Ballistic behavior of high hardness perforated armor plates against 7.62 mm armor piercing projectile

In this paper, some of the important defeating mechanisms of the high hardness perforated plates against 7.62 × 54 armor piercing ammunition were investigated. The experimental and numerical results identified three defeating mechanisms effective on perforated armor plates which are the asymmetric forces deviates the bullet from its incident trajectory, the bullet core fracture and the bullet core nose erosion. The initial tests were performed on the monolithic armor plates of 9 and 20 mm thickness to verify the fidelity of the simulation and material model parameters. The stochastic nature of the ballistic tests on perforated armor plates was analyzed based on the bullet impact zone with respect to holes. Various scenarios including without and with bullet failure models were further investigated to determine the mechanisms of the bullet failure. The agreement between numerical and experimental results had significantly increased with including the bullet failure criterion and the bullet nose erosion threshold into the simulation. As shown in results, good agreement between Ls-Dyna simulations and experimental data was achieved and the defeating mechanism of perforated plates was clearly demonstrated.     

Effects of dynamic mechanical properties on the ballistic performance of a new near-β titanium alloy Ti684

A comprehensive study of the newly developed near-β titanium alloy Ti684 has been carried out to determine the influence of the dynamic strength, dynamic hardness and critical failure strain on the ballistic impact properties. Two heat treatments of Ti684, namely β solution-treatment and α + β solution-treatment followed by aging, were carried out and the results were compared with Ti–6Al–4V. Ballistic impact tests were conducted on 7 mm thick front plates with a 20 mm thick A3 steel backing plate, using 7.62 mm armor piercing projectiles. The ballistic performance was evaluated by measuring the residual depth of penetration (DOP) in the A3 steel backing plates. It was found that the DOP values did not show obvious corresponding relation with both dynamic strength and dynamic hardness. The 800 °C solution +550 °C aged Ti684, which had the maximal dynamic strength, presented the worst ballistic performance, with a maximum DOP of 12.5 mm. In addition, the Ti–6Al–4V plate in the study with highest dynamic hardness did not show the best ballistic performance, having a DOP of 11.86 mm. However, as the critical failure strain increased, the DOP of the A3 steel backings were observed to decrease. This relationship was revealed from post ballistic microstructural observations.     

Geometry,mechanical and ballistic properties of ADI material perforated plates

In this paper, austempered ductile iron has been evaluated as an alternative to steel for perforated plates applied in the ballistic protection of military vehicles. The austempering was performed in lower and higher austempering ranges in order to obtain two types of austempered ductile iron: one with a higher strength, and the other with a higher ductility. Perforated plates having two different thicknesses of 7 and 9 mm were mounted in front of basic armour and 12.7 × 99 mm armour – piercing incendiary ammunition was fired from 100 m. It was shown that the austempered ductile iron material austempered at a lower temperature has superior ballistic resistance, providing a full (five out of five armour – piercing incendiary shots stopped) ballistic resistance if combined with 13 mm basic armour plate. The thicker austempered ductile iron perforated plate provides more significant penetrating core damage, and therefore, lower basic plate damage. On the other hand, the thinner austempered ductile iron material perforated plate can be considered optimal due to its lower weight and higher mass effectiveness. In austempered ductile iron material austempered at a higher temperature, besides a lower hardness, bulk retained low-carbon metastable austenite transforms into martensite through strain induced mechanism, causing a partial brittle fracture.     

Perforation of AA5083-H116 aluminium plates with conical-nose steel projectiles—experimental study

The interest regarding use of aluminium alloys in lightweight protective structures is today increasing. Even so, the number of experimental and computational investigations giving detailed information on such problems is still rather limited. In this paper, perforation experiments have been performed on AA5083-H116 aluminium plates with thicknesses varying between 15 and 30 mm impacted by 20 mm diameter, 98 mm long, HRC 53 conical-nose hardened steel projectiles. In all tests, initial and residual velocities of the projectile were measured and a digital high-speed camera system was used to photograph the penetration and perforation process. Based on these measurements, impact versus residual velocity curves of the target plates were constructed and the ballistic limit velocity of each target was obtained. An analytical perforation model from the open literature is then used to predict the ballistic limit velocity, and excellent agreement with the experimental data is found. The experimental results are finally compared to similar experiments on steel and concrete targets, and the capacity of the different materials is evaluated in relation to total weight.     

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

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

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

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

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.     

Influence of different back laminate layers on ballistic performance of ceramic composite armor

This paper mainly reported a new type of ceramic composite armor with a back laminate of Ti6Al4V/UHMWPE/Ti6Al4V against the 12.7 mm armor piercing projectile at a velocity of 818 m/s. The mechanism of the whole ceramic composite armor against the projectile, and the function of each layer in the back laminates were systematically investigated around the experiments and numerical simulations. The results indicated that the outermost Ti6Al4V layer provided support for the UHMWPE layer, leading to the UHMWPE layer displaying the extremely high buffer performance during the impact process. Meanwhile, the middle UHMWPE layer also had an energy balance function between the first and outermost Ti6Al4V layers to cause small damage in the back laminate layers. Thus, this configuration contributed to absorb or dissipate the more energy of the impact projectile, successfully preventing the perforation of the projectile.     

Penetration of tungsten alloy rods into shallow-cavity steel targets

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

Experimental studies on the effect of size and shape of holes on damage and microstructure of high hardness armour steel plates under ballistic impact

In the present work the effect of size and shape of regularly spaced holes on the ballistic impact behavior of high hardness steel plates has been studied. Thick backing technique was used to evaluate the efficiency of these plates when subjected to ballistic impact of 7.62 mm non-deformable hard steel core projectiles. The ballistic efficiency of these steel plates was found to be sensitive to size of the holes. Higher efficiency was found for plates with hole sizes close to the diameter of the projectile. Damage patterns and microstructure of the perforated steel plate have been compared with those of non-perforated steel plates. It has been found that presence of holes inhibits shear band formation in the target plates.     

Influence of fiber orientation and thickness on the response of glass/epoxy composites subjected to impact loading

Composite laminates, made of glass/epoxy using compression molding technique, were subjected to impact loading. The ballistic limit and energy absorption capacity of the laminates were obtained. Experiments were carried out to study the effect of fiber orientation and thicknesses on ballistic limit and energy absorption of the laminates, by using a rigid conical bullet having 9.5 mm diameter and mass of 7.5 g in an air gun. Analytical expressions were obtained to find the ballistic limit, residual velocity and energy absorption capacity of the laminates. The expressions obtained by considering the various damage modes, which were involved in penetration, when laminates subjected to impact loading. The values obtained from analysis were compared with experimental results and good agreement was found. The strain rate sensitivity of the glass/epoxy composites was considered for analysis.     

Perforation resistance of five different high-strength steel plates subjected to small-arms projectiles

Thin plates of high-strength steel are frequently being used both in civil and military ballistic protection systems. The choice of alloy is then a function of application, ballistic performance, weight and price. In this study the perforation resistance of five different high-strength steels has been determined and compared against each other. The considered alloys are Weldox 500E, Weldox 700E, Hardox 400, Domex Protect 500 and Armox 560T. The yield stress for Armox 560T is about three times the yield stress for Weldox 500E, while the opposite yields for the ductility. To certify the perforation resistance of the various targets, two different ballistic protection classes according to the European norm EN1063 have been considered. These are BR6 (7.62 mm Ball ammunition) and BR7 (7.62 mm AP ammunition), where the impact velocity of the bullet is about 830 m/s in both. Perforation tests have been carried out using adjusted ammunition to determine the ballistic limit of the various steels. In the tests, a target thickness of 6 mm and 6 + 6 = 12 mm was used for protection class BR6 and BR7, respectively. A material test programme was conducted for all steels to calibrate a modified Johnson–Cook constitutive relation and the Cockcroft–Latham fracture criterion, while material data for the bullets mainly were taken from the literature. Finally, results from 2D non-linear FE simulations with detailed models of the bullets are presented and the different findings are compared against each other. As will be shown, good agreement between the FE simulations and experimental data for the AP bullets is in general obtained, while it was difficult to get reliable FE results using the Lagrangian formulation of LS-DYNA for the soft core Ball bullet.     

Effect of joint design on ballistic performance of quenched and tempered steel welded joints

A study was carried out to evaluate the effect of joint design on ballistic performance of armour grade quenched and tempered steel welded joints. Equal double Vee and unequal double Vee joint configuration were considered in this study. Targets were fabricated using 4 mm thick tungsten carbide hardfaced middle layer; above and below which austenitic stainless steel layers were deposited on both sides of the hardfaced interlayer in both joint configurations. Shielded metal arc welding process was used to deposit for all layers. The fabricated targets were evaluated for its ballistic performance and the results were compared in terms of depth of penetration on weld metal. From the ballistic test results, it was observed that both the targets successfully stopped the bullet penetration at weld center line. Of the two targets, the target made with unequal double Vee joint configuration offered maximum resistance to the bullet penetration at weld metal location without any bulge at the rear side. The higher volume of austenitic stainless steel front layer and the presence of hardfaced interlayer after some depth of soft austenitic stainless steel front layer is the primary reason for the superior ballistic performance of this joint.     

The effect of target strength on the perforation of steel plates using three different projectile nose shapes

The effect of target strength on the perforation of steel plates is studied. Three structural steels are considered: Weldox 460 E, Weldox 700 E and Weldox 900 E. The effects of strain hardening, strain rate hardening, temperature softening and stress triaxiality on material strength and ductility are determined for these steel alloys by conducting three types of tensile tests: quasi-static tests with smooth and notched specimens, quasi-static tests at elevated temperatures and dynamic tests over a wide range of strain rates. The test data are used to determine material constants for the three different steels in a slightly modified version of the Johnson–Cook constitutive equation and fracture criterion.Using these three steel alloys, perforation tests are carried out on 12 mm-thick plates with blunt-, conical- and ogival-nosed projectiles. A compressed gas gun was used to launch projectiles within the velocity range from 150 to 350 m/s. The initial and residual velocities of the projectile were measured, while the perforation process was captured using a digital high-speed camera system. Based on the test data the ballistic limit velocity was obtained for the three steels for the different nose shapes. The experimental results indicate that for perforation with blunt projectiles the ballistic limit velocity decreases for increasing strength, while the opposite trend is found in tests with conical and ogival projectiles. The tests on Weldox 700 E and Weldox 900 E targets with conical-nosed projectiles resulted in shattering of the projectile nose tip during penetration.Finally, numerical simulations of some of the experimental tests are carried out using the non-linear finite element code LS-DYNA. It is found that the numerical code is able to describe the physical mechanisms in the perforation events with good accuracy. However, the experimental trend of a decrease in ballistic limit with an increase in target strength for blunt projectiles is not obtained with the numerical models used in this study.     

Experimental and numerical study on the ballistic resistance of steel–fibre reinforced two-layer explosively welded plates

The damage mechanism and ballistic resistance of steel–fibres reinforced two-layer explosively welded steel/aluminum targets were investigated by the methods of ballistic experiments and numerical simulation by finite element code LS-DYNA 3D. Different from the traditional monolithic and multi-layer metal targets, there are reinforced steel–fibres and good surface-to-surface combination strength between layers of the target. The total thickness of the target was 5 mm and the diameter of the spherical steel fragments was 8 mm. The effects of layer thickness distribution and fibre density on the ballistic resistance were discussed. In addition, the ballistic resistance of composite target was compared with the same combination target without reinforced steel–fibres. The results show that the failure mode of steel front plate is shearing and plugging and that of aluminum rear plate is ductile prolonging deformation when the tied interface failed by tension (or shearing and plugging when the interface combination keep tied). Meanwhile, the steel–fibres failed by bending and tensile deformation. The V₅₀ value of target was maximum when the thickness ratio of steel front plate and aluminum rear plate was 3:1. The ballistic resistance of target with reinforced steel–fibres is generally better than that of the same thickness target without reinforced steel–fibres and the ballistic resistance decreased with the decrease of the fibre density.     

Analysis of morphology and microstructure of B4C/2024Al composites after 7.62 mm ballistic impact

The effects of ballistic impact on morphology and microstructure of B₄C/2024Al composites were studied. B₄C/2024Al composites with 55% volume fraction of B₄C particles were prepared by pressure infiltration method, and the experimental test of ballistic performance of composites was carried out by 7.62 mm armor piercing projectiles. The obvious upsetting of bullet and furrows on bullet tip are generated after bullet impact. Moreover, bared B₄C particle distributes uniformly on the bullet surface, indicating that the composites target plays roles of passivation and abrasion on bullet. The protection coefficient of B₄C/2024Al composites shows trends of falling, then an upward trend, at last keeping constant as the increasing thicknesses of targets, and could reach up to 2.8. For the composites target with semi-infinite thickness, three kinds of failure morphology are presented at the bullet crater: caving, erosion and melted areas, spreading successively as the increasing depth, which indicates that the interaction between bullets and targets is different at different stage of bullet penetration. Interestingly, the interface bonding of composites keeps well after bullet impact; moreover, no interface de-bonding was observed. High density of dislocation is generated in Al matrix around the interfaces, meanwhile, dislocations and micro-cracks were found in some B₄C particles.     

Fatigue strength and fracture mechanism of steel modified by super-rapid induction heating and quenching

Four kinds of surface hardened-specimens (ordinary structural steel with carbon content of 0.45% C) having hardened thicknesses of 0.7–1.8 mm were prepared using a ‘super-rapid induction heating (SRIH) system’. Rotation bending fatigue tests were performed with special focus on the effect of a hardened thickness on fatigue properties. Measurement of residual stress and observation of the fracture surface were also carried out to investigate the fracture mechanism of the specimen with a shallow hardened layer. It was found that there is not much improvement of fatigue strength at 10⁷ cycles for specimens with shallow hardened layers in spite of having a high compressive residual stress of about 1000 MPa. This is because the fatigue crack originating from inside the hardened layer leads to the final fracture of the specimen (internal fracture mode). Improvement of fatigue strength has been achieved on the specimen with thick hardened layers, such as those about 1.8 mm thick. In this case, fatigue cracks originate from inclusions located in hardened layers, which leads to final fracture (hardened-layer fracture mode).     

Modeling of the ballistic behavior of gradient design composite armors

The application of gradient design concept in armors offers possibilities in the reduction of weight and cost without significant reduction of ballistic resistance. Experimental results of composite backed plates consisting of layers of ceramic spheres embedded in epoxy showed that a ballistic limit of 3000 ft/s (1000 m/s) can be achieved, as shown in Fig. 1, without weight penalty compared to solid ceramic tiles. The ceramic sphere facing also provides the feasibility for flexible armor manufacturing. The design of such materials includes a plethora of parameters. In order to develop a precise methodology for the optimization of gradient design composite armors, an improved understanding of the relative significance of the design parameters must be developed. One way to study the relative significance of these parameters is through computational modeling. Computational limitations impose compromises in the modeling of both geometry and material behavior. Two types of models are discussed: (a) an approximate fiber/epoxy two-phase model for the backing; and (b) a damage-based, rate-dependent model for the ceramic spheres embedded in the epoxy. The development of a library of fiber architectures based on the unit cell has been initiated, which will open the possibility of the structural optimization along with simulation of the high velocity impact phenomena of advanced composites.     

Effects of heat treatment on the ballistic impact properties of Inconel 718 for jet engine fan containment applications

The effects of heat treating Inconel 718 on the ballistic impact response and failure mechanisms were studied. Two different annealing conditions and an aged condition were considered. Large differences in the static properties were found between the annealed and the aged material, with the annealed condition having lower strength and hardness and greater elongation than the aged. High strain rate tests show similar results. Correspondingly large differences were found in the velocity required to penetrate material in the two conditions in impact tests involving 12.5 mm diameter, 25.4 mm long cylindrical Ti-6-4 projectiles impacting flat plates at velocities in the range of 150–300 m/s. The annealed material was able to absorb over 25 percent more energy than the aged. This is contrary to results observed for ballistic impact response for higher velocity impacts typically encountered in military applications where it has been shown that there exists a correlation between target hardness and ballistic impact strength. Metallographic examination of impacted plates showed strong indication of failure due to adiabatic shear. In both materials localized bands of large shear deformation were apparent, and microhardness measurements indicated an increase in hardness in these bands compared to the surrounding material. These bands were more localized in the aged material than in the annealed material. In addition, the annealed material underwent significantly greater overall deformation before failure. The results indicate that lower elongation and reduced strain hardening behavior lead to a transition from shear to adiabatic shear failure, while high elongation and better strain hardening capabilities reduce the tendency for shear to localize and result in an unstable adiabatic shear failure. This supports empirical containment design methods that relate containment thickness to the static toughness.     

Tribological characteristics of innovative Al6061–carbon fiber rod metal matrix composites

Rods made of continuous carbon fibers are being extensively used as structural materials in light weight micro-air vehicles owing to their excellent specific modulus and strength. Further, they possess excellent tribological characteristics – low friction and wear coupled with high conductivity making them an ideal reinforcement in developing light weight, high strength aluminum based metal matrix composites. In the last three decades, researchers have focused mainly on the study of mechanical and tribological behavior of discontinuous carbon fiber reinforced metal matrix composites. However, no information is available regarding the tribological behavior of carbon fibers rod reinforced metal matrix composites, although it is interesting and will result in expanding the applications of metal matrix composites (MMC) where tribological failures are expected.In the light of the above, the present work focuses on development of innovative Al6061–carbon fiber rods composites by casting route and assessing their tribological characteristics. Carbon fiber rods of 4 mm and 6 mm diameters were surface sensitized to achieve electro less nickel coating. Copper plating on the electro less nickel coated carbon fiber rods were carried out. The copper plated carbon fiber rods were arranged in cylindrical array in the metallic mold to which molten Al6061 alloy after degassing was poured at a temperature of 700 °C. The developed innovative composites were subjected to density tests, microstructure studies, hardness, friction and wear tests. A pin on disk configuration was used with hardened steel as the counter face. Load was varied from 20 N to 60 N while the sliding velocity was varied between 0.12 m/s and 0.62 m/s. Scanning electron microscopy (SEM) studies on worn surfaces and wear debris have been carried out to validate the wear mechanism. The developed innovative composites (11 Vol.% & 25 Vol.%) have exhibited lower coefficient of friction and wear rates when compared with matrix alloy.