Advanced Bulletproof and Stab- and Spike-Resistant Textiles

CHAPTER 12 Advanced bulletproof and stab- and spike-resistant textiles

Amirhossein Salehi Koohestani and Azadeh Bashari Textile Engineering Department, Amirkabir University of Technology, Tehran, Iran

12.1 Introduction The history of the development of armor and weapons begins with human history. Humans have used various forms of guards to protect themselves from war injuries and other hazardous conditions. From the use of leather in the east to the use of chain armor in the west, people have never stopped trying to find better ways to protect against dangers (Fig. 12.1). During the development of body armors, it has always been desirable to use lighter and stronger materials to improve performance by reducing weight. Modern body armors can be divided into two categories: • Hard body armors are made of metal or ceramic plates. • Soft body armors are mainly made up of different layers of fabrics consisting of high-performance fibers. Conversely, the threat from edge or tip weapons is inherently variable because they are manually driven by a population who has different abili- ties and techniques. In addition, edging weapons may cover a wide range of knives, tools, swords, and other accessories that may have various degrees of sharpness and different types of cutting edges [2]. The easiest way of providing stab resistance is to use rigid sheets of metal or composite. Such materials are sufficiently hard to defeat knives by resistance to indentation and to present a large resistance to further penetration [3]. The main disadvantages of rigid armor are in wearer comfort and coverage. To be able to move the arms and waist properly, it is necessary to reduce the coverage or provide some space inside the plates. The best solution is to use several plates; these may be loosely held in different layers, or some form of hinges may be fitted to the edges of single plates. Therefore, plate edges provide weak points; multiple layers increase both weight and bulk, while effective and durable hinging appears to be

Figure 12.1 Past to present of European body armor [1].

difficult to achieve in practice. Rigid armor has another important disad- vantage; it cannot undergo significant bend or large-scale deflection and must stop the threat within its own thickness [4]. Better solution for knife protection would be flexible textile armor and handgun protection.

12.2 The concept under using body armor The body armor is designed to protect the main body organs from damages due to bullet impact. If the bullet penetrates into the body, it will crush and displace the tissues to the organs while making temporary and permanent cavities. Since the human tissues act as a semi fluid, when the bullet creates pressure and shock waves, it damages the main organs and causes death. This is known as unsharpened trauma. More elastic and more cohesive tissues such as skeletal muscle, lung, empty intestine, nerve, blood vessel, and to some extent bone can survive from the temporary cavitation blunt trauma. However, less elastic, fewer cohesive organs, such Advanced bulletproof and stab- and spike-resistant textiles 263 as the liver, brain, and heart do not tolerate temporary cavitation blunt trauma well [5,6]. Factors that contribute to tissue damage are summarized in Table 12.1. The wound consists of three parts: • Entry wound: Usually smaller than the exit wound (Fig. 12.2A).

Table 12.1 Factors that contribute to tissue damage [7]. Factors Description Bullet size The larger the bullet, the more resistance and the larger the permanent tract Bullet Hollow point and soft nose flatten out on impact, resulting in a deformity larger surface area involved Semi jacket The jacket expands and adds to the surface area Tumbling Tumbling of the bullet causes a wider path of destruction Yaw The bullet can oscillate vertically and horizontally (wobble) about its axis, resulting in a larger surface area presenting to the tissue

Figure 12.2 Medium- and high-velocity wounds consisting of (A) the entry wound, (B) internal wound, and (C) exit wound [7]. 264 Advances in Functional and Protective Textiles

Figure 12.3 Projectile impact into a ballistic fiber [9].

• Internal wound: Medium-velocity bullets inflict damage primarily by damaging tissue that the bullet contacts, and high-velocity bullets inflict damage by tissue contact and transfer of kinetic energy (the shock wave producing a temporary cavity) to surrounding tissues (Fig. 12.2B). • Exit wound: Not all gunshot wounds will have exit wounds, and on occasion, there be multiple exit wounds due to fragmentation of bone or the bullet (Fig. 12.2C). Generally, the exit wound is larger and has ragged edges [7]. A bullet-proof vest is designed to spread the energy throughout the material while deforming the bullet at the same time. This deformation exists in hard armor only. In soft armor, bullets are entrapped by the material. Once the bullet strikes the body armor, it is caught by the strong fiber structure known as a “web,” and the energy of the bullet is absorbed into the material until the bullet is stopped. In addition, hard materials that are made from ceramic or metal plates help to protect from nonpene- trating injuries (blunt trauma) to internal organs [5]. When a projectile strikes a fabric target, the response is a combination of global and local response. Global response indicates the behavior of the material away from the impact point, and local response refers to the behavior of material directly contacting the projectile, as shown in Fig. 12.3 [8].

12.3 Material selection The bullet-resistant fabric has to avoid the bullet from penetrating and absorb its energy converting it into work of deformation. Therefore, strength, modulus, elongation at break, deformability of the bullet, and Advanced bulletproof and stab- and spike-resistant textiles 265 velocity of the transverse shock wave in the fiber are the main factors in selection of fibers for the soft body armor [10]. The details about the most commonly used fibers in bulletproof clothing are as follows.

12.3.1 Polyamide 66 Ballistic nylon fabric produced by DuPont was used as US body armor vests until 1983 and saved many lives. These types of fabric were effective against shrapnel but not effective for bullets. Therefore, they were good for aircrews because most injuries were due to shrapnel from antiaircraft fire. The early flak jackets comprised manganese steel plates sewn into a ballistic nylon vest covering the abdomen. They had a quick-release tab for emergency removal in the event of bailing out [11]. In 1945, ballistic nylon 66 (Fig. 12.4) flak jackets containing fiberglass plates were used as body armor for ground troops at the battle of Okinawa, making Okinawa possibly the primary military assault by a force of ground troops wearing body armor since the Middle Ages and certainly the initial for some centuries. Ballistic nylon vests with the Doron plates went on to be used to a significant extent in the Korean War. As of early 1953, 90,000 were dispatched to Korea. Historical evidence suggests that these ballistic nylon/ Doron vests stopped shrapnel, handgun projectiles and even grenade [12]. The US military continued to use ballistic nylon vests for its regular infantry forces until the 1980s. However, ballistic nylon is of little rele- vance to modern armor. For example, nylon usually absorbs energy more than p-aramids. In p- aramids, the transverse wave velocity is about three to four times higher than polyamide. Stress diffusion is more efficient in aramids, so the elongation of the fibers at impact area was measured around 10 µs after the shot was fired with 400 m/s speed [10]. It is evident that the strain in p-aramid fabric is spread in a larger area, and the elongation is much lower. Polyamide creeps under such high strain rates at which the ballistics operates, and melting and fusion at the interlacement points have also been noted [10]. Table 12.2 presents the properties of polyamide 66 versus other ballistic fibers.

Figure 12.4 Polyamide 66 chemical structure. 266 Advances in Functional and Protective Textiles

12.3.2 Aramids Aramid fiber, composed of aromatic polyamides, has been a key material for use in various applications due to its diversified characteristics, including high strength, impact resistance, low density, good chemical resistance, high-heat resistance, and abrasion resistance. Aromatic polyamide fibers (Fig. 12.5) have been widely used in the development of lightweight soft body armor owing to their high performance-to-weight ratio [14]. The aramid fiber is containing poly (p-phenylene terephthalamide) (PPD- T) polymer: a classical poly condensation of p-phenylene diamine (PPD) and terephthaloyl chloride in the amide solvent [15]. The aramid solution is spun by a process called the dry-jet wet spinning (Fig. 12.6). In this process, an anisotropic solution of PPD-T is extruded through the air gap into a coagu- lated bath. The resultant yarn after coagulation is washed and dried [16]. High modulus and tenacity of the fiber are due to the high orientation and strong interchain bonding and high level of crystallization of molecules in aramid polymers. On the other hand, aramid fibers have transverse bands on the surface, and the pleated structure is formed during the coagulation process. First, the fiber skin is formed under stress, allowing the fiber core to relax during the crystallization and to form pleats at a uniform periodicity. The existence of pleats gives elasticity to the fibers, which increase the elongation before break and rupture strain.

Table 12.2 Properties of ballistic fibers [13]. Fiber Tenacity Tensile Tensile Failure Density Specific Specific index modulus strength strain (g/cm3) strength modulus (GPa) (MPa) (%) Nylon-66 0.8 10 910 15À20 1.14 800 9 S-Glass N/A 90 4750 1.5 2.49 1910 36 Kevlar-29 2.1 74 3000 3.5 1.4 2140 53 Kevlar-49 2.0 105 2900 2.5 1.44 2110 73 Dyneema 3.1 171 3000 3.1 0.97 3100 176 Zylon 3.3 169 5200 3.3 1.56 3330 108 M5À2001 2.3 271 3960 2.3 1.74 2280 156

Figure 12.5 p-aramid chemical structure. Advanced bulletproof and stab- and spike-resistant textiles 267

Figure 12.6 Schematic diagram of the dry-jet wet spinning process for aramids.

Therefore, some fibers have higher initial modulus and tensile strength than aramid fibers but possess weak ballistic performance [8]. Aramid fiber is also sold under the trade names of Kevlar (DuPont), Twaron (Tejin), and Heracron (Kolon). In 1964, poly-paraphenylene terephthalamide—branded Kevlar— was invented by Stephanie Kwolek while working for DuPont. In 1970s, Kevlar 29 was used in lightweight, flexible body armor engineering. In 1988, DuPont introduced Kevlar 129, which offers increased ballistic protection capabilities against high-energy impact. In 1995, Kevlar correctional was introduced, which provides the puncture-resistant technology to both law enforcement and correctional officers against puncture type threats from knives and other sharp objects, in particular hypodermic needles. In 1996, DuPont made another addition to the Kevlar line by introducing Kevlar Protera. Kevlar Protera is a high- performance fabric that allows lighter weight, more flexibility, and greater ballistic protection in a vest design owing to the molecular structure of the fiber. It is reported that its tensile strength and energy- absorbing capabilities have been increased by the development of a new spinning process [15]. Twaron is another para-aramid fiber developed by Akzo Nobel and is made in four stages: polymerization, continuous fila- ment yarn spinning, converting to staple and short-cut fibers, and converting to pulp (Fig. 12.7). Twaron CT microfilament is 23% lighter than standard aramid yarn for protection vest. The higher number of fine microfilaments enhances the capacity to absorb energy. Therefore, Twaron CT microfilament vest is lighter, softer, and more flexible and offers more freedom of movement and comfort [8]. 268 Advances in Functional and Protective Textiles

Figure 12.7 How is Twaron produced? [17]. From 2020 perspective, the true game changer in soft body armor is proving to be Dyneema [11]. Advanced bulletproof and stab- and spike-resistant textiles 269

12.3.3 Ultra-high modulus polyethylene Ultra-high-molecular-weight polyethylene (UHMWPE) is another technical fiber used for ballistic protection. This fiber is made via gel-spinning technology. During this process, a loosely uncoiled network of cross-links could be drawn to a highly oriented and crystalline fiber. UHMWPE (Fig. 12.8) obtains its strength from the length of separate molecules, unlike aramid fibers, which derive their strength from strong bonding between adjacent short molecules. The very long polyethylene molecules with the highly crystalline region (85%) allow the fibers to have good tensile loads. UHMWPE fibers are 10 times stronger than steel and lighter than water, which can be very useful in military use [18]. Dyneema (DSM) marketed under the trade name Spectra (Honeywell) is a fiber made of UHMWPE. Dyneema is the most advanced ballistic fiber. It has the highest strength, specific strength, special modulus, and lowest density of all its competitors. Although to date Dyneema has not been produced with a modulus above 170 GPa, but its hypothetical modulus (crystal modulus) is 220 GPa, giving it an exact theoretical modulus of 220 GPa, more than three times higher than Kevlar. In its current form, its specific modulus is 2.5 times higher than Kevlar. The specific strength and tenacity of Dyneema are 50% higher than Kevlar [19]. For ballistic protection, UHMWPE is often used in the form of unidirectional fabrics such as Spectra shield and Dyneema UD, in which the fibers of each layer are oriented in a 0°/90° fashion and are bonded by thermoplastic matrices. The system is found to be far more protective than conventional woven fabrics with the same area density [20].

12.3.4 Carbon fibers About 90% of carbon fibers manufactured are made from polyacrylonitrile (PAN) via melt extrusion process followed by pyrolysis. There are typically five segments in the manufacturing of carbon fibers from the PAN process (Fig. 12.9). These are as follows: • Spinning: PAN mixed with other ingredients and spun into fibers, which are washed and stretched.

Figure 12.8 Ultra-high-molecular-weight polyethylene chemical structure. 270 Advances in Functional and Protective Textiles

Figure 12.9 (A) Upon heating to 300°C, the cyano side groups form cyclic rings with each other. (B) Further heating at 700°C causes these rings to become aromatic pyri- dine groups due to the loss of hydrogen from the carbon atoms. (C) By slowly apply- ing heat between 400°C and 600°C, adjacent chains fuse together to form ribbons, expelling more hydrogen gas. (D) In order to form wider ribbons, the temperature is increased to 600°CÀ1300°C, and nitrogen gas is expelled [23]. • Stabilizing: Chemical alteration to stabilize bonding. • Carbonizing: Stabilized fibers heated to very high temperature forming tightly bonded carbon crystals. • Treating the surface: The surface of fibers oxidized to improve the bonding properties. Advanced bulletproof and stab- and spike-resistant textiles 271

• Sizing: Fibers are coated and wound onto bobbins, which are loaded onto spinning machines that twist the fibers into different size yarns. Instead of being woven into fabrics, fibers may be formed into composites. To form composite materials, heat, pressure, or a vacuum binds fibers together with a plastic polymer [21]. Carbon fibers are not ballistic fibers because carbon fibers and composites reinforced with carbon fibers are brittle in nature. However, in certain applications, single or multiple layers of carbon fabric are used to provide structural integrity, repeated compression improvements, and other benefits [22].

12.3.5 Ballistic glass fibers Glass fibers are made of various types of broken glass. The crushed glass contains silica with varying amounts of oxides of calcium, magnesium, and sometimes boron. Glass fiber manufacturing is the high-temperature conversion of raw materials into a homogeneous melt, followed by the fabrication of this melt into glass fibers. Glass fiber production can be segmented into three phases: raw material handling, glass melting and refining, and glass fiber forming and finish- ing, this last phase being slightly different for distinct types of glass fiber production [22]. Two most common types of glass fibers used in ballistic applications are E- glass, which is alumino borosilicate glass with less than 1% w/w alkali oxides and mainly used for glass-reinforced plastics, and S-glass (alumino silicate glass withoutCaObutwithhighMgOcontent),withhigh-tensilestrength[24].

12.3.6 Other fibers 12.3.6.1 M5 fibers M5 fiber is a high-performance fiber originally developed by Akzo Nobel and currently produced by Magellan Systems International (Magellan). M5 fiber is based on the rigid-rod polymer poly (diimidazo pyridinylene (dihydroxy) phenylene) (Fig. 12.10).

Figure 12.10 Molecular structure of M5 fibers [25]. 272 Advances in Functional and Protective Textiles

The crystal structure of M5 is different from all other high-strength fibers; the fiber features typical covalent bonding in the main chain direc- tion, but it also features a hydrogen bonded network in the lateral dimen- sions. Currently, M5 fibers have a mean modulus of 310 GPa (i.e., substantially higher than 95% of the carbon fibers sold) and average tena- cities meanwhile higher than aramids (such as Kevlar or Twaron) and on a par with poly phenylene benzobisoxazole (PBO) fibers (such as Zylon), at up to 5.8 GPa [25].

12.3.6.2 Poly phenylene benzobisoxazole fibers PBO is another high-temperature ballistic fiber based on repeating aromatic structures (Fig. 12.11). The strength and the modulus of PBO fibers almost double that of p-Aramid fibers. Currently, Toyobo’s commercial rigid-rod chain molecules of poly (p-phenylene-2, 6-benzobisoxazole) (PBO)-Zylon is produced by dry-jet wet spinning from solution in phos- phoric acid [26]. In 2003, a police officer in the city of Forrest Hills, Pennsylvania, was killed when a 40 caliber bullet penetrated the Zylon-based body armor that he was wearing at the time. Preliminary investigations by the US National Institute of Justice (NIJ) indicate that there may be degradation occurring in the ballistic performance of Zylon-based body armor. Tests performed on the armor in Forest Hills incident showed that the tensile strength of single yarns were up to 30% lower than new fibers. Thus, it is evident that Zylon, when used in a body armor application, does not per- form in the expected manner. This behavior may be due to the detrimen- tal effects resulting from moisture and heat in the environment. The strength of Zylon will gradually decrease in high humidity conditions, even in temperatures of less than 100°C [27].

12.3.6.3 Polybenzimidazole fibers Polybenzimidazole (PBIs) fibers are a class of extremely heat-resistant syn- thetic fibers. They are fibers in which the fiber-forming substance is a long-chain aromatic polymer having been recurring imidazole groups as one of the main structural repeat units in the polymer backbone.

Figure 12.11 Zylon molecular structure [26]. Advanced bulletproof and stab- and spike-resistant textiles 273

Figure 12.12 Molecular structure of PBI fibers.

PBI (Fig. 12.12) is prepared from an aromatic tetra amine and an aromatic dicarboxylic acid or a derivative of it. The resin is then spun into fibers via a dry spinning process using dimethyl acetamide as a solvent. Due to the fully aromatic structure, PBI has a very high glass transition temperature (425°C) and no melting point. Its heat deflection temperature at 1.8 MPa is about 435°C. The fiber also possesses outstanding heat stability and chemical resistance, including alcohols, hydrocarbons, chlori- nated solvents, hydrogen sulfide, weak acids and bases, and many other chemicals. Its decomposition temperature is more than 700°C.

12.4 Fabric structure of soft body armor 12.4.1 Woven fabrics Apart from the high-modulus and high-strength properties of constituent yarns, the construction is what gives a fabric its unique ballistic resistance mechanism [9]. Woven fabrics are the most commonly used fabric structure in the soft body armor. These types of fabrics stop projectiles by forming a network of fiber or yarns. This network enables the fiber or yarns to be stretched, transmitting projectile kinetic energy to the fabric [28]. Plain and basket weave patterns are typically used for ballistic application. When a projectile strikes a layer of fabric, the fabric deflects trans- versely and the mesh of yarns is distended, resulting in the enlargement of the spaces between yarns as shown in Fig. 12.13. If the fabric is not too tight, and the projectile is relatively small and impacts at an angle, only a few yarns in front of the projectile break, the projectile can slip through the opening or “wedge through” by pushing yarns forward instead of breaking them. The number of broken yarns is less than the number of yarns that intersect the projectile. Therefore, lateral movement of the yarns results in less energy absorption [9]. Yarn crimp is a distinct feature in woven fabric, and it is not observed in unidirectional structures or felt. Yarn crimp is the undulation of the yarns 274 Advances in Functional and Protective Textiles

Figure 12.13 Wedge-through phenomenon [9]. caused by yarn interlacing. When a projectile strikes a fabric, the initial stage of fabric deformation gives rise to the straightening of crimped yarns. The de-crimping process reduces the modulus of the fabric at the first stage of tensile stretching [29], during which little resistance is presented to the projectile and almost no energy absorption occurs. The fabric does not function as protection until the yarns finish decrimping and begin to stretch [30].The yarns of a more crimped structure need more time to decrimp during the ballistic impact event (B100 µs)andhencearebrokenbeforethesufficient elongation is reached, that is, before they absorb potentially maximum energy [9].Chitrangad[31] proposed using weft yarns that had a longer elongation to break than the warp yarns, so that both warp and weft yarns would fail at the same moment, reducing the effect of yarn crimp. The resulting hybridized weave was found to have a higher V50 velocity than weaves composed entirely of identical yarn's material.

12.4.2 Unidirectional fabrics The unidirectional technology is based on the idea of combining the cross- plied filaments with an elastomer matrix in a laminated system. Fig. 12.14 shows a four-plied unidirectional system laminated by two films. DSM and Park Technologies provide similar fabrics for personnel protection. The unidirectional structure does not exhibit the initial decrimping phenomenon because the crimp is removed and the yarn profile in the unidirectional fabric is straight. Therefore, the high modulus of the fiber is retained in the fabric. The fibers will react quicker with laminate stiffness coupled with fiber stiffness and spread energy to a greater extent. The woven structure, however, is more compliant. This would prolong the Advanced bulletproof and stab- and spike-resistant textiles 275

Figure 12.14 Unidirectional structure. duration of fiber stretching and leads to blunter trauma underneath the impact zone [32]. The main superior performances of the UD structure over a woven structure are as follows: 1. There was around 30% improvement in either weight or performance in both flexible armor and hard composites [32]. 2. The ballistic limit for angle-plied laminates gives a higher value than woven fabricÀbased composites as the density of the panel increases [33]. 3. A 100% UD fabric panel absorbs 12.5%À16.5% more energy than a 100% woven fabric panel [34].

12.4.3 Nonwoven and knitted structures The use of nonwoven in ballistic protection is effective in capturing low- speed fragments by having some of the fibers prealigned along the projectile trajectory. Nevertheless, the current threat regarding the ballistic impact is for small projectiles at high velocity [30]. However, there have been reports of the superiority of the needle felt nonwoven nylon (18.5 kg Á cm/g) with inferior energy absorption over woven nylon (29.2 kg Á cm/g) [35].

12.4.4 Panel systems The comparison between the multilayer structure and fabrics with the backing layer showed that the spaced armor system gives better performance than the layered system except for the flat-nosed projectiles. They also concluded that the benefit of reinforcement is largely highly dependent on the impact velocity and projectile nose shape [36]. This is sup- ported by Porwal and Phoenix’s theoretical work. They developed an analytical model to study the response of materials in a double-plied Kevlar and spectra armor system. They observed that the V50 degraded progressively as the spacing of the layers increase when compared with the system without spacing [37]. 276 Advances in Functional and Protective Textiles

Cunniff also suggested that the subsequent plies of fabric may constrain the transverse deflection the front plies, which is considered to affect the performance of a panel. As a result, he believed that placing low modulus materials on the impact face and high modulus on the next ply may improve the performance of the ballistic panel [28]. When a composite panel is under impact, the projectile tends to exhibit through-the- thickness shear failure in the front layers, forming a plug; for back layers, the fiber damage mode resembles tensile failure [38]. One notable step to achieve design of hybrid panels is the combination of UD fiber-reinforced laminates with woven fabrics. Hybrid panels formed by UD fabrics and woven fabrics show better performance than single-phase panels [30].

12.5 Body armor systems, including stab and spike vests The main role of the material used in the protection against stab and spike is to prevent weapons from passing through them and penetrating the skin [39]. Stab-resistant body armor systems should provide the required protection against edged weapons such as knives, whereas spike-resistant body armor systems protect from pointed weapons, while ensuring the unre- stricted movement of the wearer (Fig. 12.15). In addition to stab and puncture protection, when selecting a body armor, requirements for comfort, flexibility, and other ergonomic issues should also be considered to ensure its acceptance, along with the second- ary factors of concealment, duration of wear, and climatic conditions. The liquid moisture transport properties of a fabric are closely associated with its comfort properties and can be reflected by a combination of air

Figure 12.15 Various stabbing weapons: (AÀC) domestic knives, (D) lock knife, (E) sheath knife, (F) combat blade, (G) pointed weapon, (H) dagger, (I) awl, and (J) screw driver [40]. Advanced bulletproof and stab- and spike-resistant textiles 277 permeability, thermal resistance, and moisture vapor evaporation, which are also governed by some structural factors [41]. Another aspect of comfort or tactile comfort is the sensation of clothing on the skin. The type of fiber, chemical finish, type of fabric, and fabric structure affect the tactile comfort. In addition, it can be affected by the tightness and heaviness of the clothing. If the clothing is hard or stiff, the wearer feels prickling or irritation when worn next to the skin [40,42]. The armor should be evaluated for the freedom of movement, appro- priateness of the design (overlap between jacket and trousers, arm length), and compatibility with other equipment worn. As stab and spike vests tend to be manufactured from multiple layers of materials, such as laminated fabrics, ergonomic issues can be more challenging [40]. The recent advancements in 3D body scanning technology can help to avoid the fit issues and help to produce customized armor for each individual. This can avoid the problems and difficulties associated with the traditional process of measurement and manual pattern development [43]. A recent review discussed the use of nano additives for stab and spike protection. Future armor will use the nano additives such as carbon nano- spheres, carbon nanotubes, and the structures of nanofibers to improve stab and spike protection [44].

12.5.1 Materials used in stab and spike vests The materials used for stab protection take on many forms. Most are based on technical textile fibers and fabrics. Some include the use of a polymeric matrix resin with a fabric. Some use active ingredients like shear-thickening fluids. Others include metallic elements in the form of chain mail or mosaics of small, triangular, metal stampings, as in the commercial product known as Turtleskin (Fig. 12.16). All material groups are reviewed in Table 12.3.

Figure 12.16 Technical fabrics: (A) Turtleskin, (B) chain mail, and (C) and metallic stab and spike vests. 278 Advances in Functional and Protective Textiles

Table 12.3 Material used in stab and spike vests [40]. Type Properties Textile Woven (1) Higher yarn packing density solution fabrics (2) Crimp (formed due to intersection of warp and weft threads) (2) Poor in-plane shear resistance (2) Reduced tensile and compressive properties compared to the structures that are free from crimp, such as UD fabrics or cross-ply laminates Nonwoven (1) Needle, punching density, hot-pressing fabrics temperature, and hot-pressing duration affect the mechanical and puncture resistance of the nonwovens. Flexible and light weight (1) UD fabrics have excellent energy absorption characteristics and low-specific weight (1) The impact stress is propagated on the fabric plane, with minimal transmission to the back of the fabric layers Knitted (1) Knitted fabrics are comparatively flexible and fabrics hence provide more wear comfort than woven and nonwoven (1) The use of knitted structures in protective material for stab can be beneficial in terms of weight, flexibility in design especially for neat shape female body armor Coated (1) The coating can be applied as a lightly tacked fabrics plastic film on one side of the fabric, or the fabric can be totally impregnated with the resin such that the fabric becomes one ply of fiber- reinforced resin, as in structural composite materials (1) The combination of coating of high- performance hard material and high tenacity fiber woven fabrics can improve the stab and slash protection (1) The use of ceramic coating increases the inter fiber friction, which prevents wave distortion and delamination during stabbing (1) The coating of the hard material blunts the sharp metal blades by abrasive action, which prevents the cutting action of the knives, and the high friction between the ceramic coating and the metal blade reduces/minimizes the knife penetration

(Continued) Advanced bulletproof and stab- and spike-resistant textiles 279

Table 12.3 (Continued) Type Properties Composites (1) Composites that are less bulky, more flexible, and resistant to puncture (1) The impregnation of films into the fabric dramatically increased the puncture resistance during quasi-static and dynamic testing with spikes (2) Composites are often not comfortable due to lower flexibility and poor thermal management properties STF-treated (1) The impregnation of STF into the fabric fabrics structure can help in increasing the stab and puncture resistance with little or no increase in the thickness or stiffness of these fabrics (1) The hardening process occurs in milliseconds, and the armor becomes flexible again shortly afterward (1) Dramatic improvements in puncture resistance (spike threat) under high- and low-speed loading conditions (2) A slight increase in cut protection (knife threat) Metal Chain mail (2) Because of their open structure, chain mail does solution not have very high puncture resistance Titanium and stainless steel are the key materials for preparing chain mail (2) Titanium foil can also be used for both puncture and cut resistance. However, they are poor in ballistic resistance and comparatively heavy Turtleskint, manufactured from high strength metals like titanium or stainless steel; they form a continuous metallic layer that immediately blunts or deflects the attacking weapon (1) An integrated backing or encapsulating, fiber- reinforced polymeric material completes the product 280 Advances in Functional and Protective Textiles

12.6 New generation of soft body armor 12.6.1 Bullet-proof vests using shear thickening fluid In soft body armors, approximately 20À50 layers of Kevlar woven fabrics are used to stop a bullet fired by a shotgun or a revolver. This means the heavy, inflexible, and uncomfortable body armor to the wearer. It is a challenge for the researchers to develop light-weight, flexible, and bullet- resistant soft body armor via new materials such as shear thickening fluid (STF) [45]. Shear thickening is a non-Newtonian behavior often observed in concentrated colloidal dispersions, which show a drastic in viscosity beyond a critical shear rate [46,47]. Thus, the liquid dispersion is transformed into solid-like properties and thereby facilitating the impact energy absorption. STF is exhibited by the nano-sized particles of certain materials (silica, calcium carbonate, poly methyl methacrylate, etc.) when they are dispersed in a career fluid. Shear thickening behavior is reversible, making the body armor flexible enough for normal mobility of the soldier [45]. Microstructure in hard-sphere colloidal suspensions and relationship between viscosity and shear stress is shown in Fig. 12.17. In equilibrium, random collision prevents flow, increasing shear rate forces to organize into layers and viscosity lowers. Yet, a higher shear rate interparticle interaction dominates over stochastic ones, and there occurs the formulation of hydroclusters, which increases viscosity [48].

Figure 12.17 Shear thinning versus shear thickening fluids [49]. Advanced bulletproof and stab- and spike-resistant textiles 281

The US Army has shown great interest in STFs. They found that impregnating Kevlar fabrics with STF improved its ballistic performance. The suspension of silica particles (average particle diameter B446 nm) in ethylene glycol is the most suitable STF for this application. The silica particles were predispersed in methanol and then blended with ethylene glycol. Afterward, the dispersion was treated by homogenization for 1 h and sonication for 10 h to improve the dispersibility. The best way to include STF into a body armor vest is to impregnate it into Kevlar fabrics. First, the fabrics are immersed in the prepared STF, after wetting, squeezed by a two-roll mangle to set the specific wet pick up and to improve the STF infiltration. At the end, the fabrics are dried in a vacuum oven at 65°C for 20 min [46,50]. Decker et al. investigated the stab resistance STF-treated fabrics. Both Nylon and Kevlar fabrics with plain-woven fabrics of various yarn counts were tested to determine the effect of fiber properties on overall STFÀfabric response [51]. STFs were generated by dispersing colloidal silica particles (average diameter B450 nm) in 200 Mw polyethylene glycol at a volume fraction of approximately 52% [52]. To fabricate the STFÀfabric composites, the STF was first diluted in ethanol at a 3:1 volume ratio of ethanol:STF. Individual fabric layers, each measuring 38.1 cm 3 38.1 cm, were then soaked in the solution for 1 min, squeezed to remove excess fluid, and dried at 65°C for 30 min. STF addition is greatest, at 27.7%, for the highest yarn count fabric (LD Nylon) and is lowest at 19.5% for the lowest yarn count fabric (HD Nylon). These STFÀfabrics were then arranged into multilayer targets. The quasistatic knife testing results show that at slow loading rates the presence of STF greatly improves the cut resistance of the Kevlar fabric. The STFÀKevlar target exceeded the performance of the neat Kevlar target even though the STFÀKevlar target had 20% fewer fabric layers. The mechanism for this enhancement can be attributed to a decrease in yarn mobility within the fabric. The STF acts to restrict relative motion of the filaments and yarns, which prevents the sharp tip of the spike from pushing aside yarns and filaments and penetrating between them. The Nylon studies show that yarn denier and count have very little influence on cut performance. In contrast, puncture resistance increases measurably as yarn deniers decrease (yarn count increases) [51,53]. Two independent mechanisms are likely responsible for this trend. Most importantly, higher yarn count fabrics restrict yarn mobility, analogous to the effects of adding STF to neat fabrics. Secondarily, since the low denier 282 Advances in Functional and Protective Textiles fabrics have lower areal densities, the number of plies in targets of fixed areal density increases as yarn deniers decreased (the LD Nylon target had 13 layers, while the HD Nylon target had 6 layers). This increased layer count introduces increased inter-ply interfaces, which could enhance the ability of the target to defeat the impactor. Comparing Nylon and Kevlar performances, the Nylon fabrics are more likely to stretch, allowing the penetrator to travel through the fabric and then reversibly recover after the penetrator is removed. The Nylon fabrics are also more likely to exhibit yarn fracture, as compared with the Kevlar fabrics, due to their lower tenacity. The Nylon studies also demonstrate that the beneficial effects of STF addition are not restricted to aramid (Kevlar) fabrics [51].

12.6.2 Graphene body armor Graphene is another material of carbon nanotechnology, also known as one of the strongest materials ever tested [54,55]. Graphene’s tensile wave speed in plane, which is about 21.3 km/s, much higher than the 17.5 km/s of diamond, offers the best penetration resistance and the fastest spread of impact loading energy [56]. Recently, the dynamic mechanical behavior of 10À100 nm multilayer graphene was studied at high strain rate of 107/s, the penetration energy was 10 times higher than the macroscopic steel sheets [57]. The failure strain (εmax) of graphene is also considered very high with a calculated value of 0.25À0.30 [58],whereasmaxi of conventional fibril armors is typically lower than 0.04 [55]. Therefore, graphene will defi- nitely be one of the best materials used to fabricate the future body armors. Graphene is the replacement of Kevlar in bulletproof vests (Fig. 12.18).

Figure 12.18 Schematic of a graphene deformed by the impact of a bullet [60]. Advanced bulletproof and stab- and spike-resistant textiles 283

Graphene has attracted a considerable attention for its superior performance as composite reinforcement owing to outstanding mechanical properties [59]. Aramid fibers used for bulletproofing have many flaws in design and performance. The vests help little in dispersing and dissipating the force applied to the wearer once the bullet has been stopped. This is a huge issue since large rounds will exert massive amounts of force on the body, even without penetration, that can easily rupture internal organs. There is also a very large chance that high velocity or large caliber rounds will penetrate the vest completely, as most are designed to stop pistol rounds, which possess much less kinetic energy and are therefore more easily absorbed by the vests [61,62]. While graphene sheets have proven themselves to be more than capable of stopping a speeding bullet, there is yet another form of the wonder material that may be even more effective. Researchers at the University of Wollongong in Australia have recently discovered a composite material of graphene and carbon nanotubes that has proven to be stronger than Kevlar [63].

12.7 Body armor performance standards The NIJ began testing and deciding on what the ballistic and stab resistance criteria should be for body armor in the mid-1970s. The NIJ’s performance standards mean that commercially available body armor meets the minimum performance requirements they set forth. The NIJ publishes their ballistic and stab resistance standards for personal body armor, which are listed in Table 12.4. Personal body armor covered by this standard is classified into five types (IIA, II, IIIA, III, and IV) by the level of ballistic performance [64].

12.7.1 Type IIA (9 mm; 0.40 S&W) Type IIA armor that is new and unworn shall be tested with 9 mm Full Metal Jacketed Round Nose (FMJ RN) bullets with a specified mass of 8.0 g (124 gr) and a velocity of 373 6 9.1 m/s (1225 6 30 ft/s) and with 0.40 S&W FMJ bullets with a specified mass of 11.7 g (180 gr) and a velocity of 352 6 9.1 m/s (1155 6 30 ft/s). Type IIA armor that has been conditioned shall be tested with 9 mm FMJ RN bullets with a specified mass of 8.0 g (124 gr) and a velocity of 355 6 9.1 m/s (1165 6 30 ft/s) and with 0.40 S&W FMJ bullets with a 284 Advances in Functional and Protective Textiles

Table 12.4 NIJ Standard 0108.01 Ballistic resistant protective materials [65].

specified mass of 11.7 g (180 gr) and a velocity of 325 6 9.1 m/s (1065 6 30 ft/s).

12.7.2 Type II (9 mm; 0.357 Magnum) Type II armor that is new and unworn shall be tested with 9 mm FMJ RN bullets with a specified mass of 8.0 g (124 gr) and a velocity of 398 6 9.1 m/s (1305 6 30 ft/s) and with 0.357 Magnum Jacketed Soft Point (JSP) bullets with a specified mass of 10.2 g (158 gr) and a velocity of 436 6 9.1 m/s (1430 6 30 ft/s). Type II armor that has been conditioned shall be tested with 9 mm FMJ RN bullets with a specified mass of 8.0 g (124 gr) and a velocity of Advanced bulletproof and stab- and spike-resistant textiles 285

379 6 9.1 m/s (1245 6 30 ft/s) and with 0.357 Magnum JSP bullets with a specified mass of 10.2 g (158 gr) and a velocity of 408 6 9.1 m/s (1340 6 30 ft/s).

12.7.3 Type IIIA (0.357 SIG; .44 Magnum) Type IIIA armor that is new and unworn shall be tested with 0.357 SIG FMJ Flat Nose (FN) bullets with a specified mass of 8.1 g (125 gr) and a velocity of 448 6 9.1 m/s (1470 6 30 ft/s) and with 0.44 Magnum Semi Jacketed Hollow Point (SJHP) bullets with a specified mass of 15.6 g (240 gr) and a velocity of 436 6 9.1 m/s (1430 6 30 ft/s). Type IIIA armor that has been conditioned shall be tested with 0.357 SIG FMJ FN bullets with a specified mass of 8.1 g (125 gr) and a velocity of 430 6 9.1 m/s (1410 6 30 ft/s) and with 0.44 Magnum SJHP bullets with a specified mass of 15.6 g (240 gr) and a velocity of 408 6 9.1 m/s (1340 6 30 ft/s).

12.7.4 Type III (rifles) Type III hard armor or plate inserts shall be tested in a conditioned state with 7.62 mm FMJ; steel jacketed bullets (U.S. Military designation M80) with a specified mass of 9.6 g (147 gr) and a velocity of 847 6 9.1 m/s (2780 6 30 ft/s). Type III flexible armor shall be tested in both the “as new” state and the conditioned state with 7.62 mm FMJ, steel jacketed bullets (U.S. Military designation M80) with a specified mass of 9.6 g (147 gr) and a velocity of 847 6 9.1 m/s (2780 6 30 ft/s). For a type III hard armor or plate insert that will be tested as an in conjunction design, the flexible armor shall be tested in accordance with this standard and found compliant as a stand-alone armor at its specified threat level. The combination of the flexible armor and hard armor/plate shall then be tested as a system and found to provide protection at the system’s specified threat level. NIJ-approved hard armors and plate inserts must be clearly labeled as providing ballistic protection only when worn in conjunction with the NIJ-approved flexible armor system with which they were tested.

12.7.5 Type IV (armor piercing rifle) Type IV hard armor or plate inserts shall be tested in a conditioned state with 0.30 caliber armor piercing (AP) bullets (US Military designation 286 Advances in Functional and Protective Textiles

M2 AP) with a specified mass of 10.8 g (166 gr) and a velocity of 878 6 9.1 m/s (2880 6 30 ft/s). Type IV flexible armor shall be tested in both the “as-new” state and the conditioned state with 0.30 caliber AP bullets (US Military designation M2 AP) with a specified mass of 10.8 g (166 gr) and a velocity of 878 6 9.1 m/s (2880 6 30 ft/s) [64].

12.8 Future trends and challenges of soft body armor Among the next challenges in body armor production is the production ofalighter-weightvestthatprovidesmaximumcomfortaswellasopti- mal protection to the wearer. Such vests will require soft, lightweight, and flexible ballistic-resistant materials. Those materials must resist the adverse effects of aging, wear, and exposure to various environmental factors (e.g., humidity, moisture, extreme temperature, ultraviolet light). Eventually, such materials could be incorporated into armor designs at the threat level IIIA. The evolution of modern body armor systems is highly dependent not only on new armor materials being produced but also on the conscious and decisive use of precise and evolved design principles. The next generation of bulletproof vests seems to be able to monitor people's biological symptoms and send information in addition to protect- ing people from projectiles. It is better to give this generation of protective clothing the name of smart body armor.

References [1] Mansoor P. Armour, protective clothing. Available from: https://www.britannica. com/topic/armour-protective-clothing. [accessed 24.11.19]. [2] Croft J, Longhurst D. HOSDB body armour standards for UK police. Part 3: knife and spike resistance. St Albans: Home Office Scientific Development Branch; 2007. [3] Horsfall I. Stab resistant body armour. Cranfield University, engineering systems department, submitted for the award of PhD; 2000. [4] Horsfall I. Key issues in body armour: threats, materials and design. Advances in military textiles and personal equipment. UK: Woodhead Publishing; 2012. p. 3À20. [5] Fernando E, et al. Design of a bullet-proof vest using shear thickening fluid. Int J Adv Sci Tech Res 2015;1(5):434À44. [6] Alexandropoulou C-A, Panagiotopoulos E. Wound ballistics: analysis of blunt and penetrating trauma mechanisms. Health Sci J 2010;4(4):225. [7] R.P. Kness. E.-P. Gunshot wounds. INHS Health Training. 2007. Available from: https://healthtraining.inhs.org/uploadedFiles/EMS_Live_at_Nite/2007/ April_10_2007/April%2007%20Handout.pdf. [accessed 26.11.19]. Advanced bulletproof and stab- and spike-resistant textiles 287

[8] Chen X, Zhou Y. 6—Technical textiles for ballistic protection. In: Horrocks AR, Anand SC, editors. Handbook of technical textiles. 2nd ed. Cambridge, England: Woodhead Publishing; 2016. p. 169À92. [9] Dimeski D, Srebrenkoska V, Mirceska N. Ballistic impact resistance mechanism of woven fabrics and their composites. Int J Eng Res Technol 2015;4(12):107À12. [10] Bajaj P. Ballistic protective clothing: An overview. Indian J Fibre Text 1997;22:274À91. [11] Ruys A. 11—Alumina in lightweight body armor. In: Ruys A, editor. Alumina cera- mics: Biomedical and clinical applications. Woodhead Publishing; 2018. p. 321À68. [12] King L. Lightweight body armor. Quartermaster Review MarchÀApril 1953. Reprinted from the JanuaryÀFebruary Ordnance. 2011. [13] Ian C. The science of armor materials. Woodhead Publishing; 2016. [14] Hirschler MM. Safety, health and environmental aspects of flame retardants. Handbook of fire resistant textiles. Woodhead Publishing; 2013. p. 108À73. [15] Yang H. Kevlar aramid fiber. Wiley: the University of Michigan; 1993. [16] Tam T, Bhatnagar A. 9ÀHigh-performance ballistic fibers. In: Wilusz E, editor. Military textiles. Cambridge, England: Woodhead Publishing; 2008. p. 207À28. [17] Teijin Aramid. What is aramid? Available from: https://www.teijinaramid.com.p.4. [18] Tam T, Bhatnagar A. 7—High performance ballistic fibers. In: Bhatnagar A, editor. Lightweight ballistic composites. Woodhead Publishing; 2006. p. 189À209. [19] Kitagawa T, Ishitobi M, Yabuki K. An analysis of deformation process on poly-p- phenylenebenzobisoxazole fiber and a structural study of the new high-modulus type PBO HM 1 fiber. J Polymer Sci Part B Polymer Phys 2000;38(12):1605À11. [20] Karahan M. Comparison of ballistic performance and energy absorption capabilities of woven and unidirectional aramid fabrics. Textil Res J 2008;78(8):718À30. [21] Johnson T. How is carbon fiber made? The manufacturing process of this lightweight material. 2019. Available from: https://www.thoughtco.com/how-is-carbon-fiber- made-820391. [22] Schorr, J., et al. Source assessment: pressed and blown glass manufacturing plants. 1977. [23] Production carbon fibers materials chemistry. Available from: http://web.mit.edu/ 3.082/www/team2_f01/chemistry.html. [accessed 14.11.19]. [24] Tam T, Bhatnagar A. 1—High-performance ballistic fibers and tapes. In: Bhatnagar A, editor.Lightweightballisticcomposites.2nded.WoodheadPublishing;2016.p.1À39. [25] Cunniff P.M., et al. High performance “M5” fiber for ballistics/structural composites. In 23rd Army Science Conference. 2002. Citeseer. [26] ZYLONs (PBO fiber) Technical Information. 2005. Toyobo CO., Ltd. p. 1. Available from: https://www.toyobo-global.com/seihin/kc/pbo/zylon-p/bussei-p/technical.pdf. [27] O'Neil JM. Factors contributing to the degradation of poly (p-phenylene benzobisoxazole) (PBO) fibers under elevated temperature and humidity conditions. MSc Thesis, Texas A&M University; 2006. [28] Cunniff PM. An analysis of the system effects in woven fabrics under ballistic impact. Textil Res J 1992;62(9):495À509. [29] Hu J, Xin B. Structure and mechanics of woven fabrics. Structure and mechanics of textile fibre assemblies. Cambridge: Woodhead Publishing; 2008. p. 48À83. [30] Zhou Y. Development of lightweight soft body armour for ballistic protection. United Kingdom: The University of Manchester; 2013. [31] Chitrangad S. Hybrid ballistic fabric. 1993. United States Patent, (5,187,003). [32] Scott B. New ballistic products and technologies. Lightweight ballistic composites. Woodhead Publishing; 2006. p. 336À63. [33] Lee B, Song J, Ward J. Failure of Spectras polyethylene fiber-reinforced composites under ballistic impact loading. J Compos Mater 1994;28(13):1202À26. 288 Advances in Functional and Protective Textiles

[34] Roylance D, Wilde A, Tocci G. Ballistic impact of textile structures. Textil Res J 1973;43(1):34À41. [35] Hearle J, Sultan M. Research on a basic study of the high-speed penetration dynam- ics of textile materials. United Kingdom: University of Manchester Institute of Science And Technology; 1974. [36] Lim C, Tan V, Cheong C. Perforation of high-strength double-ply fabric system by varying shaped projectiles. Int J Impact Eng 2002;27(6):577À91. [37] Porwal P, Phoenix S. Effects of layer stacking order on the V 50 velocity of a two- layered hybrid armor system. J Mech Mater Struct 2008;3(4):627À39. [38] Cheeseman BA, Bogetti TA. Ballistic impact into fabric and compliant composite laminates. Compos Struct 2003;61(1À2):161À73. [39] Cooper G, Gotts P. Ballistic protection. In Ballistic trauma: A practical guide. London Limited: Springer-verlag; 2005. p. 67À90. [40] Nayak R, et al. Body armor for stab and spike protection, Part 1: Scientific literature review. Textil Res J 2018;88(7):812À32. [41] Yoo S, Barker RL. Comfort properties of heat resistant protective workwear in varying conditions of physical activity and environment. Part II: perceived comfort response to garments and its relationship to fabric properties. Textil Res J 2005;75(7):531À9. [42] Barker RL. From fabric hand to thermal comfort: the evolving role of objective measurements in explaining human comfort response to textiles. Int J Cloth Sci Technol 2002;14(3/4):181À200. [43] Simmons KP, Istook CL. Body measurement techniques: comparing 3D body- scanning and anthropometric methods for apparel applications. J Fash Market Manage Int J 2003;7(3):306À32. [44] Bilisik K. Two-dimensional (2D) fabrics and three-dimensional (3D) preforms for ballistic and stabbing protection: a review. Textil Res J 2017;87(18):2275À304. [45] Majumdar A, Butola BS, Srivastava A. Optimal designing of soft body armour materials using shear thickening fluid. Mat Design 2013;46:191À8. [46] Lee YS, Wetzel ED, Wagner NJ. The ballistic impact characteristics of Kevlars woven fabrics impregnated with a colloidal shear thickening fluid. J Mat Sci 2003;38 (13):2825À33. [47] Wagner NJ, Brady JF. Shear thickening in colloidal dispersions. Phys Today 2009;62 (10):27À32. [48] Krajnc A. Shear thickening in colloidal dispersions. Slovenia: University of Ljubljana; 2011. [49] Norm Wagner JB. Shear thickening in colloidal dispersions. 2009. Available from: https://physicstoday.scitation.org/doi/10.1063/1.3248476. [accessed 14.03.20]. [50] Kang TJ, Hong KH, Yoo MR. Preparation and properties of fumed silica/Kevlar composite fabrics for application of stab resistant material. Fibers Polymers 2010;11 (5):719À24. [51] Decker M, et al. Stab resistance of shear thickening fluid (STF)-treated fabrics. Composites Sci Technol 2007;67(3À4):565À78. [52] Decker M, et al. Low velocity ballistic properties of shear thickening fluid (STF)À fabric composites. Proceedings of 22nd International Symposium on Ballistics, Vancouver, BC, Canada. PA: DESTech Publications Lancaster; 2005. [53] Wagner NJ. Novel flexible body armor utilizing shear thickening fluid (STF) composites. 14th International Conference on Composite Materials San Diego, CA, 2003. [54] Liu P, Strano MS. Toward ambient armor: can new materials change longstanding concepts of projectile protection? AdvFunctional Mat 2016;26(6):943À54. [55] Benzait Z, Trabzon L. A review of recent research on materials used in poly- merÀmatrix composites for body armor application. J Composite Mat 2018;52 (23):3241À63. Advanced bulletproof and stab- and spike-resistant textiles 289

[56] Robbins J, Ding J, Gupta Y. Load spreading and penetration resistance of layered structures—a numerical study. Int J Impact Eng 2004;30(6):593À615. [57] Lee J-H, et al. Dynamic mechanical behavior of multilayer graphene via supersonic projectile penetration. Science 2014;346(6213):1092À6. [58] Cadelano E, et al. Nonlinear elasticity of monolayer graphene. Phys Rev Lett 2009;102(23):235502. [59] Lee C, et al. Measurement of the elastic properties and intrinsic strength of monolayer graphene. Science 2008;321(5887):385À8. [60] Graphene Armour Turns Harder Than Diamond. Popular culture Research. 2019. Available from: https://grapheneindustry.org.au/2019/03/graphene-armour-turns- harder/. [61] Dixit A, Dixit D, Chandrodaya VV, Kajla A. Graphene: A new era of technology. Int. J. Emerging Technol. Adv. Eng. 2013;3:4À7. [62] Milne S. Developments in bullet proof materials using nanotechnology. Available from: http://www.azonano.com/article.aspx?ArticleID 5 3934. [accessed 12.08.14]. [63] Shin MK, et al. Synergistic toughening of composite fibres by self-alignment of reduced graphene oxide and carbon nanotubes. Nat Communicat 2012;3(1):650. [64] Standard-0101.06. Ballistic Resistance of Body Armor NIJ, U.S. Department of Justice Office of Justice Programs National Institute of Justice, 2008. [65] Standard N. 0108.01: Ballistic resistant protective materials. US Department of Justice. National Institute of Justice; 1985. 本文献由“学霸图书馆-文献云下载”收集自网络，仅供学习交流使用。

学霸图书馆（www.xuebalib.com）是一个“整合众多图书馆数据库资源，

提供一站式文献检索和下载服务”的24 小时在线不限IP 图书馆。图书馆致力于便利、促进学习与科研，提供最强文献下载服务。

图书馆导航：

图书馆首页文献云下载图书馆入口外文数据库大全疑难文献辅助工具