EN ISO 26203-1:2018

SLOVENSKI STANDARD
01-julij-2018
1DGRPHãþD
SIST EN ISO 26203-1:2011
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Metallic materials - Tensile testing at high strain rates - Part 1: Elastic-bar-type systems
(ISO 26203-1:2018)
Metallische Werkstoffe - Zugversuch bei hohen Dehngeschwindigkeiten - Teil 1:
Elastische Stoßwellentechnik (ISO 26203-1:2018)
Matériaux métalliques - Essai de traction à vitesses de déformation élevées - Partie 1:
Systèmes de type à barre élastique (ISO 26203-1:2018)
Ta slovenski standard je istoveten z: EN ISO 26203-1:2018
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.

EN ISO 26203-1
EUROPEAN STANDARD
NORME EUROPÉENNE
March 2018
EUROPÄISCHE NORM
ICS 77.040.10 Supersedes EN ISO 26203-1:2010
English Version
Metallic materials - Tensile testing at high strain rates -
Part 1: Elastic-bar-type systems (ISO 26203-1:2018)
Matériaux métalliques - Essai de traction à vitesses de Metallische Werkstoffe - Zugversuch bei hohen
déformation élevées - Partie 1: Systèmes de type à Dehngeschwindigkeiten - Teil 1: Elastische
barre élastique (ISO 26203-1:2018) Stoßwellentechnik (ISO 26203-1:2018)
This European Standard was approved by CEN on 28 February 2018.

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, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2018 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 26203-1:2018 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 26203-1:2018) 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 September 2018, and conflicting national standards
shall be withdrawn at the latest by September 2018.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 26203-1:2010.
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,
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, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Endorsement notice
The text of ISO 26203-1:2018 has been approved by CEN as EN ISO 26203-1:2018 without any
modification.
INTERNATIONAL ISO
STANDARD 26203-1
Second edition
2018-01
Metallic materials — Tensile testing at
high strain rates —
Part 1:
Elastic-bar-type systems
Matériaux métalliques — Essai de traction à vitesses de déformation
élevées —
Partie 1: Systèmes de type à barre élastique
Reference number
ISO 26203-1:2018(E)
©
ISO 2018
ISO 26203-1:2018(E)
© ISO 2018
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
Published in Switzerland
ii © ISO 2018 – All rights reserved

ISO 26203-1:2018(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principles . 1
5 Symbols and designations . 2
6 Apparatus . 3
7 Test piece . 5
7.1 Test-piece shape, size and preparation . 5
7.2 Typical test piece . 7
8 Calibration of the apparatus . 8
8.1 General . 8
8.2 Displacement measuring device . 9
9 Procedure. 9
9.1 General . 9
9.2 Mounting the test piece . 9
9.3 Applying force . 9
9.4 Measuring and recording . 9
10 Evaluation of the test result .11
11 Test report .12
Annex A (informative) Quasi-static tensile testing method .14
Annex B (informative) Example of one-bar method .16
Annex C (informative) Example of split Hopkinson bar (SHB) method .23
Bibliography .31
ISO 26203-1:2018(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.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
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. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: www .iso .org/ iso/ foreword .html.
This document 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 26203-1:2010), of which it constitutes a
minor revision.
The main changes compared to the previous edition are as follows:
— a note above 7.1 d) has been added.
A list of all parts in the ISO 26203 series can be found on the ISO website.
iv © ISO 2018 – All rights reserved

ISO 26203-1:2018(E)
Introduction
Tensile testing of metallic sheet materials at high strain rates is important to achieve a reliable analysis
3 −1
of vehicle crashworthiness. During a crash event, the maximum strain rate often reaches 10 s , at
which the strength of the material can be significantly higher than that under quasi-static loading
conditions. Thus, the reliability of crash simulation depends on the accuracy of the input data specifying
the strain-rate sensitivity of the materials.
Although there are several methods for high-strain rate testing, solutions for three significant problems
are required.
The first problem is the noise in the force measurement signal.
— The test force is generally detected at a measurement point on the force measurement device that is
located some distance away from the test piece.
— Furthermore, the elastic wave which has already passed the measurement point returns there by
reflection at the end of the force measurement device. If the testing time is comparable to the time
for wave propagation through the force measurement device, the stress-strain curve may have large
oscillations as a result of the superposition of the direct and indirect waves. In quasi-static testing,
contrarily, the testing time is sufficiently long to have multiple round-trips of the elastic wave. Thus,
the force reaches a saturated state and equilibrates at any point of the force measurement device.
— There are two opposing solutions for this problem.
— The first solution is to use a short force measurement device which will reach the saturated
state quickly. This approach is often adopted in the servo-hydraulic type system.
— The second solution is to use a very long force measurement device which allows the completion
of a test before the reflected wave returns to the measurement point. The elastic-bar-type
system is based on the latter approach.
The second problem is the need for rapid and accurate measurements of displacement or test piece
elongation.
— Conventional extensometers are unsuitable because of their large inertia. Non-contact type methods
such as optical and laser devices should be adopted. It is also acceptable to measure displacements
using the theory of elastic wave propagation in a suitably-designed apparatus, examples of which
are discussed in this document.
— The displacement of the bar end can be simply calculated from the same data as force measurement,
i.e. the strain history at a known position on the bar. Thus, no assessment of machine stiffness is
required in the elastic-bar-type system.
The last problem is the inhomogeneous section force distributed along the test piece.
— In quasi-static testing, a test piece with a long parallel section and large fillets is recommended to
achieve a homogeneous uniaxial-stress state in the gauge section. In order to achieve a valid test
with force equilibrium during the dynamic test, the test piece is to be designed differently from the
typically designed quasi-static test piece. Dynamic test pieces are intended to be generally smaller
in the dimension parallel to the loading axis than the test pieces typically used for quasi-static
testing.
The elastic-bar-type system can thus provide solutions for dynamic testing problems and is widely
3 −1
used to obtain accurate stress-strain curves at around 10 s . The International Iron and Steel
Institute developed the “Recommendations for Dynamic Tensile Testing of Sheet Steel” based on the
interlaboratory test conducted by various laboratories. The interlaboratory test results show the high
data quality obtained by the elastic-bar-type system. The developed knowledge on the elastic-bar-type
system is summarized in this document; ISO 26203-2 covers servo-hydraulic and other test systems
used for high-strain-rate tensile testing.
INTERNATIONAL STANDARD ISO 26203-1:2018(E)
Metallic materials — Tensile testing at high strain rates —
Part 1:
Elastic-bar-type systems
1 Scope
This document specifies methods for testing metallic sheet materials to determine the stress-strain
characteristics at high strain rates. This document covers the use of elastic-bar-type systems.
−3 3 −1
The strain-rate range between 10 and 10 s is considered to be the most relevant to vehicle crash
events based on experimental and numerical calculations such as the finite element analysis (FEA)
work for crashworthiness.
In order to evaluate the crashworthiness of a vehicle with accuracy, reliable stress-strain
−3 −1
characterization of metallic materials at strain rates higher than 10 s is essential.
2 −1
This test method covers the strain-rate range above 10 s .
−1 −1
NOTE 1 At strain rates lower than 10 s , a quasi-static tensile testing machine that is specified in ISO 7500-1
and ISO 6892-1 can be applied.
NOTE 2 This testing method is also applicable to tensile test-piece geometries other than the flat test pieces
considered here.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
elastic-bar-type system
measuring system in which the force-measuring device is lengthened in the axial direction to prevent
force measurement from being affected by waves reflected from the ends of the apparatus
Note 1 to entry: The designation “elastic-bar-type system” comes from the fact that this type of system normally
employs a long elastic bar as force-measuring device.
4 Principles
The stress-strain characteristics of metallic materials at high strain rates are evaluated.
ISO 26203-1:2018(E)
−1
At a strain rate higher than 10 s , the signal of the loading force is greatly perturbed by multiple
passages of waves reflected within the load cell that is used in the quasi-static test. Thus, special
techniques are required for force measurement. This may be accomplished in two opposite ways:
— one is to lengthen the force measurement device in the loading direction, in order to finish the
measurement before the elastic wave is reflected back from the other end (elastic-bar-type systems);
— another way is to shorten the force measurement device, thus reducing the time needed to attain
dynamic equilibrium within the force measurement device and realizing its higher natural frequency
(servo-hydraulic type systems).
−1 −1
Tests at low strain rates (under 10 s ) can be carried out using a quasi-static tensile testing machine.
However, special considerations are required when this machine is used for tests at strain rates higher
than conventional ones. It is necessary to use a test piece specified for high-strain-rate testing methods.
Annex A provides details of the test procedure for this practice.
5 Symbols and designations
Symbols and their corresponding designations are given in Table 1.
Table 1 — Symbols and designations
Symbol Unit Designation
Test piece
a mm original thickness of a flat test piece
o
b mm original width of the parallel length of a flat test piece
o
b mm width(s) of the grip section of a test piece
g
L mm original gauge length [see 7.1 e)]
o
L mm parallel length
c
L mm total length that includes the parallel length and the shoulders
total
L mm final gauge length after fracture
u
r mm radius of the shoulder
S mm original cross-sectional area of the parallel length
o
S mm cross-sectional area of the elastic bar
b
Time
t s time
Elongation
percentage elongation after fracture
NOTE  With non-proportional test pieces, the symbol A is supplemented with an index
A %
which shows the basic initial measured length in millimetres, e.g. A = Percentage
20mm
elongation after fracture with an original gauge length L = 20 mm.
o
A % specified upper limit of percentage elongation for mean strain rate
u
Displacement
u mm displacement by the elastic wave
u mm displacement at the end of the original gauge length
u mm displacement at the end of the original gauge length
u (t) mm displacement of the end of the elastic bar at time t
B
Strain
e — engineering strain
e — desired engineering strain before achieving equilibrium
s
ε — elastic strain
2 © ISO 2018 – All rights reserved

ISO 26203-1:2018(E)
Table 1 (continued)
Symbol Unit Designation
ε — elastic strain at the end of the elastic bar (see Annex B)
B
ε — elastic strain at section C (see Annex B)
g
Strain rate
−1
 s engineering strain rate
e
−1
s mean engineering strain rate

e
Force
F N force
F N maximum force
m
Stress
R MPa engineering stress
R MPa tensile strength
m
R MPa proof strength, total extension
t
Modulus of elasticity
E MPa modulus of elasticity
E MPa modulus of elasticity of the bar
b
Wave velocity
−1
c mm s velocity of the wave propagation in the elastic bar
−1
c mm s elastic wave propagation velocity in the test piece
Velocity
−1
v (t) mm s velocity of the impact block (see Annex B)
A
−1
v mm s particle velocity at any point in the bar (see Annex C)
−1
v mm s incident particle velocity (see Annex C)
i
−1
v mm s reflected particle velocity (see Annex C)
r
−1
v mm s transmitted particle velocity (see Annex C)
t
6 Apparatus
6.1 Elastic bar. By using a long elastic bar, the test should be finished before the elastic wave is
reflected back from the other end of the bar that is on the opposite side of the test piece. Consequently,
the force can be measured without being perturbed by the reflected waves. For this method, the one-bar
testing machine and the split Hopkinson bar (SHB) testing machine are normally used (see Annex B and
Annex C).
6.2 Input device. For the input method, open-loop-type loading is normally applied. The upper limit
−1
of the input speed is approximately 20 m s . For the SHB testing machine, a striker tube or striker bar is
used. For the one-bar testing machine, a hammer is normally used.
6.3 Clamping mechanism. A proper clamping mechanism (a method for connecting a test piece and
an elastic bar) is critical to data quality (see Annex B and Annex C).
The clamping fixtures for the SHB or one-bar testing machines are mounted directly on the elastic
bars. The clamping fixtures should be of the same material and diameter as the elastic bars to ensure
minimal impedance change when the stress wave propagates through the loading train. If a different
material or size is used, proper consideration should be made in the evaluation of stress and strain.
ISO 26203-1:2018(E)
6.4 Force measurement device. Force should be measured by strain gauges of a suitably short gauge
length, typically 2 mm, attached to elastic bars that are directly connected with the test piece.
The location of the strain gauges should be in an area where the elastic wave is not influenced by end
effects. In order to measure a one-dimensional elastic wave, the strain gauges shall be attached at a
distance at least five times the diameter of the bars from the ends of the bars (see Annex B and Annex C).
2 −1
NOTE The measurable strain-rate range by this method is 10 s or higher. It is impractical to construct a
2 −1
testing machine for strain rates below 10 s because bar lengths of several tens of metres in length would be
required.
To ensure the validity of stress-strain curves, the straightness of the elastic bars is crucial. Proper
supports or guides for the elastic bars are essential in achieving this.
6.5 Displacement measurement device. Strain in the tensile test is represented by the ratio between
the relative displacement between two points in the gauge section, e.g. the initial and final gauge lengths
of the test piece.
Generally, in quasi-static testing, an extensometer attached to the gauge section of the test piece is used
and the measurement is accurate. However, at high strain rates, it is impossible to use this method due
to the inertia effects of the extensometer. Thus, displacement or test piece elongation measurement at
high strain rates shall use the non-contact type devices or strain gauges on elastic bars.
Measuring devices that can be utilized for measuring displacement in elastic-bar-type systems are
3 −1
described in 6.5.1 to 6.5.3. These devices are recommended for strain rates up to 10 s and measured
displacements should be recorded for the duration of the test. These devices may be used in combination.
For example, when devices 6.5.1 and 6.5.3 are used in combination, the displacement at one end of the
original gauge length (L ) is measured by the non-contact type displacement gauge (6.5.1) and the other
o
end is measured by the strain gauge (6.5.3) that is attached on the surface of the bar.
6.5.1 Non-contact type displacement gauge. The displacement at one end of the original gauge
length (L ) is measured and recorded by laser, optical or similar devices.
o
By using two 6.5.1 type devices or one 6.5.1 type device and one 6.5.3 type device, the variation of
L in Figure 1 (type-A test piece in Clause 7) with time can be measured and the elongation can be
total
calculated.
6.5.2 Non-contact type extensometer. High-speed cameras, Doppler or laser extensometers, or other
non-contact systems can be applied for measuring the variation of L in Figure 2 (type-B test piece in
c
Clause 7).
6.5.3 Strain gauge. The variation of displacement of the end of the elastic bar with time should be
calculated using Formula (1) which is based on the strain history measured by the strain gauge attached
to the elastic bar.
t
ut()=ctε ()dt (1)
BB0
∫
where
u (t) is the displacement of the end of the elastic bar at time t;
B
ε is the elastic strain at the end of the elastic bar (see Annex B);
B
c is the velocity of the wave propagation in the elastic bar.
6.6 Data acquisition instruments. Amplifiers and data recorders such as oscilloscopes are used to
assess stress-strain curves from raw signals. Each instrument should have a sufficiently high frequency
response. The frequency response of all elements in the electronic measurement system shall be selected
4 © ISO 2018 – All rights reserved

ISO 26203-1:2018(E)
to ensure that all recorded data are not negatively influenced by the frequency response of any individual
component; typically, this requires minimum frequency response on the order of 500 kHz. For digital
data recorders, the minimum resolution of measured data should be 10 bits.
7 Test piece
7.1 Test-piece shape, size and preparation
Test-piece geometry is determined by the following requirements.
a) The required maximum strain rate determines the parallel length. A test piece of shorter length
can achieve higher strain rates. In order to achieve force equilibrium in the test piece, the parallel
length should be short enough at a given strain-rate range.
3 −1
b) In order to assure equilibrium of forces at the strain rates up to 10 s , the preferred parallel
length is less than 20 mm.
Uniform deformation over the parallel length of the test piece requires that the force should
be equilibrated at both ends of the test piece. Force propagates as an elastic wave. To achieve
equilibrium, at least the following inequality [see Formula (2)] should be satisfied:
L e
cs
≤ (2)

c e
where
L is the parallel length of the test piece;
c
c is the elastic wave propagation velocity in the test piece;
e is the desired engineering strain before achieving equilibrium;
s
is the testing strain rate.

e
c) The width of the test piece should be determined to obtain uniaxial stress during the test. The
following rule, shown in Formulae (3) and (4), should be applied:
L
o
≥2 (3)
b
o
b
o
≥2 (4)
a
o
where
a is the original thickness of a flat test piece;
o
b is the original width of the parallel length of a flat test piece;
o
L is the original gauge length.
o
NOTE Lower limit value of Formula (3), L /b = 2, can result in a highly non-uniform strain distribution
o o
when testing very high strength, low work-hardening materials such as Ti-6Al-4V and high strength steel.
d) Generally, unless impractical or unnecessary, the thickness of the test piece should be the full
thickness of the material as far as testing capacity permits.
ISO 26203-1:2018(E)
e) The radius at the shoulder of the type-A test piece (see Figure 1) should be small enough that L
total
is considered as the original gauge length (L ). The radius at the shoulder of the type-B test piece
o
(see Figure 2) should be large enough that L is considered as the original gauge length (L ).
c o
For type-A and type-B test pieces, uncertainties exist in uniaxial tensile data calculated from
bar displacement. These uncertainties result from the non-uniformity of axial strain within the
original gauge length, used here as the reference gauge length for strain calculations. To assess
the potential effects of strain non-uniformity, it is recommended that two sets of quasi-static true-
stress versus true-strain data be compared, i.e.
1) one obtained from strain measurements based on bar displacements (i.e. the displacements
at the bar-end positions on the test piece) and referenced to L or L for the selected high
total o
strain-rate test piece geometry, and
2) the other obtained from strain measurements with an extensometer mounted to the central
part of the parallel reduced section of a conventional tensile test piece conforming to
ISO 6892-1.
The result of this comparison should be incorporated in the test report to provide an assessment
to potential users of high-strain-rate tensile data obtained with this document. If the difference is
outside of a value agreed by the user and the tester, then strain measurements based on local strain
measurements within the gauge length should be used.
f) The grip should have a much larger cross-section than that of the parallel length of the test piece
to ensure negligible deformation and definitely no plastic deformation at the grip zone. Usually,
because the thicknesses of the grip and gauge length of the test piece are the same, the ratio of the
grip and the gauge length width shall comply with the following rule shown in Formula (5):
b R
o t
< (5)
b R
g m
where
b is the original width of the parallel length of a flat test piece;
o
b is the width of the grip section of a test piece;
g
R is the tensile strength;
m
R is the proof strength, total extension.
t
g) Machined surface should be free of cold work, cracks, notches and other surface defects, which can
cause stress concentration.
6 © ISO 2018 – All rights reserved

ISO 26203-1:2018(E)
Key
b original width of the parallel length
o
b width of the grip section
g
L parallel length
c
L total length that includes the parallel length and the shoulders
total
r radius of the shoulder
Figure 1 — Type-A test piece
Key
b original width of the parallel length
o
b width of the grip section
g
L parallel length
c
r radius of the shoulder
Figure 2 — Type-B test piece
7.2 Typical test piece
Recommended dimensions of test pieces are shown in Figures 3 and 4. The ratio between the widths of
the grip and gauge section is normally above 2.
Based on the test methods and/or test purposes, other test piece configurations can be used.
The typical test pieces in Figures 3 and 4 are appropriate when the maximum measured strain rate
3 −1
is up to 10 s and when the comparison of test results obtained at several strain rates is required.
During uniform elongation, the size effect of a test piece would be small. However, because after
uniform elongation, measured properties depend on the test-piece size, it is recommended that all test
pieces used to obtain a single data set should have the same geometry and dimensions, even for the low-
strain-rate tests.
ISO 26203-1:2018(E)
Dimensions in millimetres
b Maximum 5
o
L 10
total
r 1,5
Figure 3 — Typical dimensions of a type-A test piece
Dimensions in millimetres
b Maximum 5
o
L 10
c
r 5,0
Figure 4 — Typical dimensions of a type-B test piece
8 Calibration of the apparatus
8.1 General
The output of the strain gauge should be calibrated by applying a known static force to the strain
gauged elastic bar. Figure B.1 shows an example of the one-bar testing machine.
In the case of the SHB testing machine, stress and strain can be calculated by applying the theoretical
equation with the density, modulus of elasticity and the transmission speed of the longitudinal wave
in the elastic bar. In this case, it is necessary to carry out tests after precisely measuring each physical
property and ensuring its consistency. Details are given in Annex C.
8 © ISO 2018 – All rights reserved

ISO 26203-1:2018(E)
8.2 Displacement measuring device
For the displacement measuring devices, the appropriate calibration shall be carried out in the static
condition.
9 Procedure
9.1 General
Using the input device (6.2), high speed strain is applied on the test piece along the axial direction of
the test piece. The force applied to the test piece is measured by the force measurement device (6.4).
At the same instance, the variation of L , L or L of the test piece is measured by the displacement
total c o
measurement device (6.5).
The configuration of the test piece should be determined based on the designated strain-rate range, the
input device (6.2), the force measurement device (6.4), and the displacement measurement device (6.5).
The test is carried out at room temperature between 10 °C and 35 °C, unless otherwise specified. The
test temperature may be recorded if needed. Tests carried out under controlled conditions should be
conducted at a temperature of (23 ± 5) °C.
9.2 Mounting the test piece
When the test piece is mounted in the clamp, ensure good alignment to apply only axial force. Also, the
test piece and the elastic bar should be connected carefully to ensure a good alignment.
When a type-A test piece is selected, the test piece should be mounted such that the spacing between
grip ends is L (see Figure 1) and the test-piece reduced-gauge section should be centred within this
total
space (see Figure C.3).
9.3 Applying force
Force is applied by the methods described in 6.2. To obtain the targeted strain rate, the velocity of the
striker tube, striker bar or hammer should be determined in advance.
NOTE Guidelines on the velocity of the hammer for the one-bar method and the velocity of the striker for the
split Hopkinson bar method are provided in B.2 and C.2, respectively.
9.4 Measuring and recording
The force measurement devices (6.4) measure the time variation of elastic strain, and the displacement
measuring devices (6.5) measure the time variation of the displacement of the interfaces between the
elastic bars and the test piece or of both end points of L . These measured data shall be recorded.
o

a) Engineering strain and engineering strain rate ( ee, )

Engineering strain (e) and engineering strain rate ( e ) should be calculated from displacement data
obtained following the technique outlined in 6.5. Engineering strain and engineering strain rate should
be calculated using Formulae (6) and (7).
eu=−()uL/ (6)
12 0
ee−
nn+1

e= (7)
Δt
ISO 26203-1:2018(E)
where
u , u are displacements at the ends of the original gauge length;
1 2
e is the engineering strain at step n+1;
n+1
e is the engineering strain at step n;
n
Δt is time increment between steps n and n+1.
b) Engineering stress (R)
Using the force measured according to 6.4, the engineering stress is calculated using Formula (8).
R = F/S (8)
o
where
R is the engineering stress;
F is the force;
S is the original cross-sectional area of the parallel length.
o
c) Percentage elongation after fracture (A)
Percentage elongation after fracture should be determined using Formulae (9) and (10) as appropriate.
For a type-A test piece,
LL−
utotal
A= (9)
L
total
where
A is the percentage elongation after fracture;
L is the gauge length after fracture;
u
L is the original gauge length of a type-A test piece.
total
For a type-B test piece,
LL−
uc
A= (10)
L
c
where
A is the percentage elongation after fracture;
L is the gauge length after fracture;
u
L is the original gauge length of a type-B test piece.
c
10 © ISO 2018 – All rights reserved

ISO 26203-1:2018(E)

d) Mean strain rate ( e )
The mean value of the strain rate is obtained by averaging between strains of 1 % (0,01) and 10 % (0,1)
as shown in Formula (11):
(0,1−0,01)

e = (11)
tt−
10 1
where
−1
is mean strain rate (s );

e
t is the time at a strain of 1 %;
t is the time at a strain of 10 %.
When the fracture strain is less than 10 %, calculate the mean strain rate between a strain of 1 % and
the measured fracture strain.
By agreement, the upper limit of strain range can be changed from 10 % to another specified value such
as the strain at the peak force.
When another specified value is applied as the upper limit of percentage elongation, the symbol should
be as follows:

e
1− A
u
where A is the specified upper limit of percentage elongation for mean strain rate.
u
10 Evaluation of the test result
Due to problems in evaluation of material characteristics, a retest or a suitable interpretation of the
test data should be considered for the following cases:
a) the fracture of a test piece does not occur within a quarter distance of the gauge length from the
centre of the test piece;
b) the signal of stress has large oscillations (see Figure 5);
c) the mean strain rate is significantly different from the target strain rate and the initial rise in the
strain rate is not within the agreed strain range (e.g. 5 % of strain);
d) within the agreed strain range, the variation of strain rate exceeds ±30 % of the mean strain rate;
e) the slope of the stress-strain curve in the elastic region in the dynamic condition is significantly
different from expected slope (irregular slope, Figure 5).
ISO 26203-1:2018(E)
Key
1 data without measurement problems
2 irregular slope
3 irregular slope + oscillation
R engineering stress (MPa)
e engineering strain
Figure 5 — Example of a measurement problem in a high-strain-rate test
There are two major quality issues for high-strain-rate tensile testing: 1) load oscillation and
2) irregular slope of the stress-strain curve in the elastic region.
The first issue is due to a problem in the force measurement system. Load oscillations appear when the
test machine, or elements in the load train, are not properly aligned (e.g. non-straight or misaligned
elastic bar). This can be remedied through a careful readjustment of the machine configuration and/or
alignment of the support or guides for the elastic bar.
The second issue concerns an irregular slope in the elastic region of the stress-strain curve. This can
be due to the addition of deformation in elements of the load train outside the gauge section of the test
piece. This problem is seldom seen in bar-type systems because the displacement of the bar end can be
obtained using the theory of elastic wave propagation. However, an irregular slope can appear when
the mounting or clamping strength between the test piece and the attachment (see Figures B.2 and
B.3) is insufficient and/or when the edge of the test piece (i.e. the edge of L ) is located at a position
total
significantly different from the bar end.
In such cases, the testing configuration should be adjusted.
11 Test report
By agreement between interested parties, the test report should contain items selected from the
following:
a) a reference to this document, i.e. ISO 26203-1:2018;
b) specified materials, if known;
12 © ISO 2018 – All rights reserved

ISO 26203-1:2018(E)
c) the test method (force-measuring method, displacement-measuring method, and type of load
cell, etc.);
d) the identification of the test piece;
e) the geometry and dimensions of sampling of the test piece;
f) the location and direction of the test piece;
g) measured properties and results, i.e. stress-strain curve with strain rate, mean strain rate,
maximum tensile stress-strain, per cent elongation after fracture, etc.
ISO 26203-1:2018(E)
Annex A
(informative)
Quasi-static tensile testing method
A.1 General
This annex explains the method to be used for determination of tensile properties of metallic materials
−3 −1 −1 −1
using strain-control within an approximate strain-rate range between 10 s and 10 s .
A.2 Input method/machine types
The testing machine used for causing strain shall be in conformity with ISO 7500-1. The grade of the
testing machine shall be subject to agreement between the parties concerned. For this test, a testing
machine of the electro-mechanical or servo-hydraulic type is usually used.
A.3 Clamping method
The testing machine shall be equipped with a clamp suitable for the test piece. The clamp shall be
capable of securely holding the test piece over the operation centreline of the tester throughout the test
and shall have a construction that does not apply force other than tensile force.
A.4 Force measurement method
The force during the test is measured with a load cell usually comprising an electrical-resistance strain
gauge attached to an elastic bod
...