Nonlinear mixing of laser generated narrowband Rayleigh surface waves
16 Feb 2017-Vol. 1806, Iss: 1, pp 020004
TL;DR: In this article, a nonlinear mixing technique of two co-directionally travelling Rayleigh surface waves generated and detected using laser ultrasonics is presented, where the optical generation of Rayleigh waves on the specimen is obtained by shadow mask method.
Abstract: This research presents the nonlinear mixing technique of two co-directionally travelling Rayleigh surface waves generated and detected using laser ultrasonics. The optical generation of Rayleigh waves on the specimen is obtained by shadow mask method. In conventional nonlinear measurements, the inherently small higher harmonics are greatly influenced by the nonlinearities caused by coupling variabilities and surface roughness between the transducer and specimen interface. The proposed technique is completely contactless and it should be possible to eliminate this problem. Moreover, the nonlinear mixing phenomenon yields not only the second harmonics, but also the sum and difference frequency components, which can be used to measure the acoustic nonlinearity of the specimen. In this paper, we will be addressing the experimental configurations for this technique. The proposed technique is validated experimentally on Aluminum 7075 alloy specimen.
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08 May 2019
TL;DR: In this article, narrow band lamb wave modes were generated using a pulsed Nd-YAG laser system consisting of a spatial array illumination source, which enabled generation of specific Lamb wave modes for in-situ inspection of additively manufactured components.
Abstract: Recent developments in metal additive manufacturing (AM) has created a lot of interest in sectors including automotive, aerospace and biomedical engineering. It is imperative that the components manufactured additively be inspected for flaws, mechanical properties and dimensional accuracy. Several non-destructive testing (NDT) techniques such as X-ray computed tomography and conventional ultrasonic testing have been implemented to evaluate the quality of these components. Recently, research has been focused on techniques that can perform non-contact testing and carry out an online inspection layer by layer while the component is being fabricated. Laser based ultrasonic technique has been found to be a promising method owing to its non-contact nature and ability to operate in harsh environments. In our study, narrow band lamb waves were generated using a pulsed Nd-YAG laser system consisting of a spatial array illumination source. The generated wave modes were detected using a two-wave mixing based laser interferometer. The wavelength-matched method enabled generation of specific lamb wave modes for in-situ inspection of additively manufactured components.
7 citations
TL;DR: In this article , the authors investigated laser-induced shock excitation of elastic surface waves at a free surface and a soft solid-liquid interface using a custom-designed photoelasticity imaging technique.
Abstract: We investigated laser-induced shock excitation of elastic surface waves at a free surface and a soft solid–liquid interface using a custom-designed photoelasticity imaging technique. Epoxy-resin and pure water were selected as the solid and liquid media. The elastic surface waves were excited via a shock process induced by focusing a single nanosecond laser pulse on the solid surface. To confirm the experimental observations, the roots of the Rayleigh and Stoneley equations were calculated. For a free surface, we present an entire-field observation of elastic surface waves, which includes a super-shear evanescent wave (SEW) that propagates faster than the shear wave but slower than the longitudinal wave. For a soft solid–liquid interface, we demonstrate the presence of a non-leaky Rayleigh wave that corresponds to a real root of the Stoneley equation. We also evidence the existence of a SEW that propagates 1.7 times faster than the shear speed in the solid and corresponds to a complex conjugate root of the Stoneley equation. These results correct the previously accepted notion that the Scholte wave is the only surface wave that can be generated at a soft solid–liquid interface.
5 citations
TL;DR: In this article , the authors numerically studied the frequency mixing response induced by the nonlinear interaction of two primary Rayleigh waves in a concrete material, which is referred to as contact acoustic nonlinearity (CAN).
Abstract: Nonlinear wave mixing provides a potential method to evaluate localized micro‐damage in structures. The wave mixing technique has some unique advantages over the nonlinear ultrasonic technique based on the higher harmonic generation, such as frequency selectivity, which can separate harmonic components generated due to instrumentation. In this paper, we numerically studied the frequency mixing response induced by the nonlinear interaction of two primary Rayleigh waves in a concrete material. The nonlinearity considered in the present study is due to crack‐wave interaction, which is often called contact acoustic nonlinearity (CAN). A limited number of experimental studies were conducted on concrete prisms to evaluate surface cracks. Both numerical and experimental results illustrate the generation of the second‐ and third‐order combined harmonics, which can be utilized to detect and localize subsurface cracks in concrete structures. The newly discovered third‐order combined harmonics, which result from the mutual interaction between the primary Rayleigh waves and their induced second‐harmonic waves, can be exploited to characterize micro‐damage in various applications.
5 citations
01 Jan 2020
TL;DR: In this paper, a one and two dimensional imaging of a crack by a novel nonlinear frequency-mixing photoacoustic method is presented, where acoustic waves are initiated by a pair of laser beams intensity-modulated at two different frequencies.
Abstract: A one and two dimensional imaging of a crack by a novel nonlinear frequency-mixing photoacoustic method is presented. Acoustic waves are initiated by a pair of laser beams intensity-modulated at two different frequencies. The first laser beam, intensity modulated at a low frequency \(f_L\), generates a thermoelastic wave which modulates the local crack rigidity up to complete closing/opening of the crack, corresponding to crack breathing. The second laser beam, intensity modulated at much higher frequency \(f_H\), generates an acoustic wave incident on the breathing crack. The detection of acoustic waves at mixed frequencies \(f_H\pm nf_L\) (\(n=1,2,\dots \)), absent in the excitation frequency spectrum, provides detection of the crack, which can be achieved all-optically. The theory attributes the generation of the frequency-mixed spectral components to the modulation of the acoustic waves reflected/transmitted by the time-varying nonlinear rigidity of the crack. The crack rigidity is modified due to stationary and oscillating components from the laser-induced thermoelastic stresses. The amplitudes of the spectral sidelobes are non-monotonous functions of the increasing thermoelastic loading. Fitting such experimental evolutions with theoretical ones leads to estimating various local parameters of the crack, including its width and rigidity.
2 citations
17 May 2023
TL;DR: In this article , a wedge with two different incidence angles for the excitations of transverse and longitudinal waves is designed to generate one-way collinear mixing Rayleigh waves (MRWs) for material surface damage detection.
Abstract: Nonlinear Rayleigh waves are useful for material surface damage detection. Traditional non-destructive testing (NDT) techniques based on higher harmonics of Rayleigh waves are inevitably interfered with by the nonlinearity of measurement systems. To overcome this disadvantage, an approach based on one-way collinear mixing Rayleigh waves (MRWs) is proposed to evaluate the material surface properties. A wedge with two different incidence angles for the excitations of transverse and longitudinal waves is designed to generate one-way collinear MRWs. The one-way collinear MRWs can be generated on the whole surface of the material, and propagate along the propagation way under one excitation. Numerical simulations of one-way collinear MRWs under different surface properties, which are characterized using different third-order elastic constants, are studied on a semi-infinite aluminum. Experiments are also conducted on the aluminum specimen, whose surface is corroded by hydrochloric acid so as to change the material surface properties. Both numerical and experimental results show that the one-way collinear MRWs are generated effectively, and the defined relative acoustic nonlinearity parameter increases with the propagation distance as well as the severity of the material surface damages. The results verify the effectiveness of the proposed MRW-based method and prove that it would be a promising NDT technique for the accurate evaluation of material surface properties.
References
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TL;DR: In this article, an expanded version of a paper delivered at the scientific session of the Division of General Physics and Astronomy of the USSR Academy of Sciences on 16 January 1969 is presented.
Abstract: Expanded version of a paper delivered at the scientific session of the Division of General Physics and Astronomy of the USSR Academy of Sciences on 16 January 1969.
196 citations
TL;DR: In this paper, a small internal defect 100 µm in diameter in a carbon steel sample was successfully detected by the laser ultrasonic technique, and the dependence of the normalized amplitude of the defect signal on the defect diameter was measured.
Abstract: A small internal defect 100 µm in diameter in a carbon steel sample was successfully detected by the laser ultrasonic technique. Irradiation of a Q-switched Nd:YAG laser was used for ultrasonic generation, and a frequency-doubled CW Nd:YAG laser combined with a Fabry-Perot etalon was used for detection of ultrasonic vibration on the carbon steel surface. The ratio of the internal defect diameter to the ultrasonic wavelength (d/λ) was estimated to be about 0.07. The dependence of the normalized amplitude of the defect signal on the defect diameter was measured, and the ultrasonic reflectance by the cylindrical internal defect was roughly evaluated using the experimental results. It is considered that the laser ultrasonic technique has the ability to detect internal defects in industrial components and engineering structures, which is comparable to that of the conventional ultrasonic testing technique.
40 citations
TL;DR: The mixing of two co-directional, initially monochromatic Rayleigh surface waves in an isotropic, homogeneous, and nonlinear elastic solid is investigated using analytical, finite element method, and experimental approaches and the frequency and amplitude ratios of the fundamentals are identified to help guide effective material characterization.
Abstract: The mixing of two co-directional, initially monochromatic Rayleigh surface waves in an isotropic, homogeneous, and nonlinear elastic solid is investigated using analytical, finite element method, and experimental approaches. The analytical investigations show that while the horizontal velocity component can form a shock wave, the vertical velocity component can form a pulse independent of the specific ratios of the fundamental frequencies and amplitudes that are mixed. This analytical model is then used to simulate the development of the fundamentals, second harmonics, and the sum and difference frequency components over the propagation distance. The analytical model is further extended to include diffraction effects in the parabolic approximation. Finally, the frequency and amplitude ratios of the fundamentals are identified which provide maximum amplitudes of the second harmonics as well as of the sum and difference frequency components, to help guide effective material characterization; this approach should make it possible to measure the acoustic nonlinearity of a solid not only with the second harmonics, but also with the sum and difference frequency components. Results of the analytical investigations are then confirmed using the finite element method and the experimental feasibility of the proposed technique is validated for an aluminum specimen.
28 citations
TL;DR: In this article, the effects of damping, excitation type and signal processing window on the harmonic measurement were investigated and a theoretical model of the generation of nonlinearity was derived using perturbation and multiple scales techniques.
Abstract: The mechanisms by which a travelling wave propagates through a nonlinear medium are of interest due to the large research effort aimed at exploiting its potential in assessing the damage state of structures. Typically measurements are made to track changing signal nonlinearity due to damage on a single specimen geometry. In this special case relative changes in signal nonlinearity are potentially sufficient to indicate damage. A more robust technique would allow the signal nonlinearity to be related back to the strength of the underlying nonlinear mechanism. In the case of measuring harmonic signal generation in a medium exhibiting a bulk material nonlinearity, a nonlinear parameter exists that relates the material nonlinearity to the measured harmonic signal. However, it is based on the assumption that there is no damping and the excitation is continuous. This paper focuses on assessing the effects of damping, excitation type and signal processing window on the harmonic measurement. Using perturbation and multiple scales techniques, a theoretical model of the generation of nonlinearity is derived. A numerical solution is also developed and both approaches show that the nonlinear parameter first increases and then converges with propagation distance due to the presence of damping. This is experimentally verified. The models also capture the effects of excitation type and signal processing window and using them a correction factor is proposed that accounts for all these effects.
27 citations