INTERNATIONAL ISO
STANDARD 974
Second edition
2000-01-15
Plastics — Determination of the brittleness
temperature by impact
Plastiques — Détermination de la température de fragilité au choc
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ISO 974:2000
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Reference number
ISO 974:2000(E)
© ISO 2000
ISO 974:2000(E)
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ISO 974:2000(E)
Contents
1 Scope ..............................................................................................................................................................1
2 Normative references ....................................................................................................................................1
3 Terms and definitions ...................................................................................................................................1
4 Principle..........................................................................................................................................................2
5 Apparatus .......................................................................................................................................................2
6 Test specimens ..............................................................................................................................................3
7 Conditioning...................................................................................................................................................5
8 Procedure .......................................................................................................................................................5
9 Expression of results ....................................................................................................................................6
9.1 Graphical method ..........................................................................................................................................6
9.2 Calculation method .......................................................................................................................................6
10 Test report ......................................................................................................................................................7
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ISO 974:2000(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 3.
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 International Standard may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights.
International Standard ISO 974 was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 2,
Mechanical properties.
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This second edition cancels and replaces the first edition (ISO 974:1980), which has been technically revised.
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ISO 974:2000(E)
Introduction
Plastics are used in many applications requiring low-temperature flexing with or without impact. Polymer brittleness
is affected by any orientation produced during fabrication, by thermal history and by the application of stress to the
material, especially the rate of applied stress as in impact. Brittleness temperature data may be used to predict the
behaviour of plastic materials at low temperature only in applications in which the conditions of deformation are
similar. The brittleness temperature test was originally developed to measure the temperature at which a polymer
ceases to be flexible and becomes “glasslike”.
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INTERNATIONAL STANDARD ISO 974:2000(E)
Plastics — Determination of the brittleness temperature by impact
1 Scope
This International Standard specifies a method for the determination of the temperature at which plastics that are
not rigid at normal ambient temperature exhibit brittle failure under specified impact conditions. A supplementary
technique using notched specimens develops brittleness values at a much higher temperature than are observed
for unnotched specimens of the same plastic material. The method utilizes a statistical technique to quantify the
brittleness failure temperature. Provisions are made for the testing of sufficient specimens to permit the calculation
of the brittleness temperature on a statistical basis. Statistical techniques have been developed to quantify the
brittleness temperature as is defined in 3.1.
The method establishes the temperature at which there is a 50 % chance of failure in either unnotched or notched
specimens. This method has been found useful for specification purposes, although it does not necessarily
measure the lowest temperature at which the material may be used. In the measurement of the brittleness
temperature, the precision of the measurement should preferably be 5 °C at the worst when establishing values
used in material specifications.
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2 Normative references
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The following normative documents contain provisions ISO 974:2000
which, through reference in this text, constitute provisions of
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this International Standard. For dated references, subsequent amendments to, or revisions of, any of these
publications do not apply. However, parties 0fa18518a12e/iso-974-2000
to agreements based on this International Standard are encouraged to
investigate the possibility of applying the most recent editions of the normative documents indicated below. For
undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC
maintain registers of currently valid International Standards.
ISO 175:1999, Plastics — Methods of test for the determination of the effects of immersion in liquid chemicals.
ISO 291:1997, Plastics — Standard atmospheres for conditioning and testing.
3 Terms and definitions
For the purposes of this International Standard, the following terms and definitions apply:
3.1
brittleness temperature
the temperature at which there is a 50 % probability of failure in a specimen when tested by the method specified
It may be designated T50.
3.2
test speed
the relative velocity between the striking edge of the test apparatus and a test specimen held in the specimen
clamp
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ISO 974:2000(E)
4 Principle
Test specimens, supported as cantilever beams, are immersed in a heat-transfer medium whose temperature is
accurately known and precisely controlled. The specimens are conditioned for a specified period of time and then
impacted by a single swing of the striking edge of the apparatus at a specified constant speed. A sufficient number
of specimens are tested to permit the calculation of the brittleness temperature on a statistical basis. The
temperature at which 50 % of the specimens fail is defined as the brittleness temperature.
5 Apparatus
5.1 Test machine, consisting of a clamping device to hold the test specimens, a striking edge and a mechanical
arrangement appropriate to ensure that these are maintained in proper relation to each other and that the striking
edge moves at a constant speed relative to the test specimens.
NOTE 1 Details of the striking edge and clamping device are shown in Figures 1 and 2, and a photograph of the clamp with
mounted specimens is shown in Figure 3.
The principal dimensions of the apparatus shall be as follows:
a) radius of striking edge: 1,6 mm ± 0,1 mm;
b) radius of lower jaw of clamping device: 4,0 mm ± 0,1 mm;
distance between point of impact of striking edge and clamping device: 3,6 mm ± 0,1 mm;
c)
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d) clearance between outside of striking (standards.iteh.ai)
edge and clamping device: 2,0 mm ± 0,1 mm;
The test speed shall be 200 cm/s 20 cm/s at impactISO
and974:2000
during at least the next 0,5 cm of travel.
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NOTE 2 Commercial apparatus is available meeting the requirements of this subclause, in which the striking edge is driven
by a motor, by a solenoid, by gravity or by a spring.
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5.2 Temperature-measuring system: Any suitable device may be used. It shall be calibrated over the required
range and accurate to within 0,5 °C. The temperature-measuring device shall be placed as near to the specimen
as possible.
5.3 Liquid or gaseous heat-transfer medium, preferably liquid, which remains fluid at the test temperature and
which does not appreciably affect the material being tested. The medium shall be maintained at the test
temperature to within 0,5 °C.
NOTE Given that the time of contact between the liquid and the plastic specimens is short and the temperature low, the
use of a methanol/solid-CO2 mixture has been found suitable for most plastics. This mixture can be used successfully down to
- 76 °C. Below this temperature, other heat-transfer media are needed, for example silicone oils, dichlorodifluoromethane/liquid
nitrogen, or an air bath.
Should any doubt exist regarding the inertness of the plastics to the mixture used, measure selected physical
properties before and after 15 min exposure at the highest temperature used (see ISO 175). The values obtained
should not differ significantly.
5.4 Tank, insulated.
5.5 Stirrer, to provide thorough circulation of the heat-transfer medium.
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Dimensions in millimetres
Key
1 Striking edge
2
3
Clamping device
Test specimen
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Figure 1 — Dimensional details of striking edge and clamping device
(positioning of
ISOunnotched
974:2000 test specimen)
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6 Test specimens
6.1 For many polymers, the results of this test depend to a large degree on the conditions used for sample
preparation and on the method of specimen preparation. Unless otherwise specified, the relevant ISO material
specification shall be used for the preparation of the test sample from which the specimens are cut. Cleaner edge
cuts and the reduction or elimination of accidental notches will result in lower observed brittleness temperatures.
It is essential that the specimens be prepared in a reproducible way. A razor blade or other sharp tool shall be used
to cut the specimens, preferably in a single smooth stroke. Die-cut specimens are not recommended. Although it is
possible to prepare satisfactory specimens by hand, it is strongly recommended that an automatic method be used.
Whatever method is used, it is essential that the cutter be inspected frequently and maintained. Sharp cutters must
be used in the preparation of specimens for this test if reliable results are to be obtained.
The condition of the die may be judged by investigating the rupture point on any series of broken specimens. When
broken specimens are removed from the clamps of the test machine, it is convenient to make a pile of these
specimens and note if there is any tendency to break at or near the same point on each specimen. Rupture points
consistently at the same place may be an indication that the die is dull, nicked or bent at that particular position.
NOTE For the use of an automatic cutter for specimen preparation, see Bestelink, P.N., and Turner, S.: Low-temperature
brittleness testing of polyethylene, ASTM Bulletin No. 231, 68 (1958).
6.2 Test specimens 20,00 mm 0,25 mm long by 2,50 mm 0,05 mm wide and 2,0 mm 0,1 mm thick (see
Figure 4) shall be cut from a test sheet. Specimens can be conveniently cut to the specified dimensions from a strip
of material 20,00 mm 0,25 mm in width and of the required thickness. This is preferably accomplished using an
automatic machine (see note to 6.1).
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