TABLE OF CONTENTS This chapter will deal with an important class of waves that have widespread applications in structural health monitoring (SHM) the class of guided waves. Guided waves are especially important for structural health monitoring because they can travel at large distances in structures with only little energy loss. Thus, they enable the SHM of large areas from a single location. Guided waves have the important property that they remain confined inside the walls of a thin-wall structure, and hence can travel over large distances. In addition, guided waves can also travel inside curved walls. These properties make them well suited for the ultrasonic inspection of aircraft, missiles, pressure vessels, oil tanks, pipelines, etc.
The chapter will start with the discussion of Rayleigh waves, a.k.a., surface acoustic waves (SAW). Rayleigh waves are found in solids that contain a free surface. The Rayleigh waves travel close to the free surface with very little penetration in the depth of the solid. For this reason, Rayleigh waves are also known as surface-guided waves.
The chapter will continue with a description of guided waves in plates. In flat plates, ultrasonic-guided waves travel as Lamb waves and as shear horizontal (SH) waves. Lamb waves are vertically polarized, whereas SH waves are horizontally polarized. Ultrasonic guided waves in flat plates were first described by Lamb (1917). A comprehensive analysis of Lamb wave was given by Viktorov (1967), Achenbach (1973), Graff (1975), Rose (1999), and Royer and Dieulesaint (2000).
A simple form...
