Evaluation of Fiber Waviness in Thick Composites by Ultrasonic Test

Abstract

An analytical model, based on the ray and plane wave theories, was proposed to understand the ultrasonic wave propagation in thick composites with uniform fiber waviness. In the analysis, the composites were assumed to have continuous fibers with sinusoidal fiber waviness in a matrix and were modeled as stacks of infinitesimally short off-axis subelements with varying fiber orientation along the lengthwise direction. From the analysis, it was found that the converted wave of the same mode as that of incident wave carried most energy and this tendency was sustained throughout the thick composites. The path and traveling time of ultrasonic wave in the subelement were obtained by computing the velocity and direction of group wave. The predicted results showed that the ray paths of quasi-longitudinal and quasi-transverse waves were highly affected by the degree of fiber waviness and had tendencies to trace toward the fiber direction and to converge to the adjacent peak of fiber waviness. Some parameters that showed strong effects on the wave propagation in the composites were identified for both insonified longitudinal and transverse waves. The experiments were also conducted on the specially fabricated thick composite specimens with various degrees of uniform fiber waviness using the conventional through-transmission method to verify the predicted results. Then, the analytically determined values were compared with the actual measurements obtained from the test specimens. Good agreements were observed among them.