EN ISO 9513:2012
(Main)Metallic materials - Calibration of extensometer systems used in uniaxial testing (ISO 9513:2012, Corrected version 2015-06)
Metallic materials - Calibration of extensometer systems used in uniaxial testing (ISO 9513:2012, Corrected version 2015-06)
ISO 9513:2012 specifies a method for the static calibration of extensometer systems used in uniaxial testing, including axial and diametral extensometer systems, both contacting and non-contacting.
Metallische Werkstoffe - Kalibrierung von Längenänderungs-Messeinrichtungen für die Prüfung mit einachsiger Beanspruchung (ISO 9513:2012, korrigierte Fassung 2015-06)
Diese Internationale Norm legt ein Verfahren fest für die statische Kalibrierung von Längen-änderungs Messsystemen (Extensometer Systemen) für die Prüfung mit einachsiger Beanspruchung einschließlich axialer Systeme und diametraler Systeme (Querdehnungsaufnehmer) für berührungslose und für berührende Messungen.
Matériaux métalliques - Étalonnage des chaînes extensométriques utilisées lors d'essais uniaxiaux (ISO 9513:2012, Version corrigée 2015-06)
L'ISO 9513:2012 spécifie une méthode pour l'étalonnage statique des chaînes extensométriques utilisées lors d'essais uniaxiaux, y compris les chaînes extensométriques axiales et diamétrales, avec contact ou sans contact.
Kovinski materiali - Kalibracija ekstenzometrov, ki se uporabljajo pri enoosnem preskušanju (ISO 9513:2012
Ta mednarodni standard določa metodo za statično kalibracijo ekstenzometričnih sistemov, ki se uporabljajo pri enoosnem preskušanju, vključno z osnimi in diametričnimi ekstenzometričnimi sistemi, ki so kontaktni ali nekontaktni.
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
01-junij-2013
1DGRPHãþD
SIST EN ISO 9513:2004
Kovinski materiali - Kalibracija ekstenzometrov, ki se uporabljajo pri enoosnem
preskušanju (ISO 9513:2012
Metallic materials - Verification and calibration of extensometers used in uniaxial testing
(ISO 9513:2012)
Metallische Werkstoffe - Zugversuch - Teil 5: Prüfung und Kalibrierung von
Längenänderungs-Messeinrichtungen für die Prüfung mit einachsiger Beanspruchung
(ISO 9513:2012
Matériaux métalliques - Matériaux métalliques - Etalonnage des extensomètres utilisés
lors d''essais uniaxiaux (ISO 9513:2012
Ta slovenski standard je istoveten z: EN ISO 9513:2012
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 9513
NORME EUROPÉENNE
EUROPÄISCHE NORM
December 2012
ICS 77.040.10 Supersedes EN ISO 9513:2002
English Version
Metallic materials - Calibration of extensometer systems used in
uniaxial testing (ISO 9513:2012)
Matériaux métalliques - Étalonnage des chaînes Metallische Werkstoffe - Kalibrierung von
extensométriques utilisées lors d'essais uniaxiaux (ISO Längenänderungs-Messeinrichtungen für die Prüfung mit
9513:2012) einachsiger Beanspruchung (ISO 9513:2012)
This European Standard was approved by CEN on 14 December 2012.
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-CENELEC 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-CENELEC Management Centre has the same
status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United
Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2012 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 9513:2012: E
worldwide for CEN national Members.
Contents Page
Foreword .3
Foreword
This document (EN ISO 9513:2012) has been prepared by Technical Committee ISO/TC 164 "Mechanical
testing of metals" in collaboration with Technical Committee ECISS/TC 101 “Test methods for steel (other
than chemical analysis)” 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 June 2013, and conflicting national standards shall be withdrawn at
the latest by June 2013.
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 ISO 9513:2002.
According to the CEN/CENELEC Internal Regulations, the national standards organisations of the following
countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech
Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece,
Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,
Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom.
Endorsement notice
The text of ISO 9513:2012 has been approved by CEN as a EN ISO 9513:2012 without any modification.
INTERNATIONAL ISO
STANDARD 9513
Third edition
2012-12-01
Metallic materials — Calibration of
extensometer systems used in uniaxial
testing
Matériaux métalliques — Étalonnage des chaînes extensométriques
utilisées lors d’essais uniaxiaux
Reference number
ISO 9513:2012(E)
©
ISO 2012
ISO 9513:2012(E)
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISO’s
member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2012 – All rights reserved
ISO 9513:2012(E)
Contents Page
Foreword .iv
Introduction . v
1 Scope . 1
2 Terms and definitions . 1
3 Symbols and designations . 1
4 Principle . 2
5 Calibration equipment . 2
5.1 Calibration apparatus . 2
5.2 Calibration traceability . 2
6 Pre-calibration inspection . 2
6.1 Objective . 2
6.2 Records of the inspection . 3
6.3 Identification of extensometer system elements . 3
7 Measurement of extensometer gauge length . 3
7.1 Fixed gauge length extensometry . 3
7.2 Variable gauge length extensometry . 3
7.3 Non-contacting extensometry . 4
7.4 Extensometer gauge lengths established using setting gauges . 4
8 Calibration process . 4
8.1 Environmental considerations . 4
8.2 Position of the extensometer . 4
8.3 Calibration increments . 4
8.4 Calibration process . 6
8.5 Determination of the characteristics of the extensometer system . 6
9 Classification of the extensometer system . 7
9.1 Input data . 7
9.2 Analysis of the data . 7
9.3 Classification criteria . 7
9.4 Assessment of the results . 7
10 Uncertainty determination . 8
10.1 Uncertainty of the calibration . 8
10.2 Uncertainty budget determination . 8
11 Extensometer system calibration intervals . 8
12 Calibration certificate . 8
12.1 Mandatory information . 8
12.2 Data presentation . 9
Annex A (informative) Uncertainty of measurement .10
Annex B (informative) Calibration of the calibration apparatus .15
Annex C (informative) Example of a report of the calibration of calibration apparatus .17
Annex D (informative) Examples of extensometer system configurations .20
Annex E (informative) Laser extensometry .29
Annex F (informative) Video extensometry .37
Annex G (informative) Full field strain measurement video extensometry .41
Annex H (informative) Calibration of a cross-head measurement system .43
Bibliography .44
ISO 9513:2012(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 9513 was prepared by Technical Committee ISO/TC 164, Mechanical testing of metals, Subcommittee
SC 1, Uniaxial testing.
This third edition cancels and replaces the second edition (ISO 9513:1999), which has been technically revised.
It also incorporates the Technical Corrigendum ISO 9513:1999/Cor.1:2000.
iv © ISO 2012 – All rights reserved
ISO 9513:2012(E)
Introduction
This International Standard sets out criteria for the calibration of extensometer systems, covering general
principles, the calibration equipment to be used, pre-calibration inspection and the measurement of
gaugelength for various types of extensometer systems. Aspects of the calibration process are addressed,
as are the assessment of the results, uncertainties, calibration intervals and reporting. Criteria for calibration
apparatus, their calibration and grading are addressed, complemented by a Bibliography covering a number of
[1] to [10]
important papers related to extensometer systems and their application . Work is in progress to develop
processes for dynamic extensometer calibration, however these have not reached, at the time of writing of this
International Standard, the level of development appropriate for inclusion within this International Standard. For
further information, refer to Reference [6].
Informative annexes address calculation of uncertainties of measurement for an extensometer system
calibration (Annex A), calibration of calibration apparatus (Annex B) and an example of a calibration report
(Annex C). Subsequent annexes address examples of extensometer system configurations (Annex D), laser
extensometry (Annex E), video extensometry (Annex F), full field extensometry (Annex G) and calibration of a
crosshead measurement system (Annex H).
INTERNATIONAL STANDARD ISO 9513:2012(E)
Metallic materials — Calibration of extensometer systems used
in uniaxial testing
1 Scope
This International Standard specifies a method for the static calibration of extensometer systems used in
uniaxial testing, including axial and diametral extensometer systems, both contacting and non-contacting.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1
extensometer system
equipment used to measure displacement or strain on the surface of a test piece
NOTE For the purpose of this International Standard, the term “extensometer system” includes the indicator.
Some extensometers indicate strain directly (e.g. laser extensometers or digital image correlation techniques). Other
extensometers indicate the change in gauge length of a test piece; this is converted into strain by dividing by the relevant
gauge length.
2.2
gauge length
portion of a test piece where extension is measured
3 Symbols and designations
Symbols used throughout this International Standard are given in Table 1 together with their designation.
Table 1 — Symbols and designations
Symbol Designation Unit
L Nominal gauge length of extensometer mm
e
L’ Measured gauge length of extensometer mm
e
l Maximum limit of calibration range mm
max
l Minimum limit of calibration range mm
min
l Displacement indicated by extensometer µm
i
l Displacement given by calibration apparatus µm
t
Relative gauge length error of the extensometer system
q
L %
e
q Relative bias error of the extensometer system %
rb
q Absolute bias error of the extensometer system µm
b
r Resolution of the extensometer system µm
ISO 9513:2012(E)
4 Principle
The calibration of extensometer systems involves a comparison of the readings given by the extensometer with
known variations in length provided by a calibration apparatus.
NOTE 1 The user can define the displacement range(s) over which the calibration is to be performed. In this way, the
performance of the extensometer system can be optimized. For example, for strain-controlled low cycle fatigue, only a
small portion of the operating range of the extensometer is typically used. Hence, it would be appropriate, in this case, to
concentrate the calibration on the centre portion of the operating range.
The calibration process compares the known displacement from the calibration device with the output of
the extensometer system. This output can range from manual readings of high precision dial gauges to the
displacement indication of a transducer/electronics/data-logging system. In the latter case, the extensometer
system output would include any data curve fitting applied by the electronics/data-logging system.
NOTE 2 For certain types of extensometer systems, the calibration and classification will also be dependent upon the
ability of the extensometer system to define the gauge length.
5 Calibration equipment
5.1 Calibration apparatus
The calibration apparatus, which allows a known displacement l to be applied to the extensometer, may consist
t
of a rigid frame with suitable coaxial spindles or other fixtures to which the extensometer can be attached. The
calibration apparatus shall comprise a mechanism for moving at least one of the axial spindles together with a
device for accurately measuring the change in length produced. These variations in length can be measured by,
for example, an interferometer, a linear incremental encoder or gauge blocks and a comparator, or a micrometer.
NOTE Special attachments to the calibration apparatus spindles are utilized for the calibration of diametral
extensometers.
The calibration apparatus should be calibrated in accordance with Annex B and should meet the performance
requirements given in Table B.1.
Annex B gives a recommended calibration procedure for the calibration apparatus and details performance
criteria that indicate that the apparatus is suitable for calibrating extensometer systems in accordance with this
International Standard.
5.2 Calibration traceability
The calibration apparatus and the supporting equipment (such as micrometers, callipers, optical projection
microscopes) shall be calibrated using standards that are traceable to the International System of Units (SI).
The uncertainty associated with any measurements made by the supporting equipment shall not exceed one
third of the permissible error of the extensometer system being calibrated (see Table 2). The temperature
measurement instrument shall have a resolution of 0,1 °C.
6 Pre-calibration inspection
6.1 Objective
Prior to the calibration of the extensometer system it shall be inspected. This shall comprise, but not be limited to,
inspection of the mechanical components for, for example, free movement, damaged parts, worn knife edges,
and worn gauge length setting pins/fixtures. For extensometer systems incorporating electronic transducers,
the cabling and connectors shall be examined for damage, wear, etc.
The extensometer system shall be calibrated in the as-found condition if at all possible. The results shall be assessed
and, if necessary, the system shall be adjusted and re-calibrated. In this case, both data sets shall be reported.
2 © ISO 2012 – All rights reserved
ISO 9513:2012(E)
6.2 Records of the inspection
Records of the pre-calibration inspection shall be kept, identifying the “as-found” condition of the extensometer
system, when the inspection was performed and who performed it. These pre-calibration inspection records
can take the form of either a written report or a completed “pro-forma” checklist.
6.3 Identification of extensometer system elements
The extensometer shall be uniquely identified. Parts that may be changed by the user during normal use of the
extensometer that affect the calibration of the extensometer shall also be uniquely identified where possible.
However, this requirement does not extend to clamping devices used to attach the extensometer to the test
piece. These unique identifications form part of the records for the extensometer system.
7 Measurement of extensometer gauge length
7.1 Fixed gauge length extensometry
7.1.1 The measured gauge length, L′ , of a fixed gauge length extensometer shall be determined by either
e
direct or indirect means. In both cases, the extensometer setting pin or gauge fixture is used to set the
extensometer contact points to their pre-set displacement.
NOTE Variability of the measured gauge length might be experienced due to excessive play/wear in the gauge length
setting mechanism.
′
7.1.1.1 Direct measurement of the gauge length, L , is performed between the extensometer contact points,
e
using a calibrated measuring instrument such as a caliper or a shadowgraph/projection microscope.
7.1.1.2 Indirect measurement of the gauge length, L′ , is performed by placing the extensometer on a soft
e
metal test piece in such a way that the blades or points of the extensometer leave their marks. Once the
extensometer is removed, the distance between the marks on the test piece shall be measured, using equipment
with an accuracy consistent with the required class of extensometer.
7.1.2 The relative error on the gauge length, q , calculated from Formula (1) shall meet the requirements
L
e
given in Table 2.
′
LL−
ee
q = ×100 (1)
L
e
L
e
7.2 Variable gauge length extensometry
7.2.1 The gauge length of a variable gauge length extensometer shall be measured either directly, or indirectly.
7.2.1.1 Direct measurement of the gauge length is performed by setting the extensometer to the required
gauge length using jigs, fixtures or other tools, followed by measurement between the extensometer contact
points, using a calibrated measuring instrument such as a calliper or a shadowgraph/projection microscope.
′
7.2.1.2 Indirect measurement of the gauge length, L is performed by attaching the extensometer to a soft
e
metal test piece in such a way that the blades or points of the extensometer leave their marks. Once the
extensometer is removed, the distance between the marks on the test piece is measured, using equipment with
an accuracy consistent with the required class of extensometer.
7.2.2 Extensometers commonly used in creep, elevated temperature tensile or stress relaxation testing have
their gauge length defined by small ridges machined on the parallel length of the test piece, to which the
ISO 9513:2012(E)
extensometer is clamped. The gauge length for such extensometers shall be determined directly from the test
piece and shall be to an accuracy consistent with the required class of extensometer.
7.2.3 The relative error on the gauge length, q , calculated from Formula (1), shall meet the requirements
L
e
given in Table 2.
7.2.4 Where an extensometer sets or measures the gauge length, the relative error on the gauge length shall
be determined. If features on the test piece define the gauge length, the relative error on the gauge length does
not need to be determined.
7.2.5 Where an extensometer automatically sets the gauge length, the maximum and minimum gauge lengths
used, plus three more gauge lengths between the minimum and maximum, shall be measured. Where fewer
than five gauge lengths are used, all gauge lengths shall be measured.
7.3 Non-contacting extensometry
The gauge length for non-contacting extensometry is established in accordance with the manufacturer’s
instructions.
7.4 Extensometer gauge lengths established using setting gauges
Where an extensometer gauge length is set using a removable gauge, the relative error on the gauge length,
q , calculated from Formula (1) shall not exceed the values given in Table 2.
L
e
The uncertainty of measuring the gauge length shall be three times better than the allowable error in gauge length.
8 Calibration process
8.1 Environmental considerations
8.1.1 The ambient temperature during the calibration of the extensometer system shall be recorded.
In general, the calibration of the extensometer system should be carried out at a temperature stable to within
± 2 °C, the target temperature being within the range 18 °C to 28 °C. Temperature changes during the calibration
process may add to the uncertainty of the calibration and in some cases may affect the ability to properly
calibrate the extensometer.
8.1.2 For extensometers used for uniaxial testing at temperatures outside the range 10 °C to 35 °C, the
calibration should be carried out at or near the test temperature, if facilities exist.
8.1.3 The extensometer shall be placed near the calibration apparatus, or be mounted on it, for a sufficient
length of time prior to its calibration so that the parts of the extensometer system and of the calibration apparatus
which are in contact stabilize at the calibration temperature.
8.2 Position of the extensometer
The extensometer shall be placed, wherever feasible, in the calibration apparatus in a similar orientation to that
in which it will be used during uniaxial testing to avoid errors due to loss of equilibrium or to deformation of any
part of the extensometer.
The extensometer shall be attached in a similar way as during uniaxial testing.
8.3 Calibration increments
8.3.1 The user shall establish the range of displacements over which the extensometer system shall be calibrated.
4 © ISO 2012 – All rights reserved
ISO 9513:2012(E)
8.3.2 The number of calibration points, and the number of ranges over which calibration is performed, shall
be based upon the relationship between the minimum displacement at which a property is determined, l , and
min
the maximum displacement at which a property is determined, l .
max
8.3.3 For monotonic tests, the following series of readings shall be made.
a) If (l /l ) is less than or equal to 10, one range of at least five increments shall be recorded.
max min
b) If (l /l ) is greater than 10 but less than or equal to 100, two ranges (l to 10l and 10l to l ),
max min min min min max
or (l to 0,1l and 0,1l to l ), each of at least five increments, shall be recorded.
min max max max
c) If (l /l ) is greater than 100, three ranges (l to 10l , 10l to 100l , 100l to l ), or (l to
max min min min min min min max min
0,01l , 0,01l to 0,1l , 0,1 l to l ), each of at least five increments, shall be recorded.
max max max max max
For each of the three categories [a), b), c) above], the increment between any two adjacent points shall not
exceed one third of the range. Examples of these increments are shown in Figure 1.
Key
1 calibration points
Figure 1 — Schematic diagram showing calibration point distribution
NOTE 1 A tensile test measuring, from the extensometer, the modulus and proof stresses only, would fall into category
a). A tensile test, establishing proof stresses and elongation at failure from the extensometer, or a creep to rupture test,
would fall into category b) or category c).
NOTE 2 For fatigue tests, a range of at least five increments (with the increment between any two adjacent points not
exceeding one third of the range between l and l ) is used.
min max
NOTE 3 The values derived from the above calculations can be adjusted to the nearest convenient increments to match
those of the calibration apparatus.
8.3.4 When establishing l and l , operational factors such as thermal expansion of elevated temperature
max min
tests and additional displacement contingencies to cover matters such as test to test set-up variability shall be
taken into account.
ISO 9513:2012(E)
8.4 Calibration process
8.4.1 The calibration shall be undertaken in the as-found condition without special cleaning.
8.4.2 When the temperature has stabilized, it is recommended that, before calibration and by means of the
calibration apparatus, the extensometer be exercised twice over the calibration range of the extensometer
system. If possible, the displacement is taken to a slightly negative value and returned to zero. Where appropriate,
reset the extensometer system to zero.
8.4.3 The calibration consists of two series of measurements with the increments as defined in 8.3.
— The first series of measurements is performed and recorded; the extensometer is removed and then
placed back on the calibration apparatus.
— A second series of measurements is then made in the same manner as the first.
Depending on the expected use of the extensometer, the two series of measurements are made for increases
in length or for decreases in length, or for both.
8.5 Determination of the characteristics of the extensometer system
8.5.1 Resolution
8.5.1.1 The resolution, r, is the smallest quantity which can be read on the instrument.
8.5.1.2 For extensometers with analogue scales, the resolution of the indicator shall be obtained from the ratio
between the width of the pointer and the centre-to-centre distance between two adjacent scale graduation marks
(scale interval), multiplied by the physical dimension which one scale increment represents. The resolution shall
not be smaller than one fifth of the physical dimension represented by one scale interval unless the distance
between two adjacent marks is greater than or equal to 2,5 mm, in which case the resolution may be as small
as one tenth of a scale interval.
8.5.1.3 For extensometer systems with an electronic display, the output shall be observed for 10 s and the
maximum and minimum values recorded. One half the difference between the maximum and minimum observed
values shall be established and recorded as the resolution, r. Where the minimum and maximum values are
equal, the resolution shall be one digit on the display.
8.5.2 Bias error
8.5.2.1 Relative bias error
The relative bias error, q , for a given displacement, l , is calculated from Formula (2):
rb t
ll−
it
q = ×100 (2)
rb
l
t
8.5.2.2 Absolute bias error
The absolute bias error, q , for a given displacement, l , is calculated from Formula (3):
b t
ql=−()l (3)
bi t
6 © ISO 2012 – All rights reserved
ISO 9513:2012(E)
9 Classification of the extensometer system
9.1 Input data
The required input data for the classification of the extensometer system are:
a) the relative error of the gauge length (see 7.2.5);
b) the resolution (absolute and/or relative) of the extensometer system (see 8.5.1);
c) for each calibration data point, the bias error (absolute and/or relative) (see 8.5.2);
d) the confirmation that the calibration apparatus fulfilled the requirements of this International Standard for
each calibration data point.
9.2 Analysis of the data
The collated data are assessed as follows:
a) the relative error of the gauge length is compared to the limits in Table 2 and a grading is obtained;
b) the resolution of the extensometer system for each calibration data point is compared to the limits in
Table 2 and a grading obtained;
c) for each calibration data point, the bias error is compared to the limits in Table 2 and a grading is obtained.
9.3 Classification criteria
Table 2 gives the maximum permissible values for the relative gauge length error, the resolution and the bias error.
Table 2 — Classification of the extensometer system
a a
Class of Relative error of Resolution Bias error
extensometer the gauge length
Percentage of Absolute Relative Absolute
system
reading value value value
(r/l )·100
q
i
L
r q l - l
e rb i t
% % µm % µm
0,2 ±0,2 0,1 0,2 ±0,2 ±0,6
0,5 ±0,5 0,25 0,5 ±0,5 ±1,5
1 ±1,0 0,5 1,0 ±1,0 ±3,0
2 ±2,0 1,0 2,0 ±2,0 ±6,0
a
Whichever is greater.
9.4 Assessment of the results
9.4.1 The data specified in 9.2 are collated and the maximum classification value for each of the following
is determined:
a) the relative error of the gauge length;
b) for each calibration data point the resolution of the extensometer system;
c) for each calibration data point the bias error;
d) for each calibration data point the classification of the calibration apparatus.
This maximum value of these four parameters is defined as the ISO 9513 classification for the extensometer system.
ISO 9513:2012(E)
9.4.2 Whenever adjustments are needed for the extensometer to comply with class requirements for its
intended use, the calibration provider can, with laboratory approval, make such adjustments to enhance the
extensometer system performance. The records from the initial calibration shall be retained and supplied as part
of the calibration documentation. The post-adjustment results shall be reported on the calibration certificate.
10 Uncertainty determination
10.1 Uncertainty of the calibration
Many elements contribute to the uncertainty of the calibration process. The following shall be assessed and
incorporated into the uncertainty budget calculation:
a) calibration uncertainty of the calibration device;
b) ambient temperature fluctuations during calibration;
c) inter-operator variability where more than one person performs calibrations within a laboratory;
d) gauge length setting;
e) gauge length measurement equipment.
For further information, refer to Annex A.
10.2 Uncertainty budget determination
The uncertainty shall be determined. An example calculation, showing how to perform an uncertainty evaluation
for an extensometer system, is presented as Annex A.
NOTE The requirements of this International Standard limit the major components of uncertainty when calibrating
extensometers. By complying with this metrological standard, uncertainty is explicitly taken into account as required
by some accreditation standards. Reducing the allowable bias by the amount of the uncertainty would result in double
counting of the uncertainty. The classification of an extensometer calibrated and certified to meet a specific class does not
ensure that the accuracy including uncertainty will be less than a specific value. For example, an extensometer meeting
Class 0,5 does not necessarily have a bias including uncertainty of less than 0,5 %.
11 Extensometer system calibration intervals
11.1 The time between two calibrations depends on the type of extensometer system, the maintenance
standard and the number of times the extensometer system has been used. Under normal conditions, it is
recommended that calibration be carried out at intervals of approximately 12 months. This interval shall not
exceed 18 months unless the test is expected to last more than 18 months; in such a case the extensometer
system shall be calibrated before and after the test. Where long-term creep tests are performed according to
ISO 204, the calibration interval for their extensometer systems, based upon extensive practical experience, is
three years; a similar situation exists for long-term stress relaxation testing. In these cases, the testing standard
requirement shall take precedence over the calibration intervals defined in this clause.
11.2 The extensometer system shall be calibrated after each repair or adjustment which affects the accuracy
of measurements.
12 Calibration certificate
12.1 Mandatory information
The calibration certificate shall contain at least the following information:
a) reference to this International Standard, i.e. ISO 9513;
8 © ISO 2012 – All rights reserved
ISO 9513:2012(E)
b) name and address of the owner of the extensometer system;
c) identification of the extensometer (type, gauge length, mark, serial number and mounting position);
d) type and reference number of the calibration apparatus;
e) temperature during the calibration process;
f) nature of the variations of length for which the calibration was carried out, i.e. either for increases and/or
for decreases in length;
g) date of calibration;
h) name of the person who performed the calibration, plus the name or mark of the calibrating organization;
i) all results from the calibration (as-found condition and, if adjusted, after adjustment measurements);
j) a statement of uncertainty;
k) classification for each range of the extensometer.
Items on the certificate may be presented in a referenced report.
12.2 Data presentation
The results of the calibration shall be tabulated in the certificate and shall include individual values of the bias
error associated with each calibration point.
A graphical presentation of the results from the calibration may be presented as part of the certificate.
ISO 9513:2012(E)
Annex A
(informative)
Uncertainty of measurement
A.1 Introduction
The approach for determining uncertainty, presented in this annex, considers only those uncertainties
associated with the overall measurement performance of the length measurements. These performance
uncertainties reflect the combined effect of all the separate uncertainties.
The uncertainty of measurement of the reference instruments (calibration equipment) is indicated in the
corresponding calibration certificate. Factors influencing these quantities include:
a) environmental effects such as temperature deviations;
b) drift of the displacement standard;
c) interpolation deviation of the reference device.
These quantities should be considered. Depending on the design of the calibration equipment, there is also a
need to include the position of the extensometer related to the gauge length axis of the testing machine.
Among the measured variables of the extensometer, which are relevant for the estimation of the uncertainty,
the following components should be considered:
— axiality of the extensometer to the calibration device;
— length variation indicator;
— relative uncertainty of measurement due to the resolution of the calibration device;
— gauge length error;
— relative deviation of the calibration device;
— repeatability of the indicator of the extensometer;
— resolution of the extensometer;
— temperature influences.
It is possible to calculate the uncertainty of the extensometer systems for uniaxial testing, at the time of
calibration, either from the specification limits or from the readings obtained. These calculations are detailed
in the following sections.
Since the accuracy error, as a known bias, is usually not corrected during calibration, if it falls within specifications
of Table 2, the range within which the estimated relative error, E, could reasonably be expected to lie, should
[11][12]
be E = q ± U, where q is the relative accuracy error defined in 8.5.2 and U is the expanded uncertainty .
The condition of a calibration is fulfilled if the relative gauge length error, q (see Table 2), lies within the
L
e
given tolerance.
10 © ISO 2012 – All rights reserved
ISO 9513:2012(E)
A.2 Calibration apparatus
The standard uncertainty related to the calibration apparatus, u , is given by:
std
22 22
uu=+uu++u (A.1)
stdcal AB D
where
u is the standard uncertainty, equal to 0,5 times the expanded bias of the calibration apparatus,
cal
determined from the calibration certificate or other relevant information;
u is the relative standard uncertainty due to the temperature deviation between the calibration
A
temperature of the extensometer and the calibration temperature of the calibration apparatus;
α ⋅a
temp
u = (A.2)
A
α
is the temperature coefficient of the calibration apparatus according to the
manufacturer’s specifications;
a is the temperature deviation between the calibration temperature of the
temp
extensometer and the calibration temperature of the calibration apparatus;
u is the relative standard uncertainty due to long-term instability (drift) of the calibration apparatus;
B
a
sensitivity
u = (A.3)
B
is the long-term instability (drift) of the calibration apparatus;
a
sensitivity
u is the relative standard uncertainty due to the linear approximation to the polynomial curve (if
D
required);
a
deviation
u = (A.4)
D
is the relative deviation due the linear approximation of the polynomial curve of the
a
deviation
calibration apparatus.
A.3 Resolution
The standard uncertainty related to relative resolution, u , is derived from a rectangular distribution:
r
a
resolution
u = (A.5)
r
where a is the relative resolution of the extensometer.
resolution
ISO 9513:2012(E)
A.4 Repeatability
The standard uncertainty related to repeatability, u , is the relative standard deviation of the estimated relative
b
mean error value:
n
u = ()qq− (A.6)
b ∑ i
nn−1
()
i−1
where
n is the number of readings;
q is the measured bias error (%);
i
q is the mean measured bias error (%).
A.5 Relative mean error of the extensometer system
The uncertainty of the relative mean error of the extensometer system, u , is given by:
q
22 2
u =+uuu+
qr bstd
(A.7)
22 2 22 2
=+uu ++uu ++uu
rb cal AB D
A.6 Expanded uncertainty
Once all the relevant standard uncertainties have been allowed for (including the other contributions mentioned
above), the combined uncertainty, u , is multiplied by a coverage factor, k, to give the expanded uncertainty, U.
q
It is recommended that a value of k = 2 be used, although k may also be calculated from the number of effective
[11]
degrees of freedom based on the principles laid down in ISO/IEC Guide 98-3 (see E.4.2, E.4.3 and G.4.2).
Hence, U is given by
Uk=⋅u (A.8)
q
where
k is the coverage factor;
u is the combined uncertainty.
q
The estimated mean relative error, E, could reasonably be expected to lie within the range:
Eq=±U (A.9)
A.7 Typical values of uncertainty
In the past, measurement uncertainty was not taken into account for the purp
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