Volume 111, Issue 2, February 2002
Index of content:
- ULTRASONICS, QUANTUM ACOUSTICS, AND PHYSICAL EFFECTS OF SOUND 
111(2002); http://dx.doi.org/10.1121/1.1430687View Description Hide Description
The flow field and the energy transport near thermoacoustic couples are simulated using a 2D full Navier–Stokes solver. The thermoacoustic couple plate is maintained at a constant temperature; plate lengths, which are “short” and “long” compared with the particle displacement lengths of the acoustic standing waves, are tested. Also investigated are the effects of plate spacing and the amplitude of the standing wave. Results are examined in the form of energy vectors, particle paths, and overall entropy generation rates. These show that a net heat-pumping effect appears only near the edges of thermoacoustic couple plates, within about a particle displacement distance from the ends. A heat-pumping effect can be seen even on the shortest plates tested when the plate spacing exceeds the thermal penetration depth. It is observed that energy dissipation near the plate increases quadratically as the plate spacing is reduced. The results also indicate that there may be a larger scale vortical motion outside the plates which disappears as the plate spacing is reduced.
A model and experimental study of fiber orientation effects on shear wave propagation through composite laminates111(2002); http://dx.doi.org/10.1121/1.1430685View Description Hide Description
The strong elastic anisotropy of the discrete unidirectional plies in a composite laminate interacts sensitively with the polarization direction of a shear ultrasonic wave propagating in the thickness direction. The transmitted shear wave can therefore be used to detect errors in the ply orientation and stacking sequence of a laminate. The sensitivity is particularly high when the polarization directions of the shear wave transmitter and receiver are orthogonal to each other. To understand the interaction between normal-incident shear waves and ply orientations in a laminate, a complete analytical model was developed using local and global transfer matrices. The model predicted the transmitted signal amplitude as a function of polarization angle of the transmitter and time (or frequency) for a given laminate and input signal. To alleviate the experimental problems associated with shear wave coupling, electromagnetic acoustic transducers (EMATs) and metal delay lines were used in the angular scan of the transmitted signal. The EMAT system had the added advantage of being applicable to uncured composite laminates. Experiments were performed on both cured and uncured laminates with common layups for model verification. The sensitivity of the measured shear wave signals to fiber misorientation and stacking sequence errors was also demonstrated.