Probing of laser-induced crack modulation by laser-monitored surface waves and surface skimming bulk waves

Ni, Chao; Chigarev, Nikolay; Tournat, Vincent; Delorme, Nicolas; Shen, Zhonghua; Gusev, Vitalyi

doi:10.1121/1.3684737

Cited by 22 publications

(21 citation statements)

References 22 publications

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“…The possibility to close the crack completely locally by the stationary heating has been recently proved experimentally. 25,26,39,40 However, if m < 1 then the clapping could continue with the increasing excitation of the crack. In particular, when m < 1 and r x¼0 te ð0; PÞ ) r cr the modulation of the side-lobes does not depend anymore on the excitation level…”

Section: Theoretical Backgroundmentioning

confidence: 99%

Two dimensional nonlinear frequency-mixing photo-acoustic imaging of a crack and observation of crack phantoms

Mézil

Chigarev

Tournat

et al. 2013

Journal of Applied Physics

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A two-dimensional imaging of a crack by nonlinear frequency-mixing photo-acoustic method is reported. The imaging contrast is due to nonlinear photo-thermo-acoustic processes taking place in case of simultaneous excitation by lasers of thermo-elastic and acoustic waves in the vicinity of the cracks. The images are obtained by scanning of two co-focused laser beams in region of crack location. The first cw laser beam, modulated in intensity at low frequency f L , generates a thermoelastic wave, which is able to strongly periodically modulate the local crack rigidity up to complete closing/opening of the crack. The second cw laser beam, intensity modulated at much higher frequency f H , generates an acoustic wave incident on the breathing crack. The crack rigidity is also influenced by the stationary non-modulated inhomogeneous thermal stresses caused by the stationary heating of the sample by both lasers. The main contribution to imaging contrast comes from the strong dependence of the reflectivity of acoustic waves on the crack rigidity. The modulation of crack rigidity by thermo-elastic wave leads to the parametric modulation of the reflected acoustic waves and the generation in the spectrum of the acoustic field of the side lobes, which are separated from f H by the integer number of f L . Scan images of a crack with an amplitude dynamics up to 40 dB and a spatial resolution better than 100 lm, are obtained through the mapping of nonlinear side lobe amplitudes. The observed dependences of the images on the power of the lasers are discussed and the physical explanation of the appearance of crack phantom images at high level of optical excitation is proposed. For comparison and elucidation of spatial resolution issues related to this imaging method, the one-dimensional images, obtained with one laser beam focus position fixed and the second beam focus position scanning, are also presented and discussed.

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Section: Theoretical Backgroundmentioning

confidence: 99%

Two dimensional nonlinear frequency-mixing photo-acoustic imaging of a crack and observation of crack phantoms

Mézil

Chigarev

Tournat

et al. 2013

Journal of Applied Physics

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“…Here we focus on acoustic waves propagating along the surface of a sample and interacting with a surface breaking crack [5,6]. Unlike the frequency mixing process described above, involving initially two monochromatic waves, we deal here with wide band acoustic waves (the pulse duration is typically of several nanoseconds).…”

Section: Principle Of the All-optical Probing Of A Thermally Stressedmentioning

confidence: 99%

Probing of crack breathing by pulsed laser-generated acoustic waves

Tournat¹,

Ni²,

Chigarev³

et al. 2013

The Journal of the Acoustical Society of America

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Experimental results on all-optical monitoring of the nonlinear motion of a surface-breaking crack are reported. Crack closing is induced by quasi-continuous laser heating, while Rayleigh surface acoustic pulses and bulk longitudinal surface skimming pulses are also generated and detected by lasers. By exploiting the strong dependence of the acoustic pulses reflection and transmission efficiency on the state-open or closed-of the contacts between the crack faces, the parametric modulation of ultrasonic pulses is achieved. It is observed that bulk acoustic waves, skimming along the surface can be more sensitive to crack motion than Rayleigh surface waves. It has been found that crack closure by thermo-elastic stresses modifies the propagation paths of the acoustic rays from the point source to the point receiver. Consequently, the arrival times of the acoustic waves contain information on the state of crack closure induced by a particular intensity of laser heating. A dependence of the detected signals on the initial width/state of the crack and on the presence of necks in the crack opening profile is revealed. The mode conversion of the skimming longitudinal bulk waves incident on the crack into Rayleigh waves is found very sensitive to imperfectness of crack closure.

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“…69 In this study, localized irreversible microscopic modification in crack surfaces is monitored by utilizing the responses of laser-generated and laser-detected acoustic waves to laser-induced crack modulation. Through upgrading and improving of the experimental approaches developed in previous works, 66,67 for the first time, monitoring of the macroscopic behavior of crack motion, as well as microscopic modifications of crack surfaces (reversible/irreversible modifications of asperities) by optically inducing and probing the acoustoelastic phenomena, has been enabled. A pulsed laser was used to generate surface skimming longitudinal waves and Rayleigh-type surface acoustic waves in a cracked black glass, and a continuous wave laser was used to detect them in the beam deflection configuration.…”

Section: Introductionmentioning

confidence: 99%

“…76 Furthermore, in this study, the reported non-monotonic evolution of peak-to-peak amplitude of the mode-converted signal at the end of cooling time intervals after heating at various heating powers can be potentially used to evaluate the width of the crack in SHM. 64,66,67 Furthermore, optical generation and detection of acoustic waves presented in this study can be easily scanned over the surface of the sample; thus, linear laser ultrasonic techniques, such as time-of-flight diffraction (TOFD) 77 and scanning laser source, 29 can be realized when required in combination with the laser-induced thermoelastic loading of the crack. These techniques have been proven to be beneficial for crack detection, and numerous applications have been reported in many fields of SHM.…”

Section: Introductionmentioning

confidence: 99%

Laser ultrasonic monitoring of reversible/irreversible modification of a real crack under photothermal loading

Zhang

et al. 2020

Structural Health Monitoring

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We study the responses of laser-generated acoustic waves to localized reversible/irreversible modifications of microscopic asperities on crack surfaces during crack closure, which is an essential process in nonlinear photoacoustic/photothermal crack detection techniques. Our laser ultrasonics technique involves optical measurement of the transmission and mode conversion of the laser-generated surface acoustic waves caused by the crack. Reversible/irreversible modifications of asperities can be achieved via non-contact photothermal loading of the crack. Three photothermal loading cycles were realized in individual succession and were monitored using the laser ultrasonics technique at various experimental locations along the crack. In our experiments, each photothermal loading cycle includes multiple successive subcycles, in which the material is first heated and then cooled to its equilibrium temperature, thereby initiating local closing, followed by opening of the crack. Each subcycle is monitored twice using the laser ultrasonics technique, once each at the end of heating and cooling. Furthermore, each successive subcycle is accomplished at a higher power of heating laser than that of the previous subcycle. Significant differences in the peak-to-peak amplitude of the surface skimming longitudinal acoustic wave, which is excited by mode conversion of the Rayleigh wave by the crack, are revealed during the first cycle of photothermal loading. These differences clearly indicate a partial irreversibility of the mechanical processes occurring in the crack surfaces during subcycles of the first cycle. In a larger temporal scale, irreversible modification of crack surfaces is observed from the significant difference between the experimental results of the first photothermal loading cycle and the subsequent two cycles, whereas a reversible response of the crack surface to thermoelastic loading is observed from the similarity of the measurements accumulated during the two subsequent cycles.

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Probing of laser-induced crack modulation by laser-monitored surface waves and surface skimming bulk waves

Cited by 22 publications

References 22 publications

Two dimensional nonlinear frequency-mixing photo-acoustic imaging of a crack and observation of crack phantoms

Two dimensional nonlinear frequency-mixing photo-acoustic imaging of a crack and observation of crack phantoms

Probing of crack breathing by pulsed laser-generated acoustic waves

Laser ultrasonic monitoring of reversible/irreversible modification of a real crack under photothermal loading

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