Introduction: In 1988, the CTH shock physics hydrocode was used to study the formation of the Moon by the impact of a Mars-sized body on the Earth (Fig. 1) [1]. For that simulation, CTH was augmented with a central radial gravitational body force which proved adequate for the relatively short duration of the simulation. More recently, simulations by Canup et al. [2], Canup [3] and Wada et al. [4] have used hydrocodes equipped with self-gravitational force integrators to follow the re-accretion of material after the impact. Canup et al. used an SPH method with an N-Body gravitational interaction whereas Wada et al. used an Eulerian grid formulation with a Fast Fourier convolution method for the gravitational interaction. Both methods have strengths and weaknesses for simulating the Moon formation problem. CTH, with its Eulerian formulation [5], adaptive mesh refinement [6] and a self-gravitational interaction model [7], can capitalize on the strengths of each method and be an excellent tool for looking at the Moon formation problem.

In order to generate new properties of metals exposed to high pressure states, it is desirable to study samples loaded in one-dimensional strain. Previous work to obtain these ideal conditions, involve a technique where the sample was recovered at late times to examine its microstructure. In those experiments, the shock-loading was produced by impacting the sample with a flyer plate. In the present work, we modified the sample recovery assembly and optimized it for ramp wave loading. We describe the 2-D calculations performed with the ALEGRA MHD code that led to improved recovery assembly efficiency. Preliminary comparisons of the simulations with measurements of the sample deformation from an experiment indicate excellent agreement.

The ultimate goal of this research is to understand how the recyclable transmission lines (RTL) fail and break apart following each power generating pulse under inertial-fusion-energy-type loading. Containing and collecting the resulting dust, debris, and shrapnel so that it may be repetitively reprocessed and recycled is an especially important step, among many others, to successfully operating a power plant. In this paper the current and the dynamic pressure pulse along the RTL are simulated with the Micro-Cap network circuit code. These results are used as inputs to the CTH shock physics code that characterizes the debris formation and containment wall impacts. These models were applied to represent different sections of the RTL at two resolutions. The following discussion addresses the full size nested cone RTL for a Z-pinch IFE power plant.

In theory, a shock wave traveling through a material gives rise to a well defined Hugoniot state. However, in practice, the measurement technique used to probe the shocked state imparts on the data a unique set of experimental artifacts which can affect interpretation of this data. Two commonly used methods for acquiring shock wave data, VISAR and inclined‐mirror measurements are examined to determine the effects of the measurement technique on the final Hugoniot determination. Recent plate impact experiments on the ceramic silicon carbide are used to calibrate a one‐dimensional computer model, which is then used to simulate experimental VISAR and inclined mirror data. The results, which highlight potential pitfalls in interpretation of experimental data, will be discussed and solutions to the discrepancies will be proposed. Further, this work is extended to include ceramics that undergo phase transitions.

‡‡ Catastrophic failure of a Reusable Launch Vehicle ( RLV) during launch poses a significant engineering problem in the context of c rew escape. The explosive hazard potential of the RLV changes during the various phases of the launch. The hazard potential in the on-pad environment is characterized by relea se and formation of a gas phase mixture in an oxidizer rich environment, while the hazard d uring the in-flight phase is dominated by the boundary layer and wake flow formed around the vehicle and the interaction with the exhaust gas plume. In order to address more effect ively crew escape in these explosive environments a computational analysis program was undertaken by Lockheed Martin, funded by NASA JSC, with simulations and analyses completed by Southwest Research Institute and Sandia National Laboratories. This p aper presents then the details of the methodology used in this analysis, results of the s tudy, and important conclusions that came out of the study.

While isentropic compression experiment (ICE) techniques have proved useful in deducing the high-pressure compressibility of a wide range of materials, they have encountered difficulties where large-volume phase transitions exist. The present study sought to apply graded-density impactor methods for producing isentropic loading to planar impact experiments to selected such problems. Cerium was chosen due to its 20% compression between 0.7 and 1.0 GPa. A model was constructed based on limited earlier dynamic data, and applied to the design of a suite of experiments. A capability for handling this material was installed. Two experiments were executed using shock/reload techniques with available samples, loading initially to near the gamma-alpha transition, then reloading. As well, two graded-density impactor experiments were conducted with alumina. A method for interpreting ICE data was developed and validated; this uses a wavelet construction for the ramp wave and includes corrections for the ''diffraction'' of wavelets by releases or reloads reflected from the sample/window interface. Alternate methods for constructing graded-density impactors are discussed.

A systematic computational and experimental study is presented on impact generated debris resulting from record-high impact speeds recently achieved on the Sandia three-stage light-gas gun. In these experiments, a target plate of aluminum is impacted by a titanium-alloy flyer plate at speeds ranging from 6.5 to 11 km/s, producing pressures from 1 Mb to over 2.3 Mb, and temperatures as high as 15000 K (>1 eV). The aluminum plate is totally melted at stresses above 1.6 Mb. Upon release, the thermodynamic release isentropes will interact with the vapor dome. The amount of vapor generated in the debris cloud will depend on many factors such as the thickness of the aluminum plate, super-cooling, vaporization kinetics, the distance, and therefore time, over which the impact-generated debris is allowed to expand. To characterize the debris cloud, the velocity history produced by stagnation of the aluminum expansion products against a witness plate is measured using velocity interferometry. X-ray measurements of the debris cloud are also recorded prior to stagnation against an aluminum witness plate. Both radiographs and witness-plate velocity measurements suggest that the vaporization process is both time-dependent and heterogeneous when the material is released from shocked states around 230 GPa. Experiments suggest that the threshold for vaporization kinetics in aluminum should become significant when expanded from shocked states over 230 GPa. Numerical simulations are conducted to compare the measured x-ray radiographs of the debris cloud and the time-resolved experimental interferometer record with calculational results using the 3-D hydrodynamic wavecode, CTH. Results of these experiments and calculations are discussed in this paper.

Equation (1) is a description of the statistical fragment size distribution while Equation (2) provides the fragment size scale parameter for the preceding distribution. In these equations B and C are constants while n(M) is fragment number and M = m1/2 where m is fragment mass. Cylinder shell thickness and inner shell radius are t and d2, respectively. It is seldom noted that Mott himself, both directly and tacitly, refuted the above two relations in later results of the same study. Both theoretical and experimental alternatives were offered in his later efforts which are rich in the depths to which issues governing dynamic fragmentation were pursued. Here we propose an alternative set of relations for the fragmentation of explosively expanding shells, (3)

Understanding the fracture and fragmentation of explosively loaded devices has been the focus of investigations for many years [1,2,3]. Much of the work has concentrated upon understanding the underlying physical mechanisms that govern breakup [4]. The efforts of Grady and Kipp have resulted in the implementation of a numerical fragmentation model in the CTH shock physics code [5,6]. In this model, the average fragment size, S, is given by

In the present study we describe the development of an experimental fracture material property test method specific to dynamic fragmentation. Spherical test samples of the metals of interest are subjected to controlled impulsive stress loads by acceleration to high velocities with a light-gas launcher facility and subsequent normal impact on thin plates. Motion, deformation and fragmentation of the test samples are diagnosed with multiple flash radiography methods. The impact plate materials are selected to be transparent to the x-ray method so that only test metal material is imaged. Through a systematic series of such tests both strain-to-failure and fragmentation resistance properties are determined through this experimental method. Fragmentation property data for several steels, copper, aluminum, tantalum and titanium have been obtained to date. Aspects of the dynamic data have been analyzed with computational methods to achieve a better understanding of the processes leading to failure and fragmentation, and to test an existing computational fragmentation model.

SPH (Smoothed Particle Hydrodynamics) is a gridless Lagrangian technique which is appealing as a possible alternative to numerical techniques currently used to analyze high deformation impulsive loading events. Previously, the SPH algorithm has been subjected to detailed testing and analysis to determine the feasibility of using the coupled finite-element/SPH code PRONTO/SPH for the analysis of various types of underwater explosion problems involving fluid-structure and shock-structure interactions. Here, SPH and Eulerian simulations are used to study the details of underwater bubble collapse, particularly the formation of re-entrant jets during collapse, and the loads generated on nearby structures by the jet and the complete collapse of the bubble. Jet formation is shown to be due simply to the asymmetry caused by nearby structures which disrupt the symmetry of the collapse. However, the load generated by the jet is a minor precursor to the major loads which occur at the time of complete collapse of the bubble.

A causal link between major impact events and global processes would probably require a significant change in the thermal state of the Earth's interior, presumably brought about by coupling of impact energy. One possible mechanism for such energy coupling from the surface to the deep interior would be through focusing due to axial symmetry. Antipodal focusing of surface and body waves from earthquakes is a well-known phenomenon which has previously been exploited by seismologists in studies of the Earth's deep interior. Antipodal focusing from impacts on the Moon, Mercury, and icy satellites has also been invoked by planetary scientists to explain unusual surface features opposite some of the large impact structures on these bodies. For example, 'disrupted' terrains have been observed antipodal to the Caloris impact basis on Mercury and Imbrium Basin on the Moon. Very recently there have been speculations that antipodal focusing of impact energy within the mantle may lead to flood basalt and hotspot activity, but there has not yet been an attempt at a rigorous model. A new hypothesis was proposed and preliminary proof-of-principle tests for the coupling of energy from major impacts to the mantle by axial focusing of seismic waves was performed. Because of the axial symmetry of the explosive source, the phases and amplitudes are dependent only on ray parameter (or takeoff angle) and are independent of azimuthal angle. For a symmetric and homogeneous Earth, all the seismic energy radiated by the impact at a given takeoff angle will be refocused (minus attenuation) on the axis of symmetry, regardless of the number of reflections and refractions it has experienced. Mantle material near the axis of symmetry will experience more strain cycles with much greater amplitude than elsewhere and will therefore experience more irreversible heating. The situation is very different than for a giant earthquake, which in addition to having less energy, has an asymmetric focal mechanism and a larger area. Two independent proof-of-principle approaches were used. The first makes use of seismic simulations, which are being performed with a realistic Earth model to determine the degree of focusing along the axis and to estimate the volume of material, if any, that experiences significant irreversible heating. The second involves two-dimensional hydrodynamic code simulations to determine the stress history, internal energy, and temperature rise as a function of radius along the axis.