Propagation Velocity Of Elastic Waves Research Articles

Relation Among the Propagation Velcocities of Elastic Waves, the Elastic Modulus and the Saturation of Rock Specimens (No. 2)

It is important for the non-destructive testing carried out the measurement of wave propagation velocities to know the extent of variation of the propagation velocity of elastic waves in porous rocks by changing water content. We had been made an investigation of this problems.In this paper, we showed experimental results of the propagation velocity of elastic waves in rock specimens cured at the four circumstances which are the most easy curing method. They are (1) cooling in a desicator contained silicagel silicagel at room temparature after heating in the drying oven at 100-110°C above 24 hours, (2) drying in desicator contained silicagel to become a constant weight, (3) room dry, and (4) immersing in water during about a month to become a constant weight.On the experiment, the velocity dilatational wave Vpl and the velocity of shear wave Vps were measured by ultrasonic pulse method, and the velocity of longitudinal vibration VRl and the velocity of torsional vibration VRS were measured by resonant frequency method.Summary of this experiment are;(1) The propagation velocity of dilatational waves in racks cured at desicator with silicagel or at room dry measured by pulse method became the minimum, and the velocity increased when rock specimens were more saturated.(2) Velocities of the longitudinal vibration measured by resonant frequency method gradually decreased when rock specimens were saturated from dry state.(3) Both shear wave velocities measured by pulse method and resonant frequency method show a similar tendency of variation of the wave velocity with saturation of rocks.

APPLICATION OF GEOPHYSICAL METHODS FOR STUDYING THE TECHNICAL STATUS OF EARTH DAMS*

AbstractEarth dams are constructed on a wide scale for hydrotechnical and reclamative purposes. However, the great water permeability of soils and their bad gradation are frequently responsible for the development of mechanical suffusion and other phenomena resulting in dam destruction.Geophysical observations allow under certain conditions to forecast the development of adverse factors. They thus are, as practice shows, an important tool to observe the technical status of dams.The difference in propagation velocities of elastic waves in the zone of aeration and full saturation determines the applicability of the reflected wave method for determining the depth of seepage flow in the dam supporting mass. This can be also achieved by electrical sounding and induced polarization methods since the resistivity and polarizability of air‐dry and water‐saturated grounds differ considerably.Maps of equal potentials measured on the dam slope reflect the configuration of the contours of water table of the water flow passing through the dam. This makes it possible to obtain data on the direction and intensity of flow as well as on the presence of heterogeneous grounds filling the dam supporting mass. Besides, regime observations conducted according to the SP method allow to forecast the development of suffusion and observe the redeposition of grounds. If the SP anomalies do not increase with time, the suffusion processes can be regarded as fading out. Enhanced amplitude and increasing areas of anomalies show the intensification of these processes.Combined application of some of the above mentioned methods allowed to obtain many practical results on a number of dams in Transcaucasia and Central Asia. The true position of the depression surface determined in the dam of one of the high‐mountain water reservoirs, for instance, considerably differed from the designed one. The configuration of the seepage flow surface and its fluctuation caused by the rise and drop of the water level in the reservoir have been studied in detail on another dam situated on a plain. The sites of the most intensive outwash of fine material have also been located and the processes of soil redeposition in the dam supporting mass characterized. The data of the geophysical investigations were used to plan hydroinsulation and repair work.

Relations Amony the Propagation Velocities of Elastic Waves, the Elastic Modulus and the Saturation of Rock Specimens (No. 1).

It is important for the non-destructive testing carried out the measurement of wave propagation velocities to know the extent of variation of the propagation velocity of elastic waves in porous rocks by changing water content. We had been made an investigation of this problems.In this paper, we showed experimental results of the propagation velocity of elastic waves in rock specimens cured at the four circumstances which are the most easy curing method. They are (1) cooling in a desicator contained silicagel silicagel at room temparature after heating in the drying oven at 100-110°C above 24 hours, (2) drying in desicator contained silicagel to become a constant weight, (3) room dry, and (4) immersing in water during about a month to become a constant weight.On the experiment, the velocity dilatational wave Vpl and the velocity of shear wave Vps were measured by ultrasonic pulse method, and the velocity of longitudinal vibration VRl and the velocity of torsional vibration VRS were measured by resonant frequency method.Summary of this experiment are;(1) The propagation velocity of dilatational waves in racks cured at desicator with silicagel or at room dry measured by pulse method became the minimum, and the velocity increased when rock specimens were more saturated.(2) Velocities of the longitudinal vibration measured by resonant frequency method gradually decreased when rock specimens were saturated from dry state.(3) Both shear wave velocities measured by pulse method and resonant frequency method show a similar tendency of variation of the wave velocity with saturation of rocks.

Relaxation of dislocations in gold-silver alloys

The dissipation of elastic energy has been measured as a function of temperature in some alloys of the binary sistem Ag-Au, with small atomic percent of Ag. The height of the Bordoni peaks decreases monotonically with increasing atomic percent of Ag. The propagation velocity of the extensional elastic waves, computed from the measurements of the resonant frequency at different temperatures, increases monotonically with increasing concentration of Ag. A comparison has been made with the results obtained byBarducciet al. (1) in a similar series of alloys with small atomic percent of Au. The obtained results can be explained by taking into account the lattice constants of gold and silver and the difference between their ionic diameters in the lattice.

Energy absorbed by elastic waves during impact

The absorption of vibrational energy in the form of elastic waves generated by a transient localized force acting normally to the free surface of a semi-infinite solid is calculated in terms of the Fourier components of the force. The result is applied to tile Hertzian collision of a small body with the plane surface of a massive specimen. It is concluded that for impact velocities small compared with the propagation velocity of elastic waves in the specimen, a negligible proportion of the original kinetic energy of the small body is transferred to the specimen by the collision. The result is of some interest in justifying tlie validity of the Hertz theory for collisions between a small and a massive body. While experimental evidence for the impact of steel ball bearings on massive glass specimens shows some measure of agreement with these theoretical conclusions, results obtained for steel specimens are somewhat at variance, the observed values of the coefficient of restitution (0.90–0.95) indicating absorption of 10 %–20 % of the initial kinetic energy of the ball. A possible explanation of this anomaly is the existence, at the high rates of strain involved in such collisions, of either anelastic or viseous (dissipative) forces in the steel.

Ultrasonic Lenses of Plastic Materials

Propagation velocity and attenuation of elastic waves have been measured in some synthetic materials to determine the most convenient ones for use in ultrasonic lenses. In this respect the most favorable of the different materials tested was polymethylmethacrylate (Plexiglas) which has a velocity of 2100-m sec.−1 for longitudinal waves in rods, and of 2820-m sec.−1 for bulk waves. Its specific acoustic resistance is 3.3×105 g cm−1 sec.−1, and a rather high attenuation has been observed at 8 Mc, which must be considered when designing lenses. From preliminary experiments the most convenient shapes seem to be the plane-cylindrical and plane-spherical ones, the incident waves being parallel to the plane surface. The analytical treatment of such lenses agrees fairly well with their measured behavior. The energy focusing obtained is very important, and the sound power required to get a given energy density in a small region can be reduced ten times with a plane-cylindrical lens, and one hundred times with a plane-spherical one. The common defect of plastic lenses—that is, their solubility in many organic liquids—has been avoided by placing the lens in an envelope which has a mica window for the propagation of waves and is filled with a liquid which does not damage the Plexiglas. The acoustical characteristics of this liquid must be chosen to yield satisfactory energy focusing and good transmission through the double lens structure. Water and carbon disulfide seem to be the most satisfactory for many cases.