Rubber, vulcanized or thermoplastic — Determination of stress relaxation in compression — Part 2: Testing with temperature cycling

ISO 3384-2:2012 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.

Caoutchouc vulcanisé ou thermoplastique — Détermination de la relaxation de contrainte en compression — Partie 2: Essais avec cycles de température

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Withdrawn
Publication Date
12-Nov-2012
Withdrawal Date
12-Nov-2012
Current Stage
9599 - Withdrawal of International Standard
Completion Date
12-Aug-2019
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INTERNATIONAL ISO
STANDARD 3384-2
First edition
2012-11-15
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 3384-2:2012(E)
ISO 2012
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ISO 3384-2:2012(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2012

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any

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Published in Switzerland
ii © ISO 2012 – All rights reserved
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ISO 3384-2:2012(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 2

4 Principle ........................................................................................................................................................................................................................ 2

5 Apparatus ..................................................................................................................................................................................................................... 2

6 Calibration .................................................................................................................................................................................................................. 3

7 Test piece ...................................................................................................................................................................................................................... 3

7.1 Type and preparation of test piece ........................................................................................................................................ 3

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 .......................................................................................................................................... 4

8.1 Duration of test ....................................................................................................................................................................................... 4

8.2 Temperature of exposure ............................................................................................................................................................... 5

8.3 Immersion liquids ................................................................................................................................................................................ 5

9 Procedure..................................................................................................................................................................................................................... 5

9.1 Preparation ................................................................................................................................................................................................ 5

9.2 Thickness measurement ................................................................................................................................................................. 5

9.3 Method A ...................................................................................................................................................................................................... 5

9.4 Method B ...................................................................................................................................................................................................... 7

10 Expression of results ........................................................................................................................................................................................ 8

11 Precision ....................................................................................................................................................................................................................... 9

12 Test report ................................................................................................................................................................................................................... 9

Annex A (normative) Calibration schedule ................................................................................................................................................10

Bibliography .............................................................................................................................................................................................................................12

© ISO 2012 – All rights reserved iii
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ISO 3384-2:2012(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.

The main task of technical committees is to prepare International Standards. Draft International

Standards adopted by the technical committees are circulated to the member bodies for voting.

Publication as an International Standard requires approval by at least 75 % of the member bodies

casting a vote.

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights.

ISO 3384-2 was prepared by Technical Committee ISO/TC 45, Rubber and rubber products, Subcommittee

SC 2, Testing and analysis.

ISO 3384 consists of the following parts, under the general title Rubber, vulcanized or thermoplastic —

Determination of stress relaxation in compression:
— Part 1: Testing at constant temperature
— Part 2: Testing with temperature cycling
iv © ISO 2012 – All rights reserved
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ISO 3384-2:2012(E)
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”.

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 (see the Bibliography).

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 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.
© ISO 2012 – All rights reserved v
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INTERNATIONAL STANDARD ISO 3384-2:2012(E)
Rubber, vulcanized or thermoplastic — Determination of
stress relaxation in compression —
Part 2:
Testing with temperature cycling

IMPORTANT 1 — Persons using this part of ISO 3384 should be familiar with normal laboratory

practice. This part of ISO 3384 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 ensure compliance with any national regulatory conditions.

IMPORTANT 2 — Certain procedures specified in this part of ISO 3384 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 part of ISO 3384 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 piece are permitted: cylindrical test pieces and rings. Different shapes and sizes of

test piece give different results, and comparison of results should be limited to 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 referenced documents are indispensable for the application 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 37:2011, Rubber, vulcanized or thermoplastic — Determination of tensile stress-strain properties

ISO 188:2011, Rubber, vulcanized or thermoplastic — Accelerated ageing and heat resistance tests

ISO 1817, Rubber, vulcanized or thermoplastic — Determination of the effect of liquids

ISO 18899:2004, Rubber — Guide to the calibration of test equipment

ISO 23529, Rubber — General procedures for preparing and conditioning test pieces for physical test methods

© ISO 2012 – All rights reserved 1
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ISO 3384-2:2012(E)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
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 from chromium-

plated or stainless steel or other corrosion-resistant material, between the faces of which the test pieces

are compressed. Flatness, surface roughness, parallelism and rigidity of the plates are all important.

The surfaces of the compression plates shall be ground and polished. The compression plates shall be

flat and parallel and shall not undergo any distortion when the test load is applied.

NOTE A finish to the surface giving a roughness profile Ra (see ISO 4287) of not worse than 0,4 µm has been

found to be suitable. Such a roughness profile Ra can be obtained by grinding or polishing.

When the apparatus is assembled without a test piece, the gap between the plates shall not vary by more

than ±0,01 mm.

When the test assembly is subjected to the test load with a test piece between the plates, neither

compression plate shall bend by more than 0,01 mm.

The plates shall be of sufficient size to ensure that the whole of the compressed test piece is within the

area of the plates and can expand freely laterally.

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 a temperature chamber 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 chamber.

2 © ISO 2012 – All rights reserved
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ISO 3384-2:2012(E)

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.

5.3 Temperature chamber: For tests in air, a well designed, uniformly heated air temperature

chamber shall be used, complying, for temperatures above standard laboratory temperature, with the

requirements specified for one of the ovens used in ISO 188:2011, method A.

For cycling the temperature, the temperature chamber 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.

In the case of high-temperature tests and to avoid the surface oxidation of test pieces, other atmospheres

may be used, such as nitrogen. For tests in liquids, the compression device shall be totally immersed in

the liquid in a bath, or a closed vessel for volatile or toxic fluids, such that free circulation of the liquid can

take place through the holes in the compression plates. The liquid shall be maintained at the specified

temperature by proper control of a heater and circulation of the liquid in the bath or, alternatively, by

placing the liquid bath and compression device within a temperature chamber as specified above.

NOTE It is recommended that the air used for air exchange be passed through an air dryer to give it a dew

point not higher than –40 °C in order to avoid ice formation which can introduce friction in the measuring system.

5.4 Temperature-measuring equipment, with a sensing element having appropriate precision. The

temperature-sensing element shall be installed in such a way that it accurately measures the temperature

of t
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