Lewis A. Glenn

Mechanical and numerical modeling of a porous elastic- viscoplastic material with tensile failure

The objective of this paper is to develop simple but comprehensive constitutive equations that model a number of physical phenomena exhibited by dry porous geological materials and metals. For geological materials the equations model: porous compaction; porous dilation due to distortional deformation and tensile failure; shear enhanced compaction; pressure hardening of the yield strength; damage of the yield strength due to distortional deformation and porosity changes; and dependence of the yield strength on the Lode angle. For metals the equations model: hardening of the yield strength due to plastic deformation; pressure and temperature dependence of the yield strength, and damage due to nucleation of porosity during tensile failure. The equations are valid for large deformations and the elastic response is hyperelastic in the sense that the stress is related to a derivative of the Helmholtz free energy. Also, the equations are viscoplastic with rate dependence occurring in both the evolution equations of porosity and elastic distortional deformations. Moreover, formulas are presented for robust numerical integration of the evolution equations at the element level that can be easily implemented into standard computer programs for dynamic response of materials.

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.

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.

Design limitations on ultra-high velocity projectile launchers☆

Abstract The maximum velocity attainable in a gasdynamic gun is limited by the maximum sound speed in the driver gas. For a conventional 2-stage light gas gun, the limit is ∼ 10 km/s. Higher velocities are possible, but probably not without the destruction of the gun barrel. As long as this occurs on a time scale longer than the residence time of the projectile, a useful system may still result. Using a newly developed computer code called IGUN, we have evaluated the performance of several multistage designs capable of achieving ultra-high projectile velocities. The main problem is in maintaining the integrity of the projectile. Our calculations indicate that 20 km/s should be achievable without fracturing the projectile. If it is only required to retain near original areal density, velocities in excess of 30 km/s appear feasible.

Pressure enhanced penetration with shaped charge perforators

A downhole tool, adapted to retain a shaped charge surrounded by a superatmospherically pressurized light gas, is employed in a method for perforating a casing and penetrating reservoir rock around a wellbore. Penetration of a shaped charge jet can be enhanced by at least 40% by imploding a liner in the high pressure, light gas atmosphere. The gas pressure helps confine the jet on the axis of penetration in the latter stages of formation. The light gas, such as helium or hydrogen, is employed to keep the gas density low enough so as not to inhibit liner collapse.

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.

Optimization studies of a three-stage light gas gun

A new gasdynamic launcher is described, in which intact projectiles weighing at least 1 gram can be accelerated to mass velocities of 15–20 km/s. The system employs a conventional 2—stage light gas gun, with the barrel modified and filled with helium to act as a pump tube for a third stage. The key feature of the launcher is that the peak pressure in the third stage can be maintained below 2.5 GPa, thus assuring high efficiency and the integrity of the projectile.

Numerical Investigation into the Performance of a Rarefaction Shock Wave Cutter for Offshore Oil‐Gas Platform Removal

The phase change in iron at 13 GPa results in the formation of rarefaction shock waves (RSWs) upon release. The interaction of multiple RSWs induces high tensile stresses within a narrow zone, causing smooth spall. This effect can be exploited to sever cylindrical cross‐section pipes, such as those supporting decommissioned offshore oil and gas platforms, using a minimal amount of explosive. Consequently, costs can be reduced and environmental impact minimized. We discuss numerical techniques used to simulate RSWs and the damage to steel resulting from the interaction of multiple RSWs.

LLNL`s regional seismic discrimination research

The ability to verify a Comprehensive Test Ban Treaty (CTBT) depends in part on the ability to seismically detect and discriminate between potential clandestine underground nuclear tests and other seismic sources, including earthquakes and mining activities. Regional techniques are necessary to push detection and discrimination levels down to small magnitudes, but existing methods of event discrimination are mainly empirical and show much variability from region to region. The goals of Lawrence Livermore National Laboratory`s (LLNL`s) regional discriminant research are to evaluate the most promising discriminants, improve the understanding of their physical basis and use this information to develop new and more effective discriminants that can be transported to new regions of high monitoring interest. In this report the authors discuss preliminary efforts to geophysically characterize the Middle East and North Africa. They show that the remarkable stability of coda allows one to develop physically based, stable single station magnitude scales in new regions. They then discuss progress to date on evaluating and improving physical understanding and ability to model regional discriminants, focusing on the comprehensive NTS dataset. The authors apply this modeling ability to develop improved discriminants including slopes of P to S ratios. They find combining disparate discriminant techniques is particularly effective in identifying consistent outliers such as shallow earthquakes and mine seismicity. Finally they discuss development and use of new coda and waveform modeling tools to investigate special events.As part of the Department of Energys research and development effort to improve the monitoring capability of the planned Comprehensive Nuclear-Test-Ban Treaty international monitoring system, Lawrence Livermore Laboratory (LLNL) is testing and calibrating regional seismic discrimination algorithms in the Middle East, North Africa and Western Former Soviet Union. The calibration process consists of a number of steps: (1) populating the database with independently identified regional events; (2) developing regional boundaries and pre-identifying severe regional phase blockage zones; (3) measuring and calibrating coda based magnitude scales; (4a) measuring regional amplitudes and making magnitude and distance amplitude corrections (MDAC); (4b) applying the DOE modified kriging methodology to MDAC results using the regionalized background model; (5) determining the thresholds of detectability of regional phases as a function of phase type and frequency; (6) evaluating regional phase discriminant performance both singly and in combination; (7) combining steps 1-6 to create a calibrated discrimination surface for each stations; (8) assessing progress and iterating. We have now developed this calibration procedure to the point where it is fairly straightforward to apply earthquake-explosion discrimination in regions with ample empirical data. Several of the steps outlined above are discussed in greater detail in other DOE papers in this volume or in recent publications. Here we emphasize the results of the above process: station correction surfaces and their improvement to discrimination results compared with simpler calibration methods. Some of the outstanding discrimination research issues involve cases in which there is little or no empirical data. For example in many cases there is no regional nuclear explosion data at IMS stations or nearby surrogates. We have taken two approaches to this problem, first finding and using mining explosion data when available, and second using test-site based models to transport earthquake-explosion discrimination behavior to new regions. Finally an important component of our research is assessing improvement in the ability to discriminate events. By combining the multivariate discriminants with the threshold detection curves for the regional seismic phases used in those discriminants, we have started to make maps of the probability an event will be identified properly. These maps serve a broad range of purposes from demonstrating progress to funding agencies to prioritizing research and calibration efforts.