Papers by Keyword: Shock Wave

Abstract: The characteristics of shocked nanocrystalline aluminum are investigated by using molecular dynamics method based on the embedded atom method potential function. The result presents the particle velocity profile and the width of shock front in detail. The simulated Hugoniot relations are basically consistent with the experimental data and other molecular dynamics results. The width of shock front decreases with the particle velocity exponentially.

Abstract: The characteristics of shock wave propagation in aluminum single crystal are simulated by using the molecular dynamics (MD) method based on the embedded atom method (EAM) potential function. The structure of the shock front and the Hugonoit relation are obtained. The simulated results show that a two-wave structure exists in the aluminum single crystal for the particle velocity bellower than 2 km/s and the velocity of the elastic wave increases slightly with the shock loading. While only plastic wave exists in the aluminum single crystal for the particle velocity higher than 2 km/s and the width of the shock front decreases by exponent with the normal stress. The MD simulation results are basically consistent with the experimental results.

Abstract: The paper discusses the results of mathematical modeling the two-dimensional nonlinear dynamics of heteromodular elastic materials. The resistance of these materials under tension and compression is various. The deformation properties of the heteromodular medium are described within the framework of the isotropic elasticity theory with stress-dependent elastic moduli. In the plane strain case, it is shown that only two types of the nonlinear deformation waves can appear in the heteromodular elastic materials: a plane-polarized quasi-longitudinal wave and a plane-polarized quasi-transverse wave. Basing on obtained properties of the plane shock waves, two plane self-similar boundary value problems are formulated and solved.

Abstract: The study of the effect of Elongated Cumulative Charges (ECC) on rock formations has an important scientific and practical significance for solving a number of process problems in mining practice. The use of charges with a longitudinal concavity for a directional destruction (presplit blasting, “smoothwall” chipping) involves reducing the explosives consumption, preserving the aquifer rock mass from additional explosion-caused cracks, obtaining a smooth contour and reducing the volume of drilling works. It is noted that one of the options that provides the explosion energy redistribution in a destructible medium is the use of elongated cumulative charges with a damping core. Experimental evidences on the dynamic loading of model blocks by an explosion of an elongated cumulative charge with an inert pad of various acoustic stiffness are reported.

Abstract: The article is about the study of the obtaining process of the abrasive tool without a sheaf and the processing accuracy.

Abstract: Landmines and Improvised Explosive Devices are known to be major threats for the coalition armies in operation. In order to protect the soldiers from their effects, armored vehicle manufacturers developed some blast protective solutions. However, these solutions often reduce the vehicles’ mobility and payload capacity because of their shape or weight. Fiber Metal Laminates (FML) look like promising light weight blast protective solutions as they associate low areal densities with good bending rigidity and a high number of impedance mismatches which tend to attenuate the shock wave propagation. In this paper, three FML composed of a back plate of armored steel, a middle composite panel named A, B or C and a thin front plate made of mild steel were subjected to a blast loading. The maximum dynamic deformation of each target was recorded during the blast test. A macroscopic post-mortem analysis exhibits three similar behaviors of the back plates but very different permanent deformation patterns of the composite panels. A CT-scan of each panel was then realized to explain these three patterns and, based on these analysis, some hypothesis were made to improve the blast resistance of the B and C panels.

Abstract: Approaches to mathematical modeling of nonlinear strain dynamics in heteromodular and porous materials are discussed; the mechanical properties of media are described in terms of the simple piecewise linear elastic models. Several nonstationary 1D boundary value problems show that the singularity of model relationships gives rise to shock waves and centered Riemann waves in generalized solutions. Nonstationary load modes leading to the listed nonlinear effects are indicated separately for heteromodular and porous media.

Abstract: The unsteady supersonic jet and the shock wave injected by the small volume shock tube are experimentally studied in this paper. The experimental was performed by the background oriented schlieren method. The main parameters for the jet are the pressure ratio by the high pressure chamber/ a back pressure 10.9-53.0 and the length of high pressure chamber/diameter ratio 1 and 10. The velocity of the shock wave and supersonic jet were estimated by using the principle of the background oriented schlieren method. The results showed that the influence of the length of the high pressure chamber on the velocity of the jet.

Abstract: Collision dynamics of opposing unsteady supersonic jets injected in background gas with shock waves were calculated to simulate double pulsed laser ablation. Since the jets are deflected by collision and the motion of debris is ballistic. This characteristic can be used to reduce the number of debris when shields are mounted in front of substrate. The flow of jets through installed shields is complicated by the interaction between shields and jets, and between shields and shock waves. We investigate influence of shield position on the shock waves and the jets by numerical calculations. Axisymmetric two-dimensional compressible Euler equations were solved using the finite volume method by using ANSYS Fluent 14.0.0 code. The shields with slit was mounted parallel to the direction of initially injected jets. In order to investigate the influence of shield position on the shock waves and the jets, the shield position and background gas pressure were adopted as parameters. The jets and shock wave are deflected by collision and they can pass through the slit of shields. The passed shock wave reflects at the substrate mounted behind the slits and it forces back the jet to decrease the jet velocity. The shield position governs the velocity and amount of the jet that reach the substrate.

Abstract: Pulsed laser ablation with an elliptical cell gives well-defined thermodynamic conditions to the growth of high-quality thin films. The unsteady supersonic jet formed by the shock tube with small high-pressure chamber was used as a simple alternative model of pulsed laser ablation. The vortex ring formed by the shock wave is important to reveal behavior of unsteady supersonic jet discharged from elliptical cell. However, there has been little effort to investigate the interaction between the vortex ring and the jet. The purpose of the present study is to investigate the behavior of the vortex rings and the jet. The experiment and numerical calculation were carried out by schlieren method and by solving the axisymmetric two-dimensional compressible Navier-Stokes equations, respectively. The system of the calculation and the experiment is a model of laser ablation of a certain duration followed by a discharging process through the exit. Moreover, a parametric study was performed to demonstrate the effect of pressure ratio on the interaction among vortex rings and the supersonic jet. The interaction between the supersonic jet and the vortex rings increased the velocity of the supersonic jet up to the magnitude of the velocity at the center of the vortex rings. Closing a distance between the vortex ring and the jet is higher interaction between the vortex rings.