Non-contact excitation and focusing of guided waves in CFRP composite plate by air-coupled transducers for application in damage detection

Abstract

Guided waves have been utilized in Structural Health Monitoring (SHM) and Non-Destructive Testing (NDT) for many years. The vast majority of applications are based on contact wave excitation by using a group of piezoelectric transducers attached to the surface of a structure. However, in some cases piezoelectric transducers cannot be used directly on the structure and non-contact wave excitation methods are preferable. The paper presents the results of laboratory investigations utilizing air-coupled excitation with the use of ultrasound transmitters. The response of the specimen under various excitations by ultrasound transmitter array (UTA) was investigated. Various number of actuators and their configurations were considered. Moreover, various methods of wave focusing have been analysed. Next, the experimental verification of guided wave based damage detection system with proposed air-coupled excitation is presented. The wave sensing was non-contact as well. For this purpose the Scanning Laser Doppler Vibrometer (SLDV) was used. Full wavefield images and wave profiles for various excitation were prepared. The influence of ultrasound transmitter configuration and focusing method on the energy of induced wave was highlighted on RMS maps. Tests were carried out on the CFRP plate with dimension 500 x 500 x 1.5 mm. The delamination damage in a form of 15 x 15 mm Teflon tape insert was analysed.