentially.Data
mendations issued by the World Trade Organization Technical
that may be determined from creep-fatigue tests performed
Barriers to Trade (TBT) Committee.
under conditions in which creep-fatigue deformation and
2. Referenced Documents
damage is generated simultaneously include (a) cyclic stress-
2.1 ASTM Standards:
E4Practices for Force Verification of Testing Machines
This test method is under the jurisdiction ofASTM Committee E08 on Fatigue
and Fracture and is the direct responsibility of Subcommittee E08.05 on Cyclic
Deformation and Fatigue Crack Formation. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved May 1, 2020. Published May 2020. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 2009. Last previous edition approved in 2013 as E2714–13. Standards volume information, refer to the standard’s Document Summary page on
DOI:10.1520/E2714–13R20. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2714 − 13 (2020)
E8/E8MTest Methods for Tension Testing of Metallic Ma- ISO 7500-1–2004Metallic materials – Verification of static
terials uniaxial testing machines – Part 1. Tension/compression
E83Practice for Verification and Classification of Exten- testingmachines–Verificationandcalibrationoftheforce
someter Systems measuring system
E111Test Method for Young’s Modulus, Tangent Modulus, ISO 9513–1999Metallic materials – Calibration of exten-
and Chord Modulus someters used in axial testing
E139Test Methods for Conducting Creep, Creep-Rupture, ISO 5725–1994Accuracy (trueness and precision) of mea-
and Stress-Rupture Tests of Metallic Materials surement methods
E177Practice for Use of the Terms Precision and Bias in
2.5 JIS Standard:
ASTM Test Methods
JIS Z 2279–1992Method of high temperature low cycle
E220Test Method for Calibration of Thermocouples By
fatigue testing for metallic materials
Comparison Techniques
E230Specification for Temperature-Electromotive Force 3. Terminology
(emf) Tables for Standardized Thermocouples
3.1 Thedefinitionsinthistestmethodthatarealsoincluded
E467Practice for Verification of Constant Amplitude Dy-
in Terminology E1823 are in accordance with Terminology
namic Forces in an Axial Fatigue Testing System
E1823.
E606Test Method for Strain-Controlled Fatigue Testing
3.2 Symbols,standarddefinitions,anddefinitionsspecificto
E647Test Method for Measurement of Fatigue Crack
this standard are in 3.2.1, 3.3, and 3.4, respectively.
Growth Rates
3.2.1 Symbols:
E691Practice for Conducting an Interlaboratory Study to
Symbol Term
Determine the Precision of a Test Method
E1012Practice for Verification of Testing Frame and Speci-
d [L] Diameter of gage section
men Alignment Under Tensile and Compressive Axial
of cylindrical test specimen
D , [L] Diameter of grip ends
Force Application g
-2
E, E ,E ,[FL ] Elastic modulus, initial modulus
o N
E1823TerminologyRelatingtoFatigueandFractureTesting
of elasticity, modulus of elasticity at cycle
-2
E2368Practice for Strain Controlled Thermomechanical
E ,E [FL ] Tensile modulus,
T C
compressive modulus
Fatigue Testing
P [F] Force
2.2 BSI Standards:
l, l [L] Extensometer gage length,
o
original extensometer
BS 7270: 2000Method for ConstantAmplitude Strain Con-
gage length
trolled Fatigue Testing
L, L , [L] Length of parallel section
o
BS 1041-4:1992Temperature measurement – Part 4: Guide
of gage length, original length
of parallel section of gage length
to the selection and use of thermocouples
N, N Cycle number, cycle number
4 f
2.3 CEN Standards:
to crack formation
r,[L} Transition radius
EN 60584-1–1996Thermocouples – Reference tables (IEC
(from parallel section to grip end)
584-1)
ε ⁄ ε ,R Strain ratio
min max ε
EN 60584 -2– 1993Thermocouples – Tolerances (IEC
σ ⁄ σ ,R Stress ratio
min max σ
584-2) τ Time
T[θ] Specimen temperature
PrEN 3874–1998Test methods for metallic materials –
T [θ] Indicated specimen
i
constant amplitude force-controlled low cycle fatigue
temperature
N versus σ Crack formation or end-of-life criterion is
testing max
expressed as a percentage reduction in
PrEN 3988–1998Test methods for metallic materials –
maximum stress from the cycles,
constant amplitude strain-controlled low cycle fatigue
N versus σ curve when the stress
max
falls sharply (see Fig. 1), or a specific
testing
percentage
2.4 ISO Standards:
decrease in the modulus of elasticity ratios
in the tensile and compressive portions
ISO12106–2003Metallicmaterials–Fatiguetesting-Axial
of the hysteresis diagrams, or as a
strain-controlled method
specific increase in crack size as
ISO 12111–2005 (Draft) Strain-controlled thermo-
indicated by an electric
potential drop monitoring instrumentation.
mechanical fatigue testing method
ε, ε , ε Strain, maximum strain in the cycle,
max min
minimum strain in the cycle
ε , ε , ε Elastic strain amplitude,
ea pa ta
Available from British Standards Institute (BSI), 389 Chiswick High Rd.,
plastic strain amplitude,
London W4 4AL, U.K., http://www.bsi-global.com.
total strain amplitude
Available from European Committee for Standardization (CEN), 36 rue de
Stassart, B-1050, Brussels, Belgium, http://www.cenorm.be.
Available from International Organization for Standardization (ISO), 1, ch. de
la Voie-Creuse, Case postale 56, CH-1211, Geneva 20, Switzerland, http:// Available from Japanese Standards Organization (JSA), 4-1-24 Akasaka
www.iso.ch. Minato-Ku, Tokyo, 107-8440, Japan, http://www.jsa.or.jp.
E2714 − 13 (2020)
-2
3.3.5 initial modulus of elasticity, E , [FL ]—The modu-
∆ε , ∆ε , ∆ε Elastic strain range, plastic strain range,
e p t o
total strain range (see Fig. 2)
lus of elasticity determined during the loading portion of the
∆ε Inelastic strain range, (see Fig. 2) is the sum of
in
first cycle.
the
plastic strain range and the creep strains
-2
3.3.6 modulus of elasticity at cycle N, (E , [FL ]—The
during the cycle; it is the distance on the N
strain axis between points of intersections
averageofthemodulusofelasticitydeterminedduringincreas-
of the strain axis and the extrapolated linear
ing load portion (see E in Fig. 2) and the decreasing load
c
regions of the hysteresis loops during
tensile and compressive unloadings portion (E in Fig. 2) of the hysteresis diagram for the N
T th
σ, σ , σ Stress, maximum stress in the cycle,
max min
cycle.
minimum stress in the cycle
∆σ Stress range -2
3.3.7 stress range, ∆σ , [FL ]—The difference between the
maximum and minimum stresses.
3.3.7.1 Discussion—For creep-fatigue tests, the difference
3.3 Definitions:
between the maximum and minimum stresses is called the
3.3.1 cycle—In fatigue, one complete sequence of values of
“peak stress range” and for tests conducted under strain
force(strain)thatisrepeatedunderconstantamplitudeloading
control, the difference between the stresses at the points of
(straining)
reversal of the control parameter is called the “relaxed stress
3.3.2 hold-time, τ [T]—In fatigue testing, the amount of
h
range” (see Fig. 2b).
time in the cycle where the controlled test variable (force,
strain, displacement) remains constant with time (Fig. 3).
3.4 Definitions of Terms Specific to This Standard:
3.3.2.1 Discussion—Hold- time(s) are typically placed at
3.4.1 DCPD and ACPD—Direct current and alternating
peakstressorstrainintensionand/orcompression,butcanalso
current electrical potential drop crack monitoring instrumenta-
be placed at other positions within the cycle.
tion.
3.3.3 total cycle period, τ [T],—The time for completion of
t
3.4.2 homologous temperature—The specimen temperature
one cycle.The parameter τ can be separated into hold (τ ) and
t h
in °K divided by the melting point of the material also in °K.
non-hold (τ ) (that is, steady and dynamic) components,
nh
where the total cycle time is the sum of the hold time and the
3.4.3 crack formation—A crack is believed to have formed
non-hold time.
when it has nucleated and propagated in a specimen that was
3.3.4 hysteresis diagram—The stress-strain path during one initially un-cracked to a size that is detectable by a stated
cycle (see Fig. 2). technique.
FIG. 1 Crack Formation and End-of-Test Criterion based on Reduction of Peak Stress for (a) Hardening and (b) Softening Materials
E2714 − 13 (2020)
FIG. 2 Examples of Stress-Strain Hysteresis Diagrams (a) Without Hold Time, (b) With Hold Time (Strain Control), (c) With Hold Time
(Force Control), see 3.2.1 for list of symbols.
4. Significance and Use of round bar test specimens subjected (at least remotely) to
uniaxial loading in either force or strain control. The focus of
4.1 Creep-fatigue testing is typically performed at elevated
the procedure is on tests in which creep and fatigue deforma-
temperatures and involves the sequential or simultaneous
tion and damage is generated simultaneously within a given
application of the loading conditions necessary to generate
cycle. Data which may be determined from creep-fatigue tests
cyclic deformation/damage enhanced by creep deformation/
performed under such conditions may characterize (a) cyclic
damage or vice versa. Unless such tests are performed in
stress-strain deformation response (b) cyclic creep (or relax-
vacuum or an inert environment, oxidation can also be respon-
ation) deformation response (c) cyclic hardening, cyclic soft-
sible for important interaction effects relating to damage
ening response or (d) cycles to crack formation, or both.
accumulation. The purpose of creep-fatigue tests can be to
determine material property data for (a) assessment input data
4.3 While there are a number of testing Standards and
for the deformation and damage condition analysis of engi-
Codes of Practice that cover the determination of low cycle
neering structures operating at elevated temperatures (b) the
fatigue deformation and cycles to crack initiation properties
verification of constitutive deformation and damage model
(See Practice E606, BS 7270: 2000, JIS Z 2279–1992, PrEN
effectiveness (c) material characterization, or (d) development
3874, 1998, PrEN 3988–1998, ISO 12106–2003, ISO
and verification of rules for new construction and life assess-
12111–2005, and Practice E2368-04 and (1, 2, 3) , some of
mentofhigh-temperaturecomponentssubjecttocyclicservice
which provide guidance for testing at high temperature (for
with low frequencies or with periods of steady operation, or
example, Practice E606, ISO 12106–2003, and Practice
both.
E2368-04, there is no single standard which specifically
prescribes a procedure for creep-fatigue testing.
4.2 In every case, it is advisable to have complementary
continuous cycling fatigue data (gathered at the same strain/
loadingrate)andcreepdatadeterminedfromtestconductedas
per Practice E139 for the same material and test tempera- 7
The boldface numbers in parentheses refer to a list of references at the end of
ture(s). The procedure is primarily concerned with the testing
this standard.
E2714 − 13 (2020)
FIG. 3 Example of Creep-Fatigue Cycle Shapes
5. Functional Relationships 6.1.2 The complete loading system comprising of the force
transducer, loading grips and test specimen shall have great
5.1 Empirical relationships that have been commonly used
lateralrigiditytomeetrequirementsspecifiedin6.3.Further,it
fordescriptionofcreep-fatiguedataaregiveninAppendixX1.
must be capable of executing the prescribed cycle in either
These relationships typically have limitations with respect to
strainorforcecontrol.Thecontrolstabilityshouldbesuchthat
material types such as high temperature ferritic and austenitic
the maximum and minimum limits of the control variable are
steelsversusnickelbasealloys.Therefore,originaldatashould
maintained within 1% of its range.
be reported to the greatest extent possible. Data reduction
methods should be detailed along with assumptions. Sufficient
6.2 Force transducer:
information should be recorded and reported to permit
6.2.1 The force transducer and its associated electronics
analysis, interpretation, and comparison with results for other
shall comply with ISO 7500-1–2004. Alternatively, the force
materials analyzed using currently popular methods.
transducer calibration should be verified in accordance with
Practices E4-03 and Practice E467-04.
6. Apparatus
6.2.2 The force transducer shall be designed for tension-
compression fatigue testing and shall have high axial and
6.1 Test machines:
lateral rigidity to meet the requirements specified in 6.3. Its
6.1.1 Tests shall be conducted using a servo-controlled
capacity shall be sufficient to measure the axial forces applied
tension-compression fatigue machine that has been verified in
during the test to accuracies better than 1% of the reading.
accordance with ISO 7500-1–2004 or Practices E4-03 and
E467-04. Hydraulic and electromechanical machines are ac- 6.2.3 The force transducer shall be temperature compen-
ceptable. The testing machine shall have been designed for sated and not have zero drift nor sensitivity variation greater
smooth start-up without any backlash when passing through than 0.002% of the full scale per °C (See Practice E606–12).
zero force. It shall possess a high degree of lateral stiffness to During test, the force transducer shall be maintained at a
maintain accurate alignment during compression loading suit- temperature within its temperature compensation range speci-
able for meeting the requirements described in section 6.3. fied by the manufacturer.
E2714 − 13 (2020)
6.3 Loading Grips: of the test specimen axis (c) a second loading surface through
6.3.1 To minimize bending strains or in other words to which the load in the reverse direction is transmitted (d) an
ensure uniform axial strain throughout the gage section of the arrangement maintaining the loading surfaces in contact with
specimen, test specimen fixtures should be aligned such that thespecimen,whateverthestateofloading,withintheworking
the major axis of the test specimen closely coincides with the range of the design. Common loading train misalignment
force axis throughout each cycle. It is important that the problems that can lead to specimen bending are shown in Fig.
accuracy of alignment be kept consistent from specimen to 4 and must be avoided.
specimen.Alignmentshouldbecheckedbymeansofatrialtest
6.4 Extensometer:
diameter. The trial test specimen should be turned about its
6.4.1 Theextensometerusedshallbesuitableformeasuring
axis,installed,andcheckedforeachoffourorientationswithin
dynamic displacements over long periods during which there
thefixtures.Themaximumbendingstrainssodeterminedmust
shall be minimal drift, slippage and instrument hysteresis.
not exceed 5% of the minimum axial strain range imposed
Extensometers used for measurement and to control deforma-
during any test program for all four orientations.
tion in the test specimen gage section shall be suitable for
dynamic measurements over periods of time, that is, should
NOTE3—Forspecimenswithuniformgagelength,itisgoodpracticeto
also place similar set of gages at one or two additional axial positions
have a rapid response and with a low hysteresis (not greater
within the gage section. In such cases, one set of strain gages should be
than 0.1% of extensometer output). Strain gage or LVDT type
placed at the center of the gage length to detect misalignment that causes
transducersaregenerallyusedandshouldbecalibratedaccord-
relative rotation of the specimen ends about axes perpendicular to the
ing to Practice E83-02 and, ISO 9513–1999. Suitable exten-
specimenaxis.Theadditionalsetofgagesshouldbeplacedawayfromthe
gage length center to detect relative lateral displacement of the specimen someters that meet these requirements are those that are Grade
ends. The more uniform the axial strain and lower the bending strain, the
B2 or better as specified by Practice E83-02 or Class 0.5 or
more repeatable the test results will be from specimen to specimen.
better as specified by ISO 9513–1999.
6.3.2 The loading train should incorporate cooling arrange- 6.4.2 Extensometersforparallelgagesectiontestspecimens
ments to limit heat transfer from the hot zone to the testing
shall measure longitudinal extension. A side-entry contacting
machine and in particular the force transducer. The zero point extensometer with rounded contact edges is recommended for
and sensitivity of force transducers are subject to thermal drift
the purpose. These usually employ light spring pressure to
andmaybepermanentlydamagedbytemperaturesinexcessof maintain contact between the probes and the test specimen
50°C.Suitablecoolingarrangementsincludeforcedaircooling
surface and in such circumstances, the extensometer body
of fins at the outer ends of the loading bars or water cooling should be independently supported to minimize the forces
coils or jackets. Care should be taken to ensure that force
between the probe tips and the test specimen surface (see Note
transducercalibrationandloadtrainalignmentarenotaffected 4).
by the presence of the cooling devices.
NOTE 4—If specimens with ridges are used for characterizing cycles to
6.3.3 The loading bars incorporate grips to locate the test
crack formation, the tests should be considered invalid if cracking is
specimenandtheseshouldsatisfycertainbasicdesignrequire-
limited only to the regions near the ridges. This configuration is more
ments arising directly from the need for tension-compression desirable when the purpose of the test is only to determine cyclic
deformation properties.
loading without lost motion through zero force at the test
specimen/grip interface(4, 5, 6) and Practice E1012-12. To
6.4.3 For hour-glass profiled test specimens, an extensom-
achieve this, the design should provide the following basic eter measuring diametral deformation may be used such that
features, (a) a loading surface through which the load in one the extensometer tips contact the test specimens across the
direction will be transmitted (b) a surface ensuring alignment minimumdiameter.Theextensometershouldbesupportedand
FIG. 4 Bending Mechanisms Due to Misalignment in Fatigue Test Systems
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counterbalanced and should be adjusted to minimize the contact is achieved between test specimen and thermocouple
contact force imposed on the test specimen to prevent notch- withoutscratchingthegageportionofthetestspecimen.When
ing. using furnace heating, thermocouple beads shall be shielded
from direct radiation.
NOTE 5—The repeatability and sensitivity of diametral extensometers
are significantly lower than those for axial extensometers and are not
NOTE 8—Optical pyrometers are not recommended for test specimen
recommended as an alternative means of strain control in creep-fatigue
temperature measurement when the test material is prone to oxidation
tests when the use of an axial extensometer is feasible.
withouttheuseofsupportiveobservationsfromthermocouplesattachedto
test specimen shoulders.
6.5 Crack Monitoring:
6.5.1 A direct current (DCPD) or alternating current
6.7.2 When using induction heating, each leg of the ther-
(ACPD) electrical potential-drop crack monitoring system as
mocouple should be spot-welded 180 degrees around the
per Practice E647 may be used in certain circumstances to
shoulder of the test specimen from the other leg so that the
determine crack formation in parallel gage section test
specimen itself becomes the thermocouple junction (bead). If
specimens, although this is not required.
stress-strain behavior only is to be measured then a thermo-
couple location on the gage section is acceptable. Calibration
NOTE 6—The test specimen (or loading grips) should be electrically
and use of methods of temperature measurement shall be
insulated from the test machine loading frame and ancillary equipment in
ordertoavoidunstablepotentialdroprecordingsassociatedwithelectrical carried out according to Test Method E220-02 and Specifica-
ground loops.
tion E230-03, ISO 9513–1999 or EN 60584-1–1996, EN
60584-2–1993 and BS 1041-4:1992.
6.5.2 The DCPD or ACPD system should be capable of
reliably resolving crack extensions of at least 60.1mm along
NOTE9—Theuseofraremetalthermocouples,preferentiallyTypeRor
thespecimensurfaceaswellasalongthecrackdepthatthetest
S is recommended for use at temperatures above 400ºC.
temperature.
NOTE 10—The use of Type K thermocouples above 400ºC is recom-
mended with the following caveat. They may be used only for short
6.5.3 The use of multiple charged couple device (CCD)
duration tests (<500h) at temperatures up to 600°C. Type N thermo-
cameras placed around the test specimen is an alternative
couplesmaybeusedforshortdurationtests(<500h)attemperaturesupto
technique for observing crack development when induction
800°C
heating is employed.
6.8 Cycle Counter:
6.6 Heating System:
6.8.1 Standard practice should be to record all cycles in a
6.6.1 Heatingmethodsusedtoachieveelevatedtemperature
dataacquisitionsystem.Asaminimum,adigitaldeviceshould
include (a) resistance furnace heating (b) radiant furnace
be used to record the number of cycles applied to the test
heating (c) induction heating (see Note 7), or (d) inert gas or
specimen. Five digits are required, thus, for tests lasting less
liquid heating. The heating device shall be such that the test
than 10000 cycles, individual cycles shall be counted. For
specimencanbeuniformlyheatedtothespecifiedtemperature,
longer tests, the device shall have a resolution better than 1%
with an indicated temperature gradient across the gage section
of the actual life.
that is less than or equal to the greater of 2ºC or 1 percent of
6.9 Data recording:
the nominal test temperature throughout the duration of the
test. A resistance furnace with three individually controlled 6.9.1 An automatic digital recording system should be used
heating zones provides a good solution for isothermal creep- which is capable of collecting and simultaneously processing
fatigue testing. the force, displacement and temperature data as a function of
time and cycles. The sampling frequency of force-
NOTE 7—For induction heating, the choice radio frequency (RF)
displacement-time data shall be sufficient to ensure correct
generator frequency depends on the specimen diameter. It is advisable to
definition of the hysteresis loop and hold time transient(s). In
select a RF generator with a sufficiently low frequency such as less than
10 kHz to prevent “skin heating effects” when testing large diameter
particular,itshouldbesufficienttoidentifyvaluesofforceand
specimens (greater than 20 mm). For majority of testing, suitable RF
extension at turning points in the hysteresis loop, for example,
frequencies range between 70 kHz and 400 kHz. Caution should be
at cycle maxima and minima, and start and end of hold-time
exercised when using RF heating while testing ferritic steels. There is
values.
evidence that RF heating in ferromagnetic materials may yeild longer
creep fatigue lives in comparison to resistance heating. (7)
NOTE 11—Adequate number of data points (50 to 200) should be
6.6.2 The heating system shall be protected from draughts collected to define the hysteresis loop, and additional points (50-200 data
points should be collected to fully characterize hold-time transients.
to avoid undesirable gradients and fluctuations in temperature
Obtaining reliable deformation data from the loading portion of the
and the controlled temperature must be maintained within 6
hysteresis loop generally requires approximately 200 data points.
2°C throughout the duration of the test.
NOTE 12—The simultaneous recording of stroke position is also
recommended to assist in the retrospective diagnosis of disturbances
6.7 Temperature Measurement:
during test, for example, extensometer slippage.
6.7.1 Test specimen temperature shall be measured using
thermocouples in contact with the test specimen surface, or by 6.9.2 X-Yrecordingsmayinsteadbeusedforthepurposeof
means of other suitable sensors, for example, optical pyrom- recording force-displacement hysteresis loops. A potentiomet-
eters that have been calibrated using a trial test specimen ric X-Y recorder, or an oscilloscope equipped with a camera
equipped with thermocouples and shown to be the same or are acceptable alternatives. In addition, recorders should be
better than thermocouples. In all cases involving the use of used to monitor force, displacement and temperature as a
thermocouples, it is essential to ensure that intimate thermal function of time. This information is required particularly to
E2714 − 13 (2020)
NOTE 14—The parallel portion of the parallel gage section test
determine initiation and to monitor changes to the dependent
specimen, L , shall be longer than the extensometer gage length, l .
o o
parameter during hold-times.
However, L l mustnotbegreaterthan dtoreducethechancesoffailure
0- 0
NOTE 13—X-Y and multi-channel X-t recorders should only be used outside the extensometer gage length.
when the test conditions result in a pen velocity that will not cause NOTE 15—For cycles involving a component of loading in
inaccurate results, for example, less than half of the recorders slewing compression, l ≤ 4d is recommended to avoid buckling.
o
speed. NOTE 16—Notch sensitive materials and cyclic hardening materials
may require a minimum grip-end diameter, D , of 3.5d to avoid failure in
g
6.9.3 When DCPD or ACPD electrical crack monitoring is
the threaded ends.
used to measure crack formation reference voltages should be
7.1.2 It is important that general tolerances of the test
monitored by digital recording or using a multi-channel X-t
specimen respect the three following properties:
recorder.
Parallelism: //# 0.01 mm
6.10 Verification of Loading and Heating Systems:
Concentricity: O# 0.01 mm
6.10.1 Alignment—Bending due to misalignment in rigid Perpendicularity: '# 0.01 mm
(these values are expressed in relation to the axis or reference plane)
gripsystemsisgenerallycausedby(Fig.4)anangularoffsetof
the specimen grips or a lateral offset of the loading bars in an
7.1.3 The dimensions of the end connections shall be
ideally-rigidsystemoranoffsetintheload-trainassemblywith definedasafunctionofthetestingmachine(seeNote17).The
respect to a non-rigid system such as an actuator rod with side
loading grip arrangement shall locate the test specimen and
play in the bearings. The alignment shall be checked before provide axial alignment. It shall not permit backlash. The
each series of tests or anytime a change is made to the load
designoftheloadinggripwilldependonthetestspecimenend
train as described in 6.3. The bending strains shall be ≤5% of details. A number of solutions are given in (Fig. 6).
the minimum axial strain range imposed during the test
NOTE 17—For test specimen subject to through-zero loading, threaded
program at all strains between the maximum and minimum
and button-ended end-grip arrangements should incorporate features to
applied strain. If the check is not satisfactory when the
ensure a smooth transition from tension into compression and vice-versa.
specimen is rotated in 90° intervals to one or more positions, Thistypicallyinvolvespreloadingofthetestspecimenduringthegripping
procedure (for example, Fig. 6). For threaded ended test specimen, a
the reproducibility of the measurements shall be verified by
limited tolerance thread is also recommended.
carrying out the process several times, and it shall be estab-
NOTE 18—In general, designs for which test specimen alignment
lished if the results are attributable to the test assembly or the
depends entirely on screw threads are not recommended.
test-piece.Changestothesystemorspecimenswillbemadeto
NOTE 19—The clamping force should be greater than the cyclic load to
m
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