Projectile Surface Research Articles

Graphene origami with enhanced impact resistance and energy absorption performance

The ancient art of origami has recently shown its potential in engineering intricate three-dimensional graphene structures with unique properties. This study employs molecular dynamics simulations to investigate the dynamic mechanical behavior of graphene origami structures (GOS) under hypervelocity ballistic impact. The analysis of residual velocity, kinetic energy loss, and specific penetration energy shows that GOS exhibit superior impact resistance and energy absorption performance compared with pristine graphene. One reason for the enhancements is that highly flexible GOS can unfold to produce a conical impact zone with larger out-of-plane deformation. Another reason is that three-dimensional folded regions possess more mass, enabling them to dissipate more kinetic energy from the projectile. The impact behavior of GOS is further analyzed concerning projectile size, impact position, and surface roughness. It is found that the impact resistance and energy absorption capacity of GOS can be adjusted by altering the surface roughness, specifically the folding degree and pattern geometry. This GOS holds promise for diverse applications in impact protection, such as combat armor and spacecraft shields.

Heating patterns and temperature distribution of projectile surface in lunar regolith penetration

During penetration, a large quantity of friction-induced heat is generated, significantly increasing the projectile surface temperature. Considering that the temperature variation depends on the physical properties of the target being penetrated, understanding this relationship can aid in extraterrestrial material behavior for detection and analysis efforts. The study investigated the patterns of heat generation and the distribution of temperature on the surface of a projectile as it penetrates lunar regolith. For discrete medium penetration, large deviations appear in temperature prediction due to particle extrusion flow. Thus, a heat flux density model on the projectile surface by introducing a relative velocity factor (RVF) for correction was established. The particle flow characteristics simulation and fitting model of the introduced factor were also obtained. We constructed a theoretical relationship between the resistance and stress model parameters using dynamic modeling. Experimental projectiles recording penetration acceleration and temperature at the points of interest on the projectile surface were designed and tested to obtain recorded data. The temperature field in this process was simulated in COMSOL software to calculate the projectile surface's heat flux density and temperature distribution. The results indicate that the developed model is effective. This research infers the physical characteristics of the penetrating target under specified penetration conditions and provides more dimensional information for lunar regolith exploration.

Effects of Hugoniot properties on jet onset conditions

Jets are the earliest ejected material from a hypervelocity impact event. Jets comprises of projectile and target's surface material and are ejected at velocities higher than escape velocity for Earth. Effects of Hugoniot properties of the projectile and target material on jet initiation are not well understood. We, therefore, developed a mathematical model that incorporated the limitations imposed by Hugoniot properties on jet initiation for hypervelocity impact. This model analysed the effects of changes in Hugoniot properties of the projectile and target on the jet onset time, jet onset velocity and jetting side (projectile or target). The results reveal that (i) jet initiates earlier and at higher velocity if the jetting side has higher value of shock parameter or higher velocity of sound in the material; (ii) jet initiates later and at lower velocity if jetting side has high density; (iii) effect of s-parameter and speed of sound in material is more profound than the effect of density.

Hydrodynamics of the projectile entering the water under the ice hole constraint environment

The study of the water entry of the projectile passing through the ice hole can solve the special issue of water entry under marine environmental constraints. We conducted experiments to validate the effect of the ice hole constraint on the dynamics of the water entry cavity and then used the numerical simulations to investigate the cavity dynamics of the projectile passing through ice holes with different sizes and rotation degrees. The results show that the ice hole affects the evolution of the water entry cavity and the motion state of the projectile. The splash crown flows back and then contacts the projectile surface when passing through the small-sized ice hole. Cavity collapses before the pinch-off. The splash crown flows back at the hole as the hole size increases, the cavity morphology is complete, and the projectile's movement is more stable at the initial stage of water entry and after deep cavity pinch-off. Special oblique jets form when passing through irregular holes. The impact of the oblique jet on the cavity increases as the rotation degree increases. The type of hole has little effect on the water entry dynamics of the projectile, but has a significant effect on the cavity morphology and the jet motion near the hole. The size of the hole has a great effect on the motion stability of the projectile.

Effect of asymmetric nose shape on the cavity and mechanics of projectile during high-speed water entry

The characteristics of cavity evolution and motion in water entry created by an asymmetrical nose shape projectile at some different dimensionless excision radius are numerically investigated. CFD numerical methods are used to simulate the high-speed water entry process, the cavitation evolution, flow field and force of the projectile are monitored. The numerical results show that when the projectile enters the water with an asymmetrical nose shape, the cavity bends, and with the increase of dimensionless excision radius, the expansion and contraction speed of cavity increase, and the anticlockwise deflection angle of cavity decreases. The pressure of projectile surface shows an obvious asymmetry, and area of low pressure at the edge of the asymmetric surface is found. Meanwhile, there are two peaks of acceleration while water entry, the deflection of the projectile trajectory is caused by the asymmetric nose shape, and with the increase of dimensionless excision radius, the projectile acceleration decreases, the displacement on y direction increases, and the projectile deflection velocity decrease.

Functionally graded porous plate reinforced by carbon nanotubes subjected to low-velocity impact: an analytical and numerical analysis

PurposeThe purpose of this study is a numerical simulation and an analytical analysis about the low-velocity impact on a functionally graded porous plate with porosity distribution in the thickness direction. In this article, polymethyl methacrylate is used for matrix, and single-walled carbon nanotube (CNTs) (10,10) with consideration agglomeration sizes and lumping of CNT inside the agglomerations is applied for reinforcement.Design/methodology/approachIn analytical formulation, the non-linear Hertz contact law is applied for interaction between projectile and plate surface. High-order shear deformation plate theory is developed, and energy of the system for impactor and plate is written. The governing equations are derived using Ritz method and Lagrange equations and are solved using the fourth-order Runge–Kutta method. Also, ABAQUS finite element model of functionally graded porous plate with all edges simply supported and reinforced by CNT under low-velocity impact is simulated and is compared with those is achieved in the present analytical approach.FindingsIn parametric studies, the influence of porosity distribution patterns include uniform, non-uniform symmetric and non-uniform asymmetric on the histories of contact force and impactor displacement of simply supported plate reinforced by CNT are presented. Eventually, the effects of porosity coefficient, impactor initial velocity, impactor radius and CNTs lumping inside agglomerations for non-uniform symmetric distribution patterns are discussed in impact event in detail.Originality/valueIn this paper, the effect of combination of polymethyl methacrylate and CNTs with consideration agglomeration sizes and lumping of CNTs inside the agglomerations in the form of a functionally graded porous plate is studied in the problem of low-velocity impact analysis.

Determination of critical ricochet conditions for oblique impact of ogive-nosed projectiles on concrete targets using semi-empirical model

This paper presents a simple and efficient semi-empirical model for predicting the dynamic behaviors of rigid ogive-nosed projectiles after obliquely impacting semi-infinite concrete targets. We consider the normal stress acting on the projectile surface as a result of the target resistance. We also reflect the decrease in normal stress caused by crater formation and the presence of the free surface on the target. The normal stress is formulated as a function of the projectile geometry and the properties of the target material. To verify the proposed semi-empirical model, we establish computational frameworks combining the finite element method and smoothed particle hydrodynamics. These frameworks are confirmed to provide results consistent with the experimental data for the normal impact of projectiles on concrete targets. By comparing the results obtained from the semi-empirical model with the reference results obtained from the computational frameworks, we demonstrate that the semi-empirical model can successfully predict the penetration or ricochet of projectiles following oblique impact. Furthermore, considering the nose sharpness, slenderness, impact velocity, and oblique incidence angle of the projectiles as key parameters, we investigate their effects on the dynamic behaviors of projectiles. The penetration capabilities of projectiles increase with sharper and slenderer geometry, higher impact velocity, and lower incidence angle. In particular, considering various combinations of these parameters, we identify the critical conditions for the incidence angle and impact velocity that lead to the ricochets of projectiles. The minimum incidence angle, at which ricochets occur, increases in proportion to the nose sharpness, slenderness, and impact velocity. The maximum impact velocity, up to which ricochets occur, decreases as the nose sharpness and slenderness increase and the incidence angle decreases.

Free surface and near-wall effects on the cloud cavitating flow over an axisymmetric projectile

For high-speed underwater vehicles, cavitation can be one of the most important speed barriers. The cavitating flow can be even complex when an underwater vehicle is sailing close to the free surface/wall. In this study, the mutual effects of the free surface and near-wall on the cloud cavitating flow that surrounds an axisymmetric projectile are investigated by water tank experiment and the computational fluids dynamics (CFD). The Split-Hopkinson pressure bar (SHPB) technology is applied in the experiment to accelerate the projectile in a short time. In our numerical approach, the volume of fluid (VOF) method, the large eddy simulation (LES) turbulence model, and the Zwart-Gerber-Belamri (ZGB) cavitation model are used. The cloud cavitating flow under the free surface/wall effect is investigated by changing the distance between the projectile and free surface (df) or wall (dw). Both the experiment and the simulation show that the unstable cavity evolution includes four stages induced by the re-entrant jet: cavity growth, re-entrant jet, cavity shedding and collapsing. The results further show that as df decreases, the cavity length is shorter and the cavity becomes more stable; as dw decreases, the cavity length is longer and the cavity becomes less stable. By understanding the free surface/wall effect on the stability of the cloud cavitating flow, the parameters space spanned by df and dw can be divided into several distinct flow regimes, in which the entire shedding cavity (symmetry/asymmetry), steady and non-shedding cavity, partial cavity shedding, and ventilated cavity are identified.

Ricochets on asteroids: Experimental study of low velocity grazing impacts into granular media

Spin off events and impacts can eject boulders from an asteroid surface and rubble pile asteroids can accumulate from debris following a collision between large asteroids. These processes produce a population of gravitational bound objects in orbit that can impact an asteroid surface at low velocity and with a distribution of impact angles. We present laboratory experiments of low velocity spherical projectiles into a fine granular medium, sand. We delineate velocity and impact angles giving ricochets, those giving projectiles that roll-out from the impact crater and those that stop within their impact crater. With high speed camera images and fluorescent markers on the projectiles we track spin and projectile trajectories during impact. We find that the projectile only reaches a rolling without slipping condition well after the marble has reached peak penetration depth. The required friction coefficient during the penetration phase of impact is 4–5 times lower than that of the sand suggesting that the sand is fluidized near the projectile surface during penetration. We find that the critical grazing impact critical angle dividing ricochets from roll-outs, increases with increasing impact velocity. The critical angles for ricochet and for roll-out as a function of velocity can be matched by an empirical model during the rebound phase that balances a lift force against gravity. We estimate constraints on projectile radius, velocity and impact angle that would allow projectiles on asteroids to ricochet or roll away from impact, finally coming to rest distant from their initial impact sites.

Experimental study on structure optimization of functionally graded sandwich plates under ballistic impact

In this study, the ballistic performance of Al6061-SiC functionally graded sandwich plate (FGSP) with varying number of layers and volume fractions was examined experimentally. For this purpose, the two outmost layers of the FGSP were designed to be aluminum and the volume fraction of remaining constituents was gradually changing in intermediate layers through the plate thickness. The specimen plates were manufactured via powder stacking-hot pressing method. Ballistic tests of specimens were conducted with a single-stage gas gun, shooting 0.3 caliber fragment simulated projectiles onto specimens. After the ballistic tests, deformation and damage mechanisms in the front and rear surfaces were examined and ballistic performance evaluation was carried out in terms of depth of penetration of the projectile measurements. Results showed that the composition of the projectile impact surface, which was beneath the top aluminum layer, had a considerable effect on ballistic resistance capability. A volume fraction of ceramic constituent greater than 60% in the projectile impact surface reduced the ballistic performance of the specimen. Likewise, a decreasing volume fraction of ceramic constituent of projectile impact surface below 60% increased projectile penetration. Furthermore, increasing the number of layers within the functionally graded region did not have a significant effect on the ballistic resistance of the FGSPs.

Assessment of the quality of different pocket formulas in reproducing experimental sub-barrier fusion cross sections

In the frame of a new introduced energy scaling method, the Coulomb barrier heights calculated by using thirteen different forms of the pocket formulas are systematically analyzed for sub-barrier fusion cross sections of 58 heavy-ion fusion reactions, including O, Al, Si, S, Cl, Ca and Ti projectiles. It is found that the barrier heights, which are generated by the parameterized formulas based on the Zhang 2016, Sahu 1999, Puri 2015 and Puri 1992 approaches, seem to be more suitable for description of the experimental fusion cross sections at energies below the Coulomb barrier. The present obtained results show the importance of the projectile mass and surface energy coefficients in heavy-ion fusion at sub-barrier energies. A discussion concerning the fusion Q-value rule below barrier energies is presented for some fusion systems.

Analysis of an improved trajectory correction scheme based on mass blocks

In conventional technical trajectory correction schemes, continuous attitude adjusting mechanisms, such as canards, are inferior in terms of response time and efficiency of executing instructions. Discontinuous attitude adjusting mechanisms, such as the lateral pulse jet, have complex impact on the airflow layer of the projectile surface caused by the thrust vector jet flow. An improved two-dimensional trajectory correction mechanism is designed based on the principle of firing mass blocks by a tailor-made propellant. The mechanical properties of the thrust force (namely the correction force) is analyzed. The trajectory correction model is established to analyze the effects of correction starting moment and correction phase angle of a thrust force on the projectile's trajectory. According to the trajectory correction scheme, an improved genetic algorithm is employed to this work. The scheme is tested in the simulation. The results show that the correction scheme is effective to reduce target dispersion and increase the precision of the impact point.

Revisiting unsteady shock-induced combustion with modern analysis techniques

Numerical simulations of shock-induced combustion (SIC) with detailed H2/O2 reaction mechanisms near CJ detonation velocity were investigated. The effect of grid resolution and the chemical reaction mechanisms were examined for unsteady SIC over a blunt body at Mach number 4.48 presented by Lehr. Using high resolution schemes, it is found that Jachimowski reaction mechanism, which has been used dominantly for the SIC, develops an unphysical low frequency high amplitude oscillation at high grid resolutions. These disturbances were not observed at lower grid resolutions, while UCSD reaction mechanism is less sensitive to the spatial resolutions. The cause of the low frequency oscillation was investigated with Dynamic Mode Decomposition (DMD) and Chemical Explosive Mode Analysis (CEMA) technique. The spatial structure of the decomposed modes from DMD analysis shows that the shock wave moves closer to the projectile surface and this creates a disturbance near the projectile surface with increase in spatial resolution. Using CEMA, it is found that the influence of the reaction step H2 + OH = H2O + H is high in the burned section of the flowfield for Jachimowski mechanism and this creates the disturbance which slowly gets converted into the unphysical phenomena.

Rapid Evaluation and Analysis of the Deformation of Filled Cylindrical Casing with Deforming Charge Width Based on Self-Compiled MATLAB Program

The casing of deformable warheads warps under the action of deforming charges. The deformation profiles may be concave-, convex-, or D-shaped, but they are all symmetrical. The D-shape is considered the optimal deformation profile. The width of the deformed surface affects the number of fragments in the target area. In order to evaluate the deformable surface width of the cylindrical casing, a criterion α was established and its optimum range was determined as 20 to 30%. Based on our previous theoretical analysis, a MATLAB program that can rapidly evaluate the projectile deformation surface was compiled, which was verified using LS-DYNA and experiments. The laws influencing the deforming charge width on the deformed surface of the filled cylindrical casing were also studied using the MATLAB rapid evaluation program. As the deforming charge width increased, the deformation profile of the casing gradually transferred from “inner-concave” to the “outer-convex”. In addition, a formula that can better reflect the relationship between the deforming charge width φ and the criterion value α was fitted and verified. The conclusions obtained in this paper provide rapid guidance for the structural design of deformable warheads.

Modeling on mass loss and nose blunting of high-speed penetrator into concrete target

Mass loss and nose blunting of the projectile are often observed in high-speed penetration into concrete target. A new theoretical model is established to present the process of mass abrasion of projectile during penetration and to predict the mass loss and nose shape of the residual projectile after penetration. In order to better describe the effect of aggregate on the mass abrasion of penetrator, both the aggregate volume fraction and its shear strength are introduced into the present model. In the present model, the caliber-radius-head value of projectile nose is a key parameter and the mass loss and nose shape of projectile can be obtained easily only by solving a differential equation for the caliber-radius-head value and the penetrating velocity v, which is much more convenient than the incremental calculation and all other methods of mass receding of projectile outer surface. The calculation results show a good agreement with experimental results. According to the present model of mass abrasion, the depth of penetration of projectile and its acceleration curve during penetration are further calculated by considering the effects of mass loss and nose blunting of projectile.

Analysis of Cone Wave Reflection in Finite-Size Elastic Membranes and Extension of the Ballistic Impact Problem From Elastic to Viscoelastic Membranes

The transverse ballistic impact on a two-dimensional (2D) membrane causes a truncated deformation cone to develop in the wake of tensile implosion waves. Here, the cone wave reflected from the finite boundaries of the elastic membrane has been studied analytically. A first-order linear nonhomogeneous differential equation for the ratio of the reflected cone wave front velocity to the speed of tensile waves is derived, which is further used to calculate the traveling time taken by the reflected cone wave to reach to the projectile surface. Since the reflected wave starts when the membrane is already in a deformed configuration, the speed of the reflected cone wave is a function of radius r in the cylindrical coordinates as opposed to almost constant speed of the incoming cone wave studied in the literature. The analytical results are validated with molecular dynamics (MD) simulations of the ballistic impact of projectiles onto a single layer of coarse-grained (CG) graphene. In the second part of the paper, we analyze the membrane impact problem for linear isotropic viscoelastic materials and find that the tensile wave speed for stresses and displacements is the same as that obtained in the case of a linear isotropic elastic material. We also show that only under special conditions, self-similar solutions for the cone wave are possible in viscoelastic materials modeled by Maxwell, Kelvin–Voigt, or a combination of similar models. Our findings lay some grounds on which further studies on the ballistic response of viscoelastic materials can be performed.

Potentials of the Interaction of Atomic Particles at Large, Medium, and Small Collision Energies

A review of the most recent papers concerning the study of interatomic potentials is given. In the case of small distances, the potential values for a distance of up to 0.005a f (a f is the Firsov screening length) are obtained from a scattering experiment using proposed procedures. A new formula for the screening constant is put forward, and the influence of electron screening on cross sections for nuclear fusion reactions is described. In the range of medium internuclear distances, the experimental data on potentials agree well with the calculated ones obtained using the density functional approximation and the DMol software package for choosing the basis of wave functions. The first studies involving determination of the projectile—surface system potential from data on rainbow scattering during surface channeling are discussed.

Deformations on Hole and Projectile Surfaces Caused By High Velocity Friction During Ballistic Impact

In this study, the deformations caused by the ballistic impact on the MM composites and on projectile surfaces are examined. The hole section and grain deformation of unreinforced targets are also examined after impact. The relatively high complexity of impact problems is caused by the large number of intervening parameters like relative velocity of projectile and target, shape of colliding objects, relative stiffness and masses, time-dependent surface of contact, geometry and boundary conditions and material characteristics.The material used in this investigation are 2024 and 7075 aluminum alloys as matrix reinforced with SiC and Al2O3 particles. The matrix materials are extensively used in defense applications due to its favorable ballistic properties, moderate strength, high corrosion resistance and super plastic potential. Two different composites were produced; one by casting and the other by lamination.The ballistic tests of the composite targets were carried out according to NIJ Standard-0101.04, Temperature 21 °C, RH=65% with 7.62 mm projectiles. The bullet weight was 9.6 g and their muzzle velocities were in the range of 770–800 m/s. The projectiles consisted of a steel core, copper jacket and lead material. The composite targets were positioned 15 m from the rifle. The interaction between projectiles and the target hole created after impact were examined by light microscopy and photography. Different damage and failure mechanisms such as petalling, cracking, spalling, dishing, etc., were observed on the target body. On the other hand, dramatic wear and damages on the projectile surface were also observed. The targets were supported with Al-5083 backing blocks having 40 mm thickness.

Visualization of High-Speed Impact of Projectile in Granular Sheet with Destructive Collision of Particles

The impact and penetration of a projectile in a particle-laden space, which are expected to have frequently occurred during the formation of the solar system and will occur in the case of an impact probe for future planetary exploration, were experimentally simulated by using the ballistic range. A two-dimensional sheet made from small glass beads or emery powder was formed by the free-falling device through a long slit in the test chamber evacuated down to about 35 Pa. A polycarbonate projectile of a hemi-sphere-cylinder or sphere shape with the mass and diameter about 4 g and 25 mm, respectively, was launched at the velocity up to 430 m/s, and the phenomena were observed by the high-speed camera at 20,000 fps. From a series of images, the bow-shock-wave-like laterally facing U-shaped pattern over the projectile and the absence of particles in the trail behind it were clearly seen. At the impact of the particles on the projectile surface, fine grains were formed due to the destructive collision and injected outward from the projectile. The images obtained by different lighting methods including the laser light sheet were compared. The effects of the particle diameter, its material and the impact velocity were also investigated.

Visualization of Projectile Flying at High Speed in Dusty Atmosphere

Considering a spacecraft that encounters particle-laden environment, such as dust particles flying up over the regolith by the jet of the landing thruster, high-speed flight of a projectile in such environment was experimentally simulated by using the ballistic range. At high-speed collision of particles on the projectile surface, they may be reflected with cracking into smaller pieces. On the other hand, the projectile surface will be damaged by the collision. To obtain the fundamental characteristics of such complicated phenomena, a projectile was launched at the velocity up to 400 m/s and the collective behaviour of particles around projectile was observed by the high-speed camera. To eliminate the effect of the gas-particle interaction and to focus on only the effect of the interaction between the particles and the projectile's surface, the test chamber pressure was evacuated down to 30 Pa. The particles about 400μm diameter were scattered and formed a sheet of particles in the test chamber by using two-dimensional funnel with a narrow slit. The projectile was launched into the particle sheet in the tangential direction, and the high-speed camera captured both projectile and particle motions. From the movie, the interaction between the projectile and particle sheet was clarified.