Chemie und Prozesstechnik
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Damage Quantification in Aluminium-CFRP Composite Structures using Guided Wave Wavenumber Mapping
(2019)
The use of composite materials is associated not only with the advantages of weight reduction and improved structural performance but also with the risk of barely visible impacts or manufacturing damages. One of the promising techniques for the detection and characterisation of such damages is based on ultrasonic guided wave propagation and analysis. However, the multimodal nature and dispersive behaviour of these waves make their analysis difficult. Various signal processing techniques have been proposed for easier interpretation of guided wave signals and extraction of the necessary information about the damage. One of them is the wavenumber mapping which consists of creating a cartography of the wavenumber of a propagating mode over an inspected area, using a dense wavefield acquisition measured for example with a scanning laser Doppler vibrometer. This technique allows both the quantification of the in-plane size and the depth of damage, for example, impact-induced delamination in composite laminates.
In this contribution, wavenumber mapping is applied to a delaminated aluminium-CFRP composite structure which corresponds to composite-overwrapped pressure vessels used for storing gases in aerospace and automotive industries. The analysis of experimental data obtained from measurements of guided waves propagating in an aluminium-CFRP composite plate with impact-induced damage is performed. The output of the imaging is a three-dimensional representation of the delamination induced by the impact. Good agreement between conventional ultrasonic testing and guided wave damage mapping can be found.
Damage Quantification in Aluminium-CFRP Composite Structures using Guided Wave Wavenumber Mapping
(2019)
The use of composite materials is associated not only with the advantages of weight reduction and improved structural performance but also with the risk of barely visible impacts or manufacturing damages. One of the promising techniques for the detection and characterisation of such damages is based on ultrasonic guided wave propagation and analysis. However, the multimodal nature and dispersive behaviour of these waves make their analysis difficult. Various signal processing techniques have been proposed for easier interpretation of guided wave signals and extraction of the necessary information about the damage. One of them is the wavenumber mapping which consists of creating a cartography of the wavenumber of a propagating mode over an inspected area, using a dense wavefield acquisition measured for example with a scanning laser Doppler vibrometer. This technique allows both the quantification of the in-plane size and the depth of damage, for example, impact-induced delamination in composite laminates.
In this contribution, wavenumber mapping is applied to a delaminated aluminium-CFRP composite structure which corresponds to composite-overwrapped pressure vessels used for storing gases in aerospace and automotive industries. The analysis of experimental data obtained from measurements of guided waves propagating in an aluminium-CFRP composite plate with impact-induced damage is performed. The output of the imaging is a three-dimensional representation of the delamination induced by the impact. Good agreement between conventional ultrasonic testing and guided wave damage mapping can be found.
Guided waves (GW) are of great interest for non-destructive testing (NDT) and structural health monitoring (SHM) of engineering structures such as for oil and gas pipelines, rails, aircraft components, adhesive bonds and possibly much more. Development of a technique based on GWs requires careful understanding obtained through modelling and analysis of wave propagation and mode-damage interaction due to the dispersion and multimodal character of GWs. The Scaled Boundary Finite Element Method (SBFEM) is a suitable numerical approach for this purpose allowing calculation of dispersion curves, mode shapes and GW propagation analysis. In this article, the SBFEM is used to analyse wave propagation in a plate consisting of an isotropic aluminium layer bonded as a hybrid to an anisotropic carbon fibre reinforced plastics layer. This hybrid Composite corresponds to one of those considered in a Type III composite pressure vessel used for storing gases, e.g., hydrogen in automotive and aerospace applications. The results show that most of the wave energy can be concentrated in a certain layer depending on the mode used, and by that damage present in this layer can be detected. The results obtained help to understand the wave propagation in multi-layered structures and are important for further development of NDT and SHM for Engineering structures consisting of multiple layers.
Die Verwendung von Verbundwerkstoffen ist nicht nur mit den Vorteilen einer Gewichtsreduzierung und einer verbesserten strukturellen Leistung verbunden, sondern auch mit der Gefahr von kaum sichtbaren Impakt- oder Herstellungsschäden. Eine der vielversprechenden Methoden zur Erkennung und Charakterisierung solcher Schäden basiert auf der Ausbreitung und Analyse geführter Ultraschallwellen. Der multimodale und dispersive Charakter dieser Wellen erschweren jedoch die Analyse. Verschiedene Signalverarbeitungsmethoden wurden vorgeschlagen, um die Interpretation von Signalen und die Extraktion der notwendigen Informationen über den Schaden zu erleichtern. Eine davon ist die Erstellung einer Wellenzahlkarte. Die Wellenzahlkarte erlaubt es jeden Punkt in einer hochaufgelöste Wellenfeldaufnahme eine Wellenzahl zuzuordnen. Diese Methode ermöglicht sowohl die Quantifizierung der Größe als auch der Tiefe des Schadens.
In diesem Beitrag wird diese Bildgebungsmethode auf delaminierte Aluminium-CFK-Verbundstrukturen angewendet. Solche Strukturen entsprechen den umwickelten Druckbehältern, die zur Speicherung von Gasen in der Luft- und Raumfahrt sowie in der Automobilindustrie verwendet werden. Zunächst werden die numerischen Untersuchungen zur einfachen Delamination in unterschiedlicher Tiefe vorgestellt. Als nächstes wird die Analyse von experimentellen Ergebnissen von einer geschädigten Aluminium-CFK-Platte präsentiert. Das Ergebnis der Bildgebung ist eine dreidimensionale Darstellung, die sowohl die Größe als auch die Tiefe des Impakt-Schadens liefert.
Issues that prevent Structural Health Monitoring (SHM) based on Guided Waves (GW) from being a part of today’s monitoring solutions in industry are not all obvious to the scientific community. To uncover and overcome these issues, scientists working on SHM and GW problems joined in an expert committee under the patronage of the German Society for Non-Destructive Testing. An initiated online survey among more than 700 experts and users reveals the hurdles hindering the practical application of GWbased SHM. Firstly, methods for proof of reliability of SHM approaches are missing.
Secondly, detailed understanding of phenomenological described wave-damage interactions is needed. Additionally, there are significant unsolved implementation issues and unsolved problems of signal processing including handling of environmental influences.
To enable substantial proof of reliability without unaffordable experimental effort also efficient simulation tools including realistic damage interaction are needed, enabling the joint use of experimental and simulated data to predict the capabilities of the Monitoring system. Considering these issues, the committee focusses on simulation, signal processing, as well as probability of detection and standardization. In the presented work, recent activities of the expert committee starting with survey results are summarized. An open access data basis of life-like measurements is presented to allow testing and comparison of signal processing and simulation algorithms. Finally, a strategy for efficient proof of reliability increasing the acceptance of SHM in industry and for successful Integration of SHM into real-world engineering structures is proposed.
Lamb waves are widely used for non-destructive evaluation of material parameters as well as for detection of defects. Another application of Lamb waves is quality control of adhesive joints.
Researchers are currently investigating shear horizontal and zero-group velocity modes for characterisation of the adhesive bonding strength. In a new approach, Lamb wave mode repulsion is used to obtain the coupling strength between different layers to characterise the adhesive bonding strength. The modes of the individual layers become coupled in the multilayered systems forming particular regions, the so-called mode repulsion regions. This study investigates these modes and their interaction in two-layered plate-like structures with varying coupling strength both numerically, with the Scaled Boundary FEM, and experimentally
Lamb waves are widely used for non-destructive evaluation of material parameters as well as for detection of defects. Another application of Lamb waves is quality control of adhesive joints.
Researchers are currently investigating shear horizontal and zero-group velocity modes for characterisation of the adhesive bonding strength. In a new approach, Lamb wave mode repulsion is used to obtain the coupling strength between different layers to characterise the adhesive bonding strength. The modes of the individual layers become coupled in the multilayered systems forming particular regions, the so-called mode repulsion regions. This study investigates these modes and their interaction in two-layered plate-like structures with varying coupling strength both numerically, with the Scaled Boundary FEM, and experimentally.
Der praktische Einsatz von SHM-Verfahren mit geführten Ultraschallwellen basiert auf einem fundierten Verständnis der speziellen physikalischen Zusammenhänge der Wellenausbreitung. Das umfasst nicht nur das multimodale Verhalten, welches von den Dispersionsdiagrammen repräsentiert wird, sondern auch die Vorhersage der Interaktion zwischen verschiedenen Wellenmoden und den zu erwartenden Fehlstellen.
Ziel des Workshops ist es, das Verständnis der Ausbreitung geführter Wellen zu verbessern und die vielfältigen Anwendungsmöglichkeiten, die sich aus der multimodalen Wellenausbreitung ergeben, an praktischen Beispielen zu demonstrieren. Die vorgestellten Szenarien beschränken sich dabei nicht nur auf eine Anregung grundlegender Dehnungs- und Biegewellen, sondern beziehen auch geführte Wellenmoden höherer Ordnung zur Verbesserung der Aussagekraft des Prüfergebnisses mit ein.
Nach einer theoretischen Einführung werden ausgewählte Demonstratoren, vorrangig mit Bezug zum Automobilbau, vorgestellt. Diese schließen Fragestellungen der Integration der Sensorik in gekrümmte Faserverbundbauteile ebenso mit ein, wie die Überwachung von Metall-Faserverbund-Komposit-Materialien, die in Drucktanks zum Einsatz kommen.
Ultrasonic guided waves (UGW) have been shown to be suitable for non-destructive testing (NDT) and structural health monitoring (SHM) of many engineering structures. Development of a technique based on UGWs requires careful understanding obtained through modelling and analysis of wave propagation and mode-damage interaction due to their dispersion and multimodal character. This presentation will provide insights into the Scaled Boundary Finite Element Method and its applicability for tackling wave propagation problems. Features and limitations of the SBFEM will be presented on an example of a multi-layered plate structure consisting of isotropic and anisotropic materials bonded together. You will be guided through the process of picking up the wave modes for your application. Starting from the calculation of dispersion curves and mode shapes to the analysis of wave propagation and mode-damage interaction. The main highlight of the presentation lies in the ability to detect damage in a certain layer depending on the mode used. The resulting deeper understanding of the wave propagation in multi-layered structures is the key to further developments of NDT and SHM for engineering structures consisting of multiple layers.
Composite-Druckbehälter werden für Speicherung und Transport von Gasen unter hohem Druck verwendet. Durch die gewichtssparende Struktur, die aus einem dünnwandigem Metallgefäß und Faserverbundwerkstoff-Ummantelung besteht, sind solche Behälter insbesondere für die Luftfahrt- und Automobilindustrie interessant, z.B. als Wasserstoffspeicher.
Die Druckprüfung ist ein konventioneller Test, um die Integrität von Metalldruckbehältern zu bewerten. Im Falle des Composite-Druckbehälters könnte eine solche Prüfung jedoch den Faserverbundwerkstoff überbeanspruchen und somit die verbleibende Lebensdauer der getesteten Komponente verringern. Infolgedessen ist es notwendig, Verfahren zur zerstörungsfreien Prüfung und möglicherweise zur Zustandsüberwachung von Composite-Druckbehältern zu entwickeln. Unser Ansatz verwendet geführte Ultraschallwellen und hat das Potenzial, kritische Schäden wie Risse im Metall und Faserbrüche und Matrixrisse in Faserverbundwerkstoff zu detektieren.
In diesem Beitrag wurde die Scaled Boundary Finite Elemente Methode benutzt, um die multimodale, geführte Wellenausbreitung in einem Mehrschichtverbund, der aus Metall und Kohlenfaserverbund entsteht, zu analysieren. Das Verfahren ermöglicht die Identifizierung geeigneter Wellenmoden und die Analyse ihrer Interaktion mit verschiedenen Schäden. Diese Kenntnisse sollen für die Entwicklung von Verfahren zur Zustandsüberwachung von Composite-Druckbehältern angewendet werden.