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Ref. No.: lSO/ R 458 - 1965 (E)
IS0
I NTERN AT1 ON AL O RG A N IZAT I O N FOR STAND A RD I2 AT I ON
IS0 R ECOM MENDATI O N
R 458
PLASTICS
DETERMINATION OF STIFFNESS IN TORSION
AS A FUNCTION OF TEMPERATURE
1 st EDITION
November 1965
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belongs to IS0 Member Bodies. Reproduction of these
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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 458, Determination of Stiffness in Torsion as a Function
of Temperature, 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 1959 and led, in 1960, to
the adoption of a Draft IS0 Recommendation.
In April 1962, this Draft IS0 Recommendation (No. 469) was circulated to all the
IS0 Member Bodies for enquiry. It was approved, subject to a few modikations of an
editorial nature, by the following Member Bodies :
Australia India Spain
Austria Italy Sweden
Brazil Japan Switzerland
Chile Mexico United Kingdom
Czechoslovakia New Zealand U.S.A.
Finland Poland Yugoslavia
France Republic of South Africa
Germany Romania
Two Member Bodies opposed the approval of the Draft:
Belgium, U.S.S.R.
The Draft IS0 Recommendation was then submitted by correspondence to the IS0
Council, which decided, in November 1965, to accept it as an IS0 RECOMMENDATION.
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lSO/ R 458 - 1965 (E)
IS0 Recommendation R 458 November 1965
PLASTiCS
DETERMINATION OF STIFFNESS IN TORSION
AS A FUNCTION OF TEMPERATURE
1. SCOPE
1.1 This IS0 Recommendation describes a procedure for determining the stiffness in torsion
properties of plastics over a wide temperature range.
1.2 It is particularly used for determining the stiffness properties of non-rigid plastics at tem-
peratures below O OC.
2. PRINCIPLE OF TEST
An observation of torque and deflection is made after an arbitrarily fixed time of load application.
a wide range. It is necessary
This procedure is employed at selected temperature intervals over
that the dimension of time for load application be arbitrarily fixed because of the known " creep "
characteristics of this type of material.
The property actually measured by this method is the apparent modulus of rigidity G, sometimes
called the apparent shear modulus of elasticity. It is important to note that this property is not
the same as the modulus of elasticity E, measured in tension, flexure or compression. (See note 1.)
NOTES
1. By means of certain simplifying assumptions, an apparent modulus of elasticity may be calculated from the
apparent modulus of rigidity. This is described in the Annex A to this IS0 Recommendation.
2. The variation of the apparent shear modulus of elasticity of the material with temperature is an important
consideration in the application of various plastics.
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IS0 / R 458 - 1965 (E)
Torque pulley
Load pulley -
index I ,Stop pin
Load
.t rod
FIGURE - Torsion tester
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IS0 / R 458 - 1965 (E)
I
3. APPARATUS
The apparatus consists of the following:
(a) Testing machine capable of exerting a torque of approxim tely 0.1 to 1.2 kgfvcm (0.1 to
1.0 Ibf-in) on a test specimen with a span of 35 to 55 mm (1.4 to 2.2 in) measured to an accuracy
of 0.5 mm (3 0.02 in) and immersed in an adequately circulated heat transfer medium.
A schematic diagram of a machine suitable for this test is shown in the Figure (page 4).
(b) Different weights to vary the amount of torque and to suit the stiffness of the test specimen.
The actual amount of torque being applied by any given combination of weights, torque
pulley radii and shaft bearings should be determined by calibration, unless it can be demon-
strated that friction is negligible. This is necessary in order that frictional effects may be
eliminated.
NOTE 3.-For operation at low temperature, the shaft of the machine should be provided with a heated collar
next to the lower bearing to prevent the formation of ice.
(c) Dewar flask of 500 ml capacity, or with suitable dimensions.
c
(d) Thermometer graduated in Celsius degrees and having the necessary range. The bulb should be
located in close proximity to the test specimen.
(e) Timer accurate to 0.1 second.
(0 Heat transfer medium. For normal laboratory purposes, a substance which is liquid over
the desired temperature range should be used for the heat transfer medium, provided it has
been shown that the liquid does not soften or otherwise affect the test specimen.
NOTES
4. Among the liquids found useful are acetone, ethyl alcohol, butyl alcohol, normal hexane, silicone oil and
a mixture of methyl phosphate and water in the ratio of 87 to 13 by volume. For temperatures to 70 "C
a mixture of 50 parts ethyl alcohol, 30 parts ethylene glycol and 20 parts water may be found useful. If no
suitable liquid can be found, a gaseous heat-transfer agent may be used. In this case, great care should be
taken to ensure that sufficient time is allowed for the test specimen to reach temperature equilibrium.
5. Good stirring should be assured by appropriate means during cooling and heating.
'c,
6. For cooling, mechanical refrigeration or dry ice chest or both, according to the desired temperature, may
be used. For heating, it is possible to use an electric immersion heater in the Dewar flask.
(g) Micrometer. A dead-weight dial-type micrometer graduated to 0.01 mm (0.001 in) should be
used for thickness measurements. These measuremen
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