Lamb wave imaging with actuator network for damage quantificationin aluminum plate structures

2020 ◽  
pp. 1045389X2095253
Author(s):  
Zhaoyun Ma ◽  
Lingyu Yu
Keyword(s):  
Lamb Wave ◽  
Lamb Waves ◽  
Laser Doppler Vibrometer ◽  
Inspection System ◽  
Synthetic Image ◽  
Target Area ◽  
Time Space ◽  
Wave Imaging ◽  
Triangular Profile ◽  
Aluminum Plates

Lamb waves have been widely used for damage detection on plate-like structures. However, there are still considerable interests on quantifying damage with complex profile. In this article, quantification of complex damage in plate-like structures using a network of actuators and time-space Lamb wavefield is investigated. The actuator network inspection system is implemented with multiple PZT transducers for Lamb wave actuation in round robin pattern and scanning laser Doppler vibrometer for wavefield sensing. The PZT network is arranged in a way that the target area is fully enclosed and Lamb waves come to the damage from all directions. Waves induced by the damage are subsequently obtained through frequency-wavenumber filtering, using the experimentally acquired dispersion curves presented in the paper. The filtered waves from all wave actuators are then used to generate a synthetic image of the damage being inspected. Two cases of complex damage are evaluated on aluminum plates, mass loss with triangular profile and mass addition with a three-letter cluster profile. Our results show that the damages are not only detected but also their profiles are clearly outlined in the images. We believe the subject methods provide improved evaluation of damage profile for Lamb wavefield based damage quantification.

scholarly journals Lamb Wave Local Wavenumber Approach for Characterizing Flat Bottom Defects in an Isotropic Thin Plate

2018 ◽  
Vol 8 (9) ◽  
pp. 1600 ◽  
Author(s):  
Guopeng Fan ◽  
Haiyan Zhang ◽  
Hui Zhang ◽  
Wenfa Zhu ◽  
Xiaodong Chai
Keyword(s):  
Thin Plate ◽  
Lamb Wave ◽  
Spatial Information ◽  
Laser Doppler Vibrometer ◽  
Target Area ◽  
Flat Bottom ◽  
Wavenumber Domain ◽  
Time Space ◽  
Local Wavenumber ◽  
Rectangular Groove

This paper aims to use the Lamb wave local wavenumber approach to characterize flat bottom defects (including circular flat bottom holes and a rectangular groove) in an isotropic thin plate. An air-coupled transducer (ACT) with a special incidence angle is used to actuate the fundamental anti-symmetric mode (A0). A laser Doppler vibrometer (LDV) is employed to measure the out-of-plane velocity over a target area. These signals are processed by the wavenumber domain filtering technique in order to remove any modes other than the A0 mode. The filtered signals are transformed back into the time-space domain. The space-frequency-wavenumber spectrum is then obtained by using three-dimensional fast Fourier transform (3D FFT) and a short space transform, which can retain the spatial information and reduce the magnitude of side lobes in the wavenumber domain. The average wavenumber is calculated, as a real signal usually contains a certain bandwidth instead of the singular frequency component. Both simulation results and experimental results demonstrate that the average wavenumber can be used not only to identify shape, location, and size of the damage, but also quantify the depth of the damage. In addition, the direction of an inclined rectangular groove is obtained by calculating the image moments under grayscale. This hybrid and non-contact system based on the local wavenumber approach can be provided with a high resolution.

Thin-Plate Imaging Inspection Using Scattered Waves Cross-Correlation Algorithm and Non-Contact Air-Coupled Transducer

2020 ◽  
Vol 4 (2) ◽  
Author(s):  
Wenfeng Xiao ◽  
Lingyu Yu
Keyword(s):  
Lamb Wave ◽  
Cross Correlation ◽  
Lamb Waves ◽  
Imaging Technique ◽  
Laser Doppler Vibrometer ◽  
Correlation Method ◽  
Single Mode ◽  
Wave System ◽  
Wave Imaging ◽  
Incident Waves

Abstract This paper presents a non-contact air-coupled Lamb wave imaging technique using a two-dimensional (2D) cross-correlation method that not only detects the damage but also precisely quantifies for orientations and sizes. The air-coupled transducers (ACT) is used together with a scanning laser Doppler vibrometer (SLDV) for sensing, making a fully non-contact Lamb wave system used for this study. We first show that single-mode Lamb wave actuation can be achieved by the ACT-based on Snell's law. Detailed study and characterization of the directional ACT Lamb waves are conducted. For damage detection, a 2D cross-correlation imaging technique that uses the damage introduced scattered waves of all directions is proposed for correlating with the incident waves. The frequency-wavenumber filtering technique is used to implement the acquisition of the scatted waves and incident waves, respectively. In the end application to notches with various orientations and various sizes in terms of depth and length is given. The results show the proposed technique can precisely imaging the damages and can quantitatively evaluate the damage size in terms of length and depth.

Damage Imaging and Quantification Using Spectral Field

2015 ◽  
Author(s):  
Zhenhua Tian ◽  
Lingyu Yu
Keyword(s):  
Damage Detection ◽  
Dispersion Curve ◽  
Lamb Waves ◽  
Laser Doppler Vibrometer ◽  
Field Representation ◽  
Thickness Change ◽  
Time Space ◽  
Damage Imaging ◽  
Local Wavenumber ◽  
Aluminum Plates

This paper presents damage imaging and quantification by using the spectral field of Lamb waves. The spectral field is acquired through a piezoelectric transducer (PZT)-scanning laser Doppler vibrometer (SLDV) sensing. A wideband chirp signal is used for PZT excitation in order to generate wideband Lamb waves. With the SLDV, the time-space wavefield is acquired, and transformed into the spectral field representation through Fourier transform. The spectral field, which contains wideband Lamb wave responses of the structure, is further analyzed for damage detection and quantification. Using the spatial wavenumber analysis, the local wavenumber at each location are obtained, and represented as a spatial wavenumber image which can be used for damage detection and evaluation. Moreover, the dispersion curve regression method is developed to quantify the thickness change of a defect. For verification, experiments are performed on aluminum plates with blind holes of different depths. The experimental results show that the blind holes can be detected by both the spatial wavenumber imaging and dispersion curve regression. In addition, the dispersion curve regression can further quantify the depths of the blind holes.

Noncontact/Remote Material Characterization Using Ultrasonic Guided Wave Methods

2020 ◽  
Author(s):  
Zhaoyun Ma ◽  
Lingyu Yu
Keyword(s):  
Guided Waves ◽  
Broad Band ◽  
Laser Doppler Vibrometer ◽  
Pulsed Laser ◽  
Guided Wave ◽  
Target Plate ◽  
Ultrasonic Guided Wave ◽  
Time Space ◽  
Aluminum Plates ◽  
Wave Methods

Abstract Noncontact and remote NDE systems and methods are highly desired in a broad range of engineering applications such as material property characterization. This paper aims to develop such a noncontact/remote NDE system based on laser ultrasonic guided waves and establish its fundamental capability for material thickness evaluation. The noncontact system employs pulsed laser (PL) for guided wave actuation and scanning laser Doppler vibrometer (SLDV) for guided wave wavefield sensing. A cylindrical planoconvex lens is adopted to focus the pulsed laser beam to a line source in order to excite broad band signals in the target plate. Aluminum plates with different thicknesses are evaluated through SLDV line scans and 2D time-space wavefields are acquired. Frequency-wavenumber (f-k) spectra are obtained through 2D Fourier transform, and the A0 dispersion curve for each plate is extracted. Through Comparing the extracted A0 curve with the theoretical A0 dispersion curves, the thicknesses of the tested plates are identified. Reflective tape effect on the plates are also studied: the reflective tape attached for SLDV enhancement affects the guided waves in the target plate significantly when the plate is relatively thin.

Structural Health Monitoring of Thin Aluminum Plate Using Acoustic Sensors

2012 ◽  
Vol 622-623 ◽  
pp. 1389-1395
Author(s):  
R. Nishanth ◽  
K. Lingadurai ◽  
V. Malolan ◽  
Gowrishankar Wuriti ◽  
M.R.M. Babu
Keyword(s):  
Lamb Wave ◽  
Damage Identification ◽  
Lamb Waves ◽  
Time Domain Analysis ◽  
Ultrasonic Waves ◽  
Aluminum Plate ◽  
Identification System ◽  
Time Frequency ◽  
Thin Aluminum ◽  
Aluminum Plates

SHM is defined as “an emerging technology that can be defined as continuous, autonomous, real time, in-service monitoring of the physical condition of a structure by means of embedded or attached sensors with minimum manual intervention” .SHM provides the ability of a system to detect adverse changes within a system’s structure to enhance reliability and reduce maintenance costs. There are different Non-Destructive techniques like acoustic emission, ultrasonic, acousto-ultrasonic, guided ultrasonic waves or Lamb waves which are nowadays investigated for the development of an efficient and user-friendly damage identification system. This paper deals with the latter which is based on Lamb wave propagation. It has been developed especially for distinguishing different kinds of damages. The Lamb wave-based active SHM method uses piezoelectric (PZT) sensors to transmit and receive Lamb waves in a thin Aluminum plate. The Lamb wave modes (AO &SO) travel into the structure and are reflected by the structural boundaries, discontinuities, and damage. By studying their propagation and reflection, the presence of defect in the structure is determined. Laboratory level experiments have been carried out on thin Aluminum plates with angular, horizontal and vertical defect. The obtained waveform is filtered to avoid unwanted noise & disturbances using Savitzky-Golay filtering. The filtered waveforms are compared to differentiate the defects. Short Time Fourier Transform has been carried out on the acquired waveform. This study provides significant insight into the problem of identifying localized damages in the structure using PZT and dispersion of signal after they interact with different types of damage. Those small defects like the horizontal one that may be nearly missed in time domain analysis can also be clearly identified in the STFT analysis. Moreover the occurrence of So mode is also clearly seen. Thus, Lamb waves generated by PZT sensors and time-frequency analysis techniques could be used effectively for damage detection in aluminum plate. This study has given a complete idea of the working and the basic requirements of SHM system.

Lamb Wave Propagation Study Using Frequency-Wavenumber Analysis

2012 ◽  
Author(s):  
Zhenhua Tian ◽  
Lingyu Yu
Keyword(s):  
Wave Propagation ◽  
Lamb Wave ◽  
Experimental Testing ◽  
Wave Spectrum ◽  
Laser Doppler Vibrometer ◽  
Wave Mode ◽  
Wavenumber Domain ◽  
Time Space ◽  
Lamb Wave Propagation ◽  
Wave Modes

Lamb waves are dispersive and multi-modal. Various wave modes make the interpretation of Lamb wave signal very difficult. It is desired that different modes can be separated for individual analysis. In the this paper, we present our studies on the multimodal Lamb wave propagation and wave mode extraction using frequency-wavenumber analysis. Wave spectrum in the frequency-wavenumber domain shows clear distinction among Lamb wave modes being present. This allows separating them or extracting a desired Lamb wave mode through a novel filtering strategy. Thus a single mode Lamb can be identified and extracted for certain types of damage detection in structural health monitoring (SHM). These concepts are illustrated through experimental testing. A scanning laser Doppler vibrometer is used to acquiring the time-space wavefield regarding the multimodal Lamb wave propagation. Then the recorded wavefield was analyzed in frequency-wavenumber domain and decomposed into different wave modes.

scholarly journals A Novel Complementary Method for the Point-Scan Nondestructive Tests Based on Lamb Waves

2014 ◽  
Vol 2014 ◽  
pp. 1-7 ◽  
Author(s):  
Rahim Gorgin ◽  
Zhanjun Wu ◽  
Yuebin Zheng
Keyword(s):  
Lamb Wave ◽  
Test Piece ◽  
Damage Identification ◽  
Lamb Waves ◽  
Complementary Method ◽  
Nondestructive Tests ◽  
Damage Probability ◽  
Scan Test ◽  
Aluminum Plates ◽  
Probability Index

This study presents a novel area-scan damage identification method based on Lamb waves which can be used as a complementary method for point-scan nondestructive techniques. The proposed technique is able to identify the most probable locations of damages prior to point-scan test which lead to decreasing the time and cost of inspection. The test-piece surface was partitioned with some smaller areas and the damage probability presence of each area was evaluated.A0mode of Lamb wave was generated and collected using a mobile handmade transducer set at each area. Subsequently, a damage presence probability index (DPPI) based on the energy of captured responses was defined for each area. The area with the highest DPPI value highlights the most probable locations of damages in test-piece. Point-scan nondestructive methods can then be used once these areas are found to identify the damage in detail. The approach was validated by predicting the most probable locations of representative damages including through-thickness hole and crack in aluminum plates. The obtained experimental results demonstrated the high potential of developed method in defining the most probable locations of damages in structures.

scholarly journals Modes Control of Lamb Wave in Plates Using Meander-Line Electromagnetic Acoustic Transducers

2020 ◽  
Vol 10 (10) ◽  
pp. 3491 ◽  
Author(s):  
Yinghong Zhang ◽  
Zhenghua Qian ◽  
Bin Wang
Keyword(s):  
Magnetic Field ◽  
Lamb Wave ◽  
Lamb Waves ◽  
Single Mode ◽  
Plate Surface ◽  
Electromagnetic Acoustic Transducer ◽  
Bias Magnetic Field ◽  
Low Frequencies ◽  
Aluminum Plates ◽  
Meander Line

The multimode and dispersion characteristics of Lamb waves make them difficult to apply to nondestructive evaluation. This paper presents a paired configuration of a meander-line coil electromagnetic acoustic transducer (EMAT) to generate a single-mode symmetric and antisymmetric Lamb wave in aluminum plates. In the paired structure, the bias magnetic field of the EMAT that generates symmetric mode Lamb waves is perpendicular to the plate surface, while the bias magnetic field of the EMAT that generates antisymmetric Lamb waves is parallel to the plate surface. The symmetric and antisymmetric exciting forces generated by these two EMATs are consistent with the dispersion equations of single symmetric and antisymmetric Lamb wave modes, respectively. The numerical simulations and experiments verified that the presented paired configurations of meander-line coil EMATs can effectively control the generation of single-mode Lamb waves at low frequencies.

scholarly journals Weighted Structured Sparse Reconstruction-Based Lamb Wave Imaging Exploiting Multipath Edge Reflections in an Isotropic Plate

Sensors ◽  
2020 ◽  
Vol 20 (12) ◽  
pp. 3502
Author(s):  
Caibin Xu ◽  
Zhibo Yang ◽  
Mingxi Deng
Keyword(s):  
Lamb Wave ◽  
Isotropic Plate ◽  
Lamb Waves ◽  
Correlation Coefficients ◽  
Sparse Reconstruction ◽  
Imaging Method ◽  
Structured Sparsity ◽  
Large Area ◽  
Prediction Technique ◽  
Wave Imaging

Lamb wave-based structural health monitoring techniques have the ability to scan a large area with relatively few sensors. Lamb wave imaging is a signal processing strategy that generates an image for locating scatterers according to the received Lamb waves. This paper presents a Lamb wave imaging method, which is formulated as a weighted structured sparse reconstruction problem. A dictionary is constructed by an analytical Lamb wave scattering model and an edge reflection prediction technique, which is used to decompose the experimental scattering signals under the constraint of weighted structured sparsity. The weights are generated from the correlation coefficients between the scattering signals and the predicted ones. Simulation and experimental results from an aluminum plate verify the effectiveness of the present method, which can generate images with sparse pixel values even with very limited number of sensors.

Effect of Lamb Wave Excitation Frequency on Detection of Delamination in Composite Plates

2011 ◽  
Author(s):  
Inho Kim ◽  
Ratneshwar Jha
Keyword(s):  
Lamb Wave ◽  
Lamb Waves ◽  
Excitation Frequency ◽  
Damage Index ◽  
Laser Doppler Vibrometer ◽  
Composite Plates ◽  
Experimental Investigations ◽  
Wave Excitation ◽  
Error Norm ◽  
Hilbert Huang Transform

This paper presents experimental investigations of the effect of Lamb wave excitation frequency on detection of a given delamination in composite plates. Typical aerospace type composite plates are used and integrated piezoelectric transducers function as both actuator and sensor. Also, a scanning Laser Doppler Vibrometer (LDV) is used for preliminary sensing of structural responses when excited by a single PZT actuator. Results in time domain are quantified by a damage index calculation based on modified L2 error norm. Phase difference calculations based on complex continuous wavelet transform (CWT) and Hilbert-Huang transform (HHT) are presented. Experimental results show a significant effect of incident Lamb waves on delamination signature.

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