scispace - formally typeset
Search or ask a question

Showing papers on "Shock (mechanics) published in 1971"


Journal ArticleDOI
TL;DR: In this article, the principle of progressive shock metamorphism in nonporous silicate rocks is discussed on the basis of petrographic observations and experimental data, and six stages or zones of increasing pressure and temperature are defined.
Abstract: The principle of progressive shock metamorphism in nonporous silicate rocks is discussed on the basis of petrographic observations and experimental data. The p-T conditions and the nature of the basic types of shock effects observed in rock-forming minerals are considered as far as they are indicative of the degree of shock metamorphism of the source rock. Particular shock effects that are related to the main regimes of the Hugoniot curves of quartz and feldspar, as well as the shock-melting and vaporization behavior of the whole rock, characterize and define six stages or zones of increasing shock metamorphism. Each stage or zone represents a certain range of peak pressure and temperature. Rocks of stage O are shocked to shock states below the Hugoniot elastic limit of quartz and feldspar that are irregularly fractured. Shock stage I is characterized by diaplectic quartz and feldspar that are released from shock states in the ‘two-phase regime’ of the Hugoniot. Diaplectic glass of quartz and/or feldspar composition occurs within stage II, which is related to the lowest part of the ‘high-pressure-phase regime’ of the Hugoniot. Stage III is characterized by selective melting of feldspar minerals at sufficiently high postshock temperature. Postshock temperatures exceeding the liquidus of the whole rock produce rock glasses on pressure and temperature release (stage IV). Stage V is represented by condensation products of shockvaporized rock material. On the basis of experimental data of several authors, the proposed stages of metamorphism are tentatively correlated with a pressure-temperature scale. It is concluded that the proposed classification is generally valid for shock processes in nonporous rocks and can well be applied to the recognition and distinction of the different kinds of impact breccias of terrestrial or extraterrestrial origin.

274 citations


Journal ArticleDOI
TL;DR: In this article, the authors compared the deformation of a granite, a tonalite, and a limestone in a plane shock wave with triaxial deformation at 10−5 sec−1 under the constraint of uniaxial strain.
Abstract: Deformation of a granite, a tonalite, and a limestone in a plane shock wave is compared with triaxial deformation at 10−5 sec−1 under the constraint of uniaxial strain. For granite and for limestone at moderate pressure, the stress-strain relation is nearly identical in the two tests; strain under these conditions was elastically recoverable. For the limestone at high pressure and for the tonalite at all pressures, volume decreases permanently. This permanent deformation, compared here for shock and slow strain-rate tests, had approximately the same strain-rate dependence as has been observed typically in fracture of rocks under triaxial conditions.

139 citations


Journal ArticleDOI
TL;DR: In this paper, the laminar wave-train structure of collisionless magnetic slow shocks is investigated using two-fluid hydromagnetics with ion-cyclotron radius dispersion.
Abstract: The laminar wave-train structure of collisionless magnetic slow shocks is investigated using two-fluid hydromagnetics with ion-cyclotron-radius dispersion. For shock strengths less than the maximally strong switch-off shock, in the shock-leading edge, dispersive steepening forms a magnetic-field gradient, while in the downstream flow dispersive propagation forms a trailing wave train; dispersion scale lengths are the ion inerrial length if β > 1 and the ion cyclotron radius if β > 1. In the switch-off slow-shock leading edge, dispersion only produces rotations of the magnetic-field direction; the gradient of the magnetic-field magnitude, and hence the shock-steepening length, is determined solely by resistive diffusion. The switch-off shock structure consists of a long trailing train of magnetic rotations which are gradually damped by resistivity. The low-6 parallel fast switch-on shock has a similar wave-train structure with the magnitude of the field rotations gradually increasing toward the downstream flow.

95 citations


Journal ArticleDOI
TL;DR: In this article, the authors extended the shock layer theory to axial dispersion and applied it to the nonequilibrium exchange system with a moving coordinate scheme to establish the existence condition and uniqueness of the shock layers.

88 citations


Journal ArticleDOI
TL;DR: In this article, a simple solution for free expansion into a vacuum was found for free supernova explosion, and the propagation of a shock into a medium of decreasing density was determined, and a solution for subsequent flow behind the shock was also obtained.
Abstract: Hydrodynamic equations for one-dimensional motion, of interest in supernova explosions, are integrated in the relativistic limit. A simple solution is found for free expansion into a vacuum. The propagation of a shock into a medium of decreasing density is determined, and the solution for the subsequent flow behind the shock is also obtained.

83 citations



Book
01 Jan 1971
TL;DR: In this paper, a monograph dealing with contemporary approaches to the problem of optimum shock and vibration isolation design is presented, where the authors focus on the selection of isolators that cause an index of the system performance to be optimized; that is, to take on a value either less or greater than that associated with other candidate isolators.
Abstract: : This monograph deals with contemporary approaches to the problem of optimum shock and vibration isolation design. Isolation devices act to reduce the unwanted effects of shock and vibration disturbances on critical elements of a mechanical system. The problem of optimum design has to do with the selection of isolators that cause an index of the system performance to be optimized; that is, to take on a value either less or greater than that associated with other candidate isolators. In addition, the optimum design usually must satisfy constraints which are imposed on other aspects of the system response and the parameters which describe the isolators.

63 citations


Journal ArticleDOI
TL;DR: In this paper, a wavefront folding mechanism was proposed to produce sonic-boom signatures that have a fine structure consisting of many small pressure jumps (microshocks), each jump corresponding to a segment of the folded wavefront.
Abstract: The measured sonic‐boom rise times at ground level are typically of the order of 1–10 msec, which is two to three orders of magnitude larger than what would be predicted on the basis of a planar shock propagating in a homogeneous atmosphere. A tentative explanation of how such anomalous rise times are caused by atmospheric turbulence is given in terms of the Keller‐Friedlander geometrical acoustics theory of weak shock propagation in an inhomogeneous medium. It is suggested that the shockfront initially develops ripples that subsequently are transformed into folds in the front when the shock passes vertices of caustics. This wavefront‐folding mechanism may produce sonic‐boom signatures that have a fine structure consisting of many small pressure jumps (microshocks), each jump corresponding to a segment of the folded wavefront. This fine structure may, however, be smeared out by viscosity. To assess the mechanism's effectiveness quantitatively, a stochastic model of an initially sharp shock propagating thr...

57 citations


Patent
11 Jan 1971
TL;DR: In this paper, a shock absorbing bumper consisting of an impact distribution plate, a core of shock absorbing material, and a backing plate is presented, which is mounted with shock absorbing springs which deflect upon impact.
Abstract: A shock absorbing bumper comprising an impact distribution plate, a core of shock absorbing material, and a backing plate. The impact distribution plate may be made of steel or a rigid plastic and may be on the outer surface of the shock absorbing material or imbedded therein. The shock absorbing core consists of a foamed plastic material such as a polyurethane cellular foam and preferably consists of a high density, tight cell polyurethane foam. Connector pins attach the impact distribution plate slidably into the backing plate so that the impact plate is supported by the backing plate against forces applied substantially parallel to the impact plate but will not directly transmit to the backing plate impact forces applied substantially perpendicularly to the impact plate. The bumper may be mounted with shock absorbing springs which deflect upon impact. The bumper may be formed with a projecting leading edge. Apertures may be provided in the backing plate to permit the escape of compressed gas from the foam.

56 citations


Journal ArticleDOI
TL;DR: In this paper, the authors considered a long earthquake sequence is considered to be a stationary stochastic process, and the stored elastic energy of deformation can be shown to be an independent variable in the usual backward equation.
Abstract: If a long earthquake sequence is considered to be a stationary stochastic process, the stored elastic energy of deformation can be shown to be an independent variable in the usual ‘backward’ equation. Three unknown probability functions are introduced: the probability that the stored energy of deformation is at a certain level; the probability that, if this energy is at a given level, an earthquake will occur; and the transition probability that, if the earthquake occurs, the final energy state will be at a certain level. It is assumed that the frequency-energy distribution is known. The equations can be solved, if the transition probability is assumed to be known; and they have been solved for the model in which the transition probability is a function of the energy released in the shock but is not otherwise dependent on the final energy state. In this case, the results can be used to describe the earthquake history for some time after a great shock, and possibly for times just before a great shock. The results have some features of inconsistency with observations.

53 citations


Journal ArticleDOI
TL;DR: In this paper, an analysis of the motion of small, spherical, noninteracting solid or liquid particles through hypersonic flow fields over spheres and cones is made, based on the density ratio across the shock and a dimensionless ballistic parameter.
Abstract: An analysis is made of the motion of small, spherical, noninteracting solid or liquid particles through hypersonic flowfields over spheres and cones. It is shown that the motion of the particles depends only on the density ratio across the shock and a dimensionless ballistic parameter. Approximate solutions to the particle equations of motion are obtained in closed form in terms of these parameters for two flow configurations, a sharpcone and the stagnation region of a sphere. A technique is derived for the determination of the aerodynamic heating and melting (or vaporization) of the particles as they traverse the shock layer. Results for the particle mass loss as a result of heating are presented for the stagnation region, the more severe heating environment. Existing correlations of experimental data on the breakup of drops due to aerodynamic forces are used to predict the extent of raindrop breakup in the shock layer.

Patent
08 Apr 1971
TL;DR: In this paper, the elastic material is treated with a material having adhesive properties for delaying the return of it into the original position due to its elastic properties after a shock force causing compression of elastic material has ceased, and the inner section lying closer to the object to be protected from the shock is made from a rigid profile and supports the outer section containing the volume-elastic material.
Abstract: Shock absorbing device having an outer and an inner section supported for relative movement with respect to each other in the direction of a shock force, an intermediate section placed into the space formed by the outer and inner sections and comprising a material having volume-elastic properties, the elastic material is treated with a material having adhesive properties for delaying the return of it into the original position due to its elastic properties after a shock force causing compression of the elastic material has ceased, and wherein the outer section comprises an elastic material a portion of which is formed to receive the volume-elastic intermediate section, and the inner section lying closer to the object to be protected from the shock is made from a rigid profile and supports the outer section containing the volume-elastic material.

Journal ArticleDOI
TL;DR: In this paper, a single-encounter model was proposed to explain large enhancements and anisotropies associated with a single elastic collision with the interplanetary shock, but only if the magnetic field and the shock normal are inclined at an angle of ≳85° to each other.
Abstract: In the period May 1967 to May 1968, detailed Vela 4 observations of the properties of protons in the enhancements (‘spikes’) associated with propagating interplanetary shocks show that the proton energy spectrum does not extend beyond ∼5 Mev; the protons often possess unusually large streaming anisotropies (e.g., a pitch-angle anisotropy of >1000∶1 for the February 20, 1968, event), and the peak of the spike can occur as much as 3×105 km (∼10 min) on the sunward side of the shock front. Neither the Axford-Reid nor the Fisk model satisfactorily explains the observations: shock spikes were observed to occur when the interplanetary-field line connecting the interplanetary shock and the observer probably did not intersect the bow shock, contrary to the prediction of the Axford-Reid model; and the prediction of Fisk concerning the shape of the proton energy spectrum at the shock front was not observed at energies above 0.5 Mev. In their published form, neither model can predict an extremely large streaming anisotropy, although a recent extension of Fisk's model may be able to explain anisotropy ratios as large as 10. A single-encounter model, where particles are accelerated in a single elastic collision with the interplanetary shock, is qualitatively examined and can explain large enhancements and anisotropies only if the magnetic field and the shock normal are inclined at an angle of ≳85° to each other.


Journal ArticleDOI
TL;DR: In this paper, the existence of a critical density gradient λ (generally negative) is established: for a compression shock ρ− will increase, decrease, or remain constant according as ρx− is less than, greater than, or equal to λ.
Abstract: A differential equation is derived relating the density ρ− and the density gradient ρx− behind a shock wave when the region ahead of the wave has always been at equilibrium. The existence of a critical density gradient λ (generally negative) is established: For a compression shock ρ− will increase, decrease, or remain constant according as ρx− is less than, greater than, or equal to λ. λ is shown to be related to the critical amplitude for acceleration waves; an experimental procedure for determining λ as a function of ρ− is given.

Journal ArticleDOI
TL;DR: In this article, the authors considered two instability mechanisms which could occur under the conditions found in a perpendicular collisionless shock wave and considered the effect of the voltage jump through the shock, and the density and magnetic field gradients at the shock front.
Abstract: Two instability mechanisms which could occur under the conditions found in a perpendicular collisionless shock wave are considered. Both mechanisms are due to the negative energy character of the electron Bernstein waves propagating in the direction of the current flow in the shock. The effect of the voltage jump through the shock, and the density and magnetic field gradients at the shock front are considered. Both instability mechanisms occur only within a definite band of k values. The first mechanism is due to a resonance between the ion acoustic wave and one of the Bernstein harmonics and the second to resonant ions absorbing energy from a negative energy Bernstein mode. The first case requires Te≫Ti whereas the second case can occur for arbitrary values of the ratio Ti/Te, although the maximum effect occurs when this ratio is of order unity.

Journal ArticleDOI
TL;DR: In this paper, the diffraction of a shock of arbitrary strength by a plane interface separating two different fluids was calculated for the general case, and it was shown that for later times, the shock shape becomes tangent to the interface with decreasing strength there.

Journal ArticleDOI
TL;DR: In this paper, several variations of a simple theory of dynamic compaction of porous solids are presented and discussed, and the theory can be made to reproduce steady-wave profiles observed in the usual plate-impact experiments exactly.
Abstract: In this paper several variations of a simple theory of dynamic compaction of porous solids are presented and discussed. This theory elaborates the conventional theory of shock propagation in such a way that the shock structures observed to propagate in these materials can be described. Steady‐wave profiles are calculated for several compaction models, and the inference of constitutive equations from experimental data is discussed. It is shown that the theory can be made to reproduce steady‐wave profiles observed in the usual plate‐impact experiments exactly.


Journal ArticleDOI
TL;DR: In this article, the method of Laumbach and Probstein is applied to a point explosion in a spheroid with exponential density distribution and it is shown that the shock wave propagates strongly along the direction of symmetry axis and the envelope of the shock front elongates to the same direction.
Abstract: The method of Laumbach and Probstein is applied to a point explosion in a spheroid with exponential density distribution. It is shown that the shock wave propagates strongly along the direction of symmetry axis and the envelope of the shock front elongates to the same direction. The rate of elongation of the shock envelope increases with the eccentricity of the spheroid and finally the blowout of the shock wave along the polar axis occurs when the eccentricity exceeds some critical value. It is suggested that such a blowout of the shock may be connected with some galactic outburst having axial symmetry.

Journal ArticleDOI
TL;DR: Plate excitation by supersonic turbulent and shock boundary layers, measuring wall pressure fluctuation and panel displacement as mentioned in this paper, was used to measure wall pressure fluctuations and panel displacements.


Journal ArticleDOI
08 Mar 1971-Nature
TL;DR: By considering an idealized model of a shock source within a body of material beneath a free surface and examining the stress wave geometry, a theory of the formation of shatter cones was devised.
Abstract: By considering an idealized model of a shock source within a body of material beneath a free surface and examining the stress wave geometry, a theory of the formation of shatter cones is devised.


Journal ArticleDOI
TL;DR: A high performance electric arc driven shock tube for shock velocities up to 45 km/sec and test times over 4 microseconds, using 80/20 helium-hydrogen mixture as discussed by the authors.
Abstract: High performance electric arc driven shock tube for shock velocities to 45 km/sec and test times over 4 microseconds, using 80/20 helium-hydrogen mixture

Patent
19 May 1971
TL;DR: In this paper, an adjustable hydraulic shock absorber having a shock receiving piston is mounted over an axially disposed fluid metering tube, provided with a plurality of metering orifices, and means for adjusting the effective cross sectional areas of the meteringorifices.
Abstract: An adjustable hydraulic shock absorber having a shock receiving piston means telescopically mounted over an axially disposed fluid metering tube means provided with a plurality of metering orifices, and means for adjusting the effective cross sectional areas of the metering orifices.

Patent
07 Oct 1971
TL;DR: A body adapted to absorb energy, especially a shock or force damper, consists of a sponge or foam metal matrix with pores and, preferably, a filler of vermiculite or perlite in an expanded state.
Abstract: A body adapted to absorb energy, especially a shock or force damper, consists of a sponge or foam metal matrix with pores and, preferably, a filler of vermiculite or perlite in an expanded state. The body is predeformed through 5 to 35 percent of its original volume before it is employed as a shock or force damper.

Patent
15 Oct 1971
TL;DR: In this paper, a modified version of the car cushion bumper is presented, in which a plurality of bumper bars are separated by shock absorbing springs, with the outer pair of the bumper bars being separated by air bags for absorbing the shock of collision.
Abstract: An automobile cushion bumper in which an inner bumper bar and an outer bumper bar are separated by a plurality of air bags positioned to absorb the shock of a collision on the outer bumper bar. In a modified form of the invention a plurality of bumper bars are separated by shock absorbing springs with the outer pair of bumper bars being separated by a plurality of air bags for absorbing the shock of collision.

Patent
23 Apr 1971
TL;DR: In this article, a shock mounting and heat coupling system for X-ray spectrometers is described, which provides a shock free mounting and a heat conductive coupling between an assembly and a croystat.
Abstract: A shock mounting and heat coupling system providing shock free mounting and heat conductive coupling between an assembly such as an X-ray spectrometer and a heat reservoir such as a croystat. Heat coupling is provided by a plurality of strands of heat conducting material connected between the heat reservoir and the assembly to provide a flexible inelastic heat pathway. Structural mounting is provided by a flexible, highly damped, low heat conductive shock absorber connected between the assembly and a housing rigidly extending from the heat reservoir. An X-ray spectrometer using the mounting and coupling system is described.