705 Matching Results

Search Results

Advanced search parameters have been applied.

ALE advantage in hypervelocity impact calculations

Description: The ALE3D code is used to model experiments relevant to hypervelocity impact lethality, carried out in the 4-5 km/s velocity range. The code is run in the Eulerian and ALE modes. Zoning in the calculations is refined beyond the level found in most lethality calculations, but still short of convergence. The level of zoning refinement that produces equivalent results in uniformly zoned Eulerian calculations and ALE ones utilizing specialized zoning, weighting and relaxation techniques is established. It takes 11 times fewer zones and about 60% as many cycles when ALE capabilities are used. Calculations are compared to experimental results.
Date: October 1, 1998
Creator: Gerassimenko, M. & Rathkopf, J.
Partner: UNT Libraries Government Documents Department

Comet Shoemaker-Levy 9 fragment size estimates: How big was the parent body?

Description: The impact of Comet Shoemaker-Levy 9 on Jupiter in July, 1994, was the largest, most energetic impact event on a planet ever witnessed. Because it broke up during a close encounter with Jupiter in 1992, it was bright enough to be discovered more than a year prior to impact, allowing the scientific community an unprecedented opportunity to assess the effects such an event would have. Many excellent observations were made from Earth-based telescopes, the Hubble Space Telescope (HST) and the Galileo spacecraft en route to Jupiter. In this paper, these observations are used in conjunction with computational simulations performed with the CTH shock-physics hydrocode to determine the sizes of the fifteen fragments that made discernible impact features on the planet. To do this, CTH was equipped with a radiative ablation model and a post-processing radiative ray-trace capability that enabled light-flux predictions (often called the impact flash) for the viewing geometries of Galileo and ground-based observers. The five events recorded by Galileo were calibrated to give fragment size estimates. Compared against ground-based and HST observations, these estimates were extended using a least-squares analysis to assess the impacts of the remaining ten fragments. Some of the largest impacts (L, G and K) were greater that 1 km in diameter but the density of the fragments was low, about 0.25 g/cm{sup 3}. The volume of the combined fifteen fragments would make a sphere 1.8 km in diameter. Assuming a pre-breakup density of 0.5 g/cm{sup 3}, the parent body of Shoemaker-Levy 9 had a probable diameter of 1.4 km. The total kinetic energy of all the impacts was equivalent to the explosive yield of 300 Gigatons of TNT.
Date: December 1995
Creator: Crawford, D. A.
Partner: UNT Libraries Government Documents Department

Enhanced diffusion in shock activated Be-Al interfaces

Description: Enhanced diffusion of aluminum in shock activated beryllium has been observed. Cylindrical samples of aluminum coated beryllium rods were axisymetrically loaded up to 40 GPa and a total residual strain of up to 6.7%. The defect microstructure produced by both the shock wave and strain enabled the transport of aluminum in beryllium to exceed its equilibrium solid state saturation. This {open_quotes}super saturated{close_quotes} aluminum, upon heating exsolves out at relatively low temperatures and forms very strong interfaces with pressure mated components.
Date: May 1, 1997
Creator: Staudhammer, K.P.
Partner: UNT Libraries Government Documents Department

A Study of the Conservatism of Resonant Shock Test Fixtures

Description: Portions of a series of end-of-life tests are described for a Sandia National Li~boratories- designed space-based sensor that utilizes a mercury-cadmium-telluride focal plane array. Variations in background intensity are consistent with the hypothesis that seasonal variations in solar position cause changes in the pattern of shadows falling across the compartment containing the optical elements, filter-band components, and focal plane array. When the sensor compartment is most fully illuminated by the sun, background intensities are large and their standard deviations tend to be large. During the winter season, when the compartment is most fully shadowed by surrounding structure, backgrounci intensities are small and standard deviations tend to be small. Details in the surrounding structure are speculated to produce transient shadows that complicate background intensifies as a function of time or of sensor position in orbit. KEYwoRDs Noise measurements, background intensity, focal plane array, mercury-cadmium-telluride.
Date: December 3, 1998
Creator: Cap, J.S.
Partner: UNT Libraries Government Documents Department

Numerical simulations of glass impacts using smooth particle hydrodynamics

Description: As part of a program to develop advanced hydrocode design tools, we have implemented a brittle fracture model for glass into the SPHINX smooth particle hydrodynamics code. We have evaluated this model and the code by predicting data from one-dimensional flyer plate impacts into glass. Since fractured glass properties, which are needed in the model, are not available, we did sensitivity studies of these properties, as well as sensitivity studies to determine the number of particles needed in the calculations. The numerical results are in good agreement with the data.
Date: July 1, 1995
Creator: Mandell, D.A. & Wingate, C.A.
Partner: UNT Libraries Government Documents Department


Description: The role of materials strength in changing the shock dynamics in strongly-shocked nonenergetic materials is still a matter of investigation because materials strength properties become convoluted with other materials properties and the shock strength. The regime under consideration here is one in which the material in question is shocked strongly enough to be treated as a fluid, but not strongly enough to be treated as a simple fluid. The present work takes a case-study approach in which two models of the constitutive properties of the complex fluid are applied to shock instability for two different polymeric materials. The intent here is to obtain some measure of the sensitivity of the model predictions to variations in the complex fluid constitutive properties. The linear time-regime in a Richtmyer-Meshkov instability is modeled with the viscosity dependence of Mikaelian and the nonlinear time-regime is modeled with an aerodynamic viscous-drag model. Each combination of materials and models will be examined as a function of shock strength, Atwood number, and variation in materials constitutive properties. Although the these models are NOT the most advanced, they are useful for illustrating orders of magnitude.
Date: January 1, 2001
Creator: Valone, S. M. (Steven M.)
Partner: UNT Libraries Government Documents Department

Pyroshock simulation for satellite components using a tunable resonant fixture - phase 2

Description: Aerospace components are often subjected to pyroshock events during flight and deployment, and must be qualified to this frequently severe environment. Laboratory simulation of pyroshock using a mechanically excited resonant fixture, has gained favor at Sandia for testing small (<8 inch cube) weapon components. With this method, each different shock environment required a different resonant fixture that was designed such that it`s response matched the environment. In Phase 1 (SAND92-2135) of this research, a new test method was developed which eliminated the need to have a different resonant fixture for each test requirement. This was accomplished by means of a tunable resonant fixture that has a response which is adjustable over a wide frequency range. The adjustment of the fixture`s response is done in a simple and deterministic way. This report covers Phase 2 of this research, in which several ideas were explored to extend the Phase 1 results to a larger scale. The test apparatus developed in Phase 1 was capable of testing components with up to a 10 inches x 10 inches base. The goal of the Phase 2 research was to produce an apparatus capable of testing components with up to a 20 inches x 20 inches mounting base. This size capability would allow the testing of most satellite and missile components which frequently consist of large electronic boxes. Several methods to attain this goal were examined, including scaling up the Phase 1 apparatus. Only one of these proved capable of meeting the Phase 2 goals. This report covers all details from concept through fabrication and testing of this Phase 2 apparatus.
Date: April 1, 1997
Creator: Davie, N.T. & Bateman, V.I.
Partner: UNT Libraries Government Documents Department

Shock wave structure in heterogeneous reactive media

Description: Continuum mixture theory and mesoscale modeling are applied to describe the behavior of shock-loaded heterogeneous media. One-dimensional simulations of gas-gun experiments demonstrate that the wave features are well described by mixture theory, including reflected wave behavior and conditions where significant reaction is initiated. Detailed wave fields are resolved in numerical simulations of impact on a lattice of discrete explosive {open_quotes}crystals{close_quotes}. It is shown that rapid distortion first occurs at material contact points; the nature of the dispersive fields includes large amplitude fluctuations of stress over several particle pathlengths. Localization of energy causes {open_quotes}hot-spots{close_quotes} due to shock focusing and plastic work as material flows into interstitial regions.
Date: June 1, 1997
Creator: Baer, M.R.
Partner: UNT Libraries Government Documents Department

Design and analysis of a high-performance shipping container for large payloads

Description: The packaging, designated the H1636A is a high-performing packageing for large payloads. The H1636A is 50 in. in diameter and 113 in. in length and weighs approximately 4600 lb when empty. The design objective was to meet 1996 proposed IAEA Type C criteria for air transport of large quantities of radioactive material (RAM). That is, the package should survive the standard Type B tests and more severe tests such as an impact onto an unyielding target at 280 ft/s and a one-hour jet fuel fire. The packaging consists of a large double-walled stainless steel outer drum filled with uniform density polyurethane foam. A stainless steel containment vessel (CV) with an inside diameter of 23 in. and a length of 78 in. carries the RAM. The CV has a nominal thickness of 0.375 in. and seals with two elastomeric 0-rings. The lid of the CV is joined to the body with a unique closure called a tape joint. The tape joint utilizes interlocking features preloaded with wedges and can withstand significant deformation.
Date: May 1, 1995
Creator: York, A.R. II & Slavin, A.M.
Partner: UNT Libraries Government Documents Department

Impact mitigation using kinematic constraints and the full space parameterization method

Description: A new method for mitigating unexpected impact of a redundant manipulator with an object in its environment is presented. Kinematic constraints are utilized with the recently developed method known as Full Space Parameterization (FSP). System performance criterion and constraints are changed at impact to return the end effector to the point of impact and halt the arm. Since large joint accelerations could occur as the manipulator is halted, joint acceleration bounds are imposed to simulate physical actuator limitations. Simulation results are presented for the case of a simple redundant planar manipulator.
Date: February 1, 1996
Creator: Morgansen, K.A. & Pin, F.G.
Partner: UNT Libraries Government Documents Department

Modeling delamination growth in composites

Description: A method for modeling the initiation and growth of discrete delaminations in shell-like composite structures is presented. The laminate is divided into two or more sublaminates, with each sublaminate modeled with four-noded quadrilateral shell elements. A special, eight-noded hex constraint element connects opposing sublaminate shell elements. It supplies the nodal forces and moments needed to make the two opposing shell elements act as a single shell element until a prescribed failure criterion is satisfied. Once the failure criterion is attained, the connection is broken, creating or growing a discrete delamination. This approach has been implemented in a 3D finite element code. This code uses explicit time integration, and can analyze shell-like structures subjected to large deformations and complex contact conditions. The shell elements can use existing composite material models that include in-plane laminate failure modes. This analysis capability was developed to perform crashworthiness studies of composite structures, and is useful whenever there is a need to estimate peak loads, energy absorption, or the final shape of a highly deformed composite structure. This paper describes the eight-noded hex constraint element used to model the initiation and growth of a delamination, and discusses associated implementation issues. Particular attention is focused on the delamination growth criterion, and it is verified that calculated results do not depend on element size. In addition, results for double cantilever beam and end notched flexure specimens are presented and compared to measured data to assess the ability of the present approach to model a growing delamination.
Date: December 1, 1996
Creator: Reedy, E.D. Jr. & Mello, F.J.
Partner: UNT Libraries Government Documents Department

High velocity impact experiment (HVIE)

Description: The HVIE space project was conceived as a way to measure the absolute EOS for approximately 10 materials at pressures up to {approximately}30 Mb with order-of-magnitude higher accuracy than obtainable in any comparable experiment conducted on earth. The experiment configuration is such that each of the 10 materials interacts with all of the others thereby producing one-hundred independent, simultaneous EOS experiments The materials will be selected to provide critical information to weapons designers, National Ignition Facility target designers and planetary and geophysical scientists. In addition, HVIE will provide important scientific information to other communities, including the Ballistic Missile Defense Organization and the lethality and vulnerability community. The basic HVIE concept is to place two probes in counter rotating, highly elliptical orbits and collide them at high velocity (20 km/s) at 100 km altitude above the earth. The low altitude of the experiment will provide quick debris strip-out of orbit due to atmospheric drag. The preliminary conceptual evaluation of the HVIE has found no show stoppers. The design has been very easy to keep within the lift capabilities of commonly available rides to low earth orbit including the space shuttle. The cost of approximately 69 million dollars for 100 EOS experiment that will yield the much needed high accuracy, absolute measurement data is a bargain!
Date: February 1, 1998
Creator: Toor, A.; Donich, T. & Carter, P.
Partner: UNT Libraries Government Documents Department

Brittle failure kinetics model for concrete

Description: A new constitutive model is proposed for the modeling of penetration and large stress waves in concrete. Rate effects are incorporated explicitly into the damage evolution law, hence the term brittle failure kinetics. The damage variable parameterizes a family of Mohr-Coulomb strength curves. The model, which has been implemented in the CTH code, has been shown to reproduce some distinctive phenomena that occur in penetration of concrete targets. Among these are the sharp spike in deceleration of a rigid penetrator immediately after impact. Another is the size scale effect, which leads to a nonlinear scaling of penetration depth with penetrator size. This paper discusses the theory of the model and some results of an extensive validation effort.
Date: March 1, 1997
Creator: Silling, S.A.
Partner: UNT Libraries Government Documents Department

Impact origin of the Moon

Description: A few years after the Apollo flights to the Moon, it became clear that all of the existing theories on the origin of the Moon would not satisfy the growing body of constraints which appeared with the data gathered by the Apollo flights. About the same time, researchers began to realize that the inner (terrestrial) planets were not born quietly -- all had evidences of impacts on their surfaces. This fact reinforced the idea that the planets had formed by the accumulation of planetesimals. Since the Earth`s moon is unique among the terrestrial planets, a few researchers realized that perhaps the Moon originated in a singular event; an event that was quite probable, but not so probable that one would expect all the terrestrial planets to have a large moon. And thus was born the idea that a giant impact formed the Moon. Impacts would be common in the early solar system; perhaps a really large impact of two almost fully formed planets of disparate sizes would lead to material orbiting the proto-earth, a proto-moon. This idea remained to be tested. Using a relatively new, but robust, method of doing the hydrodynamics of the collision (Smoothed-Particle Hydrodynamics), the author and his colleagues (W. Benz, Univ. of Arizona, and A.G.W. Cameron, Harvard College Obs.) did a large number of collision simulations on a supercomputer. The author found two major scenarios which would result in the formation of the Moon. The first was direct formation; a moon-sized object is boosted into orbit by gravitational torques. The second is when the orbiting material forms a disk, which, with subsequent evolution can form the Moon. In either case the physical and chemical properties of the newly formed Moon would very neatly satisfy the physical and chemical constraints of the current Moon. Also, in both ...
Date: December 31, 1998
Creator: Slattery, W.L.
Partner: UNT Libraries Government Documents Department

The Use of a Beryllium Hopkinson Bar to Characterize In-Axis and Cross-Axis Accelerometer Response in Shock Environments

Description: The characteristics of a piezoresistive accelerometer in shock environments have been studied at Sandia National Laboratories in the Mechanical Shock Laboratory. A beryllium Hopkinson bar capability with diameters of 0.75 in. and 2.0 in has been developed to extend our understanding of the piezoresistive accelerometer, in two mechanical configurations, in the high frequency, high shock environments where measurements are being made. The in-axis performance of the piezoresistive accelerometer determined from measurements with a beryllium Hopkinson bar and a certified laser doppler vibrometer as the reference measurement is presented. The cross-axis performance of the accelerometer subjected to static compression on a beryllium cylinder, static strain on a steel beam, dynamic strain on a steel beam (ISA-RP 37.2, Paragraph 6.6), and compressive shocks in a split beryllium Hopkinson bar configuration is also presented. The performance of the accelerometer in a combined in-axis and cross-axis shock environment is shown for one configuration. Finally, a failure analysis conducted in cooperation with ENDEVCO gives a cause for the occasional unexplained failures that have occurred in some applications.
Date: January 1, 1999
Creator: Bateman, V.I. & Brown, F.A.
Partner: UNT Libraries Government Documents Department

Damage evolution and clustering in shock loaded tantalum

Description: Two grades of tantalum were shock loaded by plate impact and recovered. The loading conditions were varied to study the damage evolution in te materials from incipient to full spallation. The authors performed quantitative image analysis and optical profilometry on the recovered specimens. Statistical analyses are shown of the void sizes, void clustering, and void linking in the two material grades.
Date: December 31, 1998
Creator: Thissell, W.R.; Zurek, A.K.; Rivas, J.M.; Tonks, D.L. & Hixson, R.S.
Partner: UNT Libraries Government Documents Department

Air cushion effect in the short-pulse initiation of explosives

Description: When thin flyer plates are used to shock initiate high explosive (HE), any air present ahead of the flyer may cause a significant desensitization of the HE. The effect of the air in cushioning the impact of plastic flyers faced with metal films is analyzed here with MACRAME, a code which calculates wave interactions and traces wave propagation. The authors find that the second air shock into the HE has sufficient pressure to collapse the HE to crystal density or higher. Precompressed regions of HE do not react rapidly when the main impact pulse does arrive. Define y{sup *} as the depth where the major shock overtakes the precompression wave (for no air y{sup *} {r_arrow} 0). For various flyers and air combinations, the authors compare pressure profiles at y = y{sup *} + {epsilon}. The shock pressure profile associated with metal film impact may be greatly attenuated at the depth y{sup *}. Density profiles (p(t) at y) show that the shock heating for y > y{sup *} is greater than that for y < y{sup *}.
Date: August 1, 1997
Creator: Fritz, J.N. & Kennedy, J.E.
Partner: UNT Libraries Government Documents Department

Showmaker-Levy 9 and plume-forming collisions on Earth

Description: Computational models for the July, 1994 collision of comet Shoemaker-Levy 9 with Jupiter have provided a framework for interpreting the observational data. Imaging, photometry, and spectroscopy data from ground-based, Hubble Space Telescope, and Galileo spacecraft instruments are consistent with phenomena that were dominated by the generation of incandescent fireballs that were ballistically ejected to high altitudes, where they formed plumes that subsequently collapsed over large areas of Jupiter`s atmosphere. Applications of similar computational models to collisions into Earth`s atmosphere show that a very similar sequence of events should take place for NEO impacts with energies as low as 3 megatons, recurring on 100 year timescales or less. This result suggests that the 1908 Tunguska event was a plume-forming atmospheric explosion, and that some of the phenomena associated with it might be related to the ejection and collapse of a high plume. Hazards associated with plume growth and collapse should be included in the evaluation of the impact threat to Earth, and opportunities should be sought for observational validation of atmospheric impact models by exploiting data already being collected from the natural flux of multi-kiloton to megaton sized objects that constantly enter Earth`s atmosphere on annual to decadal timescales.
Date: December 31, 1995
Creator: Boslough, M.B.E. & Crawford, D.A.
Partner: UNT Libraries Government Documents Department