Showing papers on "Projectile published in 2016"

Energy absorption capacity of a sustainable Ultra-High Performance Fibre Reinforced Concrete (UHPFRC) in quasi-static mode and under high velocity projectile impact

Abstract: This paper investigates the energy absorption capacity of a sustainable Ultra-High Performance Fibre Reinforced Concrete (UHPFRC) in quasi-static mode and under high velocity projectile impact. The design of the sustainable concrete mixtures aims on achieving a densely compacted cementitious matrix with a relatively low binder amount, employing the modified Andreasen & Andersen particle packing model. The experiments on UHPFRC are performed using a 4-point bending test and high velocity projectile impact tests. The obtained results show that although the utilization of hybrid steel fibre enhances the mechanical properties of the developed UHPFRC, the application of fibres with hooked ends is crucial in improving the energy absorption capacity of the sustainable UHPFRC in quasi-static mode. However, under high velocity projectile impact, the UHPFRC mixture with hybrid fibres shows a much better energy absorption capacity than the one with hooked steel fibres only, particularly in resisting the scabbing at the rear surface. The intrinsic mechanisms for the energy absorption capacity of the sustainable UHPFRC in quasi-static mode and under high velocity projectile impact are studied and analysed.

Stopping dynamics of ions passing through correlated honeycomb clusters

Abstract: A combined nonequilibrium Green functions--Ehrenfest dynamics approach is developed that allows for a time-dependent study of the energy loss of a charged particle penetrating a strongly correlated system at zero and finite temperatures. Numerical results are presented for finite inhomogeneous two-dimensional Fermi-Hubbard models, where the many-electron dynamics in the target are treated fully quantum mechanically and the motion of the projectile is treated classically. The simulations are based on the solution of the two-time Dyson (Keldysh-Kadanoff-Baym) equations using the second-order Born, third-order, and $\mathrm{T}$-matrix approximations of the self-energy. As application, we consider protons and helium nuclei with a kinetic energy between 1 and 500 keV/u passing through planar fragments of the two-dimensional honeycomb lattice and, in particular, examine the influence of electron-electron correlations on the energy exchange between projectile and electron system. We investigate the time dependence of the projectile's kinetic energy (stopping power), the electron density, the double occupancy, and the photoemission spectrum. Finally, we show that, for a suitable choice of the Hubbard model parameters, the results for the stopping power are in fair agreement with ab initio simulations for particle irradiation of single-layer graphene.

Method and system for aligning a point of aim with a point of impact for a projectile device

Abstract: A method of aligning a point of aim with a point of impact for a projectile device is disclosed Using a superposition device coupled to the projectile device, at least one reference point is superposed within a first target area with at least one beam of the superposition device A position for at least one of the reference points is noted A projectile is shot from the projectile device at a second target area, while the position of the at least one reference point is maintained, to create the point of impact The point of aim for the projectile device is adjusted to correspond with the point of impact while the position of the at least one reference points is maintained

Fore-wake excitations from moving charged objects in a complex plasma

Abstract: A charged object moving at a supersonic speed in a plasma creates the familiar Mach cone structure in its wake but can also give rise to nonlinear wave excitations ahead of it. Using molecular dynamic simulations, we explore such fore-wake excitations in a strongly coupled dusty plasma and demonstrate the existence of precursor solitonic pulses and dispersive shock waves in that region. The excitation conditions as well as the propagation characteristics of such pulses are delineated as a function of the projectile velocity, the plasma density, the Coulomb coupling parameter, and the amount of charge on the projectile. Our simulation results provide a kinetic basis for earlier fluid model calculations and also give insights into the dynamical processes responsible for such excitations that can aid in future experimental and application oriented studies.

The influence of projectile ion induced chemistry on surface pattern formation

Abstract: We report the critical role of projectile induced chemical inhomogeneity on surface nanostructure formation. Experimental inconsistency is common for low energy ion beam induced nanostructure formation in the presence of uncontrolled and complex contamination. To explore the precise role of contamination on such structure formation during low energy ion bombardment, a simple and clean experimental study is performed by selecting mono-element semiconductors as the target and chemically inert or reactive ion beams as the projectile as well as the source of controlled contamination. It is shown by Atomic Force Microscopy, Cross-sectional Transmission Electron Microscopy, and Electron Energy Loss Spectroscopy measurements that bombardment of nitrogen-like reactive ions on Silicon and Germanium surfaces forms a chemical compound at impact zones. Continuous bombardment of the same ions generates surface instability due to unequal sputtering and non-uniform re-arrangement of the elemental atom and compound. This...

Ballistic limit of high-strength steel and al7075-t6 multi-layered plates under 7.62-mm armour piercing projectile impact

Abstract: THIS PAPER PRESENTS THE COMPUTATIONAL-BASED BALLISTIC LIMIT OF LAMINATED METAL PANELS COMPRISED OF HIGH STRENGTH STEEL AND ALUMINIUM ALLOY AL7075-T6 PLATE AT DIFFERENT THICKNESS COMBINATIONS TO NECESSITATE THE WEIGHT REDUCTION OF EXISTING ARMOUR STEEL PLATE. THE NUMERICAL MODELS OF MONOLITHIC CONFIGURATION, DOUBLE-LAYERED CONFIGURATION AND TRIPLE-LAYERED CONFIGURATION WERE DEVELOPED USING A COMMERCIAL EXPLICIT FINITE ELEMENT CODE AND WERE IMPACTED BY 7.62 MM ARMOUR PIERCING PROJECTILE AT VELOCITY RANGE OF 900 TO 950 M/S. THE BALLISTIC PERFORMANCE OF EACH CONFIGURATION PLATE IN TERMS OF BALLISTIC LIMIT VELOCITY, PENETRATION PROCESS AND PERMANENT DEFORMATION WAS QUANTIFIED AND CONSIDERED. IT WAS FOUND THAT THE MONOLITHIC PANEL OF HIGH-STRENGTH STEEL HAS THE BEST BALLISTIC PERFORMANCE AMONG ALL PANELS, YET IT HAS NOT CAUSED ANY WEIGHT REDUCTION IN EXISTING ARMOUR PLATE. AS THE WEIGHT REDUCTION WAS INCREASED FROM 20-30%, THE DOUBLE-LAYERED CONFIGURATION PANELS BECAME LESS RESISTANCE TO BALLISTIC IMPACT WHERE ONLY AT 20% AND 23.2% OF WEIGHT REDUCTION PANEL COULD STOP THE 950M/S PROJECTILE. THE TRIPLE-LAYERED CONFIGURATION PANELS WITH SIMILAR AREAL DENSITY PERFORMED MUCH BETTER WHERE ALL PANELS SUBJECTED TO 20-30% WEIGHT REDUCTIONS SUCCESSFULLY STOPPED THE 950 M/S PROJECTILE. THUS, TRIPLE-LAYERED CONFIGURATIONS ARE INTERESTING OPTION IN DESIGNING A PROTECTIVE STRUCTURE WITHOUT SACRIFICING THE PERFORMANCE IN ACHIEVING WEIGHT REDUCTION.

Energy dissipation in thin metallic shells under projectile impact

Abstract: The ballistic performance of hemispherical aluminium shells was studied and the energy absorption in different modes of deformation has been computed. The experiments were performed wherein blunt and ogive nosed steel projectiles of 19 mm diameter were fired on 0.7–1.5 mm thick 1100-H12 aluminum hemispherical shells of different effective spans. The mechanics of deformation and energy absorption capacity was found to be significantly influenced by the shell thickness and projectile nose shape. The ogive nosed projectile caused failure through perforation by petal formation. Against blunt nosed projectile, however, the shells underwent significant dishing and reverse bending and thus defeated the projectile by dissipating its energy in global plastic deformation. The experimental findings were reproduced numerically on ABAQUS/Explicit finite element code. The numerical results were further employed for the computation of plastic strain energy in stretching in polar, radial, elevation and shear directions of the shell in order to eventually extract the total energy absorbed in plastic deformation. For a given span diameter and thickness of shell, the energy dissipation was found maximum in shear stretching while it was minimum in polar stretching of the material.

Study of hypervelocity projectile impact on thick metal plates

Abstract: Hypervelocity impacts generate extreme pressure and shock waves in impacted targets that undergo severe localized deformation within a few microseconds. These impact experiments pose unique challenges in terms of obtaining accurate measurements. Similarly, simulating these experiments is not straightforward. This study proposed an approach to experimentally measure the velocity of the back surface of an A36 steel plate impacted by a projectile. All experiments used a combination of a two-stage light-gas gun and the photonic Doppler velocimetry (PDV) technique. The experimental data were used to benchmark and verify computational studies. Two different finite-element methods were used to simulate the experiments: Lagrangian-based smooth particle hydrodynamics (SPH) and Eulerian-based hydrocode. Both codes used the Johnson-Cook material model and the Mie-Gruneisen equation of state. Experiments and simulations were compared based on the physical damage area and the back surface velocity. The results of this study showed that the proposed simulation approaches could be used to reduce the need for expensive experiments.

Potential space debris shield structure using impact-initiated energetic materials composed of polytetrafluoroethylene and aluminum

Abstract: A whipple shield using Al/PTFE (polytetrafluoroethylene) energetic material to protect against space debris is presented. The hypervelocity impact characteristics were investigated experimentally using a two-stage light gas gun at velocities between 3 and 6 km/s. A good protection of the shield was obtained through comparative experiments which used the same bumper areal density. The results showed that the critical projectile diameter can be improved by 28% by contrast with the Christiansen ballistic limit equations. The Al/PTFE energetic material bumper can break up the projectile into smaller, less massive, and slower projectiles due to the combined effect of impact and explosion, thereby producing a sharp rise in the spacecraft protection ability.

Influence of impact conditions on plasma generation during hypervelocity impact by aluminum projectile

Abstract: For describing hypervelocity impact (relative low-speed as related to space debris and much lower than travelling speed of meteoroids) phenomenon associated with plasma generation, a self-developed 3D code was advanced to numerically simulate projectiles impacting on a rigid wall. The numerical results were combined with a new ionization model which was developed in an early study to calculate the ionized materials during the impact. The calculated results of ionization were compared with the empirical formulas concluded by experiments in references and a good agreement was obtained. Then based on the reliable 3D numerical code, a series of impacts with different projectile configurations were simulated to investigate the influence of impact conditions on hypervelocity impact generated plasma. It was found that the form of empirical formula needed to be modified. A new empirical formula with a critical impact velocity was advanced to describe the velocity dependence of plasma generation and the parameters of the modified formula were ensured by the comparison between the numerical predictions and the empirical formulas. For different projectile configurations, the changes of plasma charges with time are different but the integrals of charges on time almost stayed in the same level.

Fully differential study of wave packet scattering in ionization of helium by proton impact

Abstract: We present a fully differential study of projectile coherence effects in ionization in p + He collisions. The experimental data are qualitatively reproduced by a non-perturbative ab initio time-dependent model, which treats the projectile coherence properties in terms of a wave packet. A comparison between first- and higher-order treatments shows that the observed interference structures are primarily due to a coherent superposition of different impact parameters leading to the same scattering angle. Higher-order contributions have a significant effect on the interference term.