Guided Waves in a Plate With a Delamination-Like Discontinuity

2016 ◽  
Author(s):  
Christoph Schaal ◽  
Ajit Mal
Keyword(s):  
Cross Sections ◽  
Composite Structures ◽  
Guided Waves ◽  
Lamb Waves ◽  
Near Field ◽  
Experimental Methods ◽  
Structural Components ◽  
Inspection Systems ◽  
Frame Work ◽  
Theoretical Results

In this paper, some of the useful properties of guided Lamb waves are investigated, using analytical, numerical and experimental methods, in an effort to provide the knowledge base required for the development of viable nondestructive evaluation (NDE) systems for composite structures. An analytical frame-work that considers propagating, nonpropagating and evanescent Lamb waves to analyze the scattering of an incident ultrasonic Lamb wave at delaminations and disbonds is presented. In addition to the delamination problem, the interaction of Lamb waves with a step discontinuity, which can be found at common stiffeners, is investigated using a similar analytical approach. A near-field solution is obtained, and power flows through the cross-sections of the plate are evaluated. The agreement between experimental, numerical and theoretical results is shown to be excellent in certain frequency ranges, providing guidance for the design of reliable and effective inspection systems for modern aeronautical and aerospace structural components.

scholarly journals Warped Wigner-Hough Transform for Defect Reflection Enhancement in Ultrasonic Guided Wave Monitoring

2012 ◽  
Vol 2012 ◽  
pp. 1-15 ◽  
Author(s):  
Luca De Marchi ◽  
Emanuele Baravelli ◽  
Giampaolo Cera ◽  
Nicolò Speciale ◽  
Alessandro Marzani
Keyword(s):  
Hough Transform ◽  
Guided Waves ◽  
Lamb Waves ◽  
Guided Wave ◽  
Nonlinear Signal Processing ◽  
Localization Accuracy ◽  
Time Frequency ◽  
Ultrasonic Guided Wave ◽  
Inspection Systems ◽  
Nonlinear Signal

To improve the defect detectability of Lamb wave inspection systems, the application of nonlinear signal processing was investigated. The approach is based on a Warped Frequency Transform (WFT) to compensate the dispersive behavior of ultrasonic guided waves, followed by a Wigner-Ville time-frequency analysis and the Hough Transform to further improve localization accuracy. As a result, an automatic detection procedure to locate defect-induced reflections was demonstrated and successfully tested by analyzing numerically simulated Lamb waves propagating in an aluminum plate. The proposed method is suitable for defect detection and can be easily implemented for real-world structural health monitoring applications.

A Numerical Approach for the Investigation of Guided-Waves Propagation Mechanisms in Reinforced Polymers through a DoE Analysis

2019 ◽  
Vol 957 ◽  
pp. 329-339
Author(s):  
A. de Luca ◽  
Donato Perfetto ◽  
Francesco Caputo
Keyword(s):  
Material Properties ◽  
Composite Structures ◽  
Guided Waves ◽  
Lamb Waves ◽  
Numerical Models ◽  
Detection Sensitivity ◽  
Fe Model ◽  
Structural Health ◽  
Waves Propagation ◽  
Local Material Properties

Thanks to their high damage detection sensitivity and low requested power consumption, guided-waves (Lamb waves) have been increasingly used in the last years to monitor the structural integrity in primary and secondary composite structures. The monitoring of the structural health through the propagation of Lamb waves in composite structures is notoriously complex and, for this reason, the development of a prediction model can be a helpful tool for the improvement of Structural Health Monitoring (SHM) systems. Finite Element Method (FE) appears to be the best candidate for such type of simulation. However, since Lamb waves propagation depends strictly on the local material properties of the medium they propagate through, their numerical characterization is a thorny phase. Real composite components are usually affected by the presence of a large number of voids and defects, which cannot be reproduced in numerical models; this leads to a variability of the mechanical properties of materials, with particular reference to elastic moduli and density. These aspects get really ambitious the development of a well-established FE model. In this paper, a design of experiment (DOE) has been carried out to numerically investigate on the effects of the material properties variability on guided-waves time of flight.

Development of Lamb Waves-Based SHM Systems

2012 ◽  
Vol 518 ◽  
pp. 87-94 ◽  
Author(s):  
Lukasz Ambrozinski ◽  
Tadeusz Stepinski ◽  
Tadeusz Uhl ◽  
Janusz Ochonski ◽  
Andrzej Klepka
Keyword(s):  
Composite Structures ◽  
Guided Waves ◽  
Lamb Waves ◽  
Safety Standards ◽  
Promising Tool ◽  
Self Focusing ◽  
Half Wavelength ◽  
Damage Imaging ◽  
Synthetic Aperture Focusing ◽  
Design And Manufacture

Guided waves (GW) based methods are a promising tool for structural health monitoring (SHM) of plate-like metallic and composite structures in which high safety standards are required. In this paper we present research with the aim to design and manufacture a prototype of Lamb waves (LW) SHM system. Two approaches can be applied for SHM of plate-like structures. One of them can be based on a sparse array and damage imaging involving incoherent summation of signals envelope. The second approach involves phased arrays with transducers spaced at a distance lower than half wavelength of the excited Lamb-mode. The influence of an arrays parameters on beamforming of Lamb waves is discussed in the case of linear array. It appears that an unequivocal localization of damage on a plate requires a 2D arrays topology; therefore a star-shaped active array was designed and manufactured for the developed SHM system. Two signal processing approaches were applied for that array, the standard one, based on the delay and sum (DAS) synthetic aperture focusing scheme, and the second one, using a self-focusing technique to obtain the separate images for each scatterer existing in the plate.

scholarly journals High-Q dark hyperbolic phonon-polaritons in hexagonal boron nitride nanostructures

Nanophotonics ◽  
2020 ◽  
Vol 9 (6) ◽  
pp. 1457-1467 ◽  
Author(s):  
Georg Ramer ◽  
Mohit Tuteja ◽  
Joseph R. Matson ◽  
Marcelo Davanco ◽  
Thomas G. Folland ◽  
...  
Keyword(s):  
Boron Nitride ◽  
Cross Sections ◽  
Hexagonal Boron Nitride ◽  
Near Field ◽  
High Q ◽  
Surface Phonon Polaritons ◽  
Previous Hypothesis ◽  
Phonon Polaritons ◽  
Field Reflectance ◽  
Strong Confinement

AbstractThe anisotropy of hexagonal boron nitride (hBN) gives rise to hyperbolic phonon-polaritons (HPhPs), notable for their volumetric frequency-dependent propagation and strong confinement. For frustum (truncated nanocone) structures, theory predicts five, high-order HPhPs, sets, but only one set was observed previously with far-field reflectance and scattering-type scanning near-field optical microscopy. In contrast, the photothermal induced resonance (PTIR) technique has recently permitted sampling of the full HPhP dispersion and observing such elusive predicted modes; however, the mechanism underlying PTIR sensitivity to these weakly-scattering modes, while critical to their understanding, has not yet been clarified. Here, by comparing conventional contact- and newly developed tapping-mode PTIR, we show that the PTIR sensitivity to those weakly-scattering, high-Q (up to ≈280) modes is, contrary to a previous hypothesis, unrelated to the probe operation (contact or tapping) and is instead linked to PTIR ability to detect tip-launched dark, volumetrically-confined polaritons, rather than nanostructure-launched HPhPs modes observed by other techniques. Furthermore, we show that in contrast with plasmons and surface phonon-polaritons, whose Q-factors and optical cross-sections are typically degraded by the proximity of other nanostructures, the high-Q HPhP resonances are preserved even in high-density hBN frustum arrays, which is useful in sensing and quantum emission applications.

An Assessment of the Value of Theory in Predicting Gas-Bearing Performance

1961 ◽  
Vol 83 (2) ◽  
pp. 195-200 ◽  
Author(s):  
S. Cooper
Keyword(s):  
Steady State ◽  
Slip Velocity ◽  
Reynolds Equation ◽  
Energy Equation ◽  
Experimental Methods ◽  
Experimental Results ◽  
Theoretical Investigations ◽  
Gas Bearing ◽  
Theoretical Results

The object of the paper is to indicate the value of theoretical investigations of hydrodynamic finite bearings under steady-state conditions. Methods of solution of Reynolds equation by both desk and digital computing, and methods of stabilizing the processes of solution, are described. The nondimensional data available from the solutions are stated. The outcome of an attempted solution of the energy equation is discussed. A comparison between some theoretical and experimental results is shown. Experimental methods employed and some difficulties encountered are discussed. Some theoretical results are given to indicate the effects of the inclusion of slip velocity, stabilizing slots, and a simple case of whirl.

Semi-analytical modelling of guided waves generation on composite structures using circular piezoceramics

2015 ◽  
Author(s):  
Pierre-Claude Ostiguy ◽  
Nicolas Quaegebeur ◽  
Maxime Bilodeau ◽  
Patrice Masson
Keyword(s):  
Composite Structures ◽  
Guided Waves ◽  
Analytical Modelling

Inspection of Concrete-Metal Rod Interface Using Guided Waves

2000 ◽  
Author(s):  
Won-Bae Na ◽  
Tribikram Kundu ◽  
Mohammad R. Ehsani
Keyword(s):  
Lamb Wave ◽  
Guided Waves ◽  
Lamb Waves ◽  
Guided Wave ◽  
Ultrasonic Transducers ◽  
Interface Debonding ◽  
Long Distance ◽  
Steel Rebar ◽  
Steel Bars ◽  
Steel Rebars

Abstract The feasibility of detecting interface degradation and separation of steel rebars in concrete beams using Lamb waves is investigated in this paper. It is shown that Lamb waves can easily detect these defects. A special coupler between the steel rebar and ultrasonic transducers has been used to launch non-axisymmetric guided waves in the steel rebar. This investigation shows that the Lamb wave inspection technique is an efficient and effective tool for health monitoring of reinforced concrete structures because the Lamb wave can propagate a long distance along the reinforcing steel bars embedded in concrete as the guided wave and is sensitive to the interface debonding between the steel rebar and concrete.

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