Showing papers on "Projectile published in 2019"

Bioinspired composite segmented armour: Numerical simulations

Abstract: Nature has evolved ingenious armour designs, like the flexible carapaces of armadillo and boxfish consisting of hexagonal segments connected by collagen fibres, that serve as bioinspiration for modern ballistic armours. Here, Finite element modelling (FEM) used to analyze the effect of scale geometry and other impact parameters on the ballistic protection provided by a bioinspired segmented ceramic armour. For this purpose, the impact of cylindrical fragment simulating projectiles (FSPs) onto alumina-epoxy non-overlapping scaled plates was simulated. Scale geometrical parameters (size, thickness and shape) and impact conditions (FSP diameter, speed, location) are varied and the amount of damage produced in the ceramic tiles and the final residual velocity of the FSP after the impact are evaluated. It is found that segmentation drastically reduces the size of the damaged area without significantly reducing the ballistic protection in centred impact, provided the tile size is kept over a critical value. Such critical tile size (∼20 mm, inscribed diameter, for impacts at 650 m/s) is independent of the scale thickness, but decreases with projectile speed, although never below the diameter of the projectile. Off-centred impacts reduce the ballistic protection and increase the damaged area, but this can be minimized with an appropriate tile shape. In this sense and in agreement with the natural hexagonal tiles of the boxfish and armadillo, hexagonal scales are found to be optimal, exhibiting a variation of ballistic protection—measured as reduction of projectile speed—with impact location under 12%. Design guidelines for the fabrication of segmented protection systems are proposed in the light of these numerical results.

Anisotropy of electronic stopping power in graphite

Abstract: © 2019 American Physical Society. The rate of energy transfer from ion projectiles onto the electrons of a solid target is hard to determine experimentally in the velocity regime between the adiabatic limit and the Bragg peak. First-principles simulations have lately offered relevant new insights and quantitative information for prototypical homogeneous materials. Here, we study the influence of structural anisotropy on electronic stopping power with time-dependent density functional theory simulations of a hydrogen projectile in graphite. The projectile traveled at a range of angles and impact parameters for velocities between 0.1 and 1.4 a.u., and the electronic stopping power was calculated for each simulation. After validation with average experimental data, the anisotropic crystal structure was found to have a strong influence on the stopping power, with a difference between simulations parallel and perpendicular to the graphite plane of up to 25%, more anisotropic than expected based on previous work. The velocity dependence at low velocity displays clear linear behavior in general, except for projectiles traveling perpendicular to graphitic layers, for which a thresholdlike behavior is obtained. For projectiles traveling along graphitic planes, metallic behavior is observed with a change of slope when the projectile velocity reaches the Fermi velocity of the electrons.

Analysis of the two-dimensional fractional projectile motion in view of the experimental data

Abstract: This paper addresses the modeling of projectile motion using fractional models vis-a-vis experimental data. Recently, it was shown that an auxiliary parameter ( $$\sigma $$ ) needs to be included in the fractional modeling to preserve the dimensionality of the physical quantities. In previous studies, $$\sigma $$ was subjected to several restrictions without considering clear and meaningful reasons. Such problems are overcome here and a method for estimating $$\sigma $$ using the experimental data is introduced. A new solution for the two-dimensional projectile motion using the Caputo’s fractional derivative is obtained. An explicit formula for the trajectory of the projectile in vacuum is first derived. Then, the projectile parametric equations in a resistant medium are expressed in terms of the Mittag–Leffler function. The transcendental equations for the time of flight and the time of maximum height are solved numerically. The model agrees with the classical one as the fractional order tends to 1. In view of the superior results, the current numerical modeling approach is validated for this real-world application.

Effects of Coulomb coupling on stopping power and a link to macroscopic transport

Abstract: Molecular dynamics simulations are used to assess the influence of Coulomb coupling on the energy evolution of charged projectiles in the classical one-component plasma. The average projectile kinetic energy is found to decrease linearly with time when να/ωp ≲ 10−2, where να is the Coulomb collision frequency between the projectile and the medium, and ωp is the plasma frequency. Stopping power is obtained from the slope of this curve. In comparison to the weakly coupled limit, strong Coulomb coupling causes the magnitude of the dimensionless stopping power, (a/kBT)dE/dx, to increase, the Bragg peak to shift to several times the plasma thermal speed, and for the stopping power curve to broaden substantially. The rate of change of the total projectile kinetic energy averaged over many independent simulations is shown to consist of two measurable components: a component associated with a one-dimensional friction force and a thermal energy exchange rate. In the limit of a slow and massive projectile, these can be related to the macroscopic transport rates of self-diffusion and temperature relaxation in the plasma. Simulation results are compared with available theoretical models for stopping power, self-diffusion, and temperature relaxation.

Penetration of Steel Projectiles through Finite-Thickness Ice Targets

Abstract: A single-stage gas-driven setup is developed, which allows 0.5-kg projectiles to be accelerated to velocities of the order of 1200 m/s. Experiments with penetration of steel projectiles into a massive ice target are performed. The experimental data are compared with the results of computations performed by the REACTOR software system and numerical calculations of destruction of a finite-thickness ice target under the impact of one projectile and several projectiles. It is demonstrated that an impact of a steel ring onto a finite-thickness ice target leads to knock-out of the maximum volume of ice and almost complete loss of the kinetic energy of the ring.

Attitude Measurement for High-Spinning Projectile with a Hollow MEMS IMU Consisting of Multiple Accelerometers and Gyros.

Abstract: A low cost, high precision hollow structure MEMS IMU has been developed to measure the roll angular rate of a high-spinning projectile. The hollow MEMS IMU is realized by designing the scheme of non-centroid configuration of multiple accelerometers. Two dual-axis accelerometers are respectively mounted on the pitch axis and the yaw axis away from the center of mass of the high-spinning projectile. Three single-axis gyros are mounted orthogonal to each other to measure the angular rates, respectively. The roll gyro is not only used to judge the spinning direction, but also to measure and compensate for the low rotation speed of the high-spinning projectile. In order to improve the measurement accuracy of the sensor, the sensor output error is modeled and calibrated by the least square method. By analyzing the influence of noise statistical characteristics on angular rate solution accuracy, an adaptive unscented Kalman filter (AUKF) algorithm is proposed, which has a higher estimation accuracy than UKF algorithm. The feasibility of the method is verified by numerical simulation. By using the MEMS IMU device to build a semi-physical simulation platform, the solution accuracy of the angular rate is analyzed by simulating different rotation speeds of the projectile. Finally, the flight test is carried out on the rocket projectile with the hollow MEMS IMU. The test results show that the hollow MEMS IMU is reasonable and feasible, and it can calculate the roll angular rate in real time. Therefore, the hollow MEMS IMU designed in this paper has certain engineering application value for high-spinning projectiles.

Paleoindian Projectile-Point Diversity in the American Southeast: Evidence for the Mosaic Evolution of Point Design*

Abstract: Paleoindian projectile points occur in high numbers in the American Southeast, and when compared to other regions of the East, the Southeast has the greatest projectile-point diversity. In ...

SPH modeling of high velocity impact into ballistic gelatin. Development of an axis-symmetrical formulation

Abstract: The investigation of impact biomechanics is of extreme importance in the understanding of damages which are caused by a projectile impacting the human body. In a high-velocity impact framework, non...

Simulation and Analysis of the Railgun Muzzle Flow Field Considering the Arc Plasma

Abstract: The electromagnetic railgun is a new concept weapon with the hypersonic launch capability. During the railgun launch process, the armature is accelerated along the rails. A complex and high-speed flow field occurs in the muzzle area when the armature leaves the barrel. Meanwhile, the muzzle temperature will be very high because of the secondary arc and friction. In this paper, an analysis of the railgun muzzle fluid flow field after the armature left the barrel is presented, and a three-dimension numerical model for arc plasma is obtained based on the electromagnetic and hydrodynamic equations. The aerodynamic simulation method with moving boundary is adopted to deduce the boundary conditions of the arc model, where the coupling model and the dynamic meshing method are applied. In addition, the backflow phenomenon is considered in the arc model. The distributions of the temperature and the velocity near the muzzle are computed, especially for the dynamic distribution of the arc plasmas. As we can see from the results, the plasma near the muzzle expands outward when the armature leaves the barrel, and most of the plasma will flow back to the bore in a short time. The existence of muzzle plasma may aggravate the erosion and aluminum deposition, which will lead to negative effects on the launcher’s lifetime.