Spherical Projectile Research Articles

Effect of tensile preloading on the ballistic properties of GFRP

This paper focuses on a ballistic impact response of composite plates with a thickness of 2 mm subjected to uniaxial tension preload. It also presents experimental and numerical results of ballistic impact response studying. To generate impact damages by a spherical projectile in the range of 100–800 m/s velocities the powder gun stand was used. During the experiments, the ballistic stand was placed in an INSTRON 5882 testing machine for setting five different states of preloading. The results showed that uniaxial tension preload reduces the ballistic limit. Higher tensile preload levels were found out to lead to the smaller delamination area. This is a result of impact energy dissipation in inclined (and damaged during pretension) segments of threads which play the role of dry friction contact areas between fibres. The response time to the rupture of the specimen after penetration depends on a preload level, which was observed as another phenomenon. The finite element simulations of preloaded plates subjected to ballistic impact were carried out using ANSYS Workbench (AUTODYN3D) explicit package. As numerical results were in good agreement with the experimental data, a variation of GFRP ballistic limit with tension up to 92% of strength was numerically investigated.

Deformation and orientation effects on reaction cross-sections at intermediate and high energies

The effects of deformation and orientation on the nucleus–nucleus and proton–nucleus reaction cross-sections are investigated at intermediate and high energies, in the framework of the Coulomb modified Glauber model. The matter density of the projectile is treated by a deformed Fermi shape with quadrupole and hexadecapole deformations. In-medium effects are included through a local density- and an energy-dependent effective nucleon–nucleon total cross-section. Calculations are performed for the deformed projectiles [Formula: see text] colliding by [Formula: see text] and by protons. It is found that the average of reaction cross-section over all directions of the symmetry axis of the deformed projectile differs by about 2[Formula: see text] compared with that calculated for a spherical projectile with the same rms matter radius as the deformed one. The difference between the cross-sections calculated with and without medium effects is of the order 2[Formula: see text] for both deformed and spherical cases. The integrated reaction cross-sections over all orientation angles provide a consistent explanation of the experimental data. The orientation of the heavy projectile can produce a difference in the calculated cross-section about 35[Formula: see text] for nucleus–nucleus and about 45[Formula: see text] for proton–nucleus. This study is also useful for experiments of polarized beams that have created opportunities to study oriented collisions of deformed nuclei. The method is applied to extract the rms radius of [Formula: see text] and it is found to be about 3.56 and 3.45[Formula: see text]fm when using deformation with and without in-medium effects.

Experimental investigation on the energy absorption characteristics of honeycomb sandwich panels under quasi-static punch loading

The energy absorption characteristics of sandwich panels with aluminum plate as facesheet and metal hexagonal honeycomb as the core are investigated under quasi-static punch loading using two flat nose and spherical projectiles, experimentally. Failure modes are classified as plastic hinges, facesheet wrinkling, debonding of the adhesive layer between the facesheet and core, facesheet tearing, out of plane core crushing, in-plane core folding, core tearing and detachment from the support. Furthermore, the article examines the influences of six parameters including honeycomb wall thickness, sandwich core thickness, facesheet thickness, aspect ratio, adhesive layer between facesheet and core and existence of bottom facesheet. The results show that the increase in core thickness improves the energy absorption parameters of sandwich panel better than the increase in the facesheet thickness. Specific absorbed energy is increased linearly by increasing the honeycomb core thickness while it seems that the mentioned parameter has a meaningless dependence on the facesheet thickness. In addition, a 12 percent quota of adhesive layer between top facesheet and core is indicated in the energy absorption capacity of a sandwich panel for both flat nose and spherical projectiles, while its effect on the value of maximum force is 17% using flat nose projectile and 25% using the other one. Despite the major influence of the existence or non-existence of the bottom facesheet on the sandwich failure modes, its absorbed energy changes less than 3.5 percent; yet other parameters such as specific energy absorption and peak load are more dependent on the existence or non-existence of the bottom facesheet. Finally, keeping the honeycomb wall less thick improves the energy absorption characteristics of the sandwich panel.

A 3D measuring method of magnetic properties of impact-generated plasmas

At present, there are several ways to measure the magnetic properties of plasmas during hypervelocity impact. In this paper, we compare and analyze the merits and demerits of these methods. Then a novel technique, christened a spherical three-dimensional coil group (STDCG), is proposed, whose design principles and specific parameters are introduced. In the hypervelocity experiments, spherical aluminum projectiles (AA 2024) have been accelerated by a two-stage light gas gun to impact aluminum plates (AA 2024) at velocities from 4.2 to 6.2 km s−1, where the disk coil, the Rogowski coil and the STDCG are applied separately to detect the induced magnetic field. The results demonstrate that the magnetic properties of hypervelocity-impact-generated plasmas show temporal and spatial regularity, depending on the angle and distance of the coils.

Design of small impact test device for concrete panelssubject to high speed collision

Five key items were used to create an economical and physically small impact test device for concrete panels subject to high speed collision: an air-compressive system, carbon steel pipe, solenoid valve, carrier and carrier-blocking, and velocity measurement device. The impact test device developed can launch a 20 mm steel spherical projectile at over 200 m/s with measured impact and/or residual velocity. Purpose for development was to conduct preliminary materials tests, prior to large-scale collision experiments. In this paper, the design process of the small impact test device was discussed in detail.

Ice vs. steel: Ballistic impact of woven carbon/epoxy composites. Part II – Numerical modelling

Part I of this study covered ballistic tests, in which both solid (steel) and fragmenting (ice) spherical projectiles were fired at specimens of carbon-fibre-reinforced polymer (CFRP) composite. The velocity of impacts varied from 70 to 90 m/s for the solid projectiles and from 300 to 500 m/s for the fragmenting projectiles, resulting in three consistent and comparable levels of structural damage for both types of projectiles. The observed dynamic deformation behaviour and resultant damage were examined using a combination of non-invasive analysis techniques. The focus of this Part II is on the development of a mesoscale modelling strategy for CFRP employing a phenomenological continuum-damage approach. The developed model was validated against the data from original ballistic-impact experiments, demonstrating accurate predictions of both deformation behaviour and observed resultant damage of tested specimens for the various experimental loading conditions without modification of the modelling parameters.

Simulating the regimes of oblique detonation waves arising at detonation initiation by a small-diameter projectile

Initiating detonation in a reactive hydrogen-oxygen mixture by a spherical projectile of small diameter, flying with velocity exceeding the Chapman-Jouguet one, has been studied numerically. The mathematical model is based on the given kinetic scheme for the description of chemical reactions. At verification of the computational algorithm, the flow regimes and the detonation cell size were compared for numerical and experimental data. The agreement between the calculated and the experimental flow patterns and the quantitative correspondence of the modes of existence of inclined detonation waves have been obtained.

A comparative analysis of several material models in LS-DYNA at high velocity impact

The questions of application of the LS-DYNA finite element analysis package for describing the interaction of a spherical projectile and a massive metal obstacle are considered. Based on a comparison of the results of numerical simulation with experimental data, a qualitative possibility has been shown to determine the magnitude of the dynamic hardness of the obstacle material.A simulation of the collision of a spherical impactor and a massive metal barrier shaped as a cube is performed. Data are obtained on the penetration of the striker into the barrier.Using the simulation curve, the values of the dynamic hardness of the obstacle were restored and a comparison was made with their experimental values. The qualitative correspondence is shown.

CRIMINALISTIC RESEARCH ON AIRSOFT RIFLES MODIFIED FOR SHOOTING CARTRIDGES OF THE CALIBER 5.56×45 MM

Recently experts of the Israel police ballistic laboratory encountered a new version of the atypical firearms that is Airsoft pneumatic rifles converted for shooting cartridges of the caliber 5.56×45 mm. The Airsoft rifles are made to shoot nonmetal spherical projectiles in diameter of 6 mm. All variety Airsoft constructions can by divided into three groups: a) with spring mechanisms where the energy of compressed spring is used to produce air pressure; b) with electrical mechanisms where air pressure is provided by electrical pump; c) with mechanisms called Gas Blowback use energy of gas compressed in gas balloons. In many cases the Gas Blowback constructions of Airsoft rifle look similar to military firearms. They have similar construction of internal mechanisms. Different companies produce Airsoft copies of M-16 assault rifle. This Airsoft rifles can have the construction of trigger mechanism that is exact copy of the one used in M-16 assault rifle. Moreover, in some models detail sizes are the same as in real M-16 assault rifle. This makes possible to upgrade the Airsoft rifle for shooting cartridges of the caliber 5.56×45 mm by installing the rifled barrel (which can be bought on the Internet in USA) and using the original bolt carrier. The laboratory also received for the examination the upgraded Airsoft rifle samples with converted bolt carrier. So it made possible nоt use these firearm details. In some case identification of the evidence as atypical weapon is difficult because markings made by manufactures are identical to real M-16 assault rifles markings. This article discuses criminalistic examination methods of this homemade weapon type.

Ice vs. steel: Ballistic impact of woven carbon/epoxy composites. Part I – Deformation and damage behaviour

With extensive use of composite materials in aerospace, marine, energy and defence applications, their susceptibility to impact events is still an unresolved problem. In this paper, impacts of carbon fibre/epoxy composite specimens with solid (steel) and fragmenting (ice) spherical projectiles are studied extensively, using a combination of non-invasive analysis techniques to assess their dynamic deformation behaviour and resultant damage. The velocity magnitudes of high-intensity impacts varied between 70 and 90 m/s for solid projectiles and between 300 and 500 m/s for fragmenting ones, resulting in three consistent and comparable levels of structural damage for both cases. A new in-depth deformation analysis method based on high-speed digital image correlation was utilised to assess the effect of both the projectile type and impact velocity, resulting in a deeper understanding of the specimen’s deformation behaviour allowing detailed observation of its stages during the impact event. Additionally, both visual and non-invasive methods were employed to analyse the extent of damage related to various dynamic loading conditions. X-ray computed tomography was used to implement a full volumetric analysis of internal damage and resulted in a detailed insight into inter- and intra-ply damage modes.

Numerical simulation of the high-speed collision of the ball and the spherical fluid-filled shell

Effectiveness of a honeycomb shield assembled of gas-filled containments is discussed. A numerical tool is developed aimed at investigating hypervelocity impact of a spherical projectile on thin-walled metallic containment filled in with gas or fluid. Variation of gas density inside the containment essentially affects perforation scenario and successive fragmentation of the projectile, while variation of gas properties – adiabatic index – does not affect fragmentation, but has a strong influence on shock wave generated by fragments in the containment.

Experimental and numerical study on the cumulative damage of water-filled containers impacted by two projectiles

High-velocity impact on fluid-filled containers is a matter of interest in the studies of aircraft fuel tank vulnerability. Most of the conducted studies have addressed this problem by considering single impact. However, the present study evaluated experimentally the cumulative damage of a water-filled container impacted by two spherical projectiles with varying velocities in the range of 1000 m/s and 1500 m/s. A specially designed aluminum sabot was used to enable a 25 mm powder gun to accelerate two tungsten projectiles simultaneously. The failure modes of the plates were also analyzed after the experiments. LS-DYNA code was used to simulate this complex fluid–structure interaction problem. The residual velocity of the projectile, pressure within the water, and plate deformation profile obtained from both the experiment and simulation were compared to verify the simulation model. The experimentally verified finite element models were further used to investigate several critical factors in cumulative damage.

Comprehensive study of projectile impact on lightweight adobe masonry

We conduct a comprehensive experimental and numerical study of the impact response of lightweight adobe masonry with a density of 1.2 g/cm3. Based on two independent test cases, a simulation model for lightweight adobe is validated and applied. First, we investigate the impact of a spherical projectile on finite and semi-infinite targets. Then, the penetration behavior of a generic hollow projectile is studied. In each case, the data from the ballistic experiments is compared to the results of corresponding numerical simulations. The employed numerical model utilizes a p-α-equation of state, recently derived from planar plate impact experiments on the same lightweight adobe material [Sauer et al., Journal of Dynamic Behavior of Materials 4 (2018) 231–243]. Strength and failure modeling are based on a validated numerical description of another adobe material that has a density of 1.8 g/cm3. The simulation model for lightweight adobe is capable of simultaneously reproducing all experimental results in a quantitatively appropriate way. This reveals that, although the phenomenology and quantitative properties differ significantly, lightweight adobe (1.2 g/cm3) and adobe (1.8 g/cm3) can be described by the same approach. Hence, this work suggests that the utilized model is applicable for analyses of impact loading of the entire class of adobe materials.

Preliminary study on shielding performance of debris shield with the rear wall combining light materials and an aluminum plate

Several kinds of shields such as Whipple shield, stuffed shield and multiple-wall shield were developed to defend from orbital debris impacting on spacecraft. The shielding performance of these shields was improved notably by changing the properties of bumper or stuffed wall. This work focuses on a new way to improve shielding performance by using a combination of light material attached to a rear aluminum wall instead of a single aluminum wall with the same areal density. Hypervelocity impact tests were performed to evaluate the new shielding concepts using aluminum spherical projectiles with 5.0 mm diameter at impact velocity ranging from 4.62 km/s to 4.90 km/s. The targets were three kinds of shields (aerogel/fiberglass composite, wood plate, or polyurethane foam plate attached to the rear aluminum walls in the shields individually), and Whipple shield with the same areal density. Test results showed that the shielding performances of these three kinds of shields are better than that of Whipple shield, based on the reduced damage on the rear wall. The advantage of combined wall using light materials attached to an aluminum plate to replace a single aluminum plate in traditional shield was verified preliminarily, and a feasible way was put forward to improve the shielding performance of debris shield in this paper.

Efficient Method to Evaluate Critical Ricochet Angle of Projectile Penetrating into a Concrete Target

In this study, we propose an efficient computation method to estimate the critical ricochet angle (CRA) for oblique penetration into concrete targets which is based on the spherical cavity-expansion theory. During penetrating event, the resistance force on the projectile nose is approximated by semi-empirical function from the spherical cavity-expansion theory and projectile motion of oblique penetration is predicted to verify the proposed numerical method with the aid of finite differential approach. In order to enhance the accuracy of projectile motion, the empirical constants of the semi-empirical function are obtained with respect to the oblique angle by conducting finite element analyses of the oblique penetration. CRA is then obtained by predicting the projectile motion at the various oblique angles and verified with results of finite element analysis. Our work presents that the reliable CRA can be estimated efficiently by employing a series of the numerical simulations. We believe that our proposed numerical method will provide a useful analysis platform for designing penetrator warhead which hits the target at an oblique impact angles.

Experimental investigation of small fatigue crack growth due to foreign object damage in titanium alloy TC4

The ingestion of runway debris during takeoff, landing and low-flying of aircraft has been a major concern for gas turbine engines. The small craters or notches introduced by particles impacting blades are commonly known as foreign object damage (FOD). The objective of this paper is to identify the initiation and propagation behavior of small fatigue crack originating from FOD crater in titanium alloy TC4. FOD was simulated by firing steel sphere projectile onto the surface of flat specimen at 30°, 60° and 90°. Replication technique based on a two-part silicon mixture was used to observe the initiation and growth process of FOD-initiated crack. The results reveal that all the cracks nucleate from the micronotches at the material pileup of FOD crater rim. The growth process of FOD-initiated crack consists of two stages. In the first stage, the crack propagates merely inside the crater. Once exceeding ~500 µm in length, the crack will grow into the second stage, in which the crack extends rapidly both inside and outside the FOD crater. Moreover, the growth rates of FOD-initiated cracks are lower than naturally-initiated cracks. Of all the three tested impact angles, the 60° impact seemed to lead to the most crucial decline in fatigue resistance. A linear relationship exhibits between the fatigue lifetime and crater cross-section area of FODed specimens.

Morphological study of the development of abrasion ring around the edges of the input gunshot wounds subject to the provisions of theoretical mechanics

Background. According to most authors, the mud pies abrasion with gunshot damage is a destroyed epidermis at the edges of the skin defect, which forms the ball onto the path of penetration in the thickness of the layers of the skin and body tissue. Therefore, no complete explanation of the stages and mechanism of formation of the abrasion ring around the edges of the skin defect at the entrance gunshot gunshot wound in contact with the projectile at right angles. Objective. The objects of the study were entrance gunshot wounds, which were formed as a result of shots with bullets of 9 mm caliber, obtained from archival material of the Bureau of forensic medical examination and experimentally obtained gunshot injuries of blocks of sculptural plasticine 9 mm with elastic spherical shells. Methods. Research methods were applied: morphological, medical-criminalistic, visual, analytical and comparative. Data of theoretical mechanics were used to estimate the mechanics of skin destruction. Results. In the study of entrance gunshot wounds, which were formed when a bullet hit the body at a right angle, around its defect was found abrasions in the form of a zone irregular rounded shape, with the bottom of a brownish-brown color. That is, the area of the skin that corresponded to the localization of the abrasion was represented by the naked surface of the dermis, with no reduction in the thickness of the dermis itself. In experimental shots in blocks of sculpted clay elastic shells of spherical shape with a distance of 2 m were formed damage incorrectly rounded in shape, had deepened the crater bottom, with depths ranging from 22.0 mm to end-to-end damage to the block of clay. In not injuries through the clay, formed of the cavity criterion forms on the inner surface was discovered prints bullet round shape. The edges of the walls of the cavity had a thinned appearance, were turned outwards, radially oriented breaks of plasticine were determined at their edges, due to which the damage as a whole took the form of a crown. In the future, the stages of formation of damage to the block of plasticine, which was formed from the action of an elastic spherical projectile, were considered from the standpoint of theoretical mechanics. Conclusion. The formation of the abrasion perimeter is not associated with mechanical contact interaction (friction) of the lateral surface of the bullet and the skin, and its formation is a consequence of the detachment of the epidermis along the edge of the skin defect of the entrance gunshot wounds, due to the complex shock-wave process, which in the initial stages includes the formation of a temporary cavity in the form of a funnel and the further spread of surface Rayleigh waves, accompanied by a detachment of the epidermis.

High-velocity impact behaviour of aluminium honeycomb sandwich panels with different structural configurations

This paper presents a combined experimental and numerical study on the dynamic response and failure mechanisms of honeycomb sandwich panels subjected to high-velocity impact by a spherical steel projectile. Impact tests were performed in a velocity range from about 70 to 170 m/s to investigate the effects of facesheet thickness, core height, cell wall thickness and cell size of honeycomb on the impact behaviour of sandwich panels. These geometric parameters were found to influence the impact performance mainly by changing the deformation and failure mechanisms of both sandwich facesheets. Moreover, the ballistic limit velocity and critical perforation energy of each sandwich configuration were obtained by numerical simulation. It was found that increasing facesheet thickness and reducing honeycomb cell size were two weight-efficient ways to enhance the perforation resistance of sandwich panels when the areal density exceeded a certain value. The projectile's penetration process into the sandwich panel and the associated energy absorbing mechanisms were analysed, the results of which showed that facesheets contributed most to energy absorption. Further numerical simulation was conducted to explore the influences of core stiffness and the thickness ratio of front to back facesheet. It was found that core stiffness had a significant effect on the deformation and failure initiation of front facesheet; more specifically, the front facesheet failed more easily due to stress concentration with the increase of core stiffness. When the total thickness of front and back facesheets remained constant, increasing the front-to-back thickness ratio led to higher damage resistance but greater deformation area on the front facesheet. Finally, a discrete optimisation was conducted to generate an optimal design of sandwich structure for achieving the highest specific energy absorption without perforation under a certain impact energy. The optimised sandwich panel exhibited an increase of 23.7% in specific energy absorption compared with the initial design.

Effect of pre-tension on energy absorbed by fabric during projectile penetration

High-strength woven fabrics made of polymeric yarns are widely used for protection against projectile impact, because of their strength, low density and high toughness. Their response to projectile impact is complex, because of the woven architecture and rate-dependent behaviour of constituent yarns. This work is directed at understanding the influence of applying pre-tension to a woven fabric, on the energy absorbed during impact by a spherical projectile. An experimental arrangement that facilitates the application of pre-tension to fabric specimens, is used to investigate fabric performance in terms of the variation of energy absorbed with impact velocity, and how pre-tension affects this. The results show that the relationship between energy absorbed during projectile penetration and impact velocity, displays an increasing-decreasing parabolic-type profile. Below the ballistic limit, fabrics subjected to a higher pre-tension perform better, but for higher impact velocities, fabric subjected to lower pre-tensions absorb more energy. To explain the results, projectile impact is simulated using a numerical model that includes the geometrical features of the fabric and incorporates rate dependence of the yarn material. The model exhibits relatively good correlation with experiments, and yields a fuller understanding of the mechanisms governing fabric behaviour. Results show that the initial increase in energy absorbed by the fabric is mainly due to the transfer of projectile kinetic energy to fabric kinetic energy; pre-tension restrains yarn movement and thus decreases energy absorption. Analysis of the variation of transverse wave speed with impact velocity shows that it increases approximately linearly with impact velocity, and that a higher pre-tension also elevates transverse wave speed. The fabric studied fails rapidly when the impact velocity is sufficiently high; this is caused by stress concentration at the impact point and insufficient time for the transverse wave to propagate through the fabric; failure is aggravated by a higher pre-tension and accounts for the resulting poorer performance for impact velocities significantly higher than the ballistic limit.

Perforation of aluminium alloy-CFRP bilayer plates under quasi-static and impact loading

The ability of a metallic surface layer to protect CFRP cross-ply plates against perforation is explored. Aluminium alloy plates (either AA1050A or AA6082-T6) were placed in front of a CFRP layer, and the bilayer was subjected to either quasi-static indentation or to ballistic impact by a spherical projectile, with rigid back support or an edge-clamped boundary condition. The observed perforation mechanism of the CFRP layer is neither influenced by the presence of the metallic layer nor by the choice of loading rate (i.e. quasi-static versus ballistic). In the back-supported condition, the CFRP layers fail by an indirect tension mode that consists of tensile failure of plies in the material directly beneath the indenter or projectile. Alternatively, in the edge-clamped condition, the CFRP layers fail by a shear plugging mechanism. Although the presence of metallic layers does not suppress the shear plugging of the underlying CFRP layer, the loaded area in the CFRP layer increases by the addition of the protective metallic layer, thereby increasing the perforation resistance of the CFRP layer.