Bulletin of the American Physical Society
17th Biennial International Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 56, Number 6
Sunday–Friday, June 26–July 1 2011; Chicago, Illinois
Session M1: Inelastic Deformation, Fracture, and Spall VI |
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Chair: Gennady Kanel, Joint Institute for High Temperatures Room: Grand Ballroom II-III |
Wednesday, June 29, 2011 11:00AM - 11:15AM |
M1.00001: Laser-driven spall experiments in ductile materials in order to characterize Johnson fracture model constants Laurent Videau, Patrick Combis, Emilien Lescoute, Jean-paul Jadaud, Jean-marc Chevalier, Didier Raffestin, Fabrice Ducasse, Loic Patissou, Alain Geille, Thibaut de Resseguier We present laser-driven spall experiments on Al, Ta, Au and Steel by using the ALISE laser at CEA-CESTA. The free-surface velocity of 100-200$\mu$m targets was measured by using a VISAR diagnostic. A transverse shadowgraphy diagnostic was used to characterize the ejected matter distribution. The experimental results are compared with 1D-Lagrangian hydrodynamic simulations including the Johnson fracture model. For each material, we find new model constants which allow us to reproduce experiments over a range of laser fluence with and without spallation. In addition 2D hydrodynamic simulations are used to study the effect of the finite size of the focal spot. We finally present experimental and numerical results on thin targets (20$\mu$m) with laser energy below the spallation threshold. We study here the ductile target plastic deformation and fracture due to central laser-driven shocks. [Preview Abstract] |
Wednesday, June 29, 2011 11:15AM - 11:30AM |
M1.00002: Experimental and numerical techniques to investigate and to model dynamic fragmentation of laser shock-loaded metals Thibaut de Resseguier, Emilien Lescoute, Jean-Marc Chevalier, Pierre-Henri Maire, Jerome Breil, Guy Schurtz In this paper, complementary techniques are combined to investigate dynamic fragmentation and shrapnel generation in laser shock-loaded samples of aluminium and gold, which will be two constituents of the target assemblies designed for the inertial confinement fusion (ICF) experiments to be performed on large scale laser facilities such as the \textit{National Ignition Facility} in the USA or the \textit{Laser M\'{e}gaJoule} in France. Fast optical transverse shadowgraphy is used to observe and analyze fragment ejection while Photonic Doppler Velocimetry (PDV) provides time-resolved measurements of the free surface velocity. Experimental results are compared with two-dimensional numerical simulations involving a phenomenological fragmentation model based on a probabilistic distribution of material tensile strength within the sample. Although not physically-based at this preliminary stage, the model is shown to provide consistent predictions over the explored range of sample thickness and laser intensity. [Preview Abstract] |
Wednesday, June 29, 2011 11:30AM - 11:45AM |
M1.00003: Diffuse scattering from shock compressed single crystal copper by use of nanosecond x-ray Laue diffraction Matthew Suggit, Andrew Higginbotham, Gabriele Mogni, Giles Kimminau, Justin Wark, Andrew Comley, Nigel Park, James Hawreliak, Bruce Remington The mechanism by which plastic relaxation occurs in the shock environment is not fully understood. There is evidence that the generation and flow of dislocations must mediate the ultra-high strain rates involved, and applying Orowan's equation suggests that the dislocation densities may be up t of order $10^{13}$cm$^{-2}$, a value which has not been observed in recovery experiments. We report on recent x-ray diffraction experiments using a quasi-white-light source to probe shock compressed single crystal copper, which were performed using the JANUS laser at LLNL. The x-ray source is provided by a mixed metal backlighter foil, comprised of mid-Z elements, which produces a broad spectrum of x-rays of energy ranging from 3 to 10 keV.\footnote{Suggit et al. Rev. Sci. Instrum. \textbf{81}, 083902 (2010)} The single-shot diffraction patterns for 10$\mu$m thick single crystal Cu were recorded as well as free surface VISAR measurements. In the resulting diffraction patterns, we observed diffuse scattering around multiple diffraction peaks. We discuss the possible plasticity mechanisms responsible. [Preview Abstract] |
Wednesday, June 29, 2011 11:45AM - 12:00PM |
M1.00004: Role of Target Strength in Momentum Enhancement James Walker, Sidney Chocron Experiments with small aluminum spheres striking 2024-T4 and 1100-O aluminum targets at velocities of 4 to 7 km/s have shown an interesting effect in terms of momentum enhancement. Momentum enhancement is the amount of extra momentum delivered to the target due to the ejecta thrown back along the projectile's path. Momentum enhancement is less for the softer 1100-O material, even though the craters are larger [1]. Thus, there is not a correlation between crater volume and ejecta momentum. When straightforward computations with hydrocodes are performed, this result is not replicated; rather, the opposite occurs in that reduced flow stress for the aluminum target leads to increased momentum enhancement [2]. This paper examines the effect of linking the tensile failure behavior to the damage model by assuming a strain energy to failure for the material. Thus, larger strains produced in larger craters need not directly result more failed material and more ejecta. Computations are performed using CTH to compute the momentum enhancement for different flow stress models and damage models, providing a possible explanation of the experimental observations. [1] Denardo, BP, Nysmith CR. Proc. AGARD-NATO Specialists, Vol. 1, Gordon and Breach, New York, 1964, 389-402. [2] Walker, JD, Chocron, S. Int. J. Impact Engng, 2011, in press. [Preview Abstract] |
Wednesday, June 29, 2011 12:00PM - 12:15PM |
M1.00005: ABSTRACT WITHDRAWN |
Wednesday, June 29, 2011 12:15PM - 12:30PM |
M1.00006: The Effects of the Flyer Plate's Radius of Curvature on the Performance of an Explosively Formed Projectile Phillip Mulligan, Jason Baird, Joshua Hoffman An explosively formed projectile (EFP) is known for its ability to penetrate vehicle armor effectively. Understanding how an EFP's physical parameters affect its performance is crucial to development of an armor capable of defeating such devices. The present study uses two flyer plate radii of curvature to identify the experimental effects the flyer plate's radius of curvature has on the measured projectile velocity, depth of penetration, and projectile shape of an EFP. The Gurney equation is an algebraic relationship for estimating the velocity imparted to a metal plate in contact with detonating explosives (1). In their attempts to calculate an EFP theoretical flyer plate velocity, the authors of this research used the open-faced-sandwich Gurney equation, whereby a semi-infinite slab of explosive is in intimate contact with a semi-infinite metal flyer plate. This equation uses the flyer-weight to charge-weight ratio and the specific explosive kinetic energy to calculate the theoretical flyer plate velocity. Two EFP designs that have two different flyer plate radii of curvature, but the same physical parameters and the same flyer-weight to charge-weight ratio should theoretically have the same velocity. Test results indicate the flyer plate's radius of curvature does not affect the projectile's velocity and that using a flat flyer plate negatively affects projectile penetration and formation. [Preview Abstract] |
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