Metallic materials - Tensile testing at high strain rates - Part 1: Elastic-bar-type systems (ISO 26203-1:2018)

ISO 26203-1:2018 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.
The strain-rate range between 10−3 and 103 s−1 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 characterization of metallic materials at strain rates higher than 10−3 s−1 is essential.
This test method covers the strain-rate range above 102 s−1.
NOTE 1 At strain rates lower than 10−1 s−1, 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.

Metallische Werkstoffe - Zugversuch bei hohen Dehngeschwindigkeiten - Teil 1: Elastische Stoßwellentechnik (ISO 26203-1:2018)

Dieses Dokument legt Prüfverfahren für Bleche aus metallischen Werkstoffen fest, um Kennwerte aus dem Spannung/Dehnung-Diagramm bei Anwendung hoher Dehngeschwindigkeiten zu bestimmen. Dieses Dokument behandelt die Anwendung der Stoßwellentechnik.
Basierend auf Versuchen und Berechnungen zur Crashsicherheit, z. B. der Finite Elemente Analyse (FEA), ist für Crashtests an Fahrzeugen der Dehngeschwindigkeitsbereich zwischen 10−3 s−1 und 103 s−1 am wichtigsten.
Um eine exakte Bewertung der Crashsicherheit eines Fahrzeugs zu ermöglichen, muss das Spannungs-Dehnungs Verhalten metallischer Werkstoffe bei Dehngeschwindigkeiten über 10−3 s−1 zuverlässig charakterisiert werden.
Das hier beschriebene Prüfverfahren erfasst Dehngeschwindigkeiten oberhalb von 102 s−1.
ANMERKUNG 1   Bei Dehngeschwindigkeiten unter 10−1 s−1 kann eine quasistatische Zugprüfmaschine angewendet werden, die in ISO 7500 1 und ISO 6892 1 festgelegt ist.
ANMERKUNG 2   Dieses Prüfverfahren ist auch auf Zugproben anwendbar, die andere Maße als die hier beschriebenen Flachzugproben haben.

Matériaux métalliques - Essai de traction à vitesses de déformation élevées - Partie 1: Systèmes de type à barre élastique (ISO 26203-1:2018)

ISO 26203-1:2018 spécifie des méthodes pour les essais des tôles de matériaux métalliques en vue de déterminer les caractéristiques contrainte-déformation à vitesses de déformation élevées. Ce document couvre l'utilisation des systèmes d'essai de type à barre élastique.
La gamme de vitesses de déformation entre 10−3 s−1 et 103 s−1 est considérée être la plus pertinente pour les accidents de véhicule sur la base de calculs expérimentaux et numériques tels que le travail d'analyse par éléments finis (AEF) pour le comportement en cas d'accident.
De façon à évaluer le comportement des véhicules en cas d'accident avec précision, une caractérisation fiable des caractéristiques contrainte-déformation des matériaux métalliques à des vitesses de déformation supérieures à 10−3 s−1 est essentielle.
La présente méthode d'essai couvre la gamme de vitesses de déformation au-dessus de 102 s−1.
NOTE 1 À des vitesses de déformation inférieures à 10−1 s−1, une machine d'essai de traction quasi-statique, spécifiée dans l'ISO 7500‑1 et l'ISO 6892‑1 peut être utilisée.
NOTE 2 Cette méthode d'essai est également applicable aux géométries d'éprouvettes de traction autres que les éprouvettes plates considérées ici.

Kovinski materiali - Natezni preskus pri velikih hitrostih deformacije - 1. del: Sistem z elastičnim drogom (ISO 26203-1:2018)

Ta dokument določa metode za preskušanje kovinskih materialov v obliki plošč za določanje napetostno-deformacijskih lastnosti pri visokih stopnjah deformacije. Ta dokument zajema uporabo sistemov z elastičnim drogom.
Na podlagi eksperimentalnih in številskih izračunov, kot je analiza končnih elementov (FEA) za zagotavljanje pasivne varnosti pri trčenju, velja razpon stopnje deformacije med 10−3 in 103 s−1 za najpomembnejšega pri trčenju vozil.
Za natančno ocenjevanje pasivne varnosti pri trčenju vozila je zanesljiva opredelitev napetostno-deformacijskih lastnosti kovinskih materialov pri stopnjah deformacije nad 10−3 s−1 ključnega pomena.
Ta preskusna metoda zajema razpon stopnje deformacije nad 102 s−1.
OPOMBA 1: pri stopnjah deformacije pod 10−1 s−1 se lahko uporablja navidezno statična naprava za natezni preskus, kot jo določata standarda ISO 7500-1 in ISO 6892-1.
OPOMBA 2: ta preskusna metoda se uporablja tudi za geometrije preskusnih kosov, ki niso ploščati preskusni kosi, zajeti v tem standardu.

General Information

Status
Published
Publication Date
06-Mar-2018
Current Stage
6060 - Definitive text made available (DAV) - Publishing
Due Date
07-Mar-2018
Completion Date
07-Mar-2018

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SLOVENSKI STANDARD
SIST EN ISO 26203-1:2018
01-julij-2018
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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
SIST EN ISO 26203-1:2018 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 26203-1:2018
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SIST EN ISO 26203-1:2018
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.
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SIST EN ISO 26203-1:2018
EN ISO 26203-1:2018 (E)
Contents Page

European foreword ....................................................................................................................................................... 3

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SIST EN ISO 26203-1:2018
EN ISO 26203-1:2018 (E)
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.
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SIST EN ISO 26203-1:2018
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SIST EN ISO 26203-1:2018
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
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SIST EN ISO 26203-1:2018
ISO 26203-1:2018(E)
COPYRIGHT PROTECTED DOCUMENT
© 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
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SIST EN ISO 26203-1:2018
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 2018 – All rights reserved iii
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SIST EN ISO 26203-1:2018
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
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SIST EN ISO 26203-1:2018
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.
© ISO 2018 – All rights reserved v
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SIST EN ISO 26203-1:2018
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SIST EN ISO 26203-1:2018
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 2018 – All rights reserved 1
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SIST EN ISO 26203-1:2018
ISO 26203-1:2018(E)

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
b mm original width of the parallel length of a flat test piece
b mm width(s) of the grip section of a test piece
L mm original gauge length [see 7.1 e)]
L mm parallel length
L mm total length that includes the parallel length and the shoulders
total
L mm final gauge length after fracture
r mm radius of the shoulder
S mm original cross-sectional area of the parallel length
S mm cross-sectional area of the elastic bar
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.
A % specified upper limit of percentage elongation for mean strain rate
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
Strain
e — engineering strain
e — desired engineering strain before achieving equilibrium
ε — elastic strain
2 © ISO 2018 – All rights reserved
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SIST EN ISO 26203-1:2018
ISO 26203-1:2018(E)
Table 1 (continued)
Symbol Unit Designation
ε — elastic strain at the end of the elastic bar (see Annex B)
ε — elastic strain at section C (see Annex B)
Strain rate
 s engineering strain rate
s mean engineering strain rate
Force
F N force
F N maximum force
Stress
R MPa engineering stress
R MPa tensile strength
R MPa proof strength, total extension
Modulus of elasticity
E MPa modulus of elasticity
E MPa modulus of elasticity of the bar
Wave velocity
c mm s velocity of the wave propagation in the elastic bar
c mm s elastic wave propagation velocity in the test piece
Velocity
v (t) mm s velocity of the impact block (see Annex B)
v mm s particle velocity at any point in the bar (see Annex C)
v mm s incident particle velocity (see Annex C)
v mm s reflected particle velocity (see Annex C)
v mm s transmitted particle velocity (see Annex C)
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

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 2018 – All rights reserved 3
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SIST EN ISO 26203-1:2018
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

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.

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

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.
ut()=ctε ()dt (1)
BB0
where
u (t) is the displacement of the end of the elastic bar at time t;
ε is the elastic strain at the end of the elastic bar (see Annex 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
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SIST EN ISO 26203-1:2018
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.
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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 propagate
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