Ultrasonic Detection of Fiber Orientation in Composite Laminates for Use of Vehicular Structures

The layup of a CFRP (carbon-fiber reinforced plastics) composite laminates affects the properties of the laminate, including stiffness, strength and thermal behavior. It is very important to detect ply error before the laminate is cured for both manual procedure and fiber placement procedure. An ultrasonic technique would be very beneficial, which could be used to test the part after and before curing laminates and requires less time than the optical test. Also cross-polarized scan is very sensitive to the layup errors and ply misorientations. Scanners were set out for different measurement modalities for acquiring ultrasonic signals as a function of in-plane azimuthal angle. Firstly, a manual scanner was built for making transmission measurements using a pair of normal-incidence shear wave transducers to find the effect of fiber misorientations of composite laminates. Also a 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 a ply-by-ply vector decomposition model has been utilized for evaluating layup errors in composite laminates fabricated from unidirectional plies. Test results between after and before curing laminates with model data were compared for a fiber orientation of the laminates.