Ultrasound waves interact strongly with the orientation and sequence of the plies in a layup when propagating in the thickness direction of composite laminates. Also the layup orientation greatly influences its properties in a composite laminate. If the layup orientation of a ply is misaligned, it could result in the part being rejected and discarded. Now, most researchers cut a small coupon from the waste edge and use a microscope to optically verify the ply sequences on important parts. This may add a substantial cost to the production since the test is both labor intensive and performed after the part is cured. A nondestructive technique would be very beneficial, which could be used to test the part after curing and requires less time than the optical test. Therefore we have developed, reduced, and implemented a novel ply-by-ply vector decomposition model for composite laminates fabricated from unidirectional plies. This model decomposes the transmission of a linearly polarized ultrasound wave into orthogonal components through each ply of a laminate. High probability is found, by comparisons between the model and tests, in characterizing cured layups of the laminates by using the proposed method.
A nondestructive technique would be very beneficial, which could be used to test the
CF/Epoxy composite laminates. A new method for nondestructively determining the ply layup in a
composite laminate is presented. A one-sided pitch-catch setup was used in the detection and
evaluation of flaws and material anomalies in the composite laminates. Two Rayleigh wave
transducers were joined head-to-head and used in the pitch-catch mode on the surface of the
composites. The pitch-catch signal was found to be more sensitive than normal incidence
backwall echo of longitudinal wave to subtle flaw conditions in the composite. Also the other
method employs a normal-incidence longitudinal ultrasound to perform C-scan of ply interfaces of
the laminate, and extracts fiber orientation information from the ultrasonic reflection in the laminate.
Using 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 ply. Therefore, it is found that the efficiency of developed system
shows between the one-sided pitch-catch testing and C-scan images in characterizing ply-layup
orientation of the laminates.
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