Ultrasonic Reflection Behavior of R-zone in Carbon Fiber-reinforced Composite Structures and Its Application

Abstract

Currently composites are one of the most important materials for advanced aircrafts. Defects in R-zone of composite structures have effect on their loading abilities and load transfer. The accessibility of R-zone, complex sonic reflections, etc., affect R-zone ultrasonic inspection and defect discrimination as well as its quantitative evaluation. A broad-band short pulse ultrasonic technique was developed to be used to implement R-zone non-destructive testing and defect quantitative evaluation based on ultrasonic reflection behaviors in it. The basic calculated results show a good ultrasonic penetration can be reached when incident angle is small than 3 degrees. The ultrasonic testing results show out the remarkable differences in time-domain reflected signals and B-scan images, which resulted from the front surface, back surface, delaminations and interlaminar of R-zone. The difference of echo signal amplitude from different depth delaminations is not more than 2.5 dB for a 12-ply R-zone skin. The accuracy of delamination localization in depth is within 1 ply. A stable ultrasonic coupling between transducer and R-zone surface can be obtained by the used water-film technique. The ultrasonic reflection behaviors of incident waves in R-zones can be visualized well by using B-scan and the employed ultrasonic transducer and system. The distributions of delaminations in the section of R-zone are exhibited very well by the B-scan imaging method. The ultrasonic surface dead-zone and depth resolution can reach to a single ply thickness (approximately 0.125 mm). The destructive testing has demonstrated the correction of ultrasonic evaluation result of the delamination to be found out in R-zone in a real composite structure by using this technique. It provides a very powerful quantitative nondestructive testing and evaluation method for R-zone in composite structures, which has obtained very important practical applications.