Defect Characterization in Thick Composites by Ultrasound

In today’s application of composites, thick composites are beginning to be used for load bearing structural members. The nondestructive evaluation of composites relies heavily on ultrasound as the probing field, but the ultrasonic NDE of thick composites poses new challenges. First, to penetrate a large thickness of composite one must use ultrasound of low frequencies, but the long wavelengths at low frequencies afford only poor resolution. Secondly, with increasing thickness, the anisotropy of the material assumes a greater importance and certain simplifying assumptions acceptable in thin composites are no longer valid. Moreover, in pulsed ultrasonic measurement of thick composites, the high total attenuation associated with the large thickness and its frequency dependence often changes the spectral content of the pulses considerably [1]