Volume 118, Issue 6, December 2005
Index of content:
- ULTRASONICS, QUANTUM ACOUSTICS, AND PHYSICAL EFFECTS OF SOUND 
118(2005); http://dx.doi.org/10.1121/1.2109407View Description Hide Description
The near-field scattering of a Rayleigh wave at a surface crack is analyzed with analytical and numerical calculations complemented by detailed experimental observations. These investigations are directed towards the development of inversion schemes for surface crack sizing in mechanical components. The near-field analysis is based on a procedure that allows filtering the Rayleigh wave from the other wave modes scattered at the defect. Pointwise measurements of the out-of-plane displacement using a laser interferometer lead to a complete displacement field image in the crack near field with high spatial resolution. The numerical calculations are compared with the analytical solution and the experimental data in order to validate specific crack modeling approaches and to identify parameters for surface crack characterization. The evaluation is carried out with respect to the stress fields at the crack tip, the surface displacement near field, Rayleigh wave transmission and reflection coefficients, and the time delay of Rayleigh wave transmission. The latter appears as the most suitable parameter for crack characterization due to the relative insensitivity of the measured values on the variability of the experimental conditions. The results of the present work also highlight differences between the scatterings at cracks and narrow slots (“artificial cracks”).
118(2005); http://dx.doi.org/10.1121/1.2118307View Description Hide Description
Understanding the behavior of cavitation bubbles driven by ultrasonic fields is an important problem in biomedical acoustics. Keller-Miksis equation, which can account for the large amplitude oscillations of bubbles, is rederived in this paper and combined with a viscoelasticmodel to account for the strain-stress relation. The viscoelasticmodel used in this study is the Voigt model. It is shown that only the viscous damping term in the original equation needs to be modified to account for the effect of elasticity. With experiment determined viscoelasticproperties, the effects of elasticity on bubble oscillations are studied. Specifically, the inertial cavitation thresholds are determined using , and subharmonic signals from the emission of an oscillating bubble are estimated. The results show that the presence of the elasticity increases the threshold pressure for a bubble to oscillate inertially, and subharmonic signals may only be detectable in certain ranges of radius and pressure amplitude. These results should be easy to verify experimentally, and they may also be useful in cavitation detection and bubble-enhanced imaging.