Damage detection with the fundamental mode of edge waves

Abstract

Detection of mechanical damage using Lamb or Rayleigh waves is limited to relatively simple geometries, yet real structures often incorporate features such as free or clamped edges, welds, rivets, ribs and holes. All these features are potential sources of wave reflections and scattering, which make the application of these types of guided waves for damage detection difficult. However, these features can themselves generate so-called ‘feature-guided’ waves. This article details the first application of the fundamental mode of transient edge waves for detection of mechanical damage. The fundamental edge wave mode (ES₀) – a natural analogue to Rayleigh waves – is weakly dispersive and may decay with propagation distance. The phase and group velocities of the ES₀ wave mode are close to the fundamental shear horizontal (SH₀) and symmetric Lamb (S₀) wave modes, at low and high frequencies, respectively. It is therefore quite challenging to excite a single ES₀ mode and avoid wave coupling. However, it was found experimentally that at medium range frequencies the ES₀ mode can be decoupled from SH₀ and S₀ modes, and its decay is small, allowing for distant detection of defects and damage along free edges of slender structural components. This article provides a brief theory of edge waves, excitation methodology and successful examples of distant detection of crack-like and corrosion damage in I-beam sections, which are widely applied in engineering and construction.