Laser-Based Ultrasonics on Gr/Epoxy Composite a Systems Analysis
Critical issues are examined in the application of laser generation and detection of ultrasound to the inspection of large area air-frame composites. Among these issues are surface roughness, signal-to-noise ratio, insensitivity to the path length between the part and detector, and wide-band versus narrow-band generation. Supporting experiments are reported on broad-band and narrow-band generation in Gr/Epoxy panels and angular reflectance measurements on painted and unpainted Gr/Epoxy. On the basis of these measurements, a laser-in/laser-out systems analysis is carried out for a 10 mm diameter delamination about 1 cm deep. The analysis assumes that a Spherical Fabry-Perot interferometer is used for detection and a 10 nsec laser pulse with a peak power of 13 MW/cm2 for generation. The estimates indicate a S/N ≈ 20 dB for a detection probe laser power of about 400 mW.