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Compression waves

Similar behaviour occurs when trying to locate voids in concrete cast behind steel plates, e g. the steel liner in nuclear containment walls. Our own experience has shown that in the case of a steel liner (encast at depth 250 mm) the reflected compression waves are dominant regardless of the condition of the concrete behind the plate. [Pg.1002]

A crack in concrete with an air gap thickness of as little as 0.025 mm will hinder significant transmission of seismic compression waves [1]. [Pg.1002]

The echo from a compression wave transmitted by mechanical impact or transducer at the surface will be similtir in both cases. [Pg.1003]

The methods that are based on the reflection of compression waves will generally not give information about the concrete which lies deeper than the most shallow large planar defect (crack or void ). [Pg.1003]

The transmission times can be used to determine the depth to the defects. As yet the use of this kind of testing in concrete is based on the rektilinear propagation of compression waves from the surface. No directional transducers for use on concrete are known to exist. [Pg.1003]

Is the recorded signal a delayed compression wave or the shear wave ... [Pg.1004]

A problem obviously exists in trying to characterise anomalies in concrete due to the limitations of the individual techniques. Even a simple problem such as measurement of concrete thickness can result in misleading data if complementary measurements are not made In Fig. 7 and 8 the results of Impact Echo and SASW on concrete slabs are shown. The lE-result indicates a reflecting boundary at a depth corresponding to a frequency of transient stress wave reflection of 5.2 KHz. This is equivalent to a depth of 530 mm for a compression wave speed (Cp) of 3000 m/s, or 706 mm if Cp = 4000 m/s. Does the reflection come from a crack, void or back-side of a wall, and what is the true Cp ... [Pg.1004]

If ultrasound of a frequency in the approximate range 0.2-10 MHz is passed through a liquid, then longitudinal rarefaction and compression waves break up the liquid surface. If the amplitude of the... [Pg.147]

This frequency is a measure of the vibration rate of the electrons relative to the ions which are considered stationary. Eor tme plasma behavior, plasma frequency, COp, must exceed the particle-coUision rate, This plays a central role in the interactions of electromagnetic waves with plasmas. The frequencies of electron plasma waves depend on the plasma frequency and the thermal electron velocity. They propagate in plasmas because the presence of the plasma oscillation at any one point is communicated to nearby regions by the thermal motion. The frequencies of ion plasma waves, also called ion acoustic or plasma sound waves, depend on the electron and ion temperatures as well as on the ion mass. Both electron and ion waves, ie, electrostatic waves, are longitudinal in nature that is, they consist of compressions and rarefactions (areas of lower density, eg, the area between two compression waves) along the direction of motion. [Pg.107]

To reiterate, the development of these relations, (2.1)-(2.3), expresses conservation of mass, momentum, and energy across a planar shock discontinuity between an initial and a final uniform state. They are frequently called the jump conditions" because the initial values jump to the final values as the idealized shock wave passes by. It should be pointed out that the assumption of a discontinuity was not required to derive them. They are equally valid for any steady compression wave, connecting two uniform states, whose profile does not change with time. It is important to note that the initial and final states achieved through the shock transition must be states of mechanical equilibrium for these relations to be valid. The time required to reach such equilibrium is arbitrary, providing the transition wave is steady. For a more rigorous discussion of steady compression waves, see Courant and Friedrichs (1948). [Pg.11]

The jump conditions must be satisfied by a steady compression wave, but cannot be used by themselves to predict the behavior of a specific material under shock loading. For that, another equation is needed to independently relate pressure (more generally, the normal stress) to the density (or strain). This equation is a property of the material itself, and every material has its own unique description. When the material behind the shock wave is a uniform, equilibrium state, the equation that is used is the material s thermodynamic equation of state. A more general expression, which can include time-dependent and nonequilibrium behavior, is called the constitutive equation. [Pg.12]

In most solids, the sound speed is an increasing function of pressure, and it is that property that causes a compression wave to steepen into a shock. The situation is similar to a shallow water wave, whose velocity increases with depth. As the wave approaches shore, a small wavelet on the trailing, deeper part of the wave moves faster, and eventually overtakes similar disturbances on the front part of the wave. Eventually, the water wave becomes gravitationally unstable and overturns. [Pg.18]

For a shock wave in a solid, the analogous picture is shown schematically in Fig. 2.6(a). Consider a compression wave on which there are two small compressional disturbances, one ahead of the other. The first wavelet moves with respect to its surroundings at the local sound speed of Aj, which depends on the pressure at that point. Since the medium through which it is propagating is moving with respect to stationary coordinates at a particle velocity Uj, the actual speed of the disturbance in the laboratory reference frame is Aj - -Ui- Similarly, the second disturbance advances at fl2 + 2- Thus the second wavelet overtakes the first, since both sound speed and particle velocity increase with pressure. Just as a shallow water wave steepens, so does the shock. Unlike the surf, a shock wave is not subject to gravitational instabilities, so there is no way for it to overturn. [Pg.18]

Figure 2.6. (a) Compression wave steepens to a shock wave in a medium for which stability criteria are satisfied, where the trailing part of the wave overtakes the leading part, (b) Expansion wave broadens as the leading part of the wave outruns the trailing part. [Pg.19]

Throughout this book, a shock pulse (a steady compression wave followed by an expansion wave) will be represented as a profile, such as in Fig. 2.6. In Fig. 2.8 we show a series of P-x snapshots of pressure versus propagation distance x for an initially square pulse, at a series of times t. For a fluid with... [Pg.22]

This result, called the Riemann Integral, can be applied to unsteady isentropic compression waves as well as to expansion waves. By defining a Riemann function ... [Pg.38]

A typical shock-compression wave-profile measurement consists of particle velocity as a function of time at some material point within or on the surface of the sample. These measurements are commonly made by means of laser interferometry as discussed in Chapter 3 of this book. A typical wave profile as a function of position in the sample is shown in Fig. 7.2. Each portion of the wave profile contains information about the microstructure in the form of the product of and v. The decaying elastic wave has been an important source of indirect information on micromechanics of shock-induced plastic deformation. Taylor [9] used measurements of the decaying elastic precursor to determine parameters for polycrystalline Armco iron. He showed that the rate of decay of the elastic precursor in Fig. 7.2 is given by (Appendix)... [Pg.224]

Dynamic tensile failure, called spall, is frequently encountered in shockloading events. Tension is created as compression waves reflect from stress-free surfaces and interact with other unloading waves or release-wave profiles. Spall has been widely studied by authors such as Curran, Ivanov, Dremin, and Davison and there is considerable data. As shown in Fig. 2.19, the wave profiles resulting from spall are characterized by an additional loading pulse after release of pressure. The late pulse is caused by wave reflection from the internal void of the tensile fracture. Analysis of such wave profiles yields appropriate spall stress values. [Pg.45]

Melting, a major physical event, has small, subtle effects on shock-compression wave profiles. The relatively small volume changes and limited mixed-phase regions result in modest, localized changes in loading wave speed. Consequently, shock-induced melting and freezing remains an area with little data and virtually no information on the influence of solid properties and defects on its kinetics. [Pg.46]

The rapid expansion of a vessel s contents after it bursts may produce a blast wave. This expansion causes the first shock wave, which is a strong compression wave... [Pg.184]

When air in a room is disturbed by a person speaking the molecules of the air have movements that are along the path of the wave. If you were to draw a line from the speaker s mouth to your ear, the movement of the molecules would be along this line. This type of wave, called an acoustical wave, is said to be longitudinal. The pleasant sounds of music are produced by acoustical waves. On the other hand, destruction by a bomb blast also is caused by acoustical waves. Instead of oscillating up and down, molecules in the acoustical (or compression) wave bunch together as the wave passes. It is not a transverse wave. [Pg.1221]

The DDT mechanism for this case Is similar but not identical to that of Case B. A convective flame front propagates ahead of the compressive waves which are necessary to form a precursor shock front. In modeling DDT the convective front (and its consequences) must be included because of its influence on dp/dt in the ignition region... [Pg.931]

Mist flow, one component In a one-component system with finely dispersed drops in the mist flow, the mass transfer between phases over a large interfacial area has to be considered. For the compression wave the frozen state can be assumed to be subcooled liquid, superheated vapor conditions generated by the wave are fairly stable, and the expressions for the two-component system are valid (Henry, 1971) ... [Pg.265]

The need for different expressions for compression and rarefaction waves is consistent with the experimental observation of Barclay et al. (1969) that the compression wave travels faster than the rarefaction wave. [Pg.266]

A compression wave of low intensity is well known in ordinary sound waves in the air, or in other media. Sound is propagated with a velocity determined by the following equation ... [Pg.14]


See other pages where Compression waves is mentioned: [Pg.714]    [Pg.19]    [Pg.20]    [Pg.51]    [Pg.272]    [Pg.124]    [Pg.23]    [Pg.254]    [Pg.478]    [Pg.565]    [Pg.579]    [Pg.581]    [Pg.590]    [Pg.612]    [Pg.930]    [Pg.931]    [Pg.932]    [Pg.30]    [Pg.198]    [Pg.203]    [Pg.204]    [Pg.262]    [Pg.16]    [Pg.135]    [Pg.248]   
See also in sourсe #XX -- [ Pg.269 ]

See also in sourсe #XX -- [ Pg.269 ]

See also in sourсe #XX -- [ Pg.273 ]




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Shock wave compression

Uniaxial compression strength versus compressional wave velocity

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