Attenuation of ultrasonic Rayleigh–Lamb waves by small horizontal defects in thin aluminium plates (original) (raw)
Related papers
Defect detection in thin plates by ultrasonic lamb wave techniques
International Journal of Materials and Product Technology, 2006
In the present study, the numerical method was investigated for drawing the dispersion and displacement curves of ultrasonic lamb wave, propagated in Aluminum thin plate. Two ultrasonic lamb wave techniques, pulse-echo (a1 mode emitter) and emission (s1 mode emitter), were used for interpretation of notch defects with depths of 10%, 30% and 60% of plate thickness. Thickness of plate was 2 mm and the nominal center frequency of transducers was 2 MHz. It was observed that these techniques are sensitive to evaluate defects, especially in short probe to defect distances. Also, it was found that amplitude analysis can give some qualitative information about defects depth by using Distance-Amplitude-Correction curves, but it was not sometime repeatable. In this respect, pulse echo method showed better sensitivity of amplitude to defects depth variation.
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.
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...
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.
Journal of Nondestructive Evaluation, 2013
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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.
Damage Detection in a Thin Aluminium Plate Using Lamb Wave Based Time Reversibility Technique
Damage detection is required to be carried out in mechanical and civil structures, at an early stage to avoid sudden failure of the structures. Ultrasonic techniques are majorly used for this purpose. Lamb waves, which belong to the category of ultrasonic guided waves, are gaining popularity now a days for damage detection in thin structures, because of their ability to scan large area. In view of this, the present work deals with the damage detection in a thin aluminium plate using Lamb waves. The Time Reversibility method is used along with Lamb waves to show the presence of damage. The significance of this method of damage detection is that, it is a baseline free method, which means it does not need data from the pristine structure. Both experimental and Finite Element Simulation (FE), are carried out.
2018
Recent advances in Lamb wave-based nondestructive testing technology have demonstrated the feasibility of detecting and locating damages in structural components. However, there remains many challenges to realize defect detection quantitatively due to the uncertainty of the relationship between the features of Lamb waves and defect size. Therefore, it is important to discover an intrinsical parameter of Lamb waves that can be used as a damage sensitive feature. Local wall-thinning is a common defect in aluminium plate-like components that are in widespread use in aerospace, and other industries. The aim of this paper is to present a quantitative defect detection method for achieving damage visualization in plate-like structures based on wave propagation phenomenon. Full wavefield data of propagating Lamb waves in plates contains a wealth of information about the wave interaction with damage such as the change of wavenumber components. The wavenumber of excited Lamb wave mode is a fi...