Figure 1: Transient thermal NDT approachesThe active approach has also several applications in NDT & E. The temperature differences during the transient phase appear on the material surface and so detection of subsurface defects is possible (areas of different temperatures when compared to the sound part(s) due to the different thermal diffusivity). Since the heating or cooling features of the stimulus source are identifiable by considering the time factor quantitative assessment is also feasible.
Automation In Non-destructive Testing: New Risks And Risk Sources Example
The most common modes of active thermography are pulsed thermography, long pulsed heating or step heating transient thermography, optical lock-in thermography, and ultrasound lock-in thermography. Advantages - limitationsThe main advantage of infrared thermography over the destructive testing techniques is that large areas can be scanned fast and with no need to be destroyed during testing. This results in major savings in time, people, work and machinery. In addition, there are advantages of infrared thermography over the other non-destructive techniques.
The infrared thermographic device is risk-free, as it does not emit any radiation; it only records the infrared radiation emitted from the material that is under assessment. Moreover, infrared thermography is an area investigating technique, whereas most of the other non-destructive methods are either point or line testing methods. Furthermore, infrared thermographic testing may be performed during both day - and night - time hours.Thermography, due to the fact that it uses infrared technology it is not possible to penetrate in extended depths (only a few mm's). That of course is one of the main limitations of the technique. Finally, environmental conditions also play an important role on outdoor infrared thermographic surveys utilising the passive approach ( i.e. Cloud cover, solar radiation, wind speed).
ApplicationsAlthough the use of infrared thermography is found to be extensive mainly in terms of research purposes in NDT & E, a number of applications are presented in this section.Assessment of defects under composite patchingA composite repair patch was investigated both experimentally and by modelling, with the intention of assessing an artificially introduced delamination (Teflon). The patch was a 6-ply boron epoxy composite material that was applied on an Al 2024-T3 surface. The dimensions of the Teflon were 25 mm x 25 mm and it was positioned between the 3rd and 4th ply of the composite patch (120 mm long x 70 mm wide). The thickness of each ply was 125µmm.Experimentally the panel was investigated using a portable state-of-the-art thermographic system (Thermoscope) with an integrated flash heating system (duration of flash heating time 3.1 ms) employing a medium-wave infrared camera (Merlin 3-5µmm by Indigo). The infrared camera uses a cooled indium antimonide detector with a frame rate of 60 Hz, a focal plane array pixel format of 320 (H) x 256 (V) and an optical lens of 13 mm focal length.For the purposes of thermal modelling, the ThermoCalc-3D software was employed. It is based on solving a heat conduction problem by means of an implicit finite-element numerical scheme.
The software was used in order to calculate the three-dimensional (3D) temperature distributions of the various layers of the panel and provide information about the delamination in space and in time. The specimen was heated uniformly, whilst the thermo-physical properties and heating time parameters shown in Table 1 were used for the modelling. Table 1: Parameters used during modellingIn Figure 2, a thermogram with representative line profiles from the investigated panel are presented.
The delamination was detected by thermography. Line profiles (on both axes) at various times from the obtained thermal images were plotted in order to obtain information about the size of the delamination in relation to the thermal transient time ( e.g. Possible shrinkage due to thermal diffusion).
From the line profiles it was possible to calculate the size of the delamination employing the Full Width Half Maximum (FWHM) approach. Figure 2: Thermogram and representative line profiles of the investigated composite panelThermal images, spatial profiles and thermal contrast curves of the panel from the thermal modelling run are presented in Figure 3. The results give a good indication of how the composite material responds to thermal heating.
It shows the behaviour of a delaminated composite material after it was heated with a thermal excitation source uniformly in order to detect a sub-surface defect by means of pulsed thermography. Figure 3: Thermal modelling results of composite panel. Upper graph shows development of contrast, Delta T, over defect with time. A thermal image and spatial profiles in both axes (X and Y) are also shown.Therefore, from the obtained results it is shown that experimentally or by the use of thermal modelling it is possible to evaluate (qualitatively and quantitatively) near surface delaminations in composites.Quality assurance and structural evaluation of GRP pipes.The Thermoscope system with the Merlin infrared camera was again utilised for the experimental treatments within this research work.
A total of three samples - components were manufactured and examined using the thermography kit; in some instances due to the complexity of the investigated samples, external thermal excitation sources ( i.e. Hot air of 1200 Watts or optical lamp of 500 Watts) were also employed as alternative solution of active thermographic investigation. Furthermore, pulsed thermography (PT) and pulsed phase thermography (PPT) were used for evaluation of the components. In the case of PPT either a Santa Barbara Focal Plane SBF125camera (14 bits, InSb 320x256 FPA, 3-5µm, nitrogen-cooled) or a ThermaCAM TM Phoenix ® from FLIR Systems (14 bits, InSb 640x512 FPA, 3-5µm, Stirling closed cycle cooler).
Two high power flashes (Balcar FX 60), providing 6.4 KJ for 2-10ms each, were used as heating sources. Thermographic data was analyzed with a PC (Pentium 4, 2 GB RAM) using MATLAB ® language from The MathWorks, Inc.Representative thermal images of the investigated samples were obtained during the transient phase of the thermographic inspections and are presented. In some instances, plots of the contrast versus the transient time of the identified defects were performed; the difference in intensity (D Intensity) between the detected defect and the sound region of the sample against the transient time during the cooling down process was plotted.Although the best possible results concerning the size of a detected defect were attained at particularly short transient times, the highest contrast images were acquired at relatively longer times. Figure 8: Defect 'C'.
(a) raw themogram at t=1.26 s; (b) second derivative image (from a 7th degree polynomial fitting) 2.17 s.Since the thermal conductivity of all these three inspected samples is relatively low, the samples were tested using a reasonably low maximum frame rate. A frame rate of 15 Hz was used; with the exception of the pipe that presented impact damage, where a higher frame rate (60 Hz) was needed. Furthermore, in order to avoid the high reflectance of the pipes during investigation and so record thermal images, the samples were either painted with black colour water based paint or even polished by applying a silver polishing substance ( i.e.
Figure 9: Thermal image of investigated impact damaged area after 0.017 seconds of heatingImpact damage on CFRP panels and honeycomb sandwich structuresDamage caused by low velocity impacts is a particular concern in the aircraft industry. In this work, impact damaged CFRP panels (150 x 100mm) of 2mm thickness (16 ply with a quasi-isotropic lay-up), as well as sandwich composite samples formed after bonded to the two faces of 25 mm thick Type 6 Nomax honeycomb core were investigated. All panels were cut from the same sheet. A falling weight impactor with a hemispherical 12.5 mm radius head was used to apply impacts of controlled energy. During impact, the samples were supported around their edges over a 125 x 75 mm aperture, allowing the bulk of the panels to rebound freely on impact.
The Thermoscope pulsed transient thermographic system, employing the medium wave infrared camera (Merlin 3-5µm by Indigo), was used to image the impact damage.PT is a rapid large area technique with the additional advantages of being single-sided and non-contact. These attributes make this technique particularly suitable for surveying either single panel or sandwich structures for impact damage. Examples of thermography images impact damage in the two types of samples are shown in figure 10.In addition to the evident difference in defect size, the sandwich sample image contains a high contrast component caused by a delamination close to the surface. A comparison of contrast vs. Elapsed time for the two images shows contrast peaking at a much earlier time for the sandwich sample, consistent with delaminations close to the surface.The size and the through thickness characteristics of the impact damage produced in single panel and sandwich samples are reflected in the NDT images obtained by PT. The technique has been shown to be effective for detecting and imaging impact damage in either isolated panel or sandwich samples. Figure 10: Thermal images of 12.75J impact damage in a panel sample (left) & in a sandwich sample (right) taken 0.5s after flash heating.
ConclusionsTransient - active thermography has emerged in recent years as a means of NDT & E technique. Its advantages are that it is a rapid large area non-contact imaging technique that produces images of subsurface features ( i.e. Defects) that are relatively straightforward to interpret. In this work, thermography trials took place on different components - applications.
In some instances, the technique provided prompt results. Nonetheless, thermography is an inherently near surface technique whose effectiveness will decrease with the material's thickness.
It also depends on the thermal properties of the material (different behaviour between high thermal conductive materials such as metals and lower thermal conductive materials such as composites). References. N.P.
Dan - who started out as a modder for Morrowind, Skyrim, and Fallout New Vegas - has close to two decades of experience in the video game industry under his belt and his talk on Ten Principles for Good Level Design at the Game Developer's Conference 2013 is cu. Today we are talking to Dan Taylor, a professional level designer who has in the past worked for Eidos, Square Enix, Ubisoft, Rockstar (among others) on games such as Medal of Honor Heroes 2, Hitman: Sniper, or Shadow of the Tomb Raider. World of warcraft graphics mods.
Avdelidis, A. Moropoulou, 'Emissivity considerations in building thermography', J. Energy & Buildings 35(7), (2003), pp.
Cost of nch software photo pad. 663-667. N.P. Avdelidis, C. Ibarra-Castanedo, X. Maldague, Z.P. Marioli-Riga, D.P. Almond, 'A thermographic comparison study for the assessment of composite patches', J.
Infrared Physics & Technology 45(4), (2004), pp. Ibarra-Castanedo, N.P. Avdelidis, E.G.
Grinzato, P.G. Marinetti, L. Maldague, 'Quantitative inspection of non-planar composite specimens by pulsed phase thermography' J.
QIRT 3(1), (2006), pp.
EPFL is one of the world’s most dynamic and reputed institutes of science and technology. In the heart of Europe, it offers a combination of excitement, excellence, inspiring education, and outstanding facilities for research. Its doctoral school is organized into 21 doctoral programs, each covering a well-established discipline or one of today’s interdisciplinary research areas. They form vibrant scientific communities that energize the exchange of scientific ideas and progress. Pierre Vandergheynst, Vice President for Education.
. Over the past couple of decades Non-Destructive Testing (NDT) has seen a significant increase in the use of automation. In addition to increased reliability, objectivity, consistency, repeatability, productivity, and so on, automating parts of the process is expected to decrease the potential for human error. However, the literature on human-automation interaction suggests that automation is not only associated with benefits, but also with new risks and risk sources.
Automation In Non-destructive Testing: New Risks And Risk Sources Examples
First, this paper will present the methodology used to identify—for the first time—possible risks associated with mechanised data acquisition and corresponding data evaluation. Moreover, it will highlight possible risks, their causes, consequences, and ways of preventing them. Second, those preventive measures will be further analysed by examining new risks that can arise from their implementation, i.e. Potential for failure that can arise from (a) working with automated defect-detection and sizing aids, (b) implementing Over the past couple of decades Non-Destructive Testing (NDT) has seen a significant increase in the use of automation. In addition to increased reliability, objectivity, consistency, repeatability, productivity, and so on, automating parts of the process is expected to decrease the potential for human error. However, the literature on human-automation interaction suggests that automation is not only associated with benefits, but also with new risks and risk sources. First, this paper will present the methodology used to identify—for the first time—possible risks associated with mechanised data acquisition and corresponding data evaluation.
Moreover, it will highlight possible risks, their causes, consequences, and ways of preventing them. Second, those preventive measures will be further analysed by examining new risks that can arise from their implementation, i.e.
Automation In Non-destructive Testing: New Risks And Risk Sources Definition
Potential for failure that can arise from (a) working with automated defect-detection and sizing aids, (b) implementing human redundancy, and (c) improvement of the inspection procedures without due consideration of the procedure users. And third, some optimisations strategies will be provided. The purpose of this work is to show that mechanised testing is associated with potential for failure and that the sources of those risks go beyond single inspectors and need to be looked at in the interaction of people with other systems, i.e. The technology, the team and, most importantly, the organisation.
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