Shear wave ultrasonics

The Dow Freeport in-service inspection procedures are similar to those reported earlier in this chapter. The Dow out-of-service (internal) inspection includes ultrasonic thickness measurements at all benchmark locations. Other test methods include shear wave ultrasonics, eddy current, and radiography. Engineers use ultrasonic thickness readings to project the remaining useful life of the vessel and to determine when the next internal inspection should be scheduled. 

Lamellar tearing is generally found in the HAZ of weldments of tee and corner joints. The cause of cracking appears to be inclusions that are parallel to the rolling direction of the plate section being welded. The restraining forces in the welded joint cause the inclusions to open up and run together to form a crack. Set on-type connections welded to heavy sections are particularly susceptible to this type of defect. Where set on-type connections are used, shear-wave ultrasonic inspection of the plate in the area of the attachment and of the completed weld is recommended. 

Figure 1 shows the ultrasonic testing configuration used for detecting OSD. The ultrasonic focused probe is placed at an angle (18.9°) such that OSD are insonified by mode converted 45° shear waves. 

Ultrasonic Properties. Vitreous sihca of high purity, such as the synthetic type, has an unusually low attenuation of high frequency ultrasonic waves. The loss, is a linear function of frequency, up to the 30—40 MHz region and can be expressed a.s A = Bf, where B = 0.26 dB-MHz/m for shear waves and 0.16 dB-MHz/m for compressional waves (168). 

Chou, C.-H., Khuri-Yakub, B. T., and Liang, K. K. (1987). Acoustic microscopy with shear wave transducers. IEEE 1987 Ultrasonics Symposium, pp. 813-16. IEEE, New York. [56, 69]... 

Figure 1. Ultrasonic compression and shear waves generated by the application of a sinusoidal force F(t) to the material.

There are two distinct types of ultrasonic waves the most commonly used in fats characterization are longitudinal waves (Fig. lA) where deformations occur in the direction of propagation of the wave. It is also possible to generate shear waves with deformations normal to the direction of propagation (Fig. IB). Shear waves do not travel macroscopic distances in fluids so it is often impossible to make good measurements in foods. Throughout this work I will exclusively focus on longitudinal waves. 

Perhaps the most important change that has occurred since Qiu et al. s study is in our understanding of seismic velocities at high temperature and seismic periods, (studied by Gribb Cooper (1998, 2000) and Jackson (2000). Before those studies, laboratory measurements of seismic velocities were made at ultrasonic frequencies and the ultrasonic results extrapolated to seismic frequencies. New laboratory experiments made at seismic frequencies strongly suggest that the decrease in shear-wave velocity beneath the seismic lithosphere of the shields results from elevated temperature and is not an indication of the presence of melt (Gribb Cooper 2000). This question is discussed in more detail below. 

NoNaq"). The shear wave transducer for this sample was a 10 MHz lithium niobate transducer bonded with a cyanoacrylate polyester. For the lower density sample both PZT and quartz transducers operating at nominally 3 to 4 MHz were used for both longitudinal and shear wave propagation. They were bonded with either an alcohol-glycerine-based couplent or phenyl salicylate. The detected ultrasonic echoes were rectified and displayed on an oscilloscope equipped with time-delay circuitry for the transit time measurements. 

The ultrasonic longitudinal and shear wave speeds were measured at room temperature for two fully oxidized samples of Ba2YCu307, as described above. From these values and the measured mass density, a longitudinal modulus,, and a shear modulus, Cs, can be calculated from Equation 3. The ordinary isotropic elastic moduli are related to these two moduli by ... 

Cohen-Tenoudji, F., Pardee, W. J., Tittmann, B. R., Ahlberg, L. A., and Elsley, R. K., A Shear Wave Rheology Sensor, IEEE Trans. Ultrason. Ferroelect. Freq. Conf., Vol. UFFC-34(2), 1987, 263. 

Fig. 3.7.1. Experimental arrangement for studying the reflexion of ultrasonic shear waves at a solid-nematic interface.

The viscosity coefficients may also be determined by studying the reflexion of ultrasonic shear waves at a solid-nematic interface. The technique was developed by Martinoty and Candau. A thin film of a nematic liquid crystal is taken on the surface of a fused quartz rod with obliquely cut ends (fig. 3.7.1). A quartz crystal bonded to one of the ends generates a transverse wave. At the solid-nematic interface there is a transmitted wave, which is rapidly attenuated, and a reflected wave which is received at the other end by a second quartz crystal. The reflexion coefficient, obtained by measuring the amplitudes of reflexion with and without the nematic sample, directly yields the effective coefficient of viscosity. 

Due to their high sensitivity to strain, temperature variation, vibration, and acoustic waves, embedded extrinsic Fabry-Perot interferometric optical fiber sensors have been developed to detect delamination, based on changes in the acoustic properties of the materials before and after delamination [41]. Impact events and corrosion cracking generate ultrasonic waves, which can be characterized using elliptical core fiber sensors [40]. The in-line Fabry-Perot interferometer seems well suited for the local detection of shear waves and the characterization of impact-induced damage. 

Figure 14 Ultrasonic shear waves at the interface between two media (r, > i .).

A beam of ultrasonic waves generated by a transducer is directed on to the surface of the polymer which is immersed in a suitable liquid, for example water or silicone oil. Two refracted beams are produced, the higher velocity beam corresponding to a compressional or longitudinal wave, the other to a transverse or shear wave. There is also a reflected... 

Another anomaly in the ultrasonic attenuation of c-axis shear waves has been detected at 95.5 K by the same group (Lee et al. 1975). Applied fields along both a- and c-directions shifted the peak to higher temperatures. Volkov et al. (1974) found an extremum in the a-axis susceptibility (but not in c) together with an anomaly in the Hall resistivity at 93 K. The origin of these effects is not clearly understood, but it is presumably reflected in the magnetization curves (fig. 6.7) as the disappearance, between 95.2 K and 100.2 K, of the transition at Additional neutron diffraction studies extending Koehler s examination beyond 75 K would be helpful here. 

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