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Comparison and evaluation of different processing algorithms for the nondestructive testing of fiber-reinforced plastics with pulse thermography

Gegenüberstellung und Bewertung verschiedener Auswertemethoden für die zerstörungsfreie Prüfung von faserverstärkten Kunststoffen mit der Impulsthermografie
Vitalij Popow , Lars Budesheim and Martin Gurka
From the journal Materials Testing

Abstract

When making components out of fiber-reinforced plastics, the composite material itself is formed during the manufacturing of the component, so that suitable methods for process monitoring and quality assurance of each manufactured component regarding its structural integrity are necessary. An alternative approach to the commonly used ultrasonic testing is pulse thermography, which is suitable for the inspection of large areas. But this method is restricted regarding inspection depth, on one side, and thermal contrast and depth resolution with increasing depth, on the other side. In this paper we compare several data processing methods which can be used to overcome the limitations of this method and to optimize the contrast for detection of deeply buried defects. (1) differential absolute contrast, (2) thermographic signal reconstruction, (3) pulse phase thermography, (4) principle component thermography and (5) high order statistics are compared regarding their capability of detecting defects, e. g. delaminations, in different depths. As a measure for the achievable contrast of the different methods designed to detect various defects we compared the respective signal-to-noise-ratio. Additionally, we discuss further approaches for improving the detection capability by applying different evaluation methods in sequence or combining them with image processing methods based on geometric filters. For this purpose a CFRP specimen with 18 artificial defects was examined.

Kurzfassung

Faserverstärkte Verbundwerkstoffe entstehen erst während der Bauteilherstellung, sodass geeignete Prüfverfahren zur Prozessüberwachung und Qualitätskontrolle jedes hergestellten Bauteils unabdingbar sind. Neben der weitverbreiteten Ultraschallprüfung bietet sich hierfür die Impulsthermographie als großflächig einsetzbare Prüfmethode insbesondere für dünnwandige Bauteile an. Diese ist allerdings in der Tiefenreichweite stark beschränkt und der Kontrast und die laterale Größe der zu detektierenden Fehlstelle nimmt mit zunehmender Tiefenlage ab. Zur Aufweitung der gegebenen Grenzen und zur Verbesserung des Kontrastverhältnisses bei tieferliegender Fehlstellen werden in diesem Beitrag fünf verschiedene Auswerteverfahren (1) Differential Absolute Contrast, (2) Thermographic Signal Reconstruction, (3) Pulse Phase Thermography, (4) Principle Component Thermography und (5) High Order Statistics gegenübergestellt und auf ihre Eignung zur Detektion von Fehlstellen, insbesondere von Delaminationen in unterschiedlichen Tiefenlagen, untersucht. Dabei werden die Grenzen der Detektierbarkeit aufgezeigt und Ansätze für die weiterführende Analyse und Kombination der Methoden untereinander sowie mit Methoden geometrischer Bewertung vorgestellt. Als Probekörper kommt ein multiaxiales Verbundlaminat mit 18 künstlichen Fehlstellen zum Einsatz. Die Bewertung der Messergebnisse erfolgt durch die Bestimmung des maximal erreichbaren Kontrasts, welcher anhand des Signal-Rausch-Verhältnisses ermittelt wird.


*Correspondence Address, M.Sc. Vitalij Popow, Institut für Verbundwerkstoffe GmbH, Erwin-Schrödinger-Str. 58, D-67663 Kaiserslautern, Germany, E-mail:

M. Sc. Vitalij Popow, born in 1989, graduated in 2015 at the Technical University of Kaiserslautern, Germany with a M. Sc. degree in Industrial and Mechanical Engineering. Since 2015, he has been working as a research assistant at the Institut für Verbundwerkstoffe GmbH with the aim of obtaining his PhD. His research focus is the nondestructive testing of composite materials using thermography.

M. Sc. Lars Budesheim, born in 1989, graduated in 2017 at the Technical University of Kaiserslautern, Germany with an M. Sc. degree in Industrial and Mechanical Engineering with a specialization in automotive engineering/production management.

Dr. rer. nat. Martin Gurka, born in 1967, graduated in Physics and received a PhD in Physical Chemistry from the University of Heidelberg, Germany. He held several positions in industry: Project Manager R&D at Hoerbiger Antriebstechnik GmbH, CEO at Neue Materialien Würzburg GmbH (Smart Materials, Adaptronics, Nanocomposites), Head of Fluid-Technology at Fludicon GmbH (Development and Manufacturing of Smart Fluids). He joined IVW in 2011 as a deputy research manager, responsible for research in the areas of tailored and smart composite structures. He has worked in the field of multifunctional composite materials for more than 20 years and is a member of the German Society of Physicists (DPG), VDI/VDE-GMA Experts Group “Functional Materials for Mechatronic Systems” and the experts group “Composite Materials” of the German Society for Non-Destructive Testing (DGZFP).


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Published Online: 2018-11-15
Published in Print: 2018-06-30

© 2018, Carl Hanser Verlag, München

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