Influence of scale on the penetration of tungsten rods into steel-backed alumina targets

As ballistic tests are often performed in reduced geometrical scale, the scaling laws are important for the interpretation of the results. In this study, we tested the validity of replica scaling, by which we mean that all geometrical dimensions are scaled uniformly, while the materials and the impact velocity are kept the same. Long tungsten projectiles with length-to-diameter ratio 15 were fired against unconfined alumina targets with steel backing. The tests were carried out with impact velocities 1500 m s⁻¹ and 2500 m s⁻¹, and in three different scales with projectile lengths 30, 75 and 150 mm (diameters 2, 5 and 10 mm). The alumina targets were photographed by means of a high-speed camera, and the tungsten projectiles were photographed inside the alumina targets by means of flash radiography. Also, the residual penetrations in the steel backings were measured. The Johnson-Holmquist model for ceramic materials was implemented into the AUTODYN code, which was used for simulation of the experiments. The agreement between results of experiment and simulation was fair, and over the tested interval of scales replica scaling was found to be valid with reasonable accuracy.     

Analytical modelling of normal and oblique ballistic impact on ceramic/metal lightweight armours

This paper presents a new analytical model developed to simulate ballistic impact of projectiles on ceramic/metal add-on armours. The model is based on Tate and Alekseevskii’s equation for the projectile penetration into the ceramic tile, whilst the response of the metallic backing is modelled following the ideas of Woodward’s and den Reijer’s models. The result is a fully new analytical model that has been checked with data of residual mass and residual velocity of real fire tests of medium caliber projectiles on ceramic/metal add-on armours. Agreement observed between experimental and analytical results confirmed the validity of the model. Therefore, the model developed can be a useful tool for optimisation of ceramic/metal armour design.     

Analysis of ceramic/metal armour systems

A combined numerical and experimental study for the analysis of ceramic/metal composite armour system against 40.7 g steel projectiles has been performed. The ballistic performance of the add-on lightweight armours was examined by varying the thickness of tiles, while maintaining equal areal density of the system. A numerical study using smoothed particle hydrodynamics scheme is promising since the major distinguishing features of composite armour systems such as, projectile erosion, crack propagation, ceramic conoid formation and failure of backing plate, are successfully captured. Simulation results for ballistic limits appear to match fairly well with the test values and reveal an optimum value of the front plate to back plate thickness ratio.     

Preparation and characterisation of ceramic-faced metal–ceramic interpenetrating composites for impact applications

This article accesses the impact performance of ceramic-faced, metal–ceramic interpenetrating composites (IPCs) produced in situ from infiltrating ceramic foams with a molten aluminium–magnesium alloy. The approach had two variations, viz., the production of a metal bond between a ceramic front face and backing IPC and the creation of a ceramic bond. The impact performance of metal-bonded IPCs was evaluated using both split Hopkinson’s pressure bar (SHPB) and depth of penetration (DoP) techniques. With a 4-mm thick Al₂O₃ front face and an 8-mm thick IPC backing, the DoP was zero. In one case, a sample survived fundamentally intact with only spall damage to the dense Al₂O₃ front face. The resulting damage was thoroughly assessed using a range of techniques, including polarized light microscopy, scanning electron microscopy (SEM), 3D MicroCT and transmission electron microscopy (TEM). The metal phase deformed as a result of the formation of large numbers of dislocations, whilst the ceramic phase accommodated the deformation via localised cracking. Metal bridges across the cracks formed, increasing the damage tolerance of the IPCs. The metal bond between the ceramic front face and the IPC was also observed to withstand the impact of the armour piercing rounds without any sign of debonding occurring.     

Quasi-static penetration and ballistic properties of kenaf–aramid hybrid composites

In this research, quasi-static penetration and ballistic properties of non-woven kenaf fibres/Kevlar epoxy hybrid laminates with thicknesses ranging from 3.1 mm to 10.8 mm by hard projectile at normal incidence have been experimentally investigated. Hybrid composites were fabricated by hand lay-up technique in a mould and cured at room temperature for 24 h by static load. Hybrid composites consist of Kevlar layers and non-woven kenaf layers at three different configurations, i.e. kenaf at the innermost layers, outermost layers and at the alternating layers. Kevlar/epoxy and kenaf/epoxy composites were also fabricated for comparison purpose. Quasi-static experiments were conducted using a tensile testing machine at the speed of 1.27 mm/min and 2.54 mm/min. Ballistic tests were conducted using 9 mm full metal jacket bullet using a powder gun at speeds varying from 172 to 339 m/s, with the initial and a residual velocity of the projectiles is measured. The tested sample was carefully examined with respect to failure modes. Results showed the effect of hybridization in term of force–displacement curves, energy dissipation and damage mechanisms for quasi-static test. Maximum force to initiate penetration is higher in hybrid composites compared to kenaf/epoxy and Kevlar/epoxy composites. Hybridization of kenaf–Kevlar resulted in a positive effect in terms of energy absorbed (penetration) and maximum load. In the case of ballistic tests, hybrid composites recorded lower ballistic limit (V₅₀) and energy absorption than the Kevlar/epoxy composite. The V₅₀ of hybrid composites with kenaf at the outermost layers is superior to other hybrid composites. These finding inspired further exploration of hybrid composite for ballistic armour spall-liner application.     

Microstructure simulation and ballistic behaviour of weld zones in friction stir welds in high strength aluminium 7xxx plate

The effect of friction stir welding (FSW) on the knockdown in properties and failure mechanisms of high strength aluminium plate (AA7010-T7651) under ballistic impact has been investigated by modelling and ballistic testing, simulated, and actual weld zone microstructures, in order to systematically study the link to weld microstructural variation. FSW of thick plate leads to an extremely wide heat affected zone (HAZ). The microstructures within the weld zones were successfully modelled and simulated. However, the maximum loss of hardness in the HAZ resulted in only a 20% reduction in the ballistic limit (V₅₀). The maximum V₅₀ was associated with the highest level of hardness reached prior to a change in failure mechanism, from ductile hole enlargement, using an armour piercing (AP) projectile, or plugging with a fragment simulation projectile (FSP) to excessive spalling and associated adiabatic shear banding at too high hardness levels. The behaviour of the nugget zone has also been examined. The trends in the ballistic data are discussed in the context of the weld zone microstructures and fracture mechanisms.     

Damage evolution and energy absorption of E-glass/polypropylene laminates subjected to ballistic impact

High-velocity transverse impact of laminated fiber reinforced composites is of interest in military, marine and structural applications. The overall objective of this work was to investigate the behavior of laminated thermoplastic composites of varying thicknesses under high-velocity impact from an experimental and modeling viewpoint. In order to analyze this problem, a series of ballistic impact tests have been performed on plain weave E-glass/polypropylene (E-glass/PP) composites of different thicknesses using 0.30 and 0.50 caliber right-cylinder shaped projectiles. A gas gun with a sabot stripper mechanism was employed to impact the panels. In order to analyze the perforation mechanisms, ballistic limit and damage evaluation, an explicit three-dimensional finite element code LS-DYNA was used. Material model 162, a progressive failure model based on modified Hashin’s criteria, has been assigned to analyze failure of the laminate. The projectile was modeled using Material model 3 (MAT_PLASTIC_KINEMATIC). The laminates and the projectile were meshed using brick elements with single integration points. The impact velocity ranged from 187 to 332 m s⁻¹. Good agreement between the numerical and experimental results was attained in terms of predicting ballistic limit, delamination and energy absorption of E-glass/PP laminate.     

Numerical simulation of ballistic impact on composite laminates

The paper reports experimental and numerical simulation of ballistic impact problems on thin composite laminated plates reinforced with Kevlar 29. Ballistic impact was imparted with simulated fragments designed in accordance with STANAG-2920 on plates of different thickness. Numerical modelling was developed and used to obtain an estimate for the limit perforation velocity (V₅₀) and simulate failure modes and damage. Computations were carried out using a commercial code based on finite differences and values obtained are compared with the experimental data to evaluate the performance of the simulation. Good correlation between computational simulation and experimental results was achieved, both in terms of deformation and damage of the laminates. Future work is advanced to include the interposition of an outer ceramic layer as well as examining the influence of dry-wet and temperature cycles on the mechanical strength of the plates and their temporal evolution under accelerated ageing.     

Rebound behaviour of spheres for plastic impacts

This paper presents a study on the rebound behaviour of spheres impacted normally against a target wall using finite element methods. The emphasis is on the prediction of the coefficient of restitution and the effects of material properties and impact velocities on the rebound behaviour of the sphere. Finite deformation during plastic impact is addressed. The finite element results show that, for impacts of small plastic deformation, the coefficient of restitution is mainly dependent on the ratio of the impact velocity V_i to the yield velocity V_y which is consistent with those predicted by the theory of impact mechanics; while for impacts of finite-plastic-deformation it is also dependent on the ratio of the representative Young's Modulus E^* to the yield stress Y. The FEA results suggest that for impacts of finite-plastic-deformation the coefficient of restitution can be approximated to be proportional to [(V_i/V_y)/(E^*/Y)]^−1/2.     

Direct force measurement in normal and oblique impact of plates by projectiles

An experimental investigation of the forces produced by the penetration and perforation of thin aluminum and steel plates by cylindro-conical and hemispherically-tipped projectiles at 0, 15, 30 and 45° angles of incidence has been performed. Additionally, force histories were recorded for normal impact on Lexan, nylon and ceramic targets by conically-tipped strikers. Similar tests on Kevlar were not successful owing to the generation of voltages by rubbing of fibers that completely overwhelmed the transducer signal. A piezoelectric crystal bonded to the tail of the 12.7 mm diameter, 30 g projectiles followed by an inertial mass and a trailing wire provided the instrumentation. The strikers were propelled by means of a pneumatic gun at velocities ranging from 45 to 170 ms⁻¹. Displacement data obtained from high-speed photography for selected runs allowed curve fits to an analytical function which were compared to the directly recorded force histories.The effects of changes in initial velocity, angle of obliquity and striker tip on the peak force have been analyzed. A simple model has been developed for the perforation of plates by hemispherically-tipped projectiles at oblique incidence, and comparisons have been made with the measured force histories. A model was also devised to predict the peak forces obtained for oblique impact by cylindro-conical projectiles. The peak forces obtained experimentally were found to be relatively independent of the initial projectile velocity for shots where perforation occured. For the tests at speeds below the ballistic limit, the maximum forces were approximately proportional to the initial velocity.     

Thickness influence on ballistic impact behaviors of GLARE 5 fiber-metal laminated beams: Experimental and numerical studies

This paper presents experimental and numerical investigations on ballistic impact behaviors of GLARE 5 fiber-metal laminated (FML) beams of various thicknesses. A high-speed camera was used to measure impact and residual/rebound velocities and also to assess damage evolution in the FMLs. 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, V₅₀. The results showed that the V₅₀ varied in a parabolic trend with respect to the metal volume fraction (MVF) and specimen thickness. The interfacial debonding as well as bending and stretching in aluminum layers played the significant roles in dissipating the impact energy in the GLARE 5 FML beams. The 3D finite element (FE) code, LS-DYNA, was used to model and validate the experimentally obtained results. Good agreement between experimental and numerical results was achieved. It was found that for a given specimen configuration, by increasing the projectile incident velocity up to its V₅₀, the maximum contact force increased. By further increasing the projectile velocity above its V₅₀, the maximum contact force was relatively invariant with respect to an increase in the projectile incident velocity.     

A combined experimental and numerical approach to study ballistic impact response of S2-glass fiber/toughened epoxy composite beams

A combined experimental and 3D dynamic nonlinear finite element (FE) approach was adopted to study damage in composite beams subject to ballistic impact using a high-speed gas gun. The time-histories of dynamic strains induced during impact were recorded using strain gages mounted on the front of the composite beam specimen. During ballistic impact tests, the impact velocity was also measured. The commercially available 3D dynamic nonlinear FE code, LS-DYNA, modified with a proposed user-defined nonlinear-orthotropic damage model, was then used to simulate the experimental results. In addition, LS-DYNA with the Chang–Chang linear-orthotropic damage model was also used for comparison. Good agreement between experimental and FE results was found from the comparisons of dynamic strain and damage patterns. Once the proposed nonlinear-orthotropic damage model was verified by experimental results, further FE simulations were conducted to predict the ballistic limit velocity (V₅₀) using either the number of damaged layer approach or a numerically established relation between the projectile impact velocity versus residual velocity or energy similar to the classical Lambert–Jonas equation for metals.     

Ballistic resistance of double-layered armor plates

In this paper, the ballistic resistance of double-layered steel shields against projectile impact at the sub-ordnance velocity is evaluated using finite element simulations. Four types of projectiles of different weight and nose shapes are considered, while armor shields consist of two layers of different materials. In a previous study of the same authors, it was shown that a double-layered shield of the same metal was able to improve the ballistic limit by 7.0–25.0% under impact by a flat-nose projectile, compared to a monolithic plate of the same weight. Under impact by a conical-nose projectile, a double-layered shield is almost as capable as a monolithic plate. The present paper extends the analysis to double-layered shields with various metallic material combinations. The study reveals that the best configuration is the upper layer of high ductility and low strength material and the lower layer of low ductility and high strength material. This configuration results in some 25% gain in the ballistic limit under moderate detrimental impact. This research helps clarify the long standing issue of the ballistic resistance of the multi-layered armor configuration.     

Ballistic impact and explosive blast resistance of stitched composites

The effectiveness of stitching in increasing the damage resistance of polymer composites against ballistic projectiles and explosive blasts is determined. Glass-reinforced vinyl ester composites stitched in the through-thickness direction with thin Kevlar®-49 yarn were impacted with a bullet travelling at 0.9 km s⁻¹ or an underwater explosive shock wave moving at 1.5 km s⁻¹. The amount of delamination damage to the composite caused by a ballistic projectile was reduced slightly with stitching. Stitching was highly effective in increasing the damage resistance against explosive blast loading. The increased damage resistance was due to the stitching raising the Mode I interlaminar fracture toughness of the composite. While the stitched composites experienced slightly less damage, their flexural modulus and strength was similar to the properties of the unstitched composite after ballistic impact testing. The post-blast flexural properties of the stitched composites, on the other hand, were degraded less than the properties of the unstitched material.     

On the drop-weight testing of alumina/aluminum laminated composites

Laminated composites with ceramic front layers and metallic or composite backing layers have gained attractiveness as lightweight armours, as they exhibit the same ballistic performance with lower areal densities as compared to steels. Drop-weight testing (DWT) has potential for evaluating the low velocity impact behaviour of materials. This testing gives significant ideas and information about failure mechanisms and behaviour of materials under low velocity impact. In this study, DWT of alumina/aluminum laminated composites was done in order to investigate the effects of lamination type, density with respect to area and mechanical property of backing material on the low velocity ballistic performance of these composites. The experimental results showed that the laminated composite with ceramic front layer and aged-aluminum alloy as backing layer was the most effective among different investigated specimens against low velocity impact loads.     

Development of an ultrahigh strength low alloy steel for armour applications

Abstract

The present paper describes a steel with yield strength exceeding 1900 MPa and fracture toughness in the range of 40–50 MPa?m^1/2, in its optimum heat treated condition. Its strength is similar to that of 18 Ni (300) grade of maraging steel with good fracture toughness. When tempered at 300°C, it shows tempered martensite along with a small amount of retained austenite phase. The steel shows nearly 25% reduction in weight over typical rolled homogeneous armour (RHA) steel against high velocity hard steel core projectiles. The processing, microstructure, mechanical and ballistic properties of the steel are demonstrated.     

Ballistic impact response of laminated composite panels

Laminated ballistic composite panels are an important part of hard-plate protective body armour and may be subjected to a wide variety of impact conditions depending on the projectile, impact velocity and armour construction, to name a few.     

The design of mosaic armour: The influence of tile size on ballistic performance

Silicon carbide square tiles of different areal geometries and manufactured via two different processing routes have been bonded to polycarbonate layers to evaluate their ballistic performance. Four ceramic tile sizes were tested: 85 mm, 60 mm, 50 mm and 33 mm. In each case the residual depth-of-penetration into a polycarbonate semi-infinite backing was recorded. To elucidate the penetration and failure mechanisms, a computational model using the JH-1 ceramic model [Holmquist TJ, Johnson GR. Response of silicon carbide to high velocity impact. J Appl Phys 2002;91:5858–66] of the projectile used in the experimental study penetrating into a silicon carbide-faced polycarbonate was implemented in the hydrocode AUTODYN-2D. This paper shows that there is a critical dimension of tile that should be used in a silicon carbide-based ceramic-faced mosaic armour system design to ensure optimum system performance when each tile is struck centrally.     

An experimental study on the ballistic impact behavior of some metallic armour materials against 7.62 mm deformable projectile

The investigation describes and analyses the ballistic impact behavior of a high strength armour steel and Al-7017 alloy under 7.62 mm deformable projectiles at a velocity of 830 ± 10 m/s at normal angle of attack. The high strength armour steel is subjected to two different heat treatments to see the effect of different mechanical properties on the ballistic behavior. The ballistic result of the Al-7017 alloy is compared with that of the steel. Some observations relating to the adiabatic shear bands formation have also been presented. Experimental results showed that among the investigated materials, the best ballistic performance was attained with the armour steel at 910 °C austenitisation followed by 200 °C tempering condition.     

Ballistic impact performance of an armor material consisting of alumina and dual phase steel layers

Utilization of a ceramic front layer provides an improvement in the ballistic efficiency of monolithic metallic materials. In the current paper, the ballistic behavior of laminated composite having alumina front and dual phase steel backing layers was studied using 7.62 mm armor piercing (AP) projectiles under normal impact. The variables used were martensite content of the backing layer and the areal density of the composite. Experimental results showed that utilization of a 6 mm thick alumina front layer which was bonded to dual phase steel enhanced the ballistic resistance of the dual phase steel remarkably.