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Jun 2006

Volume 119, Issue 6, pp. 3493-EL73

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Finite element modeling of torsional wave modes along pipes with absorbing materials

Michel Castaings and Christophe Bacon

J. Acoust. Soc. Am. Volume 119, Issue 6, pp. 3741-3751 (2006); (11 pages) | Cited 15 times

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This paper describes the implementation of equations of dynamic equilibrium in a finite element (FE) code for modeling, in axisymmetry, the propagation of torsional wave modes along metallic pipes coupled to solid elements. Materials constituting either pipes and/or surrounding elements can be absorbing media, the absorption being caused by either their viscoelasticity or scattering on their internal structure (or both). Complex moduli are used as input data to equations of dynamic equilibrium, which are solved in the frequency domain rather than in the temporal domain. Their real and imaginary parts represent material elasticity and damping, respectively. A new definition of efficient and easy-to-implement absorbing regions that suppress undesired reflections from boundaries is proposed. The resolution of equations in the frequency domain, together with the use of absorbing regions, lead to significant reductions in the number of mesh elements and also in the number of iterations required for describing problems of propagation and scattering. Through two examples, the model is validated by successful comparisons of numerical predictions with experimental data. Then, a third example is presented to illustrate the importance of properly modeling waves damping when using FE models for setting-up or optimizing NDT techniques.
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43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants

Bulk conical and surface helical acoustic waves in transversely isotropic cylinders; application to the stiffness tensor measurement

M. Perton, B. Audoin, Y. D. Pan, and C. Rossignol

J. Acoust. Soc. Am. Volume 119, Issue 6, pp. 3752-3759 (2006); (8 pages)

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A point-source-point-receiver technique, based on laser generation and laser detection of acoustic waves, allows determination of mechanical properties of anisotropic cylinders. The anisotropic nature of the material and the geometry of the samples make the acoustic signature difficult to interpret. In addition to multiple surface waves, quasi-longitudinal and quasi-shear bulk waves are diffracted and acoustic rays are reflected with or without mode conversion at the cylinder surface. Moreover both bulk and surface diffracted waves have a dispersive behavior. To bypass the intricacies, wave fronts are synthesized with signals provided by scanning a straight line on the cylinder with the laser point source. Conical waves propagating in the volume and helical waves propagating along the surface are then numerically produced. The recovery of the stiffness-tensor components is based on the inversion of the bulk waves, phase velocities. The method is presented and applied to signals simulated or experimentally recorded for a composite material. The five independent stiffness coefficients of the hexagonal symmetry are thus measured with waveforms provided by a single scan along the cylinder surface. The method provides a unique mean for the noncontact measurement of elastic properties of cylindrical parts.
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43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
43.20.El Reflection, refraction, diffraction of acoustic waves

A method for modeling polymer viscoelastic data and the temperature shift function

Walter M. Madigosky, Gilbert F. Lee, and Jan M. Niemiec

J. Acoust. Soc. Am. Volume 119, Issue 6, pp. 3760-3765 (2006); (6 pages) | Cited 4 times

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Dynamic viscoelastic polymer data is traditionally time-temperature shifted to obtain a temperature shift function (TSF) and then fitted to various analytical models. The process of obtaining the TSF can introduce considerable procedural or operator bias. Nevertheless the Havriliak and Negami (HN) model using the TSF methodology can generally describe polymers that are rheologically simple. In this paper the “wicket” plot is utilized as an important tool in analyzing data, as it is completely independent of time-temperature shifting (TTS). Using the wicket plot the data is fit to the HN equation to determine the four material HN constants independent of TTS. Having obtained the complete spectra of dynamic properties the specific relaxation time (frequency) at each temperature is obtained by matching the HN curve to the experimental data at that temperature thus determining the TSF. The procedure is illustrated by analyzing computer-generated data with random error in modulus and loss and finally real data on a standard material.
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43.35.Mr Acoustics of viscoelastic materials
43.35.Fj Ultrasonic relaxation processes in gases, liquids, and solids

Acousto-mechanical and thermal properties of clotted blood

Volodymyr M. Nahirnyak, Suk Wang Yoon, and Christy K. Holland

J. Acoust. Soc. Am. Volume 119, Issue 6, pp. 3766-3772 (2006); (7 pages) | Cited 8 times

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The efficacy of ultrasound-assisted thrombolysis as an adjunct treatment of ischemic stroke is being widely investigated. To determine the role of ultrasound hyperthermia in the process of blood clot disruption, the acousto-mechanical and thermal properties of clotted blood were measured in vitro, namely, density, speed of sound, frequency-dependent attenuation, specific heat, and thermal conductivity. The amplitude coefficient of attenuation of the clots was determined for 120 kHz, 1.0 MHz, and 3.5 MHz ultrasound at room temperature (20±2 °C). The attenuation coefficient ranged from 0.10 to 0.30 Np/cm in porcine clots and from 0.09 to 0.23 Np/cm in human clots. The experimentally determined values of specific heat and thermal conductivity for porcine clotted blood are (3.2±0.5)×103 J/kg∙K and 0.55±0.13 W/m∙K, respectively, and for human clotted blood are (3.5±0.8)×103 J/kg∙K and 0.59±0.11 W/m∙K, respectively. Measurements of the acousto-mechanical and thermal properties of clotted blood can be helpful in theoretical modeling of ultrasound hyperthermia in ultrasound-assisted thrombolysis and other high-intensity focused ultrasound applications.
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43.35.Wa Biological effects of ultrasound, ultrasonic tomography
43.80.Ev Acoustical measurement methods in biological systems and media

Ultrasonic evaluation of residual stresses in flat glass tempering: Comparing experimental investigation and numerical modeling

Marc Duquennoy, Dany Devos, Mohammadi Ouaftouh, Dominique Lochegnies, and Eric Roméro

J. Acoust. Soc. Am. Volume 119, Issue 6, pp. 3773-3781 (2006); (9 pages) | Cited 6 times

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In order to control residual stress distribution in glass, techniques based on the phenomenon of photoelasticity are efficient, though subject to the inherent limitations of all optical techniques. To mitigate these limitations, we exploit the phenomenon of acoustoelasticity to estimate residual stress distribution, using surface acoustic waves. Experimental results are obtained for a 6 mm thick soda-lime silicate flat glass plate that had been subjected to nonuniform thermal tempering and whose stress distribution is calculated using finite element modeling. The estimated stress distributions provided by our ultrasonic method compare quite well with the results from the modeling, from both the qualitative and quantitative points of view.
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43.35.Zc Use of ultrasonics in nondestructive testing, industrial processes, and industrial products
43.35.Pt Surface waves in solids and liquids
43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
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