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Ultrasonic testing of adhesively bonded joints using air-coupled cellular polypropylene transducers

  • In air-coupled ultrasonic testing, the impedance mismatch between the transducer and the air is commonly being solved by adding matching layers to composite transducers. To avoid the difficult technological procedure regarding matching layers, some new piezoelectric materials have been proposed. Most promising are ferroelectrets, which are charged cellular polymers, having ferroelectric and consequently piezoelectric properties. In particular, the extreme softness of cellular polypropylene (cPP) leads to a high piezoelectric constant and to a good impedance match with the air, making matching layers redundant. Its elasticity modulus below 1 MPa causes an additional effect not observed with common piezoelectric materials: that is the electrostrictive effect, here defined as the thickness change due to the attractive force between the transducer electrodes. This effect exceeds the piezoelectric effect at excitation voltages over 1 kV. The extreme softness of cPP leads also to highIn air-coupled ultrasonic testing, the impedance mismatch between the transducer and the air is commonly being solved by adding matching layers to composite transducers. To avoid the difficult technological procedure regarding matching layers, some new piezoelectric materials have been proposed. Most promising are ferroelectrets, which are charged cellular polymers, having ferroelectric and consequently piezoelectric properties. In particular, the extreme softness of cellular polypropylene (cPP) leads to a high piezoelectric constant and to a good impedance match with the air, making matching layers redundant. Its elasticity modulus below 1 MPa causes an additional effect not observed with common piezoelectric materials: that is the electrostrictive effect, here defined as the thickness change due to the attractive force between the transducer electrodes. This effect exceeds the piezoelectric effect at excitation voltages over 1 kV. The extreme softness of cPP leads also to high flexibility, enabling easy focusing by bending the transducer. We have developed air-coupled ultrasonic transducers based on cPP. This includes the electrical matching networks for the transmitter and for the receiver. The transmitter is excited with voltages up to 2.5 kV, so that the electrostrictive effect dominates, leading to sound pressure around 145dB at the transducer surface. These transducers have been applied for testing carbon-fiber-reinforced polymer plates, adhesive joints and other composite structures. Here we report about ultrasonic transmission of two types of adhesive joints. The first one is multi-layer aluminium components with some artificial disbonds, which are common in aerospace industry, and the second one is an aluminium-steel joint with polyurethane adhesive, which is used in automotive industry.zeige mehrzeige weniger

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Metadaten
Autor*innen:Mate GaalORCiD, Elmar Dohse, Jürgen Bartusch, Enrico Köppe, Marc Kreutzbruck, W. Hillger, J. M. Amos
Dokumenttyp:Beitrag zu einem Tagungsband
Veröffentlichungsform:Verlagsliteratur
Sprache:Englisch
Titel des übergeordneten Werkes (Englisch):ECNDT 2014 - 11th European conference on non-destructive testing (Proceedings)
Jahr der Erstveröffentlichung:2014
Veröffentlichende Institution:Bundesanstalt für Materialforschung und -prüfung (BAM)
Verlag:Brno University of Technology
Erste Seite:1
Letzte Seite:8
Freie Schlagwörter:Adhesive joint; Air-coupled; Cellular polypropylene; Ferroelectret; Transducer; Ultrasonic testing
Veranstaltung:ECNDT 2014 - 11th European conference on non-destructive testing
Veranstaltungsort:Prague, Czech Republic
Beginndatum der Veranstaltung:06.10.2014
Enddatum der Veranstaltung:10.10.2014
URN:urn:nbn:de:kobv:b43-317204
ISBN:978-80-214-5018-9
Verfügbarkeit des Dokuments:Datei für die Öffentlichkeit verfügbar ("Open Access")
Lizenz (Deutsch):License LogoCreative Commons - Namensnennung-Keine Bearbeitung
Datum der Freischaltung:20.02.2016
Referierte Publikation:Ja
Datum der Eintragung als referierte Publikation:30.10.2014
Schriftenreihen ohne Nummerierung:Wissenschaftliche Artikel der BAM
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