1、Designation: E 2582 07Standard Practice forInfrared Flash Thermography of Composite Panels andRepair Patches Used in Aerospace Applications1This standard is issued under the fixed designation E 2582; the number immediately following the designation indicates the year oforiginal adoption or, in the c
2、ase of revision, the year 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.1. Scope1.1 This practice describes a procedure for detecting sub-surface flaws in composite panels
3、and repair patches usingFlash Thermography (FT), in which an infrared (IR) camera isused to detect anomalous cooling behavior of a sample surfaceafter it has been heated with a spatially uniform light pulsefrom a flash lamp array.1.2 This practice describes established FT test methods thatare curren
4、tly used by industry, and have demonstrated utility inquality assurance of composite structures during post-manufacturing and in-service examinations.1.3 This practice has utility for testing of polymer compos-ite panels and repair patches containing, but not limited to,bismaleimide, epoxy, phenolic
5、, poly(amide imide), polybenz-imidazole, polyester (thermosetting and thermoplastic), poly-(ether ether ketone), poly(ether imide), polyimide (thermoset-ting and thermoplastic), poly(phenylene sulfide), orpolysulfone matrices; and alumina, aramid, boron, carbon,glass, quartz, or silicon carbide fibe
6、rs. Typical as-fabricatedgeometries include uniaxial, cross ply and angle ply laminates;as well as honeycomb core sandwich core materials.1.4 This practice has utility for testing of ceramic matrixcomposite panels containing, but not limited to, silicon carbide,silicon nitride and carbon matrix and
7、fibers.1.5 This practice applies to polymer or ceramic matrixcomposite structures with inspection surfaces that are suffi-ciently optically opaque to absorb incident light, and that havesufficient emissivity to allow monitoring of the surface tem-perature with an IR camera. Excessively thick samples
8、, orsamples with low thermal diffusivities, require long acquisitionperiods and yield weak signals approaching background andnoise levels, and may be impractical for this technique.1.6 This practice applies to detection of flaws in a compositepanel or repair patch, or at the bonded interface between
9、 thepanel and a supporting sandwich core or solid substrate. It doesnot apply to discontinuities in the sandwich core, or at theinterface between the sandwich core and a second panel on thefar side of the core (with respect to the inspection apparatus).1.7 This practice does not specify accept-rejec
10、t criteria andis not intended to be used as a basis for approving compositestructures for service.1.8 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
11、 practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 3878 Terminology for Composite MaterialsE 1316 Terminology for Nondestructive Examinations3. Terminology3.1 DefinitionsTerminology in accordance with Termi-nologies D 3878
12、and E 1316 and shall be used where appli-cable.3.2 Definitions of Terms Specific to This Standard:3.2.1 aspect ratiothe diameter to depth ratio of a flaw. Forirregularly shaped flaws, diameter refers to the minor axis of anequivalent rectangle that approximates the flaw shape and area.3.2.2 discrete
13、 discontinuitya thermal discontinuity whoseprojection onto the inspection surface is smaller than the fieldof view of the inspection apparatus.3.2.3 extended discontinuitya thermal discontinuitywhose projection onto the inspection surface completely fillsthe field of view of the inspection apparatus
14、.3.2.4 first logarithmic derivativethe rate of change of thenatural logarithm of temperature (with preflash temperaturesubtracted) with respect to the natural logarithm of time.3.2.5 inspection surfacethe surface of the specimen that isexposed to the FT apparatus.3.2.6 logarithmic temperature-time p
15、lota plot of the natu-ral logarithm of the surface temperature with preflash tempera-ture subtracted on the y-axis versus the natural logarithm oftime on the x-axis, where time t=0 is taken to be the midpointof the flash event. Either temperature or radiance may be usedto create the plot.1This pract
16、ice is under the jurisdiction of ASTM Committee E07 on Nonde-structive Testing and is the direct responsibility of Subcommittee E07.10 onEmerging NDT Methods.Current edition approved July 1, 2007. Published July 2007.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact AST
17、M Customer Service at serviceastm.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.3.2.7 log plotsee logarithmic
18、 temperature-time plot.3.2.8 second logarithmic derivativethe rate of change ofthe first logarithmic derivative with respect to the naturallogarithm of time.3.2.9 thermal diffusivitythe ratio of thermal conductivityto the product of density and specific heat; a measure of the rateat which heat propa
19、gates in a material; units length2/time.3.2.10 thermal discontinuitya change in the thermophysi-cal properties of a specimen that disrupts the diffusion of heat.4. Summary of Practice4.1 In FT, a brief pulse of light energy from a flash lamparray heats the inspection surface of a composite specimen,
20、 andan IR camera monitors the surface temperature (or radiance) asthe sample cools. The surface temperature falls predictably asheat from the surface diffuses into the sample bulk. However,internal thermal discontinuities (for example, voids, delamina-tions or a wall or interface between the host ma
21、terial and a voidor inclusion) modify the local cooling of the surface, and thecorresponding radiation flux from the surface that is detectedby the IR camera.4.2 Fundamental detectability of a flaw will depend on itssize, depth, and the degree to which its thermal properties differfrom those of the
22、surrounding host material. For a givenflaw-host combination, detectability is a function of the aspectratio of the flaw. The minimum detectable flaw size increaseswith the depth of the flaw. Detectability is highest for largerflaws that are closer to the sample surface and have thermalproperties tha
23、t are significantly different from the host matrixmaterial.4.3 Operational parameters affecting detectability includecomponent surface emissivity and optical reflectivity, dataacquisition period, flash lamp energy, and camera wavelength,frame rate, sensitivity, optics and spatial resolution.4.4 This
24、 practice describes a single-side access examina-tion, in which the flash lamp array (excitation source) and IRcamera (temperature sensor) are both located on the same(inspection) side of the component or material under examina-tion.4.5 In common practice, signal processing algorithms areused to enh
25、ance detectability of flaws that are not detectable inthe raw IR camera signal, and to assist in evaluation andcharacterization of indications.5. Significance and Use5.1 FT is typically used to identify flaws that occur in themanufacture of composite structures, or to track flaw develop-ment during
26、service. Flaws detected with FT include delami-nation, disbonds, voids, inclusions, foreign object debris,porosity or the presence of water that is in contact with theback surface. With dedicated signal processing and the use ofrepresentative test samples, characterization of flaw depth andsize, or
27、measurement of component thickness and thermaldiffusivity may be performed.5.2 Since FT is based on the diffusion of thermal energyfrom the inspection surface of the specimen to the opposingsurface (or the depth plane of interest), the practice requiresthat data acquisition allows sufficient time fo
28、r this process tooccur, and that at the completion of the acquisition process, theradiated surface temperature signal collected by the IR camerais strong enough to be distinguished from spurious IR contri-butions from background sources or system noise.5.3 This method is based on accurate detection
29、of changesin the emitted IR energy emanating from the inspection surfaceduring the cooling process. As the emissivity of the inspectionsurface deviates from ideal blackbody behavior (emissivity =1), the signal detected by the IR camera may include compo-nents that are reflected from the inspection s
30、urface. Mostcomposite materials can be examined without special surfacepreparation. However, it may be necessary to coat low-emissivity, optically translucent inspection surfaces with anoptically opaque, high-emissivity water-washable paint.5.4 This practice applies to the detection of flaws withasp
31、ect ratio greater than one.5.5 This practice is based on the thermal response of aspecimen to a light pulse that is uniformly distributed over theplane of the inspection surface. To ensure that 1- dimensionalheat flow from the surface into the sample is the primarycooling mechanism during the data a
32、cquisition period, theheight and width dimensions of the heated area should besignificantly greater than the thickness of the specimen, or thedepth plane of interest.5.6 This practice applies to flat panels, or to curved panelswhere the local surface normal is less than 30 degrees from theIR camera
33、optical axis6. Equipment and Materials6.1 IR CameraThe camera should be capable of uninter-rupted monitoring of the sample surface for the entire durationof the acquisition. Cameras with automatic internal shutteringmechanisms should allow the shuttering to be disabled duringthe data acquisition per
34、iod. The camera should provide real-time digital output of the acquired signal. The camera outputsignal should be approximately linear over the (post-flash)temperature range of the sample. The camera wavelengthshould be in either the 2-5 micron range or the 8-14 micronrange, selected such that the t
35、est material is not IR translucentin the spectral range of the camera. The optics and focal planeshould be sufficient so that the projection of nine contiguouspixels onto the sample plane is less than or equal to theminimum flaw area that is to be detected.6.2 Flash Lamp ArrayAt least one flash lamp
36、 should beemployed to provide uniform illumination to the samplesurface. The full width at half maximum duration of the flashpulse should be less than or approximately five milliseconds.The array should be placed to avoid a direct path of the flashenergy into the IR camera lens opening. The lamps sh
37、ould beenclosed in a reflector and covered by an optically transparentwindow that suppresses IR radiation in the camera wavelengthrange (for example, borosilicate glass). The flash lamp arrayshould be enclosed in a protective hood to prevent workers inthe inspection area from direct exposure to the
38、flash, oralternately, the apparatus should be operated in a partitionedarea with appropriate safety warnings to prevent inadvertentexposure.6.3 Acquisition SystemThe acquisition system includesthe IR camera, flash lamps and a dedicated computer that isinterfaced to both the camera and flash lamps. T
39、he acquisitionE2582072system should be capable of synchronizing the triggering of theflash lamps and IR camera data acquisition. The system shouldallow data to be acquired before, during and after the flashoccurs.6.4 Analysis SoftwareThe computer software should al-low acquired sequences to be archi
40、ved and retrieved forevaluation, and allow real time display of the IR camera signal,as well as frame-by-frame display of previously acquired flashsequences which have been archived. The software shouldallow viewing of the logarithmic temperature-time for speci-fied pixels. Additional processing ope
41、rations on each rawimage sequence (for example, averaging, preflash image sub-traction, noise-reduction, calculation of first or second timederivatives) may be performed to improve detectability ofsubsurface features.7. Reference Standards7.1 Detectability StandardA reference standard withknown ther
42、mal discontinuities is used to establish operatingparameters of the apparatus and limits of detectability for aparticular application, and to periodically verify proper perfor-mance of the apparatus.7.1.1 Known discontinuities may be actual flaws, or artifi-cial features that simulate the thermophys
43、ical behavior oftypical flaws that are known to occur in the structure ofinterest.7.1.2 At least five known flaws of a particular type shouldbe included in the reference standard. The known flaws shouldrepresent the range of aspect ratios for anticipated flaws, andshould include the minimum required
44、 detectable flaw size fora given application, as determined by the cognizant engineer-ing organization.7.1.3 If the minimum detectable flaw size requirement is notknown, the reference standard should include at least fiveknown flaws of a given type, spanning the range of aspectratios from 0.5 to 10.
45、7.1.4 If different types of known flaws are to be used, atleast five instances of each type should be included.7.1.5 Known flaws should be arranged so that edge-to-edgeseparation of adjacent flaws is at least one diameter of thelarger neighboring flaw.7.1.6 Known flaws should be arranged so that the
46、 edges ofeach flaw are at least one diameter from the edge of the testsample.7.1.7 If a test standard containing actual or simulated flawsis not available, one may be constructed using flat bottom holesmachined into the back side of the panel. It should berecognized that flat bottom holes represent
47、a best case scenariofor detectability, where no heat transfer through the flawoccurs. Actual flaws are likely to be less detectable.7.2 Uniformity StandardUniformity of the distribution oflight from the flash lamp array may be determined withaluminum plate reference standard.7.2.1 Aluminum plate thi
48、ckness should be 3 mm.7.2.2 The plate surface should fully cover the field of viewof the apparatus.7.2.3 The examination surface of the plate should have auniform high emissivity finish (for example, flat black paint).Under static conditions, the paint coating should appear uni-form when viewed with
49、 an IR camera.8. Calibration and Standardization of Apparatus8.1 CalibrationThe IR camera should be calibrated andmaintained at regular intervals, following the procedure rec-ommended by the manufacturer. Non-uniformity or flat fieldcorrection should be performed according to the manufactur-ers instructions, or more frequently, if required to achieveoptimum camera performance.8.2 Measure the dimensions of a single pixel field of view atthe sample plane by placing an object with known dimensionsin the field of view at the sample plane, and determining thenumber of pi
