Nondestructive evaluation of a carbon fiber wing spar using air-coupled ultrasound

Nondestructive evaluation techniques for imaging flaws in a solid composite laminate and a method to determine the porosity content by processing micrograph images of the laminate are discussed in this thesis. Air-coupled ultrasound, the computer aided tap tester, and pitch-catch contact ultrasound are the nondestructive methods employed for the inspection of a carbon fiber reinforced composite main wing spar. Impact damage and foreign object inclusions have been inspected with all three methods. These methods have been shown to be successful in locating the test article defects. The determination of porosity levels from micrograph images is presented as a possible alternative to the acid digestion method. The image processing method developed utilizes a free open-source software package to process micrograph images of the test sample. The image processing method can be automated with simple scripts within the software package. The results from the image processing method are shown to correlate well with the acid digestion results. This research was aimed at advancing the inspection technology for an industrial composite structure. The results indicate that air-coupled ultrasound can potentially be a low cost alternative to other inspection techniques.