Showing papers on "Shock (mechanics) published in 1968"

Simulated earthquake motions

Abstract: Simulated earthquake motions suitable for design calculations are generated with the aid of a digital computer. The artificial accelerograms are sections of a random process with a prescribed power spectral density, multiplied by envelope functions chosen to model the changing intensity at the beginning and end of real accelerograms. Two each of four different types of acce lerograms have been generated to represent ground acceleration for a variety of earthquakes. Type A models the acceleration in a Magnitude 8 shock and type B the motion expected in a Magnitude 7 earthquake. The shaking expected in the epicentral area of a Magnitude 5 or 6 earthquake is modeled by type C and the motion close to the fault in a shallow Magnitude 4 or 5 shock is represented by type D. The two records of each type were generated to serve as the two horizontal components of earthquake shaking, or as two independent samples of possible ground shaking in the same type of event. Included in the report are accelerograms and derived velocity and displacement curves as well as response spectra.

Statistical measurements of deformation structures and refractive indices in experimentally shock loaded quartz

Abstract: Statistical measurements of deformation structures and refractive indices in experimentally shock loaded quartz specimens with different crystallographic orientations

Prompt gamma rays and X rays from supernovae

Abstract: The hydrodynamic origin of cosmic rays (Colgate and Johnson 1960) depends upon the shock ejection of the outer layers of the supernova. The increase in energy of the shock to c2 per gram occurs relatively deep within the star where the fraction, F, of mass external to this layer is 10−4. The relativistic shock wave continues to increase in strength in the decreasing density of the envelope. When the shock "breaks through" the surface denned as one Compton scattering mean free path at radius R, then the energy factor . The temperature in the proper frame of the shock is determined by the condition aT4 = 2γs2ρ0, where ρ0 is the initial rest density ahead of the shock. For a typical presupernova star, , and polytrope of index 3, the temperature becomes (1.7–2) × 105 eV at the surface layer. Photons emitted from the moving surface layer will be Doppler-shifted from their mean proper frame value of 3kT to a final energy .Photons originating in, and emitted from, the surface layer before the layer expands adiab...

Experimental studies on the lip shock.

Abstract: Lip shock from separation edge of half angle wedge and resultant static pressure recovery distribution along wake

On the Shock Wave Velocity and Impact Pressure in High-Speed Liquid-Solid Impact

Abstract: Shock wave velocity and pressure in high speed liquid-solid impact based on particle velocity

Intermediate Strength Blast Wave

Abstract: Equations for the trajectory and overpressure of the shock front of the intermediate strength blast wave (10 < Δp/p0 ⪝ 0.02) are developed for spherical, cylindrical, and plane blasts. These equations are based on the correct limit method that provided the trajectory of the blast wave from the inverse pinch to velocities below Mach number 1.16 (Δp/p0 = 0.4). The correct limit equations are an extension of the strong shock similarity solution of G. I. Taylor for the spherical blast and A. Sakurai and S. C. Lin for the cylindrical case. It is now possible, given the energy and ambient gas conditions, to trace the shock front trajectory and overpressure from the very strong through the very weak regimes. Conversely, the shock wave energy can be found from measurement of overpressure or arrival time. Comparisons with experimental data as well as the calculations of H. L. Brode verify the validity of the correct limit equations.

Shock wave from a lightning discharge

Abstract: A theoretical model of the shock wave from a lightning discharge ranging from the strong blast wave region out to the acoustic limit is given for the first time. The trajectory and overpressure of the strong shock wave are described by the well-known equations for cylindrical blast waves. In the intermediate shock strength region (1.1 < M < 3.3), the shock trajectory is given by the ‘correct limit’ equation of Vlases and Jones. We derive an additional ‘correct limit’ equation for overpressure that is valid out to the acoustic limit. The correct limit equations predict a much slower decay of the intermediate shock wave; thus, the shock wave is much stronger at large distances from the discharge than was previously believed. Consequently, the range of action of the lightning discharge via its shock wave, as it affects the shattering and freezing of supercooled hydrometeors, may be large.

Emission of plasma waves by the Earth's bow shock

Abstract: A general technique is given for calculating the spectrum of plasma waves emitted upstream and downstream by a turbulent shock transition for a plane shock of arbitrary structure. The problem of identifying the waves of frequency ∼1 cps that sometimes appear to emanate from the earth's bow shock is discussed.

Turbulent boundary-layer separation ahead of cylinders.

Abstract: A cylindrical protuberance mounted on a flat plate will cause the plate boundary layer to separate if the cylinder is long compared to the boundary-layer height. Tests made at M = 4.9 using an oil-flow technique are employed to determine the upstream extent of cylinder influence on a turbulent boundary layer. The results are found to be in reasonable agreement with data from other investigators for a wide range of flow conditions. A method is given for determining the angle of the oblique shock wave caused by separation. This permits calculation of the location of the triple point of the lambda shock pattern that characterizes the flow. An approximate method of calculating the peak value of the cylinder stagnation pressure and the location of the peak is also presented.

Shock deformation of polycrystalline aluminium

Abstract: The deformation microstructures associated with aluminium after shock loading and cold rolling at room temperature and at liquid nitrogen temperature are presented and discussed. A high density of point defects is produced by shock loading aluminium and it is observed that vacancy-produced dislocation loops are more numerous than those produced by interstitial clustering. Comparison is made with the response of copper and nickel to shock and it is shown that aluminium does not form dislocation cell structures as these metals do under similar loading conditions. The temperature of deformation has little effect on the microstructure in the low pressure range, but as pressure increases the temperature of deformation becomes more important. Mechanisms for the production of defects are discussed.

Interaction of the solar wind with the moon and formation of a lunar limb shock wave

Abstract: The interaction of the solar wind with a two-layered moon is considered from the point of view of the induction generator model of Sonett and Colburn (1967). We show that a highly conducting lunar core, shielded by a thin insulating outer layer, cannot reasonably be consistent with the observed absence of a lunar bow shock, since a 10-meter thick surface dust layer would require a conductivity less than 10−10 mho/m, while a 10-kilometer thick layer would require a conductivity less than 10−7 mho/m to shield the core; conductivities in this low range do not seem reasonable. We thus establish an upper limit of 10−5 mho/m for the core conductivity, but point out that this figure can be consistent with the existence of a highly conducting surface layer. Two mechanisms are suggested for the formation of a lunar limb shock wave. It is shown that in the steady-state unipolar generator model a limb shock will be expected to form in the vicinity of the plane defined by the solar wind velocity and magnetic field directions, while a limb shock may be expected to form also in the nonsteady state if the moon possesses a conducting outer layer (10−4 < σ < 10−3 mho/m) of thickness between one-tenth and several kilometers.

Hugoniot Equation of State Measurements for Eleven Materials to Five Megabars

Abstract: : An experimental technique is utilized in which a light-gas gun is used to launch flat impactor plates to high velocities (approximately 8 km/sec) at specimens suspended at the muzzle of the gun. Impact-induced shock waves at pressures to approximately 5 megabars are recorded and are used to determine the shock state in the specimen. The ability to launch unshocked, stress-free flat plates over a wide and continuous velocity range, coupled with the ability to launch impactor plates of the same material as the target, results in hugoniot measurements of relatively high precision. Measurements were made on Fansteel-77 (a tungsten alloy), aluminum (2024-T4), copper (OFHC, 99.99%), nickel (99.95%), stainless steel (type 304), titanium (99.99%), magnesium (AZ31B), beryllium (S- 200 and I-400), uranium (depleted), plexiglas, and quartz phenolic. The results are compared with those of other researchers. Deviation from linear shock velocity - particle velocity was found in aluminum beginning at approximately 1. 0 megabars, probably attributable to melting in the shock front.

An investigation of the reflected shock interaction process in a shock tube.

Abstract: Following the first interaction between the reflected shock from the end wall and the advancing contact surface in a shock tube, cold gas has been observed at the end plate at a time much earlier than that predicted on the basis of simple shock tube theory. Investigation of the nature of this cold gas has been made by an infra-red absorption technique. The driver gas hydrogen is "tagged" with a small quantity of infrared active gas, and shocks are driven with this gas mixture into an infrared inactive test gas. The time of arrival of driver gas at the end plate is measured from the absorption records and calculations based on a modification of the shock bifurcation model agree substantially with these experimental results. Use is also made of an infrared absorption/emission technique to determine the temperature of the infrared source.

Shock absorbing mat

Abstract: A SHOCK-ABSORBING MAT IN WHICH A COVER IS FILLED WITH A MIXTURE OF SMALL PIECES OF FLEXIBLE ELASTOMERIC FOAM MATERIAL, SUCH AS LATEX OR URETHANE, AND SEMI-RIGID PLASTIC FOAM MATERIAL, SUCH AS EXPANDED STYRENE OR URETHANE.

Experimental and theoretical study of the stability of plane shock waves reflected normally from perturbed flat walls

Abstract: The rate of damping of perturbations on a shock wave reflected from a perturbed flat wall was measured in a shock tube. Incident shock wave Mach numbers of 1·45 and 1·09 in air together with sinusoidal and Gaussian wall perturbations were employed. These measurements were compared with a modified form of a linearized theory due to Zaidel (1960). The linearization was performed about the basic solution of a plane shock wave reflected normally from a flat wall.The rate of decay and the frequency and phase of oscillations agreed very well with the theoretical predictions; the amplitudes of the oscillations were some-what larger than predicted. The reflected shock shape was initially in good agreement with theory, but higher frequency perturbations on the reflected shock front caused deviations from the predicted shape after the shock front had travelled about one wall-wavelength away from the wall.The generally satisfactory agreement between theory and experiment supports the use of linearized analysis in predicting shock wave stability.

Shock Compression of Porous Iron in the Region of Incomplete Compaction

Abstract: Shock loading of 4.44 and 5.32 g/cm3 pressed iron powder has been performed in the pressure region of incomplete compaction to solid density. Quartz gauges mounted in gas gun projectiles provided pressure‐particle‐velocity measurements at the impacted interface and standard quartz gauge instrumentation was used to record the transmitted waveform. Shock velocities were determined, from which pressure‐particle‐velocity states at the impact interface were estimated by the use of the Rankine‐Hugoniot equations. These states compared favorably with the same states obtained from the projectile quartz gauges. Severe attenuation of the constant‐velocity shock front, along with an anomalous behavior of the precursor wave, which did not immediately separate from the main shock, suggest that loading‐rate‐dependent processes are important for this porous material.

Technique for Accurate Measurement of the Electrical Conductivity of Shocked Fluids

Abstract: A method of accurately measuring the electrical conductivity of shock compressed fluids is described. It is shown that when optimum geometry is used and when the shock impedance of fluid and electrodes are properly taken into account, the effect of reflected shocks can be understood. Data for carbon tetrachloride over a pressure range of 65 to 160 kilobars and a conductivity range of 10−1 to 10−7 mho/cm are presented. The accuracy of the measurements is better than 10%.

Molding retainer clip

Abstract: A CLIP FOR RETAINING METAL AND OTHER MOLDINGS ON VEHICLES AND OTHER SURFACES WHICH IS SELF-ADHERING, RESISTS DISLODGMENT DUE TO VIBRATION, SHOCK, AND THE LIKE, AND OBVIATES THE NEED TO PUNCTURE OR OTHERWISE PROVIDE APERTURES IN THE SURFACE FOR THE FASTENERS OR HOLDERS WHICH RETAIN THE MOLDING IN PLACE.

Ionizing Shock Structure in a Monatomic Gas

Abstract: The structure of an ionizing shock front in a monatomic gas is described. Both atom‐atom and electron‐atom collisional ionization are considered. The ionization rates for either of these processes is assumed to be controlled by the rate of excitation from the ground state to the first excited level. In the front part of the shock, called the atom‐atom shock, atom collisional dissipative mechanisms (viscosity and thermal conductivity) determine the shock structure. A bimodal Mott‐Smith velocity distribution function is assumed for the atoms in this region, which has a thickness of the order of the atom‐atom viscosity mean free path. In the rear part of the shock front, called the relaxation zone, the collisional ionization processes determine the structure. For this region, which has a thickness proportional to the electron‐atom ionization mean free path, Maxwellian velocity distributions are assumed for the electrons, ions, and atoms. It was found that for Mach numbers of 30 or more the atom‐atom shock is...

Radiative transport in inviscid nonadiabatic stagnation-region shock layers.

Abstract: Radiative transport due to continua, molecular bands and atomic lines in inviscid nonadiabatic shock layer in stagnation region of blunt bodies

Acoustic Radiation from a Finite Line Source with N-Wave Excitation

Abstract: A shock wave with an N‐shaped pressure profile is propagated in the equatorial plane of a weak spark in air. In the present work, the directional dependence of the acoustic waveform is examined for 0.5‐ and 1.0‐cm sparks having discharge energies between 0.01 and 0.1 J. The transient signals are detected with a wide‐band capacitor microphone that has a rise time of less than 1 μsec. As the spark axis is approached, an interval with no acoustic disturbance appears near the center of the waveform. The angular dependence of both the shock amplitude and the length of this central interval is found to be in qualitative agreement with the results of a linear analysis in which it is assumed that each point along the spark acts as a source of N waves.

The propagation upward of the shock wave from a strong explosion in the atmosphere

Abstract: A method is established for the calculation of the trajectories of shocks moving upward in the atmosphere, on the basis of the assumption that they are of the self-propagating type. The results of calculations for self-similar motions are given, and these are used to establish a propagation law based upon the concepts of the Chisnell, Chester and Whitham (CCW) approximation. This propagation law enters a characteristics law based upon that proposed by Whitham, but reformulated for the computation of axisymmetric shocks with varying density.An asymptotic self-preserving shock shape is investigated, and is computed for the case γ = 1·4. A parabolic approximation scheme suggested by the self-preserving solution is developed, in which the solution near the axis is reduced to the solution of a system of ordinary differential equations. Finally, the governing equation for the general case without axial symmetry (but without winds) is presented.

Shock mitigating spring and detent pedestal

Abstract: A personnel protecting pedestal has two telescoping elements biased apart by a coil spring and held together by a limit stop. A detent prevents telescoping of the elements toward each other until a predetermined shock loading is reached. The force needed to compress the spring is less than the force needed to release the detent, so that upon occurrence of a shock wave, the spring distributes the velocity associated with the shock wave over a period of time longer than the duration of the shock wave, thus reducing the velocity and, therefore, the overall acceleration on the load to be protected.

Shock shielding structure and method

Abstract: A shock shielding structure and method for shielding against shock by the use of inflated envelopes wherein said shielding is capable of functioning at peak reflected shocks of over 2,000 pounds per square inch to reduce the peak transmitted force by 70-90 percent or more. Still further, the shielding invention herein comprises a sheltering method and structure for use against the dangers incident to war and, more specifically, relates to a method or structure for use in shielding persons or equipment against the effects of nuclear explosion, and also toxic or corrosive gases and bacteria.