RESUMEN
Lamb wave is widely recognized as one of the most encouraging tools for structural health monitoring (SHM) systems. In spite of many favourable characteristics of Lamb wave for SHM, real-world application of these systems is still quite limited. Beside the complexities derived from multi-modal, dispersive and multi-path characteristics of Lamb waves, one of the main challenges in Lamb wave based SHM is sensitivity of these systems to environmental and operational conditions (EOCs) parameters. This paper provides a state of the art review of the effects of EOCs parameters including: temperature, moisture, load, vibration and bonding (adhesive layer shear modulus and thickness, bond defects), on Lamb wave propagation. Moreover, this paper provides a summary of compensation strategies to account for EOCs effects as well as baseline free techniques. An objective is also to understand the future directions and areas requiring attention of the researchers.
RESUMEN
Lamb waves and electro-mechanical impedance (EMI) based methods are increasingly used in damage detection owing to their high sensitivity to small structural defects. Lamb wave based methods are effective in detecting damages in a large area and electro-impedance based methods are suitable for characterizing the identified damage. Based on these two methods, a novel combined damage detection method is presented in this research. To achieve this, first, a mobile transducer set is developed, which can be used for both the Lamb waves and EMI based methods. Then, a baseline-free damage detection strategy that combines the Lamb waves and EMI methods is presented. Finally, a laboratory-sized test piece is used to validate the effectiveness of the proposed approach. The results achieved with the application of the presented combined method for characterizing an L-shape crack in an aluminum plate show better location accuracy and detection efficiency than those obtained by applying only one method.