ASTM E2582-07(2014)

Standard Practice for Infrared Flash Thermography of Composite Panels and Repair Patches Used in Aerospace Applications

SIGNIFICANCE AND USE
5.1 FT is typically used to identify flaws that occur in the manufacture of composite structures, or to track flaw development during service. Flaws detected with FT include delamination, disbonds, voids, inclusions, foreign object debris, porosity or the presence of water that is in contact with the back surface. With dedicated signal processing and the use of representative test samples, characterization of flaw depth and size, or measurement of component thickness and thermal diffusivity may be performed.  
5.2 Since FT is based on the diffusion of thermal energy from the inspection surface of the specimen to the opposing surface (or the depth plane of interest), the practice requires that data acquisition allows sufficient time for this process to occur, and that at the completion of the acquisition process, the radiated surface temperature signal collected by the IR camera is strong enough to be distinguished from spurious IR contributions from background sources or system noise.  
5.3 This method is based on accurate detection of changes in the emitted IR energy emanating from the inspection surface during the cooling process. As the emissivity of the inspection surface deviates from ideal blackbody behavior (emissivity = 1), the signal detected by the IR camera may include components that are reflected from the inspection surface. Most composite materials can be examined without special surface preparation. However, it may be necessary to coat low-emissivity, optically translucent inspection surfaces with an optically opaque, high-emissivity water-washable paint.  
5.4 This practice applies to the detection of flaws with aspect ratio greater than one.  
5.5 This practice is based on the thermal response of a specimen to a light pulse that is uniformly distributed over the plane of the inspection surface. To ensure that 1- dimensional heat flow from the surface into the sample is the primary cooling mechanism during the data acquisition period, the height ...
SCOPE
1.1 This practice describes a procedure for detecting subsurface flaws in composite panels and repair patches using Flash Thermography (FT), in which an infrared (IR) camera is used to detect anomalous cooling behavior of a sample surface after it has been heated with a spatially uniform light pulse from a flash lamp array.  
1.2 This practice describes established FT test methods that are currently used by industry, and have demonstrated utility in quality assurance of composite structures during post-manufacturing and in-service examinations.  
1.3 This practice has utility for testing of polymer composite panels and repair patches containing, but not limited to, bismaleimide, epoxy, phenolic, poly(amide imide), polybenzimidazole, polyester (thermosetting and thermoplastic), poly(ether ether ketone), poly(ether imide), polyimide (thermosetting and thermoplastic), poly(phenylene sulfide), or polysulfone matrices; and alumina, aramid, boron, carbon, glass, quartz, or silicon carbide fibers. Typical as-fabricated geometries 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 matrix composite panels containing, but not limited to, silicon carbide, silicon nitride and carbon matrix and fibers.  
1.5 This practice applies to polymer or ceramic matrix composite structures with inspection surfaces that are sufficiently optically opaque to absorb incident light, and that have sufficient emissivity to allow monitoring of the surface temperature with an IR camera. Excessively thick samples, or samples with low thermal diffusivities, require long acquisition periods and yield weak signals approaching background and noise levels, and may be impractical for this technique.  
1.6 This practice applies to detection of flaws in a composite panel or repair patch, or at the bonded interface between the panel and a supporting sa...

General Information

• Status: Historical
• Publication Date: 30-Sep-2014
• ICS: 49.035 - Components for aerospace construction
• Technical Committee: E07 - Nondestructive Testing
• Drafting Committee: E07.10 - Specialized NDT Methods

Relations

• Replaces: ASTM E2582-07 - Standard Practice for Infrared Flash Thermography of Composite Panels and Repair Patches Used in Aerospace Applications
• Effective Date: 01-Oct-2014
• Referred By: ASTM E3353-22 - Standard Guide for In-Process Monitoring Using Optical and Thermal Methods for Laser Powder Bed Fusion
• Effective Date: 01-Oct-2014
• Referred By: ASTM E2533-21 - Standard Guide for Nondestructive Examination of Polymer Matrix Composites Used in Aerospace Applications
• Effective Date: 01-Oct-2014
• Referred By: ASTM E2981-21 - Standard Guide for Nondestructive Examination of Composite Overwraps in Filament Wound Pressure Vessels Used in Aerospace Applications
• Effective Date: 01-Oct-2014

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: E2582 − 07 (Reapproved 2014)
Standard Practice for
Infrared Flash Thermography of Composite Panels and
Repair Patches Used in Aerospace Applications
This standard is issued under the fixed designation E2582; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript 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. Scope 1.6 Thispracticeappliestodetectionofflawsinacomposite
panel or repair patch, or at the bonded interface between the
1.1 This practice describes a procedure for detecting sub-
panel and a supporting sandwich core or solid substrate. It does
surface flaws in composite panels and repair patches using
not apply to discontinuities in the sandwich core, or at the
Flash Thermography (FT), in which an infrared (IR) camera is
interface between the sandwich core and a second panel on the
used to detect anomalous cooling behavior of a sample surface
far side of the core (with respect to the inspection apparatus).
after it has been heated with a spatially uniform light pulse
from a flash lamp array. 1.7 This practice does not specify accept-reject criteria and
is not intended to be used as a basis for approving composite
1.2 This practice describes established FT test methods that
structures for service.
are currently used by industry, and have demonstrated utility in
1.8 This standard does not purport to address all of the
quality assurance of composite structures during post-
safety concerns, if any, associated with its use. It is the
manufacturing and in-service examinations.
responsibility of the user of this standard to establish appro-
1.3 This practice has utility for testing of polymer compos-
priate safety and health practices and determine the applica-
ite panels and repair patches containing, but not limited to,
bility of regulatory limitations prior to use.
bismaleimide, epoxy, phenolic, poly(amide imide),
polybenzimidazole, polyester (thermosetting and
2. Referenced Documents
thermoplastic), poly(ether ether ketone), poly(ether imide),
2.1 ASTM Standards:
polyimide (thermosetting and thermoplastic), poly(phenylene
D3878 Terminology for Composite Materials
sulfide), or polysulfone matrices; and alumina, aramid, boron,
E1316 Terminology for Nondestructive Examinations
carbon, glass, quartz, or silicon carbide fibers. Typical as-
fabricated geometries include uniaxial, cross ply and angle ply
3. Terminology
laminates; as well as honeycomb core sandwich core materials.
3.1 Definitions—Terminology in accordance with Termi-
1.4 This practice has utility for testing of ceramic matrix
nologies D3878 and E1316 and shall be used where applicable.
compositepanelscontaining,butnotlimitedto,siliconcarbide,
silicon nitride and carbon matrix and fibers.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 aspect ratio—the diameter to depth ratio of a flaw. For
1.5 This practice applies to polymer or ceramic matrix
irregularlyshapedflaws,diameterreferstotheminoraxisofan
composite structures with inspection surfaces that are suffi-
equivalent rectangle that approximates the flaw shape and area.
ciently optically opaque to absorb incident light, and that have
sufficient emissivity to allow monitoring of the surface tem-
3.2.2 discrete discontinuity—a thermal discontinuity whose
perature with an IR camera. Excessively thick samples, or
projection onto the inspection surface is smaller than the field
samples with low thermal diffusivities, require long acquisition
of view of the inspection apparatus.
periods and yield weak signals approaching background and
3.2.3 extended discontinuity—a thermal discontinuity
noise levels, and may be impractical for this technique.
whose projection onto the inspection surface completely fills
the field of view of the inspection apparatus.
This practice is under the jurisdiction of ASTM Committee E07 on Nonde-
structive Testing and is the direct responsibility of Subcommittee E07.10 on
Specialized NDT Methods. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Oct. 1, 2014. Published November 2014. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 2007. Last previous edition approved in 2007 as E2582-07. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/E2582-07R14. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2582 − 07 (2014)
3.2.4 first logarithmic derivative—the rate of change of the 5. Significance and Use
natural logarithm of temperature (with preflash temperature
5.1 FT is typically used to identify flaws that occur in the
subtracted) with respect to the natural logarithm of time.
manufacture of composite structures, or to track flaw develop-
3.2.5 inspection surface—the surface of the specimen that is ment during service. Flaws detected with FT include
delamination, disbonds, voids, inclusions, foreign object
exposed to the FT apparatus.
debris, porosity or the presence of water that is in contact with
3.2.6 logarithmic temperature-time plot—a plot of the natu-
the back surface. With dedicated signal processing and the use
ral logarithm of the surface temperature with preflash tempera-
of representative test samples, characterization of flaw depth
ture subtracted on the y-axis versus the natural logarithm of
and size, or measurement of component thickness and thermal
time on the x-axis, where time t=0 is taken to be the midpoint
diffusivity may be performed.
of the flash event. Either temperature or radiance may be used
5.2 Since FT is based on the diffusion of thermal energy
to create the plot.
from the inspection surface of the specimen to the opposing
3.2.7 log plot—see logarithmic temperature-time plot.
surface (or the depth plane of interest), the practice requires
3.2.8 second logarithmic derivative—the rate of change of
that data acquisition allows sufficient time for this process to
the first logarithmic derivative with respect to the natural
occur, and that at the completion of the acquisition process, the
logarithm of time.
radiated surface temperature signal collected by the IR camera
is strong enough to be distinguished from spurious IR contri-
3.2.9 thermal diffusivity—the ratio of thermal conductivity
butions from background sources or system noise.
totheproductofdensityandspecificheat;ameasureoftherate
at which heat propagates in a material; units [length /time]. 5.3 This method is based on accurate detection of changes
in the emitted IR energy emanating from the inspection surface
3.2.10 thermal discontinuity—a change in the thermophysi-
during the cooling process.As the emissivity of the inspection
cal properties of a specimen that disrupts the diffusion of heat.
surface deviates from ideal blackbody behavior (emissivity =
1), the signal detected by the IR camera may include compo-
4. Summary of Practice
nents that are reflected from the inspection surface. Most
4.1 In FT, a brief pulse of light energy from a flash lamp
composite materials can be examined without special surface
arrayheatstheinspectionsurfaceofacompositespecimen,and
preparation. However, it may be necessary to coat low-
an IR camera monitors the surface temperature (or radiance) as
emissivity, optically translucent inspection surfaces with an
the sample cools. The surface temperature falls predictably as
optically opaque, high-emissivity water-washable paint.
heat from the surface diffuses into the sample bulk. However,
5.4 This practice applies to the detection of flaws with
internal thermal discontinuities (for example, voids, delamina-
aspect ratio greater than one.
tionsorawallorinterfacebetweenthehostmaterialandavoid
5.5 This practice is based on the thermal response of a
or inclusion) modify the local cooling of the surface, and the
specimen to a light pulse that is uniformly distributed over the
corresponding radiation flux from the surface that is detected
plane of the inspection surface. To ensure that 1- dimensional
by the IR camera.
heat flow from the surface into the sample is the primary
4.2 Fundamental detectability of a flaw will depend on its
cooling mechanism during the data acquisition period, the
size,depth,andthedegreetowhichitsthermalpropertiesdiffer
height and width dimensions of the heated area should be
from those of the surrounding host material. For a given
significantly greater than the thickness of the specimen, or the
flaw-host combination, detectability is a function of the aspect
depth plane of interest.
ratio of the flaw. The minimum detectable flaw size increases
5.6 This practice applies to flat panels, or to curved panels
with the depth of the flaw. Detectability is highest for larger
where the local surface normal is less than 30 degrees from the
flaws that are closer to the sample surface and have thermal
IR camera optical axis
properties that are significantly different from the host matrix
material.
6. Equipment and Materials
4.3 Operational parameters affecting detectability include 6.1 IR Camera—The camera should be capable of uninter-
rupted monitoring of the sample surface for the entire duration
component surface emissivity and optical reflectivity, data
acquisition period, flash lamp energy, and camera wavelength, of the acquisition. Cameras with automatic internal shuttering
mechanisms should allow the shuttering to be disabled during
frame rate, sensitivity, optics and spatial resolution.
the data acquisition period. The camera should provide real-
4.4 This practice describes a single-side access
time digital output of the acquired signal. The camera output
examination, in which the flash lamp array (excitation source)
signal should be approximately linear over the (post-flash)
and IR camera (temperature sensor) are both located on the
temperature range of the sample. The camera wavelength
same (inspection) side of the component or material under
should be in either the 2-5 micron range or the 8-14 micron
examination.
range, selected such that the test material is not IR translucent
4.5 In common practice, signal processing algorithms are in the spectral range of the camera. The optics and focal plane
used to enhance detectability of flaws that are not detectable in should be sufficient so that the projection of nine contiguous
the raw IR camera signal, and to assist in evaluation and pixels onto the sample plane is less than or equal to the
characterization of indications. minimum flaw area that is to be detected.
E2582 − 07 (2014)
6.2 Flash Lamp Array—At least one flash lamp should be 7.1.6 Known flaws should be arranged so that the edges of
employed to provide uniform illumination to the sample each flaw are at least one diameter from the edge of the test
surface. The full width at half maximum duration of the flash sample.
pulse should be less than or approximately five milliseconds. 7.1.7 If a test standard containing actual or simulated flaws
The array should be placed to avoid a direct path of the flash
isnotavailable,onemaybeconstructedusingflatbottomholes
energy into the IR camera lens opening. The lamps should be machined into the back side of the panel. It should be
enclosed in a reflector and covered by an optically transparent
recognized that flat bottom holes represent a best case scenario
window that suppresses IR radiation in the camera wavelength for detectability, where no heat transfer through the flaw
range (for example, borosilicate glass). The flash lamp array
occurs. Actual flaws are likely to be less detectable.
should be enclosed in a protective hood to prevent workers in
7.2 Uniformity Standard—Uniformity of the distribution of
the inspection area from direct exposure to the flash, or
light from the flash lamp array may be determined with
alternately, the apparatus should be operated in a partitioned
aluminum plate reference standard.
area with appropriate safety warnings to prevent inadvertent
7.2.1 Aluminum plate thickness should be 3 mm.
exposure.
7.2.2 The plate surface should fully cover the field of view
6.3 Acquisition System—The acquisition system includes
of the apparatus.
the IR camera, flash lamps and a dedicated computer that is
7.2.3 The examination surface of the plate should have a
interfaced to both the camera and flash lamps. The acquisition
uniform high emissivity finish (for example, flat black paint).
systemshouldbecapableofsynchronizingthetriggeringofthe
Under static conditions, the paint coating should appear uni-
flash lamps and IR camera data acquisition. The system should
form when viewed with an IR camera.
allow data to be acquired before, during and after the flash
occurs.
8. Calibration and Standardization of Apparatus
6.4 Analysis Software—The computer software should al-
8.1 Calibration—The IR camera should be calibrated and
low acquired sequences to be archived and retrieved for
maintained at regular intervals, following the procedure rec-
evaluation, and allow real time display of the IR camera signal,
ommended by the manufacturer. Non-uniformity or flat field
as well as frame-by-frame display of previously acquired flash
correction should be performed according to the manufactur-
sequences which have been archived. The software should
er’s instructions, or more frequently, if required to achieve
allow viewing of the logarithmic temperature-time for speci-
optimum camera performance.
fied pixels. Additional processing operations on each raw
8.2 Measure the dimensions of a single pixel field of view at
image sequence (for example, averaging, preflash image
the sample plane by placing an object with known dimensions
subtraction, noise-reduction, calculation of first or second time
in the field of view at the sample plane, and determining the
derivatives) may be performed to improve detectability of
number of pixels that span the object in either the horizontal or
subsurface features.
vertical direction.
7. Reference Standards
object length
Pixel field of view size 5
number of pixels
7.1 Detectability Standard—A reference standard with
known thermal discontinuities is used to establish operating
8.3 Standardization—Operating parameters for FT inspec-
parameters of the apparatus and limits of detectability for a
tion will vary with the thickness, surface characteristics and
particular application, and to periodically verify proper perfor-
composition of the component under test, as well as the
mance of the apparatus.
geometry and thermophysical characteristics
...

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. Because
it 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 version
of the standard as published by ASTM is to be considered the official document.
Designation: E2582 − 07 E2582 − 07 (Reapproved 2014)
Standard Practice for
Infrared Flash Thermography of Composite Panels and
Repair Patches Used in Aerospace Applications
This standard is issued under the fixed designation E2582; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript 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. Scope
1.1 This practice describes a procedure for detecting subsurface flaws in composite panels and repair patches using Flash
Thermography (FT), in which an infrared (IR) camera is used to detect anomalous cooling behavior of a sample surface after it
has been heated with a spatially uniform light pulse from a flash lamp array.
1.2 This practice describes established FT test methods that are currently used by industry, and have demonstrated utility in
quality assurance of composite structures during post-manufacturing and in-service examinations.
1.3 This practice has utility for testing of polymer composite panels and repair patches containing, but not limited to,
bismaleimide, epoxy, phenolic, poly(amide imide), polybenzimidazole, polyester (thermosetting and thermoplastic), poly(ether
ether ketone), poly(ether imide), polyimide (thermosetting and thermoplastic), poly(phenylene sulfide), or polysulfone matrices;
and alumina, aramid, boron, carbon, glass, quartz, or silicon carbide fibers. Typical as-fabricated geometries 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 matrix composite panels containing, but not limited to, silicon carbide, silicon
nitride and carbon matrix and fibers.
1.5 This practice applies to polymer or ceramic matrix composite structures with inspection surfaces that are sufficiently
optically opaque to absorb incident light, and that have sufficient emissivity to allow monitoring of the surface temperature with
an IR camera. Excessively thick samples, or samples with low thermal diffusivities, require long acquisition periods and yield weak
signals approaching background and noise levels, and may be impractical for this technique.
1.6 This practice applies to detection of flaws in a composite panel or repair patch, or at the bonded interface between the panel
and a supporting sandwich core or solid substrate. It does not apply to discontinuities in the sandwich core, or at the interface
between the sandwich core and a second panel on the far side of the core (with respect to the inspection apparatus).
1.7 This practice does not specify accept-reject criteria and is not intended to be used as a basis for approving composite
structures for service.
1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
D3878 Terminology for Composite Materials
E1316 Terminology for Nondestructive Examinations
3. Terminology
3.1 Definitions—Terminology in accordance with Terminologies D3878 and E1316 and shall be used where applicable.
3.2 Definitions of Terms Specific to This Standard:
This practice is under the jurisdiction of ASTM Committee E07 on Nondestructive Testing and is the direct responsibility of Subcommittee E07.10 on Specialized NDT
Methods.
Current edition approved July 1, 2007Oct. 1, 2014. Published July 2007November 2014. Originally approved in 2007. Last previous edition approved in 2007 as E2582-07.
DOI: 10.1520/E2582-07.10.1520/E2582-07R14.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2582 − 07 (2014)
3.2.1 aspect ratio—the diameter to depth ratio of a flaw. For irregularly shaped flaws, diameter refers to the minor axis of an
equivalent rectangle that approximates the flaw shape and area.
3.2.2 discrete discontinuity—a thermal discontinuity whose projection onto the inspection surface is smaller than the field of
view of the inspection apparatus.
3.2.3 extended discontinuity—a thermal discontinuity whose projection onto the inspection surface completely fills the field of
view of the inspection apparatus.
3.2.4 first logarithmic derivative—the rate of change of the natural logarithm of temperature (with preflash temperature
subtracted) with respect to the natural logarithm of time.
3.2.5 inspection surface—the surface of the specimen that is exposed to the FT apparatus.
3.2.6 logarithmic temperature-time plot—a plot of the natural logarithm of the surface temperature with preflash temperature
subtracted on the y-axis versus the natural logarithm of time on the x-axis, where time t=0 is taken to be the midpoint of the flash
event. Either temperature or radiance may be used to create the plot.
3.2.7 log plot—see logarithmic temperature-time plot.
3.2.8 second logarithmic derivative—the rate of change of the first logarithmic derivative with respect to the natural logarithm
of time.
3.2.9 thermal diffusivity—the ratio of thermal conductivity to the product of density and specific heat; a measure of the rate at
which heat propagates in a material; units [length /time].
3.2.10 thermal discontinuity—a change in the thermophysical properties of a specimen that disrupts the diffusion of heat.
4. Summary of Practice
4.1 In FT, a brief pulse of light energy from a flash lamp array heats the inspection surface of a composite specimen, and an
IR camera monitors the surface temperature (or radiance) as the sample cools. The surface temperature falls predictably as heat
from the surface diffuses into the sample bulk. However, internal thermal discontinuities (for example, voids, delaminations or a
wall or interface between the host material and a void or inclusion) modify the local cooling of the surface, and the corresponding
radiation flux from the surface that is detected by the IR camera.
4.2 Fundamental detectability of a flaw will depend on its size, depth, and the degree to which its thermal properties differ from
those of the surrounding host material. For a given flaw-host combination, detectability is a function of the aspect ratio of the flaw.
The minimum detectable flaw size increases with the depth of the flaw. Detectability is highest for larger flaws that are closer to
the sample surface and have thermal properties that are significantly different from the host matrix material.
4.3 Operational parameters affecting detectability include component surface emissivity and optical reflectivity, data acquisition
period, flash lamp energy, and camera wavelength, frame rate, sensitivity, optics and spatial resolution.
4.4 This practice describes a single-side access examination, in which the flash lamp array (excitation source) and IR camera
(temperature sensor) are both located on the same (inspection) side of the component or material under examination.
4.5 In common practice, signal processing algorithms are used to enhance detectability of flaws that are not detectable in the
raw IR camera signal, and to assist in evaluation and characterization of indications.
5. Significance and Use
5.1 FT is typically used to identify flaws that occur in the manufacture of composite structures, or to track flaw development
during service. Flaws detected with FT include delamination, disbonds, voids, inclusions, foreign object debris, porosity or the
presence of water that is in contact with the back surface. With dedicated signal processing and the use of representative test
samples, characterization of flaw depth and size, or measurement of component thickness and thermal diffusivity may be
performed.
5.2 Since FT is based on the diffusion of thermal energy from the inspection surface of the specimen to the opposing surface
(or the depth plane of interest), the practice requires that data acquisition allows sufficient time for this process to occur, and that
at the completion of the acquisition process, the radiated surface temperature signal collected by the IR camera is strong enough
to be distinguished from spurious IR contributions from background sources or system noise.
5.3 This method is based on accurate detection of changes in the emitted IR energy emanating from the inspection surface
during the cooling process. As the emissivity of the inspection surface deviates from ideal blackbody behavior (emissivity = 1),
the signal detected by the IR camera may include components that are reflected from the inspection surface. Most composite
materials can be examined without special surface preparation. However, it may be necessary to coat low-emissivity, optically
translucent inspection surfaces with an optically opaque, high-emissivity water-washable paint.
5.4 This practice applies to the detection of flaws with aspect ratio greater than one.
E2582 − 07 (2014)
5.5 This practice is based on the thermal response of a specimen to a light pulse that is uniformly distributed over the plane of
the inspection surface. To ensure that 1- dimensional heat flow from the surface into the sample is the primary cooling mechanism
during the data acquisition period, the height and width dimensions of the heated area should be significantly greater than the
thickness of the specimen, or the depth plane of interest.
5.6 This practice applies to flat panels, or to curved panels where the local surface normal is less than 30 degrees from the IR
camera optical axis
6. Equipment and Materials
6.1 IR Camera—The camera should be capable of uninterrupted monitoring of the sample surface for the entire duration of the
acquisition. Cameras with automatic internal shuttering mechanisms should allow the shuttering to be disabled during the data
acquisition period. The camera should provide real-time digital output of the acquired signal. The camera output signal should be
approximately linear over the (post-flash) temperature range of the sample. The camera wavelength should be in either the 2-5
micron range or the 8-14 micron range, selected such that the test material is not IR translucent in the spectral range of the camera.
The optics and focal plane should be sufficient so that the projection of nine contiguous pixels onto the sample plane is less than
or equal to the minimum flaw area that is to be detected.
6.2 Flash Lamp Array—At least one flash lamp should be employed to provide uniform illumination to the sample surface. The
full width at half maximum duration of the flash pulse should be less than or approximately five milliseconds. The array should
be placed to avoid a direct path of the flash energy into the IR camera lens opening. The lamps should be enclosed in a reflector
and covered by an optically transparent window that suppresses IR radiation in the camera wavelength range (for example,
borosilicate glass). The flash lamp array should be enclosed in a protective hood to prevent workers in the inspection area from
direct exposure to the flash, or alternately, the apparatus should be operated in a partitioned area with appropriate safety warnings
to prevent inadvertent exposure.
6.3 Acquisition System—The acquisition system includes the IR camera, flash lamps and a dedicated computer that is interfaced
to both the camera and flash lamps. The acquisition system should be capable of synchronizing the triggering of the flash lamps
and IR camera data acquisition. The system should allow data to be acquired before, during and after the flash occurs.
6.4 Analysis Software—The computer software should allow acquired sequences to be archived and retrieved for evaluation, and
allow real time display of the IR camera signal, as well as frame-by-frame display of previously acquired flash sequences which
have been archived. The software should allow viewing of the logarithmic temperature-time for specified pixels. Additional
processing operations on each raw image sequence (for example, averaging, preflash image subtraction, noise-reduction,
calculation of first or second time derivatives) may be performed to improve detectability of subsurface features.
7. Reference Standards
7.1 Detectability Standard—A reference standard with known thermal discontinuities is used to establish operating parameters
of the apparatus and limits of detectability for a particular application, and to periodically verify proper performance of the
apparatus.
7.1.1 Known discontinuities may be actual flaws, or artificial features that simulate the thermophysical behavior of typical flaws
that are known to occur in the structure of interest.
7.1.2 At least five known flaws of a particular type should be included in the reference standard. The known flaws should
represent the range of aspect ratios for anticipated flaws, and should include the minimum required detectable flaw size for a given
application, as determined by the cognizant engineering organization.
7.1.3 If the minimum detectable flaw size requirement is not known, the reference standard should include at least five known
flaws of a given type, spanning the range of aspect ratios from 0.5 to 10.
7.1.4 If different types of known flaws are to be used, at least five instances of each type should be included.
7.1.5 Known flaws should be arranged so that edge-to-edge separation of adjacent flaws is at least one diameter of the larger
neighboring flaw.
7.1.6 Known flaws should be arranged so that the edges of each flaw are at least one diameter from the edge of the test sample.
7.1.7 If a test standard containing actual or simulated flaws is not available, one may be constructed using flat bottom holes
machined into the back side of the panel. It should be recognized that flat bottom holes represent a best case scenario for
detectability, where no heat transfer through the flaw occurs. Actual flaws are likely to be less detectable.
7.2 Uniformity Standard—Uniformity of the distribution of light from the flash
...