Defect Reconstruction based on Structured Illumination Techniques with a High-Power Laser

Καραγιάννη, Χριστίνα; Karagianni, Christina

dc.contributor.author	Καραγιάννη, Χριστίνα	el
dc.contributor.author	Karagianni, Christina	en
dc.date.accessioned	2020-05-28T16:37:19Z
dc.date.available	2020-05-28T16:37:19Z
dc.identifier.uri	https://dspace.lib.ntua.gr/xmlui/handle/123456789/50714
dc.identifier.uri	http://dx.doi.org/10.26240/heal.ntua.18412
dc.description	Εθνικό Μετσόβιο Πολυτεχνείο--Μεταπτυχιακή Εργασία. Διεπιστημονικό-Διατμηματικό Πρόγραμμα Μεταπτυχιακών Σπουδών (Δ.Π.Μ.Σ.) “Περιβάλλον και Ανάπτυξη"	el
dc.rights	Αναφορά Δημιουργού-Μη Εμπορική Χρήση-Όχι Παράγωγα Έργα 3.0 Ελλάδα	*
dc.rights.uri	http://creativecommons.org/licenses/by-nc-nd/3.0/gr/	*
dc.subject	Ακτινοβλία	el
dc.subject	Laser υψηλής ισχύος	el
dc.subject	Ανακατασκευή	el
dc.subject	Ασυνέχεια	el
dc.subject	Structured Illumination Techniques	en
dc.subject	Reconstruction	en
dc.subject	High-Power Laser	en
dc.subject	Structured Illumination	en
dc.title	Defect Reconstruction based on Structured Illumination Techniques with a High-Power Laser	en
dc.title	Ανακατασκευή Ασυνεχειών υλικού βάσει τεχνικών δομημένης ακτινοβολίας με χρήση laser υψηλής ισχύος	el
heal.type	masterThesis
heal.classification	Illumination Techniques	en
heal.language	en
heal.access	campus
heal.recordProvider	ntua	el
heal.publicationDate	2019-10-29
heal.abstract	The subject of this thesis is to research the effectiveness and reliability of a proposed technique, on active thermography obtained data, and evaluate those results in relation to the reliability of the characterization of different defects that are present in sub-surface areas of the tested samples and retrieve information of their separability, when they are located really close to each other. For the active thermography experiments a high power laser was used as an excitation source. The dissertation is focusing on the study of three different laser illumination analogies along with different excitation times and levels of energy, and evaluating the accuracy of each illumination related to the detection of two separate, very closely existing defects, before and after the use of a reconstruction algorithm. For the implementation of an active thermographic inspection, the test objects were excited through the aid of an external laser source and the spatial- temporal variations of the surface temperature distribution were recorded by an infrared camera. Laser Thermography has been chosen, as the use of high-power laser sources, allows for the exploration of the near-surface region of metals and layer systems with better and more accurate penetration depth and depth resolution. Also there in no additional thermal radiation from the laser source, that could interfere with the thermal emissions of the thermally excited sample. Thermographic analysis is based on the identification of those thermal contrasts recorded on the investigated surface, while the defect detection can be further enhanced through the post processing of the acquired data. To evaluate the results for defects and their features of interest, image processing algorithms have to be applied. These techniques are of high importance when it comes in handling thermographic data as they can lead to enhanced detection of the defects, through fixing a series of factors that affect the recording of the initial temperature data. With the proper reading of the processed results quantitative information on the detected features can be obtained.The present study is focused on the use of different illumination approaches, to provide a first evaluation on their effectiveness and reliability to be used as stand-alone inspection techniques and to compare those results with the original pre-processed data. More specifically, sandblasted steel composites were investigated by means of Laser Thermography (LT) aiming to internal pairs of defects identification and whether we can resolve them when they are really close to each other. The selection of the testing configuration was conducted taking into account that every material responds differently to the application of a heat flux. This response, related to the materials thermal properties, was simulated in COMSOL Multiphysics and then these results were compared with the ones from the laboratory experiment. This way an internal view of the heat flow inside the component was obtained and provided the temperature evolution at the surface of the specimen during an entire test. With the results obtained from the simulations, it is possible to estimate the thermal response obtained with a certain type of test and waveform for future experiments. Finally, a compressed sensing signal reconstruction algorithm, the Spectral Projected Gradient (SPG) method was implemented in Matlab to acquire the wanted information from the experimental data.The general conclusion of the study is that active thermal imaging can be successfully applied for the detection of defects very close to each other, and can act as a useful tool for providing sufficient internal detectability and/or separability estimations.	en
heal.sponsor	The present dissertation was conducted in the Division 8.7 Thermographic Methods of Bundesanstalt für Materialforschung und -prüfung (BAM) in Berlin in collaboration with the Remote Sensing Laboratory of the NTUA .	en
heal.advisorName	Καράντζαλος, Κωνσταντίνος	el
heal.committeeMemberName	Αργιαλάς, Δημήτριος	el
heal.committeeMemberName	Καραθανάση, Βασιλεία	el
heal.academicPublisher	Εθνικό Μετσόβιο Πολυτεχνείο. Σχολή Αγρονόμων και Τοπογράφων Μηχανικών	el
heal.academicPublisherID	ntua
heal.numberOfPages	67 σ.	el
heal.fullTextAvailability	false