ASTM E139-11(2018)

Standard Test Methods for Conducting Creep, Creep-Rupture, and Stress-Rupture Tests of Metallic Materials

SIGNIFICANCE AND USE
4.1 Rupture tests, properly interpreted, provide a measure of the ultimate load-carrying ability of a material as a function of time. Creep tests measure the load-carrying ability for limited deformations. The two tests complement each other in defining the load-carrying ability of a material. In selecting material and designing parts for service at elevated temperatures, the type of test data used will depend on the criterion of load-carrying ability that better defines the service usefulness of the material.
SCOPE
1.1 These test methods cover the determination of the amount of deformation as a function of time (creep test) and the measurement of the time for fracture to occur when sufficient force is present (rupture test) for materials when under constant tensile forces at constant temperature. It also includes the essential requirements for testing equipment. For information of assistance in determining the desirable number and duration of tests, reference should be made to the product specification.  
1.2 These test methods list the information which should be included in reports of tests. The intention is to ensure that all useful and readily available information is transmitted to interested parties. Reports receive special attention for the following reasons: (1) results from different, recognized procedures vary significantly; therefore, identification of methods used is important; (2) later studies to establish important variables are often hampered by the lack of detailed information in published reports; (3) the nature of prolonged tests often makes retest impractical, and at the same time makes it difficult to remain within the recommended variations of some controlled variables. A detailed report permits transmittal of test results without implying a degree of control which was not achieved.  
1.3 Tests on notched specimens are not included. These tests are addressed in Practice E292.  
1.4 Tests under conditions of short times are not included. These test methods are addressed in Test Methods E21.  
1.5 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.  
1.6 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.7 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.

General Information

• Status: Published
• Publication Date: 30-Sep-2018
• ICS: 77.040.10 - Mechanical testing of metals
• Technical Committee: E28 - Mechanical Testing
• Drafting Committee: E28.04 - Uniaxial Testing

Relations

• Refers: ASTM E8/E8M-24 - Standard Test Methods for Tension Testing of Metallic Materials
• Effective Date: 01-Jan-2024
• 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 E8/E8M-13 - Standard Test Methods for Tension Testing of Metallic Materials
• Effective Date: 01-Jun-2013
• Refers: ASTM E74-13a - Standard Practice of Calibration of Force-Measuring Instruments for Verifying the Force Indication of Testing Machines
• Effective Date: 01-May-2013
• Refers: ASTM E177-13 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-May-2013
• Refers: ASTM E74-13 - Standard Practice of Calibration of Force-Measuring Instruments for Verifying the Force Indication of Testing Machines
• Effective Date: 01-Mar-2013
• Refers: ASTM E74-12 - Standard Practice of Calibration of Force-Measuring Instruments for Verifying the Force Indication of Testing Machines
• Effective Date: 01-Dec-2012
• Refers: ASTM E1012-12e1 - Standard Practice for Verification of Testing Frame and Specimen Alignment Under Tensile and Compressive Axial Force Application
• Effective Date: 01-Jun-2012
• Refers: ASTM E1012-12 - Standard Practice for Verification of Testing Frame and Specimen Alignment Under Tensile and Compressive Axial Force Application
• Effective Date: 01-Jun-2012
• Refers: ASTM E8/E8M-11 - Standard Test Methods for Tension Testing of Metallic Materials
• Effective Date: 01-Dec-2011
• Refers: ASTM E177-10 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-Oct-2010

Overview

ASTM E139-11(2018): Standard Test Methods for Conducting Creep, Creep-Rupture, and Stress-Rupture Tests of Metallic Materials provides universally recognized procedures for determining the durability and load-carrying ability of metals under sustained mechanical stress and constant temperatures over prolonged periods. Issued by ASTM International, this comprehensive standard is essential for professionals involved in materials selection and component design for high-temperature applications. The test methods outlined are vital for establishing performance, safety, and serviceability of metallic materials used in demanding industrial environments.

Key Topics

The standard focuses on test methods that reveal critical time-dependent properties of metals, including:

• Creep Testing: Measures the deformation (strain) of a metallic material over time under constant tensile force and temperature, identifying load-carrying ability for limited deformation.

• Creep-Rupture Testing: Involves monitoring both the progressive deformation and the time to fracture of a specimen, providing a comprehensive picture of material endurance.

• Stress-Rupture Testing: Determines the time it takes for a material to fracture under constant stress at elevated temperature, without intermediate deformation measurements.

• Test Equipment Requirements: Specifies requirements for accurate testing machines, temperature control, extensometers, and calibration protocols.

• Reporting Standards: Defines the information that should be included in test reports to ensure clarity, reproducibility, and traceability. This includes specimen preparation, dimensional measurements, test conditions, and calibration records.

• Scope Exclusions: Tests on notched specimens (see ASTM E292) and short-duration tests (see ASTM E21) are excluded, focusing instead on unnotched, prolonged tests.

• Safety and Compliance: Stresses the user's responsibility to address safety, health, environmental, and regulatory considerations prior to conducting tests.

Applications

ASTM E139 is widely applied in industries where metallic components are exposed to high temperatures and sustained loads, such as:

• Aerospace and Power Generation: Evaluation of turbine blades, heat exchangers, boilers, and reactors, ensuring long-term reliability and preventing catastrophic failures.

• Petrochemical and Refining: Assessment of pipes, vessels, and structural supports that must withstand both operational stresses and aggressive thermal environments.

• Material Development: Critical in research and development for new alloys and metals destined for harsh service conditions.

• Component Certification and Quality Assurance: Used by manufacturers to certify materials meet contractual and regulatory requirements for high-temperature design.

By following the procedures in ASTM E139, engineers and researchers acquire trustworthy data that helps predict material behavior, optimize service performance, and enhance component durability.

Related Standards

Several ASTM standards complement or are referenced in ASTM E139 to ensure comprehensive mechanical testing:

• ASTM E292: Time-for-rupture notch tension testing of materials (for notched specimens).
• ASTM E21: Elevated temperature tension tests for metallic materials, including short-term testing methods.
• ASTM E4 / E74: Calibration and verification methods for load-measuring systems.
• ASTM E8/E8M: Standard test methods for tension testing of metallic materials.
• ASTM E83: Verification and classification of extensometer systems.
• ASTM E220 / E633: Calibration and use of thermocouples in high-temperature environments.
• ASTM E1012: Verification of testing frame and specimen alignment.

For accurate, reproducible, and internationally accepted results in high-temperature creep and rupture testing, ASTM E139 stands as a critical reference, supporting global trade, regulatory compliance, and safety in metallic materials engineering.

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: E139 − 11 (Reapproved 2018)
Standard Test Methods for
Conducting Creep, Creep-Rupture, and Stress-Rupture
Tests of Metallic Materials
This standard is issued under the fixed designation E139; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope* responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
1.1 These test methods cover the determination of the
mine the applicability of regulatory limitations prior to use.
amount of deformation as a function of time (creep test) and
1.7 This international standard was developed in accor-
the measurement of the time for fracture to occur when
dance with internationally recognized principles on standard-
sufficient force is present (rupture test) for materials when
ization established in the Decision on Principles for the
under constant tensile forces at constant temperature. It also
Development of International Standards, Guides and Recom-
includes the essential requirements for testing equipment. For
mendations issued by the World Trade Organization Technical
information of assistance in determining the desirable number
Barriers to Trade (TBT) Committee.
and duration of tests, reference should be made to the product
specification.
2. Referenced Documents
1.2 These test methods list the information which should be
included in reports of tests. The intention is to ensure that all
2.1 ASTM Standards:
useful and readily available information is transmitted to
E4Practices for Force Verification of Testing Machines
interested parties. Reports receive special attention for the
E6Terminology Relating to Methods of MechanicalTesting
following reasons: (1) results from different, recognized pro-
E8/E8MTest Methods for Tension Testing of Metallic Ma-
cedures vary significantly; therefore, identification of methods
terials
used is important; (2) later studies to establish important
E21TestMethodsforElevatedTemperatureTensionTestsof
variables are often hampered by the lack of detailed informa-
Metallic Materials
tioninpublishedreports;(3)thenatureofprolongedtestsoften
E29Practice for Using Significant Digits in Test Data to
makesretestimpractical,andatthesametimemakesitdifficult
Determine Conformance with Specifications
to remain within the recommended variations of some con-
E74Practices for Calibration and Verification for Force-
trolled variables. A detailed report permits transmittal of test
Measuring Instruments
results without implying a degree of control which was not
E83Practice for Verification and Classification of Exten-
achieved.
someter Systems
E177Practice for Use of the Terms Precision and Bias in
1.3 Testsonnotchedspecimensarenotincluded.Thesetests
ASTM Test Methods
are addressed in Practice E292.
E220Test Method for Calibration of Thermocouples By
1.4 Tests under conditions of short times are not included.
Comparison Techniques
These test methods are addressed in Test Methods E21.
E292Test Methods for ConductingTime-for-Rupture Notch
1.5 Thevaluesstatedininch-poundunitsaretoberegarded
Tension Tests of Materials
as standard. The values given in parentheses are mathematical
E633Guide for Use of Thermocouples in Creep and Stress-
conversions to SI units that are provided for information only
Rupture Testing to 1800°F (1000°C) in Air
and are not considered standard.
E1012Practice for Verification of Testing Frame and Speci-
men Alignment Under Tensile and Compressive Axial
1.6 This standard does not purport to address all of the
Force Application
safety concerns, if any, associated with its use. It is the
These test methods are under the jurisdiction of theASTM Committee E28 on
Mechanical Testing For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Oct. 1, 2018. Published November 2018. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 1958. Last previous edition approved in 2011 as E139–11. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/E0139-11R18. the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E139 − 11 (2018)
3. Terminology 4. Significance and Use
4.1 Rupturetests,properlyinterpreted,provideameasureof
3.1 Definitions—The definitions of terms relating to creep
the ultimate load-carrying ability of a material as a function of
testing, which appear in Section E of Terminology E6 shall
time. Creep tests measure the load-carrying ability for limited
apply to the terms used in this practice. For the purpose of this
deformations.Thetwotestscomplementeachotherindefining
practiceonly,someofthemoregeneraltermsareusedwiththe
theload-carryingabilityofamaterial.Inselectingmaterialand
restricted meanings given below.
designingpartsforserviceatelevatedtemperatures,thetypeof
3.2 Definitions of Terms Specific to This Standard:
test data used will depend on the criterion of load-carrying
3.2.1 axial strain—the average of the strain measured on
abilitythatbetterdefinestheserviceusefulnessofthematerial.
opposite sides and equally distant from the specimen axis.
5. Apparatus
3.2.2 bending strain—the difference between the strain at
the surface of the specimen and the axial strain. In general it
5.1 Testing Machine: The accuracy of the testing machine
variesfrompointtopointaroundandalongthereducedsection
shall be within the permissible variation specified in Practices
of the specimen.
E4.
3.2.2.1 maximum bending strain—measured at a position
5.1.1 Exercise precaution to ensure that the force on the
along the length of the reduced section of a straight unnotched
specimens is applied as axially as possible. Perfect axial
specimen.
alignment is difficult to obtain, especially when the pull rods
3.2.3 creep—the time-dependent strain that occurs after the and extensometer rods pass through packing at the ends of the
application of a force which is thereafter maintained constant.
furnace. However, the machine and grips should be capable of
applying force to a precisely made specimen so that the
3.2.4 creep-rupture test—a test in which progressive speci-
maximum bending strain does not exceed 10% of the axial
men deformation and the time for rupture are measured. In
strain,whenthecalculationsarebasedonstrainreadingstaken
general,deformationismuchlargerthanthatdevelopedduring
at the lowest force for which the machine is being qualified.
a creep test.
NOTE 1—This requirement is intended to limit the maximum contribu-
3.2.5 creep test—a test that has the objective of measuring
tion of the testing apparatus to the bending which occurs during a test. It
creep and creep rates occurring at stresses usually well below
is recognized that even with qualified apparatus, different tests may have
those which would result in fracture during the time of testing.
quite different percent bending strains due to chance orientation of a
Since the maximum deformation is only a few percent, a
loosely fitted specimen, lack of symmetry of that particular specimen,
sensitive extensometer is required. lateral force from furnace packing, and thermocouple wire, etc.
5.1.1.1 In testing of low ductility material, even a bending
3.2.6 gage length—the original distance between gage
strain of 10% may result in lower strength than would be
marks made on the specimen for determining elongation after
obtained with improved axiality. In these cases, measurements
fracture.
of bending strain on the specimen to be tested may be
3.2.7 length of the reduced section—the distance between
specificallyrequestedandthepermissiblemagnitudelimitedto
tangent points of the fillets which bound the reduced section.
a smaller value.
3.2.7.1 The adjusted length of the reduced section is greater
5.1.1.2 The testing apparatus may be qualified by measure-
than the length of the reduced section by an amount calculated
ments of axiality made at room temperature. When one is
to compensate for strain in the fillet region (see 8.2.3).
making an evaluation of equipment, the specimen form should
3.2.8 plastic strain during force application—the portion of
be the same as that used during the elevated-temperature tests.
the strain during force application determined as the offset
Theevaluationspecimenconcentricityshallbeatleastasgood
from the linear portion to the end of a stress-strain curve made
as called out in the specimen drawing. Only elastic strains
during force application. The offset construction is shown in
should occur throughout the reduced section.This requirement
Test Methods E8/E8M.
may necessitate use of a material different from that used
during the elevated-temperature test.
3.2.9 reduced section, of the specimen—the central portion
5.1.1.3 Test Method E1012, or an equivalent test method
ofthelengthhavingacrosssectionsmallerthantheendswhich
(1), shall be used for the measurement and calculation of
are gripped. The cross section is uniform within tolerances
bending strain for round, rectangular, and thin strip specimens.
prescribed in 6.6.
5.1.1.4 Axiality measurements should be made at room
3.2.10 strain during force application—the change in strain
temperature during the initial setup of the assembled test
during the time interval from the start of force to the instant of
machine, (including the pull rods, and grips) before use for
full-force application.
testing. Gripping devices and pull rods may oxidize, warp, and
3.2.11 stress-rupturetest—atestinwhichtimeforruptureis
creep with repeated use at elevated temperatures. Increased
measured, no deformation measurements being made during
bending stresses may result. Therefore, grips and pull rods
the test.
should be periodically retested for axiality and reworked when
necessary.
3.2.12 total plastic strain, at a specified time—equal to the
sum of plastic strain during force application plus creep.
3.2.13 total strain, at a specified time—equal to the sum of
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
the strain during force application plus creep. this standard.
E139 − 11 (2018)
nationordeteriorationwithuse,lead-wireerror,errorarisingfrommethod
5.1.2 Thetestingmachineshallincorporatemeansoftaking
of attachment to the specimen, direct radiation of heat to the bead,
up the extension of the specimen so that the applied force will
heat-conduction along thermocouple wires, etc.
be maintained within the limits specified in 5.1. The extension
5.3.3 Temperature measurements shall be made with cali-
of the specimen shall not allow the force application system to
bratedthermocouples.Representativethermocouplesshouldbe
introduce eccentricity of force application in excess of the
calibrated from each lot of wires used for making base-metal
limits specified in 5.1.1. The take-up mechanism shall avoid
thermocouples. Except for relatively low temperatures of
introducing shock forces, overloading due to friction or inertia
exposure, base-metal thermocouples are subject to error upon
in the force application system, or apply torque to the speci-
reuse unless the depth of immersion and temperature gradients
men.
of the initial exposure are reproduced. Consequently base-
5.1.3 The testing machine shall be erected to secure reason-
metal thermocouples should be calibrated by the use of
able freedom from vibration and shock due to external causes.
representativethermocouplesandactualthermocouplesusedto
Precautions shall be made to minimize the transmission of
measure specimen temperatures shall not be calibrated. Base-
shock to neighboring test machines and specimens when a
metal thermocouples also should not be re-used without
specimenfractures.Vibrationandshockeffectsmaybeseenas
clipping back to remove wire exposed to the hot zone . Any
noise in the curve when plotting the creep versus time. When
reuse of base-metal thermocouples after relatively low-
such effects are visible in the plotted data, vibration and shock
temperature use without this precaution should be accompa-
should not introduce apparent noise to the creep data in excess
nied by recalibration data demonstrating that calibration was
of 7.5% total creep or total plastic strain. Such external
not unduly affected by the conditions of exposure.
vibrations shall not result in applied force errors in excess of
+1% of the specified test force. 5.3.3.1 Noble-metalthermocouplesarealsosubjecttoerrors
duetocontamination,etc.,andshouldbeannealedperiodically
5.1.4 For high-temperature testing of materials which are
and checked for calibration. Care should be exercised to keep
readily attacked by their environment (such as oxidation of
the thermocouples clean prior to exposure and during use at
metalinair),thespecimenmaybeenclosedinacapsulesothat
elevated temperatures.
it can be tested in a vacuum or inert-gas atmosphere. When
suchequipmentisused,thenecessarycorrectionstoobtaintrue 5.3.3.2 Measurement of the drift in calibration of thermo-
specimen applied forces shall be made. For instance, compen- couples during use is difficult. When drift is a problem during
tests, a method should be devised to check the readings of the
sation shall be made for differences in pressures inside and
outside of the capsule and for any force application variation thermocouples on the specimens during the test. For reliable
calibration of thermocouples after use, the temperature gradi-
due to sealing-ring friction, bellows or other features.
ent of the testing furnace must be reproduced during the
5.2 Heating Apparatus: The apparatus for and method of
recalibration.
heating the specimens shall provide the temperature control
5.3.4 Temperature-measuring, controlling and recording in-
necessary to satisfy the requirements specified in 8.4.4 without
strumentsshouldbecalibratedperiodicallyagainstasecondary
manual adjustments more frequent than once in each 24-h
standard, such as a precision potentiometer. Lead-wire error
periodafterforceapplication.Automatictemperaturecontrolis
shouldbecheckedwiththeleadwiresinplaceastheynormally
preferred.
are used.
5.2.1 Heating shall be by an electric resistance or radiation
furnacewiththespecimeninairatatmosphericpressureunless 5.4 Extensometer System: The sensitivity and accuracy of
other media are specifically agreed upon in advance. thestrain-measuringequipmentshouldbesuitabletodefinethe
creep characteristics with the precision required for the appli-
NOTE 2—The media in which the specimens are tested may have a
cationofthedata.ThePracticeE83extensometerclassification
considerableeffectontheresultsoftests.Thisisparticularlytruewhenthe
should be made part of the report of test results. Suitability of
properties are influenced by oxidation or corrosion during the test,
although other effects can also influence test results. the sensor type and characteristics for creep measurement
should be determined before implementation of the system.
5.3 Temperature-Measuring Apparatus (2):
Suitability of individual sensors should be periodically evalu-
5.3.1 The method of temperature measurement must be
ated or evaluated upon occurrence of significant noise in the
sufficientlysensitiveandreliabletoensurethatthetemperature
creep curve.Acceptable noise levels should not exceed 5% of
of the specimen is within the limits specified in 8.4.4.
the total calibrated range. Laboratories employing multiple
5.3.2 Temperature shall be measured with calibrated ther-
sensorsandelectricalaveragingshouldensurethattheadditive
mocouples in conjunction with calibrated thermocouple mea-
effects of each sensor’s noise do not result in an unacceptable
surement instrumentation. Other calibrated methods of tem-
average noise level. Peak to peak noise on the raw creep data
perature measurement may be used if they are well
shouldnotexceed7.5%ofthetotalcreeportotalplasticstrain
characterized with respect to standard thermocouple measure-
for the test. Noise levels exceeding these values must be
ment methods.
documented in the test report.
NOTE 3—Such measurements are subject to two types of error.
5.4.1 Nonaxialityofforceapplicationisusuallysufficientto
Thermocouple calibration and instrument measuring errors initially intro-
causesignificanterrorsatsmallstrainswhenstrainismeasured
duce uncertainty as to the exact temperature. Secondly both thermo-
ononlyonesideofthespecimen (3).Therefore,theextensom-
couples and measuring instruments may be subject to variation with time.
etershallbeattachedtoandindicatestrainonoppositesidesof
Common errors encountered in the use of thermocouples to measure
temperaturesinclude,calibrationerror,driftincalibrationduetocontami- the specimen. The reported strain shall be the average of the
E139 − 11 (2018)
strains on the two sides, either a mechanical or electrical 6.2.1 At the center for products 38 mm (1 ⁄2 in.) or less in
average internal to the instrument or a numerical average of thickness, diameter, or distance between flats, or
two separate readings. 6.2.2 Midway from the center to the surface for products
5.4.2 Whenever possible the extensometer should be at- over 38 mm (1 ⁄2 in.) in thickness, diameter, or distance
between flats.
tachedtothespecimen,nottoanyloadcarryingpartsjoinedto
the specimen, because the intervening joints and parts intro-
6.3 Test specimens of the type, size, and shape described in
duce significant extensions which, are not accurately separable
Test Methods E8/E8M are generally suitable for tests at
from the extension in the specimen alone.
elevated temperature with the following modifications: (1)
5.4.3 To avoid the inaccuracy introduced by strain in the
tighter dimensional tolerances are recommended in 6.6; (2) for
fillets and shoulders, the extensometer should be attached to
creep tests, larger ratios of length to diameter (or width) of
the reduced portion of the specimen.
reduced section may be desirable to increase the accuracy of
5.4.3.1 It is sometimes necessary to attach the extensometer
strain measurement; and (3) for coarse-threaded specimens,
to the specimen shoulders. For example, when materials with
made from material with little ductility, the size of thread
low ductility are tested, failure tends to occur at the extensom- 7
should be at least ⁄4 the diameter of the reduced section.
eter attachments unless these are located on the specimen
According to 6.1, rectangular specimens will be used for sheet
shoulders.
and strip. Otherwise, the specimen should have a reduced
5.4.3.2 When making a creep-rupture test of a ductile
section of circular cross section. The largest diameter or
material an extensometer attached to the reduced section of a
greatest width specimen consistent with 6.1 should be used
specimen tends to loosen as the cross-sectional area decreases
exceptthatthesedimensionsneednotbegreaterthan12.5mm
during the test. In this case the extensometer may be attached
(0.5 in.).
tothespecimenshouldersortosmallribsorgroovesmachined
NOTE 4—Specimen size in itself has little effect on creep and rupture
at the ends of the reduced section of the specimen for that
properties provided the material is sound and is not subject to appreciable
purpose (4).
surface corrosion or orientation effects. A small number of grains in the
5.4.4 When it is necessary to use miniature specimens, the
specimen cross section, or preferred orientation of grains due to fabrica-
tion conditions, can have a pronounced effect on the test results. When
extensometer may be attached to the specimen holders. The
corrosionoxidationoccurs,theresultsmaybeafunctionofspecimensize.
observedvaluesofextensionshouldbeadjustedasdescribedin
Likewise, surface preparation of specimens, if affecting results, becomes
8.6.3 and 9.2.4. Even with this adjustment the strain values are
more important as the specimen size is reduced.
of inferior accuracy and the reported values should be labeled
6.4 Specimens of circular cross section should have
“approximate.” The method of measurement should be de-
threaded, shouldered, or other suitable ends for gripping that
scribed in the report.
will meet the requirements of 5.1.1.
5.5 Room Temperature Control: The temperature in the
NOTE 5—Satisfactory axial alignment may be obtained with precisely
room should be sufficiently constant so the specimen tempera-
machined threaded ends. But at temperatures where oxidation and creep
ture variations do not exceed the limits stated in 8.4.4.
arereadilyapparent,preciselyfittedthreadsaredifficulttomaintainandto
5.5.1 Extensometer readings should be taken only when the
separate after test. Practical considerations require the use of relatively
room temperature is within 63°C (65°F) of the room tem- loose-fitting threads. Other gripping methods have been successfully used
(5, 6, 7).
perature at the time of force application, unless a correction is
applied to the extensometer reading. The extensometer correc-
6.5 For rectangular specimens some modifications of the
tion equation or chart should have specimen temperature as
standard specimens described in Test Methods E8/E8M are
well as room temperature as a variable.The correction may be
usually necessary to permit application of the force to the
omittedifithasbeenestablishedthattheextensometerreading
specimen in the furnace with the axiality specified in 5.1.1.If
isnotchangedbyvariationsinroomtemperature.Inevaluating
the material available is sufficient, the use of elongated
the effect of such variations, the electronic instrumentation
shoulder ends to permit gripping outside the furnace is the
should also be calibrated at various ambient temperatures.
easiestmethod.Whenthelengthofthespecimenisnecessarily
restricted,severalmethodsofgrippingmaybeusedasfollows:
5.6 Timing Apparatus—For rupture testing machines, pro-
6.5.1 A device that applies the force through a cylindrical
vide suitable means for measuring the elapsed time between
pinineachoftheenlargedendsofthespecimen.Thepinholes
completeapplicationoftheforceandthetimeatwhichfracture
shouldbeaccuratelycenteredonextensionsofthecenterlineof
of the specimen occurs, to within 1% of the elapsed time.
the gage section. The good axiality of force application using
a grip of this type has been demonstrated (6, 7).
6. Test Specimen and Sample
6.5.2 High-temperature sheet grips similar to those illus-
6.1 The size and shape of test specimens shall be based
tratedinTestMethodsE8/E8Manddescribedasself-adjusting
primarily on the requirements necessary to obtain representa-
grips have proved satisfactory for testing sheet materials that
tive samples of the material being investigated or as required
cannotbetestedsatisfactorilyintheusualtypeofwedgegrips.
by specification.
6.5.3 Extension tabs may be welded or brazed to the
6.2 For rolled, extruded or other directionally processed specimen shoulders and extended to grips outside the furnace.
materials, unless otherwise specified, test specimens shall be When these are used, care must be exercised to maintain
oriented such that the axis of the specimen is parallel to the coaxiality of the centerlines of the extensions and the gage
direction of fabrication, and located as follows: length. Any brazing or welding should be done in a jig or
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fixture to maintain accurate alignment of the parts. Any
Force-measuring system 1 year
A
Extensometers 1 year
machining should be done after brazing or welding.
Thermocouples each lot run
6.5.4 Grips that conform to and apply force against the
Precision Potentiometers (dry cell type) 1 month
fillets at the ends of the reduced section.
Micrometers and calipers 6 months
Recording systems 6 months
6.6 The diameter (or width) at the ends of the reduced
Temperature measuring equipment/system 3 months (see 7.4)
Weights every five years (see 7.5)
section of the specimen shall not be less than the diameter (or
Dial Indicators (used to measure creep) 1 month (see 7.6)
width) at the center of the reduced section. It may be desirable
to have the diameter (or width) of the reduced section of the
A
Extensometers shall be verified for freedom of movement prior to each test.
specimen slightly smaller at the center than at the ends. The
Exceptions to this list shall be instruments in use when the test exceeds
calibration period.
diameter (or width) at the ends of the reduced section shall not
begreaterthan100.5%ofthediameter(orwidth)atthecenter
NOTE 6—In cases where the test duration exceeds the maximum
of the reduced section. When specimens of this form are used calibration frequency, it is acceptable to perform the calibration immedi-
ately following the conclusion of the test.
to test low ductility materials, failure may regularly occur at
thefillets.Inthesecases,thecenterofthereducedsectionmay
7.3 For verification of creep-rupture testing machines, non-
be made smaller by a gradual taper from the ends and the
machined blanks of material with predetermined rupture prop-
exception to the requirements above noted in the report.
ertiesareavailablefromASTMInternationalHeadquartersata
Specimen surfaces shall be smooth and free from undercuts
nominal cost.
and scratches. Special care shall be exercised to minimize
7.4 As an alternative to calibration immediately following
disturbance of surface layers by cold work, which produces
the conclusion of the test exceeding 3 months, multiple
high residual stresses plastic deformation, or other undesired
temperature measuring equipment/system can be used so that
effects.The axis of the reduced section shall be straight within
calibration of each equipment/system can staggered to elimi-
60.5% of the diameter. Threads of the specimen shall be
nate or minimize the calibration-overdue periods.
concentric with this axis within the same tolerance. Other
7.5 The metal weights used to apply the test force shall be
means of gripping shall have comparable tolerances.
certified every five years (if not painted/plated, or calibrated
6.7 For cast-to-size specimens it may not be possible to
prior to each test) to be within a limit of error of 0.5%.
adhere to the diameter, straightness, and concentricity limita-
Painted/plated weights shall be verified when paint/plating
tions of 6.6, but every effort should be made to approach these
shows wear or damage.
as closely as possible.
7.6 Dial indicators used in tests exceeding 1 month should
be exercised at least 3 times to prevent becoming stuck.
7. Calibration and Standardization
Difference in readings before and after the exercise should be
7.1 The calibration of load measuring systems,
recorded.
extensometers,thermocouples (2),potentometers,andmicrom-
eters shall be traceable to national standards, where systems of
8. Procedure
traceability exist. Applicable ASTM standards and guidance
8.1 Measurement of Cross-Sectional Area—Determine the
are listed here:
minimum cross-sectional area of the reduced section of the
Load-measuring system Practices E4 and E74
specimen as specified in Measurement of Dimensions of Test
Extensometer Practice E83
A Specimens in Test Methods E8/E8M. In addition, measure the
Thermocouples Method E220
Potentiometers Method E220 and STP 470B (2)
largest diameter (or width) in the reduced section and compare
with the minimum value to determine whether the require-
A
Method E220 melting point methods are also recommended for thermocouple
ments of 6.6 are satisfied.
calibration.
8.2 Measurement of Original Length:
7.1.1 Axiality of the force application apparatus shall be
8.2.1 Unless otherwise specified, base all values for elon-
measuredasdescribedin5.1.1anddocumentedasdescribedin
gationonagagelengthequaltofourdiameters(4D)inthecase
Practice E1012.
of round specimens and four times the width in the case of
7.2 Calibrations and verifications shall be as frequent as is rectangular specimens, the gage length being punched or
necessarytoensurethattheerrorsforeachtestarelessthanthe
scribed on the reduced section of the specimen.
permissible indicated variations listed in these test methods.
NOTE 7—Elongation values of specimens with rectangular cross sec-
The maximum period between calibrations and verifications
tions cannot be compared unless all dimensions including the thickness
shall be:
are equal. Therefore, an elongation specification should include the
specimen cross-sectional dimensions as well as the gage length. Using a
gage length equal to 4.5 times the square root of the cross-sectional area
compensates somewhat for variations in specimen thickness but even this
does not result in the same value of elongation when specimens of the
same material are machined to different thicknesses and tested (6, 7).
8.2.2 When the length-to-diameter ratio of the reduced
section is greater than standard, the gage length should be
approximatelyonediameterlessthanthelengthofthereduced
section.
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NOTE 8—Recognition must be given to the wide use of total elongation
couple wires. The remaining portions of the wires shall be
offracturedrupturespecimensinjudgingmaterials.Percentageelongation
thermally shielded and electrically insulated by a suitable
isverydependentonthegagelengthoverwhichitismeasured.Adherence
covering. If some other electrical insulation material is used in
to the customary gage length of four times the specimen diameter is,
the hot zone, it should be carefully checked to determine
therefore, very desirable. Recognition must be given, however, to the
whethertheelectricalinsulatingpropertiesaremaintainedwith
approved use of longer or shorter gage length to specimen diameter ratios
in rupture testing and the possible prohibition to using gage marks to
higher temperatures.
define the uniform gage length for elongation measurement. Therefore,
8.4.3 When the length of the reduced section is less than 50
reporting of elongation for longer gage lengths should be acceptable,
mm (2 in.) attach at least two thermocouples to the specimen,
provided the gage length is clearly indicated. For most ductile metals a
one near each end of the reduced section. For reduced sections
standard four-diameter gage length centered on a fracture occurring in a
longerthanstandardreducedsectionwillgiveahigherelongationthanthe 50 mm or greater, add a third thermocouple near the center.
standard test. For this reason the use of several, congruent, standard gage
8.4.4 Before the force is applied and for the duration of the
lengthstocoveralongreducedsectionisnotrecommended.Themajority
test do not permit the difference between the indicated tem-
of the stretching occurs near the fracture site. Since stretching is not
perature and the nominal test temperature to exceed the
uniform over the length of the reduced section, the percent elongation
following limits:
depends on the gage length.
Up to and including 1000°C (1800°F) 2°C (±3°F)
8.2.3 When testing metals of limited ductility, gage marks
Above 1000°C (1800°F) 3°C (±5°F)
punched or scribed on the reduced section may be undesirable
8.4.5 The term “indicated temperature” means the tempera-
because fracture may occur at the stress concentrations so
ture that is indicated by the temperature measuring device
caused. Then, place gage marks on the shoulders or measure
using good quality pyrometric practice.
the overall length of the specimen. Also measure the adjusted
length of the reduced section to the nearest 0.2 mm (0.01 in.)
NOTE 9—It is recognized that true temperature may vary more than the
indicatedtemperature.Thepermissibleindicatedtemperaturevariationsin
as described in 8.2.4. If a gage length, other than that specified
8.4.4 are not to be construed as minimizing the importance of good
in 8.2.1 is employed to measure elongation, describe the gage
pyrometric practice and precise temperature control. All laboratories
length in the report. In the case of acceptance tests, any
should keep both indicated and true temperature variations as small as
deviation from 8.2.1 must be agreed upon before testing.
practicable. However, should temperatures vary outside the given limits,
time and temperature of the variation shall be recorded and good
8.2.4 When the extensometer is to be attached to the
engineering judgment taken to assure the variations did not affect testing
specimen shoulders, measure the adjusted length of the re-
of the material and that the results of the test are valid. This should be
duced section between points on the two fillets where the
clearly documented in the test report. It is well recognized, in view of the
diameter(orwidth)is1.05timesthediameter(orwidth)ofthe
extreme dependency of strength of materials on temperature, that close
reduced section. This dimension is used as the divisor for
temperature control is necessary. The limits prescribed represent ranges
that are common practice.
converting the observed extension to strain in the reduced
section (see 9.2.3 and 9.3.1).
8.4.6 Temperature overshoots during heating should not
exceed the limits above. The heating characteristics of the
8.3 Cleaning Specimen—Unless otherwise requested, wash
furnace and the temperature control system should be studied
carefully the reduced section and those parts of the specimen
to determine the power input, temperature set point, propor-
which contact the grips in clean alcohol, acetone, or other
tioning control adjustment, and control-thermocouple place-
suitable solvent that will not affect the metal being tested.
ment necessary to limit transient temperature overshoots. It
Specimens may be cleaned at the machining facility prior to
may be desirable to stabilize the furnace at a temperature from
receiving at the test lab. In all cases, specimens should be
5 to 20°C below the nominal test temperature before making
handled carefully to avoid imparting oil from skin to the
the final adjustments. Report any temperature overshoot with
specimen. Cast to size specimens typically do not need
details of magnitude and duration.
cleaning.
8.4.7 Thetimeofholdingattemperaturepriortothestartof
8.4 Temperature Control:
thetestshouldbegovernedbythetimenecessarytoensurethat
8.4.1 Form the thermocouple bead in accordance with
the specimen has reached equilibrium and that the temperature
Guide E633.
can be maintained within the limits specified in 8.4.4. Unless
8.4.2 Guide E633 provides guidance on thermocouple at- otherwise specified, this time should not be less than 1 h.
tachment. In attaching thermocouples to a specimen, the Record the time to attain test temperature and the time at
junctionshallbekeptinintimatecontactwiththespecimenand temperature before force application.
shielded from radiation. Shielding may be omitted if, for a 8.4.8 Any disturbance causing the temperature of the speci-
particular furnace and test temperature, the difference in mentobeoutsidethelimitsspecifiedin8.4.4shouldrequirean
indicated temperature from an unshielded bead and a bead investigation that may necessitate using good engineering
inserted in a hole in the specimen has been shown to be less judgment regarding the impact on the creep properties. Tem-
than one half the variation listed in 8.4.4. The bead should be perature deviations may be cause for rejection of the test and
assmallaspossibleandthereshallbenoshortingofthecircuit require retesting. Allowing the temperature to fall below the
(such as could occur from twisting the thermocouple wires nominal temperature reduces creep rate and prolongs rupture
behind the bead or from a bare attachment wire touching both time, both characteristics being very sensitive to test tempera-
bare thermocouple wires). Ceramic insulators should be used ture. Low temperatures usually do not damage the material as
onthethermocouplesinthehotzonefortesttemperatureshigh can over temperature, which may considerably accelerate
enough to damage standard thermal insulation on the thermo- creep. Consequently under temperature should be cause for
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retesting only when the time at under temperature significantly not, then in order to adjust for the extension which occurs
altersthetestresultasdeterminedbyanevaluationofthecreep outside the reduced section, it is necessary to test two speci-
rate before and after the occurrence of the under temperature mens for each creep curve. One specimen should have the
condition, and/or as determined by a statistical evaluation of standard proportions, the other specimen should be made
representative data versus the test in question. shorter by omitting either the reduced section or the reduced
section and the fillets. The grip ends and shoulders of both
NOTE10—Coolingandreheatingofthespecimenunderstresscanhave
specimens should be similar. Both should be tested with an
a significant effect on subsequent creep properties and rupture times.
extensometer attached to the specimen holders (see 9.2.4).
Temperature drops of about 40°C (100°F) or cooling times of1hor
greater can reduce rupture times by one-half. Creep properties may be
8.6.4 For strain measurement during the removal of applied
similarlyaffected.Ifthestress(force)isremovedbeforetheabovetimeor
force, see 8.7.3.
temperaturedecreaseisexceeded,therupturetestcanberestartedafterthe
cause for disturbance has been corrected. It has not been determined if a 8.7 Force Application and Removal Procedure:
creep test can be restarted. The report shall indicate that the test was
8.7.1 Asmall fraction of the test force (not more than 10%
interrupted by cooling, length of interruption or decrease, or both in
for materials such as stainless steels that yield immediately
temperaturepriortoremovalofstress,andfromwhattemperaturethetest
upon force application; 15% for materials that have a linear
was restarted.
elasticportionofthestress/straincurve)maybeappliedbefore
8.5 Connecting Specimen to the Machine—Take care not to
and during heating of the specimen. This usually improves the
introduce nonaxial forces while installing the specimen. For
axiality of force application by reducing the displacement of
example, threaded connections should not be turned to the end
the specimen and load rods due to lateral forces from furnace
of the threads or bottomed. If threads are loosely fitted, apply
packing and thermocouple wires (see 8.5). The equivalent
a very small force to the specimen string and manually move
extensometer reading at zero force may be obtained by
itinthetransversedirectionandleaveinthecenterofitsrange
extrapolating the linear portion of the force-extension curve.
of motion. If packing is used to seal the furnace, it must not be
8.7.2 Apply the force in a manner that shock forces or
sotightthattheextensometerarmsorpullrodsaredisplacedor
excess forces due to inertia is avoided. The force may be
their movement restricted.
applied in increments with strain readings between increments
8.6 Strain Measurement During Test: to provide stress-strain data for the application of the force.
8.6.1 By definition, a creep or a creep-rupture test requires Makethetimeforapplyingtheforceasshortaspossiblewithin
these limitations.
measurements of strain at and following the instant of appli-
cation of full force. The strain change from zero force to the
8.7.3 Wheretotalextensionsarelimitedtothesameorderof
instant of full force application shall also be recorded (see magnitude as elastic extensions, it is important to have the
8.7.1).
elasticportionofthetotalextensionaccuratelyknown.Increep
tests, this can best be determined by measurement of the
NOTE 11—Incremental strain readings during force application are also
instantaneous contraction upon removal of the applied force at
of value for the following two reasons: (1) the elastic portion of the
the end of the test.
stress-strain curve during force application may be used to evaluate the
operation of the apparatus before the specimen is finally committed; and
NOTE 12—This measurement can only be made for tests that are halted
(2) in many applications knowledge of total plastic strain rather than of
prior to rupture.
creep alone is required, therefore the force application curve is necessary.
On the other hand, obtaining the force application curve usually requires
8.7.4 Ifatestisinterruptedforanyreason,theconditionsof
slower force application than would be used if creep only was measured.
the resumption of the test shall be recorded in the test report.
This slower force application sometimes results in greater strain at the
Exercise care to prevent excess force application to the test
instant of full force application than if the force had been applied without
piece due to contraction of the test specimen assembly.
the delays caused by incremental force application.
8.8 Measurements of Specimen After Test:
8.6.2 Take strain measurements at sufficiently frequent in-
tervalsduringatesttoadequatelydefinethetime-strain(creep)
8.8.1 For measuring elongation, fit the ends of the fractured
curve. This usually requires more frequent readings during the specimen together carefully and measure the distance between
usual rapid first-stage creep than during second-stage creep.
gage marks or the overall length to the nearest 0.2 mm (0.01
The interval for strain readings should not be more than 24 h in.) at room temperature. If any part of the fracture surface
or 1% of the estimated duration of the test, whichever is
extends beyond the middle half of the reduced section of the
longer.Laboratorieswithcomputerizeddataacquisitionshould specimen, the elongation value obtained may not be represen-
recordatshorterintervals(nolongerthanonepointevery24h) tative of the material. In the case of an acceptance test, if the
if possible so that the creep rupture curve can be more clearly elongation meets the minimum requirements specified, no
defined. Omissions of readings are allowed when the absence further testing is required; but if the elongation is less than the
of daily readings does not influence the test results or the time specified minimum, the test shall be discarded and a retest
period does not occur at a specification requirement for made.
reporting time or creep.
8.8.2 For measuring reduction of area of specimens of
8.6.3 When the stock size makes it necessary to use a circular cross section, fit the ends of the fractured specimen
specimenwiththereducedsectionlessthan6.25mm(0.25in.) together carefully and measure the maximum and minimum
in diameter, the extensometer may be attached to the specimen final diameters and record the average of maximum and
holders. The diameter of the specimen holders should be minimum final diameter to the nearest 0.02 mm (0.001 in.) at
significantlylargerthanthereducedsectionofthespecimen.If roomtemperature.Ifthefractureoccursatafilletorgagemark
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primary stage of creep, the errors tended to be larger, being 8% in the
thereductionofareamaynotberepresentativeofthematerial.
extreme case. These values are based on a ratio of length to diameter for
In the case of an acceptance test, if the reduction of area meets
the reduced portion of 5. A ratio of 10 would halve the percentage error.
thespecifiedminimum,nofurthertestingisrequired,butifthe
9.2.4 If, in the case of miniature specimens, the extensom-
reduction of area is less than the specified minimum the test
eter is attached to the specimen holders, the extension for the
may be discarded and a retest performed.
standard specimen should be reduced by the extension of a
9. Calculation
specimen without a reduced section, the force and time since
force application being the same for both specimens. The
9.1 Stress—Reported stress value is equal to the value of
difference in extension is then converted to strain in the
constant axial force applied to the specimen divided by the
reduced section by dividing by the length of the reduced
minimum cross-sectional area measured at room temperature
section(iftheshortenedspecimenincludedthefillets)orbythe
before the test.
method of 9.2.3 (if the shortened specimen did not include
9.2 Strain:
fillets).Thetestontheshortenedspecimenmaybeomittedand
9.2.1 Calculate strain by dividing the extensi
...