Understanding and Exploiting the Effects of Loading on Ultrasonic Sensing Systems for Structural Health Monitoring.

摘要

This project has investigated the effects of applied loads on the propagation of ultrasonic Lamb waves and the impact of such loads on in situ structural health monitoring (SHM) systems. The specific SHM method considered was that of a spatially distributed array of piezoelectric disc transducers, which are capable of monitoring a large area by sending and receiving guided waves between all transducer pairs. Primary accomplishments include development of the theory of acoustoelastic Lamb wave propagation, in situ estimation of applied loads using a sparse array of guided wave sensors, investigation of the effects of applied loads on baseline comparison approaches to detection and localization of damage, and development of the load-differential imaging method to image fatigue cracks without requiring damage-free baseline measurements. Load-differential imaging maps changes in ultrasonic signals caused by a small increase in applied load to an image, which enables detecting and locating fatigue cracks that open under load and thus distinguishing them from other load-dependent effects. This method was successfully demonstrated in the laboratory during fatigue tests on a variety of aluminum plate-like specimens with varying degrees of geometrical complexity.