Showing papers on "Projectile published in 2011"

The African Origin of Complex Projectile Technology: An Analysis Using Tip Cross-Sectional Area and Perimeter

Abstract: Despite a body of literature focusing on the functionality of modern and stylistically distinct projectile points, comparatively little attention has been paid to quantifying the functionality of the early stages of projectile use. Previous work identified a simple ballistics measure, the Tip Cross-Sectional Area, as a way of determining if a given class of stone points could have served as effective projectile armatures. Here we use this in combination with an alternate measure, the Tip Cross-Sectional Perimeter, a more accurate proxy of the force needed to penetrate a target to a lethal depth. The current study discusses this measure and uses it to analyze a collection of measurements from African Middle Stone Age pointed stone artifacts. Several point types that were rejected in previous studies are statistically indistinguishable from ethnographic projectile points using this new measure. The ramifications of this finding for a Middle Stone Age origin of complex projectile technology is discussed.

Finite element simulation of ceramic/composite armor under ballistic impact

Abstract: In this paper, based on LS-Dyna code, a new finite element (FE) simulation of the ballistic perforation of the ceramic/composite targets, which impacted by cylindrical tungsten projectiles, has been presented. Research on this method has been conducted by a few research groups in recent years. The ceramic material, which is the front plate, has been made of Alumina 99.5% and composite back-up plate composed of Twaron fibers. The 2-dimensional (2D), axi-symmetric, dynamic-explicit, Lagrangian model has been considered in this simulation. The Johnson–Cook, Johnson–Holmquist and Composite-Damage materials behaviors have been used for projectile, ceramic and composite materials respectively. The brittle fracture and fragmentation of ceramic conoid, the failure criteria based on fracture of fibers or matrixes of composite materials and erosion or flattening of projectile during perforation have been considered. The residual velocity and perforation time has been obtained and compared with the available analytical models. The results show that when the ceramic is impacted by a projectile, a fragmented ceramic conoid breaks from ceramic tile and the semi-angle of ceramic conoid with increasing initial velocity decreases. Furthermore, the dishing of composite layers at high impact velocities and the delamination of layers near the ballistic limit velocity decrease.

Manipulating atomic fragmentation processes by controlling the projectile coherence.

Abstract: We have measured the scattering angle dependence of cross sections for ionization in $p+{\mathrm{H}}_{2}$ collisions for a fixed projectile energy loss. Depending on the projectile coherence, interference due to indistinguishable diffraction of the projectile from the two atomic centers was either present or absent in the data. This shows that, due to the fundamentals of quantum mechanics, the preparation of the beam must be included in theoretical calculations. The results have far-reaching implications on formal atomic scattering theory because this critical aspect has been overlooked for several decades.

Evaluation of Different Projectiles in Matched Experimental Eye Impact Simulations

Abstract: Eye trauma results in 30,000 cases of blindness each year in the United States and is the second leading cause of monocular visual impairment. Eye injury is caused by a wide variety of projectile impacts and loading scenarios with common sources of trauma being motor vehicle crashes, military operations, and sporting impacts. For the current study, 79 experimental eye impact tests in literature were computationally modeled to analyze global and localized responses of the eye to a variety of blunt projectile impacts. Simulations were run with eight different projectiles (airsoft pellets, baseball, air gun pellets commonly known as BBs, blunt impactor, paintball, aluminum, foam, and plastic rods) to characterize effects of the projectile size, mass, geometry, material properties, and velocity on eye response. This study presents a matched comparison of experimental test results and computational model outputs including stress, energy, and pressure used to evaluate risk of eye injury. In general, the computational results agreed with the experimental results. A receiver operating characteristic curve analysis was used to establish the stress and pressure thresholds that best discriminated for globe rupture in the matched experimental tests. Globe rupture is predicted by the computational simulations when the corneoscleral stress exceeds 17.21 MPa or the vitreous pressure exceeds 1.01 MPa. Peak stresses were located at the apex of the cornea, the limbus, or the equator depending on the type of projectile impacting the eye. A multivariate correlation analysis revealed that area-normalized kinetic energy was the best single predictor of peak stress and pressure. Additional incorporation of a relative size parameter that relates the projectile area to the area of the eye reduced stress response variability and may be of importance in eye injury prediction. The modeling efforts shed light on the injury response of the eye when subjected to a variety of blunt projectile impacts and further validate the eye model's ability to predict globe rupture. Results of this study are relevant to the design and regulation of safety systems and equipment to protect against eye injury.

Infinite Penetration of a Projectile into a Granular Medium

Abstract: An object falling in a fluid reaches a terminal velocity when the drag force and its weight are balanced. Contrastingly, an object impacting into a granular medium rapidly dissipates all its energy and comes to rest always at a shallow depth. Here we study, experimentally and theoretically, the penetration dynamics of a projectile in a very long silo filled with expanded polystyrene particles. We discovered that, above a critical mass, the projectile reaches a terminal velocity and, therefore, an endless penetration.

Initiation of detonation by conical projectiles

Abstract: Initiation of detonation by a hypersonic conical projectile launched into a combustible gas mixture is investigated. From analytic considerations of the flowfield, energetic and kinetic limits are proposed to predict the conditions required to initiate an oblique detonation wave in the mixture. To experimentally investigate these limits, projectiles with cone half angles varying from 15° to 60° were launched into a stoichiometric mixture of hydrogen/oxygen with 70% argon dilution at initial pressure between 10 and 200 kPa. The projectiles were launched from a combustion-driven gas gun at velocities as great as 2.5 km/s (corresponding to 150% of the Chapman Jouguet velocity). Pictures of the flowfields generated by the projectiles were taken via schlieren photography. Five combustion regimes could be observed about the projectile ranging from a prompt and delayed oblique detonation wave formation, combustion instabilities, a wave splitting, and an inert shock wave. The two theoretical limits provide a means to interpret the observed flowfield regimes and are in satisfactory agreement with the experimental results.

Silicate dust size distribution from hypervelocity collisions: implications for dust production in debris disks

Abstract: Fragments generated by high-velocity collisions between solid planetary bodies are one of the main sources of new interplanetary dust particles. However, only limited ranges of collision velocity, ejecta size, and target materials have been studied in previous laboratory experiments, and the collision condition that enables the production of dust-sized particles remains unclear. We conducted hypervelocity impact experiments on silicate rocks at relative velocities of 9 to 61 km s{sup -1}, which is beyond the upper limit of previous laboratory studies. Sub-millimeter-diameter aluminum and gold spheres were accelerated by laser ablation and were shot into dunite and basalt targets. We analyzed the surfaces of aerogel blocks deployed near the targets using an electron probe micro analyzer and counted the number of particles that contained the target material. The size distributions of ejecta ranged from five to tens of microns in diameter. The total cross-sectional area of dust-sized ejecta monotonically increased with the projectile kinetic energy, independent of impact velocity, projectile diameter, and projectile and target material compositions. The slopes of the cumulative ejecta-size distributions ranged from -2 to -5. Most of the slopes were steeper than the -2.5 or -2.7 that is expected for a collisional equilibrium distribution in a collisionmore » cascade with mass-independent or mass-dependent catastrophic disruption thresholds, respectively. This suggests that the steep dust size-distribution proposed for the debris disk around HD172555 (an A5V star) could be due to a hypervelocity collision.« less

A combined molecular dynamics and Monte Carlo simulation of the spatial distribution of energy deposition by proton beams in liquid water

Abstract: We have evaluated the spatial distribution of energy deposition by proton beams in liquid water using the simulation code SEICS (Simulation of Energetic Ions and Clusters through Solids), which combines molecular dynamics and Monte Carlo techniques and includes the main interaction phenomena between the projectile and the target constituents: (i) the electronic stopping force due to energy loss to target electronic excitations, including fluctuations due to the energy-loss straggling, (ii) the elastic scattering with the target nuclei, with their corresponding energy loss and (iii) the dynamical changes in projectile charge state due to electronic capture and loss processes. An important feature of SEICS is the accurate account of the excitation spectrum of liquid water, based on a consistent solid-state description of its energy-loss-function over the whole energy and momentum space. We analyse how the above-mentioned interactions affect the depth distribution of the energy delivered in liquid water by proton beams with incident energies of the order of several MeV. Our simulations show that the position of the Bragg peak is determined mainly by the stopping power, whereas its width can be attributed to the energy-loss straggling. Multiple elastic scattering processes contribute slightly only at the distal part of the Bragg peak. The charge state of the projectiles only changes when approaching the end of their trajectories, i.e. near the Bragg peak. We have also simulated the proton-beam energy distribution at several depths in the liquid water target, and found that it is determined mainly by the fluctuation in the energy loss of the projectile, evaluated through the energy-loss straggling. We conclude that a proper description of the target excitation spectrum as well

Introducing electron capture into the unitary-convolution-approximation energy-loss theory at low velocities

Abstract: Recent developments in the theoretical treatment of electronic energy losses of bare and screened ions in gases are presented. Specifically, the unitary-convolution-approximation (UCA) stopping-power model has proven its strengths for the determination of nonequilibrium effects for light as well as heavy projectiles at intermediate to high projectile velocities. The focus of this contribution will be on the UCA and its extension to specific projectile energies far below 100 keV/u, by considering electron-capture contributions at charge-equilibrium conditions.

Rail Gun Muzzle Velocity Control With High Accuracy

Abstract: A rail gun can be used as an experimental tool to accelerate small-mass specimens up to 300 m/s to study impact phenomena. In order to obtain comparable and reproducible results, it is desirable to achieve a low statistical deviation of the final velocity. To decrease the deviation during the launch for a railgun, the movement of the projectile is observed along the barrel and the difference between the desired and the measured velocity is calculated. The driving current is then adjusted dynamically by triggering the capacitor modules earlier or later than planned. This paper presents initial experimental results within this study. A light barrier system has been set up to monitor the projectile's position in real time. The special design of the system prevents disturbances caused by magnetic fields and electromagnetic radiation. This is reported in detail. A series of shots was performed under constant conditions to measure the deviation of the final velocity. Launches were performed using the French-German Research Institute Saint Louis's augmented railgun (caliber 15 mm × 15 mm, length 1.6 m), which was supplied by a 38-kJ capacitor bank. The bank consisted of four energy modules, each module containing one capacitor and a thyristor as a switch. The modules could be triggered independently from each other. In the second series of shots, the trigger-time of the last module was varied to investigate the effect on the final velocity. The experimental results are analyzed and discussed.

Ballistic Impact Behaviour of a Tempered Bainitic Steel Against 7.62 mm Armour Piercing Projectile

Abstract: In this study, occurence of failure after the interaction between an armour piercing 7.62 mm caliber projectile and a tempered bainitic steel has been investigated. The shot was performed at zero degree with a projectile velocity of 840 m/s. After the shot, microstructural and fractographical examinations were carried out on the sample taken from the perforated region. In the etched sample, it was observed that the morphology of the original microstructure had changed and adiabatic shear bands (ASBs) were formed in regions close to the direction of penetration. Main failure is ductile (plastic) deformation was followed by cleavage after shot. Cracks due to adiabatic shear band and formation of abrasive wear were seen. The perforation mode of the steel was a typical petalling.

The Canyon Diablo impact event: 2. Projectile fate and target melting upon impact

Abstract: – Despite its centennial exploration history, there are still unresolved questions about Meteor Crater, the first recognized impact crater on Earth. This theoretical study addresses some of these questions by comparing model results with field and laboratory studies of Meteor Crater. Our results indicate that Meteor Crater was formed by a high-velocity impact of a fragmented projectile, ruling out a highly dispersed swarm as well as a very low impact velocity. Projectile fragmentation caused many fragments to fall separately from the main body of the impactor, making up the bulk of the Canyon Diablo meteorites; most of these fragments were engulfed in the expansion plume as they approached the surface without suffering high shock compression, and were redistributed randomly around the crater. Thus, the distribution of Canyon Diablo meteorites is not representative of projectile trajectory, as is usual for impactor fragments in smaller strewn fields. At least 50% of the main impactor was ejected from the crater during crater excavation and was dispersed mostly downrange of the crater as molten particles (spheroids) and highly shocked solid fragments (shrapnel). When compared with the known distribution, model results suggest an impactor from the SW. Overall, every model case produced much higher amounts of pure projectile material than observed. The projectile-target mixing was not considered in the models; however, this process could be the main sink of projectile melt, as all analyzed melt particles have high concentrations of projectile material. The fate of the solid projectile fragments is still not completely resolved. Model results suggest that the depth of melting in the target can reach the Coconino sandstone formation. However, most of the ejected melt originates from 30–40 m depth and, thus, is limited to Moenkopi and upper Kaibab material. Some melt remains in the target; based on the estimated volume of the breccia lens at Meteor Crater, our models suggest at most a 2% content of melt in the breccia. Finally, a high water table at the time of impact could have aided strong dispersion of target and projectile melt.

Two source emission behavior of projectile fragments alpha in 84 Kr interactions at around 1 GeV per nucleon

Abstract: The emission of projectile fragments alpha has been studied in 84Kr interactions with nuclei of the nuclear emulsion detector composition at relativistic energy below 2 GeV per nucleon. The angular distribution of projectile fragments alpha in terms of transverse momentum could not be explained by a straight and clean-cut collision geometry hypothesis of Participant — Spectator (PS) Model. Therefore, it is assumed that projectile fragments alpha were produced from two separate sources that belong to the projectile spectator region differing drastically in their temperatures. It has been clearly observed that the emission of projectile fragments alpha are from two different sources. The contribution of projectile fragments alpha from contact layer or hot source is a few percent of the total emission of projectile fragments alphas. Most of the projectile fragments alphas are emitted from the cold source.

The added mass of a spherical projectile

Abstract: When a ball moves through the air, the air exerts a force on the ball. For a sphere moving at constant velocity with respect to the air, this force is called the drag force and it has been well measured. If the sphere moves with a nonconstant velocity there are additional forces. These “unsteady” forces depend on the sphere’s acceleration and, in principle, also on higher derivatives of the motion. The force equal to a constant times the acceleration is called the “added mass” because it increases the effective inertia of the sphere moving through the fluid. We measure the unsteady forces on a sphere by observing the one- and two-dimensional projectile motion of light spheres around the highest point. The one-dimensional motion is well described by just the usual buoyant force and the added mass as calculated in the ideal fluid model. This measurement is an excellent experiment for introductory physics students. For spheres in two-dimensional projectile motion the downward vertical acceleration at the highest point increases with the horizontal velocity. This effect can be described by an additional force proportional to the speed times the acceleration.

Cavity dynamics and particle alignment in the wake of a supersonic projectile penetrating a dusty plasma

Abstract: The penetration of a projectile into a strongly coupled dusty plasma was studied in a radio-frequency discharge under microgravity conditions. A supersonic projectile produces an elongated dust-free cavity in its wake. The dynamics of the cavity is analyzed and compared with Langevin dynamics simulations. Besides a three-dimensional Mach cone structure, the simulation shows that the cavity dynamics can be subdivided into three phases: An opening phase with fixed time scale, a closing phase, whose duration is affected by the projectile speed and, finally, a phase of particle realignment in the target cloud, which persists for a long time after the closure of the cavity.

Virtual fly-out simulations of a spinning projectile from subsonic to supersonic speeds

Abstract: This paper describes a computational study undertaken to compute the unsteady freeflight aerodynamics of a spinning projectile using an advanced coupled computational fluid dynamics (CFD)/rigid body dynamics (RBD) technique. The CFD part uses an unstructured time-accurate Navier-Stokes computational technique. The coupled CFD/RBD method allows time-accurate virtual fly-out simulations of projectiles and simultaneously predicts the aerodynamics and the flight dynamics in an integrated manner. In addition, both static and dynamic aerodynamic coefficients can be extracted from these fully coupled timeaccurate virtual fly-out computations. Numerical computations have been performed for the spinning projectile across the speed regime from subsonic to supersonic speeds. Computed results qualitatively show the flow field for different flow regimes. Aerodynamic force and moment coefficients have been extracted and are compared with available data.

Toy projectile launcher apparatus

Abstract: A toy launcher apparatus for discharging circular projectiles, the apparatus having a housing, lower and upper panels mounted to the housing, supports mounted to the housing, a cocking slide and a slide spring connected to the supports, a projectile receptacle connected to the cocking slide, release levers mounted to the housing, a guide wall mounted to the lower panel, a positioning wheel also mounted to the lower panel, and a trigger mounted to the housing. The lower panel includes a slot positioned parallel to the guide wall but off center relative to a center point of a load projectile. Beneath the lower panel is a rotatable launch arm connected to a torsion spring and a catch structure. The upper and lower panels are parallel to one another and spaced to receive a projectile. The projectile is loaded into the projectile receptacle when the receptacle is exposed during the time the launch arm and torsion spring are cocked by a user pulling rearward on the cocking slide. The launch arm is captured by the catch structure, and the cocking slide and the receptacle are also captured. After loading the projectile, the one of the release levers is activated to snap the cocking slide, the carriage and the loaded projectile to a predetermined launch position. When a user pulls the trigger the launch arm is rapidly rotated by the torsion spring through the slot where the launch arm impacts the loaded and correctly positioned projectile and causes the projectile to be discharge with a spin.

Modeling Perforation in Glass Fiber Reinforced Composites Subjected to Low Velocity Impact Loading

Abstract: In this article, experimental results are presented investigating the response of glass fiber composites subjected to low velocity impact loading. The resulting load-displacement traces and deformation modes have been used to validate a number of numerical models. Here, finite element models have been developed to predict the impact behavior of the composite plates. Damage in the woven glass-fiber reinforced composite plate was modeled using the Hashin failure criteria. The influence of target size, projectile size, projectile shape, and striking location on the impact response of the composites was investigated. In general, good agreement was obtained in terms of the load-displacement traces and the failure modes in the composite plates. It has been shown that the perforation energy increases rapidly with target thickness, with the numerical results closely agreeing with the experimental data. Similarly, the energy required to perforate the composite targets increases with increasing projectile diameter, with the failure mechanisms being similar in all cases. Finally, increasing the bluntness of the impactor resulted in a significant increase in the energy to perforate these targets. POLYM. COMPOS., 32:1380–1388, 2011. a 2011 Society of Plastics Engineers

Ballistic penetration of conically cylindrical steel projectile into 3D orthogonal woven composite: a finite element study at microstructure level

Abstract: Ballistic penetration of conically cylindrical steel projectile into 3D orthogonal woven composite (3DOWC) was investigated from finite element analyses and ballistic impact tests. Based on the observation of the microstructure of the 3DOWC, a microstructure model was established for finite element calculation. In this model, the cross-section of warp, weft and Z-direction fiber tows was regarded as rectangular. The noninterwoven warp and weft yarns were bonded together with Z-yarns. The impact damage and energy absorption of the 3DOWC penetrated by a conically cylindrical steel projectile were calculated from the microstructure model and compared with the testing results. Good agreements with experiments have been observed, especially for deformation, damage evolution, and strain wave distribution in the 3DOWC under ballistic penetration.