Ultrasonically Mapping the Ply Layup of Composite Laminates

摘要

A new method for nondestructively determining the ply layup in a composite laminate is presented. The method employs a normal incidence longitudinal ultrasound to perform a C-scan of ply interfaces or a full waveform B-scan of the laminate and extracts fiber orientation information from the ultrasonic reflection caused by structural imperfections in the laminate. It was found that the C-scan image of a ply interface mostly contains the fiber orientation information of the two neighboring plies, with that of the upper ply often snowing more prominently. Using the two dimensional spatial Fourier transform, interface C-scan images were transformed into quantitatively angular distribution plots to show the fiber orientation information therein and to determine the orientation of the upper plies. The data collected in a full waveform B-scan were processed in a similar manner and converted into an angle/time image, where the signal amplitude revealed the orientation of all the plies in a laminate. The B-scan approach was more robust because no individual time gates were needed for the ply interfaces. Both interface C-scan and full waveform B-scan approaches were tested on several composite laminates to determine their ply layup. The mechanisms that contributed to the success of the method were investigated using model analysis.