1、Designation: E1461 11Standard Test Method forThermal Diffusivity by the Flash Method1This standard is issued under the fixed designation E1461; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in
2、parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of the thermaldiffusivity of primarily homogeneous isotropic solid materials.Thermal diffusivity values
3、 ranging from 10-7to 10-3m2s-1aremeasurable by this test method from about 75 to 2800 K.1.2 Practice E2585 is adjunct to this Test Method andcontains detailed information regarding the use of the flashmethod. The two documents are complementing each other.1.3 This test method is a more detailed form
4、 of Test MethodC714, having applicability to much wider ranges of materials,applications, and temperatures, with improved accuracy ofmeasurements.1.4 This test method is intended to allow a wide variety ofapparatus designs. It is not practical in a test method of thistype to establish details of con
5、struction and procedures to coverall contingencies that might offer difficulties to a personwithout pertinent technical knowledge, or to stop or restrictresearch and development for improvements in the basictechnique.1.5 This test method is applicable to the measurementsperformed on essentially full
6、y dense (preferably, but lowporosity would be acceptable), homogeneeous, and isotropicsolid materials that are opaque to the applied energy pulse.Experience has shown, however, that some deviation fromthese strict guidelines can be accommodated with care andproper experimental design, substantially
7、broadening the use-fulness of the method.1.6 This test method can be considered an absolute (orprimary) method of measurement, since no reference standardsare required. It is advisable to use reference materials to verifythe performance of the instrument used.1.7 The values stated in SI units are to
8、 be regarded asstandard. No other units of measurement are included in thisstandard.1.8 For systems employing lasers as power sources, it isimperative that the safety requirement be fully met.1.9 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It
9、 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:2C714 Test Method for Thermal Diffusivity of Carbon andGraphite by Thermal Pulse
10、MethodE228 Test Method for Linear Thermal Expansion of SolidMaterials With a Push-Rod DilatometerE2585 Practice for Thermal Diffusivity by the FlashMethod3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 thermal conductivity, l, of a solid materialthe timerate of steady heat flo
11、w through unit thickness of an infiniteslab of a homogeneous material in a direction perpendicular tothe surface, induced by unit temperature difference. Theproperty must be identified with a specific mean temperature,since it varies with temperature.3.1.2 thermal diffusivity, a, of a solid material
12、the prop-erty given by the thermal conductivity divided by the productof the density and heat capacity per unit mass.3.2 Description of Symbols and Units Specific to ThisStandard:3.2.1 Ddiameter, m.3.2.2 Cpspecific heat capacity, Jkg-1K-1).3.2.3 kconstant depending on percent rise.3.2.4 Kcorrection
13、factors.3.2.5 K1,K2constants depending on b.3.2.6 Lspecimen thickness, m.3.2.7 tresponse time, s.3.2.8 t12 half-rise time or time required for the rear facetemperature rise to reach one half of its maximum value, s.3.2.9 t*dimensionless time (t*=4ast/DT2).3.2.10 Ttemperature, K.3.2.11 athermal diffu
14、sivity, m2s-1.3.2.12 bfraction of pulse duration required to reachmaximum intensity.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 Dec. 1, 2011. Pub
15、lished February 2012. Originallyapproved in 1992. Last previous edition approved in 2007 as E1461 07. DOI:10.1520/E1461-11.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, re
16、fer 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.3.2.13 rdensity, kgm-3.3.2.14 lthermal conductivity, Wm-1K-1.3.2.15 Dt5T (5t12 )/T (t12 ).3.2.16 Dt10T (10t12 )/T (t12 ).3.
17、2.17 DTmaxtemperature difference between baseline andmaximum rise, K.3.3 Description of Subscripts Specific to This Standard:3.3.1 oambient.3.3.2 sspecimen.3.3.3 Tthermocouple.3.3.4 xpercent rise.3.3.5 CCowan.3.3.6 Rratio.3.3.7 mmaximum.3.3.8 ttime.4. Summary of Test Method4.1 A small, thin disc spe
18、cimen is subjected to a high-intensity short duration radiant energy pulse (Fig. 1). Theenergy of the pulse is absorbed on the front surface of thespecimen and the resulting rear face temperature rise (thermo-gram) is recorded. The thermal diffusivity value is calculatedfrom the specimen thickness a
19、nd the time required for the rearface temperature rise to reach certain percentages of itsmaximum value (Fig. 2). When the thermal diffusivity of thespecimen is to be determined over a temperature range, themeasurement must be repeated at each temperature of interest.This test method is described in
20、 detail in a number ofpublications (1, 2)3and review articles (3, 4, 5).Asummary ofthe theory can be found in Appendix X1.5. Significance and Use5.1 Thermal diffusivity is an important property, requiredfor such purposes under transient heat flow conditions, such asdesign applications, determination
21、 of safe operating tempera-ture, process control, and quality assurance.5.2 The flash method is used to measure values of thermaldiffusivity, a, of a wide range of solid materials. It isparticularly advantageous because of simple specimen geom-etry, small specimen size requirements, rapidity of meas
22、ure-ment and ease of handling5.3 Under certain strict conditions, specific heat capacity ofa homogeneous isotropic opaque solid specimen can be deter-mined when the method is used in a quantitative fashion (seeAppendix X2).5.4 Thermal diffusivity results, together with related valuesof specific heat
23、 capacity (Cp) and density (r) values, can beused in many cases to derive thermal conductivity (l), accord-ing to the relationship:l5aCpr. (1)6. Interferences6.1 In principle, the thermal diffusivity is obtained from thethickness of the specimen and from a characteristic timefunction describing the
24、propagation of heat from the frontsurface of the specimen to its back surface. The sources ofuncertainties in the measurement are associated with thespecimen itself, the temperature measurements, the perfor-mance of the detector and of the data acquisition system, thedata analysis and more specifica
25、lly the finite pulse time effect,the nonuniform heating of the specimen and the heat losses(radiative and conductive). These sources of uncertainty can beconsidered systematic, and should be carefully considered foreach experiment. Errors random in nature (noise, for example)can be best estimated by
26、 performing a large number of repeatexperiments. The relative standard deviation of the obtainedresults is a good representation of the random component of theuncertainty associated with the measurement. Guidelines inperforming a rigorous evaluation of these factors are given in(31).7. ApparatusThe
27、essential components of the apparatus are shown in Fig.3. These are the flash source, specimen holder, environmentalenclosure (optional), temperature response detector and record-ing device.7.1 The flash source may be a pulse laser, a flash lamp, orother device capable to generate a short duration p
28、ulse ofsubstantial energy. The duration of the pulse should be lessthan 2 % of the time required for the rear face temperature riseto reach one half of its maximum value (see Fig. 2), to keep theerror due to finite pulse width less than 0.5 %, if pulse widthcorrection (17, 18, 19) is not applied.7.1
29、.1 The energy of the pulse hitting the specimens surfacemust be spatially uniform in intensity.7.2 An environmental control chamber is required for mea-surements above and below room temperature.7.3 The detector can be a thermocouple, infrared detector,optical pyrometer, or any other sensor that can
30、 provide a linearelectrical output proportional to a small temperature rise. It3The boldface numbers given in parentheses refer to a list of references at theend of the text.FIG. 1 Schematic of the Flash MethodFIG. 2 Characteristic Thermogram for the Flash MethodE1461 112shall be capable of detectin
31、g 0.05 K change above thespecimens initial temperature. The detector and its associatedamplifier must have a response time not more than 2 % of thehalf-rise time value.7.4 The signal conditioner includes the electronic circuit tobias out the ambient temperature reading, spike filters, ampli-fiers, a
32、nd analog-to-digital converters.7.5 Data Recording:7.5.1 The data acquisition system must be of an adequatespeed to ensure that time resolution in determining half of themaximum temperature rise on the thermogram is at least 1 %,for the fastest thermogram for which the system is qualified.7.6 Measur
33、ement of specimens temperature is to be doneby accepted means, such as calibrated thermocouple, opticalpyrometer, platinum RTD, etc. whichever is appropriate for thetemperature range. In all cases, such a device must be inintimate contact with or trained on the sample holder, in closeproximity of th
34、e specimen. Touching the specimen withthermocouples is not recommended. Embedding thermo-couples into the specimen is not acceptable.7.7 The temperature controller and/or programmer are tobring the specimen to the temperatures of interest.8. Test Specimen8.1 The usual specimen is a thin circular dis
35、c with a frontsurface area less than that of the energy beam. Typically,specimens are 10 to 12.5 mm in diamete (in special cases, assmall as 6 mm diameter and as large as 30 mm diameter havebeen reported as used successfully). The optimum thicknessdepends upon the magnitude of the estimated thermal
36、diffusiv-ity, and should be chosen so that the time to reach half of themaximum temperature falls within the 10 to 1000 ms range.Thinner specimens are desired at higher temperatures tominimize heat loss corrections; however, specimens shouldalways be thick enough to be representative of the test mat
37、erial.Typically, thicknesses are in the 1 to 6 mm range.8.2 Specimens must be prepared with faces flat and parallelwithin 0.5 % of their thickness, in order to keep the error inthermal diffusivity due to the measurement average thickness,to less than 1 %. Non-uniformity of either surface (craters,sc
38、ratches, markings) of significant depth compared to thespecimen thickness should be avoided8.3 Specimen Surface PreparationIt is a good practice toapply a very thin, uniform graphite or other high emissivitycoating on both faces of the specimen to be tested, prior toperforming the measurements. The
39、coating may be applied byspraying, painting, sputtering, etc. This will improve thecapability of the specimen to absorb the energy applied,especially in case of highly reflective materials. For transparentmaterials, a layer of gold, silver, or other opaque materialsmust be deposited first, followed
40、by graphite coating. For someopaque reflective materials, grit blasting of the surface canprovide sufficient pulse absorption and emissivity, especially athigher temperatures, where coatings may not be stable or mayreact with the material.9. Calibration and Verification9.1 Calibrate the micrometer u
41、sed to measure the specimenthickness, so that the thickness measurements are accurate towithin 0.2 %.9.2 The Flash Method is an absolute (primary) method byitself, therefore it requires no calibration. However, actualexecution of the measurement itself is subject to random andsystematic errors. It i
42、s therefore important to periodicallyverify the performance of a device, to establish the extent theseerrors may affect the data generated. This can be accomplishedby testing one or several materials whose thermal diffusivity iswell known. While most materials used are not true certifiedstandards, t
43、hey are generally accepted industry-wide with thebest available literature data (see Appendix X3).9.2.1 It must be emphasized that the use of referencematerials to establish validity of the data on unknown materialshas often led to unwarranted statements on accuracy. The useof references is only val
44、id when the properties of the reference(including half-rise times and thermal diffusivity values) areclosely similar to those of the unknown and the temperature-rise curves are determined in an identical manner for thereference and unknown.9.2.2 One important check of the validity of data (inadditio
45、n to the comparison of the rise curve with the theoreticalmodel), when corrections have been applied, is to vary thespecimen thickness. Since the half times vary as L2, decreasingthe specimen thickness by one-half should decrease the halftime to one-fourth of its original value. Thus, if one obtains
46、 thesame thermal diffusivity value (appropriate heat loss correc-tions being applied) with representative specimens from thesame material of significantly different thicknesses, the resultscan be assumed valid.10. Procedure10.1 For commercially produced systems, follow manufac-turers instructions.FI
47、G. 3 Block Diagram of a Flash SystemE1461 11310.2 The testing procedure must contain the followingfunctions:10.2.1 Determine and record the specimen thickness.10.2.2 Mount the specimen in its holder.10.2.3 Establish vacuum or inert gas environment in thechamber if necessary.10.2.4 Determine specimen
48、 temperature unless the systemwill do it automatically.10.2.5 Especially at low temperatures, use the lowest levelof power for the energy pulse able to generate a measurabletemperature rise, in order to ensure that the detector functionswithin its linear range.10.2.6 After the pulse delivery, monito
49、r the raw or pro-cessed thermogram to establish in-range performance. In caseof multiple specimen testing, it is advisable (for time economy)to sequentially test specimens at the same temperature (includ-ing replicate tests) before proceeding to the next test tempera-ture.10.2.7 In all cases, the temperature stability (base line) priorand during a test must be verified either manually or automati-cally to be less than 4 % of the maximum temperature rise.Testing on a ramp is not recommended.10.2.8 Determine the specimen ambient temperatur
