1、Designation: E228 11 (Reapproved 2016)Standard Test Method forLinear Thermal Expansion of Solid Materials With a Push-Rod Dilatometer1This standard is issued under the fixed designation E228; the number immediately following the designation indicates the year oforiginal adoption or, in the case of r
2、evision, 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.1. Scope1.1 This test m
3、ethod covers the determination of the linearthermal expansion of rigid solid materials using push-roddilatometers. This method is applicable over any practicaltemperature range where a device can be constructed to satisfythe performance requirements set forth in this standard.NOTE 1Initially, this m
4、ethod was developed for vitreous silicadilatometers operating over a temperature range of 180 to 900C. Theconcepts and principles have been amply documented in the literature tobe equally applicable for operating at higher temperatures. The precisionand bias of these systems is believed to be of the
5、 same order as that forsilica systems up to 900C. However, their precision and bias have not yetbeen established over the relevant total range of temperature due to thelack of well-characterized reference materials and the need for interlabo-ratory comparisons.1.2 For this purpose, a rigid solid is
6、defined as a materialthat, at test temperature and under the stresses imposed byinstrumentation, has a negligible creep or elastic strain rate, orboth, thus insignificantly affecting the precision of thermal-length change measurements. This includes, as examples,metals, ceramics, refractories, glass
7、es, rocks and minerals,graphites, plastics, cements, cured mortars, woods, and avariety of composites.1.3 The precision of this comparative test method is higherthan that of other push-rod dilatometry techniques (forexample, Test Method D696) and thermomechanical analysis(for example,Test Method E83
8、1) but is significantly lower thanthat of absolute methods such as interferometry (for example,Test Method E289). It is generally applicable to materialshaving absolute linear expansion coefficients exceeding 0.5m/(mC) for a 1000C range, and under special circum-stances can be used for lower expansi
9、on materials when specialprecautions are used to ensure that the produced expansion ofthe specimen falls within the capabilities of the measuringsystem. In such cases, a sufficiently long specimen was foundto meet the specification.1.4 Computer- or electronic-based instrumentation,techniques, and da
10、ta analysis systems may be used in conjunc-tion with this test method, as long as it is established that sucha system strictly adheres to the principles and computationalschemes set forth in this method. Users of the test method areexpressly advised that all such instruments or techniques maynot be
11、equivalent and may omit or deviate from the method-ology described hereunder. It is the responsibility of the user todetermine the necessary equivalency prior to use.1.5 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.6 There
12、is no ISO method equivalent to this standard.1.7 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 regula
13、tory 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 DilatometerE220 Test Method for Calibration of Thermocouples ByComparison TechniquesE289 Test Method for Linear
14、 Thermal Expansion of RigidSolids with InterferometryE473 Terminology Relating to Thermal Analysis and Rhe-ologyE644 Test Methods for Testing Industrial Resistance Ther-mometersE831 Test Method for Linear Thermal Expansion of SolidMaterials by Thermomechanical AnalysisE1142 Terminology Relating to T
15、hermophysical Properties1This test method is under the jurisdiction ofASTM Committee E37 on ThermalMeasurements and is the direct responsibility of Subcommittee E37.05 on Thermo-physical Properties.Current edition approved Sept. 1, 2016. Published September 2016. Originallyapproved in 1963. Last pre
16、vious edition approved in 2011 as E228 11. DOI:10.1520/E0228-11R16.2For 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 we
17、bsite.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13. Terminology3.1 DefinitionsThe following terms are applicable to thistest method and are listed in Terminologies E473 and E1142:coeffcient of linear thermal expansion, thermodila
18、tometry, andthermomechanical analysis.3.2 Definitions of Terms Specific to This Standard:3.2.1 dilatometera device that measures the difference inlinear thermal expansion between a test specimen and its ownparts adjacent to the sample.3.2.1.1 DiscussionThermomechanical analyzers (TMA),instruments us
19、ed in thermal analysis, are often also character-ized as dilatometers, due to their ability to determine linearthermal expansion characteristics. Typically, they employspecimens much smaller than dilatometers; however, TMAsystems with sufficiently large specimen size capability havebeen shown to mea
20、sure thermal expansion accurately. Whenusing the small TMA specimen size, this utilization of TMAequipment should be limited to testing only very high expan-sion materials, such as polymers, otherwise the data obtainedmay be substantially in error. Conversely, some dilatometerscan perform some of th
21、e TMA functions, but the two devicesshould not be considered equivalent or interchangeable in allapplications.3.2.2 linear thermal expansion, L/L0the change in lengthrelative to the initial length of the specimen accompanying achange in temperature, between temperatures T0and T1,expressed as:LL05L12
22、 L0L0(1)3.2.2.1 DiscussionIt is a dimensionless quantity, but forpractical reasons the units most often used are m/m, (m/m)10-6, (in./in.)10-6, ppm or percent (%).3.2.3 mean (average) coeffcient of linear thermalexpansion, mthe ratio between the expansion and thetemperature difference that is causin
23、g it. It is referred to as theaverage coefficient of thermal expansion for the temperaturerange between T0and T1.m51L0LT(2)3.2.3.1 DiscussionMost commonly, it is expressed inm/(m C) or C-1, and it is determined for a sequence oftemperature ranges, starting with 20C by convention, beingpresented as a
24、 function of temperature. In case the referencetemperature differs from 20C, the specific temperature usedfor reference has to be indicated in the report.3.2.4 thermal expansivity (instantaneous coeffcient of ther-mal expansion), Tidentical to the above, except that thederivative replaces the finite
25、 differences of Eq 2. The thermalexpansivity is related to the length change for an infinitesimallynarrow temperature range, at any temperature T (essentially a“tangent” point), and is defined as follows:T51L0SdLdTDT(3)3.2.4.1 DiscussionIt is expressed in the same units as theaverage coefficient of
26、thermal expansion. In terms of physicalmeaning, the instantaneous coefficient of thermal expansion isthe derivative of the expansion curve when plotted versustemperature, at the temperature T. It has a rather limited utilityfor engineering applications, and therefore it is more commonto use the aver
27、age coefficient of thermal expansion, than theinstantaneous one.3.3 Symbols:m= mean or average coefficient of linear thermalexpansion over a temperature range, m/(mC),K-1,orC-1T= expansivity or instantaneous coefficient of linearthermal expansion at temperature T, m/(mC).K-1,orC-1L0= original length
28、 of specimen at temperature T0,mmL1= length of specimen at temperature T1,mmL2= length of specimen at temperature T2,mmLi= length of specimen at a particular temperature Ti,mmL = change in length of specimen between any twotemperatures T1and T2, T0and T1, etc., m(L/L0) = expansionT0= temperature at
29、which initial length is L0,CT1,T2= two temperatures at which measurements aremade, CTi= temperature at which length is Li,CT = temperature difference between any two tempera-tures T2and T1, T1and T0, etc., Cm = measured expansion of the reference materialt = true or certified expansion of the refere
30、nce mate-rials = assumed or known expansion of the parts of thedilatometerA = numerical calibration constant4. Summary of Test Method4.1 This test method uses a single push-rod tube typedilatometer to determine the change in length of a solidmaterial relative to that of the holder as a function ofte
31、mperature. A special variation of the basic configurationknown as a differential dilatometer employs dual push rods,where a reference specimen is kept in the second placement atall times and expansion of the unknown is determined relativeto the reference material rather than to the specimen holder.4
32、.2 The temperature is controlled either over a series ofsteps or at a slow constant heating or cooling rate over theentire range.4.3 The linear thermal expansion and the coefficients oflinear thermal expansion are calculated from the recorded data.5. Significance and Use5.1 Coefficients of linear th
33、ermal expansion are required fordesign purposes and are used, for example, to determinedimensional behavior of structures subject to temperaturechanges, or thermal stresses that can occur and cause failure ofa solid artifact composed of different materials when it issubjected to a temperature excurs
34、ion.5.2 This test method is a reliable method of determining thelinear thermal expansion of solid materials.E228 11 (2016)25.3 For accurate determinations of thermal expansion, it isabsolutely necessary that the dilatometer be calibrated by usinga reference material that has a known and reproducible
35、 thermalexpansion. The appendix contains information relating toreference materials in current general use.5.4 The measurement of thermal expansion involves twoparameters: change of length and change of temperature, bothof them equally important. Neglecting proper and accuratetemperature measurement
36、 will inevitably result in increaseduncertainties in the final data.5.5 The test method can be used for research, development,specification acceptance, quality control (QC) and qualityassurance (QA).6. Interferences6.1 Materials Considerations:6.1.1 The materials of construction may have substantial
37、impact on the performance of the dilatometer. It is imperativethat regardless of the materials used, steps be taken to ascertainthat the expansion behavior is stabilized, so that repeatedthermal cycling (within the operating range of the device)causes no measurable change.6.2 General Considerations:
38、6.2.1 Inelastic creep of a specimen at elevated temperaturescan often be prevented by making its cross section sufficientlylarge.6.2.2 Avoid moisture in the dilatometer, especially whenused at cryogenic temperatures.6.2.3 Means to separate the bath from the specimen arerequired when the dilatometer
39、is immersed in a liquid bath.6.2.4 Support or hold the specimen in a position so that it isstable during the test without unduly restricting its freemovement.6.2.5 The specimen holder and push-rod shall be made fromthe same material. The user must not practice uncontrolledsubstitutions (such as when
40、 replacing broken parts), as seriousincrease of the uncertainties in the measured expansion mayresult.6.2.6 A general verification of a dilatometer is a test runusing a specimen cut from the same material as the push rodand specimen holder. The resultant mean coefficient of linearthermal expansion s
41、hould be smaller than 60.3 m/(mC) fora properly constructed system (after applying the systemscorrection).6.2.7 Conditioning of specimens is often necessary beforereproducible expansion data can be obtained. For example,heat treatments are frequently necessary to eliminate certaineffects (stress cau
42、sed by machining, moisture, etc.) that mayintroduce irreversible length changes that are not associatedwith thermal expansion.7. Apparatus7.1 Push-Rod Dilatometer System, consisting of the follow-ing:7.1.1 Specimen HolderA structure of thermally stablematerial constructed in a fashion such that when
43、 a specimen ofthe same material is placed into it for a test, the qualificationsgiven in 6.2.7 are satisfied. In any push rod dilatometer, boththe sample holder and the push-rod(s) shall be made of thesame material, having been proven to exhibit thermal expan-sion characteristics within 61 % of each
44、 other. Illustrations oftypical tube and rod-type configurations are given in Fig. 1.Itis often practiced to configure specimen holders that are notshaped as a tube, but serve the same structural purpose. This isan acceptable practice, as long as the shape is mechanicallystable and is not prone to r
45、eversible configurational changes(such as twisting, etc.) upon heating and cooling.NOTE 2The tube and the push-rod beyond the specimen, whileparallel to each other, are expected to have identical thermal gradientsalong them, thereby identical thermal expansion. This is a critical factor,as differenc
46、es in net expansion between the tube and the push-rod willappear very much like expansion produced by the specimen. To a limitedextent, calibration (see Section 9) can be used to account for thesedifferences in the thermal expansion of the two parts, however, it is notedthat this is one of the most
47、fundamental of all practical limitations fordilatometers. To minimize this effect, the tube and the push-rod shall be inclose proximity of each other and heated slowly enough to preventsubstantial thermal gradients that occur radially.7.1.2 Test Chamber, composed of:7.1.2.1 Furnace, Cryostat, or Bat
48、h, used for heating orcooling the specimen uniformly at a controlled rate over thetemperature range of interest, and able to maintain the tem-perature uniform along the sample during its heating, cooling,or just equilibrating.NOTE 3Extreme care must be exercised in using furnaces for hightemperature
49、s, to prevent interaction with the dilatometers parts or withthe specimen. In many instances, it is necessary to protect the specimenand the dilatometer from oxidation and in some cases this may beaccomplished with the use of a muffle tube. If it is necessary, the furnace,in such cases, shall contain provisions to provide inert atmosphere orvacuum environment, as well as provisions to protect against air back-streaming on cooling.NOTE 4Unless it is absolutely necessary to have the specimen testedin vacuum, measurement
copyright@ 2008-2019 麦多课文库（www.mydoc123.com）网站版权所有
备案/许可证编号：苏ICP备17064731号-1