Active Thermography Maierhofer
Transcript of Active Thermography Maierhofer
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InnoTesting 2015 Active Thermography
Application of active thermography in production
processesChristiane Maierhofer, Mathias Ziegler, Rainer Krankenhagen,
Philipp Myrach, Florian JonietzBundesanstalt für Materialforschung und –prüfung
FB 8.7
Energy Infrastructure Environment Material
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InnoTesting 2015 Active Thermography
Content
• Principle of active thermography• Actual research for applications in production
processes: theory and experiment� Planar excitation: Comparison of flash and lockin
thermography
� Light weight constructions
� Join connections
� Local excitation: crack characterisation
� Large structures: Windmill and building structures
• Outlook: Standardisation
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Principle of active thermography
Flash thermography of an airplane side rudder
• Reflection configuration using 4 flashes from the front side
• InSb IR camera, 640x512 pixel• 100 Hz frame rate• Subtraction of zero image• Measurement duration: 10 s
ca. 300x350 mm2
C. Maierhofer et al, Composites Part B57, 2014, 35-46
Reflection configuration
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InnoTesting 2015 Active Thermography
Heating sources
• Flash lamp• Halogen lamp• Infrared radiator• LED-Array• Laser• Hot air• Ultrasonic sonotrode• Induction
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InnoTesting 2015 Active Thermography
Theory
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Non-stationary heat conduction process in anisotropic solids is described by the proportionality of heat flux and temperature gradient using the heat equation (diffusion equation):
T: temperature: position vector
t: time
Heat equation
Solution of parabolic DE:• Spatial boundary conditions
(temperature or heat flux) have to be set
• Temporal starting conditions, i.e. temperature distribution at t = 0, have to be set
• Strong attenuation
Comparison to solution of hyperbolic DE (wave equation):• Spatial boundary conditions have to be
set• Two temporal starting conditions:
temperature distribution at t = 0 and first derivative to time
• Little attenuation
λ: therm. conductivityρ: densityc: spec. heat capacity
[ ] )(),()(),(
)()( rqtrTrt
trTrcr p +∇⋅∇=
∂∂ λρ
rq: introduced heat
per volume: nabla operator∇
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InnoTesting 2015 Active Thermography
Theory of flash excitation
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Solution for Dirac pulse (flash excitation)
t
qtTe
t
qtzT tz
πεπεα == − ),0(,),( 42
1D, for semi infinite isotropic bodies
effusivity
diffusivity
cρλε =
max. traceable penetration depth Lmax depends on heat density , thermal sensitivity of IR camera (NETD) and spec. heat capacity (n=2 bis 3)NETDTnc
qL
∆⋅= 1
max ρ
Penetration depth L depends on time t and on diffusivity αtL απ=
Depth resolution ∆L depends on time resolution and thus on frame rate of the IR camerat
tLL ∆=∆
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cρλα =
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Testing of steel and copper
Comparison of penetration depths at similar ρρρρ and c(thermograms after subtraction of zero image)
copper
t = 0.11 ms t = 0.2 ms t = 0.47 ms
t = 0.5 ms t = 1.1 ms t = 3.2 ms
steel
Similar penetration depth of about 8 mm
FBH with 12 mm Ø and remaining wall thickness of 2, 4, 6 und 8 mm
Depth resolution in steel is 10x better as in cupper
TNS Project Flash Thermography >> Draft standard on flash thermography in DIN AA 062-08-27 AA Visual and thermographic testing
NETDTncq
L∆⋅
= 1max ρ
Cu steel
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3D Reconstruction: Inverse Solution
thermogram reconstruction
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back sidegeometry
z
front sidetemperature field
T(x, y, t)
inverse problemF-1(T) = z
?
direct problemF with F(z) = T
Regina Richter, DissertationTU Braunschweig, Dez. 2013
DFG-Project for reconstruction ofdamage, together with ZIBVh 8590, 2014-2017
pipe with corrosion
Wall thickness: 3.6 mm
Pre knowledge: Material parameters are known
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Objective: Determination of diameter of spot welds in reflection configuration without additional coating
M. Ziegler, IGF project Diatherm 17686 N / 1Project partner: BAM 9.3 Prof. Rethmeier
Visualisation of heat diffusion by projection of a laser line along the sample edge:P = 50 W v = 10 m/s t = 50 ms
Laser
Adhesive joint
Optimum
Diameter of spot welds
Adhesive joint
D = 2.33 mm
Optimum
D = 5.23 mm
Spatter limit
D = 6.12 mm
Full automation pf spot welding in automotive industrywww.kuka-systems.com
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Frame rate: 40 Hz
Intensity devolution at mid point
Division
Result: Good correction of inhomogeneous emissivity, radial symmetry can be recognized
� Data analysis is possible (e.g. full width at half maximum)
Diameter of spot welds
Thermogram at time of max. intensity , strong emissivity variations � no reasonable data analysis
Thermogram at the end of the sequence shows only emissivity differences (due to scratches, discoloration, pollution etc.)
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InnoTesting 2015 Active Thermography
Validation at CFRP test specimen
Comparison of flash thermography and CT, specimen R 1
3rd layer1st layer
T R
x = 1.2 mmx = 0.48 mm
Set-up:120x120x2 mm3
5 layers 0°/90°CFRP fabric6k carbon fibre bundleEpoxy matrixDefects during production:Reinjected areaAdditional fibre bundleWooden stick
TT
CT
Cooperation with BAM 8.5 and Benteler SGLEC project Thermobot (www.thermobot.eu)
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2 cm∆x = 81 µm
∆x = 240 µm
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InnoTesting 2015 Active Thermography
Comparison of flash thermography and CT, specimen R 3/4
3rd layer
x = 1.28 mm
Set-up:2 plates glued with 4 beadsDefects:Broken fibre bundleBeads:1: release agent2: without sand blasting3: o.k.4: wrong mixture
TT
CT
R
Phase image from mid
x = 2.1 mm
T3
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1
3
2
1
C. Maierhofer et al., Composites Part B, 64, 2014, 175-186
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2 cm
Validation at CFRP test specimen
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Theory of lockin excitation
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Solution for periodic heating(lockin excitation, thermal waves)
Penetration depth (or thermal diffusion length ) of thermal wave: • decreases with increasing frequency• Increases with increasing diffusivity
Phase velocity of thermal wave: • Increases with increasing frequency and
with increasing diffusivity
>> thermal waves have a high dispersion and high at tenuation>> broadening of heat impulses (multi frequency)
)4//(/0),( πω −−−− ⋅= µztiµz eeTtzT
ωα2=µ
ωαω 2=⋅= µv
1D, for semi infinite isotropic bodies
effusivity
diffusivity
cρλε =
cρλα =
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Comparison of flash/lockin thermography
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time
A
ϕ
FT(fA)
time
FT(f)A
ϕ
Flash thermography Lockin thermography
• Thermograms at raising or max. contrast• Pulse-Phase-Thermography (PPT)• Thermal signal reconstruction (TSR)
• Online FFT or 4 point method at excitation frequency
• Offline FFT at excitation frequency
f
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Comparison: 4.4 J impact damage in CFRP
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Frequency in Hz
1 Hz 0.1 Hz 0.05 Hz0.45 mm 0.63 mm 2 mm
Depth in mm
• Phase images at 1 Hz are similar• Phase images at lower frequency have less contrast for lockin
excitation• Possible reason: Material separation due to thermal expansion
is larger for flash excitation>> Comparison to laser speckle interferometry/shearography
C. Maierhofer, ECNDT 2014, Keynote, www.ndt.netCFRP samples from ZFL Haldensleben, Prof. Dr. J. Häberle, ZIM Kooperationsnetzwerk
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InnoTesting 2015 Active Thermography
Comparison: Cu-Shunts am LHC, CERN
2 mm Cu sheet
3 mm Cu sheet
Flash
Lockin1 Hz20 P.
Flash
Lockin1 Hz20 P.
www.cern.ch
Cu-Shunts are supporting the connection of two cable heads
Customer: CERN, C. ScheuerleinC. Maierhofer et al, NDT&E International, 52, 2012, 103-111
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New excitation sources: LED -Array
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Stand atControl 2014
LEDcontrol Computer
IR camera
Photo-diode
Sample
M. Ziegler, MNPQ project, 2013-2014
Advantages of LED excitation source
� Can be modulated up to 1 kHz
� Narrow spectrum, no overlap with IR camera
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Current: Pores in aluminium
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Al pressure casting: rear axle carrier of the chassis of BMW i3
http://www.springerprofessional.de/, Hengst, BMW
Cooperation with Bergakademie TU Freiberg
Thermogram after flash
Phase image at 4.6 Hz
Section of a crankcase, Length150 mm, thickness 2 mm
KCT fromBAM 8.5
Lockin excitation at 8 HzLaser widening
U. Richter, C. Maierhofer, R. Mischke, M. Röllig, Int. Foundry Research, 2015, accepted
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Flash thermography Lockin thermography
Advantages:• Very short measurement time• Multi spectral
>> all penetration depth until Lmax
Disadvantages:• Strong thermal strain• less SNR especially at higher
penetration depths
Advantages:• Less thermal strain• Higher SNR at larger penetration depth• Higher frequencies (LED, LASER)• Depth selective
Disadvantages:• Much long measurement times• Each measurement is only optimized for one
penetration depth
time
A
ϕ
FT(fA)
time
FT(f)A
ϕ
f
Comparison of flash/lockin thermography
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Cracks and local excitation
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Characterisation of vertical cracks by heating with a laser spot
Joachim Schlichting, Dissertation, TU Berlin, 2012Adolf-Martens-Award 2013
Static laser spotDetermination of crack depth and crack angle is possible
Moved laser spotFast detection of shallow and
narrow cracks is possible
time
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InnoTesting 2015 Active Thermography
Test parameters:• Scan speed: 12 mm/s
• Trace distance: 0.5 mm
• Scan time: 40 s• Power density: ~0.7 kW/cm² (9 W, 1.3 mm Spot Ø)
• Camera resol.: 39 µm/pixel
Calibration block 1 (aka MTU Nr. 3) Ø 50 mm:• Reference for MT (fluorescent) EN ISO 9934-2 Annex B • 90MnCrV8 steel, hardened, browned• Stress corrosion cracks and grinding cracks:
width: 0.1-5 µm, depth: 2 µm-1 mm, approved by microscopy
Reference specimen for magnetic particle testing
Sub-µm cracks are recognized! Below diffraction limit (~5 µm)
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Natural cracks
P. Myrach, M. Ziegler, C. Maierhofer, M. Kreutzbruck, AIP conference proceedings, QNDE, 1581, 2014, 1624-1630
INS Project Laser-Thermography M. Ziegler
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Testing of large scaled structures
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Objective:Testing and
inspection withoutscaffolding and
access aids
Building facades
Funded by
Rotor blades of windmills
VIP-Project IKARUS, BMBF R. Krankenhagen
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Testing of rotor blades
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Cross section of a rotor blade
leading edge
trailing edge
beam
foamFull GFRP
Adhesive defects
Which structures and which defects and inhomogeneities can be detected with active thermography?
18 to 22 °C
Project IKARUS (Funding program VIP of BMBF, FKZ 03V0135, 2011-2015):Infrared-Kameratechnology for non-touching Analysis of Rotor blades under Offshore conditions
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10 p.m.
~ 180 cm
~ 20
0 cm• Segment of a rotor blade with natural and
artificial defects and inhomogeneities• Comparison of measurements and numerical
simulations under different environmental conditions (solar radiation, air temperature, background radiation)
Testing of a rotor blade segment
103 cm 57 cm
Measurement Simulation
Worzewski et al, DGZfP Jahrestagung 2014
Testing of rotor blades
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InnoTesting 2015 Active Thermography
Detection of voids during solar heating
Thermogram after 3 h sun radiationTmax = 48 °C
Plaster scratches at Magdeburger Dom
From: maps.google.deFrom: maps.google.deFrom: maps.google.deFrom: maps.google.de
• Plaster scratches from 13th century• Voids and delaminations are getting warmer due to
solar heating• Heating as well as cooling down (e. g. due to
shadowing) enable further structural investigations >> active thermography
Steel engraving of central picture: Otto I. with his two wives Adelhaid and Editha
BBR project 3D-Mapping, Cooperation with with FhG IFF and IDK, local restorers
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InnoTesting 2015 Active Thermography
Alternate heating with sun and clouds
11:00 12:00 13:00 14:00 15:00 16:00
0,0
0,5
1,0
Nor
mal
isie
rt
Zeit in Stunden
Temperaturentwicklung Fassade Globalstrahlung Hukseflux
Testing of building facades
BBR project ERBE, ZukunftBau, 2013-2015
• Culture house in Cobbelsdorf, Coswig• Mural painting Industrialized agriculture of
Erich Enge 1970/71• Beam construction• Sun radiation
from 150 W/m2 to850 W/m2 on 9.9.2014
• Time: 10:45 to 15:50 o’clock
2nd phase image of the sequence
10th phase image of the sequence
steel beams
cracks
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Standardisation
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DIN 54192Active thermography
Draft standardflash thermography
Structure of draft standardlockin thermography
DIN NA 062-08-27 AA Visual and thermographic testing
CEN TC 138/WG 11 Infrared and thermographic testing
prEN 16714-1Part 1 Gener-al principles
prEN 16714-2Part 2 Equip-ment
prEN 16714-3Part 3 Terms and definitions
Active thermography
EMRP VITCEA: Validated inspection methodsfor composites in energy applications
Pre Normative EMPIR-Proposal of EURAMET Focus Group on Standardization of Thermal Imagers (from 2016): Calibration of infrared cameras, crack detection
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InnoTesting 2015 Active Thermography
Thermography Team
Thank you!
Mathias ZieglerPhilipp MyrachFlorian JonietzMarco LuchtTamara WorzewskiManoucher DoroshtnasirHenrik SteinfurthMathias Röllig
Rainer KrankenhagenNick RothbartSven AugustinErik ThielMarc KreutzbruckRegina RichterJoachim SchlichtingMercedes Reischel
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