1、Designation: E228 17Standard 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 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 covers the d
3、etermination 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 method was develope
4、d for vitreous silicadilatometers operating over a temperature range of 180C 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 same order as th
5、at 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 defined as a mate
6、rialthat, 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, glasses, rocks and min
7、erals,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 E831) but is signifi
8、cantly 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 expansion materials when
9、 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 The values stated in SI units are to be regarded asstandard. No other units of me
10、asurement are included in thisstandard.1.5 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 l
11、imitations prior to use.1.6 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organizat
12、ion TechnicalBarriers to Trade (TBT) Committee.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 TechniquesE230/E230M
13、 Specification and Temperature-ElectromotiveForce (emf) Tables for Standardized ThermocouplesE289 Test Method for Linear Thermal Expansion of RigidSolids with InterferometryE473 Terminology Relating to Thermal Analysis and Rhe-ologyE644 Test Methods for Testing Industrial Resistance Ther-mometersE83
14、1 Test Method for Linear Thermal Expansion of SolidMaterials by Thermomechanical AnalysisE1142 Terminology Relating to Thermophysical Properties3. Terminology3.1 DefinitionsThe following terms are applicable to thistest method and are listed in Terminologies E473 and E1142:1This test method is under
15、 the jurisdiction ofASTM Committee E37 on ThermalMeasurements and is the direct responsibility of Subcommittee E37.05 on Thermo-physical Properties.Current edition approved April 1, 2017. Published April 2017. Originallyapproved in 1963. Last previous edition approved in 2016 as E228 11 (2016).DOI:
16、10.1520/E0228-17.2For 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.Copyright ASTM International, 100 Barr Harbo
17、r Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendatio
18、ns issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.115 coeffcient of linear thermal expansion, thermodilatometry, andthermomechanical analysis.3.2 Definitions of Terms Specific to This Standard:3.2.1 dilatometera device that measures the difference inlinear thermal
19、 expansion between a test specimen and its ownparts adjacent to the sample.3.2.1.1 DiscussionThermomechanical analyzers (TMA),instruments used in thermal analysis, are often also character-ized as dilatometers, due to their ability to determine linearthermal expansion characteristics. Typically, the
20、y employspecimens much smaller than dilatometers; however, TMAsystems with sufficiently large specimen size capability havebeen shown to measure thermal expansion accurately. Whenusing the small TMA specimen size, this utilization of TMAequipment should be limited to testing only very high expan-sio
21、n materials, such as polymers, otherwise the data obtainedmay be substantially in error. Conversely, some dilatometerscan perform some of the TMA functions, but the two devicesshould not be considered equivalent or interchangeable in allapplications.3.2.2 linear thermal expansion, L/L0the change in
22、lengthrelative to the initial length of the specimen accompanying achange in temperature, between temperatures T0and T1,expressed as:LL05L12 L0L0(1)3.2.2.1 DiscussionIt is a dimensionless quantity, but forpractical reasons the units most often used are m/m.3.2.3 mean (average) coeffcient of linear t
23、hermalexpansion, mthe ratio between the expansion and thetemperature difference that is causing 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), and it is determined fo
24、r a sequence of temperatureranges, starting with 20C by convention, being presented as afunction of temperature. In case the reference temperaturediffers from 20C, the specific temperature used for referencehas to be indicated in the report.3.2.4 thermal expansivity (instantaneous coeffcient of ther
25、-mal expansion), Tidentical to the above, except that thederivative replaces the finite 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:T51L0SdLd
26、TDT(3)3.2.4.1 DiscussionIt is expressed in the same units as theaverage coefficient of 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 limi
27、ted utilityfor engineering applications, and therefore it is more commonto use the average coefficient of thermal expansion, than theinstantaneous one.3.3 Symbols:m= mean or average coefficient of linear thermalexpansion over a temperature range, m/(mC)T= expansivity or instantaneous coefficient of
28、linearthermal expansion at temperature T, m/(mC)L0= original length 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 twotemperatur
29、es T1and T2, T0and T1, etc., m(L/L0) = expansionT0= temperature at 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
30、the reference materialt = true or certified expansion of the reference 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 o
31、f a solidmaterial relative to that of the holder as a function oftemperature. 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 rel
32、ativeto the reference material rather than to the specimen holder.4.2 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
33、 recorded data.5. Significance and Use5.1 Coefficients of linear thermal 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
34、 of different materials when it issubjected to a temperature excursion.5.2 This test method is a reliable method of determining thelinear thermal expansion of solid materials.5.3 For accurate determinations of thermal expansion, it isabsolutely necessary that the dilatometer be calibrated by usinga
35、reference material that has a known and reproducible 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, bothE228 17215 of them equally i
36、mportant. Neglecting proper and accuratetemperature measurement 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 Consider
37、ations:6.1.1 The materials of construction may have substantialimpact 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
38、 device)causes no measurable change.6.2 General Considerations: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 separa
39、te the bath from the specimen arerequired when the dilatometer 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
40、 user must not practice uncontrolledsubstitutions (such as when 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 hold
41、er. The resultant mean coefficient of linearthermal expansion should 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 a
42、re frequently necessary to eliminate certaineffects (stress caused 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 t
43、hermally stablematerial constructed in a fashion such that when 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
44、 exhibit thermal expan-sion characteristics within 61 % of each 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, a
45、s long as the shape is mechanicallystable and is not prone to reversible 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 iden
46、tical thermal expansion. This is a critical factor,as differences 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 t
47、he two parts, however, it is notedthat this is one of the most 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.
48、1.2 Test Chamber, composed of:7.1.2.1 Furnace, Cryostat, or Bath, 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 3Extre
49、me care must be exercised in using furnaces for hightemperatures, 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.FIG. 1 Common Forms S
