1、Designation: D696 081D696 16Standard Test Method forCoefficient of Linear Thermal Expansion of PlasticsBetween 30C and 30C with a Vitreous Silica Dilatometer1This standard is issued under the fixed designation D696; the number immediately following the designation indicates the year oforiginal adopt
2、ion or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript 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
3、.1 NOTEEditorially 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 coefficientsof expansion greater than 1 101 m6 /C(m.C) by use of a vitreous silica dilatom
4、eter. At the test temperatures and under thestresses imposed, the plastic materials shall have a negligible creep or elastic strain rate or both, insofar as these properties wouldsignificantly affect the accuracy of the measurements.NOTE 1There is no known ISO equivalent to this standard.1.1.1 Test
5、Method E228 shall be used for temperatures other than 30C to 30C.1.1.2 This test method shall not be used for measurements on materials having a very low coefficient of expansion (less than1 1016/C). m/(m.C). For materials having very low coefficient of expansion, interferometer or capacitance techn
6、iques arerecommended.1.1.3 Alternative technique commonly used for measuring this property is thermomechanical analysis as described in TestMethod 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 comp
7、onent on which are superimposed changes in lengthdue to changes in moisture content, curing, loss of plasticizer or solvents, release of stresses, phase changes and other factors. Thistest method is intended for determining the coefficient of linear thermal expansion under the exclusion of these fac
8、tors as far aspossible. In general, it will not be possible to exclude the effect of these factors completely. For this reason, the test method canbe 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 p
9、arentheses 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 responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimita
10、tions prior to use.NOTE 1There is no known ISO equivalent to this standard.2. Referenced Documents2.1 ASTM Standards:2D618 Practice for Conditioning Plastics for TestingD883 Terminology Relating to PlasticsD4065 Practice for Plastics: Dynamic Mechanical Properties: Determination and Report of Proced
11、uresE228 Test Method for Linear Thermal Expansion of Solid Materials With a Push-Rod DilatometerE691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test MethodE831 Test Method for Linear Thermal Expansion of Solid Materials by Thermomechanical Analysis1 This test me
12、thod is under the jurisdiction of ASTM Committee D20 on Plastics and is the direct responsibility of Subcommittee D20.30 on Thermal Properties (SectionD20.30.07).Current edition approved Nov. 1, 2008April 1, 2016. Published November 2008April 2016. Originally approved in 1942. Last previous edition
13、approved in 20032008 asD696 03.D696 081. DOI: 10.1520/D0696-08E01.10.1520/D0696-16.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary pag
14、e on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that u
15、sers consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Cons
16、hohocken, PA 19428-2959. United States13. Terminology3.1 DefinitionsDefinitions are in accordance with Terminology D883 unless otherwise specified.4. Summary of Test Method4.1 This test method is intended to provide a means of determining the coefficient of linear thermal expansion of plastics which
17、are not distorted or indented by the thrust of the dilatometer on the specimen. For materials that indent, see 8.4. The specimen isplaced at the bottom of the outer dilatometer tube with the inner one resting on it. The measuring device which is firmly attachedto the outer tube is in contact with th
18、e top of the inner tube and indicates variations in the length of the specimen with changesin temperature. Temperature changes are brought about by immersing the outer tube in a liquid bath or other controlled temperatureenvironment maintained at the desired temperature.5. Significance and Use5.1 Th
19、e coefficient of linear thermal expansion, , between temperatures T1 and T2 for a specimen whose length is L0 at thereference temperature, is given by the following equation:5L22L 1!/L0T22T1!#5L/L 0Twhere L1 and L2 are the specimen lengths at temperatures T1 and T2, respectively. is, therefore, obta
20、ined by dividing the linearexpansion per unit length by the change in temperature.5.2 The nature of most plastics and the construction of the dilatometer make 30 to +30C (22F to +86F) a convenienttemperature range for linear thermal expansion measurements of plastics. This range covers the temperatu
21、res in which plastics aremost commonly used. Where testing outside of this temperature range or when linear thermal expansion characteristics of aparticular plastic are not known through this temperature range, particular attention shall be paid to the factors mentioned in 1.2and special preliminary
22、 investigations by thermo-mechanical analysis, such as that prescribed in Practice .D4065 for the locationof transition temperatures, may be required to avoid excessive error. Other ways of locating phase changes or transitiontemperatures using the dilatometer itself may be employed to cover the ran
23、ge of temperatures in question by using smaller stepsthan 30C (86F) or by observing the rate of expansion during a steady rise in temperature of the specimen. Once such a transitionpoint has been located, a separate coefficient of expansion for a temperature range below and above the transition poin
24、t shall bedetermined. For specification and comparison purposes, the range from 30C to +30C (22F to +86F) (provided it is knownthat no transition exists in this range) shall be used.NOTE 2In such cases, special preliminary investigations by thermo-mechanical analysis, such as that prescribed in Prac
25、tice D4065 for the locationof transition temperatures, may be required to avoid excessive error. Other ways of locating phase changes or transition temperatures using the dilatometeritself may be employed to cover the range of temperatures in question by using smaller steps than 30C (86F) or by obse
26、rving the rate of expansionduring a steady rise in temperature of the specimen. Once such a transition point has been located, a separate coefficient of expansion for a temperaturerange below and above the transition point shall be determined. For specification and comparison purposes, the range fro
27、m 30C to +30C (22F to+86F) (provided it is known that no transition exists in this range) shall be used.6. Apparatus6.1 Fused-Quartz-Tube Dilatometer suitable for this test method is illustrated in Fig. 1. A clearance of approximately 1 mm isallowed between the inner and outer tubes.6.2 Device for m
28、easuring the changes in length (dial gage,gauge, LVDT, or the equivalent) is fixed on the mounting fixture sothat fixture.Adjust its position may be adjusted to accommodate specimens of varying length (see 8.2). The accuracy shall be suchthat the error of indication will not exceed 61.0 m (4 105 in.
29、) for any length change. The weight of the inner silica tube plusthe measuring device reaction shall not exert a stress of more than 70 kPa (10 psi) on the specimen so that the specimen is notdistorted or appreciably indented.6.3 Scale or Caliper capable of measuring the initial length of the specim
30、en with an accuracy of 60.5 %.6.4 Controlled Temperature Environment to control the temperature of the specimen.Arrange the bath so a uniform temperatureis assured over the length of the specimen. Means shall be provided for stirring the bath and for controlling its temperature within60.2C (60.4F) a
31、t the time of the temperature and measuring device readings.NOTE 3If 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 isunavoidable, take care to select a fluid that will not affect the physical properties of the
32、 material under test.6.5 Thermometer or ThermocoupleThe bath temperature shall be measured by a thermometer or thermocouple capable of anaccuracy of 60.1C (60.2F).7. Sampling7.1 Sampling shall be conducted in accordance with the material specification for the material in question.D696 1628. Test Spe
33、cimen8.1 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 4If specimens shorter than 50 mm are used, a loss in sensitivity results. If spe
34、cimens greatly longer than 125 mm are used, the temperaturegradient along the specimen may become difficult to control within the prescribed limits. The length used will be governed by the sensitivity and rangeof the measuring device, the extension expected and the accuracy desired. Generally speaki
35、ng, the longer the specimen and the more sensitive themeasuring 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 themeasurement system of th
36、e dilatometer without excessive play on the one hand or friction on the other. The cross section of thespecimen shall be large enough so that no bending or twisting of the specimen occurs. Convenient specimen cross sections are:12.5 by 6.3 mm (12 in. by 14 in.), 12.5 by 3 mm (12 by 18 in.), 12.5 mm
37、(12 in.) in diameter or 6.3 mm (14 in.) in diameter. Ifexcessive play is found with some of the thinner specimen, guide sections shall be cemented or otherwise attached to the sides ofthe specimen to fill out the space.8.4 Cut the ends of the specimens flat and perpendicular to the length axis of th
38、e specimen. If a specimen indents from the useof the dilatometer, then flat, thin steel or aluminum plates shall be cemented or otherwise firmly attached to the specimen to aidin positioning it in the dilatometer. These plates shall be 0.3 to 0.5 mm (0.012 to 0.020 in.) in thickness.9. Conditioning9
39、.1 ConditioningCondition the test specimens at 23 6 2C (73.4 6 3.6F) and 50 6 10 % relative humidity for not less than40 h prior to test in accordance with Procedure A of Practice D618 unless otherwise specified by the contract or relevant materialspecification. In cases of disagreement, the toleran
40、ces shall be 61C (61.8F) and 65 % relative humidity.FIG. 1 Quartz-Tube DilatometerD696 16310. Procedure10.1 Measure the length of two conditioned specimens at room temperature to the nearest 25 m (0.001 in.) with the scale orcaliper (see 6.3).10.2 Cement or otherwise attach the steel plates to the e
41、nds of the specimen to prevent indentation (see 8.4). Measure the newlengths of the specimens.10.3 Mount each specimen in a dilatometer. Carefully install the dilatometer in the 30C (22F) controlled environment. Ifliquid bath is used, make sure the top of the specimen is at least 50 mm (2 in.) below
42、 the liquid level of the bath. Maintain thetemperature of the bath in the range from 32C to 28C (26 to 18F) 6 0.2C (0.4F) until the temperature of the specimenalong the length is constant as denoted by no further movement indicated by the measuring device over a period of 5 to 10 min.Record the actu
43、al temperature and the measuring device reading.10.4 Without disturbing or jarring the dilatometer, change to the +30C (+86F) bath, so that the top of the specimen is at least50 mm (2 in.) below the liquid level of the bath. Maintain the temperature of the bath in the range from +28 to 32C (+82 to 9
44、0F)6 0.2C (60.4F) until the temperature of the specimen reaches that of the bath as denoted by no further changes in the measuringdevice reading over a period of 5 to 10 min. Record the actual temperature and the measuring device reading.10.5 Without disturbing or jarring the dilatometer, change to
45、30C (22F) and repeat the procedure in 10.3.NOTE 5It is convenient to use alternately two baths at the proper temperatures. Great care should be taken not to disturb the apparatus during thetransfer of baths. Tall Thermos bottles have been successfully used. The use of two baths is preferred because
46、this will reduce the time required to bringthe specimen to the desired temperature. The test should be conducted in as short a time as possible to avoid changes in physical properties during longexposures to high and low temperatures that might possibly take place.10.6 Measure the final length of th
47、e specimen at room temperature.10.7 If the change in length per degree of temperature difference due to heating does not agree with the change in length perdegree due to cooling within 10 % of their average, investigate the cause of the discrepancy and, if possible, eliminate. Repeat thetest until a
48、greement is reached.11. Calculation11.1 Calculate the coefficient of linear thermal expansion over the temperature range used as follows:5L/L0T = average coefficient of linear thermal expansion per degree Celsius,L = change in length of test specimen due to heating or to cooling,L0 = length of test
49、specimen at room temperature (L and L0 being measured in the same units), andT = temperature differences, C, over which the change in the length of the specimen is measured.The values of for heating and for cooling shall be averaged to give the value to be reported.NOTE 6Correction for thermal expansion of silica is 4.3 100.437 1C.m/(m.C). If requested, this value should be added to the calculated valueto compensate for the expansion of the apparatus equival
