Theory on the air-couple wave propagation in layered composite materials with laminate defect

It has been known for many years that defects exist along interfaces between two dissimilar materials, and conventional contact ultrasonic techniques are not always enable to detect the defects, so more advanced methods are still necessary. In this paper, the spring model for the layered composite materials is built to simulate wave propagation. A stiffness matrix-based method is proposed for quantifying the transmission coefficients. The solutions of the characteristic equations are numerically efficient and stable. This work has shown that the spring models are well adapted to evaluate the quality and integrity of complex composite structures.