Impact of ultrasonic guided wave transducer design on health monitoring of composite structures

Structural health monitoring of composite materials will lead to a significant safety and economic impact on the aircraft and aerospace industries. Ultrasonic guided wave based methods are becoming popular because of an excellent compromise between coverage area and sensitivity for localized damage detection. The transducers currently used in composite health monitoring are designed mostly in an empirical manner. The work presented in this paper provides an analytical procedure to study the wave excitation phenomenon in composite laminates. A hybrid semi-analytical finite element method and global matrix method is used to obtained the guided wave modal solutions. A normal mode expansion technique is then used to simulate the guided waves excited from a surface mounted piezoelectric transducer with transient loading. Parametric studies are performed to obtain the guided wave mode tuning characteristics and to study the influence of piezoelectric wafer geometry on wave excitation. In an inverse problem, an appropriate loading pattern can be designed to achieve selective guided wave mode excitation for improved sensitivity and/or penetration power in the health monitoring of composites. A wave field reconstruction algorithm based on normal mode expansion is also introduced in this paper. This method is also very computationally efficient compared with the commonly used finite element method in wave field excitation simulation.