Ultrasonic nondestructive evaluation of cracked composite laminates

Guided wave behavior in undamaged as well as damaged fiber-reinforced composite laminates is studied in an effort to develop ultrasonic nondestructive methods for their quantitative characterization. A global matrix method is used to formulate the wave propagation problem and to calculate the reflection coefficients and dispersion curves for unidirectional and angle-ply laminates immersed in water. The depth of an interface delamination in a unidirectional plate is determined through the analysis of the reflected waves. A systematic inversion scheme of dispersion data is applied to determine the reduction in stiffness due to transverse cracks in the off-axis plies of damaged, multi-orientation laminates. Excellent agreement between the theoretical results and measured data is achieved in most cases, indicating that the model is accurate within the framework of linear theory.