Antisymmetric feature-guided ultrasonic waves in thin plates with small radius transverse bends from low-frequency symmetric axial excitation

Abstract

The influence of bends constituting annular polygonal structures on ultrasonic guided waves propagating along their axis is investigated. Considering a single bend as a bent plate connects this problem to the better-understood physics of guided waves in straight plates. Using a three-dimensional finite element simulation validated with experiments, bends in plates are shown to act as features that can concentrate and guide ultrasonic energy along their length. Two interesting feature-guided modes are identified when the bent plate is subjected to "in-plane" or axial excitation applied uniformly along a through-thickness line bisecting the bent edge. Of these, the faster traveling mode has properties similar to, but travels at group velocities lower than, the S0 (fundamental symmetric) Lamb mode in flat plates. This paper however focuses on the slower bend-guided mode that is similar to the A0 (fundamental anti-symmetric) Lamb mode in flat plates. This mode is shown to be more strongly generated in smaller angle bends where it has a low attenuation. The results are discussed in light of simple modal studies performed using the Semi-Analytical Finite Element method.

Low frequency axisymmetric longitudinal guided waves in eccentric annular cylinders

“…44 and 45). A competing mechanism for mode confinement due to velocity changes in flatter regions of eccentric pipes, similar to feature-guiding effects noted recently 39,46,47 is also revealed in a set of further studies considering more general pipe radius-thickness ratio and eccentricity cases. This paper is organized as follows.…”

Ultrasonic guided waves in elliptical annular cylinders

“…Such an effect is closely related to feature-guided wave phenomena noted in the literature in recent years. 3,7,8 Also an interesting observation is that pipe eccentricity does not seem to affect the T(0,1) mode as strongly, and its modal structure and nondispersive nature are very similar to the circular pipe even in cases of high ovalness. This paper is organized as follows.…”

“…3,7,8 Recent analytical studies (Postnova and Craster 11,12 ) have shown that curvature effects in waveguides are mathematically equivalent to local thinning. Again drawing upon the work of Postnova and Craster, 11,12 we find that for longitudinal modes, trapping is only possible for local thinning for Poisson ratio in the range of metals.…”

“…[5][6][7] Briefly, this procedure consists in casting the governing elastodynamic wave equations into the form of an eigenvalue equation for the wavenumber k, at each operating frequency x. This equation can then solved be for the wavenumber using a commercial FE package.…”

Guided waves for online monitoring of composites

“…The main challenge to the inspection of composites is the presence of multiple layers and anisotropic nature. Ultrasonic guided waves have been proven an attractive tool in inspection of large structures [2][3][4][5]. PZT and Fiber Bragg Gratings based sensors have been embedded often to monitor the crack growth during the curing process [6].…”