This paper presents a CW raster-scanning THz imaging setup, used to perform Non-Destructive Testing of Kevlar and carbon fibre samples. The setup uses a 2.5 THz Quantum Cascade Laser as a source. Delamination defect in a Kevlar sample was detected showing a sensitivity to laser polarization orientation. Detection of a break in a carbon/epoxy sample was also performed

Barbieri, Stefano

Destic, Fabien

Massenot, Sébastien

Mollier, Jean-Claude

Petitjean, Yoann

English

Fabien Destic

Yoann Petitjean

Sebastien Massenot

Jean-Claude Mollier

Stefano Barbieri

Crossref

THz QCL &amp;#x2014; Based active imaging applied to composite materials diagnostic

Open Archive Toulouse Archive Ouverte

  This is an author-deposited version published in: http://oatao.univ-toulouse.fr/ Eprints ID: 4120 To cite this document: DESTIC Fabien, PETITJEAN Yoann, MASSENOT Sébastien, MOLLIER Jean-Claude, BARBIERI Stefano. THz QCL - Based active imaging applied to composite materials diagnostic. In: 35th International Conference on Infrared Millimeter and Terahertz (IRMMW-THz) 2010, 05-10 Sept 2010, Roma, Italy.  Any correspondence concerning this service should be sent to the repository administrator: staff-oatao@inp-toulouse.fr THz QCL - based active imaging applied tocomposite materials diagnosticFabien Destic∗, Yoann Petitjean∗, Se´bastien Massenot∗, Jean-Claude Mollier∗†, and Stefano Barbieri‡∗Universite´ de Toulouse - Institut Supe´rieur de l’Ae´ronautique et de l’Espace - OLIMPES, Toulouse, Franceemail: fabien.destic@isae.fr†Office National d’E´tudes et de Recherches Ae´rospatiales - DOTA, Toulouse, France‡Universite´ Paris Diderot - Paris 7, Laboratoire Mate´riaux et Phe´nome`nes Quantiques, Paris, FranceAbstract—This paper presents a CW raster-scanning THzimaging setup used to perform Non-Destructive Testing ofKevlarTMand carbon fibre samples. The setup uses a 2.5 THzQuantum Cascade Laser as a source. Delamination defect ina Kevlar sample was detected showing a sensitivity to laserpolarization orientation. Detection of a break in a carbon/epoxysample was also performed.I. INTRODUCTIONComposite materials such as glass fibre epoxy, carbon fibreand Kevlar have experienced a rapid development during thelast decade. Their use in aeronautical engineering is now veryimportant. For example, in the Airbus A380, fibrous compositematerials have been deployed extensively in primary loadcar-rying structure to achieve a 17% lower fuel use per passengerthan comparable aircraft.Non-Destructive Testing (NDT) is useful for initial inspec-tion of test samples and analysis of reasons for failure. Severalmethods are currently used: ultrasonic testing with singleelement transducers and linear phased array probes in pulseecho and through transmission mode, resonance methods,shearography and thermography for example.NDT using THzwaves can be an alternative when “traditional” methods havepoor efficiency (composite made from soft epoxy resin, forinstance) or to improve spatial resolution.During the five past years, some works have been conductedabout characterization or imaging, in the THz range, of variouscomposite materials. Most of these works used pulsed THz-Time Domain Spectroscopy (THz-TDS). Rutz and coworkers[1], [2] studied low density polyethylene (LDPE) contain-ing titanium dioxyde nanospheres and glass-fibre reinforcedpolymers to measure the concentration of glass fibres. Theorientation of glass fibres in reinforced plastics can also bedetermined [3], sand inclusion or metal in HDPE weld jointscan be detected [4].Test of fire damages on carbon fibre using reflectivity de-pendence to polarization was reported [5], [6]. Stoik et al. [7]also used THz-TDS to detect burn damages and delaminationon glass fiber.Only a few of these works have also performed CW THzimaging: at 1.63 THz with a gas laser [5] or with Gunn diodesat 0.2 and 0.38 THz [5] or 0.6 THz [6].Composite materials diagnostic using CW THz waves pro-duced by Quantum Cascade Laser have not yet been in-vestigated. Considering the QCLs capability to emit a fewtens of mW in the [1-4] THz frequency range, with beamqualities in constant improvement, this approch seems to bevery promising.In this paper, transmission properties of Kevlar and carbonfibre samples are investigated with a QCL based imagingsetup. Measurements have been made on various samples,known to present a defect, for two orthogonal electric fieldorientations relative to sample structure.II. EXPERIMENTAL SETUPThe source used in the raster-scanning imaging experimentalsetup is a Quantum Cascade Laser (QCL)emitting at 2.5 THz.The QCL is driven by a pulsed current source. A ten ofmilliwatts at 2.5 THz are available at the output of the cryostat.The emitted beam is then collected by a set of four off-axisparabolic mirrors that allow us to focus it on the sample to beimaged. The object is moved in X and Y by two motorizedtranslation stages. Two types of detector can be used: eithera cooled NTD-Ge bolometer or a Golay cell. The signal isacquired via a lock-in amplifier.LHe cryostatPulsed current sourceLock-in amplifierNTD-Ge bolometerLHe cryostatSampleOAPM 3 OAPM 2OAPM 4 OAPM 1XYComputerLNAReference frequencyQCLZaperture diaphragmFig. 1. Experimental setupThe setup was completely characterized:• spot size is 1.09 mm along vertical axis and 1 mm alongthe horizontal one.• spatial resolution is 0.7 mm (imaging a metallic resolu-tion target with a 1 mm step and datas processing)• the CW THz power is 0.5 mW, mainly due to atmospherictransmission losses.• QCL is linearly polarized, oriented in the horizontalplane.III. COMPOSITE MATERIALS DIAGNOSTICTwo samples, one Kevlar fibres and the second carbonfibres, both with resin epoxy, with known defects have beenused. For all experiments, we performed two acquisitionsfor each sample. As the QCL is linearly polarized in thehorizontal plane, the first image is made for a given positionof the sample, taken as a reference. For the second image, thesample is rotated by 90 ◦. So, we obtain two images for twoperpendicular orientations of the electric field, relative to thesample.The first sample is made of two Kevlar sheets (thickness =0.5 mm, mesh size ≈ 2 mm), assembled with epoxy. A thinfilm, 5 mm wide, is inserted between two sheets to avoid resinpolymerization. By this way, a region of weakness is producedwhere, applying a stress, we can create delamination. Figure 2shows processed images (84x84 pixels, each pixel 0.25 mm x0.25 mm). As explained before, the two images are obtainedfor two orthogonal positions of the sample relative to laserpolarization, arrows showing electric field orientation.The delamination appears as a dark region correspondingto low transmission. This can be explained by scattering fromKevlar fibres. In fact, the stress was applied in a zone whereepoxy is not present and, as Kevlar fibres are not teared dueto their elasticity, fibres perpendicular to the delaminationdirection connect the opposite sides of the break whereas fibresparallel to the break are retracted on each side This fibresarrangement can behave as a subwavelength grating. Actually,its step Λ ≈ 10µm is well below the working wavelength(λ = 125µm): such structures are known to be polarizationdependent.On THz images, defect is more visible when electric fieldis perpendicular to the delamination main direction ie parallelto fibres main orientation (fig.2 right).Fig. 2. Processed images (84 x 84 pixels or 21 mm2)We also tested a 0.5 mm thick sample of carbon fibreepoxy. An adhesive film is also sandwiched between twosheets of fibre to create a weak region where a stress hasbeen applied to break the fibres. Figure 3 presents the 120 x100 pixels processed images, white arrow indicating electricalfiled orientation.We can clearly identify the region where fibres are broken,corresponding to a maximum in transmission. This surprisingbehavior, compared to the one observed for Kevlar, can beexplained from the fact that, in this case, fibres are totallybroken and an open failure is created. This failure dimensionsare about a few wavelengths, allowing transmission of theTHz wave with some diffraction and a low sensitivity topolarization.Fig. 3. Processed THz images (84 x 84 pixels or 21 x 21 mm2)IV. CONCLUSION AND PROSPECTSNon-Destructive Testing of Kevlar and carbon fibre sampleswas realized by THz transmission mode imaging using a 2.5THz Quantum Cascade Laser. A delamination defect in aKevlar sample was detected showing a sensitivity to laserpolarization orientation. A break in carbon/epoxy was alsodetected.As a perspective, it will be interesting to test these samplesin transmission at other frequencies and in reflection modeimaging, this evolution of the setup being essential to envisagein-situ evaluation of materials. Obviously, samples tested inthis paper are not real cases as they are thin and very damaged.However, these results seems to be promising.REFERENCES[1] F. RUTZ, M. KOCH, S. KHARE et M. MONEKE, Quality control ofpolymeric compounds using terahertz imaging, vol. 5727, p. 115–122,SPIE, 2005.[2] F. RUTZ, S. WIETZKE, M. KOCH, H. RICHTER, S. HICKMANN,V. TRAPPE et U. EWERT, Non-destructive testing of glass-fibre reinforcedpolymers using Terahertz spectroscopy, in European Conference on NonDestructive Testing (ECNDT2006), 2006.[3] C. JO¨RDENS, M. SCHELLER, S. WIETZKE, D. ROMEIKE, C. JANSEN,T. ZENTGRAF, K. WIESAUER, V. REISECKER et M. KOCH, Terahertzspectroscopy to study the orientation of glass fibres in reinforced plastics,Composites Science and Technology, vol. 70, no. 3, p. 472 – 477, 2010.[4] S. WIETZKE, C. JO¨RDENS, N. KRUMBHOLZ, B. BAUDRIT, M. BASTIANet M. KOCH, Terahertz imaging: a new non-destructive technique for thequality control of plastic weld joints, J. European Optical Society RapidPublication, 2007.[5] A. REDO-SANCHEZ, N. KARPOWICZ, J. XU et X.-C. ZHANG, Damageand defect inspection with terahertz waves, in 4th International Workshopon Ultrasonic and Adavanced methods for nondestructive Testing andmaterial Characterization (WWW.NDT.NET, e´d.), 2006.[6] N. KARPOWICZ, D. DAWES, M. J. PERRY et X.-C. ZHANG, Firedamage on carbon fiber materials characterized by THz waves, vol. 6212,p. 62120G, SPIE, 2006.[7] C. D. STOIK, M. J. BOHN et J. L. BLACKSHIRE, Nondestructiveevaluation of aircraft composites using transmissive terahertz time domainspectroscopy, Opt. Express, vol. 16, no. 21, p. 17039–17051, 2008.

and defect inspection with terahertz waves,

Fire damage on carbon ﬁber materials characterized by THz waves,

Non-destructive testing of glass-ﬁbre reinforced polymers using Terahertz spectroscopy,

Nondestructive evaluation of aircraft composites using transmissive terahertz time domain spectroscopy,

Quality control of polymeric compounds using terahertz imaging,

Terahertz imaging: a new non-destructive technique for the quality control of plastic weld joints,

Terahertz spectroscopy to study the orientation of glass ﬁbres in reinforced plastics,

THz QCL - Based active imaging applied to composite materials diagnostic

http://oatao.univ-toulouse.fr/4120/1/Destic_4120.pdf

THz QCL - Based active imaging applied to composite materials diagnostic

Abstract

Similar works

Full text

Available Versions

Crossref

Open Archive Toulouse Archive Ouverte