ISO 3384-2:2012
(Main)Rubber, vulcanized or thermoplastic — Determination of stress relaxation in compression — Part 2: Testing with temperature cycling
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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Standards Content (Sample)
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)
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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
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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
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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.
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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
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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.
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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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