Nondestructive evaluation of degree of fiber waviness in thick composites

An experimental investigation was conducted nondestructively to evaluate the degree of fiber waviness in thick composite materials using ultrasonics. An analytical model, based on the ray and plane wave theories, was proposed to understand the ultrasonic wave propagation in composites with uniform fiber waviness. In the model, the composites were assumed to have continuous fibers with sinusoidal waviness in a matrix. The experiments were conducted on the specially fabricated thick composite specimens with various degrees of uniform fiber waviness using the conventional through-transmission method. For the given positions of transmitter, the locations of receiver with the maximum energy of received wave were measured along with the traveling time of the wave. From these and conjugated results from the analytical model, the paths of ultrasonic wave, wavelength of fiber waviness, concave and convex regions of fiber waviness and amplitude of fiber waviness were determined. Then, the nondestructively determined values were compared with the actual measurements obtained from the test specimens. Good agreements were observed among them.