Session: 21-01: Poster Session

Paper Number: 98402

98402 - Interaction of Shear Horizontal Guided Waves With Small Defects 

Guided waves have the ability to inspect large areas of plates quickly whilst being sensitive to defects throughout the plate thickness, offering excellent potential for a wide range of NDT applications. Understanding how guided waves interact with discontinuities is crucial in developing new inspection systems. The shear horizontal wave fundamental mode (SH0) has the additional benefit of being non-dispersive on flat plates or sheets, and is the focus of this work. Electromagnetic acoustic transducers (EMATs) can be designed to generate shear horizontal guided waves using a periodic permanent magnet array (PPM).

When an incident SH0 wave interacts with a defect, multiple wave modes are reflected. These reflections comprise both the direct reflection of SH0 and mode converted Lamb waves. Due to the operating frequency, only the fundamental modes of both Lamb and shear horizontal are of interest. Using both simulations and experimentation this work investigates the effect that the geometry of notch-like defects has on SH0 reflections and mode converted Lamb wave reflections. The motivation for this is to understand the relationship between defect size and wavelength to assist in the design of optimised inspection setups. To target the detection of small defects, SH0 wavelengths of between 6 mm and 12 mm were used, generated by PPM EMATs. Inspection was performed on 1 mm thick titanium and aluminium sheets. This work shows that for small defect widths the defect length at which the maximum SH0 reflection occurs changes, which has not previously been reported. Furthermore, for the S0 mode converted reflection the angle at which maximum reflection occurs changes depending on the defect's width.

Presenting Author: Christian Peyton University of Warwick