1、Designation: E228 11 (Reapproved 2016)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 ca
2、se of revision, 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
3、 test method covers the determination of the linear thermal expansion of rigid solid materials using push-roddilatometers. This method is applicable over any practical temperature range where a device can be constructed to satisfy theperformance requirements set forth in this standard.NOTE 1Initiall
4、y, this method was developed for vitreous silica dilatometers operating over a temperature range of 180180C to 900C. Theconcepts and principles have been amply documented in the literature to be equally applicable for operating at higher temperatures. The precision andbias of these systems is believ
5、ed to be of the same order as that for silica systems up to 900C. However, their precision and bias have not yet beenestablished over the relevant total range of temperature due to the lack of well-characterized reference materials and the need for interlaboratorycomparisons.1.2 For this purpose, a
6、rigid solid is defined as a material that, at test temperature and under the stresses imposed byinstrumentation, has a negligible creep or elastic strain rate, or both, thus insignificantly affecting the precision of thermal-lengthchange measurements. This includes, as examples, metals, ceramics, re
7、fractories, glasses, rocks and minerals, graphites, plastics,cements, cured mortars, woods, and a variety of composites.1.3 The precision of this comparative test method is higher than that of other push-rod dilatometry techniques (for example, TestMethod D696) and thermomechanical analysis (for exa
8、mple, Test Method E831) but is significantly lower than that of absolutemethods such as interferometry (for example, Test Method E289). It is generally applicable to materials having absolute linearexpansion coefficients exceeding 0.5 m/(mC) for a 1000C range, and under special circumstances can be
9、used for lowerexpansion materials when special precautions are used to ensure that the produced expansion of the specimen falls within thecapabilities of the measuring system. In such cases, a sufficiently long specimen was found to meet the specification.1.4 Computer- or electronic-based instrument
10、ation, techniques, and data analysis systems may be used in conjunction with thistest method, as long as it is established that such a system strictly adheres to the principles and computational schemes set forthin this method. Users of the test method are expressly advised that all such instruments
11、 or techniques may not be equivalent andmay omit or deviate from the methodology described hereunder. It is the responsibility of the user to determine the necessaryequivalency prior to use.1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included i
12、n this standard.1.6 There is no ISO method equivalent to this standard.1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine th
13、e applicability of regulatorylimitations prior to use.1.6 This international standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of International Standards, Guides and Recommendations issuedby
14、 the World Trade Organization Technical Barriers to Trade (TBT) Committee.1 This test method is under the jurisdiction of ASTM Committee E37 on Thermal Measurements and is the direct responsibility of Subcommittee E37.05 onThermophysical Properties.Current edition approved Sept. 1, 2016April 1, 2017
15、. Published September 2016April 2017. Originally approved in 1963. Last previous edition approved in 20112016 asE228 11.E228 11 (2016). DOI: 10.1520/E0228-11R16.10.1520/E0228-17.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what c
16、hanges have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the of
17、ficial document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States12. Referenced Documents2.1 ASTM Standards:2D696 Test Method for Coefficient of Linear Thermal Expansion of Plastics Between 30C and 30C with a Vitreous SilicaDilatometerE
18、220 Test Method for Calibration of Thermocouples By Comparison TechniquesE230/E230M Specification and Temperature-Electromotive Force (emf) Tables for Standardized ThermocouplesE289 Test Method for Linear Thermal Expansion of Rigid Solids with InterferometryE473 Terminology Relating to Thermal Analy
19、sis and RheologyE644 Test Methods for Testing Industrial Resistance ThermometersE831 Test Method for Linear Thermal Expansion of Solid Materials by Thermomechanical AnalysisE1142 Terminology Relating to Thermophysical Properties3. Terminology3.1 DefinitionsThe following terms are applicable to this
20、test method and are listed in Terminologies E473 and E1142:coeffcient of linear thermal expansion,thermodilatometry, and thermomechanical analysis.3.2 Definitions of Terms Specific to This Standard:3.2.1 dilatometera device that measures the difference in linear thermal expansion between a test spec
21、imen and its own partsadjacent to the sample.3.2.1.1 DiscussionThermomechanical analyzers (TMA), instruments used in thermal analysis, are often also characterized as dilatometers, due totheir ability to determine linear thermal expansion characteristics. Typically, they employ specimens much smalle
22、r thandilatometers; however, TMA systems with sufficiently large specimen size capability have been shown to measure thermalexpansion accurately. When using the small TMA specimen size, this utilization of TMA equipment should be limited to testingonly very high expansion materials, such as polymers
23、, otherwise the data obtained may be substantially in error. Conversely, somedilatometers can perform some of the TMA functions, but the two devices should not be considered equivalent or interchangeablein all applications.3.2.2 linear thermal expansion, L/L0the change in length relative to the init
24、ial length of the specimen accompanying achange in temperature, between temperatures T0 and T1, expressed as:LL0 5L12L0L0 (1)3.2.2.1 DiscussionIt is a dimensionless quantity, but for practical reasons the units most often used are m/m, (m/m)10m/m.-6, (in./in.)10-6, ppmor percent (%).3.2.3 mean (aver
25、age) coeffcient of linear thermal expansion, mthe ratio between the expansion and the temperaturedifference that is causing it. It is referred to as the average coefficient of thermal expansion for the temperature range between T0and T1.m 5 1L0LT (2)3.2.3.1 DiscussionMost commonly, it is expressed i
26、n m/(m C) or CC), -1, and it is determined for a sequence of temperature ranges, starting with20C by convention, being presented as a function of temperature. In case the reference temperature differs from 20C, the specifictemperature used for reference has to be indicated in the report.3.2.4 therma
27、l expansivity (instantaneous coeffcient of thermal expansion), Tidentical to the above, except that the derivativereplaces the finite differences of Eq 2. The thermal expansivity is related to the length change for an infinitesimally narrowtemperature range, at any temperature T (essentially a “tang
28、ent” point), and is defined as follows:2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.E228 172T 5 1L0SdLdTDT
29、(3)3.2.4.1 DiscussionIt is expressed in the same units as the average coefficient of thermal expansion. In terms of physical meaning, the instantaneouscoefficient of thermal expansion is the derivative of the expansion curve when plotted versus temperature, at the temperature T.It has a rather limit
30、ed utility for engineering applications, and therefore it is more common to use the average coefficient of thermalexpansion, than the instantaneous one.3.3 Symbols:m = mean or average coefficient of linear thermal expansion over a temperature range, m/(mC), K-1, or C-1m = mean or average coefficient
31、 of linear thermal expansion over a temperature range, m/(mC)T = expansivity or instantaneous coefficient of linear thermal expansion at temperature T, m/(mC). K-1, or C-1T = expansivity or instantaneous coefficient of linear thermal expansion at temperature T, m/(mC)L0 = original length of specimen
32、 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 two temperatures T1 and T2, T0 and T1, etc., m(L/L0) = expansionT0 = temperature at w
33、hich initial length is L0, CT1, T2 = two temperatures at which measurements are made, CTi = temperature at which length is Li, CT = temperature difference between any two temperatures T2 and T1, T1 and T0, etc., Cm = measured expansion of the reference materialt = true or certified expansion of the
34、reference materials = assumed or known expansion of the parts of the dilatometerA = numerical calibration constant4. Summary of Test Method4.1 This test method uses a single push-rod tube type dilatometer to determine the change in length of a solid material relativeto that of the holder as a functi
35、on of temperature.Aspecial variation of the basic configuration known as a differential dilatometeremploys dual push rods, where a reference specimen is kept in the second placement at all times and expansion of the unknownis determined relative to the reference material rather than to the specimen
36、holder.4.2 The temperature is controlled either over a series of steps or at a slow constant heating or cooling rate over the entire range.4.3 The linear thermal expansion and the coefficients of linear thermal expansion are calculated from the recorded data.5. Significance and Use5.1 Coefficients o
37、f linear thermal expansion are required for design purposes and are used, for example, to determinedimensional behavior of structures subject to temperature changes, or thermal stresses that can occur and cause failure of a solidartifact composed of different materials when it is subjected to a temp
38、erature excursion.5.2 This test method is a reliable method of determining the linear thermal expansion of solid materials.5.3 For accurate determinations of thermal expansion, it is absolutely necessary that the dilatometer be calibrated by using areference material that has a known and reproducibl
39、e thermal expansion. The appendix contains information relating to referencematerials in current general use.5.4 The measurement of thermal expansion involves two parameters: change of length and change of temperature, both of themequally important. Neglecting proper and accurate temperature measure
40、ment will inevitably result in increased uncertainties in thefinal data.5.5 The test method can be used for research, development, specification acceptance, quality control (QC) and quality assurance(QA).6. Interferences6.1 Materials Considerations:6.1.1 The materials of construction may have substa
41、ntial impact on the performance of the dilatometer. It is imperative thatregardless of the materials used, steps be taken to ascertain that the expansion behavior is stabilized, so that repeated thermalcycling (within the operating range of the device) causes no measurable change.E228 1736.2 General
42、 Considerations:6.2.1 Inelastic creep of a specimen at elevated temperatures can often be prevented by making its cross section sufficiently large.6.2.2 Avoid moisture in the dilatometer, especially when used at cryogenic temperatures.6.2.3 Means to separate the bath from the specimen are required w
43、hen the dilatometer is immersed in a liquid bath.6.2.4 Support or hold the specimen in a position so that it is stable during the test without unduly restricting its free movement.6.2.5 The specimen holder and push-rod shall be made from the same material. The user must not practice uncontrolledsubs
44、titutions (such as when replacing broken parts), as serious increase of the uncertainties in the measured expansion may result.6.2.6 A general verification of a dilatometer is a test run using a specimen cut from the same material as the push rod andspecimen holder. The resultant mean coefficient of
45、 linear thermal expansion should be smaller than 60.3 m/(mC) for a properlyconstructed system (after applying the systems correction).6.2.7 Conditioning of specimens is often necessary before reproducible expansion data can be obtained. For example, heattreatments are frequently necessary to elimina
46、te certain effects (stress caused by machining, moisture, etc.) that may introduceirreversible length changes that are not associated with thermal expansion.7. Apparatus7.1 Push-Rod Dilatometer System, consisting of the following:7.1.1 Specimen HolderAstructure of thermally stable material construct
47、ed in a fashion such that when a specimen of the samematerial is placed into it for a test, the qualifications given in 6.2.7 are satisfied. In any push rod dilatometer, both the sample holderand the push-rod(s) shall be made of the same material, having been proven to exhibit thermal expansion char
48、acteristics within61 % of each other. Illustrations of typical tube and rod-type configurations are given in Fig. 1. It is often practiced to configurespecimen holders that are not shaped as a tube, but serve the same structural purpose. This is an acceptable practice, as long asthe shape is mechani
49、cally stable and is not prone to reversible configurational changes (such as twisting, etc.) upon heating andcooling.NOTE 2The tube and the push-rod beyond the specimen, while parallel to each other, are expected to have identical thermal gradients along them,thereby identical thermal expansion. This is a critical factor, as differences in net expansion between the tube and the push-rod will appear very muchlike expansion produced by the specimen. To a limited extent, calibration (see Section 9) can be
