A laser ultrasonic method for nondestructive evaluation of the structure of
composite materials is proposed. Specimens of graphite-epoxy composites wi
th compaction-type defects and air cavities are investigated. The method is
based on the laser thermooptical generation of wide-band acoustic pulses -
optoacoustic (OA) signals - in the material investigated. The acoustic pul
ses backscattered by structural ingomogeneities and defects are registered
by a wide-band piezotransducer, which makes it possible to detect acoustic
pulses in the frequency range from 0.1 to 30 MHz. Since the generation and
detection of acoustic pulses takes place on the front surface of the specim
en, this method allows us to carry out nondestructive evaluation with one-s
ided access to the object under study. The spectral and correlation analyse
s of backscattered OA signals are used for mathematical processing of the e
xperimental data. The method developed makes it possible to determine the t
ype of defects and the depth of their location.