Platzhalter für Bild, Bild auf Titelfolie hinter das Logo einsetzen Active Thermography NDT Method for Structural Adhesive and Mechanical Joints C. Šrajbr, A. Dillenz Automotive Circle International 2012
Outline Motivation QA of Joints Methods of Active Thermography Adhesive Joints Mechanical Joints Conclusion 18.04.2012 C. Srajbr NDT of Joints by Active Thermography Slide 2
Modern Joining Techniques in Automotive Production Structural light-weight design results in differential multi-material components [Source: Daimler AG] Mild steels High-strength steels Advanced high-strength steels Ultra high-strength steels, hot-formed Aluminium Plastics Percent by weight [%] 80 70 60 50 40 30 20 10 0 74 68 63 55 13 13 14 1415 13 10 10 6 3 4 5 4 6 4 6 1975 1985 1995 2005 Steels / iron Elastomers Plastics Aluminium Other NF-metals [Source: VDI] Adhesive bonding structural, elastic, hem flanging Mechanical Joining clinching, pierce-riveting, FDS 18.04.2012 C. Srajbr NDT of Joints by Active Thermography Slide 3
QA of Joining Processes in Automotive Production Within the joining process a multitude of flaws/imperfections in joints can occour 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 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 Application of active thermography for quality assurance of joints? 18.04.2012 C. Srajbr NDT of Joints by Active Thermography Slide 4
Outline Motivation QA of Joints Methods of Active Thermography Adhesive Joints Mechanical Joints Conclusion 18.04.2012 C. Srajbr NDT of Joints by Active Thermography Slide 5
Active Thermography General Measurement Setup Mechanical loads (Modulated) excitation of heat flow or mechanical loads in the material IR-camera Excitation source ultrasound Induction 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) Thermal answer Flaw Energy for heat flow excitation Specimen eddy currents Optical radiation Halogen, LED, Laser Convection hot or cold air 18.04.2012 C. Srajbr NDT of Joints by Active Thermography Slide 6
Principle of Flaw Detection by Heat Flow Thermography Heat flow thermography detects flaws by deviations of the heat flow resulting from different thermal properties of flawed regions Fundamentals of heat diffusion (1D case): dt Q * A* * A* T dx s Fourier heat equitation R Th s A Thermal resistance, depends on thermal properties Material Steel 15-58 PUR 0.16 Air 0.0261 Thermal diffusivity ʎ [W / (mk)] 18.04.2012 C. Srajbr NDT of Joints by Active Thermography Slide 7
Principle of Flaw Detection by Vibro-Thermography Vibro-thermography detects flaws defect-selective by a heat production resulting from friction at interfaces and boundaries or cracks Hysteresis warming Flaws in joints often provide regions with surfaces not connected but contacted Rising temperatures resulting from mechanical hysteresis (Friction = Force x Velocity): T ~ K h σ 2 Friction Dissipation W V d Local warming at regions with flaws Thermal Wave Flaw US-Converter Specimen Mechanical Wave 18.04.2012 C. Srajbr NDT of Joints by Active Thermography Slide 8
Evaluation Techniques of Transient Surface Temperature Pulse-phase-thermography Not modulated excitation of heat flow by a thermal or mechanical pulse, containing a spectrum of frequencies Lockin-thermography Sinusoidally modulated excitation of heat flow by a thermal or mechanical signal at a pre-defined Lockin-frequency amplitude Excitation pulse Thermal response Pixel A Pixel B time amplitude A φ A φ Amplitude Phase-shift time Performing a frequency analysis by a discrete Fourier transformation of the thermal response (pixel by pixel) DFT T ( f ) T ( t) e i2 tf dt Amplitude image (A) Phase image (Φ) 18.04.2012 C. Srajbr NDT of Joints by Active Thermography Slide 9 [Maldaque, X.: Nondestructive Testing Handbook, Vol. 3 Infrared and Thermal Testing]
Outline Motivation QA of Joints Methods of Active Thermography Adhesive Joints Mechanical Joints Conclusion 18.04.2012 C. Srajbr NDT of Joints by Active Thermography Slide 10
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.] 18.04.2012 C. Srajbr NDT of Joints by Active Thermography Slide 11
Ultrasound Excitation at Adhesively Bonded Joints Structural and semi-structural bonding of steel sheets Thickness of bond line t = 0.3 mm Kissing Bond (oil) Delamination (PTFE-strips) 1C PUR 2C PUR 2C EP Adhesive and cohesive defects at structural adhesively bonded steel joints detectable 18.04.2012 C. Srajbr NDT of Joints by Active Thermography Slide 12
Induction Excitation at Structural Adhesively Bonded Joints Structural bonding 1C EP adhesive Bonding of steel sheets (t = 0.8 mm) Thickness of bond line t = 0.3 mm Missing adhesive Thickness of bond line 0.15 0.5 mm Thickness of bond line 0.5 1.0 mm Kissing Bond Delamination Porosities f DFT =0.3 Hz Cohesive and geometrical defects at structural adhesively bonded steel joints detectable 18.04.2012 C. Srajbr NDT of Joints by Active Thermography Slide 13
Induction Excitation at other Adhesively Bonded Materials Structural bonding Thickness of bond line t = 0.3 mm Semi-structural bonding Thickness of bond line: t = 5 mm 1C-EP, Steel 2C-PUR, Steel 1C-EP, Aluminum 1C-PUR, Steel/Glass f DFT =0.3 Hz f DFT =0.5 Hz f DFT = 0.8 Hz Flaw: missing adhesive f DFT = 0.03 Hz Influences of materials compensable by changing the parameters (t IndP, f DFT ) 18.04.2012 C. Srajbr NDT of Joints by Active Thermography Slide 14
Induction Excitation at Hem Flanging Missing adhesive Flaws in the upper part of hem flange Porosity Flaws in the upper part of hem flange μ-ct Flaws in the lower part of hem flange Flaws in the lower part of hem flange μ-ct f DFT = 0.1 Hz 18.04.2012 C. Srajbr NDT of Joints by Active Thermography Slide 15
Outline Motivation QA of Joints Methods of Active Thermography Adhesive Joints Mechanical Joints Conclusion 18.04.2012 C. Srajbr NDT of Joints by Active Thermography Slide 16
Imperfections of Clinching Joints Various flaws of clinching joints during manufacturing processes can occur: Lateral deflection Worn-out punch / die 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 t B t N f t N Reference t B Cap thickness Neck thickness Undercut Deviations in cap thickness Cracks in neck / cap f 18.04.2012 C. Srajbr NDT of Joints by Active Thermography Slide 17
Ultrasound Excitation at Local Flawed Clinching Joints Broken punch Broken die TOX clinching joint Joining of steel (t = 0.8 mm) sheets Flawless Lateral deflection Crack in neck All local flaws in clinching joints detectable, deviations in cap thickness not detectable 18.04.2012 C. Srajbr NDT of Joints by Active Thermography Slide 18
Induction Excitation at Local Flawed Clinching Joints Broken punch Broken die TOX clinching joint Joining of steel (t= 0.8 mm) to aluminum sheets (t= 1.2 mm) Flawless Lateral deflection f DFT =0.8 Hz Crack in neck All local flaws in clinching joints detectable 18.04.2012 C. Srajbr NDT of Joints by Active Thermography Slide 19
Induction Excitation at Clinching Joints with Deviations of Cap Thickness TOX clinching joint Joining of steel (t = 0.8 mm) to aluminum sheets (t = 1.2 mm) + 0.15 mm i. O. 0.10 mm Phase [ ] -40-42 -44-46 -48-50 -52-54 -56-58 -60-62 -64-66 -68-70 40 50 60 70 80 90 100 110 120 130 140 150 Pixel [px] BD - 0,10 BD - 0,08 BD - 0,05 BD - 0,03 i.o. BD + 0,02 BD + 0,05 BD + 0,07 BD + 0,10 BD + 0,13 BD + 0,15 f DFT =0.5 Hz Reference Even small deviations in cap thickness are detectable 18.04.2012 C. Srajbr NDT of Joints by Active Thermography Slide 20
Outline Motivation QA of Joints Methods of Active Thermography Adhesive Joints Mechanical Joints Conclusion 18.04.2012 C. Srajbr NDT of Joints by Active Thermography Slide 21
Conclusion Active thermography is accurate examination of joint quality Comparison of Excitation Sources Inductive excitation + Thick materials, high energy absorption + Non-contact method + Efficient local heating, optimal for joints + Determination of thickness possible Only electrically conductive materials Adaption of inductor necessary Ultrasound excitation + Defect selective + Optimal for detection of defects frictional properties + Only materials with moderate damping properties Contact method Noise emission 18.04.2012 C. Srajbr NDT of Joints by Active Thermography Slide 22
Possibilities of System Implementation Automated online test system Testing of flaw-critical areas Automated sampling inspection Testing of whole components, one test rig for different components Manual testing Repair cases, testing of the relevant region Clamping device of ultrasound excitation Test setup for induction excitation 18.04.2012 C. Srajbr NDT of Joints by Active Thermography Slide 23
Discussion Active Thermography: Non-destructive Testing Method for Structural Adhesive and Mechanical Joints TU Braunschweig Institute of Joining and Welding Prof. Dr.-Ing. K. Dilger edevis GmbH Dipl.-Ing. Christian Šrajbr Tel.: +49 (0) 531 / 391-7826 Fax.: +49 (0) 531 / 391-5834 E-Mail: c.srajbr@tu-bs.de Dipl.-Phys. Alexander Dillenz Tel.: +49 (0) 711 933077-20 Fax.: +49 (0) 711 933077-99 E-Mail: info@edevis.de 18.04.2012 C. Srajbr NDT of Joints by Active Thermography Slide 24