1、Designation: E 228 06Standard Test Method forLinear Thermal Expansion of Solid Materials With a Push-Rod Dilatometer1This standard is issued under the fixed designation E 228; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the yea
2、r of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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 det
3、ermination 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
4、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 same order as that
5、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 materia
6、lthat, 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 minera
7、ls,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 D 696) and thermomechanical analysis(for example, Test Method E 831) but is signi
8、ficantly lowerthan that of absolute methods such as interferometry (forexample, Test Method E 289). It is generally applicable tomaterials having absolute linear expansion coefficients exceed-ing 0.5 m/(mC) for a 1000C range, and under specialcircumstances can be used for lower expansion materials w
9、henspecial precautions are used to ensure that the producedexpansion of the specimen falls within the capabilities of themeasuring system. In such cases, a sufficiently long specimenwas found to meet the specification.1.4 Computer- or electronic-based instrumentation, tech-niques, and data analysis
10、systems 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
11、 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 SI units are the standard.1.6 There is no ISO method equivalent to this standard.1.7 This standard does not purport to address all of thesafety
12、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. Referenced Documents2.1 ASTM Standards:2D 696 Test Method for Coefficient o
13、f Linear Thermal Ex-pansion of Plastics Between 30C and 30C with aVitreous Silica DilatometerE 220 Test Method for Calibration of Thermocouples ByComparison TechniquesE 289 Test Method for Linear Thermal Expansion of RigidSolids with InterferometryE 473 Terminology Relating to Thermal Analysis and R
14、he-ologyE 644 Test Methods for Testing Industrial Resistance Ther-mometersE 831 Test Method for Linear Thermal Expansion of SolidMaterials by Thermomechanical AnalysisE 1142 Terminology Relating to Thermophysical Properties3. Terminology3.1 DefinitionsThe following terms are applicable to thistest m
15、ethod and are listed in Terminologies E 473 and E 1142:1This 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, 2006. Published November 2006. Origin
16、allyapproved in 1963. Last previous edition approved in 1995 as E 22895, which waswithdrawn May 2005 and reinstated in September 2006.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume info
17、rmation, 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.coeffcient of linear thermal expansion, thermodilatometry, andthermomechanical analysis.3.2 Symbols:am= mean coe
18、fficient of linear thermal expansion, m/(mC) or C-1aT= expansivity at temperature T, m/(mC) or C-1L0= 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,mmDL = cha
19、nge 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 temperatures at which measurements are made,CTi= temperature at which length is Li,CDT = temperature difference between any two temperature
20、sT2and 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 of the parts of the dilatom-eter,A = numerical calibration constant3.3 Definitions of Terms Specific to This Standard:3.3.1 linear the
21、rmal expansion, DL/L0the change inlength relative to the initial length of the specimen accompa-nying a change in temperature, between temperatures T0andT1, expressed 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)
22、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 that is causing it. It is referred to as the averagecoefficient of thermal expansion for the temperature rangebetween T0and T1.am51L0D
23、LDT(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, beingpresented as a function of temperature. In case the referencetemperature differs from 20C, the specific temperature usedfor referen
24、ce 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 replaces the finite differences of Eq 2. The thermalexpansivity is related to the length change for an infinitesimallynarrow temperatur
25、e 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 theaverage coefficient of thermal expansion. In terms of physicalmeaning, the instantaneous coefficient of thermal expansion isthe derivative
26、 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 average coefficient of thermal expansion, than theinstantaneous one.3.3.4 dilatometera device that measures the differe
27、nce inlinear thermal expansion between a test specimen and its ownparts adjacent to the sample.3.3.4.1 DiscussionThermomechanical analyzers (TMA),instruments used in thermal analysis, are often also character-ized as dilatometers, due to their ability to determine linearthermal expansion characteris
28、tics. Typically, they 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
29、 very high expan-sion 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.4. Summary of Test Method4.1 T
30、his 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 oftemperature. A special variation of the basic configurationknown as a differential dilatometer employs dual push rods,where a reference spec
31、imen 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 The temperature is controlled either over a series ofsteps or at a slow constant heating or cooling rate over theentire range.4.3 The l
32、inear thermal expansion and the coefficients oflinear thermal expansion are calculated from the 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 tempe
33、raturechanges, or thermal stresses that can occur and cause failure ofa solid artifact composed 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 determination
34、s of thermal expansion, it isabsolutely necessary that the dilatometer be calibrated by usinga 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 invol
35、ves twoparameters: change of length and change of temperature, bothof them equally important. Neglecting proper and accurateE228062temperature measurement will inevitably result in increaseduncertainties in the final data.5.5 The test method can be used for research, development,specification accept
36、ance, quality control (QC) and qualityassurance (QA).6. Interferences6.1 Materials Considerations: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
37、 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 Inelastic creep of a specimen at elevated temperaturescan often be prevented by making its cross section sufficientlylarge.6.2.2 Avoid moist
38、ure in the dilatometer, especially whenused at cryogenic temperatures.6.2.3 Means to separate 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 f
39、reemovement.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 broken parts), as seriousincrease of the uncertainties in the measured expansion mayresult.6.2.6 A general verification of a dilatomete
40、r 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 smaller than 60.3 m/(mC) fora properly constructed system (after applying the systemscorrection).6.2.7 Conditioning of specimens is often
41、 necessary beforereproducible expansion data can be obtained. For example,heat treatments are 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
42、-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 specimen ofthe same material is placed into it for a test, the qualificationsgiven in 6.2.7 are satisfied. In any push rod dilatometer, tosatis
43、fy this standard, both the sample holder and the push-rod(s) shall be made of the same material, and have beenproven to exhibit thermal expansion characteristics within61 % of each other. Illustrations of typical tube and rod-typeconfigurations are given in Fig. 1. It is often practiced toconfigure
44、specimen holders that are not shaped as a tube, butserve the same structural purpose. This is an acceptablepractice, as long as the shape is mechanically stable and is notprone to reversible configurational changes (such as twisting,etc.) upon heating and cooling.NOTE 2The tube and the push-rod beyo
45、nd 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 expansion between the tube and the push-rod willappear very much like expansion produced by the specimen. To
46、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 fundamental of all practical limitations fordilatometers. To minimize this effect, the tube and the push-rod shall be i
47、nclose 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 for heating orcooling the specimen uniformly at a controlled rate over thetemperature range of interest, and ab
48、le 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 prevent interaction with the dilatometers parts or withthe specimen. In many instances, it is necessary to protec
49、t 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 Specimen HoldersFIG. 2 Suggested Shapes of Specimens and Push-Rod EndsE228063NOTE 4Unless it is absolutely necessary to have the specimen testedin vacuum, measurements of thermal expansion in vacuum ar
