ASTM D696-98
(Test Method)Standard Test Method for Coefficient of Linear Thermal Expansion of Plastics Between -30°C and 30°C With a Vitreous Silica Dilatometer
Standard Test Method for Coefficient of Linear Thermal Expansion of Plastics Between -30°C and 30°C With a Vitreous Silica Dilatometer
SCOPE
1.1 This test method covers determination of the coefficient of linear thermal expansion for plastic materials having coefficients of expansion greater than 1 X 10 -6 1°C by use of a vitreous silica dilatometer. At the test temperatures and under the stresses imposed, the plastic materials shall have a negligible creep or elastic strain rate or both, insofar as these properties would significantly affect the accuracy of the measurements. Note 1-There is no similar or equivalent ISO standard.
1.1.1 Test Method E228 shall be used for temperatures other than -30°C to 30°C.
1.1.2 This test method shall not be used for measurements on materials having a very low coefficient of expansion (less than 1 X 10 -6 1°C). For materials having very low coefficient of expansion, interferometer or capacitance techniques are recommended.
1.2 The thermal expansion of a plastic is composed of a reversible component on which are superimposed changes in length due to changes in moisture content, curing, loss of plasticizer or solvents, release of stresses, phase changes and other factors. This test method is intended for determining the coefficient of linear thermal expansion under the exclusion of these factors as far as possible. In general, it will not be possible to exclude the effect of these factors completely. For this reason, the test method can be expected to give only an approximation to the true thermal expansion.
1.3 The values stated in SI units are to be regarded as the standard. The values in parentheses are for information only.
1.4 This standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.>
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Designation: D 696 – 98
Standard Test Method for
Coefficient of Linear Thermal Expansion of Plastics
Between −30°C and 30°C With a Vitreous Silica Dilatometer
This standard is issued under the fixed designation D 696; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope * D 618 Practice for Conditioning Plastics and Electrical
Insulating Materials for Testing
1.1 This test method covers determination of the coefficient
D 883 Terminology Relating to Plastics
of linear thermal expansion for plastic materials having coef-
−6
D 1898 Practice for Sampling of Plastics
ficients of expansion greater than 1 3 10 1°C by use of a
D 4065 Practice for Determining and Reporting Dynamic
vitreous silica dilatometer. At the test temperatures and under
Mechanical Properties of Plastics
the stresses imposed, the plastic materials shall have a negli-
E 228 Test Method for Linear Thermal Expansion of Solid
gible creep or elastic strain rate or both, insofar as these
Materials with a Vitreous Silica Dilatometer
properties would significantly affect the accuracy of the mea-
E 691 Practice for Conducting an Interlaboratory Study to
surements.
Determine the Precision of a Test Method
NOTE 1—There is no similar or equivalent ISO standard.
E 831 Test Method for Linear Thermal Expansion of Solid
1.1.1 Test Method E 228 shall be used for temperatures Materials by Thermomechanical Analysis
other than −30°C to 30°C.
3. Terminology
1.1.2 This test method shall not be used for measurements
on materials having a very low coefficient of expansion (less 3.1 Definitions—Definitions are in accordance with Termi-
−6
nology D 883 unless otherwise specified.
than 1 3 10 1°C). For materials having very low coefficient
of expansion, interferometer or capacitance techniques are
4. Summary of Test Method
recommended.
4.1 This test method is intended to provide a means of
1.2 The thermal expansion of a plastic is composed of a
determining the coefficient of linear thermal expansion of
reversible component on which are superimposed changes in
plastics which are not distorted or indented by the thrust of the
length due to changes in moisture content, curing, loss of
dilatometer on the specimen. For materials that may indent, see
plasticizer or solvents, release of stresses, phase changes and
8.4. The specimen is placed at the bottom of the outer
other factors. This test method is intended for determining the
dilatometer tube with the inner one resting on it. The measuring
coefficient of linear thermal expansion under the exclusion of
device which is firmly attached to the outer tube is in contact
these factors as far as possible. In general, it will not be
with the top of the inner tube and indicates variations in the
possible to exclude the effect of these factors completely. For
length of the specimen with changes in temperature. Tempera-
this reason, the test method can be expected to give only an
ture changes are brought about by immersing the outer tube in
approximation to the true thermal expansion.
a liquid bath or other controlled temperature environment
1.3 The values stated in SI units are to be regarded as the
maintained at the desired temperature.
standard. The values in parentheses are for information only.
1.4 This standard does not purport to address all of the
5. Significance and Use
safety concerns, if any, associated with its use. It is the
5.1 The coefficient of linear thermal expansion, a, between
responsibility of the user of this standard to establish appro-
temperatures T and T for a specimen whose length is L at
priate safety and health practices and determine the applica-
1 2 0
the reference temperature, is given by the following equation:
bility of regulatory limitations prior to use.
a5 ~L 2 L !/@L ~T 2T !#5DL/L DT
2 1 0 2 1 0
2. Referenced Documents
where L and L are the specimen lengths at temperatures T
1 2 1
2.1 ASTM Standards:
and T , respectively. a is, therefore, obtained by dividing the
linear expansion per unit length by the change in temperature.
This test method is under the jurisdiction of ASTM Committee D-20 on Plastics
and is the direct responsibility of Subcommittee D20.30 on Thermal Properties
(Section D20.30.07). Annual Book of ASTM Standards, Vol 08.01.
Current edition approved Feb. 10, 1998. Published January 1999. Originally Annual Book of ASTM Standards, Vol 08.02.
e1 4
published as D 696 – 42. Last previous edition D 696 – 91 . Annual Book of ASTM Standards, Vol 14.02.
*A Summary of Changes section appears at the end of this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D 696
5.2 The nature of most plastics and the construction of the 6. Apparatus
dilatometer make −30 to +30°C (−22°F to +54°F) a convenient
6.1 Fused-Quartz-Tube Dilatometer suitable for this test
temperature range for linear thermal expansion measurements
method is illustrated in Fig. 1. A clearance of approximately 1
of plastics. This range covers the temperatures in which
mm is allowed between the inner and outer tubes.
plastics are most commonly used. Where testing outside of this
6.2 Device for measuring the changes in length (dial gage,
temperature range or when linear thermal expansion character-
LVDT, or the equivalent) is fixed on the mounting fixture so
istics of a particular plastic are not known through this
that its position may be adjusted to accommodate specimens of
temperature range, particular attention shall be paid to the
varying length (see 8.2). The accuracy shall be such that the
factors mentioned in 1.2 and special preliminary investigations
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error of indication will not exceed 61.0 μm (4 3 10 in.) for
by thermo-mechanical analysis, such as that prescribed in
any length change. The weight of the inner silica tube plus the
Practice D 4065 for the location of transition temperatures,
measuring device reaction shall not exert a stress of more than
may be required to avoid excessive error. Other ways of
70 kPa (10 psi) on the specimen so that the specimen is not
locating phase changes or transition temperatures using the
distorted or appreciably indented.
dilatometer itself may be employed to cover the range of
6.3 Scale or Caliper capable of measuring the initial length
temperatures in question by using smaller steps than 30°C
of the specimen with an accuracy of 60.5 %.
(54°F) or by observing the rate of expansion during a steady
rise in temperature of the specimen. Once such a transition 6.4 Controlled Temperature Environment to control the
point has been located, a separate coefficient of expansion for temperature of the specimen. Arrange the bath so a uniform
a temperature range below and above the transition point shall temperature is assured over the length of the specimen. Means
be determined. For specification and comparison purposes, the shall be provided for stirring the bath and for controlling its
range from −30°C to +30°C (−22°F to +86°F) (provided it is
temperature within 60.2°C (60.4°F) at the time of the
known that no transition exists in this range) shall be used. temperature and measuring device readings.
FIG. 1 Quartz-Tube Dilatometer
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D 696
NOTE 2—If a fluid bath is used, it is preferable and not difficult to avoid
relative humidity, unless otherwise specified by the contract or
contact between the bath liquid and the test specimen. If such contact is
relevant material specification. In cases of disagreement, the
unavoidable, take care to select a fluid that will not affect the physical
tolerances shall be 61°C (61.8°F) and 62 % relative humid-
properties of the material under test.
ity.
6.5 Thermometer or Thermocouple—The bath temperature
shall be measured by a thermometer or thermocouple capable
10. Procedure
of an accuracy of 60.1°C (60.2°F).
10.1 Measure the length of two conditioned specimens at
7. Sampling
room temperature to the nearest 25 μm (0.001 in.) with the
scale or caliper (see 6.3).
7.1 Unless otherwise specified, the material shall be
10.2 Cement or otherwise attach the steel plates to the ends
sampled as described in Sections 8 through 14 of Practice
D 1898. of the specimen to prevent indentation (see 8.4). Measure the
new lengths of the specimens.
8. Test Specimen
10.3 Mount each specimen in a dilatometer. Carefully
8.1 The test specimens may be prepared by machining,
install the dilatometer in the −30°C (−22°F) controlled envi-
molding, or casting operations under conditions which give a
ronment. If liquid bath is used, make sure the top of the
minimum of strain or anisotropy. If anisotropy is suspected on
specimen is at least 50 mm (2 in.) below the liquid level of the
the samples, cut the specimens along the principal axes of
bath. Maintain the temperature of the bath in the range from
anisotropy and the coefficient of linear thermal expansion shall
−32°C to −28°C (−26 to −18°F) 60.2°C (0.4°F) until the
be measured on each set of specimens. Annealing of the
temperature of the specimen along the length is constant as
specimens may remove anisotropy effects due to processing or
denoted by no further movement indicated by the measuring
preparation.
device over a period of 5 to 10 min. Record the actual
8.2 The specimen length shall be between 50 mm and 125
temperature and the measuring device reading.
mm.
10.4 Without disturbing or jarring the dilatometer, change to
NOTE 3—If specimens shorter than 50 mm are used, a loss in sensitivity
the +30°C (+86°F) bath, so that the top of the specimen is at
results. If specimens greatly longer than 125 mm are used, the temperature
least 50 mm (2 in.) below the liquid level of the bath. Maintain
gradient along the specimen may become difficult to control within the
the temperature of the bath in the range from +28 to 32°C (+82
prescribed limits. T
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