Acoustical imaging evaluation of thin metal-metal adhesive bonds

The problem of developing reliable ultrasonic imaging method for characterization of the structural integrity of adhesive bonds in the joints of two thin metal sheets in automotive and aerospace industry is discussed. Mismatch of acoustical impedances and reverberation lead to appearance of long-time complex vibration. Significant attenuation in the adhesive layer also brings difficulties. A new approach, based on convolution filtering of the received signal is represented for the case of sound penetration through a three-layer structure. The experiments were performed with plane and spherically focused acoustic beams in pulse-echo mode in the frequency range of 3-15 MHz. Acoustical images of basic types of defects in real industrial samples are represented and discussed.