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Eingeladener Vortrag
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Air-coupled ferroelectret ultrasonic transducers applied to testing of fiber-reinforced polymers
(2013)
Analysis of the dielectric and electromechanical properties of the cellular polypropylene ferroelectret films (EMFIT) evidences their high potential for the application in the air-coupled ultrasonic transducers. Simple prototype transducers, based on the EMFIT films, were developed and their high sensitivity was proved in the air-coupled ultrasonic experiment. Amplitude and delay time scanned images of the polyethylene step wedge with holes, obtained in both pulse-echo and transmission modes, demonstrate that non-contact ultrasonic imaging with EMFIT transducers is possible.
Charakterisierung der Wandler für Luftultraschallprüfung aus zellulärem Polypropylen-Ferroelektret
(2011)
In den letzten Jahren stieg die Anfrage für zerstörungsfreie Prüfung (ZIP) mit Luftultraschall deutlich. Die klassische ZfP mit Ultraschall nutzt Flüssigkeiten als Koppelmittel zwischen dem Wandler und dem Prüfkörper. Für die Prüfung von Gegenständen mit empfindlicher Oberfläche, die das Koppelmittel beschädigen oder verunreinigen kann, ist deswegen Luftultraschall besser geeignet. Eine mögliche Anwendung ist beispielsweise der Nachweis von Delaminationen in glas- und kohlefaserverstärkten Verbundwerkstoffen sowie Sandwichbauteilen, die in der Luftfahrt- und der Automobilindustrie eingesetzt werden.
The curing conditions play an important role in the quality assurance of composite products.
Especially as composite materials are widely used in high tech areas so that they are required to fulfil high quality Standards. Some problems which occur during curing, for instance undercuring, can hardly be detected using Standard NDT investigations, mainly because they are manifested only at high temperatures, particularly close to glass-rubber-transition. On-line eure monitoring has the outstanding advantage that it can monitor the material parameters even at the highest temperatures possible.
In recent years eure monitoring with ultrasonic methods has become more populär. In comparison to dielectric methods mechanical parameters are measured directly. The quantities to be measured are the velocity and the attenuation of the sound wave. On this basis the storage and loss modulus can be calculated. Depending on the form of excitation with longitudinal or transversal waves these moduli are referred to as long wave or shear modulus.
Well developed Computer based technology and sensor materials are available in the non-destructive testing (NDT) market. The measuring equipment employed a commercial NDT System, which worked computer-aided. With a special Software the demands of automatic Operation under industrial conditions was accomplished. This measurement equipment was tested on composites. Its structure, performance and some practical results will be presented in the following paper.