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UDC 878.51.8: 820.17
IS0
FOR STANDARD I2 AT I ON
O RG A N I Z AT I O N
I NT ERN AT I ON AL
IS0 R ECOM MEN DATI O N
R 537
PLASTICS
TESTING OF PLASTICS WITH THE TORSION PENDULUM
1st EDITION
January 1967
COPYRIGHT RESERVED
"he copyright of IS0 Recommendations and IS0 Standards
belongs to IS0 Member Bodies. Reproduction of these
documents, in any country, may be authorized therefore only
by the national standards organization of that country, being
a member of ISO.
For each individual country the only valid standard is the national standard of that country.
Printed in Switzerland
Also issued in French and Russian. Copies to be obtained through the national standards organizations.
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BRIEF HISTORY
The IS0 Recommendation R 537, Testing of Plastics with the Torsion Pendulum, was
drawn up by Technical Committee ISO/TC 61, Plastics, the Secretariat of which is held by
the American Standards Association, Inc. (ASA).
Work on this question by the Technical Committee began in 1958 and led, in 1961, to
the adoption of a Draft IS0 Recommendation.
In June 1963, this Draft IS0 Recommendation (No. 533) was circulated to all the
IS0 Member Bodies for enquiry. It was approved by the following Member Bodies:
Argentina Germany Portugal
Australia Hungary Republic of South Africa
Austria India Romania
Belgium Iran Spain
Chile
Japan Sweden
Czechoslovakia Net herlands Switzerland
Finland New Zealand U.S.A.
France Poland Yugoslavia
One Member Body opposed the approval of the Draft:
United Kingdom.
The Draft IS0 Recommendation was then submitted by correspondence to the IS0
Council, which decided, in January 1967, to accept it as an IS0 RECOMMENDATION.
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ISO/R 537-1967 (E)
IS0 Recommendation R 537
ERRATUM
August 1969
PLASTl CS
TESTING OF PLASTICS WITH THE TORSION PENDULUM
1st Edition ~ January 1967
ERRATUM
Page 8, clause 6.2
In the forniula giving the shear modulus replace “p2” by ‘k2”
Thus, the corrected formula reads :
.-
IS0 Recommendation R 537
ISO/R 537-1967 (E)
ERRATUM
June 1972
PLASTICS
TESTING OF PLASTICS WITH THE TORSION PENDULUM
1st Edition - January 1967
ERRATUM
Page 4, Clause 4.1.1, 18th line :
Replace “3 1 O g/cm’ ” by “3 1 O gxm’ ”.
Page 8, Clause 6.2 : In the definition of J, replace “grammes per square centimetre” by “gramme centimetres squared”.
O
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I
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II
IS0 / R 537 - 1967 (E)
IS0 Recommendation R 537 January 1967
PLASTICS
TESTING OF PLASTICS WITH THE TORSION PENDULUM
1. SCOPE
This method of test is designed to enable the shear modulus and the mechanical damping to be
measured as a function of temperature using free torsion oscillations. By means of this method,
measurements are made over a frequency range from 0.1 to 10 Hz. It is thus possible to determine
the mechanical properties of plastics materials at low deformation stresses and low stressing
speeds over a wide temperature range.
This method is also employed for determining the temperature range over which a plastics
material appears rigid, visco-elastic or rubber-like, and it also gives information concerning the
commencement of plastic flow. The method provides a means of easily distinguishing thermo-
plastic, thermosetting and other cross-linked polymers and between crystalline and amorphous
polymers.
When carried out at one temperature, the method is only of use as a control test of plastics whose
general properties are known. It can thus be employed to determine whether a given plastics
material is " soft " or " rigid " at a given temperature and stressing speed.
The shear modulus and the mechanical damping are physical constants which are independent of
the test method, the apparatus employed and the shape of the test specimen.
2. DEFINITIONS
2.1 Shear modulus. Quotient of the shearing stress and the resulting elastic angular deformation
for very small deformations within the elastic limit of stress to corresponding strain.
2.2 Logarithmic decrement. Mechanical damping resulting from the dissipation of internal
energy in the torsion pendulum test measured by the logarithmic decrement A. The
logarithmic decrement is defined as the natural logarithm of the ratio of the amplitudes
2 successive oscillations.
of
2.3 Mechanical loss factor. Internal energy dissipation causing damping expressed by the
mechanical loss factor d which is related to the logarithmic decrement A by an equation,
which for AG2 reduces to
A
d=-
77
3. TEST SPECIMEN
3.1 The test specimen is prepared and conditioned under the specific conditions required for
each material.
NOTE. - The conditions employed in the preparation of a test specimen should be very
accurately observed in the case of materials whose mechanical properties are influenced by
previous thermal and mechanical treatment. This applies to partially crystalline plastics
such as polyamides.
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IS0 / R 537 - 1967 (E)
In tests for the characterization of the nature of a material, the preparation by cutting of
test specimens from commercial plastics such as rod or sheet is only possible with amorphous
material when the latter is free from internal stresses.
The preparation of test specimens by cutting from rod or sheet is not possible in the case of
plastics which tend to crystallize. Here the test specimen should be brought into the desired
shape by pressing and the crystallization completed by controlled cooling from the viscous
state.
When the properties of a particular material, e.g. a piece of stressed plastic, are to be tested,
the test specimen should be prepared by punching or careful machining with precautions to
avoid heating. With such material it is advisable to carry out tests in the direction of stressing
and perpendicular to this direction.
3.2 The most suitable test specimen is a flat rod of length (I) 60 mm, width (b) 10 mm and
thickness (h) 1 mm. Other dimensions of test specimen can be employed, provided that
they ensure sufficiently rapid transfer of heat. With test specimens of thickness 0.15 down
to 0.05 mm, the oscillating system should be enclosed in a vacuum. The testing of test spe-
cimens with a thickness less than 0.05 mm is not recommended.
NOTE. - The shear modulus and logarithmic decrement A are independent of the shape of
the test specimen which can therefore be varied as desired. The equation given in section 6,
however, applies only to a test specimen of rectangular cross-section and where the test
specimen is of uniform cross-section over its entire length (see section 5).
4. APPARATUS
4.1 Torsion pendulum
Any suitable torsion pendulum can be employed which enables ihe shear modulus and the
damping of free torsional oscillations of plastics to be determined as a function of tem-
perature and which provides for uniform temperature over the entire test specimen at any
given test temperature.
Two methods are described in this IS0 Recommendation :
Method A (Fig. 1 and 2, page 5): Test specimen supporting inertia member ;
Method B (Fig. 3, page 7): Test specimen not supporting inertia member.
4.1.1 Method A. The test specimen is held at its upper end in a clamp and is attached at its
lower end to a disc of known moment of inertia (see Fig. 2). In order to obtain a
constant temperature over the whole length of the test specimen, the axes passing
through the top and bottom of the constant temperature chamber should be constructed
of a poor conductor of heat such as glass.
NOTE.-BY means of a slight twist of the upper axis, a torque is transferred to the disc
via the test specimen and the system thus brought into a state of free oscillation. A
small mirror is mounted immediately above the disc so that the reflecting surface lies in
the axis of the oscillating system. The oscillation is transferred by means of the light
beam which falls on the mirror from the light source onto a photographic strip. The
frequency and amplitude of the oscillations can be determined from the trace on the
photographic strip. The apparatus is provided with an arresting device to remove the
stress on the test specimen during the heating period between measurements. The appa-
ratus also incorporates a scale by means of which any elongation of test specimen can
be measured.
A disc with a total mass of 30 g (24.8 g for a light metal disc and 5.2 g for the lower
axis with clamp and mirror) has been found to be most suitable for test specimens
as described in clause 3.2. This corresponds to a moment of inertia of 310 g/cm2.
The dimensions of the disc are such that the total tensile stress on the test specimen
does not exceed 1 kgf/cm2. If the value of the correction term SE yields a negative value
for the shear modulus (see clause 6.2) the load is reduced.
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IS0 / R 537 - 1967 (E)
Constant
temperature
chamber
t
Test specimen
FI Therrno-
Sliding cover to
prevent draught
t
Recording strip
--G Light
source
-. Arresting
device
1
FIG. 1. - Example of a torsion pendulum (Method A)
..-
% 100mm
FIG. 2. - Moment of inertia disc including the lower clamp and the lower axis with mirror
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lSO/ R 537 - 1967 (E)
4.1.2 Method B. The difference from Method A is that the clamp for the upper end of the
test specimen and the disc of known moment of inertia are suspended by a fine wire
(or band) and are balanced by means of a counterweight. The lower clamp is fixed
(see Fig. 3).
4.2 Apparatus for temperature control
The test specimen and the clamps are enclosed in a constant temperature chamber containing
air or inert gas and provided with an arrangement for varying the temperature. The constant
temperature chamber should provide for a temperature range of at least -60 "C to +250 OC.
The temperature in the immediate vicinity of the test specimen will not vary by more than
it 1 OC.
NoTE.-A suitable form of constant temperature chamber for test specimens as described
in clause 3.2 consists of a double-walled cylinder of approximately 100 mm height and an
internal diameter of approximately 25 mm. The inner and outer walls of the cylinder are
about 10 mm apart and are suitably insulated on the outside. The chamber is so arranged
that a liquid at constant temperature can be circulated through the annular space. The
opening for the upper axis should prevent air circulation from the interior of the chamber to
the outside but at the same time
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