1、Designation: D696 081Standard 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 adoption or,
2、 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 Department of Defense.1NOTEEditor
3、ially corrected parenthetical temperature values in 5.2 in March 2013.1. Scope*1.1 This test method covers determination of the coefficientof linear thermal expansion for plastic materials having coef-ficients of expansion greater than 1 106/C by use of avitreous silica dilatometer. At the test temp
4、eratures and underthe stresses imposed, the plastic materials shall have a negli-gible creep or elastic strain rate or both, insofar as theseproperties would significantly affect the accuracy of the mea-surements.NOTE 1There is no known ISO equivalent to this standard.1.1.1 Test Method E228 shall be
5、 used for temperatures otherthan 30C to 30C.1.1.2 This test method shall not be used for measurementson materials having a very low coefficient of expansion (lessthan 1 106/C). For materials having very low coefficient ofexpansion, interferometer or capacitance techniques are rec-ommended.1.2 The th
6、ermal expansion of a plastic is composed of areversible component on which are superimposed changes inlength due to changes in moisture content, curing, loss ofplasticizer or solvents, release of stresses, phase changes andother factors. This test method is intended for determining thecoefficient of
7、 linear thermal expansion under the exclusion ofthese factors as far as possible. In general, it will not bepossible to exclude the effect of these factors completely. Forthis reason, the test method can be expected to give only anapproximation to the true thermal expansion.1.3 The values stated in
8、SI units are to be regarded asstandard. The values in parentheses are for information only.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practi
9、ces and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D618 Practice for Conditioning Plastics for TestingD883 Terminology Relating to PlasticsD4065 Practice for Plastics: Dynamic Mechanical Proper-ties: Determination and Report of Proc
10、eduresE228 Test Method for Linear Thermal Expansion of SolidMaterials With a Push-Rod DilatometerE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodE831 Test Method for Linear Thermal Expansion of SolidMaterials by Thermomechanical Analysis3. Terminology3
11、.1 DefinitionsDefinitions are in accordance with Termi-nology D883 unless otherwise specified.4. Summary of Test Method4.1 This test method is intended to provide a means ofdetermining the coefficient of linear thermal expansion ofplastics which are not distorted or indented by the thrust of thedila
12、tometer on the specimen. For materials that indent, see 8.4.The specimen is placed at the bottom of the outer dilatometertube with the inner one resting on it. The measuring devicewhich is firmly attached to the outer tube is in contact with thetop of the inner tube and indicates variations in the l
13、ength ofthe specimen with changes in temperature. Temperaturechanges are brought about by immersing the outer tube in aliquid bath or other controlled temperature environment main-tained at the desired temperature.1This test method is under the jurisdiction ofASTM Committee D20 on Plasticsand is the
14、 direct responsibility of Subcommittee D20.30 on Thermal Properties(Section D20.30.07).Current edition approved Nov. 1, 2008. Published November 2008. Originallyapproved in 1942. Last previous edition approved in 2003 as D696 03. DOI:10.1520/D0696-08E01.2For referenced ASTM standards, visit the ASTM
15、 website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Har
16、bor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States15. Significance and Use5.1 The coefficient of linear thermal expansion, , betweentemperatures T1and T2for a specimen whose length is L0at thereference temperature, is given by the following equation: 5L22 L1!/L0T22 T1!# 5 L/L0Tw
17、here L1and L2are the specimen lengths at temperatures T1and T2, respectively. is, therefore, obtained by dividing thelinear expansion per unit length by the change in temperature.5.2 The nature of most plastics and the construction of thedilatometer make 30 to +30C (22F to +86F) a convenienttemperat
18、ure range for linear thermal expansion measurementsof plastics. This range covers the temperatures in whichplastics are most commonly used. Where testing outside of thistemperature range or when linear thermal expansion character-istics of a particular plastic are not known through thistemperature r
19、ange, particular attention shall be paid to thefactors mentioned in 1.2 and special preliminary investigationsby thermo-mechanical analysis, such as that prescribed inPractice D4065 for the location of transition temperatures, maybe required to avoid excessive error. Other ways of locatingphase chan
20、ges or transition temperatures using the dilatometeritself may be employed to cover the range of temperatures inquestion by using smaller steps than 30C (86F) or byobserving the rate of expansion during a steady rise intemperature of the specimen. Once such a transition point hasbeen located, a sepa
21、rate coefficient of expansion for a tempera-ture range below and above the transition point shall bedetermined. For specification and comparison purposes, therange from 30C to +30C (22F to +86F) (provided it isknown that no transition exists in this range) shall be used.6. Apparatus6.1 Fused-Quartz-
22、Tube Dilatometer suitable for this testmethod is illustrated in Fig. 1. A clearance of approximately 1mm is allowed between the inner and outer tubes.6.2 Device for measuring the changes in length (dial gage,LVDT, or the equivalent) is fixed on the mounting fixture sothat its position may be adjuste
23、d to accommodate specimens ofvarying length (see 8.2). The accuracy shall be such that theerror of indication will not exceed 61.0 m (4 105in.) forany length change. The weight of the inner silica tube plus themeasuring device reaction shall not exert a stress of more thanFIG. 1 Quartz-Tube Dilatome
24、terD696 081270 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 lengthof the specimen with an accuracy of 60.5 %.6.4 Controlled Temperature Environment to control thetemperature of the specimen. Arrange th
25、e bath so a uniformtemperature is assured over the length of the specimen. Meansshall be provided for stirring the bath and for controlling itstemperature within 60.2C (60.4F) at the time of thetemperature and measuring device readings.NOTE 2If a fluid bath is used, it is preferable and not difficul
26、t to avoidcontact between the bath liquid and the test specimen. If such contact isunavoidable, take care to select a fluid that will not affect the physicalproperties of the material under test.6.5 Thermometer or ThermocoupleThe bath temperatureshall be measured by a thermometer or thermocouple cap
27、ableof an accuracy of 60.1C (60.2F).7. Sampling7.1 Sampling shall be conducted in accordance with thematerial specification for the material in question.8. Test Specimen8.1 The test specimens shall be prepared under conditionsthat give a minimum of strain or anisotropy, such as machining,molding, or
28、 casting operations.8.2 The specimen length shall be between 50 mm and 125mm.NOTE 3If specimens shorter than 50 mm are used, a loss in sensitivityresults. If specimens greatly longer than 125 mm are used, the temperaturegradient along the specimen may become difficult to control within theprescribed
29、 limits. The length used will be governed by the sensitivity andrange of the measuring device, the extension expected and the accuracydesired. Generally speaking, the longer the specimen and the moresensitive the measuring device, the more accurate will be the determina-tion if the temperature is we
30、ll controlled.8.3 The cross section of the test specimen may be round,square, or rectangular and shall fit easily into the measurementsystem of the dilatometer without excessive play on the onehand or friction on the other. The cross section of the specimenshall be large enough so that no bending or
31、 twisting of thespecimen occurs. Convenient specimen cross sections are: 12.5by 6.3 mm (12 in. by14 in.), 12.5 by 3 mm (12 by18 in.), 12.5mm (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
32、attached to thesides of the specimen to fill out the space.8.4 Cut the ends of the specimens flat and perpendicular tothe length axis of the specimen. If a specimen indents from theuse of the dilatometer, then flat, thin steel or aluminum platesshall be cemented or otherwise firmly attached to the s
33、pecimento aid in positioning it in the dilatometer. These plates shall be0.3 to 0.5 mm (0.012 to 0.020 in.) in thickness.9. Conditioning9.1 ConditioningCondition the test specimens at23 6 2C (73.4 6 3.6F) and 50 6 10 % relative humidity fornot less than 40 h prior to test in accordance with Procedur
34、e Aof Practice D618 unless otherwise specified by the contract orrelevant material specification. In cases of disagreement, thetolerances shall be 61C (61.8F) and 65 % relative humid-ity.10. Procedure10.1 Measure the length of two conditioned specimens atroom temperature to the nearest 25 m (0.001 i
35、n.) with thescale or caliper (see 6.3).10.2 Cement or otherwise attach the steel plates to the endsof the specimen to prevent indentation (see 8.4). Measure thenew lengths of the specimens.10.3 Mount each specimen in a dilatometer. Carefullyinstall the dilatometer in the 30C (22F) controlled envi-ro
36、nment. If liquid bath is used, make sure the top of thespecimen is at least 50 mm (2 in.) below the liquid level of thebath. Maintain the temperature of the bath in the range from32C to 28C (26 to 18F) 6 0.2C (0.4F) until thetemperature of the specimen along the length is constant asdenoted by no fu
37、rther movement indicated by the measuringdevice over a period of 5 to 10 min. Record the actualtemperature and the measuring device reading.10.4 Without disturbing or jarring the dilatometer, change tothe +30C (+86F) bath, so that the top of the specimen is atleast 50 mm (2 in.) below the liquid lev
38、el of the bath. Maintainthe temperature of the bath in the range from +28 to 32C (+82to 90F) 6 0.2C (60.4F) until the temperature of thespecimen reaches that of the bath as denoted by no furtherchanges in the measuring device reading over a period of 5 to10 min. Record the actual temperature and the
39、 measuringdevice reading.10.5 Without disturbing or jarring the dilatometer, change to30C (22F) and repeat the procedure in 10.3.NOTE 4It is convenient to use alternately two baths at the propertemperatures. Great care should be taken not to disturb the apparatusduring the transfer of baths. Tall Th
40、ermos bottles have been successfullyused. The use of two baths is preferred because this will reduce the timerequired to bring the specimen to the desired temperature. The test shouldbe conducted in as short a time as possible to avoid changes in physicalproperties during long exposures to high and
41、low temperatures that mightpossibly take place.10.6 Measure the final length of the specimen at roomtemperature.10.7 If the change in length per degree of temperaturedifference due to heating does not agree with the change inlength per degree due to cooling within 10 % of their average,investigate t
42、he cause of the discrepancy and, if possible,eliminate. Repeat the test until agreement is reached.11. Calculation11.1 Calculate the coefficient of linear thermal expansionover the temperature range used as follows: 5 L/L0TD696 0813 = average coefficient of linear thermal expansion perdegree Celsius
43、,L = change in length of test specimen due to heating or tocooling,L0= length of test specimen at room temperature (L andL0being measured in the same units), andT = temperature differences, C, over which the change inthe length of the specimen is measured.The values of for heating and for cooling sh
44、all be averagedto give the value to be reported.NOTE 5Correction for thermal expansion of silica is 4.3 1071C.If requested, this value should be added to the calculated value tocompensate for the expansion of the apparatus equivalent to the length ofthe specimen. If thick metal plates are used, appr
45、opriate correction mayalso be desirable for their thermal expansions.12. Report12.1 The report shall include the following:12.1.1 Designation of material, including name of manufac-turer and information on composition when known.12.1.2 Method of preparation of test specimen,12.1.3 Form and dimension
46、s of test specimen,12.1.4 Type of apparatus used,12.1.5 Temperatures between which the coefficient of linearthermal expansion has been determined,12.1.6 Average coefficient of linear thermal expansion perdegree Celsius, for the two specimens tested.12.1.7 Location of phase change or transition point
47、temperatures, if this is in the range of temperatures used,12.1.8 Complete description of any unusual behavior of thespecimen, for example, differences of more than 10 % inmeasured values of expansion and contraction.13. Precision and Bias13.1 Table 1 is based on a round robin conducted in 1989 inac
48、cordance with Practice E691 involving nine materials andfive laboratories. For each material, all samples are prepared atone source, but the individual specimens are prepared at thelaboratory that tested them. Each test result is the average oftwo individual determinations. Each laboratory obtained
49、onetest result for each material. WarningThe explanations of “r” and “R”(13.2-13.2.3) only are intended to present ameaningful way of considering the approximate precision ofthis test method. The data presented in Table 1 should not beapplied to the acceptance or rejection of materials, as these dataapply only to the materials tested in the round robin and areunlikely to be rigorously representative of other lots,formulations, conditions, materials, or laboratories. Inparticul
