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 S4: Continuum & Multiscale Modeling V |
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Chair: Michael Scheidler, US Army Research Laboratory Room: Hyatt Regency Constellation E |
Thursday, August 4, 2005 9:30AM - 9:45AM |
S4.00001: Shock Compression of Solid with Voids by Gridless Lagrangian SPH Katsumi Tanaka Eurelian studies for the shock propagation through an air bubble in water have shown a hot spot with locally high temperature and high pressure when incident shock pressure is enough high to generate supersonic water jet. Single air bubble which is compressed adiabatically disappeared during shock compression. Temperature rise in water was not enough to initiate emulsion type explosives for incident shock pressure lower than 1GPa. The mechanism of local hot spots with multiple voids has been studied numerically by Smoothed Particle Hydrodynamics (SPH). Effects of turbulent mixing by voids will be discussed. [Preview Abstract] |
Thursday, August 4, 2005 9:45AM - 10:00AM |
S4.00002: A Particle Method For Continua Larry Libersky, Phillip Randles We present a new numerical method for application to problems involving strong shocks in solids. The technique (Dual Particle Dynamics) uses particles and no background spatial grid enabling computation of large material deformation in a Lagrange frame. A new tensor viscosity has been formulated which is effective in resolving shocks within a meshfree framework with large anisotropy in the particle spacing. An important attribute of the method is that each DPD particle carries, in addition to the physical fields, a ruler and a clock. The ruler defines the local special metric (length scale) and the clock provides for asynchronous time integration. These space-time measures are advantageous for computational efficiency, but more importantly for stability, as a time step based on the Courant number is not adequate to ensure stability for Lagrange particle codes. Simulations involving explosively driven shocks in metals are presented to show how the method performs. [Preview Abstract] |
Thursday, August 4, 2005 10:00AM - 10:15AM |
S4.00003: Staggered Mesh Godunov (SMG) Schemes for Lagrangian Hydrodynamics Gabi Luttwak, Joseph Falcovitz Second order Godunov schemes[1] are recognized as the state of the art for Eulerian calculations.The difficulties inherent in modifying the zone-centered Godunov method into a 3D Lagrangian/ALE scheme have lead us to formulate a SMG scheme [2]. Here, we propose to bridge the Lagrange to Godunov ``conceptual gap'' comparing three SMG versions. The first two employ total energy equation. In the first one we solve face-centered RP (Riemann Problems) for the energy and zone-centered RP for the momentum. The second one [2] uses only face-centered RP. The third one, with internal energy, uses only cell-centered ``collision RP'' and is similar to Christensen's [3] split-Q scheme. In 1D,it is equivalent to a pseudo-viscosity which consists of linear and quadratic terms in the velocity gradient. The linear term requires second-order accuracy aimed at suppressing Q-heating in regions of smooth flow. This capability relies on a judiciously monotonized piecewise-linear approximation of velocities in zones. A 1D ``shockless'' compression problem was devised as a Q heating test case. A 3D implementation is also presented. [1] Ben Artzi M., Falcovitz J., ``Generalized Riemann problems in computational fluid dynamics,'' Cambridge Univ. Press, London, 2003. [2] Luttwak G., p255-258, Shock Compression of Condensed Matter-2001, ed. by Furnish M.D. et al., A.I.P. 2002 [3] Christensen R. B.,UCRL-JC-105269 (1990). [Preview Abstract] |
Thursday, August 4, 2005 10:15AM - 10:30AM |
S4.00004: Times Scales in Dense Granular Material Duan Zhang, Xia Ma Forces in dense granular material are transmitted through particle contacts. The evolution of the contact stress is directly related to dynamical interaction forces between particles. Since particle contacts in a dense granular material are random, a statistical method is employed to describe and model their motions. It is found that the time scales of particle contacts determinate stress relaxation and the fluid- like or solid-like behavior of the material. Numerical simulations are performed to calculate statistical properties of particle interactions. Using results from the numerical simulations we examine the relationship between the averaged local deformation field and the macroscopic deformation field. We also examine the relationship between the averaged local interaction force and the averaged stress field in the material. Validities of the Voigt and the Reuss assumptions are examined; and extensions to these assumptions are studied. Numerical simulations show that tangential frictions between particles significantly increase the contact stress, while the direct contribution of the tangential force to the stress is small. This puzzling observation can be explained by dependency of the relaxation time on the tangential friction. [Preview Abstract] |
Thursday, August 4, 2005 10:30AM - 10:45AM |
S4.00005: Mechanisms of Dynamic Friction Graham Ball Oblique shock loading at metal/metal interfaces produces differential tangential acceleration, resulting in sliding with dynamic friction. Here a 1D continuum code is used to predict time-dependent behaviour of the sliding interface. Processes represented are shear deformation, work hardening, thermal softening, melting, heat conduction and frictional heating. Friction is controlled by the von Mises yield limit, in pure shear, of the weaker material at the interface, and is therefore strongly coupled to thermal softening and work hardening. Results are presented for aluminium/steel in the 100 kBar range. Two behaviours are predicted, depending on the initial relative velocity. At high velocity, thermal softening dominates - after an initial warm-up transient the aluminium approaches its melt temperature asymptotically with decaying friction, while plastic deformation is confined to a thin sub-surface layer. Below a critical velocity, after an initial period of sliding, runaway work hardening reduces the relative velocity abruptly to zero, giving sustained high shear stress and deep plastic deformation. These predictions are shown to be consistent with recent HE-driven recovery experiments. [Preview Abstract] |
Thursday, August 4, 2005 10:45AM - 11:00AM |
S4.00006: Shock Physics Simulation Using a Hybrid Particle-Element Method Eric Fahrenthold Some important shock physics applications have motivated the development of numerical methods based on mixed particle-finite element formulations. Although pure continuum and pure particle based methods are well suited for use in many shock physics problems, their underlying kinematic schemes limit their utility in selected applications. An example is hypervelocity impact simulation, which requires both accurate modeling of strength effects and general descriptions of contact-impact dynamics for all structures and material fragments. In recent research the hybrid particle-element method of Shivarama and Fahrenthold (Int. J. for Num. Methods in Eng., 2004, Vol. 59, pp. 737-753) has been extended and validated in simulations of one and three dimensional shock physics problems. [Preview Abstract] |
Thursday, August 4, 2005 11:00AM - 11:15AM |
S4.00007: A Combined Discrete/Finite Element Multiscale Numerical Method and Its Application to Structure Failure Simulation under Laser Irradiation Jianlong Xu, Zhiping Tang Analysis of a variety of engineering problems requires computation at different length scales. A combined discrete/finite element numerical method is proposed and developed in this paper to meet this requirement. This method performs discrete element method at meso-scale to reach necessary precision, and finite element method at macro-scale to save the computation time and cost. The key point for this method is to define a special transition layer between discrete element zone and the finite element zone. We apply this new method to simulate the failure responses of a pre-stressed aluminum plate and a cylindrical shell with inner pressure under laser irradiation with the combination codes of DM3 (a 3D Discrete Meso-Element Dynamic Method)/plane FEM and DM3/shell FEM developed in this lab, respectively. It finds good agreement between the current computational results and the reported results in the references. [Preview Abstract] |
Thursday, August 4, 2005 11:15AM - 11:30AM |
S4.00008: Mechanical Behavior of Nanostructured Materials at High Strain Rates. Computer Simulation Vladimir Skripnyak, Evgenia Skripnyak, Mihail Nazarov In this paper, we present the new model of mechanical behavior of nanostructural materials (NsM) and nanocrystalline materials (NM) in wide range of strain rates. The model was used for computer simulation of shock wave dynamics in NsM $\alpha $-Ti, Al, Cu, Ìg and NM Al$_{2}$O$_{3}$, ZrO$_{2}$-Y$_{2}$O$_{3}$ ceramics. The inelastic strain causes by the deformation mechanisms at micro- and meso- scale levels. The results testify to distinctions of the mechanical behavior nanostructural and a course-grained ceramic materials and a metal alloys at shock wave loading. The model predicts that the shear stress of NM and NsM at high strain rates is less than ones of course-grained materials due to contributions to inelastic deformation of the grain boundary sliding. [Preview Abstract] |
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