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Unformatted text preview: Breakup of Copper shaped-charge jets: Experiment, numerical simulations, and analytical modeling Jacques Petit DGA/Centre dEtudes de Gramat, BP 80200, 46500 Gramat, France Vronique Jeanclaude and Claude Fressengeas a ! Laboratoire de Physique et Mcanique des Matriaux, Universit de Metz / CNRS, Ile du Saulcy, 57045 Metz Cedex, France s Received 23 February 2005; accepted 4 November 2005; published online 28 December 2005 d Experimental data on the fragmentation of copper shaped-charge jets are presented and the techniques used for data processing are described. A combined numerical/analytical analysis is designed to describe shaped-charge jet breakup. The method overcomes drawbacks from exclusively numerical or analytical analyses, such as mesh sensitivity or oversimplified description. It yields predictions for break-up time, total number, and cumulative length of fragments in fairly good agreement with the experimental data. The dependence of fragmentation characteristics on the grain size in the liner is also well predicted. 2005 American Institute of Physics . f DOI: 10.1063/1.2141647 g I. INTRODUCTION Material failure is often the outcome of plastic flow lo- calization. In a number of dynamical processes, the location of regions subject to intense localized strain can be straight- forwardly predicted. Such is the case when geometric dis- continuities are present, or when failure results from wave interaction, as in failure by spalling. Predicting the localiza- tion regions can be much more difficult when dealing with the fragmentation of homogeneously distributed structures. Such is the case with high speed metallic jets. In shaped charges, the latter are generated by the axisymmetric col- lapse of conical shells under explosive loading. Due to their high penetration capabilities, these jets are used to perforate armour platings or to drill oil wells. During their flight, they experience considerable stretching at velocity gradients amounting to 10 4 10 5 s-1 . Beyond a certain flight distance, they neck down in a series of locations and eventually break up into fragments, which limits their perforating capabilities. 1 Shaped-charge jet fragmentation has been the subject of intense research effort during the last 50 years, using both experiment and numerical simulations, but also by means of analytical modeling. We view the following interpretation of the physics as emerging from this bulk of literature: The instability and fragmentation of high speed jets is driven by geometrical softening in the first place, meaning that due to its decreasing cross section, the stretching jet becomes unable to sustain the tension forces involved. Thermome- chanical effects are undoubtedly involved in the jet instabil- ity, but they are not considered as its primal cause. Distur- bances to the jet uniformity grow in time, but several effects delay their development. On the one hand, the lateral inertial pressure due to radial deceleration of particles delays the...
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