No abstract

No abstract

No abstract

Introduction. Physicomathematical models for the deformation of a shaped-charge jet (SCJ) at the stage of uniform stretching preceding the necking process in the SCJ and breakup of the jet into separate nongradient elements are considered in [1, 2]. In these models, an SCJ element is represented as a cylindrical bar stretched at a constant value of the Lagrangian axial-velocity gradient. Because the indicated models are one-dimensional, they do not give an answer to the main questions: how and when does transition from the stage of uniform stretching (inertial stage) to the necking stage in a SCJ take place [1], how do separate nongradient elements and how do the geometrical and kinematic parameters of the SCJ elements and its material parameters influence the main quantitative characteristics of stretching and breakup of plastically failing SCJ?The present work reports results of physicomathematical modeling of the process of stretching and plastic failure of SCJ in a more general formulation compared to the models of [1, 2]. The results are obtained within the framework of continuum mechanics by numerical solution of the two-dimensional axisymmetric nonstationary problem of the dynamic deformation of a compressible elastoplastic bar of variable cross section.Apparently, this approach to examining the deformation of SCJ was first used by Chou et al. [3, 4]. Their studies were based on the Wilkins modification of the Lagrangian finite-difference method [5].The main differences of the present work from the ones cited above are as follows. The deformation of SCJ elements was considered from the moment they formed by collapse of the corresponding elements of the shaped-charge liner to the moment of plastic failure with formation of separate nongradient elements. This required improving the Lagrangian finite-difference method [5] and extending it to the case of large strains. As a result of the calculations, the following quantitative characteristics of stretching and breakup of SCJ were determined: the coefficient of ultimate elongation nult, the coefficient of inertial elongation ni, and the relative initial length a0 of a jet segment that forms a separate nongradient element after plastic failure, which depends on the total number N of separate elements formed after SCJ breakup. Generalization of the numerical results reveals dependences of the quantitative characteristics of stretching and breakup on the SCJ parameters and material properties. The dependences are compared to the experimental data for plastically failing jets of copper and niobium, obtained by one of the authors in the middle of the 1970s. In

Introduction. In recent years, several papers on the effect of a pulsed electric current on metallic shaped-charge jets (SCJ) have been published (see, for example, [1][2][3]). It has been shown experimentally and theoretically that the action of an electric current leads to a change in the jet "structure" and a decrease in the time of jet disruption, which, in turn, results in a severalfold decrease in penetration into the target. This effect is of great practical interest. The mechanisms of SCJ disruption by a pulsed current and their effect on the SCJ penetrationinto targets have been studied inadequately. The present paper reports results of experimental and numerical studies of SCJ disruption by an electric current.Numerical simulation was performed for the following three possible mechanisms of disruption: (a) development of MHD instability of SCJ; (b) volume fracture; (c) simultaneous development of MHD instability and volume fracture.The processes of formation, stretching, and penetration of SCJ with and without an electric current were simulated numerically.Results of the numerical simulation were compared with experimental data on the SCJ structure and penetration into steel and aluminum targets for various electric-pulse parameters.Diagram of Experiments. Diagrams of the experiments are given in Fig. la and b, where 1 is the shaped charge (SC), 2 is the electromagnetic-energy source, 3 are the electrodes, 4 are the inductive probes for measuring the current and the discharge-current derivative, 5 are the sites of radiography of the SCJ parameters (in an aluminum target and in free flight), and 6 is the target. In the diagram in Fig. lb, unlike in the diagram of Fig. la, the current can flow in the jet during jet penetration into the target. The cavern producing the target can act as an inverse current lead. In this case, the time during which the current acts on a jet element is much larger than that in the diagram shown in Fig. la. The experiments were performed with SC of 50-and 100-mm diameters and steel and aluminum targets. The energy source in the experiments was a capacitor bank with charging voltage of up to 5 kV and a capacitance of up to 20 mF. The current