Multi-path guided wave imaging for in situ monitoring of complex structures

Abstract

There is a well-recognized need within the structural health monitoring community to interrogate large, complex structures in a rapid, reliable, and cost-effective fashion. Ultrasonic guided waves hold promise because these waves have been shown to travel long distances and remain sensitive to both surface and subsurface features, even in complex structures. Distributed arrays of permanently attached, inexpensive piezoelectric transducers are perhaps the most effective means for performing guided wave structural health monitoring; however, guided wave signals recorded from these arrays are very complex and can be difficult to interpret. Current imaging algorithms used to interpret recorded guided waves address the complexity by considering only the direct-path propagation between each sensor and points of interest on the structure. Built-up structures that contain multiple features, such as stiffeners, ribs, cut-outs and fasteners, compound the difficulty of interpretation by substantially increasing the number of multi-path echoes and even precluding direct-path propagation between many portions of the structure. This work addresses the inherent challenges of working with complex structures by leveraging, rather than ignoring, the multi-path echoes present in ultrasonic guided wave signals through the use of experimentally estimated Green’s functions. The proposed approach is validated using experimental data.