Adaption of Pulsed Phase Thermography for the Quantitative NDT-CE

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1 Adaption of Pulsed Phase Thermography for the Quantitative NDT-CE R. Arndt, R. Helmerich, Ch. Maierhofer, M. Röllig and H. Wiggenhauser Division VIII.2 Non-destructive Damage Assessment and Environmental Measurement Methods Federal Institute for Material Research and Testing (BAM), Berlin, Germany BAM VIII.2 INDE

2 Division VIII.2 Non-destructive Damage Assessment and Environmental Measurement Methods Electromagnetic Methods for the Assessment of Structures; Development and Validation Acoustic Methods for Testing Building Structures Non-destructive Environmental Measurement Methods Combination and Automation of Non-destructive Testing of Buildings BAM VIII.2 INDE

3 BAM VIII.2 INDE

4 Overview Introduction Applications Quantitative Approach Conclusions Outlook BAM VIII.2 INDE

5 Introduction Applications of passive thermography at BAM Detection of heat leacages Moisture detection Detection and control of wall and floor heatings Control of electric installations *>24,5 C 24,0 23,0 22,0 21,0 20,0 19,0 *<18,5 C BAM VIII.2 INDE

6 Introduction Principles Restriction to passive thermography Existing temperature gradient, limited applications Development of active thermography - methods Pulsed thermography (Time Domain -TD) Lock-in thermography (Frequency Domain - FD) Pulsed phase thermography (FD) Step heating thermography Square pulse thermography (TD / FD) BAM VIII.2 INDE

7 Introduction Alternative stiumlation in active thermography Pulsed heating Step heating Square pulse heating Periodic heating PT PPT TRIR SPT (TD) SPT (FD) LT After Vavilov in Theory and practice of Infrared Technology for non-destructive testing, John Wiley and Sons, Inc., 2001 (tech. editor Maldague). BAM VIII.2 INDE

8 Introduction Problems of applying thermography in CE Relative low thermal conductivities of used materials Large dimensions of most building structures Flexibel equipment and high energetic heat pulses with long heating and recording times (PT SPT in time domain) Changing environmental conditions Inhomogeneous surface structures Increasing signal-to-noise ratio of the phase images, quantitative soluton with phase and amplitude data (PPT SPT in frequency domain) BAM VIII.2 INDE

9 Introduction PT / SPT time domain Lock-in- Thermography ϖ A: Amplitude ϖ : Frequency φ : Phase A φ Input Output PPT / SPT frequency domain t Fouriertransformation Frequency y A(f) x Time domain time y T(t) x y [Maldague(modified)] Frequency Frequency domain BAM VIII.2 INDE φ(f) x

10 Introduction Typical problems for active thermography in civil engineering Localisation of voids in concrete structures Localisation of delaminations of layered structures (e. g. tiles or carbon reinforced laminates on concrete) Localisation of plaster delaminations on concrete and brickwork Localisation of voids and delaminations behind tiles Localisation of enhanced moisture in the surface near region BAM VIII.2 INDE

11 Introduction Quantitative approaches PT / SPT - time domain FT PPT /SPT - frequency domain Temperature in C 30 T max reference 28 void difference Cooling time in s Transients and temperature-time-differencecurve of the cooling down process 1,5 1,0 0,5 0,0 T in K BAM VIII.2 INDE φ in rad 0,2 0,1 0,0-0,1-0,2-0,3 detection treshold f ch f b ' f b frequency in Hz φ Phase-frequency-difference-curve after FT of the transients

12 Overview Introduction Applications Quantitative Approach Conclusions Outlook BAM VIII.2 INDE

13 Applications Structure- and humidity investigations in Civil Engineering by means of impulse thermography, part 1 (TD) and part 2 (FD) (2001 to 2005) in collaboration with the Technical University of Berlin (TUB) Supported by the Deutsche Forschungsgemeinschaft On-site investigation techniques for the structural evaluation of historic masonry buildings (2001 to 2004) in collaboration with thirteen international partners Supported by the fifth supporting programme of the EC SUSTAINABLE BRIDGES Assessment for Future Traffic Demands and Longer Lives (2004 to 2007) in collaboration with thirty international partners Supported by the sixth framework programme of the EC and many small and big investigations and case studies BAM VIII.2 INDE

Applications Actice Thermography at BAM,VIII.

site Application to concrete and historic masonry structures Development of

14 Applications Actice Thermography at BAM,VIII.2 Development of equipment for manual and automated application on the building site Application to concrete and historic masonry structures Development of software tools for time and frequency related data analysis and defect quantification (e. g. SPT in frequency domain) Numerical simulation of heat transport based on Finite Differences and Finite Elements Close cooperation to TU Berlin (Prof. Hilemeier) BAM VIII.2 INDE

15 Applications ActiceThermography at BAM,VIII.2 and TUB Localisation of voids in concrete structures (DFG) Localisation of enhanced moisture in the surface near region (DFG) Localisation of poorly grouted regions in tendon ducts (TUB-DFG) Localisation of plaster delaminations on concrete (DFG) and brickwork (EU) Localisation of delaminations of layered structures (e. g. carbon reinforced laminates or tiles on concrete - DFG / EU) BAM VIII.2 INDE

- Infrared radiator - Fan heater computer Infrared radiator -

16 Applications Measuring equipment Laboratory investigations monitor infrared camera On-site investigations Heating units - Infrared radiator - Fan heater computer Infrared radiator - Halogen lamps - Flashlights specimen - Sun BAM VIII.2 INDE

17 Applications Set-up of the thermography scanner Scanner with flash lights and IR camera BAM VIII.2 INDE

Applications Location of a former door behind plaster at Wartburg Castle, Eisenach Wartburg Castle is situated on a mountain above Eisenach Eldest residential building of a

18 Applications Location of a former door behind plaster at Wartburg Castle, Eisenach Wartburg Castle is situated on a mountain above Eisenach Eldest residential building of a mediaeval castle in Germany Built between 1156 and 1172 Part of the World Heritage Martin Luther stayed here in 1521 translating the New Testament into German BAM VIII.2 INDE

19 Applications Cross section of the Palas showing cellar, ground floor and first floor BAM VIII.2 INDE

20 Applications Measurement positions at the Landgrafenzimmer BAM VIII.2 INDE

21 Applications Location of a former door behind plaster at Wartburg Castle, Eisenach Heating of the surface: Manually, area size: 1 m 2, fan heater, 5 min Observation of cooling down: Area size 1 m 2, 15 min, 2 Hz SC1000, 3.4 to 5 µm Data analysis: SPT BAM VIII.2 INDE

at 2.46 x 10-4 Hz: Structure of masonry with bricks

22 Applications Location of a former door behind plaster at Wartburg Castle, Eisenach Foto of area Phase image at 2.46 x 10-4 Hz: Structure of masonry with bricks and joints can be resolved in detail BAM VIII.2 INDE

Applications Location of connecting elements (metal and wooden nails) and possible delaminations of inlays in the New Palais, Potsdam Constructed from 1763 to 1769 by Friedrich II.

23 Applications Location of connecting elements (metal and wooden nails) and possible delaminations of inlays in the New Palais, Potsdam Constructed from 1763 to 1769 by Friedrich II. of Prussia Late baroque summer residence and guest house for the royal families Home of the last German Emperor Wilhelm II. and his family from 1889 to 1918 Restoration of the wooden parquet floors BAM VIII.2 INDE

24 Applications New Palais, Potsdam Heating of the surface: Manually, areas: 1 m² fan heater, 5 min Observation of cooling down: Area height 1 m, 15 min, 0.5 Hz SC1000, 3.4 to 5 mm Data analysis: SPT BAM VIII.2 INDE

25 Applications New Palais, Potsdam Photo Themogram Phase image 0 s 2.22 x 10-3 Hz BAM VIII.2 INDE

26 Applications Investigation of masonry walls and ceilings BAM VIII.2 INDE

Applications Location of voids below a floor paved by natural stone 32.

cooling down: Area size 1 m, 15 min, 2 Hz SC1000, 3.4 to 5 mm Temperature in o C 23.

27 Applications Location of voids below a floor paved by natural stone Heating of the surface: Manually, area size: 1 m radiator, 3 min Observation of cooling down: Area size 1 m, 15 min, 2 Hz SC1000, 3.4 to 5 mm Temperature in o C Superpositioning of an equalised digital photo and the related equalised thermogram BAM VIII.2 INDE

46 Heating of the surface: Sun radiation, 23 rd of June 2006,10 a.m.

28 Applications Location of asphalt delaminations on a concrete bridge heated up by sun radiation Temperature in o C Heating of the surface: Sun radiation, 23 rd of June 2006,10 a.m. Observation of cooling down: Shadowing of an area of 1 m 2,15 min, 2 Hz BAM VIII.2 INDE

29 Applications Location of damages at CFRP strengthed systems Damages: Insufficient application Aging effects due to heavy loads and environmental influences Further impacts >> delaminations and deteriorations Photograph: STO BAM VIII.2 INDE

30 Applications PT on CFRP-strengthened Composites Concrete block specimen with designed defects Concrete block specimen with CFRP-stripes Polystyrene patches Foam rubber patches BAM VIII.2 INDE

Applications Thermograms and temperature evolution 29.4 4 34 infrared radiator Infrared radiators Power: 3 x 2400 W Area: 1.5 x 1.

0 Temperature in C 32 30 28 26 24 22 sound area disbonded area difference between disbonded and sound area 0 20 40 60 80 100 120 140 160 Time in s 3 2 1 0 Temperature difference in K Halogen lamps

4 Temperature in C 34 32 30 28 26 24 22 20 18 50 halogen lamp -1 sound area disbonded area difference between disbonded and sound area -2 0 20 40 60 80 100 120 140 160 Time in s 4 3 2 1 0 2,0

31 Applications Thermograms and temperature evolution infrared radiator Infrared radiators Power: 3 x 2400 W Area: 1.5 x 1.5 m 2 Heating time:1 min Observation time after heating: 5 min Recorded 66 s after heating Temperature in o C 22.0 Temperature in C sound area disbonded area difference between disbonded and sound area Time in s Temperature difference in K Halogen lamps Power: 2 x 650 W Area: ~625 cm 2,, defect: 50 cm 2 Heating time: 3 s Observation time after heating: 5 min Recorded 76 s after heating Temperature in o C Temperature in C halogen lamp -1 sound area disbonded area difference between disbonded and sound area Time in s ,0 Temperature difference in K Flashlights Power: 2x1500 W Area: ~625 cm 2, defect: 50 cm 2 Heating time:7 flashes during 60s Observation time after heating: 2 min Recorded 40 s after heating BAM VIII.2 INDE Temperature in o C 22.0 Temperature in C flashlights -0,5 sound area disbonded area difference between disbonded and sound area -1, Time in s 1,5 1,0 0,5 0,0 Temperature difference in K

32 Applications Set-up of 2 test beams, 0.3 m x 0.5 m x 5.2 m, CFRP-Application:STO Lamellae: STO BPE: 100 x 1,4 mm Elasticity: < 1,2 % Tension strength: > 2500 N/mm 2 BAM VIII.2 INDE

33 Applications Set-up of the thermography scanner Heating of the surface: Automatically flash lights (1500 W each) area size: 30 cm x 30 cm 7 flashes each area Observation of cooling down: Area size: 30 cm x 30 cm 5 min, 10 Hz SC1000, 3.4 to 5 µm Data analysis: PPT BAM VIII.2 INDE

34 Applications Set-up of the thermography scanner Scanner with flash lights and IR camera BAM VIII.2 INDE

35 Applications Load test: Test set up 5200 mm 1100 mm BAM VIII.2 INDE

36 Applications Preloading 5200 mm 1100 mm BAM VIII.2 INDE

37 Applications Unloading 5200 mm 1100 mm BAM VIII.2 INDE

38 Applications Load test with repeated thermographic evaluation Critical areas 5200 mm 1100 mm BAM VIII.2 INDE

39 Applications Beam Loading ,5 kn: Debonding of CFRP-Plates Load kn After Failure: < 150 kn Load limit without strengthening Preloading ~ 90 kn 50 Weigth of the beam Load kn Deflection in the middle mm BAM VIII.2 INDE

40 Applications Phase images at critical areas during loading Frequency: 3.33 x 10-3 Hz 180 kn 285 kn 295 kn BAM VIII.2 INDE

41 Applications Total delamination after unloading Finally failed cross section ~ ca. 1/3 l at 285 / 292 kn BAM VIII.2 INDE

42 Applications Increase of debonding between adhesive and concrete Failure of concrete caused by the returning wave BAM VIII.2 INDE

43 Overview Introduction Applications Quantitative Approach Conclusions Outlook BAM VIII.2 INDE

44 Quantitative Approach Concrete specimen A with voids 20 * 20 * 10 cm³ Number of defect 1 Intended concrete cover 8 cm Radar result on concrete cover 9.2 ± 1.5 cm 2 6 cm 7.6 ± 1.5 cm 10 * 10* 10 cm³ 3 4 cm ± 0.0 cm plan view 4 2 cm ± 0.0 cm 5 2 cm 3.0 ± 1.0 cm 6 4 cm 4.3 ± 1.0 cm cross section cm 8 cm 3.5 ± 1.0 cm 4.3 ± 1.0 cm BAM VIII.2 INDE

45 Quantitative Approach Concrete specimen with A voids 20 * 20 * 10 cm³ 10 * 10* 10 cm³ plan view 15 min heating cross section 2 h cooling down BAM VIII.2 INDE

46 Quantitative Approach Temperature time curves and difference curve of the cooling down process 30 T max reference 1,5 Temperature in C void (no 7) difference 1,0 0,5 T in K , Cooling time in s BAM VIII.2 INDE

47 Quantitative Approach Time of maximum temperature difference depending on heating time Time of maximum temperature difference in s void no 1, d = 9,2 cm void no 2, d = 7,6 cm void no 3, d = 0,0-1,0 cm void no 4, d = 0,0-1,0 cm Heating time in s BAM VIII.2 INDE

48 Quantitative Approach Quantitative approaches PT / SPT - time domain FT PPT / SPT - frequency domain Temperature in C 30 T max reference void 28 difference Cooling time in s Transients and temperature-time-differencecurve of the cooling down process 1,5 1,0 0,5 0,0 T in K BAM VIII.2 INDE φ in rad 0,2 0,1 0,0-0,1-0,2-0,3 detection treshold f ch f b ' f b frequency in Hz φ Phase-frequency-difference-curve after FT of the transients

49 Quantitative Approach Quantitative PPT in NDT of thin-layered structures and pulse-heating Relationship between depth of a defect and blind frequency fb in literature [1]: z = C 1 α π f b and for bad sampled data: z = C ϕ 1 ' min α π f b ' z Depth of a defect in [m] fb...blind frequency in [Hz] Thermal diffusivity [m²/s] C1...Correlation factor α z Depth of a defect in [m] fb.. Blind frequency in [Hz] C1.. Regression coefficient.. Phase at the detection threshold in [rad] ϕ min [1] Ibarra-Castanedo, C.: Quantitative subsurface defect evaluation by pulsed phase thermography: depth retrieval with the phase, Phd thesis, Université Laval, Canada, BAM VIII.2 INDE

50 Quantitative Approach Phase contrast curves 1.0x φ φ in rad -1.0x x x x min frequency in Hz φ V1 φ V2 φ V5 φ V6 φ V7 φ V8 BAM VIII.2 INDE

51 Quantitative Approach Phase-contrast-curves for void 2 concrete specimen B for different heating times 5,0x10-2 φ of void V2 0,0 φ in rad -5,0x ,0x ,5x10-1 f ch, 2 30 min 15 min 10 min 5 min 1E-4 1E-3 0,01 frequency in Hz BAM VIII.2 INDE

52 Quantitative Approach New quantitative approach for PPT in NDT-CE Relationship between depth of a defect and the frequency of the maximum phase contrast fch: α z = f ( ) = f ch k c α f z Depth of a defect in [m] fch...characteristic frequency in [Hz] Thermal diffusivity [m²/s] kc...correction factor ch 1 α BAM VIII.2 INDE z=k c (α/f ch ) 0,5 Calculated depths for specimen A with 30 min of heating and fitted fch (depths between 3 and 8 cm), kc= and α= 8.75 x 10-7 m²/s. radar+1cm z(f ch ) with fit and k c =1 radar radar-1cm depth in cm

53 Quantitative Approach z in cm z = 1,17683x(α/f ch ) 1/2-0, Radar Linear fitting, 30 min heating R=0,99149 S d =0, (α/f ch ) 1/2 x100 z in cm z = 1,20942x(α/f ch ) 1/2-0, Radar Linear fitting, 15 min heating 4 R=0, S d =0, (α/f ch ) 1/2 x100 Figure1: Phase correlationresults for the polystyrene voids of specimens A and B for 30 (left) and 15 min (right up) of heating with an IR-radiator. z = 1,01737x(α/f ch ) 1/2-0, z = 0,95827x(α/f ch ) 1/2-0, z in cm Radar Linear fitting, 10 min heating R=0,94802 S d =0, (α/f ch ) 1/2 x100 z in cm Radar Linear fitting, 5 min heating R=0,95164 S d =0, (α/f ch ) 1/2 x100 Figure 2: Phase correlation results for the polystyrene voids of specimens A and B for 10 (left) and 5 min (right) of heating with an IR-radiator. BAM VIII.2 INDE

54 Quantitative Approach Amplitude contrast curves 4,0x10-1 A A V1 A a.u. 3,0x10-1 2,0x10-1 1,0x10-1 0,0-1,0x10-1 A V2 A V5 A V6 A V7 A V8 15 min frequency in Hz BAM VIII.2 INDE

55 Quantitative Approach Amplitude and Phase in comparison Specimen A Void / t h V1 / Phase Amplitude V2 / Phase Amplitude V5 / Phase Amplitude V6 / Phase Amplitude V7 / Phase Amplitude V8 / Phase Amplitude 30 min 1.46 (1.20) , f ch in Hz x min , min min (5.36) min Equation 1 without k c in cm 15 min min min Radar result on concrete cover in cm 9.2 ± 1.0 radar 7.6 ± 1.0 radar 3.0 ± 1.0 radar Overview of the parameters for quantitative SPT in frequency domain for heating times t h of 30, 15, 10 and 5 min and with estimated α= 8.75 x 10-7 m 2 /s for concrete, the values in () were gained by using fit-functions. BAM VIII.2 INDE ± 1.0 radar 3.5 ± 1.0 radar 4.3 ± 1.0 radar

56 Quantitative Approach Many other examples approve, also for laminated specimens with thicknesses between 1 to 2 cm BAM VIII.2 INDE

Quantitative Approach Altes Museum, Berlin, Germany Eldest museum building of Berlin Built by Karl Friedrich Schinkel between 1823 to 1829 World Heritage Regular limestone and

57 Quantitative Approach Altes Museum, Berlin, Germany Eldest museum building of Berlin Built by Karl Friedrich Schinkel between 1823 to 1829 World Heritage Regular limestone and brick masonry Dimension: m * m Partly destroyed by bombs and fire during WW II. Reconstruction in the 1960ies General rebuilding planned for 2008 BAM VIII.2 INDE

58 Quantitative Approach Position 4: Columns in the rotunda localisation of debonding between sandstone/mortar or mortar/stucco marble mortar: 2 to 3 cm stucco marble: 3 to 6 mm, cracks BAM VIII.2 INDE

Quantitative Approach Location of plaster delaminations at columns in the rotunda of the Altes Museum, Berlin Heating of the surface: Manually, area

59 Quantitative Approach Location of plaster delaminations at columns in the rotunda of the Altes Museum, Berlin Heating of the surface: Manually, area height: 1 m fan heater, 5 min Observation of cooling down: Area height 1 m, 15 min, 2 Hz SC1000, 3.4 to 5 mm Data analysis: SPT BAM VIII.2 INDE

60 Quantitative Approach Location of plaster delaminations at columns in the rotunda of the Altes Museum, Berlin column thermogram phase image Temperature range: 20 to 30 o C 5.56 x 10-4 Hz BAM VIII.2 INDE

61 Quantitative Approach Application for in-situ investigations, case study Altes Museum in Berlin z αf = 6 0, 10 x 1, x = 3 ch x 2 3, cm phase image BAM VIII.2 INDE

62 Quantitative Approach Comparison with simulations (specimen B, void 2, 15 min heating, FT) A a.u. void 2, specimen B, z=6 cm z αf = 8, 75 2, x 10 x = ch x = 5, 47 cm 6, 00 cm frequency in Hz Maul, BAM VIII.2 BAM VIII.2 INDE

63 Overview Introduction Applications Quantitative Approach Conclusions Outlook BAM VIII.2 INDE

64 Conclusions Conclusions SPT in frequency domain is a suitable enhancement for qualitative and quantitative measurements in CE with a wide span of applications The new inverse approach for quantitative thermography via characteristic frequency fch is very useful for the estimation of defects depth between 1 to 10 cm Advantage of the phase in qualitative measurements - Influence of inhomogeneous surface structures or heating is reduced - It displays deeper voids with higher contrast Advantage of the amplitude in quantitative measurements BAM VIII.2 INDE

65 Overview Introduction Applications Quantitative Approach Conclusions Outlook BAM VIII.2 INDE

66 Outlook What next? Further going analysis of experimental and numerical time sequences of thermograms with square pulse thermography (SPT) in frequency domain, parameter studies and validation Systematic investigations on the localisation and the shape of inhomogeneities Comparison of numerical simulations and experimental data Quality system for the repair and strengthening of bridges with carbon fibre, reinforced polymers (CFRP) by means of IT (Sustainable Bridges) Optimized and automated scanning system for tests with IT by using flashlights will be set-up and applied as a prototype for on-site tests at bridges BAM VIII.2 INDE

67 Thanks for your attention! and many thanks to: R. Helmerich, Ch. Maierhofer, M. Röllig and H. Wiggenauser Division VIII.2 Non-destructive Damage Assessment and Environmental Measurement Methods, Federal Institute for Material Research and Testing (BAM), Berlin, Germany Deutsche Forschungsgemeinschaft European Commission Stiftung Preussische Schlösser und Gärten Berlin-Brandenburg BAM VIII.2 INDE

68 More information and contact: lungen/abteilung_8/fg82/index.htm BAM VIII.2 INDE

Fourier analysis applied to Infrared Thermography of Fiber Composites used for the Strengthening of Structural Elements

11 th International Conference on Quantitative InfraRed Thermography Fourier analysis applied to Infrared Thermography of Fiber Composites used for the Strengthening of Structural Elements by L. Cantini,