EN ISO 204:2009

SLOVENSKI STANDARD
01-julij-2011
1DGRPHãþD
SIST EN 10291:2002
Kovinski materiali - Preskušanje nesoosnega lezenja pri nategu - Metoda
preskušanja (ISO 204:2009)
Metallic materials - Uniaxial creep testing in tension - Method of test (ISO 204:2009)
Metallische Werkstoffe - Einachsiger Zeitstandversuch unter Zugbeanspruchung -
Prüfverfahren (ISO :2009)
Matériaux métalliques - Essai de fluage uniaxial en traction - Méthode d'essai (ISO
204:2009)
Ta slovenski standard je istoveten z: EN ISO 204:2009
ICS:
77.040.10 Mehansko preskušanje kovin Mechanical testing of metals
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN ISO 204
NORME EUROPÉENNE
EUROPÄISCHE NORM
June 2009
ICS 77.040.10 Supersedes EN 10291:2000
English Version
Metallic materials - Uniaxial creep testing in tension - Method of
test (ISO 204:2009)
Matériaux métalliques - Essai de fluage uniaxial en traction Metallische Werkstoffe - Einachsiger Zeitstandversuch
- Méthode d'essai (ISO 204:2009) unter Zugbeanspruchung - Prüfverfahren (ISO 204:2009)
This European Standard was approved by CEN on 27 May 2009.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the CEN Management Centre or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the CEN Management Centre has the same status as the
official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,
Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2009 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 204:2009: E
worldwide for CEN national Members.

Contents Page
Foreword .3

Foreword
This document (EN ISO 204:2009) has been prepared by Technical Committee ISO/TC 164 "Mechanical
testing of metals" in collaboration with Technical Committee ECISS/TC 1 “Steel - Mechanical testing” the
secretariat of which is held by AFNOR.
This European Standard shall be given the status of a national standard, either by publication of an identical
text or by endorsement, at the latest by December 2009, and conflicting national standards shall be withdrawn
at the latest by December 2009.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN 10291:2000.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Cyprus, Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.
Endorsement notice
The text of ISO 204:2009 has been approved by CEN as a EN ISO 204:2009 without any modification.

INTERNATIONAL ISO
STANDARD 204
Second edition
2009-06-15
Metallic materials — Uniaxial creep
testing in tension — Method of test
Matériaux métalliques — Essai de fluage uniaxial en traction —
Méthode d'essai
Reference number
ISO 204:2009(E)
©
ISO 2009
ISO 204:2009(E)
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ii © ISO 2009 – All rights reserved

ISO 204:2009(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope .1
2 Normative references .1
3 Terms and definitions .1
4 Symbols and designations .5
5 Principle.7
6 Apparatus .7
7 Test pieces .10
8 Test procedure.13
9 Determination of results .14
10 Test validity .14
11 Accuracy of the results .15
12 Test report .15
Annex A (informative) Information concerning different types of thermocouples .21
Annex B (informative) Information concerning methods of calibration of thermocouples.22
Annex C (normative) Creep testing using test pieces with V or blunt circumferential notches.23
Annex D (informative) Method of estimating the uncertainty of the measurement in accordance
with the Guide to the expression of uncertainty in measurement (GUM).26
Annex E (informative) Representation of results and graphical extrapolation.32
Bibliography .40

ISO 204:2009(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 204 was prepared by Technical Committee ISO/TC 164, Mechanical testing of metals, Subcommittee
SC 1, Uniaxial testing.
This second edition cancels and replaces the first edition (ISO 204:1997), which has been technically revised.

iv © ISO 2009 – All rights reserved

ISO 204:2009(E)
Introduction
This International Standard is an extensive revision of the first edition of ISO 204:1997 and incorporates many
recommendations developed through the European Creep Collaborative Committee (ECCC).
New annexes have been added concerning temperature measurement using thermocouples and their
calibration, creep testing test pieces with circumferential Vee and blunt (Bridgman) notches, estimation of
measurement uncertainty and methods of extrapolation of creep rupture life.
NOTE Information is sought relating to the influence of off-axis loading or bending on the creep properties of various
materials. Consideration will be given at the next revision of this International Standard as to whether the maximum
amount of bending should be specified and an appropriate calibration procedure be recommended. The decision will need
[39]
to be based on the availability of quantitative data .

INTERNATIONAL STANDARD ISO 204:2009(E)

Metallic materials — Uniaxial creep testing in tension — Method
of test
1 Scope
This International Standard specifies the method for the uninterrupted and interrupted creep tests and defines
the properties of metallic materials which can be determined from these tests, in particular the creep
elongation and the time of creep rupture, at a specified temperature.
The stress rupture test is also covered by this International Standard, as is the testing of notched test pieces.
NOTE In stress rupture testing, elongation is not generally recorded during the test, only the time to failure under a
given load, or to note that a predetermined time was exceeded under a given force.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 286-2, ISO system of limits and fits — Part 2: Tables of standard tolerance grades and limit deviations for
holes and shafts
1)
ISO 783 , Metallic materials — Tensile testing at elevated temperature
ISO 7500-2, Metallic materials — Verification of static uniaxial testing machines — Part 2: Tension creep
testing machines — Verification of the applied force
ISO 9513, Metallic materials — Calibration of extensometers used in uniaxial testing
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
NOTE Several different gauge lengths and reference lengths are specified in this International Standard. These
lengths reflect custom and practice used in different laboratories throughout the world. In some cases, the lengths are
physically marked on the test piece as lines or ridges; in other cases, the length may be a virtual length based upon
calculations to determine an appropriate length to be used for the determination of creep elongation. For some test pieces,
L , L and L are the same length (see 3.1, 3.2 and 3.5).
r o e
1) To be revised by ISO 6892-2, Metallic materials — Tensile testing — Part 2: Method of test at elevated temperature.
ISO 204:2009(E)
3.1
reference length
L
r
base length used for the calculation of elongation
NOTE A method to calculate this value is given in 7.5 for test pieces where the extensometer is attached to either
ridges on the parallel length or to the shoulders of the test piece.
3.1.1
original reference length
L
ro
reference length determined at ambient temperature before the test
NOTE In general, L W 5D.
ro
3.1.2
final reference length
L
ru
reference length determined at ambient temperature after rupture, with the pieces carefully fitted back
together with their axes in a straight line
3.2
original gauge length
L
o
length between gauge length marks on the test piece measured at ambient temperature before the test
NOTE 1 In general, L W 5D.
o
NOTE 2 L may also be used for the calculation of elongation.
o
3.3
final gauge length after rupture
L
u
length between gauge length marks on the test piece measured after rupture, at ambient temperature, with
the pieces carefully fitted back together with their axes in a straight line
3.4
parallel length
L
c
length of the parallel reduced section of the test piece
3.5
extensometer gauge length
L
e
distance between the measuring points of the extensometer
NOTE In some cases, L = L and may also be used for the calculation of elongation.
e o
3.6
original cross-sectional area
S
o
cross-sectional area of the parallel length as determined at ambient temperature prior to testing
2 © ISO 2009 – All rights reserved

ISO 204:2009(E)
3.7
minimum cross-sectional area after rupture
S
u
minimum cross-sectional area of the parallel length as determined at ambient temperature after rupture, with
the pieces carefully fitted back together with their axes in a straight line
3.8
initial stress
σ
o
applied force divided by the original cross-sectional area (S ) of the test piece
o
3.9
elongation
∆L
r
increase of the reference length (L )
r
NOTE See 6.2.
3.10
percentage elongation
A
elongation expressed as a percentage of the original reference length (L )
ro
NOTE 1 See Figure 1.
NOTE 2 In the terms for elongation in 3.10 to 3.16, the symbol “ε ” may replace “A”.
However, when “ε ” is used, the following conventions should apply:
ε %  is the percentage strain or elongation;
ε  is the absolute strain.
3.11
percentage initial plastic elongation
A
i
non-proportional increase of the original reference length (L ) due to the application of the test force
ro
3.12
percentage creep elongation
A
f
increase in reference length at time t (∆L ) at a specified temperature expressed as a percentage of the
rt
original reference length (L ):
ro
∆L
rt
A=× 100 (1)
f
L
ro
NOTE 1 A may have the specified temperature (T ) in degrees Celsius (°C) as superscript and the initial stress (σ ) in
f o
2)
megapascals and time t (in hours) as subscript.
NOTE 2 By convention, the beginning of creep elongation measurement is the time at which the initial stress (σ ) is
o
applied to the test piece (see Figure 1).
NOTE 3 Suffix f originates from “fluage”, “creep” in French.

2) 1 MPa = 1 N/mm .
ISO 204:2009(E)
3.13
percentage plastic elongation
A
p
non-proportional increase of the original reference length (L ) at time t:
ro
A = A + A (2)
p i f
3.14
percentage anelastic elongation
A
k
non-proportional decrease of the original reference length (L ) at time t due to unloading
ro
3.15
percentage permanent elongation
A
per
total increase of the original reference length (L ) at time t determined after unloading:
ro
A = A − A (3)
per p k
3.16
percentage elongation after creep rupture
A
u
permanent increase of the original reference length (L ) after rupture (L − L ) expressed as a percentage of
ro ru ro
the original reference length (L ):
ro
LL−
ru ro
A=× 100 (4)
u
L
ro
NOTE A may have the specified temperature (T ) in degrees Celsius as superscript and the initial stress (σ ) in
u o
megapascals as subscript.
3.17
percentage reduction of area after creep rupture
Z
u
maximum change in cross-sectional area measured after rupture (S − S ) expressed as a percentage of the
o u
original cross-sectional area (S ):
o
SS−
ou
Z=× 100 (5)
u
S
o
NOTE Z may have the specified temperature (T ) in degrees Celsius as superscript and the initial stress (σ ) in
u o
megapascals as subscript.
3.18
creep elongation time
t
fx
time required for a strained test piece to obtain a specified percentage creep elongation (x) at the specified
temperature (T ) and the initial stress (σ )
o
EXAMPLE t .
f0,2
3.19
plastic elongation time
t
px
time required to obtain a specified percentage plastic elongation (x) at the specified temperature (T ) and the
initial stress (σ )
o
4 © ISO 2009 – All rights reserved

ISO 204:2009(E)
3.20
creep rupture time
t
u
time to rupture for a test piece maintained at the specified temperature (T ) and the initial stress (σ )
o
NOTE The symbol t may have as superscript the specified temperature (T ) in degrees Celsius and as subscript the
u
initial stress (σ ) in megapascals.
o
3.21
single test piece machine
testing machine that permits straining of a single test piece
3.22
multiple test piece machine
testing machine that permits straining of more than one test piece simultaneously at the same temperature
4 Symbols and designations
The symbols and corresponding designations are given in Table 1.
Table 1 — Symbols and designations
a
Unit
Symbol
D
mm Diameter of the cross-section of the parallel length of a cylindrical test piece
D mm Diameter of gauge length containing a notch
n
d mm
Diameter of gauge length without a notch in a combined notched/un-notched test piece
(see Figure C.1)
d mm Diameter across root of circumferential notch
n
For a combined notched/un-notched test piece d = d
n
b mm Width of the cross-section of the parallel length of a test piece of square or rectangular
cross-section
L mm Reference length
r
a mm Thickness of a test piece of square or rectangular cross-section [see Figure 2 b)]
L
mm Original reference length
ro
L mm Final reference length
ru
∆L mm Elongation
r
mm Increase in reference length at time t
∆L
rt
L mm Original gauge length
o
L mm Parallel gauge length containing a notch
n
L mm Final gauge length after rupture
u
L mm Parallel length
c
L mm Extensometer gauge length
e
R
mm Transition radius
r mm Notch root radius
n
S
Original cross-sectional area of the parallel length
mm
o
S Minimum cross-sectional area after rupture
mm
u
ISO 204:2009(E)
Table 1 (continued)
a
Unit Designation
Symbol
MPa Initial stress
σ
o
b
% Percentage elastic elongation
A
e
b
% Percentage initial plastic elongation
A
i
b
% Percentage anelastic elongation
A
k
b
% Percentage plastic elongation
A
p
b
% Percentage permanent elongation
A
per
b
% Percentage creep elongation:
A
f
∆L
rt
A=× 100
f
L
ro
NOTE As an example, the symbol may be completed as follows:
A : percentage creep elongation with an initial stress of 50 MPa after 5 000 h at the
f50/5000
specified temperature of 375 °C.
b
% Percentage elongation after creep rupture:
A
u
LL−
ru ro
A=× 100
u
L
ro
NOTE As an example, the symbol may be completed as follows:
A : percentage elongation after creep rupture with an initial stress of 50 MPa at the specified
u50
temperature of 375 °C.
Z % Percentage reduction of area after creep rupture:
u
SS−
ou
Z=× 100
u
S
o
NOTE As an example, the symbol may be completed as follows:
Z : percentage reduction of area after creep rupture with an initial stress of 50 MPa at the
u50
specified temperature of 375 °C.
t h Creep elongation time
fx
t
h Plastic elongation time
px
t h Creep rupture time
u
NOTE As an example, the symbol may be completed as follows:
t : creep rupture time with an initial stress of 50 MPa at the specified temperature of 375 °C.
u50
t h Creep rupture time of a notched test piece
un
T °C Specified temperature
T °C Indicated temperature
i
x % Specified percentage creep or plastic elongation
n Creep exponent
a
The main subscripts (r, o and u) of the symbols are used as follows:
r corresponds to reference;
o corresponds to original;
u corresponds to ultimate (after rupture).
b
See Note 2 in 3.10.
6 © ISO 2009 – All rights reserved

ISO 204:2009(E)
5 Principle
The test consists of heating a test piece to the specified temperature and of straining the test piece by means
of a constant tensile force or constant tensile stress (see note) applied along its longitudinal axis for a period
of time to obtain any of the following:
⎯ a specified creep elongation (uninterrupted test);
⎯ values of permanent elongation at suitable intervals throughout the test (interrupted test);
⎯ the creep rupture time (uninterrupted and interrupted test).
NOTE “Constant stress” means that the ratio of the force to the instantaneous cross-section remains constant
throughout the test. The results obtained with constant stress are generally different from those obtained with constant
force.
6 Apparatus
6.1 Testing machine
The testing machine shall apply a force along the axis of the test piece while keeping inadvertent bending or
torsion of the test piece to a minimum. Prior to test the machine should be visually examined to ensure that
loading bars, grips, universal joints and associated equipment are in a good state of repair.
The force should be applied to the test piece without shock.
The machine should be isolated from external vibration and shock. The machine should be equipped with a
device which minimizes shock when the test piece ruptures.
NOTE At present, there appears to be insufficient quantitative data in the literature demonstrating the influence of
bending upon creep and stress rupture life. It is requested that any organization with such information forwards it to
ISO/TC164 for consideration at the next revision of this International Standard.
The machine shall be verified and shall meet the requirements of at least class 1 in ISO 7500-2.
6.2 Elongation measuring device
In uninterrupted tests, the elongation shall be measured using an extensometer, which meets the performance
requirements of class 1 or better of ISO 9513 or by other means which ensure the same accuracy without
interruption of the test. The extensometer can either be directly attached to the test piece, or can be non-
contacting (e.g. a non-contacting optical or laser extensometer).
It is recommended that the extensometer is calibrated over an appropriate range based upon the expected
creep strain.
The extensometer shall be calibrated at intervals not exceeding 3 years, unless the test duration is longer than
3 years. If the predicted test exceeds the date of the expiry of the calibration certificate then the extensometer
shall be recalibrated prior to commencement of the creep test.
The extensometer gauge length shall not be less than 10 mm.
The extensometer shall be able to measure the elongation either on one side or on the opposite sides of the
test piece; the latter is the preferred option.
The type of extensometer used (e.g. single-sided, double-sided, axial, diametral) should be reported. When
the elongation is measured on the opposite sides, the average elongation should be reported.
ISO 204:2009(E)
NOTE 1 For uninterrupted creep tests, i.e. with an extensometer attached directly to the parallel section of a test piece,
the percentage creep elongation is measured over L .
e
When the elongation is measured with an extensometer attached to the grip ends of the test piece, the ends
shall be of such shape and size that it can be assumed that the observed elongation has occurred completely
within the reference length of the test piece. Percentage creep elongation is measured over L .
r
The extensometer gauge length should normally be as near as possible to the reference length. In the case of
accurate creep measurements, a gauge length as long as possible should be used to improve the accuracy of
measurements.
NOTE 2 If only the percentage elongation after creep rupture or the percentage creep elongation for a specified test
duration is determined, the use of an extensometer is not necessary.
In interrupted tests, periodically unload the test piece and cool it to ambient temperature and measure the
permanent elongation on the gauge length with an appropriate device. The precision of this device shall be
0,01 ∆L or 0,01 mm, whichever is the greater. After this measurement the test piece may be first reheated
r
and then reloaded.
NOTE 3 For low creep strain measurements, e.g. u 1% strain, on test pieces with short gauge lengths, careful
consideration needs to be given to ensure that the measuring device used has sufficient resolution.
NOTE 4 Information on the long-term stability of transducers used for creep testing and accreditation issues are given in
References [35] and [36] in the Bibliography.
Care should be taken to avoid spurious negative creep when using nickel base alloy extensometers. See the
[38]
Code of Practice by Loveday and Gibbons (2007) .
6.3 Heating device
6.3.1 Permissible temperature deviations
The heating device shall heat the test piece to the specified temperature (T ).The permitted deviations
between the indicated temperature, (T) and the specified temperature, (T ), and the permitted maximum
i
temperature variation along the test piece shall be as given in Table 2.
Table 2 — Permitted deviations between T and T
i
and maximum permissible temperature variation along the test piece
Permitted deviation between T and T
Specified temperature, T Maximum permissible temperature
i
variation along the test piece

°C °C
°C
T u 600 3
± 3
600 < T u 800 ± 4 4
800 < T u 1 000 5
± 5
1 000 < T u 1 100 6
± 6
For specified temperatures greater than 1 100 °C, the permitted values shall be defined by agreement
between the parties concerned.
The indicated temperatures (T ) are the temperatures measured at the surface of the parallel length of the test
i
piece, errors from all sources being taken into account and any systematic errors having been corrected.
8 © ISO 2009 – All rights reserved

ISO 204:2009(E)
NOTE Instead of measuring the temperature at the surface of the test piece, it is permitted to carry out indirect
measurement of the temperature of each heating zone of the furnace provided that it is demonstrated that the tolerance
defined above is fulfilled.
If an extensometer is used, the parts of this instrument outside the furnace shall be designed and protected in
such a way that the temperature variations in the air around the furnace do not significantly affect the
measurements of the variations in length.
Variations in temperature of the air surrounding the test machine should not exceed ± 3 °C.
In the interrupted test, the variation of the room temperature during all measurements of the gauge length
should not exceed ± 2 °C. If this range is exceeded, corrections for ambient temperature variations shall be
applied.
6.3.2 Temperature measurement
6.3.2.1 General
The temperature indicator shall have a resolution of at least 0,5 °C and the temperature measuring equipment
shall have an accuracy equal to or better than ± 1 °C.
6.3.2.2 Single test piece machines
In single test piece machines, for test pieces with a parallel length less than or equal to 50 mm, at least two
thermocouples should be used. For test pieces with a parallel length greater than 50 mm, at least three
thermocouples should be used. In all cases, a thermocouple should be placed at each end of the parallel
length and, if a third thermocouple is used, it should be placed in the middle region of the parallel length.
The number of thermocouples may be reduced to one if it can be demonstrated that the conditions of the
furnace and the test piece are such that the variation of temperature of the test piece does not exceed the
values specified in 6.3.1.
6.3.2.3 Multiple test piece machines
In multiple test piece machines, it is recommended that at least one thermocouple be used for each test piece.
If only one thermocouple is used it shall be positioned at the middle of the parallel length. Three
thermocouples may only be used if located at appropriate positions within the furnace, and if there is
supporting data to demonstrate that for all test pieces the temperature conforms to the requirements of 6.3.1.
In the case of indirect temperature measurement, regular control measurements are required to determine
differences between the thermocouple(s) of each heating zone and a significant number of test pieces within a
given zone. The non-systematic components of the temperature differences shall not exceed ± 2 °C up to
800 °C and ± 3 °C above 800 °C.
6.3.2.4 Notched test pieces
Temperature measurement of notched test pieces shall be in accordance with either 6.3.2.2 or 6.3.2.3. It is
recommended that one thermocouple is placed close to the notch.
6.3.2.5 Thermocouples
The thermocouple junctions shall make good thermal contact with the surface of the test piece and shall be
screened from direct radiation from the heating source. The remaining portions of the wires within the furnace
shall be thermally shielded and electrically insulated.
NOTE This clause is not applicable in the case of indirect temperature measurement.
ISO 204:2009(E)
6.3.3 Calibration of the thermocouples and temperature measuring system
NOTE Information concerning different types of thermocouples is given in Annex A.
6.3.3.1 Calibration of the thermocouples
Rare metal thermocouples in use for short duration tests (typically 500 h or less) should be calibrated at least
every 12 months. Thermocouples in use for test durations greater than 12 months should be calibrated as
follows:
⎯ 4 years for T u 600 °C;
⎯ 2 years for 600 °C < T u 800 °C;
⎯ 1 year for T > 800 °C.
If a test duration exceeds the above calibration period the thermocouple shall be calibrated upon completion
of the test. If a thermocouple is rewelded, the thermocouple shall be recalibrated before use.
It shall be demonstrated that the error of the thermocouple used has been established either at the test
temperature or is typical for a range containing the test temperature.
If it is demonstrated that the drift of the thermocouple does not affect the permissible temperature deviations
specified in 6.3.1, the period between two calibrations can be longer.
Changes in the output of a thermocouple can be due not only to chemical changes from contamination leading
to drift, but also as a consequence of handling physical damage. Information on such changes should be
recorded and should be available on request.
NOTE 1 Thermocouple drift is dependent on the type of thermocouple used and the exposure duration at temperature.
If the drift affects permissible temperature deviations, either more frequent calibrations should be carried out
or a correction may be made to the temperature indicated by the thermocouple.
NOTE 2 Information concerning methods of calibration of thermocouples is given in Annex B.
6.3.3.2 Calibration of the temperature measuring equipment
The calibration of the temperature measuring equipment (including the cable, the connection, the cold
junction, the indicator or the recorder, the data line, etc.) shall be carried out by a method traceable to the
international unit (SI) of temperature.
If practicable, this calibration should be carried out annually over the range of temperatures measured by the
equipment and the readings shall be given in the calibration report.
7 Test pieces
7.1 Shape and dimensions
In general, the test piece is a machined proportional cylindrical test piece (L = k S ) with a circular cross-
ro o
section (see Figure 2). The value k should be equal to or greater than 5,65 and the value used shall be
recorded in the test report, i.e. L W 5D.
ro
In special cases, the cross-section of the test piece may be square or rectangular or of some other shape. The
provisions concerning the cylindrical test pieces do not apply to these specific test pieces.
10 © ISO 2009 – All rights reserved

ISO 204:2009(E)
In general, L should not exceed L by more than 10 % for circular test pieces, or by more than 15 % for
ro c
square or rectangular test pieces.
The parallel length shall be joined by transition curves to the gripped ends, which may be of any shape to suit
the grips of the testing machine. The transition radius (R) should be between 0,25D and 1D for the cylindrical
test pieces, or 0,25b and 1b in the case of rectangular or square test pieces.
Unless the sample size does not permit it, the original cross-sectional area (S ) shall be greater than or equal
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to 7 mm .
NOTE In some cases, especially for brittle materials, the transition radius can be greater than 1D.
When a test piece having extensometer attachment ridges (collars) in the parallel length is used, the transition
radius of the collars may be less than 0,25d; this should be selected to minimize stress concentrations and
there should be no evidence of undercut when inspected. For test pieces with collars, the diameter between
the collar and the grip end may be up to 10 % larger than the diameter of the original gauge length; this should
ensure that fracture will occur within the gauge length.
The grip ends of test pieces shall have the same axis as the parallel length with a coaxiality tolerance of
⎯ 0,005D or 0,03 mm, whichever is greater, for cylindrical test pieces, and
⎯ 0,005b or 0,03 mm, whichever is greater, for rectangular or square test pieces.
When oxidation is a significant factor, test pieces with a larger original cross-sectional area (S ) should be
o
used.
The original reference length shall be determined to a measurement uncertainty of ± 1 %. The final reference
length should be determined to a measurement uncertainty of ± 1 %.
When a notched test piece is used, the geometry and the position of this notch should be defined by
agreement.
7.2 Preparation
The test piece shall be machined in such a way as to minimize any residual deformation or surface defects.
The shape tolerances shall conform to Table 3 for test pieces with circular cross-sections and to Table 4 for
test pieces with square or rectangular cross-sections.
Table 3 — Shape tolerances of test pieces with circular cross-sections
Dimensions in millimetres
a
Nominal dimension
Shape tolerances
D
0,02
3 < D u 6
0,03
6 < D u 10
0,04
10 < D u 18
18 < D u 30 0,05
a
Maximum deviation between the measurements of a transverse dimension determined
along the entire parallel length of the test piece (see ISO 286-2).

ISO 204:2009(E)
Table 4 — Shape tolerances of test pieces with square or rectangular cross-sections
Dimensions in millimetres
a
Nominal dimension
Shape tolerances
b
3 < b u 6 0,02
6 < b u 10 0,03
10 < b u 18 0,04
18 < b u 30 0,05
a
Maximum deviation between the measurements of a transverse dimension determined
along the entire parallel length of the test piece (see ISO 286-2).
It is recommended that the minimum original cross-sectional area should occur within the middle two thirds of
the parallel length or of the reference length, whichever is smaller.
When the test piece has a notch (see Annex C), its profile shall be checked to ensure that it conforms with the
tolerances specified in the relevant product standard.
7.3 Determination of the original cross-sectional area
The original cross-sectional area (S ) shall be calculated from measurement of appropriate dimensions within
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the parallel length. Each appropriate dimension shall be measured to a measurement uncertainty of ± 0,1 %
or 0,01 mm, whichever is greater.
The size of the test piece shall be determined at three positions along the gauge length and the minimum
calculated value of the cross-sectional area shall be used for determining the applied load corresponding to
the specified stress.
7.4 Marking of the original gauge length, L
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Each end of the original gauge length shall be marked by means of fine marks or scribed lines, or other
means, but not by notches which could result in premature fracture.
Where marked, the original gauge length shall be marked to an accuracy of ± 1 %.
NOTE In some cases, it may be helpful to draw, on the surface of the test piece, a line parallel to the longitudinal
axis, along which the gauge length is drawn. Marking of L is not necessary when a specimen with small collars is used
o
[see Figure 2 c)].
7.5 Determination of the reference length, L
r
Where extensometry is attached to either ridges on the parallel length or the shoulders of the test piece, the
reference length shall be calculated using the following equation:
2n
⎡⎤
L=+LD2/dl (6)
()
rc ∑ ii
⎢⎥
⎣⎦
i
See Figure 2 e), where
n is the stress exponent at the test temperature for the material under investigation. If this is not known,
use n = 5; and
12 © ISO 2009 – All rights reserved

ISO 204:2009(E)
l is the length increment in the transition region. Experience has shown a value of 0,1 mm to be
i
suitable for these calculations.
This calculation shall be performed for each test piece design; providing the test piece dimensions remain
within the limits defined in 7.1 and 7.2 a recalculation for each test piece produced to that design is not
required.
8 Test procedure
8.1 Heating of the test piece
The test piece shall be heated to the specified temperature (T ). The test piece, gripping device and the
extensometer shall be at thermal equilibrium.
This condition shall be maintained for at least one hour before application of the force to the test piece, unless
the product standard states otherwise. In the uninterrupted test, the maximum time that the test piece is held
at the test temperature before applying the force shall not exceed 24 h. In the interrupted test, this time should
not exceed 3 h; the time under test temperature without force after unloading should not exceed 1 h.
During the heating period, the temperature of the test piece should not, at any time, exceed the specified
temperature (T ) with its tolerances. If these tolerances are exceeded, it shall be reported.
For creep tests with extensometers, a small preload (less than 10 % of the test force) may be applied to the
test piece in order to keep the loading train in alignment whilst heating up the test piece (i.e. before t = 0).
8.2 Application of the test force
The test force shall be applied along the test axis in such a manner to minimize bending and torsion of the test
piece.
The applied force shall be known to an accuracy of at least ± 1 %. The application of the test force shall be
made without shock and should be as rapid as possible.
Special care should be taken during the loading of soft and face centred cubic (FCC) materials since they may
exhibit creep at very low loads or at room temperature.
The beginning of the creep test and measurement of creep elongation is the time (t = 0) when the full load of
the initial stress is applied to the test piece (see Figure 1).
8.3 Test interruptions
8.3.1 General
The number of periodic interruptions should be sufficient to obtain the elongation data.
8.3.2 Multiple test piece machine with several test pieces in line
After a test piece has ruptured, the string of test pieces shall be removed from the testing machine to allow
replacement. Resume testing in accordance with 8.1 and 8.2.
8.3.3 Accidental interruption of the test
For any accidental interruption of the test due to, for example, interruption of heating or current, the conditions
of resumption of the test after each interruption shall be recorded in the test report. Ensure that overloading of
the test piece due to contraction of the force assembly is prevented. It is recommended that the initial applied
force is maintained during these interruptions.
ISO 204:2009(E)
8.4 Recording of temperature and elongation
8.4.1 Temperature
Throughout the test, it is important that sufficient recordings of the temperature of the test piece are made to
demonstrate that the temperature conditions comply with the requirements of 6.3.1.
8.4.2 Elongation
Either a continuous record or a sufficient number of recordings of the elongation shall be made throughout the
test so that the creep-time curve can be traced (see Figure 3).
When only a determination of a creep elongation for a specified test duration is made, the drawing of the
creep-time diagram is not necessary. Only the initial and final measurements are required.
In the interrupted test, the number of periodic interruptions for elongation measurement shall be chosen in
order to make it possible to interpolate the creep-time curve with suffi
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