Showing papers on "Shock (mechanics) published in 1973"

Device for the fracture of the blood vessel lining

Abstract: A device for the selective fracture of the inner lining or tunica intima of a blood vessel without severing of the surrounding outer layer or tunica adventitia of the vessel is disclosed. The device comprises a combination of an anvil member having a dull blade affixed thereto which acts as one blade of a guillotine which descends upon the vessel caught between it and a hammer member of the guillotine. The hammer member is spring loaded through connection with a slider arm which extends upward toward the spring and a grip for the fingers of the user. There is provided a guide for the anvil and its blade which guide is aligned and connected with the central rod which extends between the slider arm and the spring which causes impact on the hammer member of the guillotine. The central rod acts as a core for two springs which surrounds the same. The first spring is referred to as a proximal compression spring and the second spring is referred to as distal actuator spring which is located peripherally to the proximal compression spring. The action of the first compression and the release of these two springs causes a shock to extend down the central rod or core into the slider arm and hence into the hammer portion of the guillotine. This shock action follows a first closing of the opening between the anvil and the hammer of the guillotine and is of such controlled momentum that it causes the dull blade of the anvil to fracture the inner layer of the blood vessel without severing the outer muscular layers of the blood vessel.

Shock Wave/Turbulent Boundary-Layer Interactions in Rectangular Channels

Abstract: Interaction regions created by the impingement of full span, externally generated, shock waves on a nozzle wall boundary layer were investigated. Incident shock strength was varied to produce unseparated, incipient, and fully separated flow fields. Significant departures from two-dimensionality were observed over the entire range of shock strengths tested and were identified with sidewall and corner boundary layer effects. However, comparisons of present centerline results with published two-dimensional data, obtained under similar test conditions and geometrical constraints, showed excellent agreement (e.g., incipient separation pressure levels, wall pressure distributions, free-interaction, and scale of the interaction region). This raises some question concerning the degree of two-dimensionality achieved in these previous investigations.

Dynamic fracture criteria for a polycarbonate

Abstract: Flat‐plate impact experiments were performed on polycarbonate specimens to produce various levels of fracture damage. Nucleation and growth functions for incipient shock damage were deduced from the observed damage and from measured and computed stress histories. These functions allow quantitative prediction of the shock damage produced by arbitrary stress histories in polycarbonate.

Variation of the frequency-magnitude relation during earthquake sequences in New Zealand

Abstract: Seven New Zealand earthquake sequences are studied statistically. These comprise six aftershock sequences and one earthquake swarm. The magnitude-stability law of Lomnitz does not hold. During the aftershock sequences the coefficient b , governing the frequency-magnitude relationship, is found to increase rapidly after the main shock, and then to decrease until the occurrence of the largest aftershock, when it again begins to increase. During the earthquake swarm, the coefficient b decreases logarithmically with time. This can be explained in terms of stress changes and is consistent with laboratory studies on rock deformation.

Shock pulse attenuation in a nonlinear viscoelastic solid

Abstract: T hin , one-dimensional shock pulses were generated in a nonlinear viscoelastic material (polymethyl methacrylate) by a new experimental technique. The observed pulse attenuation was compared with an approximate theory based on the viscoelastic shock amplitude equation. The central assumption of this approximate theory is that the unloading wave propagates as a simple wave. Given an initial pulse shape it is shown that the attenuation and the pulse shape at any later time are accurately approximated. The calculated attenuation in polymethyl methacrylate agreed well with the experimental results.

On shock waves in elastic-plastic solids

Abstract: T he behavior of shock waves in an elastic-plastic material is investigated with systematic reference to the theory of shocks in fluids. The classical hydrodynamic theory and the notions of the Hugoniot curve and of the Hugoniot contour are first briefly reviewed. Then, it is shown that continuous adiabatic compression is not isentropic and that, in general, the Hugoniot curve cannot be obtained by the classical rate independent elastic-plastic behavior. Two methods are proposed in order to overcome this difficulty. The second one, which is physically more satisfactory, requires the introduction of rate effects. It is shown that when the shock structure is composed of a purely elastic jump followed by a continuous profile, the Hugoniot curve can be defined independently of the precise formulation of the law for the rate effects.

Noise preventing shock absorber

Abstract: A noise preventing shock absorber adapted for silently absorbing the sound due to noise sources, as when moving machine parts engage mating surfaces and decelerate to zero velocity within a short travel distance or stroke. The shock absorber member includes a unitary resilient member which is dish-shaped in vertical cross section and provided with an axial bore therethrough, with the peripheral surface of the axial bore forming an inner force-transmitting surface. An upper force-receiving means is bonded to the inner force-transmitting surface. The resilient member is provided with a peripheral outer force-transmitting surface concentric with and axially offset downwardly from the inner force-transmitting surface. The resilient member is also provided with an axially inward extended recess on the lower side thereof around the axial bore and within the outer force-transmitting surface. A lower force-receiving means as, for example, an outer tube is bonded to the outer force-transmitting surface. The shock absorber may be used in a stacked arrangement to provide a unit of increased shock absorbing and noise preventing capacity.

Solar wind interaction with the Earth's magnetic field: 3. On the Earth's bow shock structure

Abstract: A classification of earth's bow shock structures on the basis of upstream MA, β, Δ = ∠ Bn (angle between shock normal and magnetic field direction) has been found. Typical properties for each case are studied. In particular, the downstream turbulence present in has been positively correlated with upstream β. It is suggested that the shock precursor, as far as low-frequency waves are concerned, is always due to waves generated upstream and carried by the solar wind. The use of the shock velocity allows estimation of the shock thickness: if MA > 3, the shock is a few ion gyroradii thick.

Dielectric breakdown of shock‐loaded PZT 65/35

Abstract: The dependence of dielectric breakdown in shock‐loaded ferroelectric ceramics on both the shock amplitude and the electric field strength was investigated by employing shock reverberation techniques. In these experiments thick projectile disks were impacted on relatively thin specimens of hot‐pressed PZT 65/35 [Pb0.99Nb0.02(Zr0.65Ti0.35)0.98 O3] poled to 10, 20, and 30 μC/cm2. The principal results of this investigation are: (i) dielectric breakdown is not explicitly a function of stress for stress values in the region of this study (<23 kbar), (ii) breakdown is not instantaneous, (iii) for fields greater than the breakdown threshold (≈5 kV/mm) the time between introduction of the shock into the ferroelectric and onset of breakdown decreases rapidly with increasing electric field, (iv) electric fields generated by 10‐kbar shocks in specimens poled to 30 μC/cm2 are sufficient to cause breakdown, and (v) axial release waves can travel at a velocity as much as 15% faster than the initial stress wave.

Glass breakage detector

Abstract: An alarm for sensing glass breakage having a solid state electronic shock sensor positionable on a sheet of glass and connected through a variable resistance circuit and a threshold detector SCR to a signaling device to detect the breakage of glass. The shock sensor is formed of a number of layers of materials including a piezoelectric material bonded by an electrically conductive epoxy to an electrically conductive sheet of material, such as copper, which in turn is positioned against a layer of epoxy glass, which is joined by a layer of catalyzed epoxy to a plastic case having a layer of adhesive polyurethane formed on the outside. The plastic case is mountable on a sheet of glass and when the glass is broken, the shock waves indicating breakage are transmitted through the layers of materials, which function to attenuate the signals outside the band of shock waves, to the piezoelectric material which generates an electrical signal which is transmitted via the variable resistor circuit to the threshold detector SCR to the signaling device to signal breakage of the glass.

On the structure of the turbulent bow shock

Abstract: A few short bow shock crossings have been studied (Days 44, 53, 255, and 48, 1969). The first three events are shown to be incomplete shock crossings; i.e., the satellite spent a few minutes each time within the shock layer. Large-amplitude waves are observed in |B| with frequency close to Ωi. Proton velocity distribution shows a second peak corresponding to an energy 2–4 times the upstream proton energy. This second peak is observed both with cold solar wind (first part of the shock layer) and with heated solar wind (second part of the shock layer). The possibility of a substructure is discussed. The acceleration of the bow shock is estimated to be ≈5 km/sec².

Bow shock and its interaction with interplanetary shocks

Abstract: Harbingers of significant magnetospheric motions consist of the interactions of interplanetary discontinuities with the standing bow shock. The most common discontinuity is the tangential discontinuity. Less frequent in occurrence, but of major significance to subsequent magnetospheric dynamics, is the flare-generated interplanetary shock wave and its initiation of bow shock and magnetopause motion toward Earth. Early studies utilized the ordinary gas-dynamic analogy of the well-known Riemann splitting of an initial discontinuity (i.e., bow shock) into a reflected shock (the moving bow shock) and the transmitted shock (the inward-moving interplanetary shock). It was shown that order-of-magnitude pressure increases at the subsolar point of the magnetopause are readily found for typical shock-on-shock studies. Phenomenological studies also demonstrated, in agreement with observations, that the magnetopause motion could be predicted on the basis of quasi-static variation of the solar wind dynamic pressure. Recent hydromagnetic studies (for the simplified case of perpendicular shocks) have extended the theory to predict bow shock and magnetopause velocities which appear to be observed by spacecraft. Such one-dimensional studies provide upper limits for all average plasma parameters within the region of the Sun-Earth axis. The general case of the time-dependent interaction in three dimensions has, as yet, not been done. Nevertheless, the general configurational and plasma details are, in principle, amenable to examination with the use of multiple spacecraft measurements during the interaction and the ensuing dynamic motions on a time scale of tens of min to the several hr required for the magnetopause to move to smaller geocentric distances. The physical processes of various energy transfers from kinetic to thermal and magnetic as predicted by the hydromagnetic theory could then be assessed by study of the plasma average velocity, direction of flow, magnetic field, temperature, and density. The magnetosheath plasma properties following such interactions could, on a more speculative note, provide new boundary conditions (associated with appropriate magnetosheath and magnetosphere magnetic field polarities) which could, in turn, initiate and drive the reconnection process within the magnetopause.

Steady shock profile in solids

Abstract: The hydrodynamic equations for a shock wave, propagating in a viscous material, are integrated to obtain an expression for the shock profile under steady conditions. This expression is compared with a similar one reported by other authors, and both are shown to be in reasonable agreement with the available experimental data for shock propagation in aluminum. It is also demonstrated that these expressions for the steady shock profile are different because they are based on different assumptions on the form of the shock‐vs‐particle velocity relationship. It is finally shown that the linear relation used in the present paper is in better agreement with the experimental data on velocities.

Shock attenuation in a ‘gradual’ area expansion

Abstract: The effect of the angle of divergence ϕ, the magnitude of the area ratio A 21 and the specific-heat ratio of the gas γ on the attenuation of a shock in a two-dimensional area expansion has been experimentally determined. The results are compared with current theories relating shock strength and area ratio. At some distance from the expansion the change in shock strength, for shocks with strengths up to 10, is predicted reasonably accurately by an analysis of Chisnell (1957). Close to the area change surprisingly strong shocks were observed. This is shown to result from the diffracted shock undergoing a Mach reflexion at the end of the expansion.

Fluid-dynamic shock ring for controlled flow separation in a rocket engine exhaust nozzle

Abstract: A rocket engine designed for high altitude operation with a large area ratio nozzle, is operated efficiently at sea level through controlled flow separation of the primary gas stream by generating a fluid-dynamic ''''shock ring'''' at a specified area ratio forcing the primary gas stream boundary layer to separate uniformly from the nozzle wall. The fluid-dynamic shock ring is generated by injecting uniformly a gas or liquid of low mass through a multitude of small holes or a circumferential slot extending the full circumference of the nozzle wall.

Shock resisting energy absorbing device

Abstract: A shock resisting energy absorbing device, wherein one or more indenting elements engage and move along an elastomeric member to cause progressive deformation and attendant energy absorption, the indenting elements being backed by a spring in such a manner that should a shock load occur in excess of the normal working load, the energy absorption is increased proportionally resulting in increased resistance to movement.

Shock remagnetization associated with meteorite impact at planetary surfaces

Abstract: The stages of a cratering event are considered together with four distinct magnetization volumes, taking into account the jetted material, the ejecta, the impact melt, and shock-compressed material which remains in situ. Shock classifications are discussed along with mineralogical aspects of shock remagnetization, the behavior of iron sulfides, defect cubic spinels, ilmenite-hematite series, the Fe-Ti-O system, alloys phases, and silicates. Remagnetization mechanisms considered include a first order reversible crystallographic transition in bcc iron-nickel, a second order Curie point transition in fcc iron-nickel, shock-induced anisotropy, and shock melting of iron containing silicates. Experimental results are reported together with a hypothetical crater model.

Numerical solution of viscous reacting blunt body flows of a multicomponent mixture.

Abstract: Hypersonic flow of a chemically nonequilibrium multicomponent mixture past an axisymmetric blunt body is considered on the basis of the exact Navier-Stokes and chemical rate equations. The flowfield, characterized by a sharp shock and a boundary layer, is solved numerically in the region between the shock and the body. The governing equations are first formulated in generalized orthogonal coordinates, and then recast in computational coordinates in which both the shock and the body are two straight lines and one coordinate is stretched to allow higher space resolution near the body. The thermodynamic and transport properties are obtained from the most rigorous theories and reliable data for each component and for the mixture itself. A time-marching second-order finite-difference method is used to solve the equations.

Selectively actuatable shock absorbing system for an implement control circuit

Abstract: Hydraulic control system for holding a work implement in a fixed position, said system including selectively operative shock absorbing means for negating any large force experienced by the implement on contact with an immovable object.

Reynolds Number Effects on the Shock Wave-Turbulent Boundary Layer Interaction at Transonic Speeds.

Abstract: : A Ludwieg tube experiment is described in which the pertinent features of the shock wave-boundary layer interaction on an airfoil are simulated with a two-dimensional flat plate in a supersonic nozzle. The nozzle is modified to impress an airfoil pressure distribution on the flat plate that is typical of a cruising flight condition. A normal shock wave is positioned at a fixed location on the plate, and measurements are made in the vicinity of the shock wave-boundary layer interaction zone.

Calculation of Turbulent Boundary-Layer Shock-Wave Interaction

Abstract: The value of the logarithmic-shock-polar diagram has been illustrated by its use in two examples, one of which could have necessitated the use of iteration, and one which did not. It can be further utilized to evaluate the two types of threeshock-configuration encountered in shock interaction, i.e., weak oblique wave striking a strong shock, and a weak oblique wave striking another oblique wave of the same family. Both of these have the necessary contact discontinuity line, the first in the form of a shear layer, and the second in the form of an expansion wave. The logarithmic-shock-polar family can be used to estimate the results of reflections from shock waves and expansion waves from a solid wall, or from a free shear layer. These represent all the uses of shock interaction at a point necessary to explain any of Edney's six distinct types of shock a) Flow over double wedge. b) "Logarithmic-Shock-Polar" for flow over double wedge.

Second sound in a solid under shock compression

Abstract: The propagation of a strong shock wave in a perfect, three-dimensional crystalline lattice is studied by means of molecular-dynamical calculations The results show that behind the shock front there is a region of thermal relaxation which increases with time The thermally relaxed region, therefore, propagates with a velocity lower than that of the shock front It is believed that the wave-like propagation of this thermally equilibrated region is a natural extension of second sound from the conventional low-temperature, low-pressure regime to the high-temperature, high-pressure regime The implication of this phenomenon on PVT calculations from shock-wave data is discussed briefly

Vehicle cab mounting means

Abstract: A mounting means located at the rear end of a vehicle cab that includes an adjustable air spring arrangement for cushioning vibrations and shock loads transmitted from the vehicle frame to the cab

Effects of dispersion on steady state electromagnetic shock profiles

Abstract: In nonlinear electromagnetic media the various portions of a wave can travel with different velocities, which can result in the formation of electromagnetic shock waves. The structure of such a steady state shock is determined by an equilibrium between the velocity differences that tend to sharpen the shock and the sources of dispersion that cause a broadening of the shock. Several nonlinear transmission line models are examined for the nature and existence of a single-valued steady state shock. In all cases a nonlinear shunt capacitance is assumed. If the dispersion arises from the relaxation behavior caused by a resistance in series with the nonlinear capacitance, a steady shock always exists, its width decreasing as the extent of the nonlinearity generated by the shock increases. If the series resistance is itself shunted by another capacitance, the relaxation process is not manifested at very high frequencies. This system yields a critical condition for the existence of a continuous single-valued steady state wave profile. If the line has too little dispersion the steady state profile is multivalued and therefore physically unrealizable. These dispersion requirements are equivalent to the condition that the velocity of small, high frequency signals ahead of the shock must be greater thathne velocity of the shock itself. It is believed that this condition is a broadly applicable criterion for the existence of a stable, single-valued, steady state wave profile. While this hypothesis is not proved analytically, it is supported here by plausibility arguments and by analysis of another system in which the dispersion is included in the linear series inductance rather than in the nonlinear shunt capacitance.

Structure and luminosity of strong shock waves in air

Abstract: A set of numerical computations of the thermal structure and optical luminosity of strong shock waves in air is described. The model includes radiation transport coupled with hydrodynamics under assumed conditions of steady flow. With shock velocities above 10 km/sec a thermal precursor develops ahead of the shock front, and increases in prominence with increasing shock strength. For velocities above 50 km/sec the precursor is partially opaque to visible light and the computed brightness is smaller than that of a blackbody at the shock temperature. At higher velocities the brightness decreases with increasing shock strength. Steady solutions could not be found for velocities above 80 km/sec.