infrared thermography for ndt: potentials and applications

Xavier [email protected]

http://mivim.gel.ulaval.ca

Infrared Thermography for NDT: Potentials and Applications

Chaire de recherche du CanadaTitulaire : Xavier Maldague

Xavier MaldagueNovember 2013

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Outline

1. Infrared spectrum;2. Non‐Thermal infrared NDT;3. Thermal infrared NDT: Passive thermography;4. Thermal infrared NDT : Active thermography;5. Thermal infrared NDT : More Applications;6. Conclusions.

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1. Infrared spectrum1. Infrared spectrum

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Infrared spectrum

Thermal emissions

Non-thermal reflections

Reflectography/ transmittography

Thermography

THz Terahertz imagingElectromagnetic

spectrum

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Infrared spectrum

Thermal emissions



Thermography


spectrum

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2. Non‐thermal Infrared NDT2. Non‐thermal Infrared NDT

Non‐thermal IR vision NDT: sample illumination

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NIR/SWIR reflections or transmissions Reflectography

Transmittography

NIR reflectography/transmittography of GFRP

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900 – 1700 nm

NIR: reflection NIR: transmissionvisible images

GFRP: Glass Fiber Reinforced Plastic

front

back

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Infrared spectrum

Thermal emissions



Thermography


spectrum

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3. Thermal Infrared NDT: Passive Thermography3. Thermal Infrared NDT: Passive Thermography

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Passive thermography: introduction

The passive approach is used when the object of interest has enough thermal contrast with respect to the background in order to be detected with an infrared sensor. Typical applications include: surveillance, people tracking, humidity assessment in buildings, liquid levels in storage tanks, insulation problems, electrical components, etc.

Sources : http://www.x20.org/thermal/ http://www.temperatures.com/thermalimaging.html

Aeronautical application: (1/4)Water ingress detection in honeycomb

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AA BB CC DD

EE FF GG HH

frontbackVolume, V

[ml]F 1 0.2B 1 0.4G 1 0.6C 1 0.8E 10 2D 10 4H 10 6A 10 9

Cells filled with water

Defective area

Section of a military aircraft component

10 cells with 9 ml of water

not frozen frozen


The impact of water volume

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(a) Early thermogram at t=295 s showing all defects (A to H); (b) Thermogram at t=518 s showing all defects except defect F; (c) Thermogram at t=1315 s showing only defects A, D and H.


The impact of water volume

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The sound area (dotted black line) warms up following a logarithmicgrowth with respect to time

In the presence of water, temperature profiles diverge from logarithmic behavior (since it takes longer to warm up water).

The divergent time for all defects is approximately the same (roughly around 180 s), regardless of the water extend and volume

0 200 400 600 800 1000 1200 1400800

1000

1200

1400

1600

1800

2000

2200

2400

2600Temperature profiles, Telops HD

t [s]

T [

arbi

trary

uni

ts]

Sound area0.2 ml0.4 ml0.6 ml0.8 ml2 ml4 ml6 ml9 ml


Data correlation

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0 200 400 600 800 1000 1200 1400-100

0

100

200

300

400

500

600

700

800Temperature profiles, Telops HD

t [s]

T [

arbi

trary

uni

ts]

9 ml6 ml4 ml2 ml0.8 ml0.6 ml0.4 ml0.2 ml

Time for maximum contrast = 336.2 s

V = f ( tmax )

Maximuncontrast = 146.8

V = 3.2E-08 t 2.685

R² = 0.9911

0

2

4

6

8

10

0 250 500 750 1000 1250 1500

Wat

er in

gres

s vol

ume

[ml]

Time for maximum contrast [s]

Thermograms at different distances

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268

269

270

271

272

273

274

275

276

277

278

270

275

280

285

290

295

275

280

285

290

295

275

280

285

290

295

300

305

1.5 m from target 4 m from target

10 m from target 20 m from target

0.4 ml defect

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4. Thermal Infrared NDT: Active Thermography4. Thermal Infrared NDT: Active Thermography

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Active thermography for NDT

Active thermography for NDT is based on the detection and recording by an infrared camera of thermal radiations emitted by object surface.

To detect defects, it is sometimes necessary to destabilize the object thermal state through heating or cooling (→ active thermography ).

The presence of an internal defect reveals itself on surface as atemperature perturbation above this defect.

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Thermal IR vision

Thermal emissions


Main advantages:

Possibility to perform one‐sided inspection (in reflection configuration); Carried out in real‐time; Appropriate on most composites materials and multi‐layer structures, including porous materials and industrial lines; Relatively unaffected by the object’s geometry, and well adapted for the inspection of large surfaces.

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Main problems:

Sensible to heating sources (type, duration, location);

Response time (very fast for metals => need for fast acquisition rates);

Affected by the object’s surface condition and thickness;

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Non‐uniform heating

+

=

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Advanced signal processing techniques

Thermal contrast‐based techniques (max. contrast, FWHM, etc.)

Differential Absolute Contrast, DAC

Thermographic Signal Reconstruction, TSR

Principal Component Thermography, PCT

Pulsed Phase Thermography, PPT

teQT ln

21lnln

A=USVT

)()()( tTtTtTaSd

nnN

k

Nnkjn tkTtF ImReexp

1

0

)2(

tTtttTT ddac

)(012

tTT

te

QTtT

0,0

3D diffusion equation

1D solution for a Dirac pulse

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Absolutecontrast

DAC

Example: DAC on CFRP

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Active thermography: approaches, techniques

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Pulsed thermography

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Pulsed thermography, PT

Metal corrosion, crack detection, disbonding, impact damage in composites, turbine blades, delaminations, porosity, defect characterization: depth, size, thermal properties, artworks.

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Lock‐in thermography, LT

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Phase

permanent regimesine wave heating

• same frequency• temporal shift

Thermal waves

input:

output:

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Lock‐in thermography, LT

Crack identification, disbonding, impact damage, cultural heritage inspection, artworks, cultural buildings.

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Eddy current (or Inductive) thermography, ECT

Crack detection in electro‐conductive materials, detection of impact damage in composites, inspection of soldering joints.

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Inspection of honeycomb sandwich structures

Movie: Eddy current thermography

Crack inspection: simulation

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The approach for crack detection

SimulationGeometry of the specimen

Crack inspection: experimental

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Experimental setup Coil and specimen

Segmentaion result

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Vibrothermography, VT

Coating wear, fatigue test, crack detection.

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Open microcracks in thermally‐sprayed‐coatings

The coating (~100‐200 m) is formed by a mixture of Tungsten‐Carbide and Cobalt powder accelerated and heated in aplasma jet and sprayed onto a 1 mm thick steel substrate.

12.8 mm

16 mm

~0.8 mm ~0.8 mm

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Optical PT Optical LT

Burst VT Line-scan ECT

Real crushed core produced during VT inspection

Paint detached from the surface

Comparative example: PT, LT, VT, ECT

Inspection of CF‐18 rudders (1/3)

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Impact of de‐noising with synthetic data

f=0.015 Hz f=0.04 Hz f=1.2 Hz

PPT from raw pulsed data

PPT from synthetic pulsed data

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Depth retrieval with phase profiles

0 0.2 0.4 0.58-0.05

0

0.05

0.1

0.15

f [Hz]

[rad

]

z1,raw z2,raw z1,synt z2,synt

z1=0.5 mm z2=2 mm

Sa

z1 z2

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5. Thermal Infrared NDT: More Applications5. Thermal Infrared NDT: More Applications

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Road and bridges inspection (1/3)

Notre‐Dame streetMontréal, CanadaNovember 4th, 2008

Interstate 35Minneapolis, August 3rd, 2007

Viaduc de la Concorde, Montréal, CanadaSeptember 30th, 2006

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Reinforcement using composite layers

Traditional inspection with the "tap testing" techniqueToutry Bridge, France

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Thermal stimulation

Images acquisition

Fiber distribution and orientation

Randomly‐Oriented Strands (ROS)

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Heat + Pressure

Fiber distribution and orientation

Complex‐shaped parts

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Fiber orientation measurement

Strength and stiffness

Fiber distribution and orientation: point scan

Laser point scan experimental setup

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Laboratory setup

Results show the ellipses major axes indicating the fiber direction for the same area at two different positions rotated 90o

6.37°

‐85.19°

Error of 1.5°

Artworks inspection (1/3)

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OverlayHidden drawings

NIR camera (0.9‐1.7 m) incandescent lamp 90 V

Visible photograph


OverlayDefects

Thermal camera (3‐5 m) PPT phase f=75 mHz

Visible photograph

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6. Conclusions6. Conclusions

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Conclusions

Infrared reflectography and transmittography employ the non‐thermal part of the infrared spectrum, where the opacity/transparency of materials, subjected to a specific infrared radiation, are exploited to detect internal anomalies in materials.

Infrared thermography works in the thermal part of the infrared spectrum under the principle that dissimilar materials provide different thermal signatures, useful for surface/subsurface defect detection.

Passive thermography is typically used in the field of security and surveillance, biological applications, the inspection of electrical and electronic components, and buildings among others.

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Conclusions (cont.)

Active thermography is widely used in aerospace and automobile industries and is finding new applications such as the inspection of bridges and roads and the assessment of artworks and cultural heritage.

Data processing techniques are required to enhance contrast, to improve the spatial resolution and to increase the signal‐to‐noise ratio of the infrared signal.

Continual technological progress in commercial infrared cameras and computers , as well as the constant development of new processing techniques, have promoted the appearance of new and innovative applications for infrared vision.

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Thank you for your attention !

infrared thermography for ndt: potentials and applications

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