Ultrasonic compression wave propagation in adhesive polymers described as a signal filtering process

The ability to test adhesively bonded metal structures non-destructively requires an understanding of ultrasound wave propagation in adhesive materials. This paper presents the results of an experimental study of wave absorption and phase velocity dispersion in a number of structural adhesives in terms of the frequency response and the time domain impulse response of propagation in a thin layer of material. A simple single relaxation time model provides a phenomenological basis on which to consolidate the measured data into a form that can be used to model wave propagation in more complex structures containing an adhesive. It is shown that high rates of attenuation, increasing with frequency, will seriously limit the frequency bandwidth available for ultrasonic non-destructive testing of adhered structures. Extensions to the model are appended that will provide the basis for its implementation by means of linear electric network simulation packages.