Index of content:
Volume 126, Issue 3, September 2009
- ULTRASONICS, QUANTUM ACOUSTICS, AND PHYSICAL EFFECTS OF SOUND 
The contrast-source stress-velocity integral-equation formulation of three-dimensional time-domain elastodynamic scattering problems: A structured approach using tensor partitioning126(2009); http://dx.doi.org/10.1121/1.3179672View Description Hide Description
The contrast-source stress-velocity integral-equation formulation of three-dimensional time-domain elastodynamic scattering problems is discussed. A novel feature of the formulation is a tensor partitioning of the relevant dynamic stress and the contrast source volume density of deformation rate. The partitioning highlights several features about the structure of the formulation. These can advantageously be incorporated in a computational implementation of the method. An application to the case of a scatterer composed of isotropic material and embedded in an isotropic elastic background medium shows that the corresponding newly introduced constitutive coefficients are more natural as a characterization of the media than the traditional Lamé coefficients.
126(2009); http://dx.doi.org/10.1121/1.3177268View Description Hide Description
Guided waves have been effectively used for rapid inspections of plates and pipes. However, the guided-wave technique is not generally used for measuring the remaining thickness in a plate and a pipe due to the difficulties in guided-wave motion. Instead, time-consuming and costly direct contact thickness measurements are still used in practice. This study describes a thickness measurement technique using the A0 mode of a Lamb wave generated by a laser source. A finite element analysis of Lamb wave revealed that this mode propagates with small reflections and mode conversions at a rounded shallow defect and has larger amplitude at thinner regions. Using these characteristics, it is experimentally demonstrated that the distributions of plate thickness were obtained from the amplitude of A0 mode generated by a scanning laser source and received by an angle-beam transducer. The resulting distribution images were obtained at extremely high speed compared to the conventional thickness measurements.