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
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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
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electrotechnical standardization.
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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).
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.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
...