Soft Body Armor Research Articles

Improved inter-yarn friction and ballistic impact performance of zinc oxide nanowire coated ultra-high molecular weight polyethylene (UHMWPE)

Ultra-high molecular weight polyethylene (UHMWPE) woven fabrics have been shown to possess a high strength-to-weight ratio, low density, high-energy absorption, and abrasion-resistant properties. When subjected to dynamic impact, the primary failure mode of UHMWPE woven fabric is yarn pullout, which results from poor inter-yarn friction between the weft and warp yarns. This work investigates the potential use of zinc oxide nanowires (ZnO NWs), which are grown on plasma functionalized UHMWPE woven fabric, to improve the inter-yarn friction, energy absorption, and impact response of the fabric. Yarn pullout testing is used to evaluate the inter-yarn friction of ZnO NW coated UHMWPE fabric that was treated with oxygen plasma for 30 s. This testing demonstrates a 663.5% increase in friction, while the pullout energy increased by 822.9%, relative to neat UHMWPE fabric. The improved inter-yarn friction results in a 59.13% higher V50 ballistic limit, while the energy absorbed during impact increased by 227%, relative to neat fabric. This work demonstrates a new approach to yield-improved ballistic performance of woven UHMWPE fabrics, which can further the fabric's utilization in the creation of soft body armor.

Properties of Kevlar fabric composites reinforced by STF composed of monodisperse polystyrene microspheres

Shear thickening fluid (STF) composed of monodisperse polystyrene microspheres (m-PS-m) was prepared, and soft armor composites was constructed with Kevlar fabric reinforced by this STF in this work. Both the knife and the spike stab resistance performance of this soft composite are investigated and discovered to improve significantly over the neat Kevlar fabric (NKF), and the puncture resistance of the spike is dramatically superior to the cut resistance of the knife. 8 layers of STF-impregnated Kevlar fabric (STKF) will not be punctured under the highest impact energy while 10 sheets of NKF is impaled easily even under the lowest striking energy in experiments. The tensile strength of this soft composite is increased by more than 55% compared to NKF. The highest pull-out force for single yarn in STKF is nearly 6 times that of NKF. The highest pull-out force of single yarn and tensile strength for STKF are greatly improved to make it meet more requirements of different situations. More importantly, the excellent stab resistant and burst strength performance of STKF indicate that it has broad application prospects in the field of soft body armor.

Tuning of shear thickening behavior and elastic strength of polyvinylidene fluoride via doping of ZnO‐graphene

AbstractZnO rice like nonarchitects are grafted on the graphene carbon core via a rapid microwave synthesis route. The prepared grafted systems are characterized via XRD, SEM, RAMAN, and XPS to examined the structural and morphological parameters. Zinc oxide grafted graphene sheets (ZnO‐G) are further doped in β‐phase of polyvinylidene fluoride (PVDF) to prepare the polymer nanocomposites (PNCs) via mixed solvent approach (THF/DMF). β‐phase confirmation of PVDF PNCs is done by FTIR studies. It is observed that ZnO‐G filler enhances the β‐phase content in the PNCs. Non‐doped PVDF and PNCs are further studied for rheological behavior under the shear rate of 1–100 s−1. Doping of ZnO‐G dopant to the PVDF matrix changes its discontinuous shear thickening (DST) behavior to continues shear thickening behavior (CST). Hydrocluster formation and their interaction with the dopant could be the reason for this striking DST to CST behavioral change. Strain amplitude sweep (10−3% ‐10%) oscillatory test reveals that the PNCs shows extended linear viscoelastic region with high elastic modulus and lower viscous modulus. Effective shear thickening behavior and strong elastic strength of these PNCs present their candidature for various fields including mechanical and soft body armor applications.

Moisture absorption characteristics and effects on mechanical properties of Kolon/epoxy composites

Para-aramid fibers (Kolon) are high performance polymeric fibers characterized by their high tenacity and impact resistance. They are used for the soft body armor structures in ballistics. In this study, the testing specimens were made from multilayered Kolon fabrics impregnated with epoxy resin where silicon carbide (SiC) microparticles or SiC nanofibers were added as reinforcement. The laminated composite samples were fabricated by hot compression and curing of epoxy resin.The tensile and impact strengths of the untreated specimens were compared with the ones that underwent water absorption in duration of 72 h (immersion or humidity) followed by desorption. The immersion of the specimens in water and exposure to high humidity (70%) were performed according to the ISO 62 standard while the tensile test was carried out in accordance with the ASTM D 3039 standard. In the end, the tensile test simulation of the laminated composite by using software Abaqus® was accomplished.

Investigation of the effect of a dilatant material on ballistic strength of aramid fabric used as body armour suit

Scoured (SC) and water repellent treated (WRT) types of Twaron® CT 709 ballistic fabrics have a variety of applications in soft body armour. In this study, ballistic tests were performed on armour systems prepared by impregnating certain proportions of poly (borodimethylsiloxane) -PBDMS- polymer to aforementioned fabrics. The friction effect of PBDMS between the yarns was investigated before the ballistic tests. The correlation between PBDMS ratio and ballistic performance was also investigated. It was observed that as the ratio of PBDMS impregnated to the scoured type fabrics increases, the friction force between the yarns and the ballistic strength increases up to 14.7% accordingly. On the other hand, PBDMS could not be impregnated homogeneously due to the water repellent property of WRT type fabrics and this limits the ballistic advantage.

Analysis on Injury for Light Armored Vehicle Occupant by the After-effect Fragments of Rifle Projectile

Armor-piercing projectile is one of the main threats faced by light armored vehicles. The after-effect fragments formed by projectile penetrating armor will cause injuries to the occupants. It is an important reference for evaluating the impact of the armor-piercing projectile on light armored targets. The characteristics of after-effect fragments have a great influence on the lethal efficiency of internal occupants, especially those wearing bulletproof vests. In order to study the injury effect of the after-effect fragments on occupants, the 12.7 mm multifunctional bullet was tested to 10 mm armored steel to obtain the mass distribution of after-effect fragments at different speeds, and then a finite element model of the effect of after-effect fragments on the human thorax FEM with soft body armor was established. Through numerical simulation, the impact of different after-effect fragments of bullets was obtained. The stress changes, pressure changes and etc. of human model after the impact of different after-effect fragments were obtained that provides a basis for further evaluation of the injury effect of fragments on occupants in light armored vehicles.

Ballistic Performance of Shear Thickening Fluids (STFs) Filled Paper Honeycomb Panel: Effects of Laminating Sequence and Rheological Property of STFs

In order to exploit future soft body armor to achieve a more comprehensive protection than just the torso part of the body, in this study, shear thickening fluids (STFs) with different rheological properties are fabricated by planetary mixer and three-roller mills to investigate the mixing process effect on the resultant rheological behavior. Rheological results indicate the critical shear rate and the maximum viscosity of STF are deeply influenced by the dispersion degree of nano-silica particles in PEG. These STFs are then filled into a paper honeycomb partition to prepare a STF-based protective structure. Different laminating sequences of the composite panels composed one STF structure layer and nineteen layers of Kevlar fabric are obtained by simply placing the STF structure at different positions in the composite panels. The ballistic tests are conducted according to the NIJ 0101.06—Type II standard using 9 mm Full Metal Jacketed Round Nose bullets. Our results show that the absorbed energy of the composite panel with STF that thickens at higher shear rate is higher compared to that using STF that thickens at a lower shear rate. It suggests the STF with higher critical shear rate would be optimally used in ballistic impacts. In addition, ballistic testing results confirm that the STF structure placed at the rear position can significantly contribute to the increase in impact resistance.

Effect of particle size of fumed silica on the puncture resistance of fabrics impregnated with shear thickening fluid

This paper presents an investigation into the effect of particle size of fumed silica on the puncture resistance of fabric impregnated with shear thickening fluid (STF). Two different types of STF were fabricated from fumed silica nanoparticles with particle sizes of 12 and 40 nm respectively. The effects of the particle size and weight fraction of the fumed silica on the rheological property were studied. STFs impregnated woven fabrics were fabricated and tested for stabbing resistance. STFs made of fumed silica with large particle size have better shear thickening effect. The stabbing resistant performance of STF impregnated fabrics improved notably with the same number of layers of fabric, and STFs impregnated fabric panels also outperform the untreated fabric panels with the same areal density. The results indicated that STFs made of fumed silica with larger particle size is able to fabricate a lighter soft body armor with higher stabbing protection.

Preparation and Impact Resistance Properties of Hybrid Silicone-Ceramics Composites

This article presents the method of preparation a new type of ballistic armor based on hybrid silicone-ceramic (HSC) composites with considerable flexibility. An experimental study on the ballistic behavior of HSC composites connected with soft body armor is presented against FSP.22 fragments. The effect of Al2O3 ceramics on the ballistic performance of HSC composite was investigated, and the fragmentation resistance process of the composite armor combining the HSC composite and soft aramid insert is clarified. Furthermore, impact resistance tests made with a drop tower which allows for a gravity drop of a mass along vertical guides onto a sample placed with an energy of 5 J were performed. The results presented in this paper show that the HSC composites can be successfully used as a hard body armor. However, they do not exhibit the properties of absorbing the impact energy generated during the drop tower tests. The test results show that the ballistic performance of composite armors is influenced by the hardness and Young modulus of ceramics and soft body armor panel. Additionally, in the article, the results of mechanical properties of silicones used for preparation of composites were presented and compiled to determine their role in the performance of impact protection.

INVESTIGATION OF THE EFFECT OF SHEAR THICKENING FLUID AND FABRIC STRUCTURE ON INTER-YARN FRICTION PROPERTIES IN TWARON FABRICS

It is known that shear thickening fluids increase the energy absorption capacity of high performance fabrics. For this reason, soft body armors were produced by impregnating shear thickening fluids recently on high performance fabrics. In this study, it is aimed that examine the effects of shear thickening fluid and fabric structure on the inter-yarn friction properties of para-aramid fabrics with different properties. Fumed silica was dispersed in polyethylene glycol to produce shear thickening fluid. Twaron 200 and Twaron 460 para-aramid fabrics with different properties such as threads number (105x105 and 67x67), areal density (200 gr / m2 and 460 gr / m2) and linear density (930 and 3360 Dtex) were impregnated with shear thickening fluid. It was observed that both of shear thickening fluid impregnated fabrics had higher yarn pull-out force than neat fabrics due to inter-yarn friction. When shear thickening fluid impregnated fabrics were compared to maximum yarn pull-out force; Twaron 200 and Twaron 460 fabrics requires approximately 3 times and 9 times more force to pull-out the yarn in comparison to the neat fabric respectively. In this study, it has been observed that the positive effects of shear thickening fluid impregnation on energy absorption of Twaron fabrics depend on structural parameters such as threads number, areal density and linear density.

Ballistic Performance of Natural Fiber Based Soft and Hard Body Armour- A Mini Review

Increase in awareness towards utilization of eco-friendly materials, encouraged the researchers to find a sustainable alternative to synthetic fibers for different engineering applications. High performance Kevlar fabrics are widely used in ballistic applications such as bullet proof helmets, vest, and other armour systems. Ballistic impact produces shock waves which may cause severe trauma injuries to the soldiers. Kevlar fabric based armour system provides acceptable range of protection to the soldiers. However, disposal of Kevlar affects the eco system and pollutes the environment. Replacing Kevlar fabric in the protective structures with an eco-friendly light weight material, together with an improved kinetic energy absorption and dissipation has become an interesting approach to enhance the ballistic performance of the composite panels. This mini review addresses the effect of adding different natural fibers on the ballistic performance of soft and multilayered hard body armour systems. Many researchers explored the possibility of utilizing eco-friendly natural fibers (Kenaf, Cocos nucifera sheath, Malva, rami, curaua, bagasse, jute, bamboo) as an alternate material to Kevlar fabric in the armour system and reported that natural fibers can act as a potential reinforcement in the ballistic structures.

Cutting resistance of flexible armour using multiple layers of triaxial kevlar fabric

The textiles capable of cutting resistance found applications in the industrial and military areas to construct flexible lightweight soft body armors. In the present work, a theoretical model to understand the mechanism of fabric cut resistance in a different direction for weft-knitted, triaxial, and multiple layers structures. An experimental study of cutting resistance force was done on weft-knitted fabric with Kevlar 29 triaxial fabrics in multiple layers structure to support derived mathematical model for the effect of multiple layers structure on their cutting force. The study examines specific cut resistance of the structure from four layers of Kevlar triaxial fabrics covered with knitted fabric on both sides. The angle of cutting force varied from 0°, 60°, and 90° with respect to the yarn inclination. Results show that the cutting force of the multilayer structure is linearly proportional to the number of Kevlar triaxial fabrics layers. The specific cut resistance value of the structure from four layers of Kevlar triaxial fabrics, covered with knitted fabric on both sides, reached 544, 435, and 326 (N/g/cm2) for cutting directions: angled 60°, vertical, and horizontal, respectively. In this work, the comparison between the triaxial fabric of high areal density and multiple layers of triaxial fabric with resultant same areal density indicates that a better specific cutting force was achieved in the first case. Furthermore, it investigated the relationship between triaxial surface density, the direction of cutting, and the number of triaxial fabric layers and discussed the optimum specific properties of the different structures.

Fabrication and Mechanical Characterization of Dry Three-Dimensional Warp Interlock Para-Aramid Woven Fabrics: Experimental Methods toward Applications in Composite Reinforcement and Soft Body Armor.

Recently, three-dimensional (3D) warp interlock fabric has been involved in composite reinforcement and soft ballistic material due to its great moldability, improved impact energy-absorbing capacity, and good intra-ply resistance to delamination behaviors. However, understanding the effects of different parameters of the fabric on its mechanical behavior is necessary before the final application. The fabric architecture and its internal yarn composition are among the common influencing parameters. The current research aims to explore the effects of the warp yarn interchange ratio in the 3D warp interlock para-aramid architecture on its mechanical behavior. Thus, four 3D warp interlock variants with different warp (binding and stuffer) yarn ratios but similar architecture and structural characteristics were engineered and manufactured. Tensile and flexural rigidity mechanical tests were carried out at macro- and meso-scale according to standard EN ISO 13 934-1 and nonwoven bending length (WSP 90.5(05)), respectively. Based on the results, the warp yarn interchange ratio in the structure revealed strong influences on the tensile properties of the fabric at both the yarn and final fabric stages. Moreover, the bending stiffness of the different structures showed significant variation in both the warp and weft directions. Thus, the interchange rations of stuffer and binding warp yarn inside the 3D warp interlock fabric were found to be very key in optimizing the mechanical performance of the fabric for final applications.

Designing of hybrid soft body armour using high-performance unidirectional and woven fabrics impregnated with shear thickening fluid

This study aimed to design soft body armour by evaluating the effects of panel configuration and hybridisation. Panel configuration was studied in terms of positioning of unidirectional (UD) and woven fabrics. Hybridisation was studied by using fabrics woven from high-modulus polyethylene yarn and very high-modulus aromatic fibre yarn and also through shear thickening fluid (STF) impregnation. These customised woven fabrics in combination with commercially available Dyneema® SB51 UD sheets (250 g/m2) were used to prepare ten different soft armour panels, having areal density of around 4.9 kg/m2, which varied in the layering sequence of UD, woven neat and woven shear thickening fluid impregnated fabrics. Evaluated for ballistic performance in terms of back face signature against 9 × 19 mm lead core bullet fired at 430 m/s impact velocity, the panels showed better performance when UD fabrics were placed at the strike face and shear thickening fluid treated very high-modulus fabrics at the back face. The experiments showed that ballistic performance can be altered by strategic layer sequencing.

Enhancing the Ballistic Performances of 3D Warp Interlock Fabric Through Internal Structure as New Material for Seamless Female Soft Body Armor Development

This paper investigates the effects of warp yarns ratios on the ballistic performances of three-dimensional (3D) warp interlock p-aramid fabrics. Four 3D warp interlock variants with different binding and stuffer warp yarns ratios were designed and developed. Except for warp yarns ratios, similar fabric parameters and manufacturing conditions were considered. Two-dimensional (2D) woven fabric having similar material characteristics and recommended for female seamless soft body armor are also considered for comparisons. Five ballistic panels, one from 2D plain weave fabric and the rest four from the other 3D warp interlock variants were prepared in a non-angled layer alignment and non-stitched but bust-shaped molded form. The ballistic test is carried out according to NIJ (National Institute of Justice) standard-level IIIA. Back Face Signature (BFS) was then modeled and measured to compute both trauma and panels’ energy-absorbing capability. The result showed significant ballistic improvement in the 3D warp interlock variant with optimum warp yarns ratios over traditional 2D plain weave fabrics. 3D warp interlock fabric panel made with 66.6% binding and 33.3% stuffer warp yarn ratio revealed both lower BFS depth and higher energy absorbing capacity (%) than other panels made of 2D plain weave and 3D warp interlock fabric variants.

Effect of elevated temperature and humidity on fibers based on 5-amino-2-(p-aminophenyl) benzimidazole (PBIA)

Soft body armor is typically comprised of materials such as aramid. Recently, copolymer fibers based on the combination of 5-amino-2-(p-aminophenyl) benzimidazole (PBIA) and PPTA were introduced to the body armor marketplace. The long-term stability of these copolymer fibers have not been the subject of much research, however they may be sensitive to hydrolysis due to elevated humidity because they are condensation polymers. Efforts to evaluate the impact of environmental conditions on fiber strength is very important for the adoption of these materials in armor systems. Three PBIA-based fibers were selected for the study, and were aged at 25 °C, 75 % RH; 43 °C, 41 % RH; 55 °C, 60 % RH; and 70 °C, 76 % RH for up to 524 d. Molecular spectroscopy, scanning electron microscopy, and single fiber tensile testing were performed to characterize changes in their chemical structure, tensile strength, and failure strain as a function of exposure time to different conditions. The fibers were all found to have some reduction in strength at high humidity conditions, with an approximately 14 % reduction for the copolymers and a 29 % reduction for the homopolymer. Molecular spectroscopy revealed some changes which suggest that hydrolysis of the benzimidazole ring is occurring at these elevated temperatures, possibly explaining the observed change in strength.

Determining the optimum anatomical coverage of side plates for the VIRTUS body armour and load carriage system

IntroductionSide plates are worn by UK Armed Forces as part of the VIRTUS body armour and load carriage systems to protect the thorax and abdomen from high-velocity threats. The VIRTUS...

Rheological and energy absorption characteristics of a concentrated shear thickening fluid at various temperatures

Shear thickening fluid (STF) material is a suspension with a certain amount of nano- or micro-particles dispersed into a liquid medium whose viscosity increases with the rate of shear strain. Due to its exceptional rate-dependent property, STF has been regarded as a promising energy absorption material with potential application in soft body-armour. This study examines the rheological, impact resistance and energy absorption characteristics of an STF with concentrated polymer submicron particles under various temperatures. The rheological testing was conducted using a rotational rheometer with a temperature-control hood at shear rates measured from 0.01 s−1. The studies reveal that the shear thickening behaviour of the STF is temperature-dependent and the critical shear rate for the onset of shear thickening decreases with the reduction of temperature. In particular, shear thickening behaviour of the STF at 0 °C was observed with the formation of shear bands evolving into cracks on the free surface of the STF. Low-velocity impact tests were conducted using a drop-weight tower with a temperature-control chamber. The study shows that the impact resistance of the STF increases with the decrease in temperature. In particular, the impact resistance shows an early response time when the impact resistance slowly picks up, corresponding to mechanisms of jamming-associated “solidification” and propagation of front of the “solidified” region. A simple one-dimensional model is also adopted to comprehend the response time for effective energy absorption of the STF addressing the mechanisms, and the general agreement of the predicted response time with that from the experiments demonstrates the effectiveness of the model.

A review of fibrous materials for soft body armour applications

A critical review on the factors affecting the impact resistance and various approaches adopted to enhance the performance of soft body armour materials is presented here.

Mouldability and its Recovery Properties of 2D Plain Woven P-aramid Fabric for Soft Body Armour Applications

Mouldability, along with other mechanical properties, is a very crucial material parameter in various technical textile applications, from composites to soft body armour products. Moreover, the mouldability and recovery behaviours of the material will be affected by various internal and external paramters before, during and after the forming process. The current research particularly tried to study the effects of blank-holder pressure (BHP) and the number of layers not only on the moulding characterstics but also on the recovery behaviour of plain woven p-aramid fabrics made from a high-performance yarn with a linear density of 930 dTex. Samples with various numbers of layers were arranged in the same orientation for the moulding process. The moulding approach utilised a specific moulding device in a low-speed forming process and a predefined semi-hemispherically shaped punch for all specimens.Various important dry textile material moulding characteristics and, most importantly, the moulding recovery properties, such as warp and weft direction drawing-in recovery, center high-point recovery, shear angle recovery etc. were investigated.