Towards the Concept of Design for In-Situ Structural Health Monitoring (DISHMo)

Abstract

Abstract : A significant amount of research work has been dedicated towards structural health monitoring (SHM). Much of this work is targeted towards the introduction of the monitoring techniques to existing structures. To fully exploit the benefits of structural health monitoring, the application of these monitoring techniques must be addressed at the design stage. The work reported on in this report outlines a series of works that were devoted to the understanding how structural geometry can be designed to facilitate the Lamb wave based SHM. This report also describes a computationally efficient optical approach to studying the propagation of Lamb waves in a plate-like structure. This analytical tool was used to visualize the flow of the Lamb wave energy to aid in the design of geometrically varying structural features for efficient structural health monitoring. Compared with flat plates, plate-like structures with geometry were observed to significantly differ in their Lamb wave propagation. Our work attributes these variations to the same principles established in optics, in particular, refraction and reflection. Accordingly, a verification of Snell's law was made by imaging a plate with geometry through automated laser vibrometry. A comparison was then made between the refraction angles observed in the experiment and those calculated by applying Snell's law, where the theoretical phase velocities for each Lamb wave mode were used. Excellent agreement was found. As Lamb waves adhere to Snell's law, ray tracing software was developed to model the effects of geometry on Lamb wave propagation. This tool is computationally quick, robust and accurate. The model can be solved in seconds allowing the user to explore designs and make changes an order of magnitude faster than finite element analysis.