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  • 1. Rashed A.Sultan, Samer W. Guirguis, Mahmoud M. Younes, El-Dessouky E. El-Soaly / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 3, Issue 1, January -February 2013, pp.279-288 Delamination Detection By Thermography Rashed A.Sultan, Samer W. Guirguis, Mahmoud M. Younes, El-Dessouky E. El-Soaly *Libyan Army, mechanical engineering department, Benghazi, Libya, **Military Technical College, mechanical engineering department, Cairo, Egypt, ***Military Technical College, Head of mechanical engineering department, Cairo, Egypt, ****10th of Ramadan Higher Institute of Technology, mechanical engineering department, Cairo , Egypt ,Abstract Infrared thermography is a two- front propagates, by diffusion, under the surface anddimensional, non-contact technique allowing also because of radiation and convection losses. Thesurface temperature mapping by providing presence of a defect reduces the diffusion rate socolourful images easy to interpret through the that when observing the surface temperature, defectsuse of an external energy source and an infrared appear as areas of different temperatures withdetector. The attention of the present study was respect to surrounding sound areas once the thermalfocused on the aid provided by active front has reached them. Consequently, deeperthermography for non-destructive evaluation of defects will be observed later and with a reducedcomposite material. In present work the contrast [4].experimental analysis was performed by testingseveral specimens, which were made of E glass Thermography is now a popular nonwoven with epoxy which included the most destructive testing method for detecting defects incommonly encountered kinds of damage called composite structures. Active thermography methoddelamination artificially created in composite for composites is well reported in literature [5-6].laminate specimens. From the experimental An active thermography system consists of a heaterinvestigations, the effects of delamination area on unit for controlled heating of the test specimen, anthe detection were elucidated. Also the infrared camera for capturing the surfaceapplicability of the present thermograph method temperature evolution of the specimen, and a datadepends on a relative difference of thermal acquisition system for acquiring the correspondingproperty between the delamination and its infrared images over a specific period of time.surrounding was explained. Delamination is one of the most commonKeywords: Active infrared thermography, defects for composite materials. It leads to theComposite material, Delamination. degradation of mechanical properties and also causes the failure of the overall composite1. Introduction component. To detect delaminations and ensure the Non-destructive inspection methods must safe operation of composite components, nonbe reliable, efficient, non expensive, fast and easy to destructive evaluation techniques are used. Anuse. Moreover, as materials and processes are extremely promising technique is thermography,constantly changing, inspection techniques should which has the advantage of good fault detectionadapt to this evolution, too. Among various non possibility along with the capacity to inspect a largedestructive inspection techniques currently used is area within a short time. Thermography is alsoinfrared thermography which a non-contact applicable to a wide range of materials, includinginspection tool. It is relevant whenever there is a glass fibre, carbon fibre composites and metallicthermal contrast between the inspected object and materials, where specific excitation techniques arethe surrounding area of interest [1-3]. needed for each application. To inspect defects over a large scale and at large stand-off distances, Thermography is a technique of producing integration of thermography has been investigateda live thermal picture of an object based on the [7].infrared radiation received from it (emitted by anyobject). In pulse thermography, a thermal pulse is The present paper describes experimentsapplied to the material to be inspected. Following conducted with the active thermographic procedure,the application of this thermal pulse, a measurement which consists in sending a controlled heat fluxof the temporal evolution of the specimen surface using an external heat source (hot air blower) to thetemperature is performed with an infrared camera inspected composite laminate plate. The objective ofallowing subsurface defects to be revealed. The this paper is to present results from sometemperature of the material changes rapidly after the experiments using active thermographic inspectioninitial thermal perturbation because the thermal procedure on composite material consist of E glass woven and matrix with deliberately inserted 279 | P a g e
  • 2. Rashed A.Sultan, Samer W. Guirguis, Mahmoud M. Younes, El-Dessouky E. El-Soaly / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 3, Issue 1, January -February 2013, pp.279-288 artificial delamination. Effect of delamination area Cross ply 8-layered plates include E glass fibres and variation of thermal properties between embedded in an epoxy matrix were used in present delamination and basic material were studied by experimental work, with an overall laminate analyzing the surface temperature profiles and thickness of 2.5 mm. The dimensions of square thermal contrasts obtained from experimental active specimens were (200x200) mm2. Aluminum foils as thermal imaging system. the man-made delaminations were manufactured with different areas (50x50, 100x100, 150x150) 2. Experiment 1 mm2 inserted in the central mid plane of some plates 2.1 Samples preparation as shown in Figure.1. 50mm 200mm 50mm 200mm 200mm 200mm a) Healthy plate (no delamination) b) Delamination area (50x50) mm2 150mm 100mm 150mm 100mm 200mm200mm 200mm 200mm c) Delamination area (100x100) mm2 d) Delamination area (150x150) mm2 Figure.1 Test specimens 2.2 Active thermography experimental set-up infrared thermography is shown in Figure.2. The The investigation of composite materials infrared camera measures the thermal transient at most often demands the active method. The active the surface of the plates resulting from the heating approach requires an external heat source to of the plates. The infrared camera captures the stimulate tested materials. The present thermal information and generates two dimensional experimentation was carried out by using a hot air thermogram which was saved in the camera memory blower to heat the sample with 2.5 kW output power and then transferred to the computer for further uniformly. The heat source was kept 30 cm from the processing. The emissivity was set at 1 (black investigated plate and the camera was held 70 cm body), a value which offered the image with the best from the sample. The experimental setup for active contrast with the background. 280 | P a g e
  • 3. Rashed A.Sultan, Samer W. Guirguis, Mahmoud M. Younes, El-Dessouky E. El-Soaly / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 3, Issue 1, January -February 2013, pp.279-288 Specimen Hot air blower IR camera Figure.2 Active thermography experimental set-up2.3 Results and discussion delamination, an extension of deterioration during The surface temperature distribution the manufacturing process. Thermal contrast wasimages over the laminated composite plates were obtained from the fact that, the Aluminum foil at theobtained after the end of heating time 7 seconds place of delaminations behaves like a barrier whichusing experimental set-up. All thermograms makes surface temperature above the delaminatedhighlight the delaminations in the composite plates surface slightly warmer than the round healthyaccording to their areas but with various accuracy. region. Present thermal contrast value was measuredSome of them are being influenced by non-uniform by thermography to detect delaminations whichheating, because the heating time is short. In the were used to analyze for varying areas. The surfacethermograms associated to these delaminated plates, temperature distributions obtained from activeone can observe, besides the central induced thermography experiment are shown in Figure.3. a) Healthy plate b) Delamination area (50x50) mm2 281 | P a g e
  • 4. Rashed A.Sultan, Samer W. Guirguis, Mahmoud M. Younes, El-Dessouky E. El-Soaly / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 3, Issue 1, January -February 2013, pp.279-288 c) Delamination area (100x100) mm2 d) Delamination area (150x150) mm2 Figure.3 Surface temperature distributions for healthy and delaminated platesThe temperature profiles across the centre lines of the healthy and delaminated plates are shown in Figure.4. a) Healthy plate b) Delamination area (50x50) mm2 c) Delamination area (100x100) mm2 282 | P a g e
  • 5. Rashed A.Sultan, Samer W. Guirguis, Mahmoud M. Younes, El-Dessouky E. El-Soaly / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 3, Issue 1, January -February 2013, pp.279-288 d) Delamination area (150x150) mm2 Figure.4 Surface temperature profiles across the centre line of the plateFigure.3 (a) and Figure.4 (a) show that the delamination increases, the thermal contrast wastemperature was almost uniform throughout the also increased except for largest delamination areasurface of healthy plate. From the Figure.4 (a) the (150x150) mm2 the maximum contrast decrease toaverage temperature across the length of the healthy 3.85°C because of the short time of heating, also inplate is 22.4°C experimentally. Figures.3 (b, c, d) the case of the largest delamination, there was moreand Figures.4 (b, c, d) show that there are some non- air trapped between the inserted foil and the resinuniform temperature distributions at the specific promoting the dissipation of heat in this delaminatedlocation of simulated delaminations, revealing that area, but when the time of pre heating increased tothe plate does have delamination. The 10 seconds instead of 7 seconds, the contrastapproximately maximum thermal contrasts obtained increases to 6.1°C as shown in Figure.5. Howeverexperimentally at the delamination locations were the localized contrast regions are clearly identified5.1°C and 5.7°C for delamination areas (50x50 and even for small delamination area.100x100) mm2 respectively. When the area of theFigure.5 Surface temperature profile across the centre line of plate with delamination area (150x150) mm 2 after heating 10 seconds 283 | P a g e
  • 6. Rashed A.Sultan, Samer W. Guirguis, Mahmoud M. Younes, El-Dessouky E. El-Soaly / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 3, Issue 1, January -February 2013, pp.279-288It was observed that after the end of the pre-heating are of course other limitations, mostly concernedprocess, temperature profiles revealed the internal with the size of the delamination, the resolution ofdelamination. Because of different thermal the infrared camera, the timing image capturingconductivity between delamination and healthy during the transient phase and the thermalarea existence the defect was manifested by higher properties of the examined material. Thesetemperature in the delaminated region. It is possible limitations should be account for the significantto vary heat input and heating time to obtain best accuracy to estimate the delamination shape indelamination detectability, which depends on the laminated composite structure. Generally allmaterial being tested, its thickness, depth and area objects radiate energy continuously in the form ofof the delamination. In order to get a clear picture electromagnetic waves mainly in infrared regionof searched delaminations the pre-heating time produced by thermal vibrations of the molecules.cannot be too long. Long-time pre-heating led to The relationship governing radiation power fromeven temperature distribution over entire searched hot objects according to the Stefan-Boltzmann lawsurface. This effect was observed independently on is:type of a heat source (flash or heater radiator) andon the position of the heat source. After many trials P = ε σ AT4 (1)it was stated that an appropriate warm-up time in Where,present case of composite laminate materials P = Radiated power (watts)should be about 7 seconds. It is also worth A = Radiating area (m2)mentioning that although the best possible results σ = Stefan-Boltzmann constant (5.6703 x 10-8concerning the clearest images (high thermal W/m2K4)contrast) were acquired at relatively short periods ε = Emissivity (=0.03for Aluminum foil)during the cooling down process (composites have T=Temperature of radiator (in Kelvin)relatively low thermal conductivity values). ThereThe total radiated power from delaminated specimens can be calculated according to Eq1, that showing below inTable 1 Table 1 Total radiation power from delaminated samples Delamination area (mm2 ) Total radiation power (w) 50x50 0.0322 100x100 0.129 150x150 0.290The relation between total radiation power and the delamination areas shown in Figure.6. 1.1 1 Normalized total radiation power Normalized total radiation power 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 50x50 1 2 100x100 3 4 150x150 5 6 Delaminated area Delaminated area (mm2) Figure.6 Variation of total radiation power with delaminated areas 284 | P a g e
  • 7. Rashed A.Sultan, Samer W. Guirguis, Mahmoud M. Younes, El-Dessouky E. El-Soaly / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 3, Issue 1, January -February 2013, pp.279-2883. Experiment 23.1 Specimens preparation experiment consist of different delamination thermal E glass woven with epoxy specimens were properties, such as sample 1 contains simulatedfabricated including artificial delaminations located delamination Aluminum foil coated with specialat same depth 1.25 mm Figure.7.The areas of these isolated wax and sample 2 with simulatedtest samples were (205x205) mm2, number of layers delamination air gap. All these simulatedwas 8 and the area of delamination was (60x205) delaminations have different thermal properties.mm2.The simulated test plates used in present 205 mm 60 mm 205 mm a) Sample 1 (Aluminum delamination) b) Sample 2 (Air gap delamination) Figure.7 Test specimens3.2 Delaminations description 3.3 Experimental set-up A brief description of different anomalies The schematic of the experimental setup isin the previous test specimens is provided below: shown in Figure.8. A heat blower was used as a heat1. Air gap delamination, a manufacturing defect source to all samples. The distance between thewhere air was trapped between layers of fiber glass heating element and the test plate for eachso that there was glass fiber but no resin to bond it. experiment was kept constant. A gap of2. Aluminum alloy delamination, an area of approximately 30 cm was maintained between thespecimen whereby one layer of fiber glass has heat source and the test sample.separated from the adjacent layer, by using anAluminum foil coated with special wax. Sample 2 Hot air blower IR camera Figure.8 Active thermography experimental set-up 285 | P a g e
  • 8. Rashed A.Sultan, Samer W. Guirguis, Mahmoud M. Younes, El-Dessouky E. El-Soaly / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 3, Issue 1, January -February 2013, pp.279-2883.4 Results and discussion temperature and time elapsing after pre-heating All samples considered in present interruption achieved in delamination area, wereexperiment were heated for different time periods, characterized by a higher temperature in connectioni.e. 3 seconds, 7 seconds, 12 seconds, and 1 min. A to the rest of the specimen, also the cooling processthermal camera was used to record the thermal in the area with delamination runs much longer.intensity decay data with cooling time, following the Figure.9, gives a direct impression of the behaviourremoval of the heat source. When the test samples of the temperature at the surface of the test samples,were heated for 3 seconds, no significant after the maximum value of the temperature wastemperature rise was observed whereas, when reached. The Figure shows the temperature decay ofheated for 1 minute, the thermal camera produces different simulated delamination samples aftersaturated images. Hence, for the cases considered in heating each one uniformly and separately for 7the present experiment it was observed that the seconds. However, it was observed that, temperatureoptimal heating times for delamination detection of decays in sample 1 and sample 2 cases have similardifferent thermal properties were 7 and 12 seconds. decreasing trends over the cooling cycle and wereGenerally in present case, relation between difficult to distinguish when heated for 7 seconds. 23.9 Temperature °C 23.8 Sample 1 Aluminum 23.7 delamination 23.6 Sample 2 air gap 23.5 delamination 23.4 23.3 0 5 10 15 20 25 Time (second) Figure.9 Temperature decay for different delamination thermal properties heated for 7 secondsThe thermal images show prominent thermal decay when heated for 12 seconds, compared to the case of heatingfor 7 seconds, the corresponding temperature decay is shown in Figure.10. Sample 1 attains maximumtemperature when heated for 12 seconds followed by sample 2. 25.3 Temperature °C 25 24.7 Sample 1 Aluminum 24.4 delamination Sample 2 air gap 24.1 delamination 23.8 23.5 0 5 10 15 20 25 Time (second) Figure.10 Temperature decay for different delamination thermal properties heated for 12 secondsThermal camera images for sample 1 and sample 2 are shown in Figure.11 and Figure.12. In the followingthermograms associated to delaminated samples, one can observe, besides the central artificial delamination, alittle deterioration at upper portion of the artificial delaminations during the manufacturing process. 286 | P a g e
  • 9. Rashed A.Sultan, Samer W. Guirguis, Mahmoud M. Younes, El-Dessouky E. El-Soaly / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 3, Issue 1, January -February 2013, pp.279-288 a) Sample 1 (Aluminum delamination) b) Sample 2 (Air gap delamination) Figure.11 Thermal camera images after 7 seconds of heating a) Sample 1 (Aluminum delamination) b) Sample 2 (Air gap delamination) Figure.12 Thermal camera images after 12 seconds of heatingAs heating time increases, the contrast between basic material. The present experiment confirmeddelamination and healthy area increases and that thermal properties of a delamination materialdelamination of both samples show different can be concluded from sequential recording ofcontrast depending on its thermal properties as thermograms including temperature distribution onshown before in Figure 11 and Figure 12. The the surface of the plate under test starting at theheating time of 12 seconds instead of 7 seconds beginning of the cool down phase. Thermal imagesleads to increase of the heating energy, because the allowed determination of whether specific materialheating energy must be enough to creat thermal of delamination was of higher or lower thermalcontrast between healthy and delaminated area, properties than the healthy material.which can be sensed by infrared camera. If theenergy is not enough as introduced before at 4. Conclusionsheating time 7 seconds, the delamination may be In this work, the study of delaminations indifficult to extinguish, especially when the composite laminate plates using thermographycomparing of delamination appearance was technique was done experimentally. Theaccording to the type of delamination thermal experiments were intended to detect delaminationproperties. Therefore the delamination visibility of variable areas and thermal properties existing independs strongly on the thermal properties of both composite laminate plates. The followingthe basic material and the delamination itself. It is conclusions can be drawn:demonstrated that the heating temperature plays an 1. Thermographic images analysis is an effectiveimportant role in the detection of delamination method for revealing delamination in the compositewhich increase amount of thermal radiation that the received from surface, also by increasing 2. Thermography methods require specific skills toheating time, minimized the effects of non-uniform achieve good results in delamination detection fortemperature distribution, one of the main problem composite material.that affect the quality of this type of non destructive 3. Because of different thermal conductivitytest. The suitability of infrared thermography to between delamination and healthy area existencenon destructive testing depends on the ability to the defect was manifested by higher temperature indetection of the temperature variation or thermal the delaminated region.contrast induced by a delamination which greatly 4. It is possible to vary heat input and heating timeeffected by thermal properties of delamination and to obtain best defect detectability, which depends 287 | P a g e
  • 10. Rashed A.Sultan, Samer W. Guirguis, Mahmoud M. Younes, El-Dessouky E. El-Soaly / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 3, Issue 1, January -February 2013, pp.279-288on the material being tested, its thickness, depth, aerospace materials with lock-inarea of the delamination, the timing image thermography” Engineering failurecapturing during the transient phase and the analysis, volume 13, issue 3, p.p 380–resolution of thermal camera. 388, April 2006.5. The heating temperature plays an important role [4] Clemente Ibarra Castanedo “Quantitativein the detection of delamination which increase subsurface defect evaluation by pulsedamount of thermal radiation that the camera phase thermography: depth retrieval withreceived from surface. the phase” Thèse présentée à la Faculté6. The delamination visibility depends strongly on des études supérieures de l’Universitéthe thermal properties of both the basic material Laval dans le cadre du programme deand the delamination itself. doctorat en génie électrique pour l’obtention du grade de PhilosophiaeReferences Doctor (Ph.D.) 2005. [1] G. Wróbel a, Z. Rdzawski b,c, G. Muzia b, [5] X.Maldague and S.Marinetti “Pulse phase S. Pawlak a,” Transient thermography in infrared thermography” Journal of applied the assessment of local fibre content in physics, volume 79 , issue, 5.1995. CFRP laminates”Journal of achievements [6] X.P.V. Maldague ” Introduction to NDT in materials and manufacturing by active infrared thermography” engineering,volume 31, issue 2, December Materials Evaluation,. 60, No. 9. pp. 1060- 2008. 1073 Key: citeulike: 6541620, September [2] M. Krishnapillai, R. Jones, I.H. Marshall, 2002. M. Bannister, N. Rajic “Thermography as [7] Liang Cheng and Gui Yun Tian a tool for damage assessment” Composite “Comparison of non destructive testing structures, 2005. methods on detection of delaminations in [3] Carosena Meola, Giovanni Maria composites” Journal of sensors, vol 2012, Carlomagno, Antonino Squillace, Antonio article ID 408437.2012. Vitiello “Non-destructive evaluation of 288 | P a g e