Projectile Exit Velocity Research Articles

Development of the Johnson-Cook flow stress and damage parameters for the impact response of polycarbonate: Experimental and numerical approach

The Johnson and Cook (JC) flow stress and damage model parameters of a polycarbonate (PC) plate were determined by the mechanical tests and numerical simulations of the tests. The experimental tests included quasi-static and high strain rate tension and compression, quasi-static notched-specimen tension, quasi-static indentation (QSI), low velocity impact (LVI) and projectile impact (PI). Initially, five different quasi-static flow stress-strain equations were extracted from the experimental and numerical tests. The flow stress equation determined from the experimental average true stress-true strain curve well agreed with the effective stress-strain obtained from the quasi-static numerical tension test. The numerical QSI force-displacement curve based on the experimental average true stress-true strain equation was further shown to be very similar to that of the experiment. The LVI and PI test simulations were then continued with the experimental average true stress-true strain equation using five different flow stress-strain rate relations: JC, Huh and Kang (HK), Allen-Rule and Jones (ARJ), Cowper-Symonds (CS) and the nonlinear rate approach (NLA). The rate sensitivity parameters of these relations were extracted from the quasi-static and high strain rate tests. The LVI test simulations using the stress-strain rate relations exhibited force-displacement curves higher than those of the experiments. The detected almost no strain rate sensitivity in the LVI tests was ascribed to low strain rate dependency of the flow stress at these intermediate strain rates and large strains involved. On the other side, all the stress-strain rate relations investigated nearly predicted the experimental damage types: dishing at 100 and 140 m s−1 and petalling at 160 m s−1, except the CS relation which predicted the fracture of the plate at 140 m s−1. The experimental average projectile exit velocity at 160 m s−1 was further well predicted by the used stress-strain rate relations while the experimental average petal thicknesses were under estimated by the models. The absorbed energy at 160 m s−1 PI test was determined 1.6 times that of the QSI test, which proved an increased energy absorption capability of the tested PC at the investigated impact velocities.

Development of modelling design tool for harpoon for active space debris removal

The level of debris in Earth orbit presents an increasing risk. Active debris removal, involving capture and deorbit of larger items, has been identified as important in controlling future debris population growth. One concept for capturing debris is a harpoon, with low post-penetration residual velocity being a key design requirement. Aluminium sandwich panels are common structural components on typical spacecraft and consequently a probable target structure. An ideal harpooning event is characterised with complete penetration of the sandwich panel and low harpoon residual (post penetration) velocity. This paper presents development of a numerical modelling tool for a harpoon design for active orbital debris removal. The ability to predict the ballistic limit of an aluminium sandwich panel with a honeycomb core representative of a large satellite structural element being the primary requirement for the modelling tool. The modelling approach was validated against the experimental results from normal and oblique impact tests performed for ogive and flat nose projectiles over a velocity range between 50 m/s to 120 m/s. The modelling was based on explicit finite element method, using the commercial LS-DYNA code. An element failure criterion was used to approximate material damage and failure. Sensitivity studies were performed to investigate the influence of model key features on the projectile exit velocity. The features with the strongest influence were the face sheet material model and the projectile-panel friction model. The projectile exist velocities observed in the experiments were used to select the final parameters used. The use of an element deletion criterion that incorporated the influence of stress triaxiality improved the agreement for the plate deformation behaviour between the numerical and experimental results. For the ogive nose projectile, the exit velocity agreed well with the experiments for the range of impact velocities and angles considered. For the flat nose projectile, the model overestimated the exit velocity. In the case of the normal impact this was due to the model's inability to capture the honeycomb crushing ahead of the projectile.

Ballistic performance of synergistically toughened Kevlar/epoxy composite targets reinforced with multiwalled carbon nanotubes/graphene nanofillers

AbstractThe individual and synergistic effects of multi‐walled carbon nano tubes (MWCNT) and graphene nano‐platelets (GNP) on the ballistic performance (low and high velocity) of functionalized Kevlar reinforced polymer matrix composites have been investigated. Low‐velocity impact tests were carried out on the composite targets (6 layers) using a gas gun setup. Surface hardened conical nose projectiles of 10 mm diameter were used and the inlet velocity was in the range of 122–128 m/s. Similarly, high‐velocity ballistic impact experiments were conducted on the targets (24 layers) using a 9 mm full metal jacketed (FMJ) projectile with an initial velocity of 430 ± 15 m/s. Acid treatment was done to functionalize the Kevlar fiber surface. From the low‐velocity impact experiments, the hybrid targets had better ballistic resistance when compared to the unfilled and individually filled nanocomposites. A reduced projectile exit velocity, improved impact energy absorption (32.5 J), and an improved energy absorption percentage of 27.57 were observed for the hybrid combination. Similar improvements were observed during high‐velocity ballistic experiments which were evident from the fractographic analysis. The macroscopic investigation on the target containing both the nano‐fillers had the least penetration depth of 5.8 mm and a high damage area compared to the other targets. This is due to the addition of f‐MWCNT and f‐GNP which has increased the matrix toughening and functionalization of Kevlar which increased the interfacial bonding. In addition, the crack bridging property of CNTs and encapsulation behavior of graphene due to stacking has synergistically improved the overall toughness of the composites.

Study on the Simulation of Electromagnetic Squint

This paper introduces the simulation electromagnetic gun device based on STM32, which mainly uses openmv and laser ranging module as recognition sensor. The system obtains the target position through openmv, uses PID algorithm to control the steering gear with two degrees of freedom to make the gun barrel aim at the target, then obtains the target distance through the laser ranging module, obtains the target and controls the energy storage capacitor voltage of the electromagnetic gun, increases the voltage through the DC power supply, charges and discharges the capacitor through the thyristor controlled by the relay, the capacitor discharge generates the magnetic field through the coil, and generates the magnetic field inside the steel ball Instead, a magnetic field ejects the ball. This design realizes the closed-loop control of the capacitor voltage to ensure the stability of the projectile exit velocity. The system is stable in operation and has high precision.

Study of the influence of electrical parameters on launch performance of projectile from the single-stage reluctance coil launcher

To increase the exit velocity of projectile from single-stage reluctance coil launcher, the theoretical analysis is conducted for the projectile acceleration principle. The influence law of the electrical parameters on the projectile velocity is obtained, by the imitation research about the influence rule of the variation of electrical parameters (including capacitor voltage and capacitance) in a single-stage reluctance coil emitter on the transmitting performance, using the two-dimensional transient field solver in the finite element analysis software of Ansoft. At the same time, the single-stage reluctance coil launcher is also set up to conduct relevant tests, and the correctness of simulation analysis is verified. The results show that increasing the voltage and capacitance of the capacitor is beneficial to increase the exit velocity of the projectile, in the condition that the relative position of the projectile and driving coil is constant, The capacitor voltage is less than 1000V, and the capacitor capacitance is less than 1500μF. The simulation and experiment results provide guidance for the related analysis and study of multi-stage reluctance coil launcher.

Application of the incubation time criterion for dynamic brittle fracture

The complex issue of penetration and perforation of brittle plates subjected to normal impact is addressed. Fracture and fragmentation are simulated numerically by using simultaneously two failure criteria: ductile and brittle failure. A new brittle failure criterion, which is based on incubation time, is proposed. The criterion, inspired from the Tuler–Butcher criterion, is implemented in a commercial finite element code by means of a user subroutine. It is validated by comparing numerical predictions to experimental ballistic results of normal impact on polymethylmethacrylate plates. It is shown that the projectile's exit velocity and the timing of the penetration are faithfully reproduced. It is also verified visually that the experimental damage/fracture pattern, namely radial cracking and dishing, are both well captured by the proposed criterion.

Design of a Compulsator to Drive a Railgun

Compulsators are ac generators which are used for electromagnetic launch applications over the past few decades. This paper presents the work carried out by the authors to design a compulsator for a railgun which has been built and tested with a capacitor bank of 20 kJ as the pulsed-power source in the author’s laboratory. The generator topology selected for the compulsator is a single phase, two-pole machine with iron core and passive compensation. The design is based on the criterion of achieving maximum projectile exit velocity with the additional condition that natural current zero is synchronized with the instant of the projectile’s exit. The effect of varying the different parameters of the compulsator on the performance of the system has also been studied and discussed in this paper. By means of performance analysis, the necessary background for the design of the actual compulsator has also been achieved.

Prediction of the ballistic limit of an aluminium sandwich panel

This paper presents research on modelling the impact of a 150g projectile on a 35mm thick aluminium sandwich panel. The objective of the work is a predictive modelling capability for the ballistic limit of the panel. A predictive modelling capability supports the design of capture and deorbit missions for large items of space debris such as satellites and rocket upper stages. A detailed explicit finite element model was built using the LSDYNA software and results were compared with experimental data for the projectile exit velocity to establish key parameters. The primary parameters influencing the model behaviour were the strength and failure of the aluminium face sheets and the friction between projectile and panel. The model results showed good agreement with experimental results for ogive nose projectiles, but overestimated the exit velocity for flat nose projectiles.

Study of the relevant geometric parameters of the channel leak method for blast overpressure attenuation for a large caliber cannon

This study examines the effect of relevant geometric parameters on blast overpressure attenuation and projectile exit velocity loss due to the channel leak method on a muzzle-loaded large caliber cannon. There are four basic geometric parameters which can be varied independently. These include the number of channels, channel length, channel height and channel width. From these basic parameters, three relevant parameters are selected which are expected to be most influential. These three relevant parameters include total leak volume, channel length, and total aspect ratio. Reduction in blast overpressure, and thus peak overpressure, is most affected by the leak volume, however, leak volume needs to be selected carefully to limit the loss in the projectile exit velocity. On the other hand, use of shorter channels is found to be detrimental for peak overpressure attenuation while a lower total aspect ratio has a positive effect. The best configuration, CLM-A1, shows over 50% reduction in peak overpressure at all monitored locations with about 4.8% loss in the projectile exit velocity which translates to the largest average Figure of Merit of 0.534. Shock structure and strength are also examined for the three best leak configurations, CLM-A1, CLM-E1 and CLM-E2, as well as the baseline configuration.

Research and Progress of Electromagnetic Coil Gun Ranging

The armature trigger position of multi-stage electromagnetic coil gun has great influence on the exit velocity of projectile. The energy conversion efficiency of the coil gun can be improved effectively if the armature is triggered in the optimum position. So it is important to detect the projectile position in time. Several typical electrical and optical methods for position detection are summarized in this paper. The advantages and disadvantages of each method are analyzed and evaluated. And a new laser scattering measurement method is proposed. Results show that optical detection method is simple and easy to implement, but it is susceptible to environmental impacts.

Numerical Investigation of Channel Leak Geometry for Blast Overpressure Attenuation in a Muzzle Loaded Large Caliber Cannon

This study examines the effect of channel leak geometry on blast overpressure attenuation in the rear of a muzzle-loaded large caliber cannon. Effects of three primary geometric parameters including leak volume as well as number and length of channels are studied. Reduction in blast overpressure, and thus peak overpressure, is most influenced by the leak volume; however, leak volume needs to be selected carefully to limit the loss in the projectile exit velocity. Modification of the channel height in the current range has a minimal effect on peak overpressure, but the number of channels can have a significant effect due to the constriction experienced by the leaking flow, thereby limiting the attenuation. Two channel lengths are considered where the longer channel length, is found to be more effective. The best configuration showed over 50% reduction in peak overpressure at all monitored locations with about 4.8% loss in the projectile exit velocity.

Investigation on Electromagnetic Launching for Single Stage Coilgun

This paper presents the investigation on electromagnetic launch for single stage coilgun. The proposed coilgun and its excitation circuit were designed for launching small objects few meters. A transient simulation for the projectile motion through the launcher was done using transient finite element commercial software ANSYS MAXWELL. Also a comparative comparison between different parameters is introduced including the effect of number of turns, voltage, induced current and length of coil on the exit velocity of projectile while leaving the barrel. Detailed studied cases have been investigated. The results confirm a direct proportional relation between the velocity of projectile and number of turns, voltage and induced current in coil while confirming an inverse proportional relation with the length of coil.

The high-rate brittle microplane concrete model: Part II: application to projectile perforation of concrete slabs

In this paper, we examine the behavior of the High-Rate Brittle Microplane (HRBM) concrete model based on a series of penetration experiments. These experiments were conducted with three different slab thicknesses (127, 216 and 254 mm) that provided a significant challenge for the numerical simulations. The 127 mm slab provided little resistance, the 216 mm slab provided nominal resistance and the 254 mm slab approached the perforation limit thickness of the projectile. These experiments provide a good baseline for evaluating material models since they have been shown to be extremely challenging; in fact, we have not encountered many material models that can provide quantitatively predictive results in terms of both projectile exit velocity and material damage. In a companion paper, we described the HRBM material model and its fit to various quasi-static material property data for WES-5000 concrete. In this paper, we show that, when adequately fit to these quasi-static data, the HRBM model does not have significant predictive capabilities, even though the quasi-static material fit may be exceptional. This was attributed to the rate-dependent response of the material. After various rate effects were introduced into the HRBM model, the quantitative predictive nature of the calculations dramatically increased. Unfortunately, not much rate-dependent material property data are in the literature; hence, accurate incorporation of rate effects into material models is difficult. Nonetheless, it seems that rate effects may be critical in obtaining an accurate response for concrete during projectile perforation events.

Propellant Driven Water Acceleration and Its Influence on System Durability

The work presented investigates numerically and experimentally a formation of high velocity liquid projectiles in the course of the unsteady water acceleration by gaseous products of a propellant combustion. The projectiles were generated in a water launcher, a cylindrical enclosure entailed with a tapered converging nozzle. Previous studies demonstrated that liquid projectiles could be utilized as forming, microforming, welding, and boring tools. It is expected that other applications, such as detonation free explosive neutralization or emission-free coal combustion, are also possible. While the effectiveness of a water projectile is determined directly by its velocity, the principal constraint of the proposed technology is water pressure developed in the launcher. Numerical and experimental studies of the correlation between the water pressure and projectile velocity were performed. The work involved application of a computational fluid dynamics (CFD) package, strain gauge tests, and direct measurement of water projectile velocity. Several assumptions were made for the development of a numerical procedure. The behavior of propellant combustion products, at the pressure approaching 1 GPa, was approximated by the Noble–Abel equation, and the process is assumed to be adiabatic. Moreover, the formalism of the equilibrium thermodynamics is applied to a high pressure (∼1 GPa) supersonic fluid flow. Recorded enclosure strains and projectile velocities confirmed the practical accuracy of the numerical method applied. The major finding of this study is the influence of traveling compression waves on water pressure developed in the barrel and projectile exit velocity. The high pressure, cyclically amplified by wave processes, is a significant engineering obstacle compromising durability of the system.

Modifications of RHT material model for improved numerical simulation of dynamic response of concrete

Sophisticated numerical models are increasingly used to analyze complex physical processes such as concrete structures subjected to high-impulsive loads. Among other influencing factors for a realistic and reliable analysis, it is essential that the material models are capable of describing the material behaviour at the pertinent scale level in a realistic manner. One of the widely used concrete material models in impact and penetration analysis, the RHT model, covers essentially all macro features of concrete-like materials under high strain rate loading. However, the model was found to exhibit undesirable performance under certain loading conditions and some of the modeling issues have been discussed within a recent review paper by the authors. The present paper provides a more in-depth evaluation of the RHT model and proposes modifications to the model formulation to enhance the performance of the model as implemented in the hydrocode AUTODYN. The modifications include Lode-angle dependency of the residual strength surface, tensile softening law and the dynamic tensile strength function. The improvement of the performance of the modified RHT model is demonstrated using numerical sample tests, and further verified via simulations of two series of physical experiments of concrete penetration/perforation by steel projectiles. The results demonstrate an overall improvement of the simulation with the modified RHT model. In particular, the depth of penetration, projectile exit velocity and the crater size are predicted more favourably as compared to the test data. It is also shown that the modeling of the concrete tensile behaviour can affect sensibly the predicted perforation response (e.g., the projectile exit velocity), as is generally expected when the impact velocity exceeds the ballistic limit.

Protection of Honeycomb Sandwich Armours Against the Ballistic Attacks

Evolution of the ballistic threat has taken place, principally, in the contexts of general war, terrorism and crime. The threat has been developed to cause injury or damage to personal, land vehicles, ships, aircraft and structures. Inert projectiles will cause only localized damage to structural targets and therefore normally constitute a less potent threat to the survival of the structure than rounds which have high explosive contents. This paper describes the spectrum of ballistic threats on armoured structures. The results from FEM simulations of steel projectile penetrating sandwich honeycomb armours are discussed. The simulations are performed in 3D AUTODYN software [1]. Finally, the armours with composite systems and different materials subjected to blast loads will be discussed. The results show that the ceramic-faced armours cause reduction in projectile exit velocity by about 29.4 % and 39.6% for ceramic thicknesses 10 mm and 20 mm respectively. Also the result indicate that the honeycomb reduce the displacement due to blast loads by about 77.24%, only with 3.586 % increasing in the total weight of the armours.

Experiment assessment of the ballistic response of composite pyramidal lattice truss structures

Sandwich panels with lattice cores have attracted significant interest as multifunctional structures. The lattices consist of 3D repeating unit cells constructed from plates or trusses oriented to efficiently support applied stresses. These systems show promise for supporting structural loads and mitigating the blast effects of explosions. Here, a preliminary study has been conducted to investigate the ballistic behavior of a model lattice and to explore the effect of filling the lattices void spaces with polymers and ceramics. A sheet folding and brazing method has been used to fabricate pyramidal lattice truss structures from 304 stainless steel. The impact response of the various panels was assessed after impact by spherical, 12 mm diameter, 6.9 g projectiles with an incident, zero obliquity velocity of ∼600 m/s. Empty lattice sandwich panels with an areal density of 27.7 kg m −2 do not prevent the perforation of the sandwich panel. The impact with proximal face sheet reduced the projectile velocity to ∼450 m/s (by about 25%). Interactions with the lattice trusses and the distal face sheet further slowed the projectile resulting in an exit velocity at the distal face sheet of ∼360 m/s. The projectiles energy was dissipated by face sheet plastic dishing and fracture by petaling, and by truss plastic deformation. Infiltration of the lattice with polyurethane elastomers further reduced the projectile exit velocity. The strength of the effect depended upon the modulus of the polymer (and therefore its glass transition temperature, T g). Only high modulus (high T g) elastomers fully arrested the projectile. The energy of the projectile in this case was dissipated by a combination of face sheet stretching and polymer deformation and fracture. Low modulus elastomers reduced the projectile exit velocity by about 45% (to ∼250 m/s) and also resulted in resealing of the projectile path within the sandwich panel core. The incorporation of ballistic fabric within the polymer infiltrated systems had little effect on the ballistic resistance. A hybrid sample containing metal encased Al 2O 3 prism inserts provided the greatest resistance to penetration. In this case the projectiles were arrested within a sphere diameter of the sample front surface. Several of these hybrid systems offer promise as multifunctional, ballistic resistant, load-bearing structures.

Parametric Optimization of Electrothermal-chemical (ETC) Launchers

The research on a 30 mm electrothermal-chemical (ETC) gun including theoretical simulation and experimental results is presented in this paper. The predictions of the theoretical model which is composed of three parts (i.e., pulse forming network, plasma generator and interior ballistics) are in good agreement with the experiments. In addition, we have performed some liquid propellant and solid propellant experiments, respectively. Among the solid propellant experiments, we have investigated the ignition modes of propellant and high velocity launchers. As a result, the 25: 75 mixture of octane and hydrogen peroxide has a better effect than other liquid propellants. When the propellants are ignited nearby the bottom of projectile in chamber by using an ullage tube connected with the plasma generator, the kinetic energy of projectile will increase, while the chamber pressure will decrease. With a total input electrical energy of 180 kJ, the exit velocity of projectile is up to 2.1 km/s or so.

Subsonic single-phase flow in a gun simulator

Reported here are the time-resolved and ensemble mean and rms fluid velocities obtained by laser Doppler anemometry in a subsonic gun simulator with an inert single-phase flow and a projectile exit velocity of 40 m/s. The results presented also include the time-resolved measurements of the projectile velocity and breech pressure. The results show that, based on measured breech-pressure record, the calculated projectile velocities are almost exactly equal to the measured values and confirm that the friction of the system is negligible. Fluid velocity traces, together with ensemble mean and rms velocity profiles, indicate the presence of a wall boundary layer occupying up to 20% of the tube radius and having a growth rate similar to that of steady turbulent boundary layers. The nature of velocity fluctuations and the shape of velocity profiles inside the boundary layer also suggest that the boundary layers are turbulent in the wake of the projectile.

Effect of target bending in normal impact of a flat-ended cylindrical projectile near the ballistic limit

The current work is concerned with the normal impact of flat-nosed cylindrical projectiles striking at a velocity in the vicinity of the ballistic limit on metallic targets. The ratio of target thickness to striker diameter ranges from ¼ to ½. The resulting penetration model extends existing theories to include the extensive deformation of the target resulting from the bending effect. The dynamic and static stress-strain relations of 2024-0 aluminum are obtained by means of the split-Hopkinson bar technique and an Instron machine, respectively. A series of tests with 0.8 mm diameter pre-drilled holes in each target is conducted to assess the relative effects of bending and shear on the plate deformation. A total of 20 shots are executed to examine the phenomenon of the plate response under impact loading. The 12.7 mm diameter hard-steel projectiles are fired with a pneumatic gun against 3.18, 4.76, and 6.35 mm aluminum targets at a velocity of up to 182 m s−1. A dynamic plastic bending theory is proposed that will be superposed on the previously developed one-dimensional phenomenological penetration model of Liss et at. (Int. J. Impact Engng 1, 321–324 (1983)), to permit a more accurate prediction of target response. This phenomenological model is numerically analyzed and compared with the experimental findings and the two-dimensional Lagrangian computational codes Dyna2d and Autodyn using a Cray X/MP-48 and PC-AT, respectively. Excellent correspondence with data is obtained for the projectile exit velocity when a higher impact speed is employed. The final deformation field computed from the model is not limited to a narrow zone and shows good correlation with the experimental data, especially for thinner targets.