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Numerical modeling of thermoelastic generation of ultrasound by laser irradiation in the coupled thermoelasticity.

Veres IA, Berer T, Burgholzer P - Ultrasonics (2012)

Bottom Line: Moreover, the coupling leads to dispersion influencing the wave velocities at low frequencies.The numerical simulations are compared to theoretical results available in the literature.Wave fields generated by a line focused laser source are presented by the numerical model for isotropic and for transversely isotropic materials.

View Article: PubMed Central - PubMed

Affiliation: Research Center for Non-Destructive Testing GmbH (RECENDT), Altenberger Str. 69, 4040 Linz, Austria. istvan.veres@recendt.at

No MeSH data available.


Related in: MedlinePlus

(a)–(b) Influence of the thermal feedback in the isotropic case (aluminum) and in the transversely isotropic case (zinc). (c)–(d) Variation of the waveforms on the epicentral axis at different times emphasizing the attenuation. (e) Time domain signals on the epicentral axis in different depths. (f) Fourier transform of the time domain signals in (e). (g) Influence of the thermal feedback on the generated Rayleigh waves. (h) Theoretical variation of the coupled longitudinal wave velocity and its attenuation over frequency.
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f0025: (a)–(b) Influence of the thermal feedback in the isotropic case (aluminum) and in the transversely isotropic case (zinc). (c)–(d) Variation of the waveforms on the epicentral axis at different times emphasizing the attenuation. (e) Time domain signals on the epicentral axis in different depths. (f) Fourier transform of the time domain signals in (e). (g) Influence of the thermal feedback on the generated Rayleigh waves. (h) Theoretical variation of the coupled longitudinal wave velocity and its attenuation over frequency.

Mentions: Coupling, or thermal feedback, is the result of volume changes [37, p. 394], occured by normal strains. We expect the largest effect on the generated bulk longitudinal or quasilongitudinal waves along the epicentral axis and focus our investigations on these waves. A direct comparison of the displacements on the epicentral axis in Fig. 5a and b for simulations with and without thermal feedback shows a broadening of the pulses with a decrease in amplitude. Although, the effect is considerable for the isotropic aluminum, it becomes stronger for zinc. This attenuation is predicted in [37] as an effect of the thermal feedback. The propagating stress wave results in a small thermal disturbance along its propagation converting the mechanical energy into heat, hence the observed attenuation. Attenuation of the pulses on the epicentral axes are shown in Fig. 5c and d. In the simulation a pulse width of 2 μm was applied, but this width is strongly widening for larger propagation depths (Fig. 4c) due to leakage into the bulk. Hence, geometrical attenuation appears also for the uncoupled cases. For the quasilongitudinal wave in zinc the influence of the thermal feedback becomes particularly strong as shown in Fig. 5d.


Numerical modeling of thermoelastic generation of ultrasound by laser irradiation in the coupled thermoelasticity.

Veres IA, Berer T, Burgholzer P - Ultrasonics (2012)

(a)–(b) Influence of the thermal feedback in the isotropic case (aluminum) and in the transversely isotropic case (zinc). (c)–(d) Variation of the waveforms on the epicentral axis at different times emphasizing the attenuation. (e) Time domain signals on the epicentral axis in different depths. (f) Fourier transform of the time domain signals in (e). (g) Influence of the thermal feedback on the generated Rayleigh waves. (h) Theoretical variation of the coupled longitudinal wave velocity and its attenuation over frequency.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4067043&req=5

f0025: (a)–(b) Influence of the thermal feedback in the isotropic case (aluminum) and in the transversely isotropic case (zinc). (c)–(d) Variation of the waveforms on the epicentral axis at different times emphasizing the attenuation. (e) Time domain signals on the epicentral axis in different depths. (f) Fourier transform of the time domain signals in (e). (g) Influence of the thermal feedback on the generated Rayleigh waves. (h) Theoretical variation of the coupled longitudinal wave velocity and its attenuation over frequency.
Mentions: Coupling, or thermal feedback, is the result of volume changes [37, p. 394], occured by normal strains. We expect the largest effect on the generated bulk longitudinal or quasilongitudinal waves along the epicentral axis and focus our investigations on these waves. A direct comparison of the displacements on the epicentral axis in Fig. 5a and b for simulations with and without thermal feedback shows a broadening of the pulses with a decrease in amplitude. Although, the effect is considerable for the isotropic aluminum, it becomes stronger for zinc. This attenuation is predicted in [37] as an effect of the thermal feedback. The propagating stress wave results in a small thermal disturbance along its propagation converting the mechanical energy into heat, hence the observed attenuation. Attenuation of the pulses on the epicentral axes are shown in Fig. 5c and d. In the simulation a pulse width of 2 μm was applied, but this width is strongly widening for larger propagation depths (Fig. 4c) due to leakage into the bulk. Hence, geometrical attenuation appears also for the uncoupled cases. For the quasilongitudinal wave in zinc the influence of the thermal feedback becomes particularly strong as shown in Fig. 5d.

Bottom Line: Moreover, the coupling leads to dispersion influencing the wave velocities at low frequencies.The numerical simulations are compared to theoretical results available in the literature.Wave fields generated by a line focused laser source are presented by the numerical model for isotropic and for transversely isotropic materials.

View Article: PubMed Central - PubMed

Affiliation: Research Center for Non-Destructive Testing GmbH (RECENDT), Altenberger Str. 69, 4040 Linz, Austria. istvan.veres@recendt.at

No MeSH data available.


Related in: MedlinePlus