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The relationship between the failure mechanism and the microstructural features of the Ti–6Al–4V targets was established in this paper. The 12.7 mm armour piercing (AP) projectiles were fired against the Ti–6Al–4V targets having equiaxed and lamellar microstructures with thickness ranging from 30 to 45 mm. Ductile hole enlargement characterized by delamination and spall fragments from the rear surface was observable in the Ti–6Al–4V targets having equiaxed microstructure, while brittle fragmentation characterized by plugging and star fragments from the rear surface was observable in the Ti–6Al–4V targets having lamellar microstructure. The distinctly different propagating features of adiabatic shear bands in Ti–6Al–4V targets having equiaxed and lamellar microstructures determined the failure mechanism analyzed. In the equiaxed microstructure, the regularly spaced propagating features of adiabatic shear bands facilitated the failure mechanism of ductile hole enlargement. In the lamellar microstructure, the net-like propagating features of adiabatic shear bands facilitated the failure mechanism of brittle fragmentation. [ABSTRACT FROM AUTHOR]

A Hopkinson bar was employed to conduct transverse impact testing of twisted Kevlar KM2 fiber yarns at the same impact speed. The speed of Euler transverse wave generated by the impact was measured utilizing a high speed digital camera. The study included fiber yarns twisted by different amounts. The Euler transverse wave speed was observed to increase with increasing amount of twist of the fiber yarn, within the range of this investigation. The higher transverse wave speeds in the more twisted fiber yarns indicate better ballistic performance in soft body armors for personal protection. [ABSTRACT FROM AUTHOR]

The ballistic response of suspensions of solid particles (cornstarch, silicon carbide, and silicon dioxide) in a liquid (ethylene glycol) is experimentally investigated. Some of the suspensions are at sufficient volume fraction to exhibit shear-thickening behaviour, while the others are Newtonian or mildly shear-thinning. The response of neat (liquid) ethylene glycol is also studied. Capsules containing the suspensions are impacted with a chisel-nosed fragment-simulating projectiles at velocities between 200 and 700 m/s. The residual projectile velocity upon exit from the capsule is measured via direct videography. The results are analysed using a number of different energy-based and momentum-based penetration models. A momentum-based model that normalizes the effect of the density of the suspension is seen to perform the best in terms of collapsing the results onto a single curve for the liquid and non-shear thickening suspensions. Only shear thickening suspensions with particles having sufficient strength (SiO 2 and SiC) show significant deviation from hydrodynamic-dominated response, resulting in significant velocity decrements in the projectile attributable to the shear strength of the suspensions. These shear strength effects diminish as the projectile velocity increases, suggesting that the strength of the solid material in the interparticle contacts is overcome by the impact-generated stresses. [ABSTRACT FROM AUTHOR]

A numerical technique for the simulation of pre-stressed confined ceramic targets under long rod projectile (LRP) impact, using explicit software, AUTODYN ® , is proposed. The proposed model is validated by comparing the ballistic performance results with the available experimental data in the literature. Impact simulations of the confined ceramic targets with different pre-stress conditions, namely radial, axial and hydrostatic, as well as without pre-stress for benchmarking are reported. The effects of these different pre-stress conditions on the ballistic performance of the ceramic target are explored. The upper limits of transition velocity for the targets of different pre-stress conditions are obtained. It is shown that dwell of the LRP on the ceramic interface is influenced by the pressure, obtained from pre-stressing, at the initial failure position in SiC target. It is shown that pressure at the initial failure position increases linearly with the upper limit of transition velocity. [ABSTRACT FROM AUTHOR]

Perforation of welded aluminum structures by small-arms bullets is studied both experimentally and numerically in this paper. From the chemical composition, artificial aging history, and welding procedure, the spatial distribution of the flow stress at ambient temperature of MIG-welded AA6082-T6 aluminum extrusions was determined by using a thermal finite element model and a nano-scale material model. The resulting flow-stress curves which are functions of the distance from the weld center line were used in a mechanical 3D finite element model to investigate the effect of the heat affected zone (HAZ) on the ballistic properties of welded aluminum extrusions. For experimental validation, 10 mm, 20 mm and 30 mm thick extruded profiles were processed and welded to correspond to the numerical method. Hardness measurements and ballistic impact experiments were performed in the weld metal, HAZ, and base material. Uniaxial tension tests were conducted for the base material of the 10 mm and 30 mm profiles. These tests provided sufficient data for experimental validation of the numerical method. Temperature distribution, hardness values, equivalent stress-strain curves, and ballistic limit curves are reported from both the experiments and the numerical simulations. In general, the experimental results correspond well with the numerical predictions and the predicted ballistic limit velocities are within 10% of the experimental ones, suggesting that this method is a possible alternative to performing expensive and time consuming experimental testing in the early stages of the design of protective aluminum structures. The HAZ was found to impair the ballistic performance locally, but the difference between the ballistic limit for the base material and HAZ was never more than 10% in this study. [ABSTRACT FROM AUTHOR]

• High hardness steel (HHS) sheet with UHMWPE composite backing were tested against a hardened steel core projectile. • The projectile core was eroded by the HHS sheet and stopped in UHMWPE composite. • It is observed that only a core eroded to a certain length and weight by armor system can be defeated. • In numerical modeling core failure strain was determined from the residual weight of cores. • The numerical model can be used to evolve armor design. Thin high hardness steel sheets can be an alternative to expensive ceramic armor systems designed to defeat hardened core projectiles. A thin high hardness steel sheet backed with UHMWPE fiber-reinforced composite was ballistically tested against a 7.62 × 39 mm hardened steel core projectile in a single-stage gas gun. Thin steel sheets of 530 BHN hardness were adhesively bonded with UHMWPE fiber-reinforced composite to fabricate armor plates. Armor plates were able to defeat the projectile showing considerable potential. Tensile strength of steel sheet and UHMWPE-fiber reinforced ply was also determined. A detailed numerical simulation of the impact event was also performed to understand the phenomenon of defeat and penetration in greater detail. The numerical model was calibrated from the recovered projectile's core after the ballistic test. [ABSTRACT FROM AUTHOR]

The concept of ballistically equivalent metals for ductile plate perforation has been defined and demonstrated for five aluminium alloys. Heuristic derivation of a semi-empirical relation between specific cavitation energy s c and hole slenderness ratio h / D (the ratio between plate thickness h and projectile nose base diameter D which is also known as the normalized plate thickness) has exposed a logarithmic dependence which is verified by experimental data. A closed-form logarithmic expression for s c which takes into account the h / D effect has led to a closed-form formula for the ballistic limit. The expression for s c is based on the spherical cavitation yield stress Y c S which serves as a scaling yield stress for strain-hardening (softening) response. It is found that ballistically equivalent metals should have practically the same values of Y c S and elastic modulus. The perforation of aluminium targets by 7.62 mm APM2 bullets is discussed and vast amount of experimental data is used to validate the particular ballistic limit formula. Application of the closed-form model is also demonstrated with connection to the more general concept of ballistically equivalent targets . The h / D effect on perforation of multilayered targets is examined and it is found that for ductile plate perforation the ballistic limit of a monolithic target is higher than the ballistic limit of any combination of its air-gapped parts. Under the constraint of n air-gapped protective layers with total thickness h the minimum ballistic limit is obtained for n identical layers. [ABSTRACT FROM AUTHOR]

In this study, the penetration behaviour of a Mild Steel Cored (MSC) round, 7.62 mm in diameter and 39 mm in length, commonly known as the AK47 round, was studied since it still forms an important part of the threat spectrum for personnel body armour systems. Likewise, boron carbide strike face materials were selected since this armour material is often the material of choice for ultralightweight body armour systems for protection against this particular threat. The presence of two, relatively soft, intermediate materials (the copper jacket and filler material of the bullet, and a fibre-reinforced polymer cladding layer on the ceramic) between the mild steel core and the boron carbide target was examined using reverse ballistics techniques, flash x-radiography and round recovery measurements. This was supported by selective numerical simulations using the computer code ANSYS-AUTODYN. It was found that stripping of the jacket, from the AK47 MSC rounds, makes a difference to its penetrating ability: the mild steel core is significantly reduced in length, and mass, when the jacket is not present. The magnitude of this effect is much greater than previously reported for high-strength steel-cored rounds and for tungsten carbide-cored rounds. The penetration event appears to be a twostage process: mushrooming of the mild steel core on, or near, the surface of the ceramic, followed by a linear erosion process as the core penetrates the ceramic itself. The second step has not been reported previously for MSC rounds. [ABSTRACT FROM AUTHOR]

Ductile thermoplastics, for example Ultra High Molecular Weight Polyethylene (UHMWPE), are of interest for their impact energy absorbing capabilities. While the impact perforation mechanisms of metallic targets have been investigated in some detail, far less progress has been made towards understanding the impact resistance of ductile polymers. The aim of this investigation is to identify the relationship between the projectile tip geometry and impact energy absorption of semi-crystalline thermoplastics. The focus of the study is light-weight monolithic plates of extruded polymer impacted normally by rigid projectiles at velocities up to 100 ms −1 . Three polymers will be considered: Low Density Polyethylene (LDPE), High Density Polyethylene (HDPE) and Ultra High Molecular Weight Polyethylene (UHMWPE). Polyethylene provides a convenient test material, as variations in microstructure provide a contrast in mechanical properties, without significant variations in density. Three distinct projectile nose shapes are considered: blunt, hemi-spherical and conical. For a conical tip, perforation occurs by ductile hole expansion. For this nose shape the high yield strength and strain rate sensitivity of HDPE offers an advantage over the other two polyethylenes. Perforation by blunt and hemi-spherical projectiles is more sensitive to deformation localisation. The high strain hardening of UHMWPE, which increases with strain rate, results in a significantly greater impact resistance than either HDPE or LDPE. The perforation mechanisms and energy absorption of these PE plates are contrasted with those of thin aluminium alloy targets that have the same total mass. UHMWPE outperforms these metallic targets for all three projectile nose shapes. Finally, the influence of target thickness on the impact perforation of LDPE is considered. All three nose shapes show a linear increase in perforation energy with target thickness. [ABSTRACT FROM AUTHOR]

This paper proposes a simple formulation for the impact analysis of a deformable projectile on reinforced concrete targets. This approach assumes the presence of soft strikers and rigid targets. Based on an energy balance, it aims to predict a perforation limit for different targets under soft impacts. The procedure employed is validated by means of tests performed on a rigid target (pendulum test) and reinforced concrete slabs. The article discusses various estimations of the crushing force of projectiles, as derived from experimental results and numerical approaches. The efficiency of simplified approaches is highlighted from an engineering point of view. The limit between soft and hard impacts is also analyzed according to a recent criterion. Moreover, the paper proposes validating the approach using experimental tests with both perforating and non-perforating impact tests on nine slabs. [ABSTRACT FROM AUTHOR]

Ballistic performance of an armour steel at different tempering conditions against a tungsten heavy alloy long rod kinetic energy projectile has been investigated. The ballistic performance was found to increase with decreasing tempering temperature but the performance increments were not proportional to the strength increase caused by the tempering. Both target and projectile underwent fragmentation at the penetration interface in all the three targets. Apart from the strength target material deformation behaviour also showed considerable influence on ballistic performance. The ballistic performance appears to increase with decreasing toughness for a given strength. [ABSTRACT FROM AUTHOR]

The database for depth of penetration by projectiles into semi-infinite targets is quite extensive. The objective is to use the experimental semi-infinite penetration data to predict finite-thickness target effects. Similitude considerations are used to represent penetration response as a function of a normalized impact velocity, which is the ratio of the penetration pressure to the target strength. Then, a least-squares regression analysis methodology was applied to the normalized experimental data to provide an analytic expression for the normalized depth of penetration as a function of the normalized impact velocity over a very large velocity range, typically a few hundred meters per second to over 3500 m/s. We use the analytic expression, along with some simplifying assumptions, to estimate ballistic limit thickness T 50 and/or the ballistic limit velocity V 50 . If a target is overmatched, i.e., perforated by the projectile, an estimate is also made for the projectile residual velocity and residual length. The experimental data on which the regression fit is based consists of L / D 10 projectiles, so a procedure is also developed to account for different projectile aspect ratios. A series of examples are provided to demonstrate the utility and accuracy of the approach. [ABSTRACT FROM AUTHOR]

In this paper an experimental and numerical work is reported concerning the process of perforation of thin steel plates using different projectile nose shapes. The main goal is to analyze how the projectile shape may change the ballistic properties of materials. A wide range of impact velocities from 35 to 180 m/s has been covered during the tests. All the projectiles were 13 mm in diameter and the targets were 1 mm thick, as such the projectile can be regarded as rigid and the target sheets were of interstitial-free (IF) steel. The mass ratio (projectile mass/steel sheet mass) and the ratio between the span of the steel sheet and the diameter of the projectile were kept constant, equal to 0.38 and 3.85 respectively. To define the thermoviscoplastic behavior of the target material, the Rusinek-Klepaczko (RK) constitutive model [1] was used. The complete identification of the material constants was done based on a rigorous material characterization. Numerical simulations of some experimental tests were carried out using a non-linear finite element code ABAQUS/Explicit. It was found that the numerical models are able to describe the physical mechanisms in the perforation process with a good accuracy. [ABSTRACT FROM AUTHOR]

The widespread use of composite materials in load-carrying components leads to the need of studying their behaviour also in extreme situations, like ballistic impacts. At present the design of these structures against ballistic impacts is strongly dependent upon expensive experimental tests. To reduce the costs, numerical and analytical models have been developed in recent years, which allow a preliminary setting of the main parameters in the experiments, without substituting for them completely. With this aim, an investigation on the analytical modelling technique for ballistic impacts of blunt projectiles on composite plain-woven fabrics with a polymeric matrix has been carried out and is presented in this paper. An analytical model has been developed with original contributions and has then been compared with experimental results and data from the literature. The analytical model is based on the wave theory and on the energy balance between the kinetic energy of the projectile and the dissipation modes of the target: the kinetic energy is absorbed by the “V-tent” deformation moving ahead the projectile tip, the deformation energy of primary and secondary yarns, the delamination and matrix cracking energies, the energy associated to the bending of the layers (which has a considerable contribution in thick targets), the dissipation by the compression of the layer, and finally the energy dissipated by the shear plugging of the layers (if it takes place). The energy dissipated by friction between the projectile and the target and between the woven yarns is neglected. In addition, the model reproduces the sequential failure of the layers under the impact of the projectile, allowing the prediction of the impact velocities at which the projectile remains stuck inside without complete perforation. The aim is to provide a reliable tool able to work on a broad range of conditions and target configurations (thick and thin). From the energy balance, the deceleration of the projectile and the velocity at every time step, together with other parameters like contact duration, radius and depth of the conoid can be determined. The quasi-static properties of the materials are employed in the model. Performances and the pros/cons are evaluated. [ABSTRACT FROM AUTHOR]

The manuscript presents a systematic study for the characterization of mild steel under varying stress-triaxiality, strain rate and temperature. The effect of stress triaxiality was studied by performing tension tests on notched cylindrical specimens. The radius of the notch has been varied as 0.2, 0.4, 0.6, 0.8, 1, 2, 3, 4, 5 and 10 mm. The smooth cylindrical specimens were tested under tension at varying strain rate and temperature. The strain rate in the range, 0.0006 s −1 –1500 s −1 , was obtained on a universal testing machine and the Hopkinson pressure bar apparatus. The tests at elevated temperature were carried out using a portable furnace which enabled the variation of temperature from 100 °C to 750 °C. All the material parameters for the Johnson–Cook elasto-viscoplastic material model have been calibrated. The parameters thus obtained were validated by numerically simulating the material characterization under high strain rate using ABAQUS/Explicit finite element code. The numerical simulations were also carried out for the ballistic evaluation of 12 and 16 mm thick mild steel plates impacted by 7.62 AP projectiles at varying incidence velocities in order to obtain the ballistic limit. The angle of incidence has also been varied until the occurrence of critical ricochet. The numerical results have been validated by the experiments reported in earlier studies, Gupta and Madhu [1,2]. [ABSTRACT FROM AUTHOR]

An analytical formulation is presented for the prediction of ballistic impact behavior of multi-walled carbon nanotube (MWCNT) dispersed epoxy resin. The formulation is based on stress wave propagation and energy balance between the projectile and the target. During the ballistic impact event, the energy lost by the projectile is absorbed by the target through various damage and energy absorbing mechanisms such as compression of the target directly below the projectile, compression in the region surrounding the impacted zone, shear plugging, formation of ring and radial cracks in the resin leading to tensile failure and energy absorbed due to the presence of carbon nanotubes. Complete failure of the target was due to catastrophic brittle fracture and shattering. Experimental studies are carried out on ballistic impact behavior of neat epoxy and MWCNT dispersed epoxy. Typical results on ballistic limit velocity and energy absorbed by various mechanisms are presented. Ballistic impact behavior of neat epoxy resin and MWCNT dispersed epoxy resin are compared. A good match is observed between the analytical and experimental results. [ABSTRACT FROM AUTHOR]

The objective of the present study is to provide understanding of potential energy absorption and dissipation mechanisms and benefits of topologically interlocked material (TIM) assemblies under impact loading. The study is motivated by earlier findings that TIMs under low rate loading demonstrated attractive properties including the capability to arrest and localize cracks and to exhibit a quasi-ductile response even when the unit elements are made of brittle materials. It is hypothesized that TIMs due to their modularity would possess advantageous impact characteristics. In order to test this hypothesis, a series of computational experiments on the dynamic loading of TIMs are conducted. Results obtained in this study are presented for a planar TIM configuration based on a dense packing of tetrahedral unit elements to form an energy absorption layer. Finite element models are calibrated on samples fabricated using fused deposition modeling (FDM) additive manufacturing (AM). With employing the Lambert–Jonas formula to interpret the numerical data, it is demonstrated that TIMs can absorb more impact energy than conventional solid plates. An extended Lambert–Jonas model is defined such that accurate description of the impact response of TIMs is obtained. [ABSTRACT FROM AUTHOR]

The ballistic performance of thin aluminium targets and influence thereon of different circumferential fixity conditions were studied both experimentally and by finite element simulations. A pressure gun was employed to carry out the experiments while the numerical simulations were performed on ABAQUS/Explicit finite element code using Johnson–Cook elasto-viscoplastic material model. 1 mm thick 1100-H12 aluminium plates of free span diameter 255 mm were normally impacted by 19 mm diameter ogive and blunt nosed projectiles. The boundary conditions of the plate were varied by varying the region of fixity along its circumference as 100%, 75%, 50% and 25% in experiments and the numerical simulations. Further, simulations were carried out to compare the response of the plates with 50% and 75% continuous fixity with those with two and three symmetrical intermittent regions of 25% fixity respectively. The variation in the boundary condition has been found to have insignificant influence on the failure mode of the target however; it significantly affected the mechanics of target deformation and its energy absorption capacity. The ballistic limit increased with decrease in the region of fixity. It decreased for intermittent fixity in comparison with equivalent continuous fixity. And, it has been found to be higher for the impact with projectile having blunt nose in comparison with the one having ogive nose. [ABSTRACT FROM AUTHOR]

Composite laminates made of glass/epoxy with and without nano fillers were subjected to projectile impact. The laminates of different thicknesses were prepared by hand lay-up and compression molding processes. Laminates were made from glass woven roving mats of 610 gsm, epoxy resin and nano clay of 1–5 wt.% of matrix. A piston type gas gun setup was used to impact a spherical nose projectile of diameter 9.5 mm and mass of 7.6 g, on the nanocomposite laminates at impact velocities in the range of their ballistic limit and above. The energy absorbed during penetration and ballistic limit of the nanocomposite laminates were studied both experimentally and analytically. The analytical model also predicts the energy absorbed in various failure modes due to tensile failure of primary fibers, deformation of secondary fibers, delamination and matrix crack. Mechanical properties like tensile modulus, stress–strain function, shear modulus, and strain energy release rate were used as input to the analytical model. Laminates of three, five and eight layers have been considered for the analysis. The effect of clay dispersion in the matrix for different failure modes is discussed. Ballistic limit obtained from the model is validated with experimental results and good agreement is found. [ABSTRACT FROM AUTHOR]

Polymer composites comprising ultra-high molecular weight polyethylene (UHWMPE) fibers in a compliant matrix are now widely used in ballistic applications with varying levels of success. This is primarily due to a poor understanding of the mechanics of penetration of these composites in ballistic protection systems. In this study, we report experimental observations of the penetration mechanisms in four model systems impacted by a 12.7 mm diameter spherical steel projectile. The four model targets designed to highlight different penetration mechanisms in Dyneema ® UHWMPE composites were: (i) a bare aluminum plate; (ii) the same plate fully encased in a 5.9 mm thick casing of Dyneema ® ; (iii) the fully encased plate with a portion of the Dyneema ® removed from the front face so that the projectile impacts directly the Al plate; and (iv) the fully encased plate with a portion of the Dyneema ® removed from the rear face so that the projectile can exit the Al plate without again interacting with the Dyneema ® . A combination of synchronized high speed photography with three cameras, together with post-test examination of the targets via X-ray tomography and optical microscopy was used to elucidate the deformation and perforation mechanisms. The measurements show that the ballistic resistance of these targets increases in the order: bare Al plate, rear face cutout target, fully encased target and front face cutout target. These findings are explained based on the following key findings: (a) the ballistic performance of Dyneema ® plates supported on a foundation is inferior to Dyneema ® plates supported along their edges; (b) the apparent ballistic resistance of Dyneema ® plates increases if the plates are given an initial velocity prior to the impact by the projectile, thereby reducing the relative velocity between the Dyneema ® plate and projectile; and (c) when the projectile is fragmented prior to impact, the spatially and temporally distributed loading enhances the ballistic resistance of the Dyneema ® . The simple model targets designed here have elucidated mechanisms by which Dyneema ® functions in multi-material structures. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the ballistic performance of double-layered steel plates of different materials impacted by blunt- and ogival-nosed projectiles is experimentally investigated by a gas gun. The ballistic limit velocity for each configuration is obtained and compared on the investigation of the effect of the order of layers and the nose shape of projectiles on the ballistic resistance of targets. The experimental results showed that the ballistic limit velocities are higher for the double-layered plates of the upper layer of high strength and low ductility material and the lower layer of low strength and high ductility material than the configuration of the opposite layering order. Moreover, the ballistic limit velocities of ogival-nosed projectiles are significantly smaller than those of blunt-nosed projectiles. Furthermore, the keep integrity ability of ogival-projectiles is obvious stronger than that of blunt-nosed projectiles, and also the blunt-nosed projectiles lose some mass and their length shorten, but the loss of mass and length of ogival-nosed projectiles are tiny that can be neglected. The differences in the ballistic limit velocities between various impact conditions can be related to the transitions of perforation mechanisms and failure models of plates and projectiles. [Copyright &y& Elsevier]

Abstract: Ballistic limit equation (BLE) is an important tool for spacecraft shield design. An approach for constituting dual/multi wall BLE by single wall BLE is proposed. A new single wall BLE is built first based on the current BLE form analysis. A total of 100 experimental test data collected from the literature are introduced for verifications and comparisons. The new single wall BLE has obtained a better correct prediction rate of 83% than other tested BLEs. Secondly, the new Whipple shield (double wall) BLE is constituted of the new single wall BLE. In the low velocity regime the projectile isn't completely fragmented behind the bumper, the Whipple shield BLE is therefore obtained just by the summation of the single wall BLEs of the bumper and the rear wall. While in the hypervelocity regime, the expansion effect of the completely fragmented debris cloud is taken into consideration. The single wall BLE of the rear wall is multiplied by a correction term of the spacing between the two walls before the summation. The shatter regime BLE is obtained by the linear interpolation of the endpoints. A total of 268 experimental test data collected from the literature are introduced for verifications and comparisons. The new Whipple shield BLE has obtained a better correct prediction rate of 72% than other tested BLEs. Finally, the new multi-shock shield BLE is preliminarily constituted of the new single wall BLE and the Whipple shield BLE. The new multi-shock BLE is used to predict 5 experimental test cases and all of which are correct. [Copyright &y& Elsevier]

Abstract: Experimental, analytical and numerical simulations were performed to study the ballistic resistance of 6061-T6 aluminium plates subjected to a normal impact of small calibre armour piercing bullets. Two types of bullets were used, steel and tungsten carbide core bullets. Three plate thicknesses, 101.6 mm, 76.2 mm and 25 mm, were considered. Bullets were impacted at ordnance velocity thus results range from deep penetration to complete perforation with residual velocity. Ballistic results, deformations of the plates and of the bullets are discussed and reproduced through numerical simulations using both LS-DYNA and ABAQUS solvers; analytical models by means of a cavity expansion approach are also used. Exploiting analytical and numerical models the ballistic behaviour of the two bullets on the three plates is discussed with emphasis on the capability of the models to reproduce the physical features of the phenomena. X-ray diffraction measurements for the residual stress patterns of the plate's surface were also performed on all of the plates both before and after the tests and the experimental measurements are compared with the numerical model results. A specific discussion about tungsten carbide core bullet behaviour is reported highlighting the importance of the sabot in the impact phenomena. Although the work focuses on monolithic plates, the results and discussion can be of interest for the design of optimised multilayer armour shields. [Copyright &y& Elsevier]

Abstract: In order to establish the survivability of a composite structure under an impact load, it is important to be able to predict the impact behaviour of composite laminate. In this work, a modified analytical model is proposed to study the impact process of different nose projectiles penetrating into a unidirectional glass fibre reinforced cross ply laminate. This model is based on energy conservation law, where the energy possessed by the projectile is absorbed by the composite laminate by different energy absorbing mechanisms. The energy absorbing mechanisms considered are cone formation of the back face of the composite laminate, deformation of the secondary yarns, tensile failure of the primary yarns, delamination, matrix cracking and friction between the projectile and the laminate during penetration. Analytical formulation is presented for all the energy absorbing mechanism. Using the analytical formulation, ballistic limit, energy absorption and the damage area have been predicted for unidirectional cross ply laminates. The analytical results are compared with the experimental results and found that they are in good agreement. [Copyright &y& Elsevier]

Abstract: 2024 Aluminum sheet and plate are known to have anisotropic strength characteristics with regard to plasticity. However, numerical investigations of the impact behavior of sheet metals rarely consider anisotropic behavior. The effect of anisotropy in an impacted 2024 aluminum target is investigated experimentally and numerically. Normal impact experiments of titanium alloy and tool steel projectiles, with impact velocities ranging from 190 to 299 m/s, into 3.175 mm thick 2024-T3 sheet and 12.7 mm thick 2024-T351 plate are presented. Rear surface strains and displacements are measured using three-dimensional digital image correlation (DIC). Simulations of selected impact experiments, using a six-component anisotropic plasticity model for the target, are compared to the experimental data. Two model parameter sets are used. The first set accounts for initial anisotropic strength properties of the target, while the second reduces to an isotropic (von Mises) yield function. The objective of the numerical simulations is to study the difference in the results between the anisotropic and isotropic parameter sets. Results show that the yield function parameters used for simulations of both the 3.175 mm sheet and 12.7 mm plate have a significant effect on the calculated residual velocity of the projectile. The anisotropic parameter set simulations agree with experimental rear surface panel displacements and strains for both target thicknesses. There is experimental evidence of anisotropic deformation behavior only in the case of the 3.175 mm thick 2024-T3 target panels. The results demonstrate that the form of the yield function has a significant effect on the results of the impact simulations. [Copyright &y& Elsevier]

The mechanisms of projectile penetration of extruded 6061T6 aluminum alloy sandwich panels with empty and alumina filled, triangular corrugated cores have been experimentally investigated using zero obliquity, 12.7 mm diameter hard steel projectiles whose diameter was about a half that of the core's unit cell width. We find that low momentum impacts are laterally deflected by interactions with the inclined webs of the empty core. Complete penetration occurred by shear-off within the impacted front face sheet, followed by stretching, bending and tensile fracture of the core webs and finally shear-off within the back face sheet. This combination of mechanisms was less effective at dissipating the projectiles kinetic energy than the shear-off (plugging) mechanism of penetration of the equivalent solid aluminum panel. Inserting ballistic grade alumina prisms in the triangular cross section spaces of the corrugated core significantly increased the panel's ballistic resistance compared to the empty panel. The presence of the hard ceramic led to severe plastic deformation and fragmentation of the projectile and comminution and macroscopic fracture of the ceramic. The Al/Al2O3 hybrid panel ballistic limit was reached when pairs of parallel cracks formed in the rear face sheet at core web-face sheet nodes. The separation distance between these cracks was dependent upon the location of the impact with respect to that of the web-face sheet nodes. Nodal impacts resulted in pairs of fractures that were separated by one cell width and a critical velocity below that of the equivalent solid plate. Impacts mid-way between pairs of nodes resulted in back face sheet crack pairs separated by twice the cell width, and a critical velocity higher than the equivalent solid plate. Using X-ray tomography we show this resulted from the formation of oval (not circular) cross section fracture conoids in the ceramics. The conoid angle was about 60° in the extrusion direction but only 30° in the transverse direction. This observation may have interesting consequences for a panel's resistance to a second, close proximity impact. [ABSTRACT FROM AUTHOR]

Abstract: A series of hybrid sandwich structures were fabricated by shrink-fitting precision-ground prisms of alumina (CoorsTek grade AD 995) with triangular, trapezoidal or rectangular cross-sections into the voids of extruded sandwich panels made from Al 6061-T6. The panels were subjected to impact tests using hard steel spheres over the velocity range 570–1800 m s−1. A combination of X-ray tomography, high-speed video imaging and cross sectioning of impacted samples was used to investigate the penetration mechanisms. We find that the ballistic performance of these structures, characterized by the ballistic limit and the exit velocity of impact ejecta beyond this limit, is significantly improved when triangular prisms are replaced by trapezoidal prisms, provided the base width of the prism exceeds about three times the projectile diameter. Additional performance improvements are obtained when the trapezoidal prisms are replaced by rectangular prisms, albeit at the expense of an increase in the lateral extent of damage. The variations in impact response are found to arise from: (i) the effect of prism size and shape on the degree of confinement of the ceramic by the metallic webs, (ii) the core web structure, which influences the fracture conoid angle in the transverse plane, and (iii) the spacing of web-face nodes on the back face, which governs the deflection and fracture of the back-face sheet. [Copyright &y& Elsevier]

Abstract: The present article describes a comparative study of the impact resistance of two commercial TiC/Ni cermets and an armor-grade alumina, each in the form of plates backed by thin steel sheets. Performance is assessed on the basis of the ballistic limits of the targets and, below the ballistic limit, on the magnitude and the shape of the back-sheet deflection profile. The operative damage and deformation mechanisms are characterized via optical and scanning electron microscopy on plugs of material recovered from the impact site. We find that, over the range of conditions probed by the present experiments, the cermets exhibit ballistic performance comparable to that of the alumina on an areal density basis yet suffer significantly less extended cracking and fragmentation. Furthermore, for both of the cermets and the alumina, failure at the highest velocities occurs via shear plugging, thereby producing cylindrical plugs with diameter somewhat greater than that of the projectile. Complementary finite element simulations of impulsively loaded steel sheets show that the magnitude and the shape of the deflection profile are dictated by the size of the loading patch. Upon comparison of the simulations with experimentally-measured profiles we find that the inferred effective radius over which the impact load is transmitted from the striker-plate to the backing sheet is broadly consistent with the observed radii of ejected plugs. Furthermore, this radius generally decreases with increasing projectile velocity. On this basis, we suggest that the combination of the maximum back-sheet deflection and the shape of the deflection profile provides a useful measure of the efficacy of the plates in spreading the impact load and mitigating the effects of the impact on back-sheet deflection. [Copyright &y& Elsevier]

Abstract: Sphere structures for ballistic protection have rarely been studied. In this paper a novel unit cell, called Square Based Pyramid Unit Cell (SBPUC), is created as a fundamental building block of sphere structures for the purpose of ballistic protection. Although it has been proved by the other authors that the arrangement of spheres in a tapered chain is an efficient way for impact energy absorption (Sokolow A, Pfannes JM, Doney RL, Nakagawa M, Agui JH. Absorption of short duration pulses by small, scalable, tapered granular chains. Appl Phys Lett 2005;87:1–3), it is very difficult to convert this 1D concept to 3D application in reality with arbitrary tapering angle. The adoption of SBPUCs may provide a good solution. In this research, the core of a sandwiched sphere structure is build with such SBPUCs and is characterized with increasing sphere diameter, decreasing sphere thickness, and increasing sphere cap thickness. From the numerical simulation results with ABAQUS/Explicit, the sandwiched sphere structure can absorb at least 11.6% more impact energy compared with the monolithic plate with the same area density. This study might provide a potential armor design platform which makes further performance improvement possible by optimizing the large parameter space associated with material selection and structure design. [Copyright &y& Elsevier]

Effect of adding amino-functionalized multi-walled carbon nanotubes (NH2-MWCNTs) on the ballistic performance of E-glass/epoxy composites was investigated in this study. E-glass/epoxy panels were prepared with and without MWCNTs. Two different weight percentages of 0.3 and 0.5% MWCNTs were used to modify the epoxy resin. MWCNTs were dispersed in epoxy resin through a combination of sonication and 3-roll mill methods. Laminated composite panels with E-glass plain weave fabrics were made through hand lay-up followed by compression molding process. Samples of size 120 × 120 × 5.25 mm were then cut from the panels and subjected to spherical projectile impacts using a gas-gun set-up at different velocities to determine the ballistic limit velocity (V BL ). Additionally, ballistic limit velocity was statistically determined through polynomial and power regression using experimental results. Ballistic limit increased by about 15–19 m/s (5–6.5%) for laminates with 0.3 wt.% MWCNTs. On the other hand, the performance of laminates with 0.5 wt.% MWCNTs was comparable with that of control samples. Damage size as determined by ultrasonic c-scan studies was considerably less for the laminates with MWCNTs at a given impact velocity below and above ballistic limit. [ABSTRACT FROM AUTHOR]

Abstract: This paper details a numerical modeling and experimental test program focused on high energy ballistic impacts on composite rib-stiffened structures. The numerical model used in this paper is designated as the Multiconstituent Composite Model (MCM), which is implemented within the CTH shock physics code for simulation of ballistic impact damage on composite structures. The presented work utilized a building block approach, where component level flat panels were studied first, followed by sub-structure level T-joint specimens, both fabricated from a carbon/epoxy composite material. All numerical studies and experimental tests utilized the military grade 0.50 caliber M2 Ball round as a projectile. Following testing, each panel was inspected both visually and using Ultrasonic C-Scan techniques to determine the extent of damage sustained upon impact. Finally, comparisons of the experimental data with the numerical predictions are presented and discussed. Both the flat panel and T-joint damage predictions were in good agreement with the experimental data. [Copyright &y& Elsevier]

Abstract: The ballistic properties of the aluminium alloy AA6070 in different tempers are studied, using target plates of 20 mm thickness in tempers O (annealed), T4 (naturally aged), T6 (peak strength) and T7 (overaged). The stress–strain behaviour of the different tempers was characterised by quasi-static tension tests and was found to vary considerably with temper in regards to strength, strain hardening and ductility. Ballistic impact tests using 7.62 mm APM2 bullets were then carried out, and the ballistic limit velocities were obtained for all tempers. In the material tests it was shown that the O-temper was most ductile and almost no fragmentation took place during the ballistic impact tests. The T6-temper proved to be least ductile, and fragmentation was commonly seen. The experiments show that despite fragmentation, strength is a more important feature than ductility in ballistic impact for this alloy, at least for the given projectile and within the velocity range investigated. A thermoelastic–thermoviscoplastic constitutive relation and a ductile fracture criterion were determined for each temper, and finite element analyses were performed using the IMPETUS Afea Solver with fully integrated 3rd-order 64-node hexahedrons. The numerical simulations predicted the same variation in ballistic limit velocity with respect to temper condition as found in the experiments, but the results were consistently to the conservative side. In addition, analytical calculations using the cylindrical cavity expansion theory (CCET) were carried out. The ballistic limit velocities resulting from these calculations were found to be in good agreement with the experimental data. [Copyright &y& Elsevier]

This paper reports the ballistic impact damage of three-dimensional angle-interlock woven composite (3DAWC) under a hemispherical rigid projectile penetration on the basis of high strain rate constitutive equations of fiber tows and multi-scale geometrical model of the 3DAWC. The constitutive equations of the Twaron® fiber tows (poly paraphenylene terepthalamide, PPTA) under high strain rates have been established to characterize the mechanical behaviors under impact loading. The Twaron® fiber tows were assumed as transversely isotropic viscoelastic material to derive the constitutive equations. The maximum strain failure criterion was adopted for defining the failure of the PPTA fiber tows. A user-defined subroutine UMAT (FORTRAN user-material subroutine) was written for combining both the constitutive equations and the failure criterion in numerical calculation. Based on a micro-scale geometrical model of the 3DAWC, the UMAT for the PPTA fiber tows was combined with a commercial available finite element method (FEM) software package LS-DYNA to calculate the ballistic impact damage when the 3DAWC panel penetrated under a hemispherical–cylindrical steel projectile. It was found that the FEM simulation agrees well with the experimental results. The impact damage morphologies and damage propagations, the energy absorptions and the stress distributions in the 3DAWC panel were presented to elucidate the ballistic penetration damage mechanisms for optimizing the ballistic protection capacity of the 3-D woven composite material. [ABSTRACT FROM AUTHOR]

• A simplified 2-DOF motion model was presented and compared with older models. • Penetration experiments were conducted and analyzed using two rifle bullets. • The two bullets showed different tumbling features. • The present model showed the best consistency with the experimental results. • The striking yaw angle plays a decisive role in the yawing motion. Ballistic gelatin is a widely used tissue simulant in terminal ballistics. To investigate the yawing motion of rifle bullets in gelatin, this paper presented a simplified 2-DOF motion model describing the translation and rotation of the bullets. Penetration experiments were conducted using rifle bullets of two different calibers. By comparing with the experimental results, the parameters in the present yawing motion model were estimated and analyzed. The present model can predict the yawing motion of the two rifle bullets in gelatin with much higher accuracy than previous models. The yawing motion of rifle bullets was discussed in detail by making comparisons between calculations of two different rifle bullets and comparisons between calculations with different initial conditions. The striking yaw angle was found to play a decisive role in the growth of the yaw angle and thus to noticeably affect the penetration depth when the bullet tumbles through 90°. [ABSTRACT FROM AUTHOR]

Abstract: An artificial neural network model has been developed for predicting the perforation limits of spaced aluminium armour (aka Whipple shield) under impact of aluminium projectiles at hypervelocity. The network, utilizing a multilayer perceptron architecture, was trained on data from 769 impact tests, for which it accurately predicted the perforation of the shield rear wall (or lack thereof) 92% of the time. Comparatively, the leading empirical approach was found to accurately predict the outcome of 71% of the impact tests. The network output is an analogue probability of perforation, which is adjusted to a binary “Pass”/”Fail” result via a sigmoid fit that also provides physically plausible confidence bounds (i.e. error bars). Interrogation of the network was performed to identify the input parameters that most heavily correlated with the output prediction. Although the majority of the traditional parameters (i.e. those identified in the empirical ballistic limit equation) were amongst the most influential, some unexpected (and potentially spurious) parameters were also identified. A more widely sampled set of training data incorporating increased diversity in projectile and target materials would likely improve the network internal weighting for material properties and avoid accidental identification of biases in the training exemplars. [Copyright &y& Elsevier]

Abstract: Porous-ceramic, thermal protection systems were used heavily on the Orbiter, and they are currently being used on the next generation of US manned spacecraft, Orion. These systems insulate reentry critical components of a spacecraft against the intense thermal environments of atmospheric reentry. Additionally, these materials are highly exposed to space environment hazards like solid particle impacts. This paper discusses impact studies up to 10 km/s on nominally 8 lb/ft3 alumina-fiber-enhanced-thermal-barrier (AETB8) tiles coated with a toughened-unipiece-fibrous-insulation/reaction-cured-glass layer (TUFI/RCG). A first principles impact model that describes projectile dispersion is described that provides excellent agreement with observations over a broad range of impact velocities, obliquities and projectile materials.© 2012 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of the International Hypervelocity Impact Society. [Copyright &y& Elsevier]

Abstract: The present study describes the ballistic impact behaviour of a high strength metastable near beta Ti alloy, β-CEZ in different microstructural conditions against 7.62 mm armour piercing projectiles. Ballistic trials were carried out on 10 mm thick β-CEZ and Ti–6Al–4V plates clamped with 50 mm thick 7017 Al alloy backing. The ballistic performance of different conditions was evaluated by measuring residual depth of penetration (DOP) in 50 mm thick Al-7017 alloy backing. In the present study, even though the β-CEZ titanium alloy in as-rolled and α + β solution treated + aged conditions had significantly higher strength and hardness compared to conventionally used Ti–6Al–4V, significant improvement in ballistic impact resistance was not observed. Post ballistic microstructural observation of crater cross section showed formation of adiabatic shear bands (ASBs) and ASB induced cracks in all conditions. As-rolled, α + β solution treated and aged conditions of β-CEZ alloy showed more ASBs, ASB induced cracks in comparison to Ti–6Al–4V. The β-solution treated and quenched condition of β-CEZ had less number of ASB and highest residual depth of penetration. In this study the ballistic results are discussed based on the post ballistic microstructural observations. [Copyright &y& Elsevier]

Abstract: This paper examines experimental and numerical investigations on ballistic impact behaviors of GLARE 5 (3/2) fiber-metal laminated (FML) beams of various stacking sequences. The ballistic impact tests were conducted using a high-speed gas gun equipped with a high-speed camera. Optical imaging and mechanical sectioning techniques as well as high-speed-camera footage were used to characterize the impact damage in the specimens. The incident projectile impact velocity versus the residual velocity (V I ∼ V R) was plotted and numerically fitted according to the classical Lambert–Jonas equation for the determination of ballistic limit velocity, V 50. The results showed that the unidirectional [90°4] specimen offered the least resistance to the projectile perforation. In addition, except for the unidirectional [90°4] specimen, the ballistic limit was almost insensitive with respect to change in stacking sequence. The interfacial delamination/debonding as well as bending and stretching in aluminum layers played significant roles in dissipating the impact energy in the GLARE 5 (3/2) FML beams. The ballistic impact tests were modeled using a 3D finite element (FE) code, LS-DYNA. The FE prediction was validated using the experimentally obtained V I ∼ V R trends, damage patterns and bullet residual length. Good agreement between experimental and numerical results was achieved. Moreover, the FE predicted V 50 as a function of specimen stacking sequence was in good agreement with its experimental counterpart. The validated FE model was then utilized to obtain some insights to the ballistic impacts of which experimental results were not available. It was found that the cross-ply specimen offered the highest contact resistance force while the unidirectional [90°4] lay-up orientation offered the lowest. The maximum contact force for the unidirectional [0°4] and quasi-isotropic panels were almost the same. The results showed that when subjected to ballistic impact, the specimen with [0°/90°]s lay-up orientation dissipated more energy compared to the other lay-up orientations. [Copyright &y& Elsevier]

Abstract: We have used forward ballistic, reverse ballistic and computational analysis techniques to interrogate the effect of the gilding jacket from a 7.62 mm × 51 mm FFV armour-piercing bullet during the penetration of ceramic-faced targets. When the gilding jacket is removed, it is shown that greater damage occurs to the core suggesting that the presence of the jacket is pre-damaging the ceramic before core arrival. This is confirmed through computational analysis. This work highlights possibilities in enhancing protection by pre-stripping the bullet''s jacket prior to ceramic impact. [Copyright &y& Elsevier]

Abstract: This paper presents the results of an experimental investigation on the axial splitting of thin-walled aluminium extrusions by means of blast load. Plastic explosive (PE4) was used to accelerate the circular extrusions onto a cutting die backed by a curved deflector. The apparatus was mounted on a ballistic pendulum to measure the impulse imparted by the explosive. A load cell was used to measure the transient axial load response during the cutting process. Explosive masses, varied from 15 g to 40 g, produced different lengths of cut (28–137 mm) within the extrusion. The specimens, which were made from three grades of aluminium, AA6061-T4, AA6061-T6 and AA6063-T6, had a nominal diameter of 51 mm, a wall thickness of either 1/16″ (1.6 mm) or 1/8″ (3.2 mm) and were 300 mm in length. Similar energy dissipation mechanisms as previously observed for quasi-static and dynamic loading conditions was observed in the blast load testing applications applied in this study. Furthermore, localised plastic deformation and dynamic progressive buckling were also observed which were not noted in previous impact testing conditions. The performance of the circular extrusions was assessed through determination of the mean cutting load, peak cutting load and cutting force efficiency (CFE). The length of cut increased with an increase in charge mass. An increase in material hardness showed a decrease in the overall cut depth and (CFE). [Copyright &y& Elsevier]

Abstract: This paper presents a semi-analytical approach on the performance of ceramic/metal armor under ballistic impact. Numerical simulations for alumina/aluminum armor impacted by 20 mm APDS in AUTODYN were carried out and verified against the experimental data. Comprehensive numerical simulations were performed using the verified numerical model material parameters providing corroborative data for ensuing discussions. A semi-analytical model relating projectile residual velocity, impact velocity and armor ballistic limit velocity (BLV) is presented for impact of hard projectile against ceramic/metal armor. It is shown that the projectile residual velocity and BLV satisfy the replica scaling laws. Based on the replica scaling laws of projectile residual velocity and BLV, an empirical equation for BLV is obtained and used for armor optimization applications giving reasonable results similar to experiments available in the literature. [Copyright &y& Elsevier]

Abstract: This paper presents results from both experiments and numerical simulations of frontal and lateral ballistic impacts on a Hybrid III headform equipped with Advanced Combat Helmets (ACH) of two different interior cushioning designs, namely the strap-netting system and the Oregon Aero (OA) foam padding. It aims to study the differences between two different impact orientations for these two different interior cushioning systems. The experiments involve frontal and lateral ballistic impacts of a 11.9g spherical steel projectile traveling at speeds of approximately 200m/s, striking on the helmet-cushion-headform assemblies. The dynamic interaction between various components of the helmet-cushion-headform assemblies are investigated with the use of high-speed photography while post-test evaluation of the damaged helmets are performed using visual observation, optical microscopy and computed tomography (CT) scan. A series of ballistic impact simulations with finite element (FE) models of the two assemblies reconstructed from CT images, are performed to correlate with experimental results. The commercial software, Abaqus™, is used for the FE analyses. In general, there is reasonable correlation between numerical and experimental observations and on quantitative parameters, such as head accelerations, helmet damage and deflections. It is also found that softer foams with low stiffness are more effective as shock absorbing cushion against ballistic impacts under certain condition. Additionally, results of the two interior cushioning systems are compared with various injury criteria to assess their acceleration levels. It is found that, for frontal impact, the helmet with strap-netting system fails both the Wayne State Tolerance Curve (WSTC) and Federal Motor Vehicles Safety Standards (FMVSS) 218 criteria while the one with OA foam-padding passes both. [Copyright &y& Elsevier]

Abstract: The shock Hugoniot is a fundamental relationship between pressure, volume, and energy for a given medium. Accurate knowledge of the Hugoniot for a material is critical in order to determine its response to shock waves and high-velocity impacts. Traditionally, the shock Hugoniot is measured on a point-by-point basis by a series of high-velocity impact experiments. Observations are typically confined to pointwise pressure or velocity measurements at the free-surfaces of the sample. In this work, shock waves are initiated in transparent polyurethane and semi-opaque polyurea samples using exploding bridgewires, aluminum ballistic projectiles, and gram-scale explosive charges. Shock waves and material motion are observed optically by shadowgraphy using a high-speed-digital camera recording at up to 106 frames/s. Ballistic impact, producing a constant-strength shock wave, is combined with these optical techniques to obtain a single shock Hugoniot point per test. A gram-scale explosive charge produces a shock wave in the material sample that is initially strong, but attenuates to near the bulk sound speed as it transits the polymer sample. With optical access to the entire sample, multiple shock and particle velocity combinations may be observed in a single test, allowing the measurement of a shock Hugoniot curve in fewer experiments than by traditional methods. These techniques produce data in general agreement with an extrapolation of published Hugoniot data for polyurethane and polyurea. [Copyright &y& Elsevier]

Abstract: The main objective of this work was to investigate the relationship between microstructural defects and ballistic variability in hot pressed SiC. Two plates, 4” × 4” × 1” thick, from the same manufacturing lot, identified as samples A and B, were subjected to nominally identical high velocity impacts on the 4” × 4” face under which sample B performed more poorly than A. The exposed microstructural defects on fragments of the two samples were carefully characterized using scanning electron and optical microscopy. Two types of inclusion defects were identified: carbonaceous and aluminum-iron-oxide phases. While only small inclusions were found on polished cross sections, the rubble fracture surfaces were found to contain disproportionate numbers of large inclusions, strongly suggesting an influence on crack formation. A statistical function derived previously by Jayatilaka and Trustrum was successfully used to describe the defect populations. Sample A had more numerous, but smaller inclusions on its fragments than sample B. The exponent (n) of the distribution function can be related to the Weibull modulus (m) used to describe the strength variation of brittle materials by the relation m = 2n, a relationship that may be useful in efforts to represent defect distributions in micromechanical models. The data suggests that sample B has a higher probability of having a large inclusion on its fragments than sample A, which had more numerous smaller inclusions. Therefore, sample B would have a greater likelihood of crack nucleation and resulting failure at high strain rates from the distribution of large defects. The Pareto Principle, which suggests that 20% of the large inclusions in the tail of the distribution account for 80% of the total performance may be applicable. [Copyright &y& Elsevier]

Abstract: A ply-level material constitutive model for plain-weave composite laminates has been developed to enable computational analyses of progressive damage/failure in the laminates under high velocity ballistic impact conditions. In this model, failure-initiation criteria and damage evolution laws are introduced to account for the major fiber-failure modes (tensile, compressive, punch shear and crush loading). In addition, two matrices related failure modes (in-plane shear and through the thickness delamination) are also accounted for. These types of fiber and matrix failure modes are commonly observed during a ballistic event. The composite-material model has been implemented within LS-DYNA as a user-defined material subroutine and used successfully to predict the damage and ballistic behavior of composite laminates subjected to various ballistic impact conditions. It is hoped that the availability of this material model will help facilitate the development of composite structures with enhanced ballistic survivability. [Copyright &y& Elsevier]

Abstract: The effect of rubber, Teflon and aluminum foam interlayer material on the ballistic performance of composite armor was investigated both experimentally and numerically. Although, rubber interlayer did not cause any significant delay in the initial stress build-up in the composite layer, Teflon and aluminum foam interlayer caused a significant delay and reduction in the magnitude of the stress transmitted to the composite backing plate. Damage in the ceramic layer was found to be highly localized around the projectile impact zone for the configuration without interlayer and rubber interlayer while aluminum foam and Teflon interlayer spread the damage zone in the radial direction. Relatively large pieces of the ceramic around the impact axis in the rubber interlayer configuration were observed while the ceramic layer was efficiently fragmented in aluminum foam and Teflon interlayer configuration. [Copyright &y& Elsevier]

Abstract: Armour steel plates of 25mm thickness were tempered at various temperatures from 200°C to 600°C and tested against ballistic impact of 7.62mm AP projectiles. Hardness decreases with increase in tempering temperature resulting in corresponding increase in depth of penetration. Least depth of penetration was observed in the plate tempered at 200°C. Post-impact microstructure of the crater region in the tested plates show adiabatic shear band (ASB) induced cracking for tempering temperatures up to 400°C and no ASB is seen for 600°C. ASB induced cracking was also observed in the crater region of a 5mm thick plate tempered at 200°C and tested under similar conditions. Plates of thickness 5mm with drilled holes of diameter nearly equal to that of the projectile were also tested. The result showed that ASB formation can be partially inhibited in these plates due to presence of holes. [Copyright &y& Elsevier]

Abstract: This paper presents a ballistic impact simulation of an armour-piercing projectile in hybrid ceramic/fiber reinforced composite armour. The armour is composed by an alumina plate and an ultra high molecular weight polyethylene composite. In order to model the armour behavior three different constitutive models were formulated and implemented into ABAQUS/Explicit finite element code. Comparisons between numerical predictions and experimental results in terms of damage shape/extent and V50 are also presented and discussed in the paper. [Copyright &y& Elsevier]

Abstract: Three-dimensional numerical simulations were carried out with ABAQUS/Explicit finite element code to study the influence of target span and configuration on its ballistic limit. 1 mm thick 1100-H12 aluminum targets of varying span diameter and configuration were impacted by blunt and ogive nosed projectiles of 19 mm diameter and 52.5 g mass. The effect of target span was studied by varying the span diameter of 1 mm thick monolithic target as 50 mm, 100 mm, 204 mm, 255 mm and 500 mm. The effect of configuration was studied by taking the monolithic, double layered in-contact and double layered spaced targets of 1 mm equivalent thickness and 255 mm span diameter. The spacing between the layers was varied as 2 mm, 5 mm, 10 mm, 20 mm and 30 mm. In each case the target was impacted normally by blunt and ogive nosed projectile to obtain the ballistic limit. The highest ballistic limit was observed for monolithic target followed by layered in-contact and spaced targets respectively. The variation of spacing between the layers did not have significant influence on the ballistic limit in the case of ogive projectile but some effect was seen in the case of blunt projectile. The ballistic limit was found to increase with increase in target span diameter for both the projectiles and it was found to be higher for blunt nosed projectile as compared to that of ogive nosed projectile for all the spans considered excepting in the case of 50 mm span for which it was higher for ogive nosed projectile. [Copyright &y& Elsevier]

Abstract: We evaluate the performance of the Optimal Transportation Meshfree (OTM) method of Li et al. , suitably extended to account for seizing contact and fracture, in applications involving terminal ballistics. The evaluation takes the form of a conventional Verification and Validation (V&V) analysis. In support of the validation analysis, we have conducted tests concerned with the normal impact of Aluminum alloy 6061-T6 thin plates by S2 tool steel spherical projectile over a range of plate thicknesses of [0.8 mm, 1.6 mm] and a range of impact velocities of [100, 400]m/s. The tests were conducted at Caltech’s GALCIT gas-gun Plate-Impact Facility. We find excellent agreement between measured and computed perforation areas and a ballistic limits over the thickness and velocity ranges considered. Our verification analysis consists of model-on-model comparisons and an assessment of the convergence of the OTM method. Specifically, we find excellent agreement between the incident vs. residual velocities predicted by the OTM method and by the power-law relation of Recht and Ipson . We also find robust linear convergence of the OTM method as measured in terms of residual velocity error vs. number of nodes. [Copyright &y& Elsevier]