DEFECT VISUALIZATION IN CARBON-FIBER COMPOSITE USING LASER ULTRASOUND

A non-contacting laser ultrasound system has been developed to visuali ze laminar defects in carbon fiber composite materials. Laser-generate d ultrasound (LGU) was produced from a Nd:YAG Q-switched laser. Ultras ound was detected with the use of an actively stabilized Fabry-Perot i nterferometer using a 400 mW argon-ion laser source. It detected ultra sound in a typical frequency range of 1 to 10 MHz. Through-transmissio n C-scan measurements were made in carbon fiber composite materials of thickness 1 to 20 mm. Peak-to-peak amplitudes of the first longitudin al ultrasonic pulse were measured, with attenuation used as the basis of defect examination. Digital filtering was adopted to enhance defect visibility. Results showed that images with size resolution better th an 1 mm can be achieved. Such measurements take into account any varia tion of surface reflectivity which can arise in industrial materials.