Evaluation of layered composites by laser optoacoustic transducers

An ultrasonic method for evaluation of composite structures by laser-excite d wide-band acoustic pulses is proposed. Two types of laser optoacoustic tr ansducers, in transmission and reflection modes, are used in the spectral r ange of 0.1-10 MHz. In the first case, the frequency dependence of the atte nuation factor of ultrasound is measured. In the reflection node, the optoa coustic transducer allows us to obtain the time-dependent shape and spectru m of the backscattered acoustic signal with one-sided access to a specimen or product. Specimens of a layered graphite-epoxy composite of different po rosity (up to 1.2%) are studied. In the frequency range of 1-5 MHz, the att enuation factor of ultrasound measured in the transmission. mode is the gre ater the higher the porosity of the specimen. The "noise" part of the backs cattered acoustic pulse is found to increase with increasing porosity of th e specimens. A 1% growth in porosity causes a threefold increase in the noi se power. The results obtained confirm the advantages of the laser optoacou stic method for evaluation of composite materials and products during their manufacturing and operation.