1、Designation: E831 14Standard Test Method forLinear Thermal Expansion of Solid Materials byThermomechanical Analysis1This standard is issued under the fixed designation E831; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year
2、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.1. Scope1.1 This test method determines t
3、he technical coefficient oflinear thermal expansion of solid materials using thermome-chanical analysis techniques.1.2 This test method is applicable to solid materials thatexhibit sufficient rigidity over the test temperature range suchthat the sensing probe does not produce indentation of thespeci
4、men.1.3 The recommended lower limit of coefficient of linearthermal expansion measured with this test method is 5 m/(mC). The test method may be used at lower (or negative)expansion levels with decreased accuracy and precision (seeSection 11).1.4 This test method is applicable to the temperature ran
5、gefrom 120 to 900C. The temperature range may be extendeddepending upon the instrumentation and calibration materialsused.1.5 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.6 This test method is related to ISO 11359-2 but iss
6、ignificantly different in technical detail.1.7 This standard does not purport to address all of thesafety problems, 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 regulato
7、ry limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D696 Test Method for Coefficient of Linear Thermal Expan-sion of Plastics Between 30C and 30C with a VitreousSilica DilatometerD3386 Test Method for Coefficient of Linear Thermal Ex-pansion of Electrical Insulating Materials (Wit
8、hdrawn2005)3E228 Test Method for Linear Thermal Expansion of SolidMaterials With a Push-Rod DilatometerE473 Terminology Relating to Thermal Analysis and Rhe-ologyE1142 Terminology Relating to Thermophysical PropertiesE1363 Test Method for Temperature Calibration of Thermo-mechanical AnalyzersE2113 T
9、est Method for Length Change Calibration of Ther-momechanical Analyzers2.2 ISO Standards:4ISO 11359-2 PlasticsThermomechanical Analysis(TMA)Part 2: Determination of Coefficient of LinearThermal Expansion and Glass Transition Temperature3. Terminology3.1 DefinitionsThermal analysis terms in Terminolo
10、giesE473 and E1142 shall apply to this test method, includingcoeffcient of linear thermal expansion, thermodilatometry, andthermomechanical analysis.3.2 Definitions of Terms Specific to This Standard:3.2.1 mean coeffcient of linear thermal expansion, (m)the change in length, relative to the specimen
11、 length at ambienttemperature, accompanying a unit change in temperatureidentified by the midpoint temperature of the temperature rangeof measurement.1This test method is under the jurisdiction ofASTM Committee E37 on ThermalMeasurements and is the direct responsibility of Subcommittee E37.10 onFund
12、amental, Statistical and Mechanical Properties.Current edition approved Aug. 1, 2014. Published August 2014. Originallyapproved in 1981. Last previous edition approved in 2013 as E831 13. DOI:10.1520/E0831-14.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Custom
13、er Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3The last approved version of this historical standard is referenced onwww.astm.org.4Available from American National Standards Institute (ANSI), 25 W.
14、43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States14. Summary of Test Method4.1 This test method uses a thermomechanical analyzer orsimilar device to determine the linear thermal
15、 expansion ofsolid materials when subjected to a constant heating rate.4.2 The change of the specimen length is electronicallyrecorded as a function of temperature. The coefficient of linearthermal expansion can be calculated from these recorded data.5. Significance and Use5.1 Coefficients of linear
16、 thermal expansion are used, forexample, for design purposes and to determine if failure bythermal stress may occur when a solid body composed of twodifferent materials is subjected to temperature variations.5.2 This test method is comparable to Test Method D3386for testing electrical insulation mat
17、erials, but it covers a moregeneral group of solid materials and it defines test conditionsmore specifically. This test method uses a smaller specimenand substantially different apparatus than Test Methods E228and D696.6. Apparatus6.1 Thermomechanical Analyzers (TMA)The essential in-strumentation re
18、quired providing minimum thermomechanicalanalytical or thermodilatometric capability for this test methodincludes:6.1.1 Rigid Specimen Holder, of inert, low expansivitymaterial (0.5 m/(mC) to center the specimen in thefurnace and to fix the specimen to mechanical ground.6.1.2 Rigid Expansion Probe,
19、of inert, low expansivitymaterial (0.5 m/(mC) that contacts the specimen with anapplied compressive force.6.1.3 Sensing Element, linear over a minimum range of 2mm to measure the displacement of the rigid expansion probeto within 650 nm resulting from changes in length of thespecimen.6.1.4 Weight or
20、 Force Transducer, to generate a constantforce of 1 to 100 mN (0.1 to 10 g) that is applied through therigid expansion probe to the specimen.6.1.5 Furnace, capable of providing uniform controlledheating (cooling) of a specimen to a constant temperature or ata constant rate between 2 and 10C/min with
21、in the applicabletemperatures range of between 150 and 1000C.6.1.6 Temperature Controller, capable of executing a spe-cific temperature program by operating the furnace betweenselected temperature limits at a rate of temperature change of2 to 10C/min constant to within 60.1C/min or at anisothermal t
22、emperature constant to 60.5C.6.1.7 Temperature Sensor, that can be attached to, in contactwith, or reproducibly positioned in close proximity to thespecimen capable of indicating temperature to 60.5C.6.1.8 A means of sustaining an environment around thespecimen of inert gas at a purge gas rate of 10
23、 to 50 mL/min.NOTE 1Typically, greater than 99 % pure nitrogen, argon, or heliumis used when oxidation in air is a concern. Unless effects of moisture areto be studied, use of dry purge gas is recommended and is essential foroperation at subambient temperatures.6.1.9 Data Collection Device, to provi
24、de a means ofacquiring, storing, and displaying measured or calculatedsignals, or both. The minimum output signals required forthermomechanical analysis are a change in linear dimension,temperature and time.6.2 Cooling Capability, to sustain a subambient specimentemperature (if subambient measuremen
25、ts are to be made) or tohasten cool down of the specimen from elevated temperatures.6.3 Micrometer, or other length-measuring device with arange of up to 10 mm to determine specimen dimensions towithin 625 m.7. Test Specimens7.1 Specimens shall be between 2 and 10 mm in length andhave flat and paral
26、lel ends to within 625 m. Lateral dimen-sions shall not exceed 10 mm.NOTE 2Specimens of other dimensions may be used but dimensionsshall be reported.NOTE 3It has been found with some materials that this level offlatness and parallelness cannot be attained. Specimens that do not meetthese requirement
27、s may result in increased imprecision.7.2 The specimens are ordinarily measured as received.Where some heat or mechanical treatment is applied to thespecimen prior to test, this should be noted in the report.NOTE 4Some materials, particularly composites, may require heattreatment to condition the sp
28、ecimen prior to test to relieve stresses ordistortions. Such heat treatment must be included in the report.8. Calibration8.1 Prepare the instrument for operation according to theprocedures in the manufacturers operation manual.8.2 Calibrate the temperature signal using Test MethodE1363.8.3 Calibrate
29、 the length change signal using Test MethodE2113 at the same heating rate as that to be used for the testspecimens. The observed expansion must be corrected for thedifference in expansion between the specimen holder and probeobtained from a blank run in which no sample or a specimen ofthe material o
30、f construction of the probe is run (see 10.1).9. Procedure9.1 Measure the initial specimen length in the direction ofthe expansion test to 625 m at 20 to 25C.NOTE 5Direct readout of zero position and specimen length using theanalyzer sensing element, where available, with a sufficient range has been
31、found to be an accurate means of length determination.9.2 Place the specimen in the specimen holder under theprobe. Place the specimen temperature sensor in contact withthe specimen or as near to the specimen as possible.9.3 Move the furnace to enclose the specimen holder. Ifmeasurements at subambie
32、nt temperature are to be made, coolthe specimen to at least 20C below the lowest temperature ofinterest. The refrigerant used for cooling shall not come intodirect contact with the specimen.9.4 Apply an appropriate load force to the sensing probe toensure that it is in contact with the specimen. Dep
33、ending on theE831 142compressibility of the specimen and the temperature range tobe investigated, a force of between 1 and 100 mN (0.1 to 10 g)is adequate. The actual incremental force, mass, or stress abovethat required to make contact with zero force shall be noted inthe report.9.5 Heat the specim
34、en at a constant heating rate of 5C/minover the desired temperature range and record the changes inspecimen length and temperature to all available decimalplaces.NOTE 6Other heating rates may be used but shall be noted in thereport.NOTE 7Normally, the expansion increases with the increase intemperat
35、ure as shown in the schematic diagram of Fig. 1. An abruptchange in slope of the expansion curve indicates a transition of thematerial from one state to another.NOTE 8For best results, specimen temperature gradients should besmall. High heating rates, large specimen sizes, and low specimen thermalco
36、nductivity may lead to large specimen temperature gradients. Theeffects of specimen temperature gradients may be compensated for bycorrection found through the use of suitable reference materials whosesize and thermal conductivity are close to that of the test specimen.9.6 Measure the measurement in
37、strument baseline by re-peating 9.3 through 9.5 using the same test parameters butwithout a test specimen, that is, with the probe in contact withthe specimen holder. The measured L for the specimen shouldnormally be corrected for this instrument baseline, especiallyfor low expansion specimens.10. C
38、alculation10.1 Calculate the mean coefficient of linear thermal expan-sion rounded to the nearest 0.1 m/(mC) for a desiredtemperature range as follows:m5Lsp3kL 3 T(1)where:m= mean coefficient of linear thermal expansion, m/(mC),k = calibration coefficient, from Test Method E2113,L = specimen length
39、at room temperature, m,Lsp= change of specimen length, m,T = temperature difference over which the change inspecimen length is measured, C, andT = midpoint temperature of the temperature range T.NOTE 9For low-expansion specimens, L should be corrected for theexpansion of the sample holder displaced
40、by the specimen.Lspor Lref! 5 Lobs1L T holder2 Lblank(2)where:Lobs= measured change in length, m,holder= mean coefficient of linear thermal expansion forholder, m/(mC), andLblank= change of baseline due to heating, m.If the holder is composed of vitreous silica, holder= 0.52 60.02 m/(mC) from 20 to
41、700C.10.2 Select a 100C temperature range (T) from a smoothportion of the thermal curves in the desired temperature rangesymmetically around the temperature of interest; then obtainL as depicted in Fig. 1. The mshall not be calculated froma temperature range in which a transition point is noted.NOTE
42、 10Other ranges of temperature (for example, 50C) may beused but shall be reported.NOTE 11Values for T generally range between 50 and 100C. Valuesless than 50C may lead to poor precision; values greater than 100C maymask small change in the expansion coefficient.11. Report11.1 The report shall inclu
43、de the following:11.1.1 Designation of the material, including the name ofthe manufacturer and information on lot number and chemicalcomposition when known,11.1.2 Specimen orientation with respect to the original partor the direction of the oriented fiber fillers if a compositematerial is used,11.1.
44、3 Method of test specimen preparation,11.1.4 Dimensions of the specimen,11.1.5 Description of the thermomechanical analysisapparatus, including manufacturer and model number,11.1.6 Purge gas and cooling medium, if used,11.1.7 The midpoint temperature (T) and the temperaturerange (T) at which the coe
45、fficient of linear thermal expansionhas been determined,11.1.8 The technical coefficient of linear thermal expansionin m/(mC),11.1.9 Expansion curves obtained, and11.1.10 The specific dated version of this test method used.12. Precision and Bias512.1 Precision of thermal expansion measurements depen
46、dson the length of the specimen, the temperature range of5Supporting data have been filed at ASTM International Headquarters and maybe obtained by requesting Research Report RR:E37-1000. ContactASTM CustomerService at serviceastm.org.FIG. 1 Specimen Expansion Versus TemperatureE831 143interest, and
47、the change in the specimen length. Maximumimprecision in the calculated mean coefficient of linear thermalexpansion may be estimated from the imprecisions in theindividual measurements by the following equation./m5 L/6L!21L/L!21T/T!2#1/2(3)where:m= mean coefficient of linear thermal expansion, m/(mC
48、),= imprecision in the measurement of , m/(mC),L = change of specimen length due to heating, m,L = imprecision in the measurement of L, m,L = specimen length at room temperature, m,L = imprecision in the measurement of L,m,T = temperature difference over which the change inspecimen length is measure
49、d, C, andT = imprecision in the measurement of T, C.12.1.1 Example:L 5 8 mm (4)L 5625 m (5)L 5 60 m (6)L 561 m (7)T 5 100C (8)T 560.5C (9)/m5 1 m/60m!2125 31026m/8 31023m!210.5C/100C!2#1/2(10)or expressed as percent:/m561.8% (11)12.1.2 Intralaboratory precision measurements confirm therelationship above.12.2 Interlaboratory precision of this test method for coef-ficient of thermal expansion was determined from the res
