Ultrasonic detection and characterization of delaminations in thin composite plates using signal processing techniques

For the detection of delaminations in thin multilayered composite plates, two different techniques based on the processing of band-limited ultrasonic pulses reflected from the sample under investigation are presented. The first technique exploits the differences between the signals reflected from the flawless and delaminated regions, which are revealed using the modified iterative L1 norm deconvolution. From filtered A-scans, two-dimensional C-type scans are produced in two different ways. The second technique is based on a spectroscopic analysis of the differential signature of a sample, which is obtained by subtracting from the reference signal, reflected by a flawless region, the pulse received at any arbitrary point and presentation of two-dimensional images at various frequencies. The experimental results indicate that both techniques enable one to determine between which layers delamination took place. (C) 1997 Elsevier Science B.V.