What was a great mystery until recently was how to establish the quality and durability of adhesive bonds. It was an uncertainty based on blind faith and honest hope, in which one simply had to believe that a bond would stick, and would continue doing so for as long as possible.
Researchers at the Fraunhofer-Institut für Zerstörungsfreie Prüfverfahren IZFP (Fraunhofer-Institute for Non-Destructive Testing Methods) in Saarbrücken saw an opportunity to take a closer look at adhesive bonds using a well-proven method - ultrasonic testing.
As Dr. Silvia Fassbender, a specialist in this field, explains: The principle has been clearly defined - the transmitter emits ultrasonic sinus wave forms and we evaluate the echo returned. An undistorted sinus wave is returned when the adhesive bond is firm. However, this only appears when the so-called restoring forces are linear, signifying that stability against the effect of outside forces has been maintained. In other words, if the reflected sinus wave is distorted, the restoring forces have deviated from linear uniformity. thus proving poor adhesion and inferior firmness in the bond. The greater the distortion, the poorer the bond. According to Silvia Fassbender, Results can be differentiated still further. The ultrasonic technique even allows us to identify the type of fault. whether it was caused by trapped air, moisture of foreign particles. This constitutes a quantum leap in adhesive bonding.
The Fraunhofer researchers are continuing their tests on different adhesive bonds to create a broad range of applications for their testing technique.
Dr.-Ing. Silvia Faßbender
Telefon 0681/30238-72, Fax: +49 (0) 6 81/ 3 02-3 95 80, e-mail:fassbender@izfp.fhg.de
Fraunhofer-Institut für zerstörungsfreie Prüfverfahren
IZFP
Universität, Gebäude 37
D-66123 Saarbrücken
Rolf Diederichs 30. Jan.1996, info@ndt.net