Showing papers on "Shock (mechanics) published in 1977"
01 Jan 1977
TL;DR: In this article, the authors reviewed the advances in time-resolved shock-wave instrumentation which are currently being used and described the analysis techniques which have been developed to relate shockwave profiles to the thermomechanical processes occurring during shock compression.
Abstract: Recent advances in time-resolved shock-wave instrumentation and improved methods for analyzing continuous stress-wave data are providing a clearer picture of the processes of yielding and phase transformation occurring during shock compression of rocks and minerals. The present report reviews the advances in time-resolved shock-wave instrumentation which are currently being used and describes the analysis techniques which have been developed to relate shock-wave profiles to the thermomechanical processes occurring during shock compression. Evidence for complicating features resulting from yielding in silicates and oxides is reviewed and a physical model for phase transitions based on heterogeneous deformation and thermal activation is discussed. New supporting data on the shock compression and relief properties of periclase and calcite are presented and considered in terms of a mechanism of heterogeneous deformation.
106 citations
TL;DR: The principal Hugoniot of molybdenum has been determined at a pressure of 2.0 TPa by measuring directly both the shock velocity and the particle velocity behind the shock.
Abstract: The principal Hugoniot of molybdenum has been determined at a pressure of 2.0 TPa by measuring directly both the shock velocity and the particle velocity behind the shock. Neutrons from an underground nuclear explosion were used to generate a high‐pressure shock in a slab of molybdenum by rapidly fission heating an adjacent slab of enriched uranium. A shock velocity of 18.2 mm/μs (±5%) was obtained by determining the transit time of the planar shock between two points in the molybdenum separated by 9.87 mm. A particle velocity of 10.7 mm/μs (±5%) was obtained by observing the Doppler shifts of six neutron resonances in the energy region from 200 to 800 eV in the moving shocked molybdenum. The pressure and density derived from this pair of measurements are 2.0 TPa (20 Mbar) and 24.8 g cm−3, respectively. This experiment represents the first direct determination of a point on the Hugoniot of any material in this pressure region, and the resulting data point is in good agreement with theoretical estimates. This measurement was a successful demonstration that the Doppler‐shift technique can be used to obtain particle velocities in this pressure region. It appears that errors in both the shock velocity and the particle velocity can be reduced to approximately ±2% in an improved measurement, resulting in a well‐defined Hugoniot for molybdenum, which can be used as a standard in future impedance‐matching experiments.
83 citations
TL;DR: From a matrix of models of plane-parallel radiating shocks with varying elemental abundances and shock conditions, a set of diagnostic diagrams analogous to those used for many years for H II regions has been computed as discussed by the authors.
Abstract: From a matrix of models of plane-parallel radiating shocks with varying elemental abundances and shock conditions, a set of diagnostic diagrams analogous to those used for many years for H II regions has been computed. This should enable abundances and shock conditions to be calculated for any reasonably evolved optical supernova remnant provided adequate spectrophotometric data are available.
72 citations
Patent•
07 Oct 1977
TL;DR: In this paper, the authors propose to add highly shock absorbent closed cell foamed metal plates to the battery aggregate, and to spacing these in such a way that the impact absorption occurs gradually, so that the deceleration at no point exceeds that of 7 times gravity acceleration.
Abstract: Storage batteries and/or aggregates thereof are constructed to provide a high impact absorbency, so that their mass will serve a dual function: storing electricity and absorbing collision impacts. The collision protection for humans also involves two separate functions: impact absorption and gradual deceleration. The former is achieved by adding highly shock absorbent closed cell foamed metal plates to the battery aggregate, the second by spacing these in such a way that the impact absorption occurs gradually, so that the deceleration at no point exceeds that of 7 times gravity acceleration. To this end the battery aggregate is designed so that the shock energy absorption occurs in many centers or zones of the battery aggregate, thus providing a safe deceleration curve over a distance equal to the distance from leading side to trailing side of the battery aggregates as installed. The liquid electrolyte in the battery cells will contribute to the smooth action, as it is released in case of crushing impact, and then provides hydrostatic uniform pressure on some of the energy absorbing plates during the critical milliseconds, thereby favoring gradual compression as distinct from rupture. The shock absorbent closed cell metal may be used in electrodes or grids of some or all of the cells, or it may be employed as foamed auxiliary plates or inserts without electrogalvanic functions. The invention also contemplates electrically powered vehicles in which the weight of the electric storage aggregates are designed to maximally increase collision protection by specific design criteria.
62 citations
01 Jan 1977
TL;DR: Shatter cones, a form of rock fracture in impact structures, apparently form as a shock front interacts with inhomogeneities or discontinuities in the rock as mentioned in this paper, and it is thought that shatter cones are produced within a limited range of shock pressures extending from about 20 to perhaps 250 kbar.
Abstract: Shatter cone characteristics are surveyed. Shatter cones, a form of rock fracture in impact structures, apparently form as a shock front interacts with inhomogeneities or discontinuities in the rock. Topics discussed include morphology, conditions of formation, shock pressure of formation, and theories of formation. It is thought that shatter cones are produced within a limited range of shock pressures extending from about 20 to perhaps 250 kbar. Apical angles range from less than 70 deg to over 120 deg. Tentative hypotheses concerning the physical process of shock coning are considered. The range in shock pressures which produce shatter cones might correspond to the range in which shock waves decompose into elastic and deformational fronts.
61 citations
Patent•
09 Dec 1977
TL;DR: A foot cushioning device to absorb shock primarily due to heel strike which device is insertable in or may be incorporated in footwear is described in this article, where the body of the device is a heel cup and the primary and secondary shock absorbing members are defined by longer and shorter ribs extending longitudinally and transversely along the outer surface of the heel cup.
Abstract: A foot cushioning device to absorb shock primarily shock due to heel strike which device is insertable in or may be incorporated in footwear. The exterior of the body of the device carries primary shock absorbers extending at least from the portion of the device in the heel area. The primary shock absorber deforms to protect the foot by absorbing initial shock loads. Secondary shock absorbers are also provided which with increased deformation will provide resistance to higher shock load so that a non-linear force displacement behavior similar to that occurring in the natural heel pad occurs. In the preferred embodiment, the body of the device is a heel cup and the primary and secondary shock absorbing members are defined by longer and shorter ribs extending longitudinally and transversely along the outer surface of the heel cup in a grid-like pattern.
61 citations
TL;DR: In this paper, a quasi-parallel bow shock structure was observed with field and particle detectors of both HEOS 1 and OGO 5 and the typical magnetic pulsation structure was at least 1 to 2 earth radii thick radially and was accompanied by irregular but distinct plasma distributions characteristic of neither the solar wind nor the magnetosheath.
Abstract: A thick, quasi-parallel bow shock structure was observed with field and particle detectors of both HEOS 1 and OGO 5. The typical magnetic pulsation structure was at least 1 to 2 earth radii thick radially and was accompanied by irregular but distinct plasma distributions characteristic of neither the solar wind nor the magnetosheath. Waves constituting the large pulsations were polarized principally in the plane of the nominal shock, therefore also in the plane perpendicular to the average interplanetary field. A separate interpulsation regime detected between bursts of large amplitude oscillations was similar to the upstream wave region magnetically, but was characterized by disturbed plasma flux and enhanced noise around the ion plasma frequency. The shock structure appeared to be largely of an oblique, whistler type, probably complicated by counterstreaming high energy protons. Evidence for firehose instability-based structure was weak at best and probably negative.
57 citations
01 Jan 1977
TL;DR: In this paper, the authors introduce a general shock and wear model which can be used to study fatigue loading due to random vibrations, wear in vacuum tubes due to hits by electrons whose energy levels vary stochastically, and quite generally, to study the damage process in situations where individual shocks do not cause any measurable damage, but there are very many shocks during even very small intervals.
Abstract: . Our objective is to introduce a general shock and wear model which extends the available models in several directions. The model can be used to study fatigue loading due to random vibrations, wear in vacuum tubes due to hits by electrons whose energy levels vary stochastically, and quite generally, to study the damage process in situations where individual shocks do not cause any measurable damage, but there are very many shocks during even very small intervals.
42 citations
TL;DR: In this paper, a closed-form analytical "weak shock" solution for the subsequent propagation of such a wave has been obtained, which is in good agreement with the Kirkwood-Bethe theory, existing measurements, and the widely used experimentally based semi-empirical similarity formulas.
Abstract: The initial pressure wave measured at modest distances from an underwater explosion is often modeled as a spherical shock wave with an exponential decay. A closed‐form analytical ’’weak‐shock’’ solution for the subsequent propagation of such a wave has been obtained. The resulting simple formulas for peak pressure and decay constant as function of reduced range allow the prediction of the amplitude and initial slope of the wave given only the amplitude and decay constant of the original exponential shock and the density, sound speed, and parameter of nonlinearity of the water. The results are in good agreement with the Kirkwood–Bethe theory, existing measurements, and the widely used experimentally based semi‐empirical similarity formulas. An expression which gives a close approximation to the shape of the waveform as a function of distance is also derived.
42 citations
TL;DR: In this paper, the authors compare different theories valid in different plasma regimes for the earth's bow shock with different theories in the solar wind, and compare them with the results of a variety of diagnostics, revealing that the bow shock is a permanent feature of solar wind interaction with the earth.
Abstract: A fast mode collisionless bow shock is a permanent feature of the solar wind interaction with the earth. The shock is approximately stationary in earth coordinates, its structure, however, changes in space due to different [MATH] values, and in time, due to different solar wind conditions (Mach number M and β, Te/T1...). The earth's bow shock has revealed itself as an impressive tool for studying collisionless shock waves. After the large theoretical efforts in studying collisionless shock waves, in the past, it is possible, today, to verify experimentally that different dissipation mechanisms are at work in different plasma regimes. The extensive examination of bow shock morphology allow us, today, to correlate distinctions in bow shock structure, revealed by a variety of diagnostics, with M, β and Bn in the solar wind. For quasi parallel geometries and apparently for any M and β, the shock layer broadens and breacks up, showing limited level of plasma wave noise and marked precursor effects. For quasi perpendicular shock waves, on the contrary, electromagnetic turbulence increases with β, almost independent of M ; while electrostatic noise level increase with M, almost independent of β. Comparison with the different theories valid in the different plasma regimes is the present task.
TL;DR: The study reveals that the size, length, and time and place of event occurrence are strongly influenced by the magnitude and degree of homogeneity in the elastic, viscous, and friction parameters of the fault region.
Abstract: In a computer simulation study of earthquakes a seismically active strike slip fault is represented by coupled mechanical blocks which are driven by a moving plate and which slide on a friction surface. Elastic forces and time independent friction are used to generate main shock events, while viscoelastic forces and time dependent friction add aftershock features. The study reveals that the size, length, and time and place of event occurrence are strongly influenced by the magnitude and degree of homogeneity in the elastic, viscous, and friction parameters of the fault region. For example, periodically reoccurring similar events are observed in simulations with near-homogeneous parameters along the fault, whereas seismic gaps are a common feature of simulations employing large variations in the fault parameters. The study also reveals correlations between strain energy release and fault length and average displacement and between main shock and aftershock displacements.
TL;DR: Rochechouart crater is deeply eroded and the present ground level is exactly (± 50m) tangent to the crater floor as mentioned in this paper, which implies restrictions for the late excavation stage: part of the material lying above the crater boundary was never ejected, but only mixed with small relative displacement.
TL;DR: In this paper, a method for obtaining the elastic response of a shell, with internal structure, submerged in an infinite acoustic fluid, to a shock wave is presented. And the structure-fluid interaction is accounted for by means of an approximate relation between the radiated fluid pressure and velocity.
TL;DR: In this article, the authors derived a more precise value for the krypton-krypton collision excitation crosssection, S*Kr-Kr −Kr = 1.2 × 10−19 cm2/eV with or without the addition of hydrogen.
Abstract: At shock Mach numbers in pure krypton, at initial pressures p0 ~ 5 Torr, and final electron number densities ne ~ 1017 cm−3, the translational shock front in a 10 cm × 18 cm hypervelocity shock tube develops sinusoidal instabilities which affect the entire shock structure including the ionization relaxation region, the electron-cascade front and the final quasi-equilibrium state. By adding a small amount of hydrogen (~0.5% of the initial pressure), the entire flow is stabilized. However, the relaxation length for ionization is drastically reduced to about one half of its pure-gas value. Unlike argon the stability appears to diminish with the addition of hydrogen beyond about 0.5%. Using the familiar two-step collisional model coupled with radiation-energy loss and the appropriate chemical reactions, it was possible from dual-wavelength interferometric measurements to deduce a more precise value for the krypton–krypton collision excitation cross-section, S*Kr–Kr = 1.2 × 10−19 cm2/eV, with or without the pr...
01 Jun 1977
TL;DR: In this article, three basic types of shock boundary-layer interaction are discussed: (1) a normal shock wave at transonic speeds, (2) a compression corner shock at supersonic speeds, and (3) an incident oblique shock at hypersonic speeds.
Abstract: Zero-equation (algebraic), one-equation (kinetic energy), and two-equation (kinetic energy plus length scale) turbulence eddy viscosity models were used in computing three basic types of shock-separated boundary-layer flows. The three basic types of shock boundary-layer interaction discussed are: (1) a normal shock wave at transonic speeds, (2) a compression corner shock at supersonic speeds, and (3) an incident oblique shock at hypersonic speeds. The models tested are simple, unmodified models used extensively for incompressible, unseparated flows. A comparison of computed and measured results for the compressible, separated flows described herein indicates that model performance is dependent on flow configuration with no distinct superiority of one model over the other for all three flow configurations.
TL;DR: In this article, the authors compare and contrast the results obtained in a hydrodynamical calculation and in the TDHF calculations of Bonche, Koonin and Negele for the collision of two slabs of nuclear matter.
TL;DR: In this article, a second-order, discontinuity-fitting, finite-difference approach was used to determine the flow field resulting from the interaction of a moving planar shock wave with a compression corner.
Abstract: The unsteady, two-dimensional flowfield resulting from the interaction of a moving planar shock wave with a compression corner is determined using a second-order, discontinuity-fitting, finite-difference approach. The time-dependent Euler equations are transformed to normalize the distance between the body and peripheral shock and to include the existing self-similar property of the flow. The resulting set of partial differential equations in conservation-law form is then solved in a time-dependent fashion using MacCormack's scheme. The vortical singularity, which lies on the body surface, and the single reflected shock are both treated as discontinuities in the numerical procedure. The results of the numerical simulation compare quite favorably with existing experimental interferograms and yield better flowfield resolution than previous first-order, shock-capturing, numerical solutions.
TL;DR: In this article, the authors present a set of devices for affording an indication when a predetermined mechanical shock has been received, characterized by a base, or means for attaching to a container to be monitored, and an indicator for indicating to an observer that the event has occurred.
Abstract: A device for affording an indication when a predetermined mechanical shock has been received, characterized by a base, or means for attaching to a container to be monitored; structure for measuring when a predetermined acceleration has been received by the container and the device; and an indicator for indicating to an observer that the shock has been received. Disclosed are devices having (1) a mechanical structure with a breaking point; (2) a mechanical structure with a biasing means; and (3) a structure employing an interfacial tension phenomenon. The devices may be of the "go-no go" type or may afford an indication and history of the shock, or acceleration forces, received. Also disclosed are the specific details of the respective embodiments.
Dissertation•
01 Dec 1977
TL;DR: An analog system subject to the Poisson Shock is modeled using past performance data and a decision rule is introduced which is based on the criteria of simultaneously maximizing lifetime and minimizing the cost of on-line failures.
Abstract: : An analog system subject to the Poisson Shock is modeled using past performance data. Failure Dynamics of the system is estimated by curve fitting techniques. Algorithms for fault prediction in an on-line maintenance process are described. Several sequential refinement schemes are introduced to improve fault prediction. Some formulas and properties of system's statistics have been developed. A decision rule is introduced which is based on the criteria of simultaneously maximizing lifetime and minimizing the cost of on-line failures. Poisson Shock generator is implemented by computer for simulation of the on-line maintenance process. The computer simulations of a perfect, no measurement errors and identical drifting parameters, system are presented. The simulations of an imperfect system are studied by adding a noise to the system performance data. (Author)
TL;DR: In this paper, the behavior of duralumin and copper under conditions of specimen loading by two successive shock waves and during unloading after the shock compression was studied under the assumption that the amplitude of the first shock wave was 150-250 kbar.
Abstract: The behavior of duralumin and copper is studied under conditions of specimen loading by two successive shock waves and during unloading after the shock compression. The amplitude of the first shock wave was 150–250 kbar. Direct measurements were performed of the difference in main stresses behind the shock front in duralumin. The results obtained do not agree with existing concepts of the behavior of solids under dynamic loading. Possible causes of this divergence are considered.
TL;DR: In this article, the changes in different terms of the Fokker-Planck equation, which describes energetic particle propagation, were analyzed in a theoretical blast wave model, which incorporates the interaction with plane polarized Alfven waves.
Abstract: Energetic particles, ejected from the Sun during solar flare events, may encounter interplanetary plasma/field conditions, which deviate considerably from the quiet time values used normally to describe the particle propagation. This is due to the presence of a hydromagnetic shock, which is emitted from the Sun at the time of the explosion. In a theoretical blast wave model, which incorporates the interaction with plane polarized Alfven waves, we have analysed the changes in different terms of the Fokker-Planck equation, which describes energetic particle propagation. In this treatment, the shock influence on energy changes and on the transport coefficients are discussed.
TL;DR: In this paper, the dynamic response of two layer and three layer viscoelastically damped beams subjected to half sine shock excitation has been carried out and the effects of rotary and longitudinal inertias have been included in the analysis in addition to the effect of transverse inertia.
TL;DR: In this paper, the authors apply the shock-fitting method to transonic small-disturbance equations and demonstrate substantial improvement in accuracy for mesh size in the range of practical interest, the iteration convergence of the shockfitting solutions can also be improved with the use of acceleration algorithms based on the power method; a savings in computer time of a factor of four is demonstrated.
Abstract: Shock-fitting is applied to relaxation solutions of transonic small-disturbance equations. Finite-difference algorithms expressing conservation laws across the discontinuity are introduced in a manner consistent with the type-sensitive difference schemes of Murman and Cole. Results are presented for flows involving embedded as well as bow shocks. Comparison with shock-capturing solutions based on the shock-point operator (SPO) is made for the same grid with comparable computation time. Substantial improvement in accuracy by the shockfitting is demonstrated for mesh size in the range of practical interest, the iteration convergence of shock-fitting solutions can also be improved with the use of acceleration algorithms based on the power method; a savings in computer time of a factor of four is demonstrated.
TL;DR: In this article, an empirical model for predicting the noise from inverted-velocity profile coaxial or coannular jets is presented and compared with small-scale static and simulated flight data.
Abstract: An empirical model for predicting the noise from inverted-velocity-profile coaxial or coannular jets is presented and compared with small-scale static and simulated flight data. The model considered the combined contributions of as many as four uncorrelated constituent sources: the premerged-jet/ambient mixing region, the merged-jet/ambient mixing region, outer-stream shock/turbulence interaction, and inner-stream shock/turbulence interaction. The noise from the merged region occurs at relatively low frequency and is modeled as the contribution of a circular jet at merged conditions and total exhaust area, with the high frequencies attenuated. The noise from the premerged region occurs at high frequency and is modeled as the contribution of an equivalent plug nozzle at outer stream conditions, with the low frequencies attenuated.
Patent•
28 Oct 1977
TL;DR: In this paper, a method of and apparatus for driving piles by the impact force delivered by a hammer disposed in a housing from the bottom end of which there extends downwardly a pile sleeve in which a pile anvil is held captive.
Abstract: A method of and apparatus for driving piles by the impact force delivered by a hammer disposed in a housing from the bottom end of which there extends downwardly a pile sleeve in which a pile anvil is held captive, in which shock absorbing means separate from the hammer are interposed between the bottom end of the housing and the pile anvil for absorbing rebounce forces reaching the top of the pile of lower magnitude to that of the impact force. A pile driving apparatus constructed according to another aspect of the invention comprises a hammer and resilient means in the path of travel of the hammer for transmitting the impact force of the hammer to a pile, and stop means for cutting out the resilient effect of the resilient means on the impact force by delivering a non-resilient blow to the pile.
TL;DR: In this paper, a plastically deformable material is alternately passed over at least two rod members which are fixed to a relatively stationary portion, and the stap is subjected to sucessive plastical deformations by pulling the strap from the rod members to damp a large force suddenly applied to the strap member.
Abstract: A strap of plastically deformable material is alternately passed over at least two rod members which are fixed to a relatively stationary portion. The stap is subjected to sucessive plastical deformations by pulling the strap from the rod members to damp a large force suddenly applied to the strap member.
Patent•
16 Aug 1977
TL;DR: In this article, a falling weight deflectometer is used to transmit shock energy upon its fall to an intermediate weight and to a holder for a pressure plate engaging the ground, where a shock absorber of elastically yieldable material such as shock absorbing rubber is interposed.
Abstract: A falling weight deflectometer operates with a falling weight, transmitting shock energy upon its fall to an intermediate weight and to a holder for a pressure plate engaging the ground. Between the falling weight and the intermediate weight is interposed a shock absorber of elastically yieldable material such as shock absorbing rubber, and a corresponding shock absorber is interposed between the intermediate weight and the holder.