Ultrasonic Study of Quasi-Isotropic Composites

Abstract

Advanced composites used for aerospace applications usually have multilayered structure with differently oriented plies. Most ultrasonic inspections of such composites are performed using normally incident ultrasonic waves. The use of oblique incident waves is complicated by strong ply scattering and difficulties in wave propagation analysis. In this paper we investigate both theoretically and experimentally ultrasonic wave propagation in multi-ply composites depending on ply orientation and angle of incidence. We compare computational efficiency and rederive algorithms for transfer and global matrix methods. Many authors have considered transfer matrix algorithm for isotropic and anisotropic cases [1–8]; however, the computational instability of the transfer matrix method when the layer thickness is comparable to and greater than the wavelength makes it impractical. Dunkin [9] and Levesque & Piche [10] have developed a stable transfer matrix method for the isotropic case. A stable method for the anisotropic case has been developed by Hosten and Castaings [11][12]. In contrast to the transfer matrix approach, the global matrix method assembles solutions for all layers in a single matrix which is large; however the method is computationally stable.