ISO 3384-2:2019

INTERNATIONAL ISO
STANDARD 3384-2
Second edition
2019-08
Rubber, vulcanized or
thermoplastic — Determination of
stress relaxation in compression —
Part 2:
Testing with temperature cycling
Caoutchouc vulcanisé ou thermoplastique — Détermination de la
relaxation de contrainte en compression —
Partie 2: Essais avec cycles de température
Reference number
©
ISO 2019
© ISO 2019
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
Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Apparatus . 2
6 Calibration . 3
7 Test piece . 3
7.1 Type and preparation of test pieces . 3
7.1.1 General. 3
7.1.2 Cylindrical test pieces . 3
7.1.3 Ring test pieces. 4
7.2 Measurement of dimensions of test pieces . 4
7.3 Number of test pieces . 4
7.4 Time interval between forming and testing . 4
7.5 Conditioning of test pieces . 4
8 Duration, temperature and test liquid . 5
8.1 Duration of test . 5
8.2 Temperature of exposure . 5
8.3 Immersion liquids . 5
9 Procedure. 5
9.1 Preparation . 5
9.2 Thickness measurement . 5
9.2.1 Cylindrical test pieces . 5
9.2.2 Ring test pieces. 5
9.3 Method A . 6
9.4 Method B . 7
10 Expression of results . 8
11 Precision . 9
12 Test report . 9
Annex A (normative) Calibration schedule .11
Bibliography .14
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 of 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 www .iso
.org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 45, Rubber and rubber products,
Subcommittee SC 2, Testing and analysis.
This second edition cancels and replaces the first edition (ISO 3384-2:2012), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— the requirement for compression device (5.1) has been harmonized with other International
Standards;
— other changes have been made to keep the consistency with ISO 3384-1 throughout the document.
A list of all parts in the ISO 3384 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/members .html.
iv © ISO 2019 – All rights reserved

Introduction
When a constant strain is applied to rubber, the force necessary to maintain that strain is not constant
but decreases with time; this behaviour is called “stress relaxation”. Conversely, when rubber is
subjected to a constant stress, an increase in the deformation takes place with time; this behaviour is
called “creep”.
Tests in compression are normally made under continuous stress conditions (i.e. the test piece remains
strained throughout the test), and are hence a measure of sealing force. Note that the terms continuous
and discontinuous used in this standard refer to whether the measure of force is made continuously of
at intervals.
Tests to use stress relaxation in tension as a measure of ageing are given in ISO 6914.
The processes responsible for stress relaxation can be physical or chemical in nature, and under
all normal conditions both types of process will occur simultaneously. However, at normal or low
temperatures and/or short times, stress relaxation is dominated by physical processes, while at high
temperatures and/or long times chemical processes are dominant.
If the life-time of a material is to be investigated, it can be determined using the method described in
ISO 11346.
In addition to the need to specify the temperatures and time intervals in a stress relaxation test, it is
necessary to specify the initial stress and the previous mechanical history of the test piece since these
can also influence the measured stress relaxation, particularly in rubbers containing fillers.
The most important factor in achieving good repeatability and reproducibility when making stress
relaxation tests is to keep the compression constant during all measurements.
The two cycling test methods specified are designed to carry out the following:
— age the test piece by stress relaxation and determine the sealing force at low temperatures
(method A);
— introduce thermal stress by stress relaxation and determine the sealing force at low temperatures
(method B).
For products used in outdoor applications where the temperature can cycle between a low temperature
(e.g. −40 °C) and a high temperature (e.g. 150 °C), it is important to also consider the shrinking of the
rubber at low temperatures when assessing performance in the anticipated application and life-time.
For polymers that crystallize at low temperature, the crystallization will add to the shrinking of
the rubber. For example, for hoses and seals in automotive applications, the product might work
satisfactorily at the normal working temperature, but might leak at a low temperature.
INTERNATIONAL STANDARD ISO 3384-2:2019(E)
Rubber, vulcanized or thermoplastic — Determination of
stress relaxation in compression —
Part 2:
Testing with temperature cycling
WARNING 1 — Persons using this document should be familiar with normal laboratory practice.
This document does not purport to address all of the safety problems, if any, associated with its
use. It is the responsibility of the user to establish appropriate safety and health practices and to
determine the applicability of any other restrictions.
WARNING 2 — Certain procedures specified in this document might involve the use or generation
of substances, or the generation of waste, that could constitute a local environmental hazard.
Reference should be made to appropriate documentation on safe handling and disposal after use.
1 Scope
This document specifies two methods for determining the decrease in counterforce exerted by a test
piece of vulcanized or thermoplastic rubber which has been compressed to a constant deformation and
then undergoes temperature cycling.
Method A: The temperature is cycled at intervals between a high temperature for ageing and a low
temperature for checking the sealing force at this low temperature.
Method B: The temperature is cycled continuously between a high temperature and a low temperature
to introduce thermal stress in the test piece.
The counterforce is determined by means of a continuous-measurement system.
Two forms of test pieces are specified in this document: cylindrical test pieces and rings. Comparison of
results is valid only when made on test pieces of similar size and shape.
The use of ring test pieces is particularly suitable for the determination of stress relaxation in liquid
environments.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 37:2017, Rubber, vulcanized or thermoplastic — Determination of tensile stress-strain properties
ISO 188:2011, Rubber, vulcanized or thermoplastic — Accelerated ageing and heat resistance tests
ISO 18899:2013, Rubber — Guide to the calibration of test equipment
ISO 23529:2016, Rubber — General procedures for preparing and conditioning test pieces for physical
test methods
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
compression stress relaxation
reduction in compressive force, expressed as a percentage of the initial force, which occurs with time
after the application of a constant compressive strain
3.2
thermal stress
mechanical stress induced in a body when some or all of its parts are not free to expand or contract in
response to changes in temperature
4 Principle
A test piece of vulcanized or thermoplastic rubber is compressed to a constant deformation at which it
is maintained. The decrease in counterforce is then measured.
The temperature is cycled between a high temperature and a low temperature to check the sealing force
at this low temperature. The shrinkage of the rubber in going from the high to the low temperature
decreases the counterforce.
5 Apparatus
5.1 Compression device, consisting of two parallel, flat, highly polished plates made of chromium-
plated steel or stainless-steel or any corrosion-resistant material, between the faces of which the test
piece is compressed.
The plates shall be:
— sufficiently rigid to ensure that, with a test piece under load, no compression plate bends by more
than 0,01 mm;
— of sufficient size to ensure that the whole of the test piece, when compressed between the plates,
remains within the area of the plates and can expand freely laterally.
NOTE A surface finish not worse than Ra 0,4 μm (see ISO 4287) has been found to be suitable. Such an Ra can
be obtained by a grinding or polishing operation.
When the apparatus is assembled without a test piece, the gap between the plates shall not vary by
more than ±0,1 mm.
For ring test pieces, the plates shall have holes of at least 2 mm diameter drilled through their centre
portions to allow equalization of pressure and circulation of fluid inside the ring-shaped test piece.
It shall be possible to connect the compression device to suitable equipment for compressing the test
piece to the specified compression at the specified speed and for measuring the counterforce exerted
by the compressed test piece with an accuracy of 1 % of the measured value.
The device shall be capable of setting the compression and maintaining it during the whole duration of
the test, and it shall be possible to keep the device in an oven at the specified test temperatures. Care
shall be taken to ensure that there is no loss of heat from the test piece, for example by conduction
through metal parts which are connected with the outside of the oven.
2 © ISO 2019 – All rights reserved

5.2 Counterforce-measuring device, capable of measuring compression forces in the desired range
with an accuracy of 1 % of the measured value.
The continuous-measurement system monitors the test piece during the whole duration of the test, thus
making continuous measurement of the change in counterforce with time possible. The deformation of
the test piece shall be kept within ±0,01 mm for the duration of the test. If it is not possible to keep the
deformation constant within this tolerance due to the spring effect in load cells, a correction may be
done mechanically or mathematically.
5.3 Test environment
5.3.1 For tests in gaseous media, an air oven in accordance with the requirements of ISO 188 shall be
used. An oven meeting the requirements specified for one of the ovens used in ISO 188:2011, method A,
is recommended.
For cycling the temperature, the oven shall have a cooling and heating capability and be able to change
the temperature at a rate of 1,0 °C/min ± 0,5 °C/min.
If the testing is done in nitrogen, oxidative ageing will be elimina
...