1、Designation: E228 11Standard 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 Department of Defense.1. Scope1.1 This test method covers the determ
3、ination 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 developed for
4、 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 same order as that for
5、silica 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 materialth
6、at, 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 minerals,
7、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 (for ex-ample, Test Method D696) and thermomechanical analysis (forexample, Test Method E831) but is significan
8、tly lower than thatof absolute methods such as interferometry (for example, TestMethod E289). It is generally applicable to materials havingabsolute linear expansion coefficients exceeding 0.5 m/(mC)for a 1000C range, and under special circumstances can beused for lower expansion materials when spec
9、ial precautionsare used to ensure that the produced expansion of the specimenfalls within the capabilities of the measuring system. In suchcases, a sufficiently long specimen was found to meet thespecification.1.4 Computer- or electronic-based instrumentation, tech-niques, and data analysis systems
10、may be used in conjunctionwith this test method, as long as it is established that such asystem 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 equivalent and may omi
11、t 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 is no ISO method equiv
12、alent 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 regulatory limitations prior
13、 to use.2. Referenced Documents2.1 ASTM Standards:2D696 Test Method for Coefficient of Linear Thermal Ex-pansion of Plastics Between 30C and 30C with aVitreous Silica DilatometerE220 Test Method for Calibration of Thermocouples ByComparison TechniquesE289 Test Method for Linear Thermal Expansion of
14、RigidSolids with InterferometryE473 Terminology Relating to Thermal Analysis and Rhe-ologyE644 Test Methods for Testing Industrial Resistance Ther-mometers1This test method is under the jurisdiction ofASTM Committee E37 on ThermalMeasurements and is the direct responsibility of Subcommittee E37.05 o
15、n Thermo-physical Properties.Current edition approved April 1, 2011. Published April 2011. Originallyapproved in 1963. Last previous edition approved in 2006 as E228 06. DOI:10.1520/E0228-11.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serv
16、iceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.E831 Test Method for Linear Thermal Expansion of SolidM
17、aterials 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:coeffcient of linear thermal expansion, thermodilatometry, andthermomechanical
18、 analysis.3.2 Symbols:am= mean or average coefficient of linear thermal expansionover a temperature range, m/(mC), K-1,orC-1aT= expansivity or instantaneous coefficient of linear ther-mal expansion at temperature T, m/(mC). K-1,orC-1L0= original length of specimen at temperature T0,mmL1= length of s
19、pecimen at temperature T1,mmL2= length of specimen at temperature T2,mmLi= length of specimen at a particular temperature Ti,mmDL = change in length of specimen between any two tem-peratures T1and T2, T0and T1, etc., m(DL/L0) = expansionT0= temperature at which initial length is L0,CT1, T2= two temp
20、eratures at which measurements are made,CTi= temperature at which length is Li,CDT = temperature difference between any two temperaturesT2and T1, T1and T0, etc., Cm = measured expansion of the reference material,t = true or certified expansion of the reference material,s = assumed or known expansion
21、 of the parts of the dilatom-eter,A = numerical calibration constant3.3 Definitions of Terms Specific to This Standard:3.3.1 linear thermal expansion, DL/L0the change inlength relative to the initial length of the specimen accompa-nying a change in temperature, between temperatures T0andT1, expresse
22、d as:DLL05L1 L0L0(1)3.3.1.1 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 (%).3.3.2 mean (average) coeffcient of linear thermal expan-sion, amthe ratio between the expansion and the temperaturedifference
23、 that is causing it. It is referred to as the averagecoefficient of thermal expansion for the temperature rangebetween T0and T1.am51L0DLDT(2)3.3.2.1 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, b
24、eingpresented as a function of temperature. In case the referencetemperature differs from 20C, the specific temperature usedfor reference has to be indicated in the report.3.3.3 thermal expansivity (instantaneous coeffcient of ther-mal expansion), aTidentical to the above, except that thederivative
25、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:aT51L0SdLdTDT(3)3.3.3.1 DiscussionIt is expressed in the same units as theave
26、rage 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 limited utilityfor engineering applications, and therefore it is more c
27、ommonto use the average coefficient of thermal expansion, than theinstantaneous one.3.3.4 dilatometera device that measures the difference inlinear thermal expansion between a test specimen and its ownparts adjacent to the sample.3.3.4.1 DiscussionThermomechanical analyzers (TMA),instruments used in
28、 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 measure
29、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 the TMA
30、 functions, but the two devicesshould not be considered equivalent or interchangeable in allapplications.4. 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 oftempe
31、rature. 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.4.2
32、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 therm
33、al 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 excursion
34、.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 reference material that has a known and reproducible thermalE228 112ex
35、pansion. 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 will inev
36、itably 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 substantialimpact on
37、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:6.2.1 Inel
38、astic 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 is immerse
39、d 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 replacing
40、 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 should be s
41、maller 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 caused by mac
42、hining, 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 a specime
43、n 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 other. Il
44、lustrations 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 reversible
45、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 differences in net
46、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 fundamenta
47、l 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 Bath, used fo
48、r 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 hightemperatures, to prev
49、ent 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 beFIG. 1 Common Forms Specimen HoldersFIG. 2 Suggested Shapes of Specimens and Push-Rod EndsE228 113accomplished 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 4Unle
