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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

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

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

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

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

EFFECTS OF MATERIALS STRENGTH ON STRONGLY-SHOCKED NONENERGETIC MATERIALS

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

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

Ignition dynamics of high explosives

Description: Mechanical insults of granular high explosives (HE) can result in localized areas of elevated temperature, or hot spots. The evolution of these hot spots is a central issue of HE science. Because of the complexity involved, it is worthwhile to study mechanical and reaction processes in isolation. Mechanical processes are isolated and studied using inert materials or weak insults where reaction may be minimal. Likewise, purely thermal processes can be considered to isolate HE reaction response. In this work the authors study the radiant ignition of various HEs of interest, including HMX (C{sub 4}H{sub 8}N{sub 8}O{sub 8}), PBX 9501 (95% HMX, 2.5% Estane, 2.5% BDNPA/BDNPF), RDX (C{sub 3}H{sub 6}N{sub 6}O{sub 6}), TATB (C{sub 6}H{sub 6}N{sub 6}O{sub 6}), and PBX 9502 (95% TATB, 5% Kel-F) and aged PBX 9502. Initial work has included unconfined samples at ambient pressure in air. Diagnostics have included photodiodes to record first light emission, high speed photography, microthermocouple and IR emission measurement to obtain surface temperature, IR emission of gases above the pellet, and a novel nonlinear optical technique to characterize the dynamic {beta}-{delta} solid phase transformation and the formation of a liquid layer. The authors find that ignition delays at various power levels is very similar for HMX and RDX; except that the minimum radiant flux needed for RDX ignition is higher. The addition of only 5% binder (PBX 9501) causes significantly longer ignition delays at lower heat fluxes compared with HMX alone. TATB and TATB-based explosives exhibit much longer ignition delays than HMX. In contrast to HMX, however, no measurable difference is observed in TATB by the addition of a binder (PBX 9502, aged or pristine).
Date: December 31, 1998
Creator: Ali, A.N.; Son, S.F.; Sander, R.K. & Asay, B.W.
Partner: UNT Libraries Government Documents Department

The shock Hugoniot of glass microballoons

Description: Shock Hugoniot measurements were made on glass microballoons. Input pressures ranging from 0.37-3.9 GPa produced compression from 860-690%. The Hugoniot curves were found to be anomalous in that the density shocked to decreases with increasing pressure.
Date: December 1, 1994
Creator: Simpson, R. & Helm, F.
Partner: UNT Libraries Government Documents Department

Shock initiation of an {epsilon}-CL-20-estane formulation

Description: The shock sensitivity of a pressed solid explosive formulation, LX-19, containing 95.2% by weight epsilon phase 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (HNIW) and 4.8% Estane binder, was determined using the wedge test and embedded manganin pressure gauge techniques. This formulation was shown to be slightly more sensitive than LX-14, which contains 95.5% HMX and 4.5% Estane binder. The measured pressure histories for LX-19 were very similar to those obtained using several HMX-inert binder formulations. An Ignition and Growth reactive model for LX-19 was developed which differed from those for HMX-inert binder formulations only by a 25% higher hot spot growth rate.
Date: July 19, 1995
Creator: Tarver, C.M.; Simpson, R.L. & Urtiew, P.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

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

Ground motion measurements from the demolition of steel towers

Description: Steel towers from a decommissioned heavy water plant were to be demolished. Ground motions due to the proposed felling were estimated in order to assess the structural integrity of neighboring buildings and piping systems. The extraction towers were 125 feet (38.1 m) high in two sizes: 6.5 and 11 feet (1.98 and 3.35 m) inside diameters weighing 215 X 10{sup 3} and 470 X 10{sup 3} lb (956 X 10{sup 3} and 2.1 X 10{sup 6} N). The total potential energy of the tower collapse was about 15 X 10{sup 6} and 32 X 10{sup 6} ft-lb (20.3 X 10{sup 6} and 43.4 X 10{sup 6} Nm) for the small and large towers, respectively. The ground motion predictions were based on a credible theoretical relationship with constants estimated from data available for a different location at the site for dynamic compaction with an energy input an order of magnitude less than that for the towers. Due to the uncertainty of prediction of ground motions a coefficient of variation of 2.0 was used in the structural assessment. Ground motion from the collapse of the extraction towers were monitored by several 3- and 6-components seismographs. Recorded measurements indicated that the ground motion was less than the predicted values. Peak radial motions were approximately equal to the vertical ones. Video tapes of the demolition suggested significant internal energy losses. The measurements suggested that the tower potential energy conversion to dynamic impact energy was about 25 percent. 7 figs.
Date: December 31, 1998
Creator: Joshi, J.R. & Lee, R.C.
Partner: UNT Libraries Government Documents Department

Liner target interaction experiments on Pegasus II

Description: The Los Alamos High Energy Density Physics program uses capacitively driven low voltage, inductive-storage pulse power to implode cylindrical targets for hydrodynamics experiments. Once a precision driver liner was characterized an experimental series characterizing the aluminum target dynamics was performed. The target was developed for shock-induced quasi-particle ejecta experiments including holography. The concept for the Liner shock experiment is that the driver liner is used to impact the target liner which then accelerates toward a collimator with a slit in it. A shock wave is set up in the target liner and as the shock emerges from the back side of the target liner, ejecta are generated. By taking a laser hologram the particle distribution of the ejecta are hoped to be determined. The goal for the second experimental series was to characterize the target dynamics and not to measure and generate the ejecta. Only the results from the third shot, Pegasus II-26 fired April 26th, 1994, from the series is discussed in detail. The second experimental series successfully characterized the target dynamics necessary to move forward towards the planned quasi-ejecta experiments.
Date: September 1, 1995
Creator: Hockaday, M.P.; Chrien, R.E. & Bartsch, R.
Partner: UNT Libraries Government Documents Department

Spall wave-profile and shock-recovery experiments on depleted uranium

Description: Depleted Uranium of two different purity levels has been studied to determine spall strength under shock wave loading. A high purity material with approximately 30 ppm of carbon impurities was shock compressed to two different stress levels, 37 and 53 kbar. The second material studied was uranium with about 300 ppm of carbon impurities. This material was shock loaded to three different final stress level, 37, 53, and 81 kbar. Two experimental techniques were used in this work. First, time-resolved free surface particle velocity measurements were done using a VISAR velocity interferometer. The second experimental technique used was soft recovery of samples after shock loading. These two experimental techniques will be briefly described here and VISAR results will be shown. Results of the spall recovery experiments and subsequent metallurgical analyses are described in another paper in these proceedings.
Date: November 1, 1997
Creator: Hixson, R.S.; Vorthman, J.E.; Gustavsen, R.L.; Zurek, A.K.; Thissell, W.R. & Tonks, D.L.
Partner: UNT Libraries Government Documents Department

Spallation studies on shock loaded uranium

Description: Several spallation experiments have been performed on uranium using gas gun driven normal plate impacts with, VISAR instrumentation and soft recovery. The shock pressures achieved were 81, 53, and 37 kbar. This paper will focus on modeling the free surface particle velocity trace U with of 300 ppm carbon using the 1 d characteristics code CHARADE. The spallation model involves the growth and coalescence of brittle cracks. Metallographical examination of recovered samples and details of the experimental apparatus are discussed in separate papers.
Date: December 1, 1997
Creator: Tonks, D.L.; Hixson, R.; Gustavsen, R.L.; Vorthman, J.E.; Kelly, A.; Zurek, A.K. et al.
Partner: UNT Libraries Government Documents Department

Direct measurement of strain field evolution during dynamic deformation of an energetic material

Description: The authors previously reported results showing displacement fields (at a single instant in time) on the unconfined surface of an explosive during deformation using white light speckle photography. They have now successfully obtained similar data in confined samples showing the evolution in time of the strain field using laser-induced fluorescence speckle photography. A modified data analysis technique using methods borrowed from particle image velocimetry was used in conjunction with an eight frame electronic CCD camera. For these tests, projectiles of varying shape were fired into an explosive sample. Localization of strain was observed in all cases and was found to be a strong function of the projectile shape, with ignition occurring in those cases where shear appears to play a dominant role. Results from this and continuing studies provide experimental evidence for strain localization, and for the first time allow the direct comparison to computer model predictions. The data are also being used in the design of more realistic and reliable constitutive models.
Date: September 1, 1997
Creator: Asay, B.W.; Henson, B.F.; Dickson, P.M.; Fugard, C.S. & Funk, D.J.
Partner: UNT Libraries Government Documents Department