Soft Body Armor Research Articles

Effects of silica morphology on the shear‐thickening behavior of shear thickening fluids and stabbing resistance of fabric composites

ABSTRACTShear‐thickening fluid (STF) refers to a system where nonaggregating solid particles are suspended in a specific fluid. Due to its unique viscosity variation, STFs have attracted a lot of attention as soft body armor materials for impact protection. In this work, two kinds of STFs were designed using polyethylene glycol (PEG) and spherical or irregularly shaped silica particles. Rheological results showed that shear thickening can even occur at lower shear rates in the irregularly shaped silica‐based STF; however, the thickening range of the spherical silica‐based STF was broader. Meanwhile, the composites prepared with STFs and aramid fabrics exhibited better antistab properties than neat fabrics. Compared to composite prepared with irregularly shaped silica‐based STF, spherical silica‐based STF/aramid composite had better stabbing resistance. In addition to the binding effect of silica particles to the fiber bundle, it was considered that when the fabric composite was subjected to impact, spherical particles were easier to slide so that the STF was more likely to be thickened to achieve a greater viscosity, resulting in the better stabbing resistance performance. Our studies will provide guidance for the design of the high‐performance soft body armor equipment. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48809.

Design strategy for optimising weight and ballistic performance of soft body armour reinforced with shear thickening fluid

This study presents some soft armour panel design strategies using shear thickening fluid (STF) reinforced Kevlar® fabric. The effect of size of silica nano and sub-micron particles on the ballistic performance of soft body armour panels against the small arms ammunition (velocity ~ 430 ± 15 m/s) has been analysed. Two STFs, namely STF-500 and STF-100, were prepared by dispersing silica particles of 500 nm and 100 nm diameter, respectively, in polyethylene glycol (PEG) 200. Kevlar® fabrics were impregnated with both the STFs. Multiple layers (20–24) of fabrics were stitched to prepare 13 soft armour panels which were evaluated for back face signature (BFS) against 9 × 19 mm lead core bullet. Soft armour panels comprising of fabrics impregnated with STF-500 yielded lower BFS than the respective panels comprising of fabrics impregnated with STF-100. This study also revealed that STF impregnation of Kevlar® fabrics can reduce the BFS by 2.5 mm–2.8 mm while keeping the areal density of the panel same (5 kg/m2). The areal density of soft armour panel can be reduced further by 10% (4.5 kg/m2), while keeping the BFS comparable to or lower than that of an STF impregnated homogenous panel, by judiciously placing the STF impregnated fabrics at the rear side while neat fabrics are placed at the strike face of the panel. STF impregnated panels were found to stop the impacting bullet earlier than neat panel.

Incorporation of shear thickening fluid effects into computational modelling of woven fabrics subjected to impact loading: A review

Soft armour consisting of multi-layered high-performance fabrics are a popular choice for personal protection. Extensive work done in the last few decades suggests that shear thickening fluids improve the impact resistance of woven fabrics. Shear thickening fluid–impregnated fabrics have been proven as an ideal candidate for producing comfortable, high-performance soft body armour. However, the mechanism of defeating a projectile using a shear thickening fluid–impregnated multi-layered fabric is not fully understood and can be considered as a gap in the research done on the improvement of soft armour. Even though considerable progress has been achieved on dry fabrics, limited studies have been performed on shear thickening fluid–impregnated fabrics. The knowledge of simulation of multi-layered fabric armour is not well developed. The complexity in creating the geometry of the yarns, incorporating friction between yarns and initial pre-tension between yarns due to weaving patterns make the numerical modelling a complex process. In addition, the existing knowledge in this area is widely dispersed in the published literature and requires synthesis to enhance the development of shear thickening fluid–impregnated fabrics. Therefore, this article aims to provide a comprehensive review of the current methods of modelling shear thickening fluid–impregnated fabrics with a critical analysis of the techniques used. The review is preceded by an overview of shear thickening behaviour and related mechanisms, followed by a discussion of innovative approaches in numerical modelling of fabrics. A novel state-of-the-art means of modelling shear thickening fluid–impregnated fabrics is proposed in conclusion of the review of current methods. A short case study is also presented using the proposed approach of modelling.

Improved Interyarn Friction, Impact Response, and Stab Resistance of Surface Fibrilized Aramid Fabric

AbstractImprovement of the ballistic performance of aramid fabric is an important topic in the study of soft body armors, especially with their increasing use in such applications over the past decades. To enhance and tailor the performance of fabrics, having control over one of its primary energy absorption mechanisms, interyarn friction, is required. Here, a recently reported surface fibrilization method is exploited and optimized to improve interyarn friction in aramid fabrics. Through tow pullout testing of fibrilized fabrics, the fibrilization treatment is shown to provide up to seven times higher pullout energy and six times higher peak load. To correlate the effects of the treatment on the ballistic response, impact tests are conducted on treated fabric targets using a gas gun setup. The fibrilized fabrics displayed a 10 m s‐1 increase in V50 velocity, compared to that of untreated fabrics, while retaining its original flexibility and mechanical strength. Similarly, the fibrilization treatment also resulted in 230% improvement in depth of penetration when dynamically stabbed using a spike impactor. The results demonstrate the potential of the proposed surface fibrilization treatment as a fast and cost‐effective technique to improve the ballistic and stab performance of aramid‐based soft body armors.

Projectile strength effects on the ballistic impact response of soft armor targets

Upon impact with a target panel, a portion of a projectile's striking kinetic energy is dissipated via heat loss or deformation. Typical ballistic performance determination standards require strict projectile hardness values of Rc 29 ± 2 for consistency and repeatability, but it is of interest to examine if these required hardness values give a lower bound where the ballistic performance determination is independent of the strength of the projectile. In this study, a large range of yield strengths of metallic right-circular cylinders were used to test the effects on the ballistic response of a multi-ply soft body armor. The results show that with an increase in projectile yield strength, the ballistic limit velocity decreases. This degradation in ballistic performance of the soft armor target levels off at higher yield strengths to about 75% of the expected ballistic performance for Rc 29, indicating that there may be a minimum projectile strength after which the influence of strength is no longer significant. The degree of deformation of projectiles during impact is related to the striking velocity and the off-axis failure of the soft armor target material.

Hybrid approach for augmenting the impact resistance of p-aramid fabrics: grafting of ZnO nanorods and impregnation of shear thickening fluid

A novel hybrid approach has been developed and implemented to enhance the impact resistance of p-aramid fabric-based soft armour material. ZnO nanorods of diameter ca. ~ 100 nm were developed on the surface of p-aramid (Kevlar®) fabrics by seed and growth method followed by impregnation of fabrics with silica-based shear thickening fluid (STF) having 65% (w/w) concentration. The impact resistance of neat Kevlar fabric (KF), ZnO nanorod grafted Kevlar fabric (ZnO-KF), STF impregnated Kevlar fabric (STF-KF) and ZnO nanorod grafted-STF impregnated Kevlar fabric (ZnO-STF-KF) was studied. The impact energy absorption by ZnO-KF and STF-KF was higher by 29.6% and 10%, respectively, as compared to that of neat fabric (KF). The hybrid approach of modifying the Kevlar fabric with ZnO nanorods and impregnation with STF (ZnO-STF-KF) enhanced the impact energy absorption by 36.6% as compared to that of neat Kevlar fabric. The substantial increase in impact energy absorption in the case of ZnO-STF-KF can be attributed to the combined contribution of increased inter-yarn friction caused by ZnO nanorods and shear thickening behaviour of STF. The ZnO nanorod grafted high-performance fabrics impregnated with STF could be a promising candidate for the development of soft body armour material.

3D warp interlocks p-aramid fabrics for composite reinforcement and ballistic vest applications: Effect of yarn density on its formability characteristics

The material forming capability becomes one of the most important characteristic of textile performance in the manufacturing of three-dimensional (3D) components to fit a 3D surface in various technical applications. In this study, different forming characteristics of 3D warp interlock fabrics in dry fabric condition were investigated. 3D warp interlock architecture with different areal density from same para-aramid yarn with a linear density of 168dtex were systematically designed and produced on automatic dobby loom with standard atmospheric conditions. The approach utilizes a low speed forming process with a predefined hemispherical shape of punch for the analysis of different forming behaviour of the fabrics specimen. The same blank-holder pressure was chosen for all the samples for better comparisons. Among several forming properties, some important characteristics have been observed, measured and analysed for a better understanding of the material forming behaviour of the different samples specimen. The research results with independent warp and weft yarn densities show a significant impact on the forming behaviours 3D warp interlock fabric. Moreover, the result of the investigation also will give a better understanding on different forming behaviours of 3D warp interlock fabric with various densities while applying in different textile application including women soft body armour.

Anti-impact behavior of a novel soft body armor based on shear thickening gel (STG) impregnated Kevlar fabrics

A novel Kevlar/STG (Kevlar fabrics immersed with shear thickening gel) fabrics composite with high anti-impact performance was fabricated. By utilizing a unique multi-sensor force testing system, both low- and high-velocity impact experiments were conducted to investigate the anti-impact performance of Kevlar/STG fabrics. In low-velocity testing, the attenuation of the impact center force for Kevlar/STG was 64.1%, which was much larger than the Kevlar (27.0%). Under high-velocity loading, the impact force of Kevlar/STG attenuated from 805 N to 223 N with the increase of layers from 5-layers to 20-layers, while they reduced from 1125 N to 460 N for Kevlar fabrics. Meanwhile, the failure mode was analyzed and it was found that the high anti-impact performance was originated from the shear thickening effect and enhanced friction. In consideration of the good flexibility and excellent safe guarding property, the Kevlar/STG showed promising perspective in body armor.

Lobster inspires soft but strong body armor

Lobster inspires soft but strong body armor

Soft body armour development by silica particle based shear thickening fluid coated p-aramid fabrics

Soft body armour panels using p-aramid (Technora) fabrics with three different levels of thread densities were developed in this research. Shear thickening fluid (STF) was synthesized using silica nano-particle (100 nm) and polyethylene glycol (PEG). Fabrics were coated with 60% (w/w) STF to improve their resistance against low-velocity bullets (165 m s−1). For neat fabrics, all the bullets fired from 0.38″ calibre revolver pierced the multilayer fabric panel. However, impact energy absorption increased with the increase in thread density in fabric. After coating with shear thickening fluid, panels having four layers of fabric stopped all the bullets fired. It was possible to reduce the weight of panel by 23% after the STF treatment whilst ensuring bullet stoppage.

Soft body armor time-dependent back face deformation (BFD) with ballistics gel backing

This paper presents a method for obtaining time dependent back face deformation (BFD) data for body armor during ballistic impact using a clear ballistics gelatin backing and high-speed cameras to capture the deformation profile. Using this method, baseline fabric characterization data was obtained for samples comprised of varying layers of 467 g/m2 Kevlar K29 fabric impacted with 8.24 g steel ball projectile and backed with NATO standard 20% clear ballistics gelatin. For these tests, deformation depths were seen to increase with increasing impact energy and decreasing total areal density. A limited study of the various test parameters was performed by testing one additional fabric, projectile, and ballistics gelatin. From these comparisons, it was observed that 122 g/m2 Kevlar KM2+ fabric performs better per weight than 467 g/m2 Kevlar K29 fabric in terms of BFD, 9 mm FMJ projectiles produce deeper BFDs than 12.7 mm steel ball projectiles, and backing a sample with FBI standard 10% ballistics gel increases the BFD considerably over NATO standard 20% ballistics gel.

Rheology Based Design of Shear Thickening Fluid for Soft Body Armor Applications

The ballistic resistance of high-strength fabrics improves upon impregnation with Shear Thickening Fluids (STFs). The performance of such STF treated fabrics depends on the rheological properties of the STF which in turn are governed by the physicochemical properties of the STF. The present study utilizes rheological characterization of shear thickening silica-polyethylene glycol dispersions (of different material configurations in terms of packing fraction, particle size and continuous phase viscosity) to assess their performance and obtain the best STF material configuration for ballistic body armor applications based on the design criteria proposed herein. The ballistic performance assessment results showed that the STFs with high packing fractions which thicken discontinuously, are highly effective compared to the continuously shear thickening fluids. Furthermore, the use of smaller particle size dispersed phase in the STF formulation was determined to be economical. Also, the use of lower molecular weight dispersion medium was suggested as it allows for a broader working temperature range of the STF. Additionally, the technological issues associated with the development and the practical application of STF-Armor were addressed.

Soft body armour

A detailed and timely progress of soft body armour against stab and ballistic impact is presented in this monograph. The classification and the evolution of body armour is briefly presented, demonstrating the change of material choice with time. The energy absorption capacity of soft body armour and the mechanisms by which this energy is absorbed or dissipated are dependent upon various parameters and a detailed review is highlighted to best understand the material and structural influence. Various stab and ballistic resistance standards against which armour is currently evaluated are presented in detail. Additionally, the different techniques used to evaluate the performance of armour, from a single layer high-performance fabric to a full armour panel assembly are explained in depth, focusing on yarn pull-out, dynamic impact and ballistic test. Further, different approaches adapted to improve the impact or ballistic response of a high-performance fabric used for soft armour panels is reported exhaustively, with special attention drawn to the application of natural rubber, shear thickening fluid (STF) and surface modification of fibre. Among these, the use of STF is given greater importance, minutely exploring the mechanism of shear thickening, the factors affecting shear thickening behaviour and the methods adopted to improve the thickening or viscosity of STFs. Furthermore, emphasis is laid upon the failure mechanisms of a single high-performance fabric to low velocity impact and of an armour panel to high velocity impact, both for neat and STF treated structures. Moreover, the effectiveness or applicability of soft body armour is valid only when certain conditions are met, a list of which is concisely outlined. Finally, with new techniques and approaches being explored at research level, a futuristic and revolutionalised concept of soft body armour is anticipated- the application of nanomaterials, the use of smart textiles and the concept of biomimetics in armour design.

Optimization of Soft Body Armor with Laminates of Carbon–aramid Fiber and Polyester Fiber Using the Taguchi Method

Body armor is a vital instrument for Tentara Nasional Indonesia-Indonesian National Armed Forces (TNI) and Polisi Republik Indonesia-Indonesian National Police (POLRI) to protect themselves from any projectile penetration and the spread of explosive material. One type of body armor is soft body armor, commonly used for handling community riots. The forming material of soft body armor should be strong and flexible. For that, selecting appropriate materials to optimize their ability is necessary. This research aims to develop soft body armor with carbon–aramid and polyester laminate as materials using a quasi–static impact test. The method used was the Taguchi experiment, the advantage of which is its ability to optimize the desired quality characteristics based on the best factor. The results showed that the optimal combination of polyester and carbon–aramid composite materials showed a median result from the quasi–static impact test of 61 259.91 N with the optimum compositions of factor D level 1, factor A level 2, factor B level 1, factor E level 2, factor C level 2, factor F level 1, and factor G level 2.

A systematic pattern generation system for manufacturing customized seamless multi-layer female soft body armour through dome-formation (moulding) techniques using 3D warp interlock fabrics

Female participants in different perilous tasks including law enforcement offices have been considerably increased in the last few decades. However, they mostly wear men’s body armour with smaller sizes which brings a negative upshot not only in ballistic protection performance, comfort, fitness but also in a psychological point of view. Hence, manufacturing female soft body armour based on their unique morphological differences for better ballistic protection without conceding fitness and comfort are in great demand. This research work presented a novel method using a systematic 3D design approach through parametrization process to generate block patterns for manufacturing successive layer in the panels. The deformable mesh on the 3D virtual adaptive female model was developed with grading values of zero. Parametrization process based on the thickness of each layer in the 3D design database was applied to generate the different successive meshes on the virtual mannequin with appropriate coordinates. Later, the multi-layers mesh developed on the virtual 3D female body has been flattened to acquire the different layer’s pattern. Due to its excellent mouldability behaviour, 3D warp interlock fabrics made of high-performance fibre has been designed and developed to manufacture the seamless female body armour with a dome-formation process. The manufactured multi-layer panels were draped on the standard female physical mannequin for experimental validations. The result shows that the new 3D design approach and its manufacturing system was found easy and precise to generate the different multi-layer panels pattern for developing seamless female soft body armour.

Disentangling High Strength Copolymer Aramid Fibers to Enable the Determination of Their Mechanical Properties.

Traditionally, soft body armor has been made from poly(p-phenylene terephthalamide) (PPTA) and ultra-high molecular weight polyethylene. However, to diversify the fiber choices in the United States body armor market, copolymer fibers based on the combination of 5-amino-2-(p-aminophenyl) benzimidazole (PBIA) and the more conventional PPTA were introduced. Little is known regarding the long-term stability of these fibers, but as condensation polymers, they are expected to have potential sensitivity to moisture and humidity. Therefore, characterizing the strength of the materials and understanding their vulnerability to environmental conditions is important for evaluating their use lifetime in safety applications. Ballistic resistance and other critical structural properties of these fibers are predicated on their strength. To accurately determine the strength of the individual fibers, it is necessary to disentangle them from the yarn without introducing any damage. Three aramid-based copolymer fibers were selected for the study. The fibers were washed with acetone followed by methanol to remove an organic coating that held the individual fibers in each yarn bundle together. This coating makes it difficult to separate single fibers from the yarn bundle for mechanical testing without damaging the fibers and affecting their strength. After washing, fourier transform infrared (FTIR) spectroscopy was performed on both washed and unwashed samples and the results were compared. This experiment has shown that there are no significant variations in the spectra of poly(p-phenylene-benzimidazole-terephthalamide-co-p-phenylene terephthalamide) (PBIA-co-PPTA1) and PBIA-co-PPTA3 after washing, and only a small variation in intensity for PBIA. This indicates that the acetone and methanol rinses are not adversely affecting the fibers and causing chemical degradation. Additionally, single fiber tensile testing was performed on the washed fibers to characterize their initial tensile strength and strain to failure, and compare those to other reported values. Iterative procedural development was necessary to find a successful method for performing tensile testing on these fibers.

Performance of police personal protective equipment challenged with a military grenade

Police body armour in the United Kingdom (UK) is designed to provide protection from edged weapons and low-velocity pistol ammunition. Recent events have raised concern about whether UK police body armour and associated personal protective equipment (PPE) provides protection from military threats such as improvised explosive devices (IED) and grenades. In this paper PPE worn by specialised police officers was assessed for its protective performance from a specified grenade threat. The major cause of injury suffered by police officers challenged by a modern military grenade would be from the associated fragmentation which perforated coveralls, boots, helmet and soft body armour, but not hard armour plates.

Influences of fabric density on mechanical and moulding behaviours of 3D warp interlock para-aramid fabrics for soft body armour application

For the past many decades’ enormous research has been done on mechanical and moulding properties of 2D woven and non-woven fabrics. The current paper presents a comprehensive investigation of the tensile, bending and moulding behaviours of 3D orthogonal warp interlock fabrics with different fabric densities. Four 3D warp interlock fabrics with different areal density made from 168Tex linear density p-aramid Kevlar yarn were manufactured on dobby loom in GEMTEX laboratory. Based on the investigation both fabric density and yarn density shows a significant effect on bending and tensile properties of the fabrics. The bending rigidity in the warp and weft directions become higher in preforms with denser weft and warp yarn densities respectively. In general, as the yarn density in the respective warp or/and weft direction increases, the maximum tensile load with maximum strain increases. Moreover, the fabric and yarn density has also shown a great impact on various mouldability characteristics of 3D warp interlock preforms while deformation. The study finally elucidated that, like other parameters, fabric and the yarn density of 3D warp interlock influenced greatly the tensile, bending and moulding properties where those parameters should be considered carefully while applying in various technical textile applications i.e., soft body armour.

Determination of Materials for Hybrid Design of 3D Soft Body Armour Panels

In order to optimise the construction of soft body armour panels by hybridization, this study aims to identify materials determination for hybrid panel. Different ballistic characteristics of aramid woven fabrics and Ultra High Molecular Weight Polyethylene uni-directional laminates were investigated through ballistic test and fractorgaphic analysis. With an increasing of total layer numbers in a panel, specific energy absorption of Twaron woven panel shows a decrease trend, and Dyneema UD panel exhibits an increasing trend. Such reverse trend of ballistic performance is due to different failure modes of two materials. According to fractorgraphic analysis, Twaron fabric has large transverse deformation for back layers in a perforated panel. This results in higher energy absorption in back layers. For Dyneema UD, thermal damage is the dominant failure mode, which can result in performance degradation especially for front layers on the strike face. In addition, Dyneema UD exhibits significant advantage of minimize Backface Signature (BFS) and a little higher perforation ratio than that of Twaron woven panels. Based on these findings, an optimized hybrid panel is designed by combing Twaron woven fabric before Dyneema UD. In comparison with other panels with different layer sequences, this hybridization manner exhibited better ballistic performance, including improvement of energy absorption, minimized BFS of the non-perforated panel and reduction of perforation ratio. These findings indicated that material determination for hybrid design should be based on ballistic characteristics of different materials and requirements of different regions in a panel.

Female seamless soft body armor pattern design system with innovative reverse engineering approaches

Significant efforts have been made so far to improve the overall performance of female soft body armor. However, still designing female soft body armor which accommodates the bust area for different women morphological differences with good comfort, fitness, and better ballistic protection is in its great demand. This research paper presents an efficient reverse engineering approach (2D-3D-2D pattern generation) for developing appropriate 2D patterns from 3D female adaptive virtual mannequin for female soft body armor seamless front panel. The method was mainly used to attain the required bust volume in the pattern by eliminating the involvement of darts and another design element. Before the process, using computer-aided design (CAD), parameterization has been applied to develop a female model with an adaptive bust from a scanned body. The method starts with identifying the different strategic anthropometric points on the front body side contours of adaptive mannequin using specific 90B size bust cup. Based on these points, delimiting of the outer contour of the pattern has been done. Later, horizontal (weft) and vertical (warp) projection grids in front of the virtual mannequin were marked to generate block pattern using curve measurement from the body couture, while during projection, an accurate measurement using precise projection system and bust points has been considered. Finally, the material deformation has been also analyzed using classical 3D-to-2D flattened pattern. The result shows that the new flattened pattern reveals better shape to accommodate the deformation with low distortion throughout the fabric surface while flattening. This will later greatly help to keep similar fabric distribution throughout the panel and give better ballistic protection, fit-ensured, and good comfort for the wearer.