Active Thermography – NDT Method for Structural · PDF fileActive Thermography ... Nondestructive Testing Handbook, Vol. 3 Infrared and Thermal Testing] Pulse-phase-thermography

Platzhalter fr Bild, Bild auf Titelfolie hinter das Logo einsetzen
Institut fr Fge- undSchweitechnik
C. rajbr, A. Dillenz
Automotive Circle International 2012
Active Thermography NDT Method for Structural Adhesive and Mechanical Joints

18.04.2012 | C. Srajbr | NDT of Joints by Active Thermography | Slide 2Institut fr Fge- undSchweitechnik
Outline
Motivation QA of Joints
Methods of Active Thermography
Adhesive Joints
Mechanical Joints
Conclusion

Modern Joining Techniques in Automotive Production
Adhesive bonding structural, elastic, hem flanging
Mechanical Joining clinching, pierce-riveting, FDS
Structural light-weight design results in differential multi-material components
Mild steelsHigh-strength steelsAdvanced high-strength steelsUltra high-strength steels, hot-formedAluminiumPlastics[Source: Daimler AG]
7468
63
55
13 13 14 14
610
13 15
3 5 610
4 4 4 6
0
10
20
30
40
50
60
70
80
1975 1985 1995 2005
Perc
ent b
y w
eigh
t [%
]
Steels / ironElastomersPlasticsAluminiumOther NF-metals
[Source: VDI]

QA of Joining Processes in Automotive Production
Requirements on a non-destructive testing method Detection of the relevant flaws/imperfections Automation possible, ideally contact-less Simple evaluation of results, robust testing procedure
Conventional methods of joints quality assurance Process control systems (monitoring of adhesive
beads, force-displacement measurement, etc.) Manually carried out destructive tests (random checks) Tactile, manual measurement of comparator figures
Within the joining process a multitude of flaws/imperfections in joints can occour
Application of active thermography for quality assurance of joints?

Outline
Adhesive Joints
Mechanical Joints
Conclusion

Active Thermography General Measurement Setup
(Modulated) excitation of heat flow or mechanical loads in the material
Reflection or heat production at imperfection
Recording of surface heat radiation by IR- camera
Examination of transient temperature differences (PT) of surface or angular phase shifts between excitation and thermal answer (PPT/Lockin) Specimen
IR-camera
Thermalanswer
Energy for heatflow excitation
Excitationsource
Flaw
Mechanical loads
Induction
Optical radiation
Convection
hot or cold air
eddy currents
ultrasound
Halogen, LED, Laser

Principle of Flaw Detection by Heat Flow Thermography
Fundamentals of heat diffusion (1D case):
Fourier heat equitation
TAsdx
dTAQ ****
Thermal resistance, depends on thermal properties
Material Thermal diffusivity [W / (mK)]
Steel 15-58
PUR 0.16
Air 0.0261
As
RTh
Heat flow thermography detects flaws by deviations of the heat flow resulting from different thermal properties of flawed regions

Vibro-thermography detects flaws defect-selective by a heat production resulting from friction at interfaces and boundaries or cracks
Flaw
Mechanical Wave
US-Converter
Specimen
Thermal Wave
Flaws in joints often provide regions with surfaces not connected but contacted
Local warming at regions with flaws
Friction
Hysteresis warming
Principle of Flaw Detection by Vibro-Thermography
dVW
T ~ Kh2
Rising temperatures resultingfrom mechanical hysteresis
(Friction = Force x Velocity):
Dissipation

Evaluation Techniques of Transient Surface Temperature
time
ampl
itude
A
A
AmplitudePhase-shift
[Maldaque, X.: Nondestructive Testing Handbook, Vol. 3 Infrared and Thermal Testing]
Pulse-phase-thermographyNot modulated excitation of heat flow by a thermal or mechanical pulse, containing a spectrum of frequencies
time
ampl
itude
Excitation pulse
Thermal response
Pixel APixel B
Lockin-thermographySinusoidally modulated excitation of heat flow by a thermal or mechanical signal at a pre-defined Lockin-frequency
Performing a frequency analysis by a discrete Fourier transformation of the thermal response (pixel by pixel)
DFT
Amplitude image (A)Phase image ()
dtetTfT tfi2)()(

Outline
Adhesive Joints
Mechanical Joints
Conclusion

Imperfections of Adhesively Bonded Joints
Various flaws of adhesive bonds during manufacturing processes can occur:
Due to faulty adhesive application Trapped air in adhesive seam,
i.e. voids and porosities Necking Impurities of adhesive Inhomogeneous adhesive layers Kissing/Weak Bonds
Due to handling stresses or internal strains Cracks Delaminations
Due to insufficient mixing ratios or curing Hardening failures
[Source: Adams et al.]

Kissing Bond (oil) Delamination (PTFE-strips)
Structural and semi-structural bonding of steel sheets Thickness of bond line t = 0.3 mm
Adhesive and cohesive defects at structural adhesively bonded steel joints detectable
Ultrasound Excitation at Adhesively Bonded Joints
2C E
P2C
PU
R1C
PU
R

Induction Excitation at Structural Adhesively Bonded Joints
Missing adhesive
Porosities
Thickness of bond line 0.15 0.5 mm
Kissing Bond
Delamination
Thickness of bond line 0.5 1.0 mm
fDFT=0.3 Hz
Cohesive and geometrical defects at structural adhesively bonded steel joints detectable
Structural bonding 1C EP adhesive Bonding of steel sheets (t = 0.8 mm) Thickness of bond line t = 0.3 mm

Induction Excitation at other Adhesively Bonded Materials
1C-EP, Steel
2C-PUR, Steel
1C-EP, Aluminum
fDFT=0.3 Hz fDFT=0.5 Hz
Influences of materials compensable by changing the parameters (tIndP, fDFT)
fDFT= 0.8 Hz fDFT= 0.03 Hz
Structural bondingThickness of bond line t = 0.3 mm
Flaw
: mis
sing
adh
esiv
e
1C-PUR, Steel/Glass
Semi-structural bondingThickness of bond line: t = 5 mm

Flaws in the upper part of hem flange
Missing adhesive
-CT
-CT
Flaws in the lower part of hem flange
Flaws in the upper part of hem flange
Porosity
Flaws in the lower part of hem flange
fDFT= 0.1 Hz
Induction Excitation at Hem Flanging

Outline
Adhesive Joints
Mechanical Joints
Conclusion

18.04.2012 | C. Srajbr | NDT of Joints by Active Thermography | Slide 17
Institut fr Fge- undSchweitechnik
Imperfections of Clinching Joints
Various flaws of clinching joints during manufacturing processes can occur:
Due to faulty materials or parameters: Deviations in cap thickness Necking or cracks in the point neck
or the cap
Due to handling stresses or internal strains Buckling
Due to defects of clinching tools or machine Lateral or angular deflection Worn-out punch or die Not closing die lamella
Reference
tBtN
f
tB Cap thicknesstN Neck thicknessf Undercut
Lateral deflection Worn-out punch / die
Cracks in neck / capDeviations in cap thickness

TOX clinching joint Joining of steel (t = 0.8 mm)
sheets
All local flaws in clinching joints detectable, deviations in cap thickness not detectable
Ultrasound Excitation at Local Flawed Clinching Joints
Lateral deflection
Flawless
Broken punch Broken die
Crack in neck

18.04.2012 | C. Srajbr | NDT of Joints by Active Thermography | S

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Active Thermography – NDT Method for Structural · PDF fileActive Thermography ... Nondestructive Testing Handbook, Vol. 3 Infrared and Thermal Testing] Pulse-phase-thermography