Reflection study of SH0 mode with plate edge at different incident angles
08 May 2019-Vol. 2102, Iss: 1, pp 050022
TL;DR: In this article, the reflection behavior of SH0 guided wave mode from a flat plate edge is investigated using Periodic Permanent Magnet - Electromagnetic Acoustic Transducers (PPM-EMAT) of constant wavelength (λ).
Abstract: This study investigates the reflection behaviour of SH0 guided wave mode from a flat plate edge. SH0 is generated using Periodic Permanent Magnet - Electromagnetic Acoustic Transducers (PPM-EMAT) of constant wavelength (λ). Reflection characteristics of this mode are studied by varying the angle of incidence from 0° to 70°. The probes are positioned in such a way that incident and reflected angles are equal. The response of SH0 mode at the various angle of incidents is explored in terms of amplitude variation. 3D finite element model is developed to investigate reflection characteristics of SH0 mode further. The exact configuration of the PPM-EMAT has been simulated using a two-stage modelling approach. The spatially varying Lorentz force was calculated in the electrodynamic module and then applied to the elastodynamic module, and the resulting elastic disturbances are compared with experimental results.
Citations
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TL;DR: In this article, a comparison analysis of double-row Halbach EMATs with doublerow PPM EMAT was performed using Finite Element based simulation models for SH0 ultrasonic wave generation.
Abstract: Halbach EMATs can efficiently generate shear horizontal (SH) guided wave modes. Using the Halbach magnet structure, the EMATs can enhance the magnetic flux density within a material forming ultrasonic waves with relatively large amplitude. The paper first presents a comparison analysis of double-row Halbach EMATs with double-row PPM EMATs using Finite Element based simulation models for SH0 ultrasonic wave generation. The study then analyses the wave interference effects created by the staggered double-row Halbach EMAT configurations. This is also performed using numerical Finite Element Models (FEM) and experimentally validated in an Aluminum plate specimen. It is observed that the steering of the ultrasonic guided waves can be associated and predicted for different double-row staggered PPM EMAT configurations.
5 citations
TL;DR: In this paper, the authors explored the Halbach magnet array pattern as an alternate to the conventional periodic permanent magnet (PPM) structure, and compared the amplitude generated from multiple single-row Halbach EMATs with singlerow PPM EMAT configurations using finite-element-based simulation models for SH0 ultrasonic wave generation.
Abstract: Electromagnetic acoustic transducers (EMATs) can efficiently generate the shear horizontal (SH) guided wave modes. In this article, the Halbach magnet array pattern is explored as an alternate to the conventional periodic permanent magnet (PPM) structure. The magnetic field strength of a Halbach array is significantly higher on one side of the structure while it is weak on the opposite side of the array. This magnetic field distribution enables Halbach EMATs to generate ultrasonic waves with relatively large amplitude. To observe this phenomenon, this study compares the amplitude generated from multiple single-row Halbach EMATs with single-row PPM EMAT configurations using finite-element-based simulation models for SH0 ultrasonic wave generation. This article then presents the ultrasonic wave fields generated by various double-row Halbach EMAT configurations using finite-element-based simulation models and experimentally validated for guided fundamental SH0 mode generated in an aluminum plate specimen. It is observed that distinct ultrasonic guided wave beam patterns be associated and predicted for different double-row Halbach EMAT configurations.
3 citations
10 Oct 2022
TL;DR: In this article , the authors discussed the observation of a simultaneously propagating dual-mode second-harmonic (DMSH) fundamental symmetric (s 0.
Abstract: It is vital to detect material degradation in structures early to ensure their structural safety. Nonlinear ultrasonic techniques in the guided medium are employed to interpret the material nonlinearity by quantifying the harmonic responses from the ultrasonic guided wave. In this work, we discuss the observation of a simultaneously propagating dual-mode second-harmonic (DMSH) fundamental symmetric (s 0 ) mode and an orthogonal-shear horizontal $(\mathbf{sh}_{0}^{\perp})$ mode generated on a weekly nonlinear isotropic elastic plate while excited with a primary shear horizontal (SH 0 ) mode. The presence of two dominant second harmonic modes is the reason for terming the phenomenon DMSH. Numerical simulations demonstrate the existence of dual harmonics on a thin aluminium plate. As the DMSH possesses different group velocities, each wave packet was identified in time domain analysis as separate signals. The observation is validated experimentally, and dual-mode harmonics were determined by a short-time Fourier transform (STFT) analysis of the time domain signal. A locally enhanced material nonlinearity study was conducted via numerical simulations, and the responses from DMSH were studied. It was found that the second-harmonic $\mathbf{sh}_{0}^{\perp}$ mode was sensitive to locally enhanced material nonlinearity, while the second harmonic s 0 and primary SH 0 were seemingly unaffected. Improved insights from this work may provide important implications for accurate early-state defect detection in structural health monitoring and non-destructive evaluation applications of critical structures.
1 citations
01 Jan 2021
TL;DR: The pulse compression-based coded excitation technique for low-power operation and enhanced SNR results for guided ultrasonic wave NDE is presented.
Abstract: Ultrasonic non-Destructive evaluation (NDE) techniques are widely used to ensure the integrity and strength of structures. Guided ultrasonic waves are typically used for inspecting inaccessible and hidden locations of complex structures. For rapid inspection, non-contact transduction methods such as air-coupled ultrasonic transducers and electromagnetic acoustic transducers (EMAT) are preferred. However, the major downside of these techniques is the high-power requirement. To overcome this challenge, a pulse compression-based signal processing technique called coded excitation is proposed. By using temporally long low-power transmission signals, results comparable in signal-to-noise ratio (SNR) to high-power transmissions are achieved. The pulse compression-based coded excitation technique for low-power operation and enhanced SNR results for guided ultrasonic wave NDE is presented.
1 citations
DOI•
TL;DR: In this article , the authors discussed the observation of a simultaneously propagating dual-mode second-harmonic (DMSH) fundamental symmetric (s0) mode and an orthogonal-shear horizontal (SH 0) mode generated on a weekly nonlinear isotropic elastic plate while excited with a primary shear horizontal mode.
Abstract: It is vital to detect material degradation in structures early to ensure their structural safety. Nonlinear ultrasonic techniques in the guided medium are employed to interpret the material nonlinearity by quantifying the harmonic responses from the ultrasonic guided wave. In this work, we discuss the observation of a simultaneously propagating dual-mode second-harmonic (DMSH) fundamental symmetric (s0) mode and an orthogonal-shear horizontal $(\mathbf{sh}_{0}^{\perp})$ mode generated on a weekly nonlinear isotropic elastic plate while excited with a primary shear horizontal (SH0) mode. The presence of two dominant second harmonic modes is the reason for terming the phenomenon DMSH. Numerical simulations demonstrate the existence of dual harmonics on a thin aluminium plate. As the DMSH possesses different group velocities, each wave packet was identified in time domain analysis as separate signals. The observation is validated experimentally, and dual-mode harmonics were determined by a short-time Fourier transform (STFT) analysis of the time domain signal. A locally enhanced material nonlinearity study was conducted via numerical simulations, and the responses from DMSH were studied. It was found that the second-harmonic $\mathbf{sh}_{0}^{\perp}$ mode was sensitive to locally enhanced material nonlinearity, while the second harmonic s0 and primary SH0 were seemingly unaffected. Improved insights from this work may provide important implications for accurate early-state defect detection in structural health monitoring and non-destructive evaluation applications of critical structures.
References
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TL;DR: The results indicate that Lamb waves may be used to find notches when the wavelength to notch depth ratio is on the order of 40, and the 2-D Fourier transform method is used to quantify Lamb wave interactions with defects.
Abstract: The interaction of individual Lamb waves with a variety of defects simulated by notches is investigated using finite-element analysis, and the results are checked experimentally. Excellent agreement is obtained. It is shown that a 2-D Fourier transform method may be used to quantify Lamb wave interactions with defects. The sensitivity of individual Lamb waves to particular notches is dependent on the frequency-thickness product, the mode type and order, and the geometry of the notch. The sensitivity of the Lamb modes a/sub 1/, alpha /sub 0/, and s/sub 0/ to simulated defects in different frequency-thickness regions is predicted as a function of the defect depth to plate thickness ratio and the results indicate that Lamb waves may be used to find notches when the wavelength to notch depth ratio is on the order of 40. Transmission ratios of Lamb waves across defects are highly frequency dependent. >
912 citations
01 Jan 1997
TL;DR: In this article, a general-purpose program that can create dispersion curves for a very wide range of systems and then effectively communicate the information contained within those curves is presented, using the global matrix method to handle multi-layered Cartesian and cylindrical systems.
Abstract: The application of guided waves in NDT can be hampered by the lack of readily available dispersion curves for complex structures. To overcome this hindrance, we have developed a general purpose program that can create dispersion curves for a very wide range of systems and then effectively communicate the information contained within those curves. The program uses the global matrix method to handle multi-layered Cartesian and cylindrical systems. The solution routines cover both leaky and non-leaky cases and remain robust for systems which are known to be difficult, such as large frequency-thicknesses and thin layers embedded in much thicker layers. Elastic and visco-elastic isotropic materials are fully supported; anisotropic materials are also covered, but are currently limited to the elastic, non-leaky, Cartesian case.
485 citations
TL;DR: Experimental aspects of guided wave analysis include phase velocity, group velocity, and attenuation dispersion curves; boundary element model analysis for reflection and transmission factor analysis; use of wave structure for defect detection sensitivity; source influence on the phase velocity spectrum, and the use of angle beam and comb transducer technology.
Abstract: Recent developments in guided wave generation, reception, and mode control show that increased penetration power and sensitivity are possible. A tone burst function generator and appropriate signal processing are generally used. Variable angle beam and comb-type transducers are the key to this effort. Problems in tubing, piping, hidden corrosion detection in aging aircraft, adhesive and diffusion bonding, and ice detection are discussed. Additionally, sample configurations, inspection objectives, and logic are being developed for such sample problems as defect detection and analysis in lap splice joints, tear straps, cracks in a second layer, hidden corrosion in multiple layers, cracks from rivet holes, transverse cracking in a beam, and cracks in landing gear assembly. Theoretical and experimental aspects of guided wave analysis include phase velocity, group velocity, and attenuation dispersion curves; boundary element model analysis for reflection and transmission factor analysis; use of wave structure for defect detection sensitivity; source influence on the phase velocity spectrum, and the use of angle beam and comb transducer technology. Probe design and modeling considerations are being explored. Utilization of in-plane and out-of-plane displacement patterns on the surface and longitudinal power distribution across the structural cross-section are considered for improved sensitivity, penetration power, and resolution in nondestructive evaluation. Methods of controlling the phase velocity spectrum for mode and frequency selection are available. Such features as group velocity change, mode cut-off measurements, mode conversion, amplitude ratios of transmission, and reflection factors of specific mode and frequency as input will be introduced for their ability to be used in flaw and material characterization analysis.
155 citations
TL;DR: In this article, the authors present a model and subsequent solution to a boundary value problem that can evaluate the source influence as a function of the comb transducer design parameters, along with an insight into future directions.
149 citations
TL;DR: It is demonstrated that it is possible to use this method to obtain the reflection from a notch of any depth and at any frequency, and the limits of this method in approximating cracklike defects have been studied.
Abstract: The scattering of the SH0 mode from discontinuities in the geometry of a plate has been studied. Both finite element and modal decomposition methods have been used to study the reflection and transmission characteristics from a thickness step in a plate, obtaining very good agreement. The significance of nonpropagating modes in the scattering from steps in plates has been specifically investigated. A method to approximate the reflection from rectangular notches by superimposing the reflection from a step down (start of the notch) and a step up (end of the notch) has been proposed. It is demonstrated that it is possible to use this method to obtain the reflection from a notch of any depth and at any frequency. The effect of frequency on the reflection from notches has been examined. The limits of this method in approximating cracklike defects have also been studied.
89 citations