Bulletin of the American Physical Society
2005 14th APS Topical Conference on Shock Compression of Condensed Matter
Sunday–Friday, July 31–August 5 2005; Baltimore, MD
Session J4: Continuum & Multiscale Modeling III |
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Chair: Donald Curran, SRI International Room: Hyatt Regency Constellation E |
Tuesday, August 2, 2005 11:00AM - 11:15AM |
J4.00001: Impulsive loading of cellular media in sandwich construction Joseph Main, George Gazonas Motivated by recent efforts to mitigate blast loading using energy absorbing materials, this paper investigates the uniaxial crushing of cellular media in sandwich construction under impulsive pressure loading. The cellular core material is modeled using a rigid, perfectly-plastic, locking idealization, as in previous studies, and the front and back faces are modeled as perfectly rigid. Pressure loading is applied to the front face with the back face unrestrained, and two forms of pressure input are considered: a triangular pulse and an idealized impulse of zero duration. The equation of motion for this system, which generalizes previous results for a fixed back face, is derived in nondimensional form in terms of a single coordinate representing the remaining mass fraction of uncompressed core material. Predictions of this analytical model show excellent agreement with computational simulations using the explicit finite element code LS-DYNA. This analytical model is used to investigate the influence of the relative distribution of mass among the core and the front and back faces, with the total mass held constant. An optimal mass distribution is obtained by maximizing the total impulse that can be absorbed, while limiting the back-face accelerations to a specified level. [Preview Abstract] |
Tuesday, August 2, 2005 11:15AM - 11:30AM |
J4.00002: Modeling the Shock Compression of Concrete Under 20 GPA Eric Buzaud, Pierre-Louis Hereil, Christophe Pontiroli, Philippe Lambert The aim of the authors is to model the shock response of concrete in a range of pressure levels from 0 to 20 GPA. The limitations of current computers imply the need to homogenize the response of the different constituents of concrete into a single macroscopic model. Though concrete is currently the most widely used construction material, the knowledge concerning its response under shock loading response remains rather modest. An exhaustive review of the research effort in this field illustrates this fact. The origin of the important dispersion that affects the limited available data is analysed and discussed. The authors propose a simple method to predict the shock Hugoniot of concrete based on a mixture theory, considering concrete as a mix of cement hydrates, free water, rock and voids. The potential of this approach is illustrated by comparisons to the available data. Finally, experimental results recently obtained on special concrete compositions are presented. Those results allow to relate the wave structure to the size of the aggregates, and so, the level of heterogeneity of the composition. Complementary numerical simulations illustrate the ability of a mesoscopic model to describe this phenomenon, and the failure of the homogenized approach to do so. [Preview Abstract] |
Tuesday, August 2, 2005 11:30AM - 11:45AM |
J4.00003: Transient Stress Optimization of Elastic and Viscoelastic Composite Strips Rich Laverty, George Gazonas In this study we will examine transient wave propagation in elastic and viscoelastic composite strips generated by an impulse stress, a step in stress and low velocity impact by rigid and elastic strikers. In the case of impulse, step and rigid body impact we seek combinations of material parameters that lead to optimal designs, defined as the maximum stress achieved in the composite layer most distant from the applied stress. In the case of impact from an elastic body, we define an optimal design as one in which the maximum stress is achieved in the striker, not the composite. The primary purpose of these results is benchmarking larger numerical studies coupling a finite element code (DYNA3D) with several optimization routines, but these problems are also interesting from a basic mechanics perspective. [Preview Abstract] |
Tuesday, August 2, 2005 11:45AM - 12:00PM |
J4.00004: Computational Design Study for Recovery of Shock Damaged Silicon Carbide Kaushik Iyer, Dattatraya Dandekar Recovery of shock-damaged specimens of technologically important brittle materials is desirable for relating damage characteristics to the load-unload history. Recovery also provides an opportunity for direct measurement of mechanical properties of the damaged material by performing a second shock experiment. Specimens subjected to standard mechanical characterization tests, e.g. low-rate compression, split Hopkinson pressure bar or plate impact, typically fail explosively and produce highly fragmented debris which makes the relation the load history to recognizable damage features difficult. Definitive data and constitutive models for the residual strength of dynamically impacted ceramics are presently lacking for this reason. This paper presents a computational design study of experimental configurations that may permit the recovery of weak-shock loaded high-strength ceramics such as silicon carbide and alumina. A set of 8 configurations involving nominally planar shock loading ($\sim $ 4 GPa) and a system of impedance matched or impedance graded momentum traps is analyzed using finite element models. Differences in the principal stress and lateral strain histories at a number of locations within the silicon carbide or alumina specimen are examined to identify the influences of the following design modifications: introducing a hole in the specimen center, configuration dimensions and impedance graded trapping. [Preview Abstract] |
Tuesday, August 2, 2005 12:00PM - 12:15PM |
J4.00005: Fragment Impact Toolkit: A Toolkit for Modeling Fragment Generation and Impacts on Targets Daniel Shevitz, Larry Luck In this talk we will detail the status of the Fragment Impact Toolkit. The toolkit is used to model nearby explosion problems and assess probabilities of user-specified outcomes. The toolkit offers a framework, without locking the user into any particular set of states, assumptions, or constraints. The toolkit breaks a fragment impact problem into five components, all of which are extendable: (1) source description that includes the geometry of the source; (2) fragment generation that comprises the fragmentation process, including fragment size distributions (if required) and assignment of initial conditions, such a velocity; (3) fragment flight that includes what occurs to fragments while airborne; (4) target intersection that includes specification of target geometry, position, and orientation; and (5) target consequence that includes what occurs when fragments hit a target. Two notable contributions of the toolkit are the ability to have sources that break up with position-dependent and user-specifiable size probability distributions and then impact targets of arbitrary complexity. In this paper we will show examples of how to use the toolkit and simulate targets, including airplanes and stacks of munitions. [Preview Abstract] |
Tuesday, August 2, 2005 12:15PM - 12:30PM |
J4.00006: Numerical Modeling of Mixing and Venting from Explosions in Bunkers Benjamin Liu, Ilya Lomov, Lewis Glenn 2D and 3D numerical simulations were performed to study the dynamic interaction of explosion products in a concrete bunker with ambient air, stored chemical or biological warfare (CBW) agent simulant, and the surrounding walls and structure. The simulations were carried out with GEODYN, a multi-material, Godunov-based Eulerian code, that employs adaptive mesh refinement and runs efficiently on massively parallel computer platforms. Tabular equations of state were used for all materials with the exception of any high explosives employed, which were characterized with conventional JWL models. An appropriate constitutive model was used to describe the concrete. Interfaces between materials were either tracked with a volume-of-fluid method that used high-order reconstruction to specify the interface location and orientation, or a capturing approach was employed with the assumption of local thermal and mechanical equilibrium. A major focus of the study was to estimate the extent of agent heating that could be obtained prior to venting of the bunker and resultant agent dispersal. Parameters investigated included the bunker construction, agent layout, energy density in the bunker and the yield-to-agent mass ratio. Turbulent mixing was found to be the dominant heat transfer mechanism for heating the agent. [Preview Abstract] |
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