Lightweight Armor Research Articles

Lightweight ceramic composite armour system

The development of lightweight armour systems for ballistic protection is under continuing attention of the manufacturers and users. A new design of the composite armour systems has been developed and ballistically tested. A new armour system consists of a ceramic plate, an intermediate ceramic–polymer layer and a polymer fibre lining as a backing material. The proposed composite armour systems prepared with a use of specially selected compositions of the intermediate layer promoting the absorption of the kinetic energy of projectiles provide adequate ballistic protection to National Institute of Justice (NIJ) level III and level IV, and they successfully withstand multiple hits.

On the comparison of the ballistic performance of steel and laminated composite armors

Steels have been widely used as armor materials in defense applications, but they have the disadvantage of a relatively high density. Hence, they are not suitable for lightweight armor production. On the other hand, laminated composites have important potential on the reducing armor weight compared to steels for the same ballistic protection. This study presents the ballistic performance of steel against 7.62 mm armor piercing projectiles. High strength low alloy steel (50CrV4) was chosen as steel armor for ballistic testing. Three areal density values were kept constant to compare ballistic performance of steel armor specimens with alumina/aluminum laminated composite specimens. In addition, in steel samples, the effect of hardness on the ballistic performance was examined. Furthermore, failure mechanisms were investigated after ballistic testing. According to the experimental results, laminated composites maintained 26% weight saving compared to steel.

A computational analysis of the ballistic performance of light-weight hybrid composite armors

The ability of hybrid light-weight fiber-reinforced polymer–matrix composite laminate armor to withstand the impact of a fragment simulating projectile (FSP) is investigated using a non-linear dynamics transient computational analysis. The hybrid armor is constructed using various combinations and stacking sequences of a high-strength/high-stiffness carbon fiber-reinforced epoxy (CFRE) and a high-ductility/high-toughness Kevlar fiber-reinforced epoxy (KFRE) composite laminates of different thicknesses. The results obtained indicate that at a fixed thickness of the armor both the stacking sequence and the number of CFRE/KFRE laminates substantially affect the ballistic performance of the armor. Specifically, it is found that the armor consisting of one layer of KFRE and one layer of CFRE, with KFRE laminate constituting the outer surface of the armor, possesses the maximum resistance towards the projectile-induced damage and failure. The results obtained are rationalized using an analysis of the elastic wave reflection and transmission behavior at the inter-laminate and laminate/air interfaces.

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.

Titanium–titanium diboride composites as part of a gradient armour material

In the world today there is an increasing use of small-calibre armour piercing projectiles and these constitute a growing threat. This threat is most eminent for wearers of body armour and to lightly armoured combat vehicles. As part of the solution to this problem, new generations of lightweight armour designs are under development. One promising possibility has been found to be the use of functionally gradient materials as armour materials. In such materials, the high hardness of ceramics is combined with the ductility of metals; in our study the system of Ti–TiB 2 was used. As compaction and consolidation process the spark plasma sintering process was used. Though similar to conventional hot pressing, no external heat source is needed; instead a pulsed direct current is passed through the electrically conducting pressure die and through the sample. At low sintering temperatures with short holding times (minutes), fully dense materials can be obtained, benefiting in little grain growth. Mechanical and impact experiments of single ceramic metallic composites layers have been carried out. The ballistic tests were done on discs glued to steel backings, and tungsten core projectiles, calibre 7.62 mm, were used. The ballistic results indicate a suitable composition, which does not have to be a pure ceramic, for the outer high hardness armour layer. To verify the suitability of the spark plasma sintered material, a comparison was made on the mechanical and ballistic properties between SPS-(Ti) 0.05(TiB 2) 0.95 and HIP-TiB 2, and it was found that the SPS-material was the overall better protective material.

Histology of ankylosaur osteoderms: implications for systematics and function

ABSTRACT Here, we provide a comparative survey of the histology of postcranial dermal-armor osteoderms of ankylosaurs, including material of polacanthids (Polacanthus foxii, Gastonia sp.), ankylosaurids (e.g., Saichania chulsanensis, Pinacosaurus grangeri, Ankylosauridae indet.), and nodosaurids (e.g., Struthiosaurus austriacus, Nodosauridae indet.). Samples of osteoderm-bearing outgroups (Scelidosaurus harrisonii, phytosaurs, and crocodiles) as well as literature data on Stegosaurus stenops plates and spikes helped to elucidate histological evolution and character polarity. The complex histology of ankylosaur osteoderms seems to be of systematic value, as the sectioned osteoderms can be classified into three distinctive groups. All polacanthid osteoderms share a relatively generalized histology with a thickened, uniform cortex completely surrounding trabecular bone. Nodosaurid osteoderms only have an external cortex with the underlying internal spongiosa being much thicker and forming a rather flat base. Ankylosaurids have very thin osteoderms that were greatly strengthened by the incorporation of structural collagen fiber bundles, similar but not identical to Sharpey's fibers, into the thin primary cortex and, uniquely, the secondary bone tissue. Structural fibers are also abundant in nodosaurids but there are significant differences in arrangement and occurrence, being random in ankylosaurids but highly ordered in nodosaurids. In their cortex, the latter have two sets of 3D-orthogonal fibers rotated at 45° to each other. The combination of the greatly strengthened external cortex covering a thick cushion of cancellous bone thus serves to resist local penetration. Ankylosaurid and nodosaurid osteoderms are thus highly optimized towards a resistant yet light-weight armor.

Fracture behaviour of mullite fibre reinforced–mullite matrix composites under quasi-static and ballistic impact loading

The fracture behaviour and damage development in mullite fibre reinforced–mullite matrix composites have been investigated using chevron notch technique and ballistic impact tests. Fracture toughness ( K Ic) values in the range of 1.8–3.3 MPa m 1/2 were determined using the chevron notched specimen technique. A large variability of K Ic data due to the complex (heterogeneous) composite microstructure was found. Extensive fibre pull-out occurred during failure, which was due to a favourable matrix/fibre interfacial bond given by NdPO 4 coating of the fibres. The materials response under ballistic impact loads was studied using a gas gun. The projectiles were glass balls of 10.15 mm in diameter and weighing 1.4 g. The projectile velocity was in the range 77.6–207.5 m/s. The remanent load carrying capability of composite samples after ballistic tests was measured to quantify ballistic impact induced microstructural damage. The composites retained some of their load bearing capacity even after penetration of the projectile, since structural damage caused by projectiles remained localised, preventing catastrophic failure. Penetration by the projectile occurred at impact energy of about 4 J for the conditions investigated. Understanding crack propagation and damage development under ballistic impact loads may open new opportunities for the use of these composites in lightweight armour applications.

Optimization of two-component composite armor against ballistic impact

Using Florence's model we determined an optimal design of a two-component ceramic-faced lightweight armor against normal ballistic impact. The solution is found in a closed form that allowed us to determine the thicknesses of the plates in the optimal armor as functions of the specified areal density of the armor, parameters determining the material properties of the armor's components and characteristics of the impactor.

Numerical modeling of the impact behavior of new particulate-loaded composite materials

Ballistic efficiency and cost are the main considerations in the design of lightweight armors. Metallic materials have the drawback of their high density. Mixed armors, of ceramic tiles backed by a metallic plate, are an efficient shield against low and medium caliber projectiles since they combine the light weight and high resistance of a ceramic with the ductility of a metal. The drawback is their high cost. The authors developed a new material composed of ceramic particles and a polymeric matrix. It fills the gap between metallic and ceramic materials and could be interesting for applications in which weight is not the primary concern and cost benefits are welcome. A model of the mechanical behavior of this composite is presented in this paper, implemented in a numerical code and validated by experimental results.

The adaptive and erosive numerical modelling of confined boron carbide subjected to large-scale dynamic loadings with element conversion to undeformable meshless particles

In recent years, developments in the field of lightweight armour have been of primary importance to the defence industry. This necessity has led to many organisations adopting composite armours comprising both traditional heavy armours and new lighter weight ceramic armours. The numerical modelling of metal based armour systems has been well documented over the years; and more recently advanced numerical methods have been utilised for the computational modelling of ceramic armour systems. It is the goal of this paper to demonstrate how a commercial finite and discrete element code, such as ELFEN, can be used in the further understanding of the response of combined ceramic/metal armour systems when subjected to large-scale dynamic loads through the combined techniques of adaptive remeshing, material erosion and particulate methods. It is well established that penetration processes can be modelled using standard material erosion techniques. However for many brittle materials, including ceramics, the material regions close to the impact interface undergo comminution, which can effectively be numerically modelled as a continuum that will typically exhibit flow like behaviour. Furthermore, use of the commonly employed erosive techniques allows unavoidable material relaxation through element removal leaving voids at the impact interface, which for ceramic type materials introduces an invalid increased rate of damage accrual and hence an incorrect material response. One of the primary objectives of this paper is to present a new computational method which automatically transforms deformed finite elements into undeformable meshless particles. In addition, to overcome severe element conditioning associated with large deformation problems; it will be shown that this technique can be successfully coupled with adaptive remeshing techniques, which are themselves coupled to standard material erosion processes. An example presenting the potential benefits of this form of domain update method, in contrast to the traditionally used material erosion techniques, will be demonstrated for the computational modelling of brittle materials used in multiple component armour systems, which are frequently encountered within today's defence industry.

The numerical modelling of ceramics subject to impact using adaptive discrete element techniques

In recent years, developments in the field of lightweight armour have been of primary importance to the defence industry. This necessity has led to many organisations adopting composite armours comprising both the traditional heavy armours and new lighter weight ceramic armours. The numerical modelling of metal based armour systems has been well documented over the years using purely continuum based methods; and also the modelling of brittle systems using discrete element methods, therefore it is the objective of this paper to demonstrate how a coupled finite and discrete element approach, can be used in the further understanding of the quantitative response of ceramic systems when subjected to dynamic loadings using a combination of adaptive continuum techniques and discrete element methods. For the class of problems encountered within the defence industry, numerical modelling has suffered from one principal weakness; for many applications the associated deformed finite element mesh can no longer provide an accurate description of the deformed material, whether this is due to large ductile deformation, or for the case of brittle materials, degradation into multiple bodies. Subsequently, two very different approaches have been developed to combat such deficiencies, namely the use of adaptive remeshing for the ductile type materials and a discrete fracture insertion scheme for the modelling of material degradation. Therefore, one of the primary objectives of this paper is to present examples demonstrating the potential benefits of explicitly coupling adaptive remeshing methods to the technique of discrete fracture insertion in order to provide an adaptive discontinuous solution strategy, which is computationally robust and efficient.

Carbon, polyethylene and PBO hybrid fibre composites for structural lightweight armour

Abstract The properties of hybrid composite materials (based on carbon and organic fibres) have been investigated, with a view to using these materials in polymer composites lightweight structural armour. Laminates were manufactured and their specific ballistic properties and specific compressive strength after impact were determined. The introduction of organic fibres in order to improve ballistic properties has been successful. The associated reduction of specific compressive strength can be more than compensated for by an increase of specific ballistic properties. To achieve this, fractions of each fibre type and their distribution must be optimised and matrices must be optimised to the function of the respective fibre.

Aluminum foam integral armor: a new dimension in armor design

Closed-cell aluminum foam offers a unique combination of properties such as low density, high stiffness, strength and energy absorption that can be tailored through design of the microstructure. During ballistic impact, the foam exhibits significant non-linear deformation and stress wave attenuation. Composite structural armor panels containing closed-cell aluminum foam are impacted with 20-mm fragment-simulating projectiles (FSP). One-dimensional plane strain finite element analysis (FEA) of stress wave propagation is performed to understand the dynamic response and deformation mechanisms. The FEA results correlate well with the experimental observation that aluminum foam can delay and attenuate stress waves. It is identified that the aluminum foam transmits an insignificant amount of stress pulse before complete densification. The ballistic performance of aluminum foam-based composite integral armor (CIA) is compared with the baseline integral armor of equivalent areal-density by impacting panels with 20-mm FSP. A comparative damage study reveals that the aluminum foam armor has finer ceramic fracture and less volumetric delamination of the composite backing plate as compared to the baseline. The aluminum foam armors also showed less dynamic deflection of the backing plate than the baseline. These attributes of the aluminum foam in integral armor system add a new dimension in the design of lightweight armor for the future armored vehicles.

Ballistic protection mechanisms in personal armour

High strength and high modulus fibres have revolutionised the design of lightweight armour, main fibre reinforced ballistic products are: ballistic helmets, vests, blankets and add-on car armour. Modelling of the ballistic properties of multi-layer fibre reinforced armour is still in the development stage, structural models that can be used to describe the penetration of such armour by deformable projectiles, and to design new armour, are not yet available. A simple model has been developed that can be used to calculated the performance of Dyneema armour against deformable bullets and FSPs. Most important in this model is that the number of input values is very small. For calculating the performance of Dyneema UD-based armour only two materials related parameters are required. Four projectile related parameters are needed. For non-deformable projectiles the number reduces to a single material related and two projectile related parameters.

GFRP materials under high-velocity impact loading

Depth of penetration experiments with long rods impacting GFRP blocks of different thicknesses with high velocities yield residual penetrations in a steel-backing which indicate the ballistic performance of the investigated target. The material-related ballistic protection performances of three composites are compared with those of ductile and brittle target materials. One of the major aims of this investigation is to separate the dependence of the material of a target layer on the protective power from the influence of its environment, e.g. confinement A formerly introduced ballistic material parameter, called ductile limit of the equivalence factor, sufficiently describes the protective power of brittle and ductile target materials. This approximation is successfully applied to GFRP's. It has been found that the ballistic resistance of a thick GFRP block grows with increasing penetration depth. The penetration behaviour of these composites differs completely from that of ductile or brittle materials and thus makes GFRP materials interesting for light-weight armour applications. Additionally a material-related explanation for the growing ballistic resistance is given.

Optimization of Light Weight Armor Using Experimental Data

It is shown how the experimental data on ballistic limit velocity (BLV) of two-component ceramic target may be directly used for the analysis and optimization of the armor. The suggested approach is applied for two sets of data available in the literature.

10.2172/1116744

INL researchers have proposed prototypes for future lightweight armor systems that reside in a technology gap between explosive reactive armor and passive armor. The targets were designed to react under impact and throw a steel front plate into the path of the projectile, forcing the projectile to engage more of the front plate during its penetration process. These prototypes are intended to exhibit the enhanced efficiency of explosive reactive armor without the collateral damage often associated with explosive reactive armor. One of the prototype systems, Semi Energetic Reactive Armor (SERA), functions similarly to explosive reactive armor, but features a reactive material that reacts much slower than explosive reactive armor. Two different SERA test groups were built and featuring different ratios of aluminum Teflon(copyright) powders pressed into 0.5 in. thick energetic tiles and sandwiched between 0.25 in. thick RHA plates. The other prototype system, Non Energetic Reactive Armor (NERA), utilizes the strain energy in compressed rubber to launch a front flyer plate into the path of an incoming projectile. It is comprised of a 1 in. thick rubber layer sandwiched between two 0.25 in. thick RHA plates with bolt holes around the perimeter. Bolts are inserted through the entire target and tightened to compress the rubber sheet to significant strain levels (approximately 40%). A fourth group of targets was tested as a control group. It featured a 0.5 in. thick rubber sheet sandwiched between two 0.25 in. thick RHA plates, similar to the NERA test articles, but the rubber is uncompressed. The four test groups (uncompressed rubber, compressed rubber, 70/30 Al/PTFE, 50/50 Al/PTFE) were each fabricated with three identical test articles in each group. All twelve targets were subjected to ballistic testing at the National Security Test Range on July 17, 2013. They were tested with 0.5 in. diameter steel rods shot at a consistent velocity at each target. In order to characterize the energetic materials, break wires were embedded in the targets and burn velocities were measured. The residual mass method was used to compare the target performance of each group and final performance data is presented below.

MODELING PENETRATION OF CERAMIC/METAL LIGHTWEIGHT —1 ARMOURS BY SMALL AND MEDIUM CALIBER PROJECTILES

In this paper, an analytical model is developed to describe the penetration of ceramic/metal lightweight armours by small and medium caliber-projectiles, 4 respectively. Both the projectile and back plate materials are assumed to behave as rigid-perfectly plastic with respect t9, .their nominal stress-engineering strain relationships. Two modes are associated with the back plate and the projectile, respectively, during the penetration 'Ptocess; these are erosion and rigid The model identifies three main phases for the penetration of a lightweight armour; these are: (i) ceramic fragmentation, (ii) penetration of fragmented ceramic and (iii) penetration of back plate. Phase (i) consists mainly of one stage, whereas the other two, i.e. phase (ii) and phase (iii), consist mainly of different penetration stages, respectively. The current penetration stage is ascertained according to the relative velocities between the projectile mass and the mass of remaining ceramic and/or the mass of the back plate ahead of projectile. The main equations representing each penetration stage are derived based on momentum conservation principle. The present model is capable of predicting the time-histories of the velocities of the moving masses and the projectile penetration depth through ceramic/metal lightweight armour as well as post-perforation results. Matching predicted results of the present model with the experimental and numerical results of other investigators serves to determine the flow stress of the ceramic material globally. The present results are concerned with design optimization of ceramic/metal lightweight armours capable of defeating small and medium caliber projectiles. The influence of ceramic thickness and strength as well as back plate thickness and strength on the ballistic limit of the armours considered is presented and discussed. Moreover, the effect of ceramic thickness on projectile remaining mass and residual velocity are discussed.

A numerical investigation of penetration in multilayered material/structure systems

The response of multilayered ceramic/steel targets to high velocity impact and penetration has been investigated through finite element simulations. A multiple-plane microcracking model has been used to describe the inelastic constitutive behavior of ceramics in the presence of damage. The model has been integrated into the finite element code EPIC95, which possesses contact and erosion capabilities particularly suitable for ballistic simulations. The integrated code has been used to analyze the depth of penetration (DOP) and interface defeat (ID) ceramic target configurations. Parametric analyses have been carried out to establish the effect of ceramic materials, target configuration design for ceramic confinement, diameter/length ( d/L) ratio of the penetrator, material erosion threshold levels and the use of a shock attenuator on the response of multilayered targets subjected to high velocity impact. The response characteristics are established in terms of the parameters which can be measured experimentally. The analyses show that the integrated code is able to predict the response of ceramic targets in confirmation with experimental findings reported in the literature. The penetration process is found to be less dependent on the ceramic materials as usually assumed by most investigators. By contrast, the penetration process is highly dependent on the multilayered configuration and the target structural design (geometry, and boundary conditions). From a simulation standpoint, it has been found that the erosion parameter plays an important role in predicting the deformation history and interaction of the penetrator with the target. These findings show that meaningful lightweight armor design can only be accomplished through a combined experimental/numerical study in which relevant ballistic materials and structures are simultaneously investigated.

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.