Air-Coupled Excitation of a Slow A0 Mode Wave in Thin Plastic Films by an Ultrasonic PMN-32%PT Array

Ultrasonic non-destructive testing techniques (NDT) based on the application of guided waves are already used for inspection of plate-type structures made of various materials, including composite materials. Air-coupled ultrasonic techniques are used to test such structures by means of guided waves. The objective of this research was development and investigation of air-coupled excitation of a slow A0 Lamb wave mode in thin plastic films by a PMN-32%PT ultrasonic array. It is known that when the velocity of the A0 mode in the film is less than the ultrasound velocity in air no leaky wave is observed in a surrounding air. It opens new possibilities for NDT of composite structures. The influence of the airborne wave may be eliminated by 3D filtering in a wavenumbers-frequency domain. A special filter and corresponding signals processing technique were developed in order to obtain directivity patterns and velocity maps of the waves propagating in all directions. The measured ultrasound velocity values prove that, with the proposed method, it is possible to excite a slow A0 Lamb wave mode and to separate it from other parasitic waves propagating in air. Measurements of the parameters of the slow A0 mode, such as the propagation velocity in the plastic film, may be applied for the material characterization.

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Defect Estimation in Non-Destructive Testing of Composites by Ultrasonic Guided Waves and Image Processing

Electronics ◽

10.3390/electronics8030315 ◽

2019 ◽

Vol 8 (3) ◽

pp. 315 ◽

Cited By ~ 4

Author(s):

Kumar Anubhav Tiwari ◽

Renaldas Raisutis ◽

Olgirdas Tumsys ◽

Armantas Ostreika ◽

Kestutis Jankauskas ◽

...

Keyword(s):

Image Processing ◽

Composite Structures ◽

Guided Waves ◽

Low Frequency ◽

Processing Technique ◽

Image Processing Technique ◽

Discrete Wavelet ◽

Non Destructive Testing ◽

Destructive Testing ◽

Non Destructive

The estimation of the size and location of defects in multi-layered composite structures by ultrasonic non-destructive testing using guided waves has attracted the attention of researchers for the last few decades. Although extensive signal processing techniques are available, there are only a few studies available based on image processing of the ultrasonic B-scan image to extract the size and location of defects via the process of ultrasonic non-destructive testing. This work presents an image processing technique for ultrasonic B-scan images to improve the estimation of the location and size of disbond-type defects in glass fiber-reinforced plastic materials with 25-mm and 51-mm diameters. The sample is a segment of a wind turbine blade with a variable thickness ranging from 3 to 24 mm. The experiment is performed by using a low-frequency ultrasonic system and a pair of contact-type piezoceramic transducers kept apart by a 50-mm distance and embedded on a moving mechanical panel. The B-scan image acquired by the ultrasonic pitch-catch technique is denoised by utilizing features of two-dimensional discrete wavelet transform. Thereafter, the normalized pixel densities are compared along the scanned distance on the region of interest of the image, and a −3 dB threshold is applied to the locations and sizes the defects in the spatial domain.

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Numerical Investigation of Excitation of Various Lamb Waves Modes in Thin Plastic Films

Applied Sciences ◽

10.3390/app12020849 ◽

2022 ◽

Vol 12 (2) ◽

pp. 849

Author(s):

Rymantas Jonas Kazys ◽

Justina Sestoke ◽

Egidijus Zukauskas

Keyword(s):

Numerical Investigation ◽

Lamb Wave ◽

Guided Waves ◽

Phased Array ◽

Ultrasonic Transducer ◽

Guided Wave ◽

Ultrasonic Guided Waves ◽

Plastic Films ◽

Thin Plastic ◽

Wave Modes

Ultrasonic-guided waves are widely used for the non-destructive testing and material characterization of plates and thin films. In the case of thin plastic polyvinyl chloride (PVC), films up to 3.2 MHz with only two Lamb wave modes, antisymmetrical A0 and symmetrical S0, may propagate. At frequencies lower that 240 kHz, the velocity of the A0 mode becomes slower than the ultrasonic velocity in air which makes excitation and reception of such mode complicated. For excitation of both modes, we propose instead a single air-coupled ultrasonic transducer to use linear air-coupled arrays, which can be electronically readjusted to optimally excite and receive the A0 and S0 guided wave modes. The objective of this article was the numerical investigation of feasibility to excite different types of ultrasonic-guided waves, such as S0 and A0 modes in thin plastic films with the same electronically readjusted linear phased array. Three-dimensional and two-dimensional simulations of A0 and S0 Lamb wave modes using a single ultrasonic transducer and a linear phased array were performed. The obtained results clearly demonstrate feasibility to excite efficiently different guided wave modes in thin plastic films with readjusted phased array.

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Attenuation of a Slow Subsonic A0 Mode Ultrasonic Guided Wave in Thin Plastic Films

Materials ◽

10.3390/ma12101648 ◽

2019 ◽

Vol 12 (10) ◽

pp. 1648 ◽

Cited By ~ 2

Author(s):

Rymantas Kažys ◽

Reimondas Šliteris ◽

Liudas Mažeika ◽

Olgirdas Tumšys ◽

Egidijus Žukauskas

Keyword(s):

Guided Waves ◽

High Efficiency ◽

Lamb Waves ◽

Ultrasonic Transducer ◽

Plane Waves ◽

Ultrasound Velocity ◽

Guided Wave ◽

Low Frequencies ◽

Plastic Films ◽

Thin Plastic

The ultrasonic testing technique using Lamb waves is widely used for the non-destructive testing and evaluation of various structures. For air-coupled excitation and the reception of A0 mode Lamb waves, leaky guided waves are usually exploited. However, at low frequencies (<100 kHz), the velocity of this mode in plastic and composite materials can become slower than the ultrasound velocity in air, and its propagation in films is accompanied only by an evanescent wave in air. To date, the information about the attenuation of the slow A0 mode is very contradictory. Therefore, the objective of this investigation was the measurement of the attenuation of the slow A0 mode in thin plastic films. The measurement of the attenuation of normal displacements of the film caused by a propagating slow A0 mode is discussed. The normal displacements of the film at different distances from the source were measured by a laser interferometer. In order to reduce diffraction errors, the measurement method based on the excitation of cylindrical but not plane waves was proposed. The slow A0 mode was excited in the polyvinylchloride film by a dry contact type ultrasonic transducer made of high-efficiency PMN-32%PT strip-like piezoelectric crystal. It was found that that the attenuation of the slow A0 mode in PVC film at the frequency of 44 kHz is 2 dB/cm. The obtained results can be useful for the development of quality control methods for plastic films.

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Application of Air-Coupled Ultrasonic Arrays for Excitation of a Slow Antisymmetric Lamb Wave

Sensors ◽

10.3390/s18082636 ◽

2018 ◽

Vol 18 (8) ◽

pp. 2636 ◽

Cited By ~ 4

Author(s):

Rymantas Kazys ◽

Almantas Vilpisauskas ◽

Justina Sestoke

Keyword(s):

Lamb Wave ◽

Guided Waves ◽

Ultrasound Velocity ◽

Optimization Procedure ◽

Wave Mode ◽

Zero Order ◽

Air Gap ◽

Thin Plates ◽

Low Frequencies ◽

Excitation Method

Air-coupled excitation and reception of ultrasonic guided waves is already used for non-destructive testing and evaluation (NDT & E). Usually for air-coupled NDT & E purposes the lowest zero-order antisymmetric Lamb wave mode A0 is used, because it is most sensitive to internal defects and thickness variations. The velocity of the A0 mode is reduced with a reducing frequency and at low frequencies may become slower than the ultrasound velocity in air. Such a wave is named a slow Lamb wave. The objective of this research was the development and investigation of an air-coupled excitation method of the slow zero-order antisymmetric Lamb wave based on application of a piezoceramic ultrasonic array. We have proposed to excite the A0 mode by a planar air-coupled phased array with rectangular elements. The array is matched to the wavelength of the A0 mode in the film. Performance of such an excitation method was investigated both theoretically and experimentally. Two excitation methods of the array were analysed: when all array elements were excited simultaneously or one by one with a proper delay. In order to reduce crosstalk between array elements via the air gap, we have proposed an optimization procedure based on additional shifts of electric excitation impulses of the array elements. For experimental verification of the proposed approach a prototype of the air-coupled eight element array made of Pz-29 piezoceramic strips was manufactured. Experimental validation confirmed the possibility of exciting the slow A0 Lamb wave mode through the air gap in thin plates and films.

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Air-Coupled Reception of a Slow Ultrasonic A0 Mode Wave Propagating in Thin Plastic Film

Sensors ◽

10.3390/s20020516 ◽

2020 ◽

Vol 20 (2) ◽

pp. 516 ◽

Cited By ~ 2

Author(s):

Rymantas J. Kazys ◽

Almantas Vilpisauskas

Keyword(s):

Evanescent Wave ◽

Ultrasound Velocity ◽

Thin Plates ◽

Destructive Testing ◽

Low Frequencies ◽

Plastic Films ◽

Additional Signal ◽

Virtual Array ◽

Thin Plastic ◽

Coupled Technique

At low frequencies, in thin plates the phase velocity of the guided A0 mode can become slower than that of the ultrasound velocity in air. Such waves do not excite leaky waves in the surrounding air, and therefore, it is impossible to excite and receive them by conventional air-coupled methods. The objective of this research was the development of an air-coupled technique for the reception of slow A0 mode in thin plastic films. This study demonstrates the feasibility of picking up a subsonic A0 mode in plastic films by air-coupled ultrasonic arrays. The air-coupled reception was based on an evanescent wave in air accompanying the propagating A0 mode in a film. The efficiency of the reception was enhanced by using a virtual array which was arranged from the data collected by a single air-coupled receiver. The signals measured at the points corresponding to the positions of the phase-matched array were recorded and processed. The transmitting array excited not only the A0 mode in the film, but also a direct wave in air. This wave propagated at ultrasound velocity in air and was faster than the evanescent wave. For efficient reception of the A0 mode, the additional signal-processing procedure based on the application of the 2D Fourier transform in a spatial–temporal domain. The obtained results can be useful for the development of novel air-coupled ultrasonic non-destructive testing techniques.

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Wave Propagation Analysis in Composite Laminates Containing a Delamination Using a Three-Dimensional Spectral Element Method

Mathematical Problems in Engineering ◽

10.1155/2012/659849 ◽

2012 ◽

Vol 2012 ◽

pp. 1-19 ◽

Cited By ~ 7

Author(s):

Fucai Li ◽

Haikuo Peng ◽

Xuewei Sun ◽

Jinfu Wang ◽

Guang Meng

Keyword(s):

Wave Propagation ◽

Lamb Wave ◽

Composite Laminates ◽

Composite Structures ◽

Spectral Element Method ◽

Three Dimensional ◽

Spectral Element ◽

Wave Mode ◽

Diagonal Form ◽

Element Method

A three-dimensional spectral element method (SEM) was developed for analysis of Lamb wave propagation in composite laminates containing a delamination. SEM is more efficient in simulating wave propagation in structures than conventional finite element method (FEM) because of its unique diagonal form of the mass matrix. Three types of composite laminates, namely, unidirectional-ply laminates, cross-ply laminates, and angle-ply laminates are modeled using three-dimensional spectral finite elements. Wave propagation characteristics in intact composite laminates are investigated, and the effectiveness of the method is validated by comparison of the simulation results with analytical solutions based on transfer matrix method. Different Lamb wave mode interactions with delamination are evaluated, and it is demonstrated that symmetric Lamb wave mode may be insensitive to delamination at certain interfaces of laminates while the antisymmetric mode is more suited for identification of delamination in composite structures.

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Numerical Simulation on Micro-damage Detection In CFRP Composites Based on Nonlinear Ultrasonic Guided Waves

Structural Health Monitoring ◽

10.21741/9781644901311-39 ◽

2021 ◽

Keyword(s):

Damage Detection ◽

Composite Structures ◽

Guided Waves ◽

Second Harmonic ◽

Wave Mode ◽

Guided Wave ◽

Reinforced Plastics ◽

Matrix Cracks ◽

Nonlinear Ultrasonic ◽

Contact Acoustic Nonlinearity

Abstract. Micro-damages such as pores, closed delamination/debonding and fiber/matrix cracks in carbon fiber reinforced plastics (CFRP) are vital factors towards the performance of composite structures, which could collapse if defects are not detected in advance. Nonlinear ultrasonic technologies, especially ones involving guided waves, have drawn increasing attention for their better sensitivity to early damages than linear acoustic ones. The combination of nonlinear acoustics and guided waves technique can promisingly provide considerable accuracy and efficiency for damage assessment and materials characterization. Herein, numerical simulations in terms of finite element method are conducted to investigate the feasibility of micro-damage detection in multi-layered CFRP plates using the second harmonic generation (SHG) of asymmetric Lamb guided wave mode. Contact acoustic nonlinearity (CAN) is introduced into the constitutive model of micro-damages in composites, which leads to the distinct SHG compared with material nonlinearity. The results suggest that the generated second order harmonics due to CAN could be received and adopted for early damage evaluation without matching the phase of the primary waves.

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