Ultrasonic Characterization of Ply-Layup Interface Using CF/Epoxy Composite Laminates Under Before and After Curing Conditions
Published August 22, 2005 by Society of Automotive Engineers of Korea in South Korea
The layup orientation of CF (Carbon fiber)/Epoxy composites greatly influences its properties in a composite laminate. A nondestructive technique would be very beneficial, which could be used to test the part before and after curing and requires less time than the optical test. 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 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. Also a physical model based on the decomposition and recombination of shear polarization has been adopted for composite laminates fabricated from unidirectional plies. This model was used in the interpretation and prediction of test results. In order to develop these methods into practical inspection tools, a motorized system has been developed for different measurement modalities for acquiring ultrasonic signals as a function of in-plane angle. It is found that high probability shows between the model and tests developed in characterizing cured/uncured layups of the laminates. It was found that the C-scan image of a ply interface contains mostly the fiber orientation information of the two neighboring plies of CF/Epoxy composite laminates.