Recent research by the authors has revealed the presence of shear horizontal-type of feature-guided (SHB) waves in plates with 90° transverse bends. The SHB mode is non-dispersive and has low attenuation over a range of higher frequencies (500 kHz - 1 MHz). This mode is attractive for Non-destructive Evaluation (NDE) of bends in practical structures such as aerospace spar joints. Here the interaction of the SHB mode with transverse small-width notches (cracks) running across bends in plates is studied using 3D finite element simulations and validated by experiments. For through-thickness cracks, the influence of transverse crack length on SHB mode reflection is studied. For part-depth but long cracks (transverse length greater than operating wavelength), influence of crack depth on mode reflection is studied. The results demonstrate the potential of the SHB mode for NDE of bent plate structures. © 2015 The Authors.

Prabhu Rajagopal

Department of Mechanical Engineering

Prabhakaran Manogharan

Cracks

finite element method

Guided electromagnetic wave propagation

INDIUM PLATING

Nondestructive examination

Plates (structural components)

Shear flow

3D finite-element simulation

GUIDED MODES

Higher frequencies

NON DESTRUCTIVE EVALUATION

Operating wavelength

THROUGH-THICKNESS CRACKS

TRANSVERSE CRACK

Ultrasonic testing

Fulltext

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IIT Madras

Physics Procedia

Recent research by the authors shows that bends in plates can act as features that can concentrate and guide ultrasonic energy along their axis. At low frequencies, two 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 slower mode has properties similar to the A0 (fundamental antisymmetric) Lamb mode in flat plates. This paper focuses on the faster bend-guided mode that is similar to the S0 (fundamental symmetric) Lamb mode in flat plates. Using 3D finite element (FE) simulation validated with experiments, this mode is shown to be more strongly generated in smaller angle bends. Features of the mode including velocity, attenuation and modal structure are considered in detailed studies. Results are discussed in light of simple modal studies using the Semi Analytical Finite Element (SAFE) method, suggesting a relationship of bend-guided waves to modes of curved bars. © 2014 Elsevier B.V. All rights reserved.

Ultrasonics

Symmetric low-frequency feature-guided ultrasonic waves in thin plates with transverse bends

Ultrasonic guided waves are attractive for rapid remote screening of large structures and today they are widely used in several practical applications including the inspection of pipe and plate installations. More recently, guided wave modal solutions confined in extended local features have attracted much research interest, offering the possibility of inspecting complex geometric or topographical features. Such feature-guided wave (FGW) modes have been reported in plate waveguides with local cross-section variation or curvature, and in annular circular cylinders with cross-sectional anomalies. This paper focuses on FGW phenomena in 90 degree structural bends in plate structures, which commonly occur in various industrial structures. Modal studies are carried out using the Semi-Analytical Finite Element (SAFE) method, while 3D finite element (FE) simulations are used to gain visualization of results and also obtain cross-validation. Our studies reveal, perhaps for the first time, the possibility of bend-guided modes of the shear-horizontal (SH) family, in addition those of the Rayleigh-Lamb family reported earlier in the literature. This mode has attractive properties including low attenuation and limited dispersion. We investigate effects of plate thickness and bend radius on the physics of FGW in bends, arguing the strong role of geometry and curvature effects in causing mode confinement. Preliminary experiments have also been carried out to validate the existence of such bend-guided mode. © 2015 AIP Publishing LLC.

AIP Conference Proceedings

Feature-guided waves (FGW) in plate structures with 90° transverse bends

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. © 2013 Acoustical Society of America.

Journal of the Acoustical Society of America

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

NDT & E International

Interaction of weld-guided waves with defects

The Journal of the Acoustical Society of America

Scattering of the fundamental shear horizontal guided wave by a part-thickness crack in an isotropic plate

Interaction of the shear horizontal bend guided mode (SHB) with transverse cracks

Journal	Data powered by TypesetPhysics Procedia
Publisher	Data powered by TypesetElsevier
ISSN	18753884
Open Access	Yes