Use of wavelet packet transform for signal analysis in adhesive bond testing

Adhesives are widely used and often preferred as a means of fastening parts together. Aircraft applications in bonding large areas or bonding parts of vehicle chassis, has brought about the need for highly reliable techniques in non destructive testing of adhesive bonds. Among a wide range of different methods, a variety of ultrasonic techniques are used for non destructive testing of adhesive bonds including pulse echo or through signal. In all cases the ultrasonic signal response is analysed and conclusions are drawn with regard to the quality of the adhesive bond. Features of the ultrasonic signal such as amplitude and frequency are used for analysis. Even though there have been great improvements in testing adhesive bonds, it is not always easy to extract conclusive information from the signals for clear discrimination between different levels of bond quality. The method introduced in this paper, enhances the capability of discriminating between varying degrees of bond quality compared with existing methods in ultrasonic testing. Signal Processing with Wavelet Packets was used for this research and the results show significant improvements in differentiating between "good" and "bad" bonds.