1、Designation: D 696 08Standard Test Method forCoefficient of Linear Thermal Expansion of PlasticsBetween 30C and 30C with a Vitreous Silica Dilatometer1This standard is issued under the fixed designation D 696; 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.1. Scope*1
3、.1 This test method covers determination of the coefficientof linear thermal expansion for plastic materials having coef-ficients of expansion greater than 1 3 106/C by use of avitreous silica dilatometer. At the test temperatures and underthe stresses imposed, the plastic materials shall have a neg
4、li-gible creep or elastic strain rate or both, insofar as theseproperties would significantly affect the accuracy of the mea-surements.NOTE 1There is no similar or equivalent ISO standard.1.1.1 Test Method E 228 shall be used for temperaturesother than 30C to 30C.1.1.2 This test method shall not be
5、used for measurementson materials having a very low coefficient of expansion (lessthan 1 3 106/C). For materials having very low coefficient ofexpansion, interferometer or capacitance techniques are rec-ommended.1.2 The thermal expansion of a plastic is composed of areversible component on which are
6、 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 linear thermal expansion under the exclusion ofthese factors as far as possib
7、le. 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 SI units are to be regarded asstandard. The values in parentheses are for info
8、rmation 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 practices and determine the applica-bility of regulatory limitations prior to use.2.
9、 Referenced Documents2.1 ASTM Standards:2D 618 Practice for Conditioning Plastics for TestingD 883 Terminology Relating to PlasticsD 4065 Practice for Plastics: Dynamic Mechanical Proper-ties: Determination and Report of ProceduresE 228 Test Method for Linear Thermal Expansion of SolidMaterials With
10、 a Push-Rod DilatometerE 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodE 831 Test Method for Linear Thermal Expansion of SolidMaterials by Thermomechanical Analysis3. Terminology3.1 DefinitionsDefinitions are in accordance with Termi-nology D 883 unle
11、ss 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 thedilatometer on the specimen. For materials that indent, see 8.4.The specime
12、n 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 length ofthe specimen with changes in temperature. Temperaturechanges ar
13、e brought about by immersing the outer tube in aliquid bath or other controlled temperature environment main-tained at the desired temperature.5. Significance and Use5.1 The coefficient of linear thermal expansion, a, betweentemperatures T1and T2for a specimen whose length is L0atthe reference tempe
14、rature, is given by the following equation:1This test method is under the jurisdiction ofASTM Committee D20 on Plasticsand is the direct responsibility of Subcommittee D20.30 on Thermal Properties(Section D20.30.07).Current edition approved Nov. 1, 2008. Published November 2008. Originallyapproved i
15、n 1942. Last previous edition approved in 2003 as D 696 03.2For referenced ASTM standards, visit the ASTM 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.1*
16、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.a5L22 L1!/L0T22T1!# 5DL/L0DTwhere L1and L2are the specimen lengths at temperatures T1and T2, respectively. a is, therefor
17、e, 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 +54F) a convenienttemperature range for linear thermal expansion measurementsof plastics. This range covers the temp
18、eratures 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 range, particular attention shall be paid to thefactors mentioned in 1.2 and special prelim
19、inary investigationsby thermo-mechanical analysis, such as that prescribed inPractice D 4065 for the location of transition temperatures,may be required to avoid excessive error. Other ways oflocating phase changes or transition temperatures using thedilatometer itself may be employed to cover the r
20、ange oftemperatures in question by using smaller steps than 30C(54F) or by observing the rate of expansion during a steadyrise in temperature of the specimen. Once such a transitionpoint has been located, a separate coefficient of expansion fora temperature range below and above the transition point
21、 shallbe determined. 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-Tube Dilatometer suitable for this testmethod is illustrated in Fig. 1. A clearance of appr
22、oximately 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 adjusted to accommodate specimens ofvarying length (see 8.2). The accuracy shall be such that thee
23、rror of indication will not exceed 61.0 m (4 3 105in.) forany length change. The weight of the inner silica tube plus themeasuring device reaction shall not exert a stress of more than70 kPa (10 psi) on the specimen so that the specimen is notdistorted or appreciably indented.6.3 Scale or Caliper ca
24、pable 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 the bath so a uniformFIG. 1 Quartz-Tube DilatometerD696082temperature is assured over the length of the specimen. Meansshall be pr
25、ovided 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 difficult to avoidcontact between the bath liquid and the test specimen. If such contact isunavoida
26、ble, 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 capableof an accuracy of 60.1C (60.2F).7. Sampling7.1 Sampling shall be conducted in accordanc
27、e 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 casting operations.8.2 The specimen length shall be between 50 mm and 125mm.NOTE 3If speci
28、mens 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 limits. The length used will be governed by the sensitivity andrange of the measuring devi
29、ce, 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 well controlled.8.3 The cross section of the test specimen may be round,square, or rectangula
30、r 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 twisting of thespecimen occurs. Convenient specimen cross sections are: 12.5by 6.3 mm (12
31、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 attached to thesides of the specimen to fill out the space.8.4 Cut the ends of the specimen
32、s 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 specimento aid in positioning it in the dilatometer. These plates shall be0.3 to 0.5 mm (0.0
33、12 to 0.020 in.) in thickness.9. Conditioning9.1 Conditioning Condition 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 Procedure Aof Practice D 618 unless otherwise specified by the contract orrelevant material specif
34、ication. 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 in.) with thescale or caliper (see 6.3).10.2 Cement or otherwise attach the steel plates t
35、o 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-ronment. If liquid bath is used, make sure the top of thespecimen is at least 50 mm (2 in.)
36、 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 further movement indicated by the measuringdevice over a period of 5 to 10 min. Record the
37、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 level of the bath. Maintainthe temperature of the bath in the range from +28 to 32C (+82to 9
38、0F) 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 measuringdevice reading.10.5 Without disturbing or jarring the dilatometer, change to30C
39、 (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 Thermos bottles have been successfullyused. The use of two baths is preferred because this
40、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 low temperatures that mightpossibly take place.10.6 Measure the final length of the speci
41、men 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 the cause of the discrepancy and, if possible,eliminate. Repeat the test until agreement i
42、s reached.11. Calculation11.1 Calculate the coefficient of linear thermal expansionover the temperature range used as follows:a5DL/L0DTa = average coefficient of linear thermal expansion perdegree Celsius,DL = change in length of test specimen due to heating or tocooling,L0= length of test specimen
43、at room temperature (DL andL0being measured in the same units), andDT = temperature differences, C, over which the change inthe length of the specimen is measured.D696083The values of a for heating and for cooling shall be averagedto give the value to be reported.NOTE 5Correction for thermal expansi
44、on of silica is 4.3 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, appropriate correction mayalso be desirable for their thermal expansions.12. Report12.
45、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 dimensions of test specimen,12.1.4 Type of apparatus used,12.1.5 Temperatures between which
46、 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 tem-peratures, if this is in the range of temperatures used,12.1.8 Complete descr
47、iption 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 inaccordance with Practice E 691 involving nine materials andfive laboratories. For
48、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 onetest result for each material. WarningThe explanations of“r” and “R”(13.2-13
49、.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, formula-tions, conditions, materials, or laboratories. In particular, withdata from less than six laboratories, the between laboratoriesresults are likely to have a very hig
