PRACTICAL CONSIDERATIONS FOR THE RAPID INSPECTION OF COMPOSITE-MATERIALS USING LASER-BASED ULTRASOUND

An automated laser-based ultrasound system is described that has suffi cient sensitivity to detect typical flaws of interest in composite mat erials without causing surface damage to the part under test. An impor tant step in achieving a rapid scanning laser-in/laser-out system has been the integration of a galvanometer mirror scan head in conjunction with a novel data acquisition scheme. This has allowed both flat and curved composite materials to be inspected with scanning speeds in exc ess of 18.5 m2 h-1, based on a 12.5 mm x 12.5 mm pixel size. In additi on, a reference signal technique has been developed which superimposes a known phase modulation onto the probe laser beam. Real-time process ing of the reference signal allows changes in the ultrasonic signal am plitude due to ultrasonic attenuation to be distinguished from those d ue to the variations in the amount of light reflected from the surface of the test specimen as the specimen is scanned. This technique thus eliminates problems resulting from 'scanning noise.'. These results re present a significant step toward developing a field-usable automated laser-based ultrasonic scanning system for flaw detection in advanced composite materials.