Showing papers on "Lamb waves published in 2017"
TL;DR: This work proposes and experimentally demonstrate source illusion devices to manipulate flexural waves using metasurfaces for shifting, transforming, and splitting a point source with agreement from numerical simulations and the Huygens-Fresnel theory.
Abstract: Inspired by recent demonstrations of metasurfaces in achieving reduced versions of electromagnetic cloaks, we propose and experimentally demonstrate source illusion devices to manipulate flexural waves using metasurfaces. The approach is particularly useful for elastic waves due to the lack of form invariance in usual transformation methods. We demonstrate compact and simple-to-implement metasurfaces for shifting, transforming, and splitting a point source. The effects are measured to be broadband and robust against a change of source positions, with agreement from numerical simulations and the Huygens-Fresnel theory. The proposed method is potentially useful for applications such as nondestructive testing, high-resolution ultrasonography, and advanced signal modulation.
176 citations
TL;DR: In this article, a phononic crystal Luneburg lens was constructed using hexagonal unit cells with blind holes of different diameters, which were determined by finite element simulations of the lowest asymmetric mode Lamb wave band structure.
Abstract: We explore a phononic crystal Luneburg lens through design, fabrication, and analysis for omnidirectional elastic wave focusing and enhanced energy harvesting both numerically and experimentally. The proposed lens is formed using hexagonal unit cells with blind holes of different diameters, which are determined according to the Luneburg lens refractive index distribution obtained by finite-element simulations of the lowest asymmetric mode Lamb wave band structure. Wave simulations are performed numerically under plane wave excitation from a line source, and focusing is observed at the opposite border of the lens with respect to the incident wave direction. Numerically simulated elastic wave focusing results are validated through a set of experiments. Omnidirectionality is demonstrated by testing the lens under plane wave excitation for different angles of incidence. With piezoelectric energy harvesters located at the boundary of the phononic crystal Luneburg lens, more than an order of magnitude larger po...
144 citations
TL;DR: In this paper, nonlinear Lamb wave-mixing was applied in the detection of micro-cracks in plates, and the analysis of the nonlinear interaction of these waves with cracks of various lengths and widths was performed using finite-element simulations.
Abstract: In engineering practice, failures due to fatigue cracks in metallic structures have always been difficult to predict. In our study, nonlinear Lamb wave-mixing was applied in the detection of micro-cracks in plates. The analysis of the nonlinear interaction of these waves with cracks of various lengths and widths was performed using finite-element simulations. The simulation results showed that the sideband at the sum frequency provide a sensitive means for micro-crack detection. Moreover, the sideband amplitudes show a monotonic increase with micro-crack length, but a decrease with micro-crack width. Experiments using Lamb wave-mixing were conducted on plates with fatigue cracks. The experimental results show that a proposed acoustic nonlinearity parameter related to the sideband at the sum frequency is sensitive to micro-cracks in plate, and is well correlated with the damage degree.
101 citations
TL;DR: In this article, a Lamb wave based nonlinear method is used to detect delamination in a composite laminate and a new hybrid method is introduced, wherein the spectral and temporal data are used together in order to locate a delamination.
99 citations
TL;DR: A new acoustic emission (AE) source localization for isotropic plates with reflecting boundaries that has no blind spot leverages multimodal edge reflections to identify AE sources with only a single sensor is presented.
97 citations
TL;DR: In this paper, the propagation of time harmonic plane waves is investigated in an infinite nonlocal elastic solid material with voids, and the governing relations and equations are derived for nonlinear elastic solid with void.
Abstract: In this paper, the governing relations and equations are derived for nonlocal elastic solid with voids. The propagation of time harmonic plane waves is investigated in an infinite nonlocal elastic solid material with voids. It has been found that three basic waves consisting of two sets of coupled longitudinal waves and one independent transverse wave may travel with distinct speeds. The sets of coupled waves are found to be dispersive, attenuating and influenced by the presence of voids and nonlocality parameters in the medium. The transverse wave is dispersive but non-attenuating, influenced by the nonlocality and independent of void parameters. Furthermore, the transverse wave is found to face critical frequency, while the coupled waves may face critical frequencies conditionally. Beyond each critical frequency, the respective wave is no more a propagating wave. Reflection phenomenon of an incident coupled longitudinal waves from stress-free boundary surface of a nonlocal elastic solid half-space with voids has also been studied. Using appropriate boundary conditions, the formulae for various reflection coefficients and their respective energy ratios are presented. For a particular model, the effects of non-locality and dissipation parameter (
$\tau $
) have been depicted on phase speeds and attenuation coefficients of propagating waves. The effect of nonlocality on reflection coefficients has also been observed and shown graphically.
81 citations
TL;DR: A parallel algorithm to model the nonlinear dynamic interactions between ultrasonic guided waves and fatigue cracks and the explicit contact formulation, the parallel algorithm, as well as the GPU-based implementation facilitate LISA's high computational efficiency over the conventional finite element method (FEM).
80 citations
TL;DR: In this paper, a wave vector analysis is conducted that enables selection of primary waves traveling in any direction that generate phase matched secondary waves, and the authors have tabulated many sets of primary wave and secondary wave sets.
Abstract: The extraordinary sensitivity of nonlinear ultrasonic waves to the early stages of material degradation makes them excellent candidates for nondestructive material characterization. However, distinguishing weak material nonlinearity from instrumentation nonlinearity remains problematic for second harmonic generation approaches. A solution to this problem is to mix waves having different frequencies and to let their mutual interaction generate sum and difference harmonics at frequencies far from those of the instrumentation. Mixing of bulk waves and surface waves has been researched for some time, but mixing of guided waves has not yet been investigated in depth. A unique aspect of guided waves is their dispersive nature, which means we need to assure that a wave can propagate at the sum or difference frequency. A wave vector analysis is conducted that enables selection of primary waves traveling in any direction that generate phase matched secondary waves. We have tabulated many sets of primary waves and ...
72 citations
TL;DR: In this paper, a 3D finite element (FE) model was built in Abaqus/Explicit software with the help of user material subroutine to capture the wave propagating features in WGF/epoxy composite plate.
69 citations
TL;DR: In this paper, a method for addressing temperature effects using Lamb waves is developed with application to baseline comparison damage detection, which is based on baseline signal stretch with an improved minimum residual allowing correction over a larger temperature range.
Abstract: In this article, a method for addressing temperature effects using Lamb waves is developed with application to baseline comparison damage detection. The proposed method is based on baseline signal stretch with an improved minimum residual allowing correction over a larger temperature range. The effectiveness of the proposed approach in detecting (artificial) damages is demonstrated experimentally over a large temperature. The method is also shown to accurately detect and localise a crack in an aluminium panel and actual impact damage on a carbon fibre reinforced polymer panel.
67 citations
TL;DR: In this paper, an explicit asymptotic formulation for Rayleigh and Rayleigh-type interfacial and edge waves was derived for steady-state and transient problems for a moving load on an elastic half-space.
Abstract: Explicit asymptotic formulations are derived for Rayleigh and Rayleigh-type interfacial and edge waves. The hyperbolic–elliptic duality of surface and interfacial waves is established, along with the parabolic–elliptic duality of the dispersive edge wave on a Kirchhoff plate. The effects of anisotropy, piezoelectricity, thin elastic coatings, and mixed boundary conditions are taken into consideration. The advantages of the developed approach are illustrated by steady-state and transient problems for a moving load on an elastic half-space.
TL;DR: In this article, the impact of transducer configurations, electrode materials, electrode thicknesses, and interdigital transducers duty factors on the k2eff dispersive characteristics of one-port AlN Lamb wave resonators was investigated.
Abstract: AlN Lamb wave resonators enjoy advanced and attractive properties for enabling the next-generation single-chip radio frequency front-end, but their moderate effective electromechanical coupling coefficient (k2eff) poses a limit to their application in filters and multiplexers. Despite the fact that the reported k2eff enhancement techniques of doped AlN thin films which are expensive and trade off the quality factor (Q), the transducer topology itself extensively impacts the k2eff value. Although an AlN cross-sectional Lame mode resonator exhibiting a k2eff of 6.34% has been demonstrated without the need for changing the piezoelectric material, a detailed study of transducer design for AlN Lamb wave resonators has not been conducted. In this work, we investigate the impact of (i) transducer configurations, (ii) electrode materials, (iii) electrode thicknesses, and (iv) interdigital transducer duty factors on the k2eff dispersive characteristics of one-port AlN Lamb wave resonators by using the finite eleme...
TL;DR: In this article, a damage identification approach based on guided ultrasonic waves and 3D laser Doppler vibrometry is proposed, which is based on the fact that the symmetric and antisymmetric Lamb wave modes differ in amplitude of the in-plane and out-of-plane vibrations.
TL;DR: This study theoretically reveals that the low frequency S0 mode of Lamb waves can be used as the fundamental waves to quantitatively identify micro‐cracks in thin plates.
TL;DR: In this paper, a summary review of different types of interdigital transducers is presented and their salient features are presented in terms of their applicability in the Lamb wave based SHM systems.
Abstract: Interdigital transducers (IDTs), thanks to their multiple capabilities have the potential of increasing versatility of SHM systems. Migration of the IDT technology in SHM systems and devices is reviewed in this paper. A summary review of different types of IDTs is presented and their salient features are presented in terms of their applicability in the Lamb wave based SHM systems. Comprehensive review is provided concerning the implementation of the IDT capabilities towards the development of SHM systems. Experimental results obtained with prototype IDTs are provided for illustration. Finally, future development directions of the IDTs dedicated to SHM systems are outlined.
TL;DR: The correlation coefficient of benchmark and signal with damage at double frequency in the time domain was calculated and an imaging method was introduced to locate the fatigue crack in steel plates with and without CFRP laminates.
TL;DR: In this article, the authors theoretically investigate acoustic metasurfaces consisting of either a single pillar or a line of identical pillars on a thin plate, and report on the dependence on the geometrical parameters of both the monopolar compressional and dipolar bending modes.
Abstract: We theoretically investigate acoustic metasurfaces consisting of either a single pillar or a line of identical pillars on a thin plate, and we report on the dependence on the geometrical parameters of both the monopolar compressional and dipolar bending modes We show that for specific dimensions of the resonators, bending and compressional modes may be simultaneously excited We study their interaction with an antisymmetric Lamb wave, whether or not they occur at the same frequency, with particular consideration for the amplitude and phase of waves emitted by the pillars at resonance Especially, the analysis of both the amplitude and the phase of the wave at the common resonant frequency downstream from a line of pillars demonstrates that the reemitted waves allow for the transmission with phase shift of \ensuremath{\pi}
TL;DR: In this paper, a stiffness/velocity degradation model is proposed based on three distinctive damage mechanisms: fiber breaks, matrix cracks and delamination, all of which are always involved in fatigue damage process.
TL;DR: In this article, the relative acoustic nonlinearity parameter (RANP) of Lamb wave signals is linked to barely visible impact damage (BVID) in composites, and a probabilistic model is established to evaluate the statistical distribution of the RANP.
TL;DR: In this article, the propagation of Lamb waves in a one-dimensional tunable phononic metastrip composed of a periodic sequence of hollow pillars that can be selectively filled with water was studied.
Abstract: We study the propagation of Lamb waves in a one-dimensional tunable phononic metastrip composed of a periodic sequence of hollow pillars that can be selectively filled with water. Band structures and transmission properties are computed numerically for metastrips with different fluid fillings by using the finite element method. Good agreement is observed with experimental results obtained with an aluminum metastrip. In particular, it is found that the frequency range of bandgaps and passbands can be controlled through fluid filling. Our results imply that Lamb waves in the solid metastrip can be harnessed through changing the properties of the pillars via fluid-solid interaction. The work in this paper is relevant to practical design of tunable acoustic devices.
TL;DR: The method consists of construction of a baseline quantification model using finite element simulation data and Bayesian updating with limited Lamb wave data from target structure to update the baseline model with a few measurements acquired from the actual target structure.
Abstract: This paper presents a systematic and general method for Lamb wave-based crack size quantification using finite element simulations and Bayesian updating. The method consists of construction of a baseline quantification model using finite element simulation data and Bayesian updating with limited Lamb wave data from target structure. The baseline model correlates two proposed damage sensitive features, namely the normalized amplitude and phase change, with the crack length through a response surface model. The two damage sensitive features are extracted from the first received S₀ mode wave package. The model parameters of the baseline model are estimated using finite element simulation data. To account for uncertainties from numerical modeling, geometry, material and manufacturing between the baseline model and the target model, Bayesian method is employed to update the baseline model with a few measurements acquired from the actual target structure. A rigorous validation is made using in-situ fatigue testing and Lamb wave data from coupon specimens and realistic lap-joint components. The effectiveness and accuracy of the proposed method is demonstrated under different loading and damage conditions.
TL;DR: In this paper, a structural health monitoring (SHM) guided wave system for advance carbon fiber reinforced plastic (CFRP) composite materials is presented, where a circular defect of 10mm in diameter was drilled in the plate, which is similar to the delamination size introduced by a low velocity impact event in a composite plate.
Abstract: This investigation aimed to adapt the total focusing method (TFM) algorithm (originated from the synthetic aperture focusing technique in digital signal processing) to accommodate a circular array of piezoelectric sensors (PZT) and characterise defects using guided wave signals for the development of a structural health monitoring system. This research presents the initial results of a broader study focusing on the development of a structural health monitoring (SHM) guided wave system for advance carbon fibre reinforced plastic (CFRP) composite materials. The current material investigated was an isotropic (aluminium) square plate with 16 transducers operating successively as emitter or sensor in pitch and catch configuration enabling the collection of 240 signals per assessment. The Lamb wave signals collected were tuned on the symmetric fundamental mode with a wavelength of 17 mm, by setting the excitation frequency to 300 kHz. The initial condition for the imaging system, such as wave speed and transducer position, were determined with post processing of the baseline signals through a method involving the identification of the waves reflected from the free edge of the plate. The imaging algorithm was adapted to accommodate multiple transmitting transducers in random positions. A circular defect of 10 mm in diameter was drilled in the plate, which is similar to the delamination size introduced by a low velocity impact event in a composite plate. Images were obtained by applying the TFM to the baseline signals, Test 1 data (corresponding to the signals obtained after introduction of the defect) and to the data derived from the subtraction of the baseline to the Test 1 signals. The result shows that despite the damage diameter being 40 % smaller than the wavelength, the image (of the subtracted baseline data) demonstrated that the system can locate where the waves were reflected from the defect boundary. In other words, the contour of the damaged area was highlighted enabling its size and position to be determined.
TL;DR: In this article, a two-dimensional elastic metamaterial with periodically square concrete-filled steel piles embedded in soil is proposed to achieve a seismic shield for guided Lamb waves and surface waves.
Abstract: Controlling the propagation of seismic waves to protect critical infrastructure via metamaterial is of new topical interest. This approach can be implemented by remote shielding of incoming waves rather than with vibration isolating structures. In this paper, a two-dimensional elastic metamaterial with periodically square concrete-filled steel piles embedded in soil is proposed to achieve a seismic shield for guided Lamb waves and surface waves. Its properties are numerically investigated using the finite element method. For Lamb waves, we first identify complete bandgaps appearing in a periodic composite with cylindrical piles. By comparison, it is found that if the shape of the pile is replaced with the square shape, the bandgaps become wider and shift to the lower frequencies, which is more suitable for practical applications. Furthermore, it is demonstrated that a complete low frequency bandgap also exists for surface waves. The vibration modes for both types of waves at the bandgap edges are computed and analyzed to clarify the mechanism of the bandgap generation. The study focuses on realistic structures that can be effective in the frequency ranges for seismic waves. Although we have focused on the geophysical setting, elastic waves are also very important in applications involving acoustic wave devices.
TL;DR: In this article, the authors analyzed the interaction of fundamental symmetric (S0) and anti-symmetric (A0) mode Lamb waves with the start and the end of a delamination using finite element simulations.
TL;DR: In this article, a finite element model assisted method was used to evaluate the detection capability of two short range circumferential guided wave setups which use both the reflected and transmitted signals, and two separate methods were used to determine the probability of detection (POD) for either the reflection or transmission signals.
Abstract: There is an increasing interest in high frequency short range guided waves to screen or monitor for corrosion. This contrasts with long range guided waves (LRGWs) which screen pipes for large patches of corrosion and have been successfully used in corrosion management for the past twenty years. The fundamental setup described in this paper uses circumferential guided waves, which are excited at a single location on a pipe and travel around the pipe wall and are detected at the same location. The study uses a finite element model assisted method to evaluate the detection capability of two short range circumferential guided wave setups which use both the reflected and transmitted signals. The setups themselves consist of either an axial array of transducers, for monitoring, or a single transducer which axially scans a pipe. Both setups have an array or scan pitch between either adjacent transducers or measurements. The detection capability of the fundamental Lamb wave modes (A0 and S0) in both reflection and transmission have been compared, as well as a hybrid shear horizontal wave setup, which uses the SH0 mode in reflection and the SH1 mode in transmission. A sensitivity analysis was conducted using two separate methods to determine the probability of detection (POD) for either the reflection or transmission signals. Both methods determine a POD for a specific defect, noise level, and array or scan pitch. Probability images are produced which map the POD for a range of defect sizes. For the parameters investigated in this study, it was found that in transmission large diameter defects have a higher detectability, whereas deep, narrow diameter defects are more detectable in reflection. A generalised overview of the sensitivity of short range guided waves is presented by combining both the reflection and transmission PODs. The data fused sensitivity of the S0 and SH hybrid modes are given as 0.6% and 0.75% cross sectional area (CSA) respectively, allowing for the comparison with LRGWs. The A0 mode was excluded from the POD analysis because it was much less sensitive than the other two modes.
TL;DR: A novel ultrasonic guided wave tomography system based on self-designed piezoelectric sensors is presented for on-line corrosion monitoring of large plate-like structures and reconstructed thicknesses show good agreement with analytical predictions obtained by Faraday’s law and laser measurements.
Abstract: Corrosion is a major safety and economic concern to various industries. In this paper, a novel ultrasonic guided wave tomography (GWT) system based on self-designed piezoelectric sensors is presented for on-line corrosion monitoring of large plate-like structures. Accurate thickness reconstruction of corrosion damages is achieved by using the dispersive regimes of selected guided waves and a reconstruction algorithm based on full waveform inversion (FWI). The system makes use of an array of miniaturised piezoelectric transducers that are capable of exciting and receiving highly dispersive A0 Lamb wave mode at low frequencies. The scattering from transducer array has been found to have a small effect on the thickness reconstruction. The efficiency and the accuracy of the new system have been demonstrated through continuous forced corrosion experiments. The FWI reconstructed thicknesses show good agreement with analytical predictions obtained by Faraday's law and laser measurements, and more importantly, the thickness images closely resemble the actual corrosion sites.
TL;DR: A combination of plate-guided ultrasound and air-coupled ultrasonics is used to locate and visualize delaminations in composite laminates using wave visualization method as mentioned in this paper.
Abstract: This article reports on the characterization of delamination damages in composite laminates using wave visualization method. A combination of plate-guided ultrasound and air-coupled ultrasonics is used to locate and visualize delaminations. The study focuses on the physics of Lamb wave propagation and interaction with delaminations at various through-thickness locations and positions. Three-dimensional finite element simulations are used to study, in detail, the changes in wave features such as mode velocity, wavelength and wave refraction in the delamination region. These wave features provide information on the location, position and orientation of the delamination. These studies are validated by experimental measurements. The influence of position of source and delamination on wave refraction in the delamination region is examined. This method also correlates the results obtained from experiments and finite element simulations to theoretical dispersion curves in order to distinctly determine the delami...
TL;DR: A Lamb wave damage quantification method using a least square support vector machine (LS-SVM) and a genetic algorithm (GA) to evaluate the crack size using three damage sensitive features.
Abstract: Lamb waves have been reported to be an efficient tool for non-destructive evaluations (NDE) for various application scenarios. However, accurate and reliable damage quantification using the Lamb wave method is still a practical challenge, due to the complex underlying mechanism of Lamb wave propagation and damage detection. This paper presents a Lamb wave damage quantification method using a least square support vector machine (LS-SVM) and a genetic algorithm (GA). Three damage sensitive features, namely, normalized amplitude, phase change, and correlation coefficient, were proposed to describe changes of Lamb wave characteristics caused by damage. In view of commonly used data-driven methods, the GA-based LS-SVM model using the proposed three damage sensitive features was implemented to evaluate the crack size. The GA method was adopted to optimize the model parameters. The results of GA-based LS-SVM were validated using coupon test data and lap joint component test data with naturally developed fatigue cracks. Cases of different loading and manufacturer were also included to further verify the robustness of the proposed method for crack quantification.
TL;DR: The possibility of application of Lamb wave-based structure health monitoring in bolted joint-like composite structures was achieved and results indicated that S0/A0 wave amplitudes decrease with the increasing of load.
Abstract: Online and offline monitoring of composite bolted joints under tensile load were investigated using piezoelectric transducers. The relationships between Lamb wave signals, pre-tightening force, the applied tensile load, as well as the failure modes were investigated. Results indicated that S0/A0 wave amplitudes decrease with the increasing of load. Relationships between damage features and S0/A0 mode were built based on the finite element (FE) simulation and experimental results. The possibility of application of Lamb wave-based structure health monitoring in bolted joint-like composite structures was thus achieved.