Ultrasonic velocities have been measured in single phase Bi_1.7 Pb_0.3Sr2CaCu2O8+x and Bi1.7Pb0.3Sr2Ca2O10+x polycrystalline samples. Anomalous changes of both longitudinal and transverse velocities were observed near...Ultrasonic velocities have been measured in single phase Bi_1.7 Pb_0.3Sr2CaCu2O8+x and Bi1.7Pb0.3Sr2Ca2O10+x polycrystalline samples. Anomalous changes of both longitudinal and transverse velocities were observed near 200K, which indicates that some structural phase transitio might occur. The elastic constants of these samples have been determined from the measured ultrasonic velocity data, which are much smaller than those of YBa2 Cu3 O7-y and BaTiO3, manifesting that the interlayer coupling will dramatically decrease when the c - axes of the unit cells of these perovstite-like multilayer ceramics increase. The values of Poisson ratio, however, of those ceramics are very close, implying similar interatomic bonding forces. Corrected to void-free state, the Debye temperature of these materials is estirnated as 270 ±20k. The temperature dependence of Debye temperatures for these materials is also calculated by using the same method and reported for the first time.展开更多
Active ultrasonic monitoring in rock joints and gouge materials has the potential to detect the signatures of shear failure for a wide range of sliding modes,from slow and stable movements to fast and unstable sliding...Active ultrasonic monitoring in rock joints and gouge materials has the potential to detect the signatures of shear failure for a wide range of sliding modes,from slow and stable movements to fast and unstable sliding.While these collected measurements currently are being used to identify the seismic precursors to shear failure in rock joints and gouge materials,the underlying physical processes and contact scale mechanisms that control the changes in ultrasonic wave attributes are still poorly understood.To address this knowledge gap,this paper aims to investigate the relationship between the variations in ultrasonic wave attributes and the underlying particle scale mechanisms during both compression and shearing.Our double direct shear experiments were coupled with ultrasonic wave propagation measurements on granular quartz gouges,in which the gouge layers were sheared under different sliding velocities and constant normal stress conditions.Simultaneously,ultrasonic waveforms were continuously recorded during shearing with a fast data acquisition system and three pairs of ultrasonic wave transducers embedded at the two sides of the gouge layers.Different particle comminution mechanisms were observed from the non-uniform distribution of normal and shear stresses through the changes in ultrasonic transmissivity and scanning electron microscope(SEM)images.Our results show that the signatures of the geometry-and time-dependent variations of the inter-particle contact quality and pore volume changes with sliding velocity and slip accumulation were clearly captured from the variations in the transmitted wave amplitude and the dominant frequency,respectively.In addition,we found that variations in dominant frequency corresponded to dilation and compaction of the granular gouge layer during compression as well as stable and unstable sliding.Our results therefore confirmed that nondestructive acoustic techniques are capable of capturing a variety of micromechanical processes during fault gouge deformation and may prove useful in natural settings.展开更多
Ultrasonic attenuation in liquid hydrogen has been messured with the pulse-echo technique as a function of temperature from 13.84K to 20.50K, at 45MHz . The results indicate that the temperature dependence of ultrason...Ultrasonic attenuation in liquid hydrogen has been messured with the pulse-echo technique as a function of temperature from 13.84K to 20.50K, at 45MHz . The results indicate that the temperature dependence of ultrasonic attenuation in liquid hydrogen is mainly determined by volume viscosity effect. Ultrasonic attenuatin due to volume viscosity is getting more and more with cooling. The ratio between volume viscous coefficient and shear viscous coefficient is from 1.4 to 4.2 within the measured temperature region.展开更多
基金The project is supported by the National Center of ResearchDevelopment on Supperconductivity of China+1 种基金the National Science Foundation of Chinathe Third World Academy of Sciences
文摘Ultrasonic velocities have been measured in single phase Bi_1.7 Pb_0.3Sr2CaCu2O8+x and Bi1.7Pb0.3Sr2Ca2O10+x polycrystalline samples. Anomalous changes of both longitudinal and transverse velocities were observed near 200K, which indicates that some structural phase transitio might occur. The elastic constants of these samples have been determined from the measured ultrasonic velocity data, which are much smaller than those of YBa2 Cu3 O7-y and BaTiO3, manifesting that the interlayer coupling will dramatically decrease when the c - axes of the unit cells of these perovstite-like multilayer ceramics increase. The values of Poisson ratio, however, of those ceramics are very close, implying similar interatomic bonding forces. Corrected to void-free state, the Debye temperature of these materials is estirnated as 270 ±20k. The temperature dependence of Debye temperatures for these materials is also calculated by using the same method and reported for the first time.
基金The authors would like to acknowledge the supports provided by the Southern California Earthquake Center(Grant No.17242)the U.S.Department of Energy(Grant No.DE-SC0019117).
文摘Active ultrasonic monitoring in rock joints and gouge materials has the potential to detect the signatures of shear failure for a wide range of sliding modes,from slow and stable movements to fast and unstable sliding.While these collected measurements currently are being used to identify the seismic precursors to shear failure in rock joints and gouge materials,the underlying physical processes and contact scale mechanisms that control the changes in ultrasonic wave attributes are still poorly understood.To address this knowledge gap,this paper aims to investigate the relationship between the variations in ultrasonic wave attributes and the underlying particle scale mechanisms during both compression and shearing.Our double direct shear experiments were coupled with ultrasonic wave propagation measurements on granular quartz gouges,in which the gouge layers were sheared under different sliding velocities and constant normal stress conditions.Simultaneously,ultrasonic waveforms were continuously recorded during shearing with a fast data acquisition system and three pairs of ultrasonic wave transducers embedded at the two sides of the gouge layers.Different particle comminution mechanisms were observed from the non-uniform distribution of normal and shear stresses through the changes in ultrasonic transmissivity and scanning electron microscope(SEM)images.Our results show that the signatures of the geometry-and time-dependent variations of the inter-particle contact quality and pore volume changes with sliding velocity and slip accumulation were clearly captured from the variations in the transmitted wave amplitude and the dominant frequency,respectively.In addition,we found that variations in dominant frequency corresponded to dilation and compaction of the granular gouge layer during compression as well as stable and unstable sliding.Our results therefore confirmed that nondestructive acoustic techniques are capable of capturing a variety of micromechanical processes during fault gouge deformation and may prove useful in natural settings.
文摘Ultrasonic attenuation in liquid hydrogen has been messured with the pulse-echo technique as a function of temperature from 13.84K to 20.50K, at 45MHz . The results indicate that the temperature dependence of ultrasonic attenuation in liquid hydrogen is mainly determined by volume viscosity effect. Ultrasonic attenuatin due to volume viscosity is getting more and more with cooling. The ratio between volume viscous coefficient and shear viscous coefficient is from 1.4 to 4.2 within the measured temperature region.
