Abstract
The continuing difficulty of detecting critical flaws in advanced materials requires novel approaches that enhance sensitivity to defects that might impact performance. This study compares different approaches for imaging a near-surface resin-rich defect in a thin graphite/epoxy plate using backscattered ultrasound. The specimen, having a resin-rich void immediately below the top surface ply, was scanned with a 1 in. dia., 5 MHz center frequency, and 4 in. focal length transducer. A computer controlled apparatus comprised of an x-y-z motion controller, a digitizer (LeCroy 9400A), and an ultrasonic pulser/receiver (Panametrics 5800) was used to acquire data on a 100 ×100 grid of points covering a 3 × 3 in. square. At each grid point 256 512-word, 8-bit backscattered waveforms, were digitized, signal averaged, and then stored on computer for off-line analysis. The same backscattered waveforms were used to produce peak-to-peak, signal energy, as well as entropy images. All of the entropy images exhibit better border delineation and defect contrast than the either peak-to-peak or signal energy. The best results are obtained using the joint entropy of the backscattered waveforms with a reference function. Two different references are examined: a reflection from a stainless steel reflector, and an approximate optimum obtained from an iterative parametric search. The joint entropy images produced using the optimum reference exhibit ~3 times the contrast obtained in previous studies.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
