Shear wave propagation, experimental

Through the photo-elastic facility, the early stages of the damage pattern were recorded. Fig. 9 shows the experimental fringe pattern and the numerical contour plots of maximum shear stress at about 42 ps after impact. Note the clear shock wave pattern in both cases. This implies that the crack propagates at a velocity above the shear wave speed of the core material Homalite, and is therefore inter-sonic. 

Theoretical analyses predicted the propagation of low-frequency shear waves in both semidilute polymer solutions [49] and dilute colloidal crystals [50]. Different experimental techniques were applied for their detection and for the determination of the shear modules of colloidal samples [51-54]. The dispersion equation of the transverse waves for the low-frequency regime (wavelengths much larger than the interparticle distance) [55]... 

There are three ways of measuring ultrasonic birefringence. To measure stress in an entire specimen, one may measure the time of flight of ultrasonic waves as a function of propagation direction. For smaller sections of sample, shear wave velocities are measured as a function of the orientation of the plane of oscillation of the shear wave. Surface stress can be ultrasonically measured using the velocity of Rayleigh waves as a function of direction. Any of these methods will yield the direction of principle stress and relative stress intensities between samples of identical materials. To find actual values of stress, one must know the value of the acoustoelastic coefficient of the material. An experimental setup for measuring bulk acoustoelastic coefficients has been reported by Koshti. ... 

Another analysis method was based on the local wave vector estimation (LFE) approach applied on a field of coupled harmonic oscillators.39 Propagating media were assumed to be homogeneous and incompressible. MRE images of an agar gel with two different stiffnesses excited at 200 Hz were successfully simulated and compared very well to the experimental data. Shear stiffnesses of 19.5 and 1.2 kPa were found for the two parts of the gel. LFE-derived wave patterns in two dimensions were also calculated on a simulated brain phantom bearing a tumour-like zone and virtually excited at 100-400 Hz. Shear-stiffnesses ranging from 5.8 to 16 kPa were assumed. The tumour was better detected from the reconstructed elasticity images for an input excitation frequency of 0.4 kHz. 

It is worthwhile mentioning that similar experiments were performed earlier by Taylor (1939) and Klebanoff (1971). Klebanoff called this the breathing mode of motion. Apart from the fact that TS waves are not seen experimentally, corresponding two-dimensional linear instability studies also do not reveal the presence of any eigen-solutions (TS waves) that decay with height up to the edge of the shear layer. As observed experimentally, the disturbance field is three-dimensional, but it propagates predominantly in the streamwise direction. 

The response of piezoelectric devices propagating shear horizontal acoustic plate modes (SH-APMs) has been modeled and experimentally characterized for variations in surface mass, liquid rheological properties, and solution dielectric coefficient and electrical conductivity. The nature of the SH-APM and its propagation characteristics are outlined and used to describe a range of Interactions at the solid/liquid interface. Sensitivity to sub-monolayer mass changes is demonstrated and a Cu sensor is described. The APM device is compared to the surface acoustic wave device and the quartz crystal microbalance for liquid sensing applications. 

---