Copyright c  2004 Tech Science Press CMC, vol.1, no.4, pp.327-336, 2004 Lamb Wave Interaction with Delaminations in CFRP Laminates Jiayong Tian 1 , 2 , Ulrich Gabbert 2 , Harald Berger 2 , Xianyue Su 1 Abstract: In this paper, we investigate Lamb wave in- teraction with delamination in an infinite carbon fiber re- inforced plastics (CFRP) laminate by a hybrid method. The infinite CFRP laminate is divided into an exterior zone and an interior zone. In the exterior zone, the wave fields are expressed by wave mode expansion. In the interior zone, the wave fields are modeled by the finite element method (FEM). Considering the continuity con- dition at the boundary between the exterior and interior zones, the global wave fields can be calculated. Lastly, numerical examples show how a delamination in the lam- inate influences the mode conversion of different incident wave modes. keyword: Lamb Wave, Delamination, CFRP Lami- nates, Finite Element Method, Wave Function Expansion 1 Introduction Recently, considerable work has been focused on the de- velopment of smart structures. Smart structures can self- sense and self-process the environment information so that such structures offer new possibilities for a charac- terization of structures in the future. Carbon fiber rein- forced plastics (CFRP) with surface bonded or embed- ded thin piezoceramic patches used as sensors and/or actuators are very attractive for designing smart struc- tures. [Gabbert and Tzou (2001)] The main advantages of such structures are i) its light weight, high stiffness and high strength of material, which results from a tailored anisotropic layered design, and ii) its sensing and actuat- ing capability which enables such structures to adaptively react to changing environmental conditions. But during manufacturing and also during operating such structures often inevitable imperfections can be observed in the smart piezoceramic CFRP laminates, such as local con- centrations of fibers or epoxy, delaminations, debond- 1 Department of Mechanics and Engineering Science, Peking Uni- versity, Beijing, 100871, P.R.China 2 Institute of Mechanics, Otto-Von-Guericke University, Magde- burg, 39106, Germany ing of active ceramics, local fiber cracks, voids, inclu- sion etc. [Pohl, Mook, and Michel (2000), Gabbert and Cao (1999)] In extension to conventional non-destructive evaluation methods (NDE), the smart material them- selves can be used to monitor and to detect such dam- ages and imperfections. Such real-time health monitor- ing techniques can increase the reliability of smart struc- tures, reduce the operational costs and offer many unique opportunities to assess the structural integrity. There are some kinds of health monitoring method for smart piezo- ceramic CFRP laminates, such as electrical impedance spectroscopy, Lamb wave techniques etc. [Pohl, Mook, and Michel (2000)] From all of these methods, Lamb wave method seems to be the most attractive method for health monitoring in smart piezoceramic CFRP lam- inates. Lamb waves are one kind of guided waves that propagate in thin plates, which are also called plates modes. There are a finite number of symmetrical or anti-symmetric Lamb wave modes at a given frequency- thickness product, which are called S 0 , S 1 ,..., S n and A 0 , A 1 , ..., A m . These Lamb waves modes have different phase velocity and group velocity. The integrated piezo- ceramic patches can actuate and sense ultrasonic Lamb waves propagating in the plane of CFRP laminates. The ultrasonic Lamb wave can propagate for a long distance so that the lamb wave method is suitable for global health monitoring of smart structures. Furthermore, ultrasonic Lamb waves are very sensitive to delamination, which are typical defects in smart CFRP laminates. [Kundu, Karpur, Matikas, and Nicolau (1996)] For quantitative evaluations by Lamb wave techniques, it is important to investigate Lamb wave interaction with delamination. As a first step in this paper infinite CFRP laminates are in- vestigated. The wave scattering due to defects in plates has re- ceived considerable attention in the literature. Pao and Mow [Pao and Mow (1973)] used the wave function ex- pansion method to investigate the diffraction of elastic wave by a circular hole in an infinite isotropic plate. But the wave function expansion method is only suit-