Composite Armor Research Articles

Analysis and investigation of ballistic impact on ceramic/metal composite armour

The subject of this paper is to analyze the impact of projectiles against ceramic/metal armour using a simple one-dimensional mode. The model allows the calculation of the loss of projectile mass and its velocity, and gives the deflection of the backup material. This work also investigates the influence of grain size of the ceramic material on ballistic performance, which is very useful during selection of the best material for each application. Therefore, two formulations of the same ceramic material were produced. They had the same chemical composition, the same mechanical properties, but different grain size. The ballistic performances were compared measuring the maximum velocity each formulation was able to support, without perforation.

A one-dimensional stress wave analysis of a lightweight composite armour

Existing work in the literature has addressed the synthesis and analysis of lightweight composite armour, consisting of ceramic, polymer composite and metal foam layers. The aim of this paper is to apply classical one-dimensional stress wave theory to the analysis of the behaviour of the armour, due to an impact from a fragment simulating projectile. Good agreement between the results from the literature and the stress wave model, discussed here, is achieved, and the developed model is then used to gain insight into the effect of the variation of various parameters, e.g. layer material, layer thickness and impact velocity.

Wave propagation in lightweight composite armor

Wave propagation in lightweight composite armor

Wave propagation in lightweight composite armor

Lightweight structural armor designs consist of multiple layers of ceramic, composite materials, metallic foams and other materials. Under ballistic impacts, the propagation of stress waves through the thickness is of interest to designers. It is recognized that events occurring during the early stages of the impact determine how well the armor will resist it. Extensive finite element analyses have been performed and a few publications have shown that capering the essential features of this problem numerically can be difficult. In this article, an exact solution is presented for analyzing the one-dimensional impact of a foreign object against a multi-layered structure. The approach is simple, it leads to a better understanding of the physics of the problem, and provides results that are difficult to duplicate numerically.

Numerical simulation of normal and oblique ballistic impact on ceramic composite armours

This paper presents three-dimensional finite element models that investigate the performance of ceramic–composite armours when subjected to normal and oblique impacts by 7.62 AP rounds. The finite element results are compared with experimental data from different sources both for normal and oblique impact, respectively. Simulation of the penetration processes as well as the evaluation of energy and stresses distributions within the impact zones highlight the difference between normal and oblique ballistic impact phenomena. The findings show that the distributions of global kinetic, internal and total energy versus time are similar for normal and oblique impact. However, the interlaminar stresses at the ceramic–composite interface and the forces at the projectile–ceramic interface for oblique impact are found to be smaller than those for normal impact. Finally, it is observed that the projectile erosion in oblique impact is slightly greater than that in normal impact.

Effect of the manufacturing process on the interfacial properties and structural performance of multi-functional composite structures

A composite integral armor (CIA) structure consists of various layers such as ceramics, rubber and polymer composites assembled in a precise sequence to provide superior ballistic and structural performance at low areal density. CIA structures were originally manufactured in a labor-intensive multi-step process. In recent years, vacuum-assisted resin transfer molding (VARTM) has emerged as an affordable manufacturing method for CIA structures. In this paper, the relationship between the manufacturing processes (i.e. VARTM and multi-step) and the mechanical performance of CIA beams is investigated by four-point bend tests. The behavior of the CIA is found to be highly dependent on the mechanism of stress transfer between the layers and the structures are found to fail progressively and provide significant ductility and capacity. The VARTM process is found to produce structures with superior mechanical performance. Moreover, the level of interface adhesion achieved during processing is shown to control the structural behavior of the CIA. Consequently, the Mode I fracture testing of VARTM and multi-step manufactured double-cantilever beams, representative of one interface of the CIA, is characterized. The resistance to crack growth of the specimens is also related to the manufacturing process, with the VARTM specimens achieving the highest fracture toughness.

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.

Comparative analysis of oblique impact on ceramic composite systems

An experimental programme is presented which investigated the performance of oblique, ceramic/metal, bilayer composite armours. The ceramics, alumina and silicon carbide, were backed by either Rolled Homogeneous Armour steel (RHA) or 7000 series aluminium. Using a model scale tungsten penetrator at two velocities (representing current and future ordnance threats) the effect of configuration on ballistic limit or depth of penetration (DOP) areal densities was determined. Areal densities of the DOP targets decreased with increasing ceramic thickness, achieving a minimum at zero residual penetration in the backing. The bilayer targets, loaded at the ballistic limit needed a larger areal density to defeat the penetrator. This areal density also decreased with ceramic thickness but showed a minimum with respect to ceramic thickness, as a result of reduced support by the thinner metallic backing. At 1450ms −1 the most efficient system was found to be a SiC/Al, which demonstrated a 25% weight saving over the monolithic aluminium reference target. The Al-alloy backing performs better than RHA, and SiC better than Al 2O 3.

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.

Affordable processing of thick section and integral multi-functional composites

Abstract The use of multi-functional integral armor is of current interest in armored vehicles and military carriers. In the present study, thick-section laminated composites and multi-layered integrated composites have been processed/manufactured with the aim of providing multi-functionality including easy reparability, quick deployment, enhanced ballistic damage and fire protection, as well as lightweight advantages. The design of an integral armor utilizes a combination of thick-section structural composite, ceramic tiles, resilient rubber, fire retardant laminate liner and a composite durability cover. Processing techniques such as automated fiber placement and/or autoclave molding are traditionally used to process dissimilar multi-layered structure, but prove to be expensive. This work focuses on emerging cost-effective liquid molding processes such as vacuum assisted resin transfer/infusion molding (VARTM) for the production of thick-section and integral armor parts (up to 50 mm thick). While thick-section composites have applications in a variety of structures including armored vehicles, marine bodies, civil infrastructure, etc. in the present work they refer to the structural laminate within the integral armor. The processing steps of thick-section composite panels and integral armor have been presented. The integrity of the interfaces has been evaluated through scanning electron microscopy (SEM). Representative results on static and dynamic response (high strain rate, HSR and ballistic impact) of the VARTM processed thick-section composite panels are presented. Wherever applicable, comparisons are made to conventional closed-mold resin transfer molding (CMRTM). Process sensing by way of flow and cure monitoring of the resin in the fiber perform has been conducted using embedded direct current (DC)-based sensors in the thick-section preform and integral armor interfaces. The feasibility of cost-effective VARTM for producing thick-section composites and integral armor has been demonstrated.

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.

The effects of glass-fiber sizings on the strength and energy absorption of the fiber/matrix interphase under high loading rates

The interphases of various sized E-glass-fiber/epoxy-amine systems were tested at displacement rates in the range 230–2450 μm/s by a new experimental technique (dynamic micro-debonding technique). By this method, the rate-dependent interphase properties, apparent shear strength and absorbed energies due to debonding and frictional sliding, were quantified. The systems include unsized, epoxy-amine compatible, and epoxy-amine incompatible glass fibers. The high displacement rates that induce high-strain-rate interphase loading were obtained by using the rapid expansion capability of piezoelectric actuators (PZT). The results of dynamic micro-debonding experiments showed that the values of interphase strength and specific absorbed energies varied in a manner that is dependent on the sizing and exhibited significant sensitivity to loading rates. The unsized fibers exhibit greater frictional sliding energies that could provide better ballistic resistance, while the compatible sized fibers show higher strength values that improve the structural integrity of the polymeric composites. In addition, significantly higher amounts of energy are absorbed within the frictional sliding regime compared to debonding. By using the experimental data obtained, a case study was performed to reveal the importance of the interphase related micro damage modes on energy absorption (and therefore ballistic performance) of glass/epoxy composite armor.

Performance Metrics for Composite Integral Armor

Future combat systems necessarily focus on lightweight, highly mobile and transportable armored vehicles. Lightweight composite integral armor systems are being developed to meet these needs. The goal of this paper is to centrally document the myriad design requirements for composite integral armors that serve multifunctional roles including ballistic, structural, shock, electromagnetic, and fire protection. Structural and ballistic performance requirements as well as manufacturing and life-cycle performance issues of integral armor are presented. Specific areas addressed include high-strain-rate testing and modeling, ballistic testing and modeling, low-cycle fatigue, damage tolerance, repair, reduced-step processing, through-thickness reinforcement, energy dissipation and rate-dependent failure mechanisms, and non-linear mechanics.

Modeling of the ballistic behavior of gradient design composite armors

Abstract 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.

Ceramic/polymer Composite Armours

Ceramic/Polymer Composite Armours are increasingly used as a protective barrier against 7.62 and 12.7 mm AP projectiles in various civil and military applications. The experimental behaviour of these composite armours shows a clear improvement compared to monolithic steel or aluminium alloy protections. This paper illustrates the experimental results of the ceramic tiles and polymeric composites under ballistic test. The observation of the materials before projectile interaction and the ceramic rubble after the experiments was a valuable application of the ESEM. The Environmental Scanning Electron Microscope allows the examinations of almost any kind of nonconductive sample without special preparation. The experimental results and analyses performed allow us to select the best way to increase the laboratory capacity for design and test of composite ceramic/polymeric composite protective structures under shock and impact.

核融合炉ダイバータターゲットプレート接合部の機械的特性に与える照射効果

In order to evaluate neutron irradiation effect on divertor target plate component, brazed specimens of C/C composite armor tiie on alumina dispersed copper and HIPed specimen of beryllium on alumina dispersed copper were irradiated up to a fluence of 2.8×1023n/m2 (>0.18MeV) at 746-788K, and their strength tests were performed. From these tests, the following results were obtained. (1) MFC-1/alumina dispersed copper brazed-specimen Tensile and 4 point bending strength of irradiated brazed-specimen was 30-55% of that of unirradiated one. Tensile and 4point bending strength of unirradiated and irradiated brazed-specimen increased as the test temperature was increased, however these strength decreased above 600K. Remarkable degradation of tensile strength was observed for the irradiated brazed-specimen above 600K. Fracture position of irradiated specimen shifts from MFC-1 side brazed zone to alumina dispersed copper as the testing temperature increases. (2) Beryllium/alumina dispersed copper HIPed specimen Under tensile and bending loading, irradiated HIPed-specimen exhibits similar deformation behavior as copper alloy, but fracture strength of the specimen was dominated by fracture strain limitation of beryllium material. Tensile and 4 point bending strength of irradiated HIPed-specimen showed 10-20% lower values than that of unirradiated one. The room-temperature strength of irradiated joint was about 3 times higher than that of the irradiated MFC-1/alumina dispersed copper brazed-specimen. Tensile and 4 point bending fracture strains of irradiated joint showed 0-30% lower values than that of unirradiated one. Fracture of irradiated HIPed-specimens was observed at joined area.

Structural ballistic armour for transport aircraft

This paper describes the structural response of a current ceramic-faced composite armour system and a proposed structural armour system for aircraft use. The proposed structural ballistic armour system is shown to be capable of providing significant structural integrity even after ballistic impact whilst providing ballistic protection equivalent to an existing appliqué system. The addition of a carbon fibre reinforced plastic front panel to the existing ceramic faced composite armour system improves the bend strength by a factor of 3 and improves the energy to break by almost an order of magnitude.

A new approach for improving ballistic performance of composite armor

An experimental investigation of the ballistic performance of composite armor with geometric modifications was carried out. The armor was simulated using polymeric materials. Four different geometric modifications were incorporated into the front plate of the armor, and two different adhesives were considered in this study. High-speed photography was employed to observe the real-time evolution of impact damage and to obtain the projectile penetration history. The nature and extent of damage for each modification and adhesive was estimated by postmortem inspection of the impacted armor and was compared to that obtained in unmodified armor of equal weight. The results of the study indicate that the geometric modifications after the nature and extent of damage significantly compared to conventional composite armor. The strong adhesive causes tearing of the back plate, whereas the compliant adhesive results in extensive delamination without any back plate damage. The modifications assist in spreading the damage laterally away from the impact site, thus distributing the load onto a larger area of the back plate. Calculations using a one-dimensional theoretical model also conclude that geometrical modifications improve the ballistic performance of the armor.

Confined compression of elastic adhesives at high rates of strain

Elastic adhesives are used in composite armours to bond the ceramic front face and the metallic backing plate. The mechanical behaviour of different elastic adhesives under impact loads have been studied by means of dynamic compression tests performed in a split Hopkinson pressure bar. In this experiments, the stress–strain curve of confined materials at high strain rates and the capability of transmitting and reflecting the impact energy have been determined. The influence of thickness and ageing on the response of the adhesive layer have been also considered.