ASTM D696-16

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Designation: D696 − 08 D696 − 16
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 D696; 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 (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
ε NOTE—Editorially corrected parenthetical temperature values in 5.2 in March 2013.
1. Scope*
1.1 This test method covers determination of the coefficient of linear thermal expansion for plastic materials having coefficients
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of expansion greater than 1 × 101 μm /°C⁄(m.°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 known ISO equivalent to this 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
−6
1 × 101 /°C). μm/(m.°C). For materials having very low coefficient of expansion, interferometer or capacitance techniques are
recommended.
1.1.3 Alternative technique commonly used for measuring this property is thermomechanical analysis as described in Test
Method E831, which permits measurement of this property over a scanned temperature range.
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 standard. The values in parentheses are for information only.
1.4 This standard does not purport to address all of the safety concerns, 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.
NOTE 1—There is no known ISO equivalent to this standard.
2. Referenced Documents
2.1 ASTM Standards:
D618 Practice for Conditioning Plastics for Testing
D883 Terminology Relating to Plastics
D4065 Practice for Plastics: Dynamic Mechanical Properties: Determination and Report of Procedures
E228 Test Method for Linear Thermal Expansion of Solid Materials With a Push-Rod Dilatometer
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
E831 Test Method for Linear Thermal Expansion of Solid Materials by Thermomechanical Analysis
This test method is under the jurisdiction of ASTM Committee D20 on Plastics and is the direct responsibility of Subcommittee D20.30 on Thermal Properties (Section
D20.30.07).
Current edition approved Nov. 1, 2008April 1, 2016. Published November 2008April 2016. Originally approved in 1942. Last previous edition approved in 20032008 as
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D696 – 03.D696 – 08 . DOI: 10.1520/D0696-08E01.10.1520/D0696-16.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*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
D696 − 16
3. Terminology
3.1 Definitions—Definitions are in accordance with Terminology D883 unless otherwise specified.
4. Summary of Test Method
4.1 This test method is intended to provide a means of determining the coefficient of linear thermal expansion of plastics which
are not distorted or indented by the thrust of the dilatometer on the specimen. For materials that indent, see 8.4. The specimen is
placed at the bottom of the outer dilatometer tube with the inner one resting on it. The measuring device which is firmly attached
to the outer tube is in contact with the top of the inner tube and indicates variations in the length of the specimen with changes
in temperature. Temperature changes are brought about by immersing the outer tube in a liquid bath or other controlled temperature
environment maintained at the desired temperature.
5. Significance and Use
5.1 The coefficient of linear thermal expansion, α, between temperatures T and T for a specimen whose length is L at the
1 2 0
reference temperature, is given by the following equation:
α5 L 2 L / L T 2 T 5 ΔL/L ΔT
@ ~ !#
~ 2 1! 0 2 1 0
where L and L are the specimen lengths at temperatures T and T , respectively. α is, therefore, obtained by dividing the linear
1 2 1 2
expansion per unit length by the change in temperature.
5.2 The nature of most plastics and the construction of the dilatometer make −30 to +30°C (−22°F to +86°F) a convenient
temperature range for linear thermal expansion measurements of plastics. This range covers the temperatures in which plastics are
most commonly used. Where testing outside of this temperature range or when linear thermal expansion characteristics of a
particular plastic are not known through this temperature range, particular attention shall be paid to the factors mentioned in 1.2
and special preliminary investigations by thermo-mechanical analysis, such as that prescribed in Practice .D4065 for the location
of transition temperatures, may be required to avoid excessive error. Other ways of locating phase changes or transition
temperatures using the dilatometer itself may be employed to cover the range of temperatures in question by using smaller steps
than 30°C (86°F) or by observing the rate of expansion during a steady rise in temperature of the specimen. Once such a transition
point has been located, a separate coefficient of expansion for a temperature range below and above the transition point shall be
determined. For specification and comparison purposes, the range from −30°C to +30°C (−22°F to +86°F) (provided it is known
that no transition exists in this range) shall be used.
NOTE 2—In such cases, special preliminary investigations by thermo-mechanical analysis, such as that prescribed in Practice D4065 for the location
of transition temperatures, may be required to avoid excessive error. Other ways of locating phase changes or transition temperatures using the dilatometer
itself may be employed to cover the range of temperatures in question by using smaller steps than 30°C (86°F) or by observing the rate of expansion
during a steady rise in temperature of the specimen. Once such a transition point has been located, a separate coefficient of expansion for a temperature
range below and above the transition point shall be determined. For specification and comparison purposes, the range from −30°C to +30°C (−22°F to
+86°F) (provided it is known that no transition exists in this range) shall be used.
6. Apparatus
6.1 Fused-Quartz-Tube Dilatometer suitable for this test method is illustrated in Fig. 1. A clearance of approximately 1 mm is
allowed between the inner and outer tubes.
6.2 Device for measuring the changes in length (dial gage,gauge, LVDT, or the equivalent) is fixed on the mounting fixture so
that fixture. Adjust its position may be adjusted to accommodate specimens of varying length (see 8.2). The accuracy shall be such
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that the error of indication will not exceed 61.0 μm (4 × 10 in.) for any length change. The weight of the inner silica tube plus
the measuring device reaction shall not exert a stress of more than 70 kPa (10 psi) on the specimen so that the specimen is not
distorted or appreciably indented.
6.3 Scale or Caliper capable of measuring the initial length of the specimen with an accuracy of 60.5 %.
6.4 Controlled Temperature Environment to control the temperature of the specimen. Arrange the bath so a uniform temperature
is assured over the length of the specimen. Means shall be provided for stirring the bath and for controlling its temperature within
60.2°C (60.4°F) at the time of the temperature and measuring device readings.
NOTE 3—If a fluid bath is used, it is preferable and not difficult to avoid contact between the bath liquid and the test specimen. If such contact is
unavoidable, take care to select a fluid that will not affect the physical properties of the material under test.
6.5 Thermometer or Thermocouple—The bath temperature shall be measured by a thermometer or thermocouple capable of an
accuracy of 60.1°C (60.2°F).
7. Sampling
7.1 Sampling shall be conducted in accordance with the material specification for the material in question.
D696 − 16
FIG. 1 Quartz-Tube Dilatometer
8. Test Specimen
8.1 The test specimens shall be prepared under conditions that give a minimum of strain or anisotropy, such as machining,
molding, or casting operations.
8.2 The specimen length shall be between 50 mm and 125 mm.
NOTE 4—If specimens shorter than 50 mm are used, a loss in sensitivity results. If specimens greatly longer than 125 mm are used, the temperature
gradient along the specimen may become difficult to control within the prescribed limits. The length used will be governed by the sensitivity and range
of the measuring device, the extension expected and the accuracy desired. Generally speaking, the longer the specimen and the more sensitive the
measuring device, the more accurate will be the determination if the temperature is well controlled.
8.3 The cross section of the test specimen may be round, square, or rectangular and rectangular, shall fit easily into the
measurement system of the dilatometer without excessive play on the one hand or friction on the other. The cross section of the
specimen shall be large enough so that no bending or twisting of the specimen occurs. Convenient specimen cross sections are:
1 1 1 1 1 1
12.5 by 6.3 mm ( ⁄2 in. by ⁄4 in.), 12.5 by 3 mm ( ⁄2 by ⁄8 in.), 12.5 mm ( ⁄2 in.) in diameter or 6.3 mm ( ⁄4 in.) in diameter. If
excessive play is found with some of the thinner specimen, guide sections shall be cemented or otherwise a
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