Showing papers on "Projectile published in 2017"

Water Ice Radiolytic O2, H2, and H2O2 Yields for Any Projectile Species, Energy, or Temperature: A Model for Icy Astrophysical Bodies

Abstract: O2, H2, and H2O2 radiolysis from water ice is pervasive on icy astrophysical bodies, but the lack of a self-consistent, quantitative model of the yields of these water products versus irradiation projectile species and energy has been an obstacle to estimating the radiolytic oxidant sources to the surfaces and exospheres of these objects. A major challenge is the wide variation of O2 radiolysis yields between laboratory experiments, ranging over 4 orders of magnitude from 5 × 10−7 to 5 × 10−3 molecules/eV for different particles and energies. We revisit decades of laboratory data to solve this long-standing puzzle, finding an inverse projectile range dependence in the O2 yields, due to preferential O2 formation from an ~30 A thick oxygenated surface layer. Highly penetrating projectile ions and electrons with ranges ≳30 A are therefore less efficient at producing O2 than slow/heavy ions and low-energy electrons (≲ 400 eV) which deposit most energy near the surface. Unlike O2, the H2O2 yields from penetrating projectiles fall within a comparatively narrow range of (0.1–6) × 10−3 molecules/eV and do not depend on range, suggesting that H2O2 forms deep in the ice uniformly along the projectile track, e.g., by reactions of OH radicals. We develop an analytical model for O2, H2, and H2O2 yields from pure water ice for electrons and singly charged ions of any mass and energy and apply the model to estimate possible O2 source rates on several icy satellites. The yields are upper limits for icy bodies on which surface impurities may be present.

Parameters of Holmquist–Johnson–Cook model for high-strength concrete-like materials under projectile impact:

Abstract: Holmquist–Johnson–Cook constitutive model has been widely used in analyzing the dynamic responses of concrete-like materials under projectile impact and explosive loadings, the constitutive paramet...

Effect of projectile nose geometry on the critical velocity and failure of yarn subjected to transverse impact

Abstract: Three different types of yarn have been subjected to transverse impact experiments in efforts to gain an understanding of local yarn failure and to provide input parameters for future transverse ya...

Ballistic performances of concrete targets subjected to long projectile impact

Abstract: Concrete is a widely used material in the construction of strategic and important structures such as nuclear containments, bridges, storage structures and military bunkers. In the present study perforation experiments and simulations on finite element code ABAQUS/Explicit have been carried out to understand the behavior of concrete against projectile impact. Penetration tests were conducted on square (450 mm×450 mm) targets of plain and reinforced concrete of unconfined compressive strength 48 MPa. To investigate the effect of reinforcement, 8 mm diameter steel grid was incorporated at the center of thickness of the target. The targets were subjected to normal impact by 0.5 and 1 kg ogival nosed hardened steel projectiles of caliber radius head (CRH) 3 and length to diameter (l/d) ratio 23.7 and 11.8 respectively. The velocity regime of the projectile was considered in the range 43–178 m/s. The results thus obtained were presented and influence there on the ballistic performance due to the variation in l/d ratio of projectiles have been discussed. In comparison to plain concrete, the ballistic limit of the reinforced concrete target was found to have increased by 14%. A fair agreement was found between actual and predicted residual velocities obtained in the present study. The actual and simulated ballistic limit against 0.5 kg projectile differed by 10.8% and 5.1% for plain and reinforced concrete target respectively. This deviation has been found to be 16.1% and 6.7% respectively against 1 kg projectile.

Convergent close-coupling approach to light and heavy projectile scattering on atomic and molecular hydrogen

Abstract: The atomic hydrogen target has played a pivotal role in the development of quantum collision theory. The key complexities of computationally managing the countably infinite discrete states and the uncountably infinite continuum were solved by using atomic hydrogen as the prototype atomic target. In the case of positron or proton scattering the extra complexity of charge exchange was also solved using the atomic hydrogen target. Most recently, molecular hydrogen has been used successfully as a prototype molecule for developing the corresponding scattering theory. We concentrate on the convergent close-coupling computational approach to light projectiles, such as electrons and positrons, and heavy projectiles, such as protons and antiprotons, scattering on atomic and molecular hydrogen.

Comparative numerical and experimental study of projectile impact on reinforced concrete

Abstract: Concrete structures in military areas are subject to projectile impact both as a result of direct fire and in the form of splinters from explosives. These structures may be damaged, resulting in partial loss of integrity, but must leave the objects or individuals within them unharmed to the largest extent possible. The degree of damage depends on a variety of factors relating to the projectile, including its mass, geometry, impact velocity, trajectory and material properties. A number of controllable factors also relate to the characteristics of the concrete structure itself and the reinforcing material used to produce barriers. In order to analyse the structural response and optimize design parameters, various dynamics simulations have been performed in this work relating to projectile impact on concrete structures. To correctly model the impact, both non-linear material response and progressive finite element erosion have been taken into account. The numerical results have been discussed and compared with experimental results for three different impact scenarios, with good alignment achieved in terms of both penetration depth and crater size. This correspondence also demonstrated the pertinence of a specific material model, the Riedel-Hiermaier-Thoma (RHT) model within the LS Dyna FEM software package, in guiding and interpreting physical experiments in the case of impulsive projectile loading and penetration of concrete. The alignment between experiments and simulations also confirmed the robustness of the material model, specifically selected for this particular application.

Dynamic characteristics of aluminium foams under impact crushing

Abstract: The dynamic behavior of metal foams under impact crushing is of great interest for both fundamental research and engineering applications. This paper presents a systematical and thorough investigation on the dynamic response of a colliding mass impacting on metal foams that exhibit strain hardening. Experimental investigation, finite element (FE) simulation and analytical modelling are conducted in this study. In the experimental work, an instrumented projectile acting as a colliding mass was designed and implemented by using a novel in situ deceleration measurement unit embedded within a metal body. This projectile measures in situ rigid-body deceleration and provides a measure for net resistance on the projectile during the dynamic impact test. In each test, the impact velocity and crushing depth of the projectile were recorded. Based on the metal foams that exhibit strain hardening in this study, an exponential stress-strain relation is proposed to model the static strength of aluminium foam specimens, which is used for subsequent FE simulation and the analytical model. The predictions of the proposed analytical model are compared with an earlier analytical model based on Rigid Perfectly-Plastic-Locking (RPPL) idealization. RPPL can only well approximate the stress-strain characteristic of metal foams with low strain hardening. It is found that the proposed analytical model matches the experimental results much better than the earlier analytical model based on RPPL. The experimental results also agree well with the FE simulation results that are obtained based on the proposed exponential stress-strain model.

In‐flight dynamics of volcanic ballistic projectiles

Abstract: Centimeter to meter-sized volcanic ballistic projectiles from explosive eruptions jeopardize people and properties kilometers from the volcano, but they also provide information about the past eruptions. Traditionally, projectile trajectory is modeled using simplified ballistic theory, accounting for gravity and drag forces only and assuming simply shaped projectiles free moving through air. Recently, collisions between projectiles and interactions with plumes are starting to be considered. Besides theory, experimental studies and field mapping have so far dominated volcanic projectile research, with only limited observations. High-speed, high-definition imaging now offers a new spatial and temporal scale of observation that we use to illuminate projectile dynamics. In-flight collisions commonly affect the size, shape, trajectory, and rotation of projectiles according to both projectile nature (ductile bomb versus brittle block) and the location and timing of collisions. These, in turn, are controlled by ejection pulses occurring at the vent. In-flight tearing and fragmentation characterize large bombs, which often break on landing, both factors concurring to decrease the average grain size of the resulting deposits. Complex rotation and spinning are ubiquitous features of projectiles, and the related Magnus effect may deviate projectile trajectory by tens of degrees. A new relationship is derived, linking projectile velocity and size with the size of the resulting impact crater. Finally, apparent drag coefficient values, obtained for selected projectiles, mostly range from 1 to 7, higher than expected, reflecting complex projectile dynamics. These new perspectives will impact projectile hazard mitigation and the interpretation of projectile deposits from past eruptions, both on Earth and on other planets.

Coilgun Velocity Optimization With Current Switch Circuit

Abstract: An inductive coil gun is a solenoid surrounding a cylindrical metallic armature (the projectile), both electromagnetically coupled. One or more capacitors discharge a stored voltage quickly through the coil, configuring a kind of RLC circuit, with the pulse-shaped current generating a magnetic field inside the coil that accelerates the projectile. Once the projectile crosses an equilibrium point inside the coil, the existing magnetic field pulls the armature back, therefore reducing the final muzzle velocity and decreasing the efficiency—defined as the ratio between the available capacitor electrostatic versus the slug kinetic energies. This paper describes a system that monitors the armature position inside the coil, with a laser beam, and automatically cuts the current when the projectile reaches the equilibrium point. The system, named current switch circuit, enables higher velocities using the same set of coilgun and projectiles, providing a higher efficiency.

Electron-impact ionization of H 2 O at low projectile energy: Internormalized triple-differential cross sections in three-dimensional kinematics

Abstract: Xueguang Ren,1 Sadek Amami,2 Khokon Hossen,1 Esam Ali,2 ChuanGang Ning,3 James Colgan,4 Don Madison,2 and Alexander Dorn1 1Max-Planck-Institut für Kernphysik, 69117 Heidelberg, Germany 2Physics Department, Missouri University of Science and Technology, Rolla, Missouri 65409, USA 3Department of Physics, State Key Laboratory of Low-Dimensional Quantum Physics, Tsinghua University, Beijing 100084, China 4Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA (Received 18 November 2016; published 2 February 2017)

Experimental Study on Behind-Plate Overpressure Effect by Reactive Material Projectile

Abstract: The behind-plate overpressure effect by a reactive material projectile with a density of 7.7 g cm−3 was investigated by ballistic impact and sealed chamber tests. The reactive projectile was launched onto the initially sealed test chamber with a 2024-T3 aluminum cover plate with a thickness of 3 mm, 6 mm, and 10 mm, respectively. Moreover, the overpressure signals in the test chamber were recorded by a pressure sensor and a data acquisition system. The experimental results show that the behind-plate overpressure effect is significantly influenced by plate thickness and impact velocity. For a given plate thickness, the peak overpressure in the test chamber shows an increasing trend with increase of impact velocity. However, for a given impact velocity, when impacting the 6 mm thick aluminum plate, the peak overpressure measured and the impulse delivered to chamber are higher than the values recorded for the 3 mm and 10 mm thick aluminum plates. As such, it is inferred that there is an optimum plate thickness to maximize the behind-plate overpressure effect by reactive projectile.