Defect detection in thin plates by ultrasonic lamb wave techniques (original) (raw)
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Cross-correlation based Imaging of Defects in Plate using Ultrasonic Lamb Waves
2019
Notch like defects may occur in thin metallic structures and components. These defects are often not detected due to their smaller size and if unattended may lead to leakages, causing industrial accidents and economic losses. Therefore, early detection of these defects is essential. The current work presents preliminary studies on an ultrasonic Lamb wave based imaging technique for detection of these defects. Experimental investigations are presented on a thin plate to demonstrate the developed technique. An A0 mode dominated Lamb wave field is generated using wedge technique which suppresses the higher Lamb wave modes. Notches of different sizes are created in the plate and are imaged in the plane of plate using the Planar Synthetic Aperture Focusing Technique (P-SAFT). The resulting images are improved by performing cross correlation between the received ultrasonic field and the incident A0 mode Lamb wave field. The SAFT images constructed from the crosscorrelated waveforms show i...
Detection and Classification of Defects in Thin Structures Using Lamb Waves
The possibility of using Lamb waves in contact mode to detect and classify defects in thin structures is analyse in this work. By the fact that is usually desirable to transmit a single mode, excitation method and limitations are discussed, as well as the necessity of signal processing to correct identify the propagation modes. For this propose two different techniques are used: amplitude and phase spectrum methods. Experimental results obtained on aluminium samples agree very well with theory. The detection of notches of different depths, widths and orientations using pulse-echo and transmission techniques are investigate. Phase velocity and spectrum behaviour are correlated with defect dimensions/orientations with satisfactory results.
Attenuation of ultrasonic Rayleigh–Lamb waves by small horizontal defects in thin aluminium plates
International Journal of Mechanical Sciences, 1999
The present paper illustrates how horizontal symmetric crack-like defects can be detected rapidly in thin isotropic plates by using longitudinal ultrasonic waves. The use of such longitudinal waves offers the potential of being significantly faster for non-destructively detecting defects than conventional ultrasonic techniques, which rely on transverse waves propagating through the thickness of a plate. Computational and analytical methods are used to predict reflection coefficients due to the attenuation of a longitudinal ultrasonic wave by physically small defects. It is shown that detectable attenuation ('10%), i.e. reflection coefficients, of the lowest order symmetric Rayleigh-Lamb wave (S ) occurs for a range of small defects (sub-millimeter in length) when using high-frequency waves (MHz range).
Health Monitoring and Smart Nondestructive Evaluation of Structural and Biological Systems III, 2004
This paper portrays work for the development of a Lamb wave scanning method for the detection of defects in thin plates. The approach requires the generation of an ultrasonic A o and S o-Mode Lamb Wave using an incident transmitter excited with a tone burst centered at a near non-dispersive frequency. With a fixed relative separation both transmitter and receiving transducer, remotely scan a specific line section of the plate. The arrival time information coming from incident and reflected waves contain information associated with the location of reflection surfaces or potential flaws. The Hilbert-Huang transform is applied to the intrinsic mode functions which permit the computation of the signal energy as a function of time, proportional to the square of the amplitude of the analytical signal. The arrival times and amplitudes of the notch-reflected energy are used to calculate by means of two geometric methods, the coordinates of the source of the reflections. The resulting coordinates outline the extent and relative direction of notches in two different scenarios. One is having notches in a 0 to 22.5 degree orientation in respect to the far edge of the plate and two with notches of various sizes at a single rivet hole. Results of experiments conducted on 1.6mm-thick Aluminum square plates, with an arrangement of notches as described compare favorably with the actual notches.
Angular Crack Monitoring of Aluminum Plate by Lamb Wave Analysis
Many structural health monitoring (SHM) methods are developed for detection of the surface cracks. The guided Lamb wave approach is one of the most effective SHM methods for identification of the defects at the surfaces of the aluminum and composite plates. In this study, feasibility of the Lamb wave approach was investigated for detection of the angular cuts created at the surface of an aluminum plate. Surface waves were generated by using a piezoelectric element (PZT) and their propagation was monitored by using two sensors made of the same material.
Detecting Cracks in Thin Plates by Using Lamb Wave Scanning: Geometric Approach
A crack in a thin plate reflects ultrasonic waves; therefore, it is reasonable to determine the location of the crack by measuring the reflected waves. The problem of locating the crack can be reformulated in purely geometric terms. Previously, time-consuming iterative numerical methods were used to solve the resulting geometric problem. In this paper, we show that explicit (and fast to compute) formulas can be used instead.
Detection of cracks at rivet holes in thin plates using Lamb-wave scanning
Smart Nondestructive Evaluation and Health Monitoring of Structural and Biological Systems II, 2003
This paper describes a Lamb-wave scanning method for the detection of notches simulating cracks at rivet holes in thin plates. The approach requires the generation of an ultrasonic S o -Mode Lamb wave using an incident transmitter excited with a tone burst centered at a near non-dispersive frequency. Area scans are performed on a plate with a hole with a notch to generate times series information which is used to create animations illustrating the wave propagation characteristics. The time series are subject to a sifting process to obtain intrinsic mode functions which contain narrow frequency banded information of the signals. The Hilbert-Huang transform is applied to the intrinsic mode functions which permit the computation of the signal energy as a function of time, proportional to the square of the amplitude of the analytical signal. Animations of the propagation of the Lamb-wave energy illustrate that a potential scanning approach is to acquire time series along a line between the transmitter and the hole, capturing wave scattering from the hole and reflections from the notches. The times of flight and amplitudes of the notch-reflected energy are used to calculate coordinates of the source of the reflections by a geometric approach. The identified coordinates of the reflections outline the extent of the notch at the rivet hole. Results of experiments conducted on thin square plates with a single hole with notches of various sizes compare favorably with the actual notches.
Experimental Study of Lamb Waves Using Acousto-Ultrasonic Technique
Journal of emerging technologies and innovative research, 2020
Non Destructive testing is a wide group of analysis techniques used in science and industry to evaluate the properties of a material components or system without causing damage. NDT methods include visual inspection, dye penetrant method, radiographic method, magnetic particle method, eddy current testing method, ultrasonic testing method. Acousto-Ultrasonics is also one of the NDT methods which can overcome most of the disadvantages of other methods. The term-acousto-ultrasonics denotes a combination of some aspects of acoustic emission methodology with ultrasonic characterization. In acousto-ultrasonic technique, a broadband ultrasonic wave is injected onto the surface at one location of the test plate with the help of a piezoelectric sensor coupled to the same surface at another location. Thus, understanding the propagation characteristics of the ultrasonic wave is essential for successful application of the technique. The dominant acousto-ultrasonics waves produced experimentally in thin plates were multi-mode Lamb waves. The broadband generation and detection of Lamb waves has been performed in aluminium plate using the acousto-ultrasonic method. Using the same procedure, experiments are conducted on non-defective and defective plates with transducers of different frequencies. By comparing the results obtained in both the cases, defects can be detected. Similar plots can be obtained with the transducers of different frequencies.
As a part of structural health monitoring, ultrasonic technique using Lamb wave has emerged as a promising method for damage detection in thin structures which typically prevail in aerospace applications. In the present work, Lamb wave based pitch catch strategy is implemented for damage detection in an aluminium plate. Piezoelectric transducers are used for generating and sensing Lamb wave. The response data picked up at the sensor is processed using Root Mean Square Deviation (RMSD) and Hilbert Haung Transform (HHT) to identify the presence of damage and its severity. The damage considered is a V-notch. The RMSD values calculated for increasing notch depths, with respect to the undamaged specimen response, show increasing trend. HHT plots between phase and time show clear change in the trend with change in the notch depth. The results obtained through experiments are compared with those obtained through Finite Element simulation and are reported in the paper.