Bulletin of the American Physical Society
16th APS Topical Conference on Shock Compression of Condensed Matter
Volume 54, Number 8
Sunday–Friday, June 28–July 3 2009; Nashville, Tennessee
Session J3: ID-5: Fragmentation and Shock Ejecta |
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Chair: Dennis Grady, Applied Research Associates Room: Hermitage C |
Tuesday, June 30, 2009 11:00AM - 11:15AM |
J3.00001: A Relation for Fragment Sizes of Explosive Loaded Aluminum Cylinders J. Leadbetter, L. Donahue, R.C. Ripley, F. Zhang It is well established that the fragment size from explosively-loaded metal cylinders can be related to the expansion rate driven by high pressure explosive detonation products. During expansion, high strain rates alter material properties, and failure mechanisms influencing fragment size distribution become dependent on dynamic phenomena such as localized shear banding. The purpose of this paper is to extend known relations for steel fragment size to aluminum cylinders. The present approach utilizes high strain rate properties of aluminum with Grady and Kipp dynamic fragmentation theory to determine mean fragment size, and a statistical fragment distribution to account for randomness in the aluminum cylinder material. To determine the expansion strain rate, the explosive detonation and cylinder expansion are modeled using a two-way coupled fluid structure interaction routine. Experimental results for an aluminum-cased C4 charge are provided for model validation. Further analysis of a series of modeling results is shown to establish relationships for aluminum fragment size as a function of detonation pressure and the metal to explosive mass ratio. [Preview Abstract] |
Tuesday, June 30, 2009 11:15AM - 11:30AM |
J3.00002: Implementation of void growth model to predict ductile fragmentation Jessica Meulbroek, K.T. Ramesh Fragment sizes following an impact depend on the energy partitioning and material behavior at high strain rates. The kinetic energy of the incoming projectile is converted to energy to create new surfaces and the kinetic energy of the fragments. There are a number of models which predict the average fragment size for brittle materials (i.e. Grady-Kipp, Zhou-Molinari-Ramesh) by taking into account these factors. The fragmentation of ductile materials cannot be predicted by these models. Energy partitioning for ductile materials should also include dissipation to plastic work and failure mechanisms which are different from those present in brittle failure. In order to characterize ductile fragmentation, a recent model for dynamic void growth and interaction will be implemented into a 1D simulation. From the simulation, a model for 1D ductile fragmentation will be formulated and an average fragment size for different strain rates predicted. [Preview Abstract] |
Tuesday, June 30, 2009 11:30AM - 11:45AM |
J3.00003: Multi diagnostic experiment to access striction phenomena analysis of copper structure under dynamic expansion C. Voltz, J.-M. Lagrange, G. Besnard, B. Etchessahar When a structure is submitted to expansion, thinning occurs until fracture appears. Some tens of microseconds before destruction, localizations of deformation are created which induces local variations of thickness and mechanical striction. According to this phenomenon, we have studied the behavior of a copper cylinder under quasi-plane deformation constraint. Nitro methane explosive driven apparatus achieves the dynamic expansion. To acquire pertinent information about the mechanical behavior, we have conducted a dynamic expansion experiment with different kind of diagnostics. With the interferometry we monitor the free surface velocity for particular locus. We use two high-speed framing cameras. The first one is set to obtain phenomenological views of the experiment (surface aspect, expansion shape, plastic instabilities and fracture) and the second one is devoted to 3D surface evolution and displacement fields measurements by the stereovision technique. To access to the residual thickness, at given time, we associate flash X-Ray imaging. All these diagnostics are operated in the same experiment. This paper describes the experiment and associated measurements results. We present numerical simulation of the expanding shell related to velocimetry, stereovision and the analysis of X-ray films. The results are discussed according to the mechanical loading of the different parts of the specimen. [Preview Abstract] |
Tuesday, June 30, 2009 11:45AM - 12:00PM |
J3.00004: Transverse shadowgraphy and new recovery techniques to investigate dynamic fragmentation of laser shock-loaded metals Emilien Lescoute, Thibaut De Resseguier, Jean-Marc Chevalier, Michel Boustie, Jean-Paul Cuq-Lelandais, Laurent Berthe With the development of high energy laser facilities for inertial confinement fusion, such as the Laser M\'egaJoule and the National Ignition Facility, the question of debris ejection from metallic shells subjected to intense laser irradiation has become a key issue. We have developed two diagnostics to investigate this phenomenon. Transverse shadowgraphy is an optical time-resolved diagnostic. It provides successive images of the fragments motion, that allow characterizing different fragmentation processes such as micro-jetting and spallation. A continuous laser probe is divided by beamsplitters and sent to cameras (acquisition time is few tens nanoseconds) with different delays. Quasi-instantaneous pictures of the debris clouds are obtained and ejection velocities can be measured. Complementary data are provided by post-shock analysis of recovered fragments. Such recovery can be achieved in aerogels, but their brittleness and low transparency make the analysis difficult. Instead, we have used a new technique, based on a highly transparent gel of density 0.9\,g/cm$^3$, which allows soft recovery and easy observation of the fragments sizes, shapes and penetration depths, with a spatial resolution of micrometer-order. [Preview Abstract] |
Tuesday, June 30, 2009 12:00PM - 12:15PM |
J3.00005: Influence of shockwave profile on ejecta: An experimental and computational study Michael Zellner, Timothy Germann, James Hammerberg, Paulo Rigg, Gerald Stevens, William Turley, William Buttler This effort investigates the relation between shock-pulse shape and the amount of micron-scale fragments ejected (ejecta) upon shock release at the metal/vacuum interface of shocked Sn targets. Two shock-pulse shapes are considered: a supported shock created by impacting a Sn target with a sabot that was accelerated using a powder gun; and an unsupported or Taylor shockwave, created by detonation of high explosive that was press-fit to the front-side of the Sn target. Ejecta production at the back-side or free-side of the Sn coupons were characterized through use of piezoelectric pins, Asay foils, optical shadowgraph, and x-ray attenuation. In addition to the experimental results, SPaSM, a short-ranged parallel molecular dynamics code developed at Los Alamos National Laboratory, was used to investigate the relation between shock-pulse shape and production of ejecta from a first principles point-of-view. [Preview Abstract] |
Tuesday, June 30, 2009 12:15PM - 12:30PM |
J3.00006: Estimation of Spectral Characteristics of Particles, Which Are Ejected From Free Surface of Liquid Under Effect of Shock Wave Viktor Raevsky Basing on common physical notion and the known analytical solution of Richtmyer, approximations are obtained for the equation to estimate spectral characteristics of particles ejected from surface of liquid under effect of shock wave. The basic characteristics of spectrum, namely, distributions of number and weights of particles in sizes, are determined by intensity of shock wave, spectrum of initial perturbations on surface, viscosity, and surface tension. [Preview Abstract] |
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