1、Designation: E1461 11E1461 13Standard 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 nu
2、mber in 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 thermal diffusivity of primarily homogeneous isotropic solid materials.Thermal diffusivi
3、ty values ranging from 100.1-7 to 101000-3 m(mm)2s s-1 are measurable by this test method from about 75 to2800 K.1.2 Practice E2585 is adjunct to this Test Methodtest method and contains detailed information regarding the use of the flashmethod. The two documents are complementing each other.1.3 Thi
4、s test method is a more detailed form of Test Method C714, having applicability to much wider ranges of materials,applications, and temperatures, with improved accuracy of measurements.1.4 This test method is intended to allow a wide variety of apparatus designs. It is not practical in a test method
5、 of this typeto establish details of construction and procedures to cover all contingencies that might offer difficulties to a person withoutpertinent technical knowledge, or to stop or restrict research and development for improvements in the basic technique.1.5 This test method is applicable to th
6、e measurements performed on essentially fully dense (preferably, but low porosity wouldbe acceptable), homogeneeous,homogeneous, and isotropic solid materials that are opaque to the applied energy pulse. Experiencehas shown, however, shows that some deviation from these strict guidelines can be acco
7、mmodated with care and properexperimental design, substantially broadening the usefulness of the method.1.6 This test method can be considered an absolute (or primary) method of measurement, since no reference standards arerequired. It is advisable to use reference materials to verify the performanc
8、e of the instrument used.1.6 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.7 For systems employing lasers as power sources, it is imperative that the safety requirement be fully met.1.8 This standard does not purport to ad
9、dress 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 the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C714 Test Meth
10、od for Thermal Diffusivity of Carbon and Graphite by Thermal Pulse MethodE228 Test Method for Linear Thermal Expansion of Solid Materials With a Push-Rod DilatometerE2585 Practice for Thermal Diffusivity by the Flash Method3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 therma
11、l conductivity, , of a solid materialthe time rate of steady heat flow through unit thickness of an infinite slab ofa homogeneous material in a direction perpendicular to the surface, induced by unit temperature difference. The property must beidentified with a specific mean temperature, since it va
12、ries with temperature.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 Dec. 1, 2011Sept. 1, 2013. Published February 2012October 2013. Originally app
13、roved in 1992. Last previous edition approved in 20072011as E1461 07.E1461 11. DOI: 10.1520/E1461-11.10.1520/E1461-13.2 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
14、 the standards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes
15、 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 official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. Unite
16、d States13.1.2 thermal diffusivity, , of a solid materialthe property given by the thermal conductivity divided by the product of thedensity and heat capacity per unit mass.3.2 Description of Symbols and Units Specific to This Standard:3.2.1 Ddiameter, m.3.2.2 Cpspecific heat capacity, JkgJg-1K-1)3.
17、2.3 kconstant depending on percent rise.3.2.4 Kcorrection factors.3.2.5 K1, K2constants depending on .3.2.6 Lspecimen thickness, m.mm.3.2.7 tresponse time, s.3.2.8 t121/2half-rise time or time required for the rear face temperature rise to reach one half of its maximum value, s.3.2.9 t*dimensionless
18、 time (t* = 4s t/DT2).3.2.10 Ttemperature, K.3.2.11 thermal diffusivity, m(mm)2s/s.-1.3.2.12 fraction of pulse duration required to reach maximum intensity.3.2.13 density, kgmg/(cm)-33.3.2.14 thermal conductivity, Wm-1K-1.3.2.15 t5T(5t12) /T(t12).3.2.16 t10T(10t12) /T(t12).3.2.17 Tmaxtemperature dif
19、ference between baseline and maximum rise, K.3.2.18 pulse duration (see Fig. 1).3.3 Description of Subscripts Specific to This Standard:3.3.1 oambient.3.3.2 sspecimen.3.3.3 Tthermocouple.3.3.1 xpercent rise.3.3.5 CCowan.3.3.2 Rratio.3.3.3 mmaxmaximum.3.3.4 tptime.constant pressure.4. Summary of Test
20、 Method4.1 A small, thin disc specimen is subjected to a high-intensity short duration radiant energy pulse (Fig. 12). The energy of thepulse is absorbed on the front surface of the specimen and the resulting rear face temperature rise (thermogram) (thermal curve)is recorded. The thermal diffusivity
21、 value is calculated from the specimen thickness and the time required for the rear facetemperature rise to reach certain percentagesa percentage of its maximum value (Fig. 23). When the thermal diffusivity of thespecimen is to be determined over a temperature range, the measurement must be repeated
22、 at each temperature of interest. Thistest method is described in detail in a number of publications (1, 2) and review articles (3, 4, 5). A summary of the theory can befound in Appendix X1.FIG. 71 Laser Pulse ShapeE1461 132NOTE 1This test method is described in detail in a number of publications (1
23、, 2)3 and review articles (3, 4, 5).Asummary of the theory can be foundin Appendix X1.5. Significance and Use5.1 Thermal diffusivity is an important transient thermal property, required for such purposes under transient heat flowconditions, such as design applications, determination of safe operatin
24、g temperature, process control, and quality assurance.5.2 The flash method is used to measure values of thermal diffusivity, , of a wide range of solid materials. It is particularlyadvantageous because of simple specimen geometry, small specimen size requirements, rapidity of measurement and ease of
25、handlinghandling.5.3 Under certain strict conditions, specific heat capacity of a homogeneous isotropic opaque solid specimen can be determinedwhen the method is used in a quantitative fashion (see Appendix X2).5.4 Thermal diffusivity results, together with related values of specific heat capacity (
26、Cp) and density () values, can be usedin many cases to derive thermal conductivity (), according to the relationship:5Cp . (1)5Cp (1)6. Interferences6.1 In principle, the thermal diffusivity is obtained from the thickness of the specimen and from a characteristic time functiondescribing the propagat
27、ion of heat from the front surface of the specimen to its back surface. The sources of uncertainties in themeasurement are associated with the specimen itself, the temperature measurements, the performance of the detector and of thedata acquisition system, the data analysis and more specifically the
28、 finite pulse time effect, the nonuniform heating of the specimenand the heat losses (radiative and conductive). These sources of uncertainty can be considered systematic, and should be carefullyconsidered for each experiment. Errors random in nature (noise, for example) can be best estimated by per
29、forming a large numberof repeat experiments. The relative standard deviation of the obtained results is a good representation of the random componentof the uncertainty associated with the measurement. Guidelines in performing a rigorous evaluation of these factors are given in(6).3 The boldface numb
30、ers given in parentheses refer to a list of references at the end of the text.FIG. 12 Schematic of the Flash MethodFIG. 23 Characteristic Thermogram Thermal Curve for the Flash MethodE1461 1337. ApparatusThe essential components of the apparatus are shown in Fig. 34. These are the flash source, spec
31、imen holder, environmentalenclosure (optional), temperature response detector and recording device.7.1 The flash source may be a pulse laser, a flash lamp, or other device capable to generate a short duration pulse of substantialenergy. The duration of the pulse should be less than 2 % of the time r
32、equired for the rear face temperature rise to reach one halfof its maximum value (see Fig. 23), to keep the error due to finite pulse width less than 0.5 %, if pulse width correction ).(7, 8,9) is not applied.NOTE 2A pulse length correction may be applied (7, 8, 9) permitting use of pulse durations
33、greater than 0.5 %.7.1.1 The energy of the pulse hitting the specimens surface must be spatially uniform in intensity.7.2 An environmental control chamber is required for measurements above and below room temperature.7.3 The temperature detector can be a thermocouple, infrared detector, optical pyro
34、meter, or any other sensor that can providea linear electrical output proportional to a small temperature rise. It shall be capable of detecting 0.05 K change above thespecimens initial temperature. The detector and its associated amplifier must have a response time not more than 2 % of thehalf-rise
35、 time value.7.4 The signal conditioner includes the electronic circuit to bias out the ambient temperature reading, spike filters, amplifiers,and analog-to-digital converters.7.5 Data Recording:7.5.1 The data acquisition system must be of an adequate speed to ensure that time resolution in determini
36、ng half of themaximum temperature rise on the thermogram is at least 1 %, half-rise time on the thermal curve is no more than 1 % of thehalf-rise time, for the fastest thermogram thermal curve for which the system is qualified.7.6 Measurement of specimens temperature is to be done by accepted means,
37、 performed using calibrated temperature sensorssuch as calibrateda thermocouple, optical pyrometer, platinum RTD, etc. whichever is appropriate for the temperature range. In allcases, such a device must resistance temperature detector (RTD), etc. The temperature sensor shall be in intimate contact w
38、ith ortrained on the sample holder, in close proximity of the specimen. Touching the specimen with thermocouples is not recommended.Embedding thermocouples into the specimen is not acceptable.NOTE 3Touching the specimen with thermocouples is not recommended. Embedding thermocouples into the specimen
39、 is not acceptable.7.7 The temperature controller and/or programmer are to bring the specimen to the temperatures of interest.FIG. 34 Block Diagram of a Flash SystemE1461 1348. Test Specimen8.1 The usual specimen is a thin circular disc with a front surface area less than that of the energy beam. Ty
40、pically, specimensare 10 to 12.5 mm in diamete (in special cases, as small as 6 mm diameter and as large as 30 mm diameter have been reportedas used successfully). The optimum thickness depends upon the magnitude of the estimated thermal diffusivity, and should bechosen so that the time to reach hal
41、f of the maximum temperature falls within the 10 to 1000 ms range. Thinner specimens aredesired at higher temperatures to minimize heat loss corrections; however, specimens should always be thick enough to berepresentative of the test material. Typically, thicknesses are in the 1 to 6 mm range.8.2 S
42、pecimens must be prepared with faces flat and parallel within 0.5 % of their thickness, in order to keep the error in thermaldiffusivity due to the measurementmeasured average thickness, to less than 1 %. Non-uniformity of either surface (craters,scratches, markings) of significant depth compared to
43、 the specimen thickness should be avoided8.3 Specimen Surface PreparationIt is a good practice to apply a very thin, uniform graphite or other high emissivity coatingon both faces of the specimen to be tested, prior to performing the measurements. The coating may be applied by spraying,painting, spu
44、ttering, etc. This will improve the capability of the specimen to absorb the energy applied, especially in case of highlyreflective materials. For transparent materials, a layer of gold, silver, or other opaque materials must be deposited first, followedby graphite coating. For some opaque reflectiv
45、e materials, grit blasting of the surface can provide sufficient pulse absorption andemissivity, especially at higher temperatures, where coatings may not be stable or may react with the material.9. Calibration and Verification9.1 Calibrate the micrometer used to measure the specimen thickness, so t
46、hat the thickness measurements are accurate to within0.2 %.9.1 The Flash Method is an absolute (primary) method by itself, therefore it requires no calibration. However, actual executionof the measurement itself is subject to random and systematic errors. It is therefore It is important to periodica
47、lly verify theperformance of a device, device and to establish the extent these errors may affect the data generated. This can be accomplishedby testing one or several materials whose thermal diffusivity is well known. While most materials used are not true certifiedstandards, they are generally acc
48、epted industry-wide with the best available literature data known (see Appendix X3).9.1.1 It must be emphasized that the The use of reference materials to establish validity of the data on unknown materials hasoften led can lead to unwarranted statements on accuracy. The use of references is only va
49、lid when the properties of the reference(including half-rise times and thermal diffusivity values) are closely similar to those of the unknown and the temperature-risecurves are determined in an identical manner for the reference and unknown.9.1.2 OneAn important check of the validity of data (in addition to the comparison of the rise curve with the theoretical model),when corrections have been applied, is to vary the specimen thickness. Since the half times vary as L2, decreasing the specimenthickness b
