Time-resolved penetration into glass: Experiments and computations

The penetration behavior of tungsten-alloy long-rod penetrators into glass targets is investigated and contrasted at two impact velocities, 1.25 km/s and 1.70 km/s. Penetration depths and residual rod lengths were measured by means of a 600-kV flash X-ray system at different times during penetration. The wavecode CTH was used to simulate numerically the experiments using a Drucker–Prager constitutive model, where the constitutive constants were determined from independent characterization experiments. The numerical results are compared to the experimental data and good agreement is shown.     

An investigation on mass loss of ogival projectiles penetrating concrete targets

Mass loss of an ogival projectile during its normal penetration in concrete target was investigated in this paper. Experiments of 38CrSi short-rod projectiles with ogival nose shape penetrating into concrete targets were conducted in the striking velocity range of 500–1500 m/s. Discussions revealed that projectile mass loss derives mainly from the nose part for both short-rod and long-rod projectiles during the penetration process. Furthermore, an engineering model was proposed to determine upper limit of rigid penetration regime as the maximum value of the striking velocity, which was based on the feature of projectile mass loss in the hydrodynamic transition between rigid penetration regime and semi-hydrodynamic penetration regime. Good agreements are obtained between engineering predictions and experimental results.     

THE PENETRATION OF ASYMMETRIC LONG-ROD PROJECTILES AT 2.6 km/s

The penetration ability of asymmetric long-rod projectiles at 2.6 km/s is investigated in this numerical study. Five different projectile cross sections were considered. Results from the simulations indicate that the penetration velocity of the projectiles is only marginally influenced by the cross-sectional shape of the penetrator; the greatest reductions are seen for the projectiles with the largest area moment of inertias. The largest disparity in total penetration between the different shapes is about 4%. Physical mechanisms leading to these distictions are discussed.     

Resistance of high-strength concrete to projectile impact

This paper presents the results of an experimental study on the impact resistance of concrete with compressive strengths of 45–235 MPa when subjected to impact by 12.6 mm ogive-nosed projectile at velocities ranging from ∼620 to 700 m/s. The results indicate that the penetration depth and crater diameter in target specimens exhibit an overall reduction with an increase in the compressive strength of the concrete. However, the trend is not linear. Further increase in the compressive strength requires a reduction in the water-to-cementitious material ratio and the elimination of coarse aggregates. However, doing these does not result in reduction of the penetration depth and crater diameter. The presence of coarse granite aggregates appears to be beneficial in terms of reducing penetration depth, crater diameter, and crack propagation, thus contributing to impact resistance. Incorporation of steel fibers in the concrete reduced the crater diameter and crack propagation, but did not have a significant effect on penetration depth. An increase in the curing temperature from 30°C to 250°C did not alter the impact resistance of the concrete significantly. Based on the present findings and cost consideration, high-strength fiber-reinforced concrete with a compressive strength of ∼100 MPa appears to be most efficient in protection against projectile impact.     

Penetration of concrete targets with ogive-nose steel rods

We conducted depth of penetration experiments in concrete targets with 3.0 caliber-radius-head, steel rod projectiles. The concrete targets with 9.5 mm diameter limestone aggregate had a nominal unconfined compressive strength of 58.4 MPa (8.5 ksi) and density 2320 kg/m³. To explore geometric projectile scales, we conducted two sets of experiments. Projectiles with length-to-diameter ratio of ten were machined from 4340R_c 45 steel, round stock and had diameters and masses of 20.3 mm, 0.478 kg and 30.5 mm, 1.62 kg. Powder guns launched the projectiles to striking velocities between 400 and 1200 m/s. For these experiments, penetration depth increased as striking velocity increased. When depth of penetration data was divided by a length scale determined from our model, the data collapsed on a single curve. Thus, a single dimensionless penetration depth versus striking velocity prediction was in good agreement with the data at two geometric projectile scales for striking velocities between 400 and 1200 m/s. In addition, we conducted experiments with AerMet 100R_c 53 steel projectiles and compared depth of penetration and post-test nose erosion data with results from the 4340R_c 45 steel projectiles.     

Experimental investigation of the role of frictional yarn pull-out and windowing on the probabilistic impact response of kevlar fabrics

The probabilistic impact responses of single layer greige and scoured plain-weave Kevlar KM2 fabrics are experimentally studied. Single-layer, 101 cm × 101 cm fabric targets are mounted in a novel equilateral octagon (EO) fixture that leaves the principal yarns unclamped. A probabilistic velocity response (PVR) curve, which describes the probability of fabric penetration as a function of projectile impact velocity, is generated through a series of thirty impact tests using a spherical steel projectile impacted at velocities between 69 and 113 m/s. Additional experiments are conducted by impacting targets repeatedly at identical velocities, and comparing the resulting residual velocities of the penetrating projectiles. Fabric penetration in all cases is entirely accommodated by yarn pull-out and windowing, without any principal yarn failure at the impact site. The results indicate that frictional yarn sliding and pull-out are the primary energy dissipating mechanisms during these impact conditions. Controlled yarn pull-out experiments are conducted on the same greige and scoured fabrics to statistically characterize the yarn pull-out loads. Variability in pull-out forces in the greige fabrics are measurably higher than the variability in pull-out forces for the scoured fabrics, which correlates well with variability trends in the PVR and residual velocity ballistic experiments. Additional factors, such as yarn-projectile friction and differences in filament packing efficiency, are hypothesized to also contribute to the observed differences in the greige and scoured fabric impact responses.     

A methodology for hydrocode analysis of ultra-high molecular weight polyethylene composite under ballistic impact

Ballistic performance analysis of ultra-high molecular weight polyethylene (UHMW-PE) is critical for the design of armour systems against ballistic threats. However, no validated modelling strategy has been published in literature for UHMW-PE composite that captures the penetration and damage mechanisms of thick targets impacted between 900 m/s and 2000 m/s. Here we propose a mechanistically-based and extensively validated methodology for the ballistic impact analysis of thick UHMW-PE composite. The methodology uses a non-linear orthotropic continuum model that describes the composite response using a non-linear equation of state (EoS), orthotropic elastic–plastic strength with directional hardening and orthotropic failure criteria. A new sub-laminate discretisation approach is proposed that allows the model to more accurately capture out-of-plane failure. The model is extensively validated using experimental ballistic data for a wide range of UHMW-PE target thicknesses up to 102 mm against 12.7 mm and 20 mm calibre fragment simulating projectiles (FSPs) with impact velocities between 400 m/s and 2000 m/s. Very good overall agreement with experimental results is seen for depth of penetration, ballistic limit and residual velocity, while the penetration mechanisms and target bulge behaviour are accurately predicted. The model can be used to reduce the volume of testing typically required to design and assess thick UHMW-PE composite in ballistic impact applications.     

Transient atmosphere generated by large meteoroid impacts onto an atmosphereless cosmic body: gasdynamic and physical processes

Impact of a large meteoroid or a man-made projectile with an atmosphereless cosmic body (Moon, Mercury, asteroid and comet) produces a transient atmosphere. Several physical aspects in the early and late phases of the impact generated vapor plume evolution are considered numerically and analytically. Intensity of light flashes and velocities versus mass distribution function are determined. For a 10 kg mass of impacting meteoroid, the plume intensively interacts with the solar wind in the region with the size of several hundred kilometers. For a 350 kg man-made projectile of the Deep Impact Mission hitting the P9 Comet Temple 1 with the velocity of about 10 km/s the size of the disturbed zone is of the order of 10⁴ km. The expulsion of the interplanetary magnetic field, formation of the collisionless shock wave structure associated with intense electrostatic turbulence, electron heating, and even production of X-rays lasting for several minutes are characteristic features of such impacts. These effects give the basis for new techniques of remote detection of meteoroid impacts.     

An examination of long-rod penetration

The one-dimensional modified Bernoulli theory of Tate [J. Mech. Phys. Solids 15, 287–399 (1967)] is often used to examine long-rod penetration into semi-infinite targets. The theory is summarized and the origins of the target resistance term examined. Numerical simulations were performed of a tungsten-alloy, long-rod projectile into a semi-infinite hardened steel target at three impact velocities sufficiently high to result in projectile erosion. The constitutive responses of the target and projectile were varied parametrically to assess the effects of strain hardening, strain-rate hardening, and thermal softening on penetration response. The results of one of the numerical simulations were selected to compare and contrast in detail with the predictions of the Tate model.     

Penetration mechanisms in glass laminate/resin structures

The ballistic response of composite structures comprising differing laminated float glass/polycarbonate replacement resin (PRR) elements was studied. In order to provide materials data for future modelling work, sphere-impact tests were employed to determine the high strain-rate response of the elastomeric resin. Larger-scale armour simulants comprising glass-laminate-fronted cylinders of PRR were also investigated using lead antimony-cored 7.62 mm × 51 mm NATO Ball rounds in order to interrogate their behaviour under impact. Penetration mechanisms were studied via the use of high-speed video equipment. Projectile defeat in the resin was observed to depend on the degree of projectile disruption, with a greater degree of comminution leading to enhanced behaviour. This confirmed the importance of the elastomeric properties of the resin in behaviour under ballistic impact in these structures. The interaction between the glass disrupting layer and the backing absorber was found to be key to minimising subsequent penetration. The use of asymmetric float glass laminates incorporating a thinner disrupting outer surface was found to reduce subsequent depth of penetration by as much as 52% compared to similar areal density monolithic systems. High-speed video footage implied that the thinner outer layer acted to blunt the incident projectile, while the backing thick layer of glass exhibiting a Hertzian cone-like “plugging” failure mechanism. In addition analysis of high-speed video showed that the penetration rate in the resin was initially constant, implying penetration analogous to hydrodynamic behaviour.     

Impact of thick PMMA plates by long projectiles at low velocities. Part II: Effect of confinement

A hybrid experimental–numerical investigation of the penetration process in unconfined and confined thick polymethylmethacrylate (PMMA) plates was carried out. The confinement was applied by insertion of the polymeric plate into a conical steel ring. The response of such plates to the impact of long hard steel projectiles having an ogive-head shape in the range of velocities of 165 < V₀ < 260 (m/s), was investigated experimentally. The results show that unconfined targets were perforated and broken due to combined effect of penetration and cracking. By contrast, the confined targets were not perforated and could withstand repeated impacts due to suppression of the brittle damage mechanism by the confinement. The tests were modeled using 3D explicit finite element analyses. A good agreement regarding the trajectory of the projectile and the depths of penetration was obtained. The numerical results show that the confinement introduces a negative triaxiality and even some plasticity within the confined plates prior to impact. The increase of plastic failure strain of the PMMA at negative triaxiality reduces the ductile damage during penetration, while the hydrostatic pressure reduces significantly the brittle fracture mechanism. The resisting force to the penetration depends on the failure strain–triaxality relationship, and does not necessarily increase with higher confinement levels.     

Impact of thick PMMA plates by long projectiles at low velocities. Part I: Effect of head’s shape

A hybrid experimental–numerical investigation of the penetration process in thick polymethylmethacrylate (PMMA) plates was carried out. The response of such plates to the impact of long hard steel projectiles having either blunt, hemispherical or ogive-head shapes was investigated experimentally in the range of velocities of 100 (m/s) < V₀ < 250 (m/s). The penetration process can be divided into 3 stages: entrance, propagation and backwards bouncing. The last two stages are associated with brittle fracture of the plates. The tests were modeled using 3D explicit finite element analyses. The numerical results provide insight regarding the variations of field variables such as stresses, velocities, resisting forces and energies. A good agreement regarding the trajectory of the projectile and the depths of penetration is obtained. The enhanced backwards bouncing phenomenon is explained, and it is shown that the average deceleration during the penetration process is constant. The resisting force to the penetration is higher for blunt projectiles. It is 10% lower for the hemispherical head and 50% lower for ogive-headed projectiles.     

Penetration of tungsten alloy rods into shallow-cavity steel targets

This paper presents a combined numerical and experimental study on penetration of tungsten heavy alloy long rods (length-to-diameter ratio of 10) into thick RHA (rolled homogeneous armor) steel plates. The main objective of this study was to establish the effects of a shallow cavity at the front of the steel plate on the penetration process. Three experiments were performed at 1.5 km/s on target plates with a shallow-cavity of 19 mm diameter. These results were compared to existing penetration data obtained for flat plates over a range of 1.1–1.7 km/s. In the code simulations three target configurations were considered: a flat target surface without a cavity and two target plates with different cavity diameters (19 and 11.54 mm). The effect of the target’s free surface on the characteristic time that the penetrator takes to reach quasi-steady-state penetration into the target was investigated for three configurations. Based on the experimental results the effect of the shallow-cavity wall constraint on the penetration process was found to be insignificant. The code results matched the measured depths of penetration within the limits of the experimental accuracy for all configurations examined.     

Momentum exchange alteration in projectile/target impact

This research represents an effort to alter the exchange of momentum per unit area when a projectile centrally impacts a circular 6061-T6 aluminum target, 6.35 mm thick, at normal incidence. This is achieved by cutting a circular groove of appropriate depth and diameter in the back of the target. This procedure effectively reduces the strength of the plate at the groove so that under certain conditions the part of the target inscribed by the groove is ejected as a plug.Two independent sequences of experiments were executed. Initially, a number of tests were conducted to establish the ballistic limit, v₅₀, for ungrooved plates and to ascertain possible variations in target response mechanisms when 40° triangular grooves with a constant diameter of 25.4 mm and depths ranging from 0.79 to 3.175 mm were cut into the back of the targets. This preliminary series established the behavior pattern of the momentum transfer to the target.A subsequent series of tests utilized a standard 60° triangular groove, a constant groove depth of 4.76 mm and varied groove diameters ranging from 19.1 to 44.4 mm. Initial impact velocities ranged up to 950 m/s, mostly with the pointed end making initial contact. Several regimes of projectile/target behavior were observed: (1) Rebound without plugging, (2) Plugging without perforation, (3) Perforation of a subsequently dislodged plug, and (4) Perforation without plugging. These regimes are defined by a relation between plug diameter and a range of initial striker speed. The momentum transferred to the targets was also determined.     

High velocity impact response of Kevlar-29/epoxy and 6061-T6 aluminum laminated panels

The high velocity impact response of composite laminated plates has been experimentally investigated using a nitrogen gas gun. Tests were undertaken on sandwich structures based on Kevlar-29 fiber/epoxy resin with different stacking sequence of 6061-T6 Al plates. Impact testing was conducted using cylindrical shape of 7.62 mm diameter steel projectile at a range of velocities (180–400 m/s) were investigated to achieve complete perforation of the target. The numerical parametric study of ballistic impact caused by same conditions in experimental work is undertaken to predict the ballistic limit velocity, energy absorbed by the target and comparison between simulation by using ANSYS Autodyn 3D v.12 software and experimental work and study the effects of shape of the projectile with different (4, 8 and 12 mm) thicknesses on ballistic limit velocity. The sequence of Al plate position (front, middle and back) inside laminate plates of composite specimen was also studied. The Al back stacking sequence plate for overall results obtained was the optimum structure to resist the impact loading.The results obtained hereby are in good agreement with the experimental (maximum error of 3.64%) data where it has been shown that these novel sandwich structures exhibit excellent energy absorbing characteristics under high velocity impact loading conditions. Hence it is considered suitable for applications of armor system.     

Numerical multi-scale modeling for textile woven fabric against ballistic impact

In this study, a FEM analysis has been carried out to find out pertinent multi-scale model for an investigation of a ballistic impact on 2D KM2® plain-woven fabrics. Multi-scale models are a combination between macroscopic and mesoscopic models. This study aims at testing a multi-scale model in order to minimize the computing time. Three configurations were analyzed by varying the ratio of macroscopic and mesoscopic areas: 75.3–24.7%, 65.5–34.5%, 56.3–43.7% with two impact velocities 60 m/s and 245 m/s. In these multi-scale models, the continuity in macroscopic–mesoscopic interfaces is ensured by checking the evolution of global displacements of the fabric during impact. The effect of the macroscopic area of multi-scale models on the ballistic performance of the fabric is also investigated. The optimal multi-scale model was validated by comparison with results obtained from a mesoscopic model in terms of the evolutions of the projectile velocity, energy forms, the overall behavior of the fabric during impact and the force applied on the projectile. The failure criterion Forming Limited Diagram (FLD) is suggested for bundle failure. The observed damage mechanisms of the fabric during penetration time of the projectile are discussed and compared among numerical models.     

Time-resolved penetration of long rods into steel targets

The penetration behavior of tungsten alloy, long-rod penetrators into high-hard steel is investigated at two impact velocities; 1.25 km/s and 1.70 km/s. The positions of the nose and tail of the projectile were measured by means of a 600 kV flash X-ray system at different times during penetration. The wavecode CTH was used to numerically simulate the experiments. The computational results are in very good agreement with the experimental position-time data. Additionally, the computational model reproduces the qualitative behavior for impact conditions near the ballistic limit.     

Analytical and numerical investigation of polyurea layered aluminium plates subjected to high velocity projectile impact

This paper discusses on the penetration of high velocity projectiles through aluminium–polyurea composite layered plate systems. An analytical model has been proposed to predict the residual velocity of aluminium–polyurea composite plates, and validated with both experimental and numerical investigations. Full metal jacket (FMJ) projectiles (5.56 mm × 45 mm), corresponding to NATO standard SS109, were fired at the aluminium–polyurea composite layered plate systems from a distance of 10.0 m at a fixed velocity of 945 m/s. Four different composite plate configurations were used with thicknesses varying from 16 to 34 mm. Each configuration consisted of six specimens. Residual velocities for each individual test were recorded. Numerical simulations of the penetration process have been performed using advanced finite element code LS-DYNA®. The well-established Johnson–Cook and Mooney–Rivlin material models were used to represent the stress–strain behaviour of aluminium and polyurea in the numerical analysis. The analytical and numerical models provided good approximations for the residual velocities measured during the experimental tests. Polyurea layers contributed positively towards the reduction of residual velocity of the projectile in composite plate systems. In addition, ballistic limit curves for different composite systems have been established based on the validated models. As the results showed that polyurea contributes positively towards the reduction of residual velocity of projectiles, the findings of this study can be effectively used for the similar applications in future armour industry.     

Effect of thin oblique moving plates on long rod projectiles: A reverse impact study

The geometry and motion of long rod projectiles after penetrating thin obliquely oriented and moving armour plates were studied. Plates moving in their normal directions towards as well as away from the projectile (scalar product of velocities negative and positive, respectively) were considered. The influences of plate velocity and obliquity (angle between the normal of the plate and the axis of the projectile) were investigated through small-scale reverse impact tests with tungsten projectiles of length 30 mm and diameter 2 mm, and with 2 mm-thick steel plates. The obliquity (30°, 60° and 70°) and the plate velocity (300 to −300 m/s) were varied systematically for a projectile velocity of 2000 m/s. The disturbing effect of the plate on the projectile was characterised in terms of changes in length, velocity, angular momentum, linear momentum and kinetic energy. Plates with obliquity 60–70° moving away from the projectiles with velocity 200–300 m/s were found to cause extensive fragmentation of the projectile and to have large disturbing effects in terms of all measures used.     

The influence of confinement on the penetration of ceramic targets by KE projectiles at 1.8 and 2.6 km/s

This paper presents the results of scale size experiments using a tungsten-alloy long-rod projectile fired against 97.5% Al₂O₃ ceramic targets at 1.8 and 2.6 km/s. Two targets were used, one having lateral steel confinement; the other without. The projectile overmatched the target, and residual projectile length and velocity were recorded using ballistic-syncro photography. Flash radiography was used during penetration of the unconfined target to obtain the penetration velocity. Manganin pressure gauges were also used to obtain additional data on the response of the ceramic target during penetration. Results from the eight experiments indicate that the confinement reduced the residual energy of the projectile at both impact velocities. Expressed in terms of the projectile impact energy, 55–56% was lost in the unconfined target at 2.6 km/s compared with 60% for the confined design. The same trend was found at 1.8 km/s with 68% and 72–73% for the unconfined and confined, respectively. Predictions using the QinetiQ GRIM2D hydrocode and a simplified form of the Johnson–Holmquist ceramic material model agreed well with the experiments for three out of the four test configurations. The predicted projectile erosion and retardation against the confined target at 1.8 km/s was excessively high. Analytical predictions using the Tate modified Bernoulli equation also gave reasonably accurate predictions for three of the tests, but values for the Tate target ‘strength’ extracted from experiments using a different target configuration were not accurate for the target design used in this paper.