Ilya N. Lomov

Explosion in the Granite Field: Hardening and Softening Behavior in Rocks

Properties of rock materials under quasistatic conditions are well characterized in laboratory experiments. Unfortunately, quasistatic data alone are not sufficient to calibrate models for use to describe inelastic wave propagation associated with conventional and nuclear explosions, or with impact. First, rock properties are size‐dependent. Properties measured using laboratory samples on the order of a few centimeters in size need to be modified to adequately describe wave propagation in a problem on the order of a few hundred meters in size. Second, there is lack of data about the damage (softening) behavior of rock because most laboratory tests focus on the pre‐peak hardening region with very little emphasis on the post‐peak softening region. This paper presents a model for granite that accounts for both the hardening and softening of geologic materials, and also provides a simple description of rubblized rock. The model is shown to reproduce results of quasistatic triaxial experiments as well as peak ...

Dynamic behavior of berea sandstone for dry and water-saturated conditions

Abstract Wave profile measurements have been performed on dry and water-saturated Berea sandstone under shock compression loading conditions using a single-stage light gasgun. The wave motion was monitored with a VISAR velocity interferometer. The impact velocities achieved in the experiment were in the range between 433 m/s and 1013 m/s. Significant differences were observed in the dynamic response of dry and water-saturated Berea sandstone. This work presents the experimental results as well as simulation results obtained using a phenomenological model of Berea sandstone. The model includes effects of compaction, plastic yielding and damage. In the model, the behavior of the water-saturated material was addressed with a modified effective stress model. The simulated wave profiles agree with the experimental data for both dry and water-saturated conditions. This validates the current model and provides a baseline for its further application.

Three Dimensional Simulation of the Baneberry Nuclear Event

Baneberry, a 10‐kiloton nuclear event, was detonated at a depth of 278 m at the Nevada Test Site on December 18, 1970. Shortly after detonation, radioactive gases emanating from the cavity were released into the atmosphere through a shock‐induced fissure near surface ground zero. Extensive geophysical investigations, coupled with a series of 1D and 2D computational studies were used to reconstruct the sequence of events that led to the catastrophic failure. However, the geological profile of the Baneberry site is complex and inherently three‐dimensional, which meant that some geological features had to be simplified or ignored in the 2D simulations. This left open the possibility that features unaccounted for in the 2D simulations could have had an important influence on the eventual containment failure of the Baneberry event. This paper presents results from a high‐fidelity 3D Baneberry simulation based on the most accurate geologic and geophysical data available. The results are compared with available ...

A strength and damage model for rock under dynamic loading

A thermodynamically consistent strength and failure model for granite under dynamic loading has been developed and evaluated. The model agrees with static strength measurements and describes the effects of pressure hardening, bulking, shear-enhanced compaction, porous dilation, tensile failure, and failure under compression due to distortional deformations. This paper briefly describes the model and the sensitivity of the simulated response to variations in the model parameters and in the inelastic deformation processes used in different simulations. Numerical simulations of an underground explosion in granite are used in the sensitivity study.

Simulations of an underground explosion in granite

This paper describes the results of a computational study performed to investigate the behavior of granite under shock wave loading conditions. A thermomechanically consistent constitutive model that includes the effects of bulking, yielding, material damage, and porous compaction on the material response was used in the simulations. The model parameters were determined based on experimental data, and the model was then used in a series of one-dimensional simulations of PILE DRIVER, a deeply-buried explosion in a granite formation at the Nevada Test Site. Particle velocity histories, peak velocity and peak displacement as a function of slant range, and the cavity radius obtained from the code simulations compared favorably with PILE DRIVER data.

Application of schemes on moving grids for numerical simulation of hypervelocity impact problems

Abstract We describe a numerical technique for solving hypervelocity impact problems. Computational method is based on Godunov scheme on moving grid. To describe flows with strong deformations a technique of decomposition of numerical region into subregions is developed. The boundaries of subregions can be moved both in Eulerian and Lagrangian fashion. Using the method developed several multimaterial problems with strong deformations have been solved. To apply Godunov method for elastic-plastic flow conservative form of governing equations is used, which allows one to obtain jump conditions in the case of discontinuous flow.

Mesoscale studies of mixing in reactive materials during shock loading

One of the requisite processes for chemical reactions between solid powder particles resulting from shock loading is that the particles undergo large deformations, exposing new surfaces while mixing with surrounding material. Reactions under shock loading occur in a reaction zone, the extent of which is defined by the interfacial surface area and the depth of the diffusion layer. The former depends on the level of hydrodynamic mixing of heterogeneous material under shock, while the latter depends on temperaturedependent species diffusion. To investigate diffusion-limited reactions at the grain scale level, mass diffusion and simple reaction kinetics depending on the interfacial surface area have been implemented in an Eulerian hydrocode GEODYN. Diffusion-reaction processes that are initiated by rapid heating of a Ni/Al nanolaminate and by shock loading of a micron-scale Ni/Al powder mixture are considered.

Simulation of Explosion Ground Motions Using a Hydrodynamic‐to‐Elastic Coupling Approach in Three Dimensions

Abstract Near‐field ground motions from explosions are governed by hydrodynamics and nonlinear material response. However, the calculation of the response using hydrodynamic solvers to observational distances, where motions are elastic, is computationally challenging. In order to propagate explosion ground motions from the near‐source region to the far field, we developed a hybrid modeling approach with a hydrodynamic‐to‐elastic coupling in three dimensions. Near‐source motions are computed with a Eulerian hydrodynamics code with adaptive mesh refinement. Motions on a dense grid of points are saved, resampled, and then passed to an elastic finite‐difference code for seismic‐wave modeling. Our coupling strategy is based on the uniqueness theorem, where motions are introduced into the elastic code as time‐dependent boundary sources and propagate as elastic waves at much lower computational cost than with the hydrodynamics code. We developed and verified the methodology to compute the hydrodynamic responses in either 2D or 3D into the elastic region and pass these to the elastic solver as 3D boundary motions. The accuracy of the numerical calculations and the coupling strategy is demonstrated in cases with a purely elastic medium as well as a nonlinear medium. Importantly, we show that our hydrodynamics code can accurately model motions for shallow sources in an elastic medium including surface waves, which is essential to insure that near‐source motions are correct. An application of our hybrid modeling approach is shown for a problem with scattering by 3D heterogeneity. Our strategy is capable of incorporating complex nonlinear effects near the source as well as volumetric and topographic material heterogeneity along the propagation path to receiver, making it very powerful for modeling a wide variety of effects and providing new prospects for modeling and understanding explosion‐generated seismic waveforms.

MESOSCALE SIMULATIONS OF POWDER COMPACTION

Mesoscale 3D simulations of shock compaction of metal and ceramic powders have been performed with an Eulerian hydrocode GEODYN. The approach was validated by simulating a well‐characterized shock compaction experiment of a porous ductile metal. Simulation results using the Steinberg material model and handbook values for solid 2024 aluminum showed good agreement with experimental compaction curves and wave profiles. Brittle ceramic materials are not as well studied as metals, so a simple material model for solid ceramic (tungsten carbide) has been calibrated to match experimental compaction curves. Direct simulations of gas gun experiments with ceramic powders have been performed and showed good agreement with experimental data. The numerical shock wave profile has same character and thickness as that measured experimentally using VISAR. The numerical results show reshock states above the single‐shock Hugoniot line as observed in experiments. We found that for good quantitative agreement with experiments...

SIMULATION OF COMET IMPACT AND SURVIVABILITY OF ORGANIC COMPOUNDS

Comets have long been proposed as a potential means for the transport of complex organic compounds to early Earth. For this to be a viable mechanism, a significant fraction of organic compounds must survive the high temperatures due to impact. We have undertaken three‐dimensional numerical simulations to track the thermodynamic state of a comet during oblique impacts. The comet was modeled as a 1‐km water‐ice sphere impacting a basalt plane at 11.2 km/s; impact angles of 15° (from horizontal), 30°, 45°, 65°, and 90° (normal impact) were examined. The survival of organic cometary material, modeled as water ice for simplicity, was calculated using three criteria: (1) peak temperatures, (2) the thermodynamic phase of H2O, and (3) final temperature upon isentropic unloading. For impact angles greater than or equal to 30°, no organic material is expected to survive the impact. For the 15° impact, most of the material survives the initial impact and significant fractions (55%, 25%, and 44%, respectively) satisf...