Ultrasonic testing of adhesive bonds of thin metal sheets

This article discusses the use of pulse-echo ultrasonic testing for the ins pection of adhesive bonds between thin metal sheets (0.8 mm). The method is based on the measurement of the reflection coefficient at the metal/adhesi ve interface. After describing briefly the physical aspects of the phenomen on, an index is defined to detect defective zones of the joint (both for th e lack of adhesive and for insufficient adhesion); the influence of the exp erimental variables (transducer frequency, coupling medium and contact forc e) on the measurement is discussed. The analysis shows that coupling medium and transducer frequency do not influence the results and that the method is robust with respect to the variation of contact force. By means of a con trol experiment it is shown that the statistical distribution of the index corresponding to good and defective adhesion zones are sufficiently separat e to be distinguished. Finally, a procedure based on the statistical theory of decisions is proposed to evaluate the integrity of the joint under test . (C) 1999 Elsevier Science Ltd. All rights reserved.