Remote Excitation Ultrasonic Waveguide-Based SHM for Critical Applications

Ultrasonic SHM approaches using bulk or guided waves has been well documented. Here the waves are generate using PZT transduction that requires excitation inputs using either high voltage or high current or both. Several critical applications such as component in explosion susceptible environment, extreme temperature condition, etc. have limitations in deployment of high voltage/current excitation. In this paper, the use of wave-guide-based excitation is explored for plate and pipe like geometries. The waveguide help isolate the excitation part of the ultrasound generation, away from the component that may be in a hostile condition. The ultrasound wave modes excited in the waveguide is coupled to the structure and optimized to generate the desired guided wave modes in the geometry of the structures using Finite Element Wave Propagation models. The reception of these modes are also explored using similar ultrasonic waveguides. The detection of defects, in an SHM mode, using this remote generation approach is also demonstrated on a plate geometry component. This article demonstrates the detection of fundamental symmetric wave mode (S0), shear horizontal waves (SH0) and antisymmetric wave mode (A0) in an steel plate by placing a thin wire-like stainless steel waveguide sensor. In order to uniquely identify the three-fundamental plate-guided modes, we map the experimentally measured group velocities as detected by the waveguide sensor to theoretically obtained group velocity dispersion curves. The analytically obtained FEM results are evaluated experimentally using time-of-flight measurements. In future, this sensor arrangement may be utilized in areas like high-temperature furnaces, engines and aircrafts for detecting cracks.