| Popis: |
Composite materials are attractive for a wide range of applications because of high performance engineering structures. In particular, the importance of carbon‐fiber reinforced plastics (CFRP) has been generally recognized in both space and civil aircraft industries; so, CFRP composite laminates are widely used. It is very important to detect defects in composite laminates because they cause the mechanical properties (stiffness, strength) of the laminate to be reduced. As well known for ultrasonic technique for evaluating the defect of CFRP composite laminates, a pitch‐catch technique was found to be more practical than normal incidence backwall echo of longitudinal wave to arbitrary flaws in the composite, including fiber orientation, low level porosity, ply waviness, and cracks. The measurement depth using Rayleigh probes can be increased by increasing the separation distance of the transmitting and receiving probes. Also, with the aid of the automatic scanner, the one‐sided pitch‐catch probe was used to produce C‐scan images for mapping out the images with beam profiles. Especially pitch‐catch beam path was nondestructively characterized for the specimens when measuring a peak‐to‐peak amplitude and time‐of‐flight in order to build the beam profile modeling in the unidirectional CFRP composite laminates. Also, the pitch‐catch simulation was performed to predict the beam profile trend of wave propagation in the unidirectional CF/Epoxy composite laminates. Therefore, it is found that the experimentally Rayleigh wave variation of pitch‐catch ultrasonic signal was consistent with simulated results and one‐side ultrasonic measurement might be very useful to detect the defects in CFRP composites. |
