Broadband immersion laser ultrasonic tomography of graphite-epoxy composite

Laser ultrasonic tomography uses pulsed laser light for photoacoustic excitation of short probe ultrasonic pulses in a special light-absorbing plate. These pulses propagate through the immersion liquid, then they are reflected from the surface of the object and scattered by the inhomogeneities inside the object. Scattered and reflected waves are recorded by a broadband multi-element piezoelectric array and used to reconstruct the image. The wide spectral band (0.1-15 MHz) of probe pulses is well suited to the problem of inspection of carbon-fiber-reinforced polymers (CFRPs), allowing visualization of individual carbon fiber layers and defects with high accuracy. In this paper, laser ultrasonic tomography is proposed for inspection of CFRPs. The experimental results of the inspection of a graphite-epoxy composite sample with inclusions and defects are presented.