J.-W. Park, K.-H. Im, D. K. Hsu, J.-A. Jung, I.-Y. Yang
The Journal of Mechanical Science and Technology, vol. 26, no. 7, pp.2147-2150, 2012

Abstract : "The importance of carbon fiber reinforced plastics (CFRP) has been generally recognized, and CFRP composite laminates have become widely used. Thus, a nondestructive technique would be very useful for evaluating CF/epoxy composite laminates. A pitch-catch UT signal is more sensitive than is a normal incidence backwall echo of a longitudinal wave in composites. The depth of the sampling volume where the pitch-catch UT signal came from is relatively shallow, but the depth can be increased by increasing the separation distance of the transmitting and receiving probes. Moreover, a method is utilized to determine the porosity content of a composite lay-up by processing micrograph images of the laminate. The porosity content of a composite structure is critical to the overall strength and performance of the structure. The image processing method developed utilizes software to process micrograph images of the test sample. The results from the image processing method are compared with existing data. Beam profile is characterized in unidirectional CFRP using pitch-catch Rayleigh probes. The one-sided and two-sided pitch-catch techniques are utilized to produce C-scan images with the aid of an automatic scanner. The pitch-catch ultrasonic signal corresponds with the simulated results of unidirectional CFRP composites."

Keyword : Carbon fiber reinforced plastics; NDE; Ply-up; Pitch-catch method; Porosity level