Feasibility of using a 3D laser-based transduction system for monitoring the integrity of I-Beams using Rayleigh waves

This paper acquaints the investigations using Rayleigh waves to surveil the structural integrity of an I-Beam. Unlike the conventional contact-type of sensors, such as the piezoelectric transducers and magnetostrictive sensors, a fully non-contact 3D type of laser-based transduction system was used in the present study to generate and receive the propagating Rayleigh waves. This laser-based transduction system is a new and attractive inspection technique because it can be used where contactable sensors cannot be applied directly to the target structure; such as those with high temperature surface, having limited access for mounting the sensors, and operating in a hazardous environment. In this study, a high power and pulsed Nd: YAG laser was used to generate the Rayleigh waves. The emission and sensing were effectuated simultaneously and the wave propagation data was recorded by scanning the surface of the I-beam sequentially. The 3D laser scanner measured the in-plane and out-of-plane velocities across a user-defined grid. Note that less research effort had been focused on specimens like I-Beam due its structural complexity and complex wave propagation phenomena. Explication of wave propagation in such specimens is still a challenge. The research presented here is an attempt to fill these gaps and solve these problems. Additionally, numerous experiments are conducted in order to corroborate the effectiveness of the proposed experimental setup in detecting the defect. An artificial defect was created on the web part of the I-beam which mimics a real damage case. The responses were recorded using the 3D laser-based transduction system before and after creating the defect. The presented results thereby confirm the robustness of the non-contact generation and measurement setup for the structural health monitoring of I-Beams. The aptness of using such totally laser-based transduction system to unveil the characteristics of the propagating Rayleigh waves and its interaction with defects are notable.