Thermo-optical modulation of ultrasonic surface waves for NDE

Zhang, Yan; Nagy, Péter B.

doi:10.1016/s0041-624x(02)00237-8

Cited by 11 publications

(5 citation statements)

References 10 publications

(13 reference statements)

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“…First, it was demonstrated that the modulation of crack rigidity can be achieved by inducing thermoelastic stresses through the absorption of pulsed-periodic laser radiation. 18 This modulation of crack parameters was transferred in the modulation of the Rayleigh surface acoustic waves, which were generated and detected by in-contact transducers for probing laser-induced breathing of the crack. In case of the modulation frequencies, which were vanishingly small in comparison with the frequency of the probing Rayleigh waves, the observed nonlinear acoustic phenomenon of frequency-mixing or parametric modulation could be classified as acoustoelasticity, 15,17 where, however, the modification of the material=crack elasiticity was caused not by static pressure, as it is in the classical acoustoelasticity, but by the quasi-static thermo-elastic stress and took place not in the whole volume of the sample but locally.…”

Section: Introductionmentioning

confidence: 99%

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

Ni¹,

Chigarev²,

Tournat³

et al. 2012

The Journal of the Acoustical Society of America

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All-optical monitoring of the nonlinear motion of a surface-breaking crack is reported. Crack closing is induced by quasi-continuous laser heating, while Rayleigh surface acoustic pulses and bulk longitudinal surface skimming acoustic 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.

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Section: Introductionmentioning

confidence: 99%

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

Ni¹,

Chigarev²,

Tournat³

et al. 2012

The Journal of the Acoustical Society of America

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“…It has been shown that the new frequency components in the acoustic spectrum generated by the interaction of powerful ultrasound launched with piezoelectric transducers with cracks can be detected by a commercial laser vibrometer [9,10]. As well, it has also been demonstrated that the modulation of crack closure and, consequently, of crack rigidity can be achieved by thermoelastic stresses induced through heating of the cracked region by intensity-modulated IR laser radiation [11,12]. In these experiments, laserinduced modulation of crack parameters was manifested in the modulation of the ultrasonic surface acoustic waves reflected from the crack, which were both launched and detected using in-contact, interdigital transducers.…”

mentioning

confidence: 99%

All-optical probing of the nonlinear acoustics of a crack

et al. 2011

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Experiments with an all-optical method for the study of the nonlinear acoustics of cracks in solids are reported. Nonlinear acoustic waves are initiated by the absorption of radiation from a pair of laser beams intensity modulated at two different frequencies. The detection of acoustic waves at mixed frequencies, absent in the frequency spectrum of the heating lasers, by optical interferometry or deflectometry provides unambiguous evidence of the elastic nonlinearity of the crack. The high contrast in crack imaging achieved by remote optical monitoring of the nonlinear acoustic processes is due to the strong dependence of the efficiency of optoacoustic conversion on the state of the crack. The highest acoustic nonlinearity is observed in the transitional state of the crack, which is intermediate between the open and the closed ones.

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“…On the other hand, nonlinear acoustic 8,33–55 and vibro-thermography methods 56–58 have been proven to potentially overcome the limitations of linear UT techniques, because they depend on the nonlinear elastic/inelastic properties of cracks, which are known to be relatively different from those of artificial defects. 45 The nonlinear methods are extremely sensitive in characterizing non-perfectly contacting material surfaces, cracks and fatigue damage, by monitoring various nonlinear acoustic phenomena, such as harmonic generation, 8,35,40,51,53–55 subharmonic generation, 35,36,40 parametric modulation, 37,41 modulation transfer, 42 and acoustoelasticity.…”

Section: Introductionmentioning

confidence: 99%

“…Furthermore, this ultrasonic method was proposed to be improved via modulation of crack rigidity by inducing thermoelastic stresses through the absorption of pulsed laser radiation. 44 This modulation is transferred into the variation of reflectivity of the surface acoustic waves, which is measured by the conventional ultrasonic technique. If the modulation frequency is smaller than that of the ultrasonic waves, the observed nonlinear acoustic phenomenon of frequency-mixing could be classified as acoustoelasticity, 45 in which the modification of material elasticity is caused by thermoelastic stress instead of static pressure.…”

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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Thermo-optical modulation of ultrasonic surface waves for NDE

Cited by 11 publications

References 10 publications

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

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

All-optical probing of the nonlinear acoustics of a crack

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

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