Advanced Materials for Defense

In the context of the EU raw materials strategy, this work identifies the raw and processed materials important to the European defence industry. 47 processed materials, including different alloys, composites and compounds were identified as highly important for the manufacturing of defence applications systems. A further assessment based on the composition of these 47 high-performance processed materials indicates that 39 raw materials are necessary for their production. Out of these 39 raw materials, 20 are currently critical for the EU economy and have associated potential supply risk.

In recent years several approaches to the optical monitoring of Molecularly Imprinted Polymers (MIPs) via optical fibers have been developed with very promising developments in the field of sensing. In this paper, we report about sensing platforms based on MIPs combined with Plastic Optical Fiber (POF) which appear to be useful for security and defense. In particular, two optical chemical sensor configurations for 2,4,6-trinitrotoluene (TNT) detection in water are reported. These sensor configurations are based on the same Molecularly Imprinted Polymer receptor, but the first one is combined with a Surface Plasmon Resonance (SPR) platform and the second one with a Localized Surface Plasmon Resonance (LSPR) platform, both realized exploiting D-shaped Plastic Optical Fibers (POFs).

A simple and effective approach using infrared (IR) irradiation and diazonium chemistry has been applied to decorate multi-wall carbon nanotubes (MWCNTs) with lanthanum hydroxide nanoparticles (LaH NPs). The decoration process comprised four steps: purification, functionalization, impregnation and calcination. The resulting materials were characterized with XPS, TEM, PXRD, EDX and Raman spectroscopy. Sodium hydroxide treatment led to the purification of MWCNTs (p-MWCNTs). Functionalizing purified MWCNTs with in situ generated tricarboxylic aryl diazonium salts (p-MWCNTs-D3) followed by impregnation using IR irradiation was the key step in efficiently impregnating p-MWCNTs-D3 with lanthanum nitrate (p-MWCNTs-D3/LaN). Calcination of p-MWCNTs-D3/LaN at 500 °C under argon atmosphere resulted in homogeneously distributed LaH NPs on MWCNTs (p-MWCNTs/LaH) in the size range of 1.5–6.0 nm, with a Gaussian mean diameter of 3.0 nm. LaH nanoparticles were found to be amorphous. This method is applicable to large-scale production, which opens interesting outlooks for nanotechnology applications such as energy storage material and sensor for detection of chemical warfare agents in the defense sector.

This research considers a possibility of improving the impact and ballistic resistance of composite materials based on aramid fabric impregnated with poly (vinyl butyral), PVB, with the application of multi-layer inorganic nanotubes of tungsten disulfide (INT-WS₂) as the reinforcement. Multi-layered nano-structures of tungsten disulfide are known by their excellent mechanical resistance, especially shock absorbing properties, which promote their use as a reinforcement in composite materials. INT-WS₂ used in this research were observed using scanning electron microscope and the obtained images were analyzed in program Image Pro Plus. Before the application in the composite they were ultrasonically deagglomerated. Ballistic composites were prepared impregnating the aramid fabric with system PVB/INT-WS₂ and by pressing defined number of layers under high pressure and defined temperature. Charpy impact test, ballistic shooting with two different ammunition calibers and stab resistance test with controlled knife penetration were performed on prepared composite samples, and resulted in significant improvements for samples with nano-reinforcement regarding the absorbed energy of impact, toughness and the ballistic resistance.

Body armour systems need to be improved for defeating new threats of asymmetric warfare and terrorism. Nowadays, new technologies like graphene-based nanocomposites constitute one of the most active research fields in high performance materials, due to the fact that this nanomaterial improves the properties of diverse polymers in a notable way. However, in the field of the application of these nanocomposites to improve the dynamic strength against supersonic impacts, experimental data are practically non-existent. Looking for improvements in this field, our research group has fabricated, following a similar procedure to that described in one of our previous patents, several laminated plates of graphene-based nanocomposites, composed of a polyester resin matrix doped with pristine few-layer graphene (FLG) and reinforced with a fibreglass woven fabric (FGRP), using doping percentages ranging between 0.25 and 1% in weight. The ballistic limit (V\( _{0}\)) of such plates against 7.62\(\,\times \,\)51 mm NATO FMJ ammunition, fired with an Accuracy International AW sniper rifle, has been investigated in accordance with the NATO STANAG 2920 standard. The tensile mechanical properties (tensile strength and Young’s modulus) and impact properties (Charpy impact strength) of the laminates were also characterised in accordance with UNE-EN ISO 527-4 and UNE-EN ISO 179-1 standards, respectively. The V\( _{0}\) increases with the increment of the graphene doping percentage, reaching a maximum value of 266.4 m s\(^{-1} \) at 1% w/w, which means an improvement of a 72.2% with regard to the undoped FRGP laminate. The graphene doped samples also showed better tensile and impact properties. These results support the viability of the development of new graphene-based nanocomposites with improved mechanical and ballistic protection properties for security and defence applications.

This work shows the need to create a new light energy-intensive armored material to protect against bullets and fragments of modern ammunition. Comparative characteristics of modern ceramics, which are used for ballistic protection of people and equipment, are given. The ballistic stability (the limit of the rear strength) of composites based on boron carbide B₄C, Al₂O₃ corundum and developed high-strength glass ceramics based on lithium disilicate Li₂Si₂O₅ (armored glass) was compared. Ballistic tests confirmed the possibility of using armored glass in protective structures with a surface density of 35–38 kg/m² in the 5-th class of the RF standard P 50744-95/2014 and the 3rd class of the US NIJ standard. One of the options for reducing the surface density and the cost of composite armor when using high-strength glass ceramics (armored glass) is shown.

Ultra-high-performance fibre-reinforced concrete (UHPFRC) was subjected to projectile impact using in-service bullets. UHPFRC is an advanced cementitious composite with enhanced mechanical properties where high tensile strength and ductility benefit mainly from the disperse fibre reinforcement. Steel micro-fibres used in this study were straight and smooth with a tensile strength of 2800 MPa. The fibre content in the UHPFRC was set as the main test variable in the framework of this study. It was found that an increase in the fibre volume fraction resulted in an increase in both the tensile strength and the energy dissipation capacity. Cylinder compressive strength of the UHPFRC was determined to be 150 MPa. The UHPFRC slabs used as targets against full metal jacket soft lead core (FMJ-SLC) and full metal jacket mild steel core (FMJ-MSC) projectiles were 50 mm and 45 mm thin, respectively. Both projectiles were fired from the semi-automatic rifle. The weight of the projectiles was 8.04 g and muzzle velocity was determined to be 710 m/s. Damage parameters such as depth of penetration, crater diameter, residual velocity, residual penetration potential and debris fragment loss were determined. Based on the experimental observations it was found that the optimal fibre content in the UHPFRC mixture with respect to damage parameters induced by the high-speed projectile impact is about 2% by volume.

This manuscript presents the findings of an experimental study aiming to develop an Ultra High Performance Fibre Reinforced Concrete (UHPFRC) best suitable for impact loading. The mechanical properties of this material and the failure mechanisms under impact loading were investigated. The UHPFRC developed in this research program is a cement–based material with increased percentage of microsilica and a combination of two types of steel fibres: 6 mm long with 0.16 mm diameter and 13 mm long with 0.16 mm diameter. It includes local calcarenite sand with grains 125–500 μm in size. Four composition mixtures were produced, three UHPFRC and one Ultra High Performance Concrete (UHPC), without steel fibres. The influence of the amount and type of steel fibres was examined. Slabs with dimensions: 200 × 200 mm and thickness of 15, 30, 50 and 70 mm were produced and were subjected to projectile impact (real shotgun used). The penetration depth and material volume loss were measured.

The modeling based design and optimization has been widely used in many engineering fields to avoid the high cost of extensive experiments. A reduced-order model, which mainly considers the critical degrees of freedom in the design, is even more efficient and effective in significantly saving computational efforts without losing the design accuracy and optimization reliability. The information generated from the reduced-order model in the early design stages then will be a useful guideline for further comprehensive analysis in a full-order model. A new reduced-order modeling method has been developed for evaluating the dynamic performance of a lightweight multilayer armor plate subjected to blast and impact loadings. Based on the reduced-order model, a fast optimization framework is introduced in this paper and utilized as a computational efficient tool for rapidly identifying the optimal design from a large number of candidate configurations. A simplified human model seated on the multilayer plate and its lumbar injury criteria is employed as a target screening metric. Four design cases with a combination of steel, SiC, Al-Alloy, Ti-Alloy, and copper are analyzed, compared, and validated by a commercial finite element analysis package. A good design balance between structural weight reduction and protection capacity enhancement has been achieved by using this optimization framework.

Nowadays, one of the risks related to the use of lightweight body armour systems is the risk on injury caused by a non-perforating impact. The dynamic deflection of the inner surface of the body armour can be sufficient to cause serious or even lethal injuries even if there is no full perforation of the body armour. The work presented here describes a methodology for an armour representative of an advanced ballistic helmet design and the human head. Using different experimental measurement methods, the traditional witness backing material method and more advanced methods using anthropomorphic test devices (ATD), reliable finite element models are created for the composite (poly-aramid and poly-ethylene) helmet shell. This is followed by numerical simulations where the interaction between the different armour solutions and the human body are studied in detail. Lastly, the results are linked to real-life injuries using the Abbreviated Injury Scale (AIS).

Composite high-pressure vessels have been used in many engineering fields. Contrary to the civil sector, where the quantity of impact incidents is relatively low, in the military the application of composite cylinders under circumstances that lead to mechanical impacts occurs far more frequently. Since the standard tests are time and cost consuming, other methods to monitor the operational status of COPV have been searched for. One of them could be the vibration-based method. In this work, three groups of composite overwrapped pressure vessels were examined. In the first group they were non-impacted, while in the second and third ones they were subjected to two different load levels. The modal test and FEM simulations were performed to investigate possibility of damage detection based on the vibration analysis. It was proved that damage induced by the impact load has a noticeable influence on natural frequencies, and thus the modal analysis seems a useful tool for the impact detection in carbon epoxy overwrapped pressure vessels.

In this work, an experimental and numerical study of the mechanical behaviour of combat helmets against ballistic impact of spherical projectiles of 1.7 g has been carried out. A numerical model, that has been calibrated and validated with experimental results of plates with different thicknesses, has been developed. Once the model has been validated, experimental tests have been carried out on the combat helmet. To conclude, it is noteworthy that the location of the impact on the helmet has a significant influence on the ballistic limit. It should be noted that the numerical model includes each layer of the combat helmet which may be beneficial for future research on helmets by using aramid or other materials.

The article contains a comparison of selected numerical methods describing the structure of polymer composite. This work focuses on different FEM modeling methods using homogenization of composite material parameters. The estimation is based on comparing visual results of real ballistic test and numerical simulations. The main goal of this comparison is estimation of computer description accuracy of ballistic impact by 9 mm projectile type Luger.

This work deals with modeling the interactions between projectile, protection and plastilina backing during a non-perforating ballistic impact. For its mechanical behavior, ballistic plastilina was considered as a fluid. A capillary rheometry analysis over a wide range of shear rates was performed to obtain its dynamic viscosity. The mechanical response of ballistic plastilina was deduced from the rheology of plasticine using a strain rate based power law formalism. Based on the spherical cavity expansion theory, it was predicted that ballistic impact is capable of generating very high strain rates behind the impacted region. An experimental study assessed the influence of the impact velocity and the rigidity of the protection on the ballistic response of plastilina blocks, depending on indentation depths of the plastilina behind the impact region. Numerical simulations of the ballistic impact response of the plastilina covered by different ballistic protections allowed the assessment of the dynamic behavior of such systems. Good correlations were obtained between experimental and numerical analysis. It turned out that indentation depths obtained numerically are generally lower than for the experimental measurements.

The research conducted under this effort aimed at analyzing thermal barrier concepts intended to reduce visual signature of small caliber weapon systems (barrels, suppressors, etc.) resulting from high rates of firing. Analysis of heat transfer mechanisms and modeling and simulation of thermal barrier concepts were conducted. Basic principles were explored to identify limitations of application conditions and influencing system design parameters. Modeled results representing live fire test cases were in good correlation with both standard M4A1 test data and vacuum barrier results. Barrier effectiveness was shown to decrease with higher heating rates as barrel temperatures increase and radiation exchange between barrel and barrier rises.

This work deals with the development of a STANAG 4569 level III PLUS (12.7 × 99 mm AP M2) ballistic protection of ceramic panels (add on) for a Brazilian armored personnel carrier. The research started with the study of the physical characteristics of different hexagonal ceramic chips and their best assembly on the plate. After the selection of the best ceramic chip the final configuration of the ballistic panel was completed following the procedures according to NATO STANAG AEP-55—volume 1 [1]. The ballistic test panels were produced by “ALLTEC Indústria de Componentes em Materiais Compostos”, in Brazil and the ballistic tests were carried out by the “Centro de Avaliação do Exército (CAEx)”, the Brazilian Army Proving Ground, in Rio de Janeiro. After many ballistic tests led by the CAEx technical staff, finally an assembled panel was produced by ALLTEC with the choice of ceramic chip configuration, as well as a special bonding material and the backing support in aramid fiber fabric. The best results achieved led the researchers to produce a prototype panel that was approved after exhaustive tests carried out by CAEx to consolidate the results and to approve the final product. The homologation and validation of the entire additional ballistic protection panel (ADD ON) was homologated by the Brazilian Army to be applied on its personnel armored carrier.