For improving quality of a carbon fiber reinforced composite material (CFRP) by
preventing defects such as delamination and void, it should be inspected in fabrication process. Novel
non-contacting evaluation technique is required because the transducer should be contacted on the
CFRP in conventional ultrasonic technique during the non-destructive evaluation and these
conventional contact techniques can not be applied in a novel fiber placement system. For the
non-destructive evaluation of delamination in CFRP, various methods for the generation and
reception of laser-generated ultrasound are applied using piezoelectric transducer, air-coupled
transducer, wavelet transform technique etc. The high frequency component of laser-generated
guided wave received with piezoelectric sensor disappeared after propagating through delamination
region. Air-coupled transducer was tried to be adopted in reception of laser-generated guided wave
generated by using linear slit array in order to generate high frequency guided wave with a frequency
of 1.1 MHz. Nevertheless, it was failed to receive high frequency guided wave in using air-coupled
transducer and linear slit array. Transmitted laser-generated ultrasonic wave was received on
back-wall and its frequency was analyzed to establish inspecting technique to detect delamination by
non-contact ultrasonic method. In a frequency spectrum analysis, intensity ratio of low frequency and
center frequency was approvable parameter to detect delamination.
Guided-Wave Tomographic Imaging of Plate Defects by Laser-Based Ultrasonic Techniques
