ASTM E821-16(2023)

Standard Practice for Measurement of Mechanical Properties During Charged-Particle Irradiation

ABSTRACT
This practice covers the measurement of the mechanical properties of materials during charged-particle irradiation, with the test materials designed to simulate or provide understanding of, or both, the mechanical behavior of materials when exposed to neutron irradiation. This practice includes requirements for test material and particle beam characterization (such as for strain, load, temperature monitoring and control, and specimen environment monitoring), and recommended procedures for measuring mechanical properties and for calculating radiation damage (such as particle ranges, damage energy, damage rates, and damage gradients). Methods for comparing ion damage with neutron damage are also recommended.
SCOPE
1.1 This practice covers the performance of mechanical tests on materials being irradiated with charged particles. These tests are designed to provide an understanding of the effects of neutron irradiation on the mechanical behavior of materials. Practices are described that govern the test material, the particle beam, the experimental technique, and the damage calculations. Reference should be made to other ASTM standards, especially Practice E521. Procedures are described that are applicable to creep and creep rupture tests made in tension and torsion test modes.2  
1.2 The word simulation is used here in a broad sense to imply an approximation of the relevant neutron irradiation environment. The degree of conformity can range from poor to nearly exact. The intent is to produce a correspondence between one or more aspects of the neutron and charged-particle irradiations such that fundamental relationships are established between irradiation or material parameters and the material response.  
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.5 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: 31-Dec-2022
• ICS: 19.100 - Non-destructive testing
• Technical Committee: E10 - Nuclear Technology and Applications
• Drafting Committee: E10.02 - Behavior and Use of Nuclear Structural Materials

Relations

• Refers: ASTM E170-17 - Standard Terminology Relating to Radiation Measurements and Dosimetry
• Effective Date: 01-Jun-2017
• Refers: ASTM E170-16a - Standard Terminology Relating to Radiation Measurements and Dosimetry
• Effective Date: 01-Oct-2016
• Refers: ASTM E170-16 - Standard Terminology Relating to Radiation Measurements and Dosimetry
• Effective Date: 15-Feb-2016
• Refers: ASTM E170-15a - Standard Terminology Relating to Radiation Measurements and Dosimetry
• Effective Date: 01-Sep-2015
• Refers: ASTM E170-15 - Standard Terminology Relating to Radiation Measurements and Dosimetry
• Effective Date: 15-Mar-2015
• Refers: ASTM E170-14a - Standard Terminology Relating to Radiation Measurements and Dosimetry
• Effective Date: 15-Oct-2014
• Refers: ASTM E170-14 - Standard Terminology Relating to Radiation Measurements and Dosimetry
• Effective Date: 01-Sep-2014
• Refers: ASTM E170-10 - Standard Terminology Relating to Radiation Measurements and Dosimetry
• Effective Date: 01-Jun-2010
• Refers: ASTM E170-09a - Standard Terminology Relating to Radiation Measurements and Dosimetry
• Effective Date: 15-Aug-2009
• Refers: ASTM E521-96(2009)e1 - Standard Practice for Neutron Radiation Damage Simulation by Charged-Particle Irradiation
• Effective Date: 01-Aug-2009
• Refers: ASTM E521-96(2009)e2 - Standard Practice for Neutron Radiation Damage Simulation by Charged-Particle Irradiation
• Effective Date: 01-Aug-2009
• Refers: ASTM E521-96(2009) - Standard Practice for Neutron Radiation Damage Simulation by Charged-Particle Irradiation
• Effective Date: 01-Aug-2009
• Refers: ASTM E170-09 - Standard Terminology Relating to Radiation Measurements and Dosimetry
• Effective Date: 15-Jun-2009
• Refers: ASTM E170-08d - Standard Terminology Relating to Radiation Measurements and Dosimetry
• Effective Date: 01-Nov-2008
• Refers: ASTM E170-08c - Standard Terminology Relating to Radiation Measurements and Dosimetry
• Effective Date: 01-Jun-2008

Overview

ASTM E821-16(2023): Standard Practice for Measurement of Mechanical Properties During Charged-Particle Irradiation is a critical international standard developed by ASTM to guide the assessment of material mechanical properties while undergoing charged-particle irradiation. This practice is especially relevant for simulating and understanding the mechanical behavior of materials as they would perform under neutron irradiation-commonly encountered in nuclear environments. Through detailed procedures and stringent requirements for specimen preparation, beam characterization, and measurement techniques, ASTM E821 helps ensure consistent, accurate, and comparable results across laboratories and applications.

Key Topics

• Mechanical Testing Under Irradiation: Procedures for conducting mechanical tests such as creep and creep rupture during the course of charged-particle irradiation.
• Specimen Preparation & Characterization: Detailed documentation of source material, chemical composition, microstructure, mechanical properties before and after irradiation, and specimen dimensions.
• Beam Characterization: Methods to ensure precise control of particle beam composition, energy, intensity distribution, and monitoring for uniform exposure.
• Measurement Techniques: Requirements and recommendations for monitoring and measuring strain, load, and temperature during irradiation, including calibration and error minimization.
• Environmental Control: Procedures for maintaining specimen environment purity-including vacuum system management and continuous environment monitoring-to minimize extraneous influences on test results.
• Radiation Damage Calculation: Describing approaches to calculate damage energy, displacement per atom (dpa), particle range, and methods to compare the effects of ion and neutron damage.
• Simulation of Neutron Effects: Leveraging charged-particle irradiation as a surrogate to approximate, as closely as possible, the impact of neutron environments on materials.

Applications

ASTM E821 is widely employed in research and industry sectors where understanding the durability and performance of materials under irradiation is essential. Key applications include:

• Nuclear Reactor Materials Testing: Simulating neutron irradiation environments to forecast the long-term mechanical performance and reliability of reactor structural materials, fuels, and claddings.
• Material Qualification and R&D: Qualifying new alloys or composites intended for nuclear applications by subjecting them to accelerated damage scenarios using charged-particle beams.
• Fundamental Research: Investigating the fundamental mechanisms of radiation-induced degradation, such as creep, embrittlement, and swelling, to develop more resilient materials.
• Industrial Quality Assurance: Ensuring that metallic and non-metallic components destined for irradiation-intensive environments meet strict performance standards.
• Cross-Comparisons: Providing a standardized framework for comparing experimental results from ion irradiation with those from actual neutron exposure, facilitating broader scientific collaboration.

Related Standards

The ASTM E821 standard aligns with and references several related ASTM standards and international guidelines to ensure comprehensive and coordinated best practices. Notable related standards include:

• ASTM E521: Practice for Investigating the Effects of Neutron Radiation Damage Using Charged-Particle Irradiation
• ASTM E170: Terminology Relating to Radiation Measurements and Dosimetry
• Other ASTM E10 Standards: Covering nuclear technology and the behavior of structural materials under irradiation

These interconnected standards provide a robust toolkit for measuring, interpreting, and benchmarking mechanical property changes in materials exposed to high-energy particles, whether for nuclear power, space applications, or advanced materials development.

Keywords: ASTM E821, charged-particle irradiation, mechanical property measurement, neutron irradiation simulation, material testing standards, nuclear materials, radiation damage, creep testing, specimen environment, beam characterization.

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: E821 − 16 (Reapproved 2023)
Standard Practice for
Measurement of Mechanical Properties During Charged-
Particle Irradiation
This standard is issued under the fixed designation E821; 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.
PART I—EXPERIMENTAL PROCEDURE mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
1. Scope
2. Referenced Documents
1.1 This practice covers the performance of mechanical
2.1 ASTM Standards:
testsonmaterialsbeingirradiatedwithchargedparticles.These
E170Terminology Relating to Radiation Measurements and
tests are designed to provide an understanding of the effects of
Dosimetry
neutron irradiation on the mechanical behavior of materials.
E521Practice for Investigating the Effects of Neutron Ra-
Practices are described that govern the test material, the
diation Damage Using Charged-Particle Irradiation
particle beam, the experimental technique, and the damage
calculations. Reference should be made to other ASTM
3. Terminology
standards, especially Practice E521. Procedures are described
that are applicable to creep and creep rupture tests made in 3.1 Definitions:
tension and torsion test modes. 3.1.1 Descriptions of relevant terms are found in Terminol-
ogy E170.
1.2 The word simulation is used here in a broad sense to
imply an approximation of the relevant neutron irradiation
4. Specimen Characterization
environment.Thedegreeofconformitycanrangefrompoorto
4.1 Source Material Characterization:
nearly exact. The intent is to produce a correspondence
4.1.1 The source of the material shall be identified. The
between one or more aspects of the neutron and charged-
chemicalcompositionofthesourcematerial,assuppliedbythe
particle irradiations such that fundamental relationships are
vendor or of independent determination, or both, shall be
established between irradiation or material parameters and the
stated. The analysis shall state the quantity of trace impurities.
material response.
Thematerial,heat,lot,orbatch,etc.,numbershallbestatedfor
1.3 The values stated in SI units are to be regarded as
commercial material. The analytical technique and composi-
standard. No other units of measurement are included in this
tional uncertainties should be stated.
standard.
4.1.2 The material form and history supplied by the vendor
1.4 This standard does not purport to address all of the
shall be stated. The history shall include the deformation
safety concerns, if any, associated with its use. It is the
process (rolling, swaging, etc.), rate, temperature, and total
responsibility of the user of this standard to establish appro-
extentofdeformation(givenasstraincomponentsorgeometri-
priate safety, health, and environmental practices and deter-
cal shape changes). The use of intermediate anneals during
mine the applicability of regulatory limitations prior to use.
processing shall be described, including temperature, time,
1.5 This international standard was developed in accor-
environment, and cooling rate.
dance with internationally recognized principles on standard-
4.2 Specimen Preparation and Evaluation:
ization established in the Decision on Principles for the
4.2.1 The properties of the test specimen shall represent the
Development of International Standards, Guides and Recom-
properties of bulk material. Since thin specimens usually will
be experimentally desirable, a specimen thickness that yields
bulk properties or information relatable to bulk properties
This practice is under the jurisdiction of ASTM Committee E10 on Nuclear
should be selected. This can be approached through either of
Technology and Applications and is the direct responsibility of Subcommittee
E10.02 on Behavior and Use of Nuclear Structural Materials.
Current edition approved Jan. 1, 2023. Published January 2023. Originally
approved in 1981. Last previous edition approved in 2016 as E821–16. DOI: For referenced ASTM standards, visit the ASTM website, www.astm.org, or
10.1520/E0821-16R23. contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
These practices can be expanded to include mechanical tests other than those Standards volume information, refer to the standard’s Document Summary page on
specified as such experiments are proposed to Subcommittee E10.02. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E821 − 16 (2023)
two techniques: (1) where the test specimen properties exactly ex-reactor neutron irradiation the accelerator, neutron flux and
equalbulkmaterialproperties;and(2)wherethetestspecimen spectrum, temperature, environment, and stress shall be stated,
properties are directly relatable to bulk properties in terms of including descriptions of the measurement techniques. The
deformation mechanisms, but a size effect (surface, texture, dpa/s and dpa should be calculated (see Sections7–10). For
etc.) is present. For the latter case, the experimental justifica- heliumimplantationusinganaccelerator,theaccelerator,beam
tion shall be reported. energy and current density, beam uniformity, degrader system,
temperature, environment, stress, helium content, and helium
4.2.2 The specimen shape and nominal dimensions shall be
stated and illustrated by a drawing. Deviations from ASTM measurement technique and any post-implantation annealing
shall be stated. The helium distribution shall be calculated as
standards shall be stated. The dimensional measurement tech-
niquesandtheexperimentaluncertaintyofeachshallbestated. shalltheresultingdpa(orshowntobenegligible);seeSections
7 and 8 and Practice E521 for assistance. If another helium
Themethodofspecimenpreparation,suchasmilling,grinding,
etc.,shallbestated.Thedegreeofstraightness,flatness,surface implantation technique is used, a description shall be given of
thetechnique.Itisrecommendedthatchemicalanalysisfollow
condition,edges,fillets,etc.,shallbedescribed.Themethodof
gripping the specimen during the test shall be stated and, any of the above preconditioning procedures.
4.3.2 The microstructure of irradiation preconditioned ma-
preferably, illustrated by a drawing.
terial shall be characterized with respect to dislocation loop
4.2.3 The heat treatment conditions such as time,
size and density, total dislocation density, voids, and any
temperature, atmosphere, cooling rate, etc., shall be stated.
microstructural changes from the unirradiated condition.
Because of the small specimen dimensions, it is essential to
Specimen density changes or dimensional changes shall be
anneal in a non-contaminating environment. Reanalysis for O,
reported.Itisrecommendedthatchangesinhardnessortensile
N, C, and other elements that are likely to change in concen-
strength, or both, be reported. Furthermore, any change in
tration during heat treatment is recommended.
surface condition, including coloration, shall be reported.
4.2.4 Specialcareshallbeexercisedduringspecimenprepa-
ration to minimize surface contamination and irregularities
4.4 Analysis After Charged-Particle Irradiation:
because of the possible effect the surface can have on the flow
4.4.1 The physical, mechanical, and chemical properties of
properties of small specimens. Visible surface contamination
the specimen should be characterized prior to irradiation and
during heat treatment shall be reported as a discoloration or,
any irradiation-induced changes reported. Practice E521 pro-
preferably, characterized using surface analysis technique. It is
videsinformationonpost-irradiationspecimenpreparationand
recommended that surface roughness be characterized.
examination.
4.2.5 The pre-irradiation microstructure shall be thoroughly
4.4.2 After charged-particle irradiation, the specimen di-
evaluated and reported, including grain size, grain shape,
mensions and density shall be measured. The microstructure
crystallographic texture, dislocation density and morphology,
and surface conditions shall be reexamined, with changes
precipitate size, density, type, and any other microstructural
being reported. Chemical analysis for those elements likely to
features considered significant. When reporting TEM results,
change during the mechanical test (O, C, N, H) shall be
the foil normal and diffracting conditions shall be stated. The
performed on the test specimen or on a dummy specimen held
specimen preparation steps for optical and transmission elec-
under conditions closely approximating those during irradia-
tron microscopy shall be stated.
tion. It is recommended that changes in hardness, tensile
4.2.6 The pre-irradiation mechanical properties shall be
strength, or creep strength, or both, be measured and reported.
measured and reported to determine deviations from bulk
behavior and to determine baseline properties for irradiation
5. Particle Beam Characterization
measurements.Itisrecommendedthatcreepratesbemeasured
5.1 Beam Composition and Energy:
for each specimen before and after irradiation. The thermal
5.1.1 Most accelerator installations include a calibrated
creep rate shall be obtained under conditions as close as
magnetic analysis system which ensures beam purity and
possible to those existing during irradiation. The temperature,
provides measurement and control of the energy and energy
strain rate, atmosphere, etc., shall be stated.
spread,bothofwhichshouldbereported.Apossibleexception
4.2.7 It is recommended that other material properties
will occur if analog beams are accelerated. For example, a
including microhardness, resistivity ratio, and density be mea-
16 4+
cyclotron can produce simultaneous beams of O (Z/A= ⁄4)
sured and reported to improve interlaboratory comparison.
12 3+ 2
and C (Z/A= ⁄4) at different energies (E+ E Z /A) which
o
4.3 Irradiation Preconditioning: cannot easily be separated magnetically or electrostatically.
4.3.1 Frequently the experimental step preceding charged- This situation, normally only significant for heavy ion beams,
particle irradiation will involve neutron irradiation or helium can be avoided by judicious choice of charge state and energy.
implantation. This section contains procedures that character- ForVandeGraaffacceleratorsanalogbeamsoflightions,such
+ ++
ize the environment and the effects of this irradiation precon- as D and He , can be generated, and under certain circum-
stances involving two-stage acceleration and further ionization
ditioning. For reactor irradiations the reactor, location in
+ + ++
reactor, neutron flux (fluence rate), flux history and spectrum, (for example, He → 5 MeV He → 5 MeV He ), beams of
impurityionscanbeproducedthatmaynotbeeasilyseparated
temperature, environment, and stress shall be reported. The
+
methods of determining these quantities shall also be reported. from the primary beam (for example, 5 MeV H ).
The displacement rate (dpa/s) and total displacement (dpa) 5.1.2 For most cases, ion sources are sufficiently pure to
shall be calculated; see Practice E521 for directions. For remove any concern of significant beam impurity, but this
E821 − 16 (2023)
problem should be considered. Beam energy attenuation and this should be reported. When scanning a pulsed beam at a
changes in the divergence of the beam passing through subharmonic of its natural frequency, it should be noted that
windows and any gaseous medium shall be estimated and the beam spot will strike the specimen at discrete locations,
reported. rather than be distributed continuously across the specimen.
The raw beam spot must therefore be considerably larger than
5.2 Spatial Variation in Beam Intensity:
the distance between these locations or a very nonuniform
5.2.1 The quantity of interest is beam intensity/unit area at
intensity distribution will result. It is most desirable to use a
thespecimen.Itisusuallydesirabletoproduceauniformbeam
continuous rather than rastered beam. If a rastered beam is
density over the specimen area so that this quantity can be
used, the degree of defect annealing between pulses shall be
inferred from a measurement of the total beam intensity and
considered.
area.
5.2.2 Total beam intensity should be measured using a
6. Mechanical Testing Apparatus
Faraday cup whenever possible; however, this may not be
6.1 Strain Measurement:
possible on a continuous basis during irradiation. The Faraday
−5
6.1.1 The strains measured during light ion irradiation tests,
cup shall be evacuated to P<10 and shall be electron-
for measurement periods ;1 day and for conditions where the
suppressed; otherwise, spurious results may be generated.
irradiation has a significant effect on the elongation rate, are
Various secondary beam monitors may then be used, such as
−3 −5
very small (typically ;10 to 10 ). Therefore, the strain
ionization chambers, secondary emission monitors, transform-
resolutionnormallyrequiredforcontinuousmeasurementsis1
ers or other induction devices (for pulsed beams), beam
−6
to 10×10 . The strain resolution as well as displacement
scanners, or particles scattered from a foil. All such devices
resolution shall be reported.
shall be calibrated through Faraday cup measurements or
6.1.2 Normally for these experiments the limiting factor in
through activation analysis. These calibrations shall be re-
strain measurement is not the resolution of the actual displace-
ported.
ment measuring device (for example, LVDT, LVDC, strain
5.2.3 Displacement rate gradients occur in charged-particle
gage, laser extensometer, etc.); it is the ability of the apparatus
irradiation specimens in the Z (beam) direction because of
to transmit the displacement with fidelity. To minimize these
changes in ion energy and, therefore, displacement cross
displacement measurement errors, it is recommended that the
sectionwithpenetration(see10.5.1),andinthe Xand Y(lateral
temperature be monitored or controlled, or both, on each
and longitudinal specimen axes, respectively) directions be-
critical part of the apparatus and that thermal sensitivity
cause of spatial variations in beam intensity.
experiments be performed; that is, a local temperature fluctua-
NOTE1—Nonuniformspecimencrosssectionmaygiverisetodisplace-
tion should be imposed on individual elements of the strain-
ment rate variations in the x- and y-directions, even under a spatially
measuring system while the strain signal is monitored. It is
uniform beam.
recommendedthatthestrainsensitivitytoambienttemperature
5.2.3.1 Displacement rate ratios of 1.2 to 2.5 (ratio of
fluctuations be recorded. It is recommended that the strain
displacement rate at exit surface to rate at entrance surface of
sensitivity to vibrations and coolant flow rates be monitored
specimen in the Z-direction) are common, but it is recom-
and reported. The strain-measuring resolution, linearity, and
mended that this ratio be minimized. In the case of foil
reproducibilityshouldbeexaminedatseveraltesttemperatures
specimens it is also recommended that the variations in beam
on a regular basis using calibrated standards developed for
intensity in the X-direction be minimized, since a gradient in
such a purpose.
this direction will affect both the temperature and the creep
6.1.3 The sensitivity of the strain measurement shall be
compliance so as to maximize the stress gradient from speci-
considered with respect to large magnetic or electrostatic
men center to edge.
fields, both of which may be present in these experiments.The
5.2.4 The beam may be rastered over the specimen to
effect of stray ion currents caused by secondary radiation
improve uniformity. The frequency of rastering shall be re-
should also be considered. The effect of lead length and
ported. The beam profile shall be measured regularly during
shielding between the strain transducer(s) and the indicating
the irradiation experiments, if possible. If this is not possible,
device should be considered. Grounding may give rise to
some secondary measurement, such as temperature gradient,
problems, especially with long lead lengths and associated
should be made.Analysis of the variation in specimen activity
ground potential differences.
along the gauge section can provide an integrated average of
6.1.4 The means of defining the deforming gage length of
the spatial variation in beam intensity; this is recommended.
the specimen should be reported along with the accuracy of its
measurement. Possible errors arising from deformation occur-
5.3 Time Variation in Intensity:
ring outside the gauge section should be reported. It is also
5.3.1 Accelerator beams often have a built-in time structure
recommended that strain measurement errors caused by speci-
whichmustbeaccepted;thisshouldbereported.Thehistoryof
men bending be evaluated and reported.
beam interruptions due to occasional electrical breakdown
shallbereported.Thelong-termstabilityofbeamfocusingand 6.2 Load Application and Measurement:
directing equipment shall be considered. If the beam spot is 6.2.1 The requirements for load measurement in these
rastered to produce a uniform intensity profile, a further time experiments are much less stringent than those for strain
dependence will be introduced, depending on the frequency measurements; accuracies of ≤1 % are recommended.
and amplitude of the scan, and the size of the raw beam spot; Temperature, pressure, and vibration sensitivity measurements
E821 − 16 (2023)
should be performed on the load-measuring device. The 6.3.1.1 Thermocouples—There are several problems associ-
load-measuringresolution,linearity,andreproducibilityshould ated with the use of thermocouples applied directly to speci-
be examined on a regular basis using calibrated standards. mensfortheseexperiments.Thethinspecimensnormallyused
are subject to local perturbations in temperature through heat
6.2.2 Theeffectofsecondaryradiation,electric,ormagnetic
conduction from specimen to thermocouple wire. Thermal
fields on the load transducer should be considered, along with
analysis shall be performed to determine the magnitude of
lead length and shielding. Variations in ground potentials shall
temperature error associated with this thermal shunting. An-
be considered.
other difficulty with applying the thermocouple directly to the
6.2.3 Possible loading errors associated with misalignment
specimen is the effect on the specimen material at the point
shall be evaluated and reported. Frictional forces shall be
where the thermocouple is welded. The “heat-affected” zone
measured where applicable, since friction anywhere in a
shall be minimized, and the percent of the total cross section
mechanical load train may affect the strain measurement. The
thatisaffectedbytheweldingoftwothermocouplewiresshall
hysteresis in load application and measurement should be
be reported. Radiation can affect the performance of thermo-
reported in relation to the strain measurement.
couples. Radiation damage and, to a lesser degree, transmuta-
6.3 Temperature Monitoring and Control—For these
tion will affect thermocouple calibration. Therefore, it is
experiments, temperature monitoring and control capabilities
recommended that thermocouples that are irradiated during an
maybethedominantfactorsthatlimittheoverallaccuracyand
experiment should be calibrated before and after each experi-
resolution of the primary strain measurement. For uniaxial
ment. Radiation can also affect the temperature of the thermo-
tension the temperature dependence of the strain error arises
couple junction. Radiation heating shall be included in the
−5
from thermal expansion (dε/dT ; 10 /K) and, to a lesser
thermal analysis mentioned above.Another possibly important
degree, from the temperature dependence of the modulus
effect of radiation is ionization events which can occur in the
−7
(dε/dT ; 10 /K). For torsion experiments, the temperature-
thermocouple wire, in its insulation, or in the medium sur-
dependent strain error is that of the modulus only. Primary
roundingabarethermocouplewire.Inallthesecases,spurious
emphasis will be given to uniaxial tension experiments, since
voltages or currents can give rise to errors (only, of course,
strain resolution requirements are likely to limit the allowable
when the two thermocouple wires are ionized to dissimilar
temperature variations to less than 1 K over the desired
degrees). Furthermore, thermocouples that are not directly in
temperature range (from room temperature to about 1000 K).
the beam, but that receive significant gamma radiation, will
The overall reproducibility from experiment to experiment
undergoionization.Theseeffectsshouldbeconsidered.Special
may not be so stringent, however. If this reproducibility is 5 K
problems can arise when split thermocouples are employed.
or less, reasonably good agreement between thermal creep
Forexample,whenanelectricalheatingcurrentpassesthrough
rates will be obtained, and very good agreement should be
the specimen, the output voltage of the thermocouple will
obtained on radiation-induced mechanical property changes.
reflect the IR drop between the two points of contact of the
6.3.1 Temperature Monitoring—This section is devoted to
thermocouple wires. Caution shall be exercised in the use of
the description of techniques for detecting the absolute tem-
split thermocouples for the following reasons: (1) the
perature of the specimen (accuracy) and for detecting changes
specimen, with its radiation-sensitive Seebeck coefficient, may
in specimen temperature from some set point (resolution).
undergo the equivalent of thermocouple decalibration, (2) split
Each of the following techniques may be important for either
thermocouples can mask temperature spikes or hot spots
the accuracy or resolution of the temperature measurement, or
between the wire contact points, and (3) the averaging of
both. In a given experiment, one technique may be utilized for
temperaturegivesrisetoerror,exceptundertheidealcondition
estimating the overall specimen temperature to within several
of linear variation in temperature between the contact points.
K; whereas, in another experiment the same technique may be
6.3.1.2 Infrared Pyrometers—The accuracy of infrared py-
used to resolve small (;0.1 K) temperature fluctuations
rometers is dependent upon several factors. First, the surface
(presumably in conjunction with the temperature control func-
emissivitymustremainconstant.Thisshallbedemonstratedin
tion). However, it should be kept in mind that beam heating at
pre- and post-experimental evaluation. If specimen pre-
high beam currents can adversely affect the temperature
oxidation is necessary for keeping the emissivity constant, it
resolution. It is recommended that direct monitoring of the
shall be demonstrated that thermal creep properties in the
specimen temperature be performed. If, however, an indirect
temperature and stress range of interest are not affected by the
monitoringtechniqueisused(forexample,adummyspecimen
oxidation treatment. Second, since instruments will receive a
oranambientheatsinktemperaturemeasurementisused)then
significant level of gamma radiation during some experiments,
it should be demonstrated that the factors controlling the heat
these infrared pyrometers shall be regularly calibrated.
transfer from the specimen to the point where temperature is
6.3.1.3 Resistance Thermometry—Resistance thermometry
monitored remain constant. For example, if heat transfer must
is potentially a very high-accuracy approach to temperature
occurthroughanoxidefilmonthespecimenor,perhaps,onan
measurement.AcomprehensivereferenceonthissubjectisRef
adjacent heat sink, the stability of this film during an experi-
(1). Amajor source of error is associated with a change in the
ment
...