Analytical Modeling of Lamb Waves for Structural Health Monitoring (Preprint)

摘要

Structural health monitoring techniques are being developed to reduce cost, increase availability, and maintain safety of current and future air vehicle systems. Various techniques have been investigated depending on the scale of the damage to be detected. For example, damage such as fastener failure may have a more global effect on the structural dynamics and therefore modal-based damage detection techniques may be suitable. This paper focuses on detecting smaller scale damage, such as cracking or corrosion, which typically has a highly localized effect on the system dynamics. The use of Lamb waves, guided elastic waves in a plate, has shown promise in detecting such highly localized damage due to the relatively short wavelengths of the propagating waves. However, the Lamb wave behavior, is fairly complex as various waveforms may exist and the waves are dispersive, so the wave speed is a function of frequency. To examine the complex Lamb wave behavior, analytical models are being developed. This paper explores the use of explicit time integration finite element analysis. Key modeling issues are addressed including appropriate time increments and element lengths for accurate, yet efficient, solutions and the material properties used for the media through which the wave propagates. With these issues addressed, attention is focused on the effects of damage on the Lamb waves and the use various excitation waveforms. Lastly, potential improvements through advanced techniques, such as beamforming, are discussed.