Modified Epoxy Resin on the Burning Behavior and Mechanical Properties of Aramid Fiber Composite

Aramid fiber/epoxy resin (AF/EP) composite has been heavily used as an impact protection material due to its excellent mechanical properties and lightweight merits. Meanwhile, it is also necessary to concern the flammability of matrix resin and the wick effect of aramid fiber, which would constitute a fire risk in harsh environments. In this work, a multifunctional flame-retardant modifier (EAD) was incorporated into the AF/EP system to improve the flame retardation. The addition of 5 wt% EAD made the AF/EP composite exhibit a high limiting oxygen index (LOI) value of 37.5%, self-extinguishment, as well as decreased total heat release and total smoke release. The results from thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA) demonstrated that the treated composites maintained good thermal stability. Due to the combined action of covalent and noncovalent bonds in the matrix-rich region, the interfacial bonding improved, which endowed AF/EP composite with strengthening and toughening effects. Compared with the control sample AF/EP, the tensile strength and ballistic parameter (V50) of the sample with 5 wt% EAD increased by 17% and 10%, accompanied with ductile failure mode. Furthermore, the flame-retardant mechanism was obtained by analyzing the actions in condensed and gaseous phases. Thanks to good compatibility and interfacial adhesion, the incorporation of EAD solved the inconsistent issue between flame retardancy and mechanical properties, which further expanded the application of AF/EP composite in the protection field.

Structural Design and Performance of Cut-Resistant Fabrics with Concave-Convex Arrays

As the risk of social security increases, it is crucial to develop flexible protective materials that combine flexibility with high protective performance. Ultra-high-molecular-weight polyethylene (UHMWPE) was selected as the raw material, and four types of flat-knitting cut-resistant fabrics were ultimately designed and prepared from a three-dimensional longitudinal dimension and concave-convex array structure based on rib knitting. A series of experiments must be conducted on fabrics in order to study the law of protection performance of different structural fabrics. They were thus subjected to comprehensive evaluation and theoretical analysis of cut resistance. The results demonstrate that the four structural fabrics exhibited resilience in abrasion tests, withstanding over 100,000 cycles without failure. A weighting algorithm was employed to determine the comprehensive cutting resistance of the S1, S2, S3, and S4 structural fabrics, resulting in values of 1939.9 gf, 2298.6 gf, 2577.1 gf, and 2822.2 gf, respectively. Therefore, S1 reached class A4, which is sufficient to address a medium cut hazard. Similarly, S2, S3, and S4 reached class A5, which is adequate to address a high cut hazard. The obtained fitting equation, with uniform yarn fineness T as the dependent variable, demonstrates that the cut resistance improved as the concave-convex density level increased.

Hybrid Soft Ballistic Panel Packages with Integrated Graphene-Modified Para-Aramid Fabric Layers in Combinations with the Different Ballistic Kevlar Textiles

The purpose of the research discussed in this article is to explore the possibility of creating hybrid soft ballistic panel (BP) package variants by integrating into their composition layers of graphene-modified para-aramid fabrics in combinations with the different ballistic Kevlar textiles to improve the durability of the first layers of the soft ballistic panel. To address this goal, the liquid-phase exfoliation (LPE) method was used for integrating dispersions into composites to solve a number of topical problems in the stages of the technological sequence development of processing methods and optimizing processing parameters in accordance with the processing specifics of aramid textiles to achieve the desired properties of modified ballistic fabric, including the provision of coating adhesion to the surface to be modified. To test the results, ballistic experiments were performed and the back-face signature (BFS) of bullet impact on a backing material was analysed according to standards. Bullet impacts on the first ballistic protective fabric layers were also studied.

Shear thickening fluid (STF) in engineering applications and the potential of cork in STF-based composites

Shear thickening fluids (STFs) are a unique type of fluids that can quickly transform into a solid-like state when subjected to forces (rate dependent). These fluids are created by dispersing micro and nanoparticles within a medium. When the force is removed, they return to their original liquid state. Shear thickening fluids can absorb a significant amount of impact energy, making them useful for reducing vibrations and serving as a damper. This study provides a comprehensive and brief overview of existing literature on shear thickening fluids, including their properties, classification, and the rheological mechanisms behind the shear thickening behaviour. It also examines the use of these fluids in various applications, such as improving resistance to stabs and spikes, protecting against low- and high-velocity impacts, and as a new medium for energy dissipation in industries such as battery safety, vibration control and adaptive structures. Lastly, this work reviews the promising combination of STFs with cork. Given the sustainability of cork and its energy absorption capacity, cork-STF composites are a promising solution for various impact-absorbing applications. Overall, the paper underscores the versatility and potential of STFs, and advocates for further research and exploration.

Optimizing non-Newtonian fluids for impact protection of laminates

Non-Newtonian fluids can be used for the protection of flexible laminates. Understanding the coupling between the flow of the protecting fluid and the deformation of the protected solids is necessary in order to optimize this functionality. We present a scaling analysis of the problem based on a single coupling variable, the effective width of a squeeze flow between flat rigid plates, and predict that impact protection for laminates is optimized by using shear-thinning, and not shear-thickening, fluids. The prediction is verified experimentally by measuring the velocity and pressure in impact experiments. Our scaling analysis should be generically applicable for non-Newtonian fluid-solid interactions in diverse applications.

Optimization the Stab Resistance and Flexibility of Ultra-High Molecular Weight Polyethylene Knitted Structure Fabric with Response Surface Method

At present, the challenging issue of the compatibility between stab resistance and flexibility of materials frequently appears. Thus, this study proposes a novel method to enhance the comprehensive performance of the material matrix with stab resistance. Based on the stab-resistant mechanism analysis of the textile matrix, the influence of four factors on the performance of ultra-high molecular weight polyethylene (UHMWPE) knitted fabric was discussed. And, the optimal process conditions of material for achieving high stab resistance and high flexibility were obtained by the response surface method. A series of experiments proved that among all factors, the fabric structure had the greatest influence on the flexible stab-resistant knitted material. Following that, the thickness of the yarn also plays a significant role. Under the optimal process conditions, the stab peak force of the knitted material was promoted to 52.450 N, and the flexibility was enhanced to 93.6%. Meanwhile, through comparison with products that have undergone the same treatment, there was little difference in stab resistance but significantly improved flexibility. It achieves the initial stab resistance and comfortable wearing softness of the fabric through process optimization. This improvement in overall performance of the textile matrix enables further enhancement treatments.

Statistical approach on the inter-yarn friction behavior of the dual-phase STF/ρ-Aramid impregnated fabrics via factorial design and 3D-RSM

Shear thickening fluids (STFs) refer to non-Newtonian fluids of the dilatant variety, wherein their viscosity experiences a significant surge with an escalation in the shear rate. In this investigative work, the friction behavior between yarns (pull-out) and absorption of static and kinetic energy during the phenomenon of friction between yarns in STFs are performed by monophase (MP-STF) adding nano SiO2 and dual-phase (MP-STF) adding carbon nanotubes. The ρ-Aramid fabrics were reinforced via the "foulard process", and carried out on MP-STF, and DP-STF/ρ-Aramid-impregnated fabrics to evaluate and compare with the enhancement in interfacial friction properties between yarns. The results showed that DP-STF has more significant than MP-STF and MP-STF in ultimate load, kinetic shear stress, static shear stress, and friction energy level effects. The DP-STF exhibits various friction enhancement mechanisms at the yarn interface, leading to higher absorption of static and kinetic energy related to interfacial friction, as indicated by the results obtained. Furthermore, the DP-STF/ρ-Aramid impregnated fabrics exhibited ultimate load (22.23 ± 0.522 N), kinetic shear stress (35.73 ± 0.850 MPa*100), static shear stress (36.28 ± 0.900 MPa*100), and friction energy level (610.33 ± 0.250). Increased ultimate load (581.7% and 180.7%), kinetic shear stress (621.4% and 174.6%), static shear stress (550.5% and 159.1%), and friction energy level (680.2 and 186.7%) compared to WT-STF and MP-STF, respectively. The current discoveries hold immense potential for various applications in the fields of engineering and smart material technologies. These applications span a multiplicity of industries, including sports products, medical advancements, space technology, as well as protective and shielding products.

Anti-Ballistic Performance of PPTA/UHMWPE Laminates

Poly(p-phenylene terephthalamide) (PPTA) and ultra-high-molecular-weight polyethylene (UHMWPE) are high-performance polymer materials largely used for body armor applications. Although composite structures from a combination of PPTA and UHMWPE have been created and described in the literature, the manufacture of layered composites from PPTA fabrics and UHMWPE films with UHMWPE film as an adhesive layer has not been reported. Such a new design can provide the obvious advantage of simple manufacturing technology. In this study, for the first time, we prepared PPTA fabrics/UHMWPE films laminate panels using plasma treatment and hot-pressing and examined their ballistic performance. Ballistic testing results indicated that samples with moderate interlayer adhesion between PPTA and UHMWPE layers exhibited enhanced performance. A further increase in interlayer adhesion showed a reverse effect. This finding implies that optimization of interface adhesion is essential to achieve maximum impact energy absorption through the delamination process. In addition, it was found that the stacking sequence of the PPTA and UHMWPE layers affected ballistic performance. Samples with PPTA as the outermost layer performed better than those with UHMWPE as the outermost layer. Furthermore, microscopy of the tested laminate samples showed that PPTA fibers exhibited shear cutting failure on the entrance side and tensile failure on the exit side of the panel. UHMWPE films exhibited brittle failure and thermal damage at high compression strain rate on the entrance side and tensile fracture on the exit side. For the first time, findings from this study reported in-field bullet testing results of PPTA/UHMWPE composite panels, which can provide important insights for designing, fabricating, and failure analysis of such composite structures for body armors.

Shear Thickening Fluid and Its Application in Impact Protection: A Review

Shear thickening fluid (STF) is a dense colloidal suspension of nanoparticles in a carrier fluid in which the viscosity increases dramatically with a rise in shear rate. Due to the excellent energy absorption and energy dissipation of STF, there is a desire to employ STFs in a variety of impact applications. In this study, a comprehensive review on STFs' applications is presented. First, several common shear thickening mechanisms are discussed in this paper. The applications of different STF impregnated fabric composites and the STF's contributions on improving the impact, ballistic and stab resistance performance have also been presented. Moreover, recent developments of STF's applications, including dampers and shock absorbers, are included in this review. In addition, some novel applications (acoustic structure, STF-TENG and electrospun nonwoven mats) based on STF are summarized, to suggest the challenges of future research and propose some more deterministic research directions, e.g., potential trends for applications of STF.

Stab-Resistant Polymers-Recent Developments in Materials and Structures

Stab-resistant garments have been used for centuries, utilizing metals, paper, or polymeric structures, often inspired by natural structures such as scales. Nowadays, stab-resistant vests or vest inserts are used by police and security personnel, but also by bus drivers, ambulance officers, and other people who are empirically often attacked on duty. Since stab protection garments are often heavy and thus uncomfortable and not well accepted, whether in the form of chain-mail or metal inserts in protective vests, researchers are striving to find lightweight, drapable alternatives, often based on polymeric materials. These research attempts have recently focused on textile fabrics, mostly with impregnation by shear-thickening fluids (STFs) or ceramic coatings, as well as on lightweight composites. The first studies on 3D printed polymeric objects with tailored shapes, as well as theoretical investigations of the stab-protective effect of different materials, have been published throughout the last years. Here, we discuss different measurement methods, including dynamic and quasistatic methods, and correlations of stab-resistance with other physical properties, before we give an overview of recent developments of stab-resistant polymers, using different materials/material combinations and structures.

Fabric Impregnation with Shear Thickening Fluid for Ballistic Armor Polymer Composites: An Updated Overview

As destructive power of firearms raises over the years, ballistic armors are in continuous need of enhancement. For soft armors, this improvement is invariably related to the increase of stacked layers of high-strength fiber fabrics, which potentially restrains wearer mobility. A different solution was created in the early 2000s, when a research work proposed a new treatment of the ballistic panels with non-Newtonian colloidal shear thickening fluid (STF), in view of weight decreasing with strength reinforcement and cost-effective production. Since then, databases reveal a surge in publications generally pointing to acceptable features under ballistic impact by exploring different conditions of the materials adopted. As a result, several works have not been covered in recent reviews for a wider discussion of their methodologies and results, which could be a barrier to a deeper understanding of the behavior of STF-impregnated fabrics. Therefore, the present work aims to overview the unexplored state-of-art on the effectiveness of STF addition to high-strength fabrics for ballistic applications to compile achievements regarding the ballistic strength of this novel material through different parameters. From the screened papers, SiO2, Polyethylene glycol (PEG) 200 and 400, and Aramid are extensively being incorporated into the STF/Fabric composites. Besides, parameters such as initial and residual velocity, energy absorbed, ballistic limit, and back face signature are common metrics for a comprehensive analysis of the ballistic performance of the material. The overview also points to a promising application of natural fiber fabrics and auxetic fabrics with STF fluids, as well as the demand for the adoption of new materials and more homogeneous ballistic test parameters. Finally, the work emphasizes that the ballistic application for STF-impregnated fabric based on NIJ standards is feasible for several conditions.

Stab-Resistant Performance of the Well-Engineered Soft Body Armor Materials Using Shear Thickening Fluid

Stab-resistant body armor can effectively prevent sharp instruments from attacking the protected parts and reduce the threat to human bodies. Shear thickening fluid (STF) is a kind of smart material with variable viscosity and its viscosity can change significantly with external stimuli. The soft and adaptive characteristics of STF provide a new idea for improving the performance of stab-proof materials. In this work, three kinds of soft anti-stabbing materials were designed and prepared with aramid, poly-p-phenylene benzodioxazole (PBO), and carbon fiber fabrics impregnated with STF. Quasi-static puncture tests and dynamic impact tests were conducted to compare the performance of different anti-stabbing structures. The results showed that the peak piercing force of the STF-treated fabrics in the puncture testing was greatly increased than that of neat samples. Against the D2 knife, the maximum impact load of STF/PBO fiber fabric was increased from 55.8 N to 72.9 N, increasing by 30.6%. Against the D3 spike, the maximum impact load of STF/aramid fabric was increased from 128.9 N to 254.7 N, increasing by 197.6%. The mechanical properties of fibers were important factors for the resistance to knives, and the fabric structure was the key point to bear the spike. Optical photographs of fabric fractures and scanning electron microscope analysis indicated that the STF effectively limited the slip of the fiber bundle when the tool penetrated the fabric, which played a positive role in maintaining the tightness and integrity of the fabric structure.

Fragment-Resistant Property Optimization within Ballistic Inserts Obtained on the Basis of Para-Aramid Materials

A high protection level without an excessive weight is a basic assumption in the design of modern armors and protection systems. Optimizing armors is a task of development of the utmost importance, and is the subject of the work contained within this article. Optimization of ballistic inserts was carried out using multicriterial analysis (MCA), which enables the selection of the optimal composition, taking into account properties such as ballistic resistance, physicomechanical, and/or functional properties. For this purpose, various types of composite systems were produced and tested in terms of their fragment-resistant properties according to STANAG 2920 and the composite areal density of different ballistic inserts: Soft inserts made of Twaron® para-aramid sheets, hard ballistic inserts made of multilayer hot-pressed preimpregnated sheets, and hybrid hard ballistic inserts prepared on the basis of multilayer hot-pressed preimpregnated sheets and ceramics. The application of MCA and performance of experimental fragment resistance tests for a wide spectrum of para-aramid inserts are part of the novelty of this work. The obtained test results showed that depending on the composition of the composite system, we could obtain a wide range of fragmentation resistance in the range of 300 to >1800 m/s, which depended on the areal density and type of composite system used. The results also confirmed that MCA is a good computational tool to select the optimal design of para-aramid ballistic inserts.

Extreme Dynamic Performance of Nanofiber Mats under Supersonic Impacts Mediated by Interfacial Hydrogen Bonds

Achieving extreme dynamic performance in nanofibrous materials requires synergistic exploitation of intrinsic nanofiber properties and inter-fiber interactions. Regardless of the superior intrinsic stiffness and strength of carbon nanotubes (CNTs), the weak nature of van der Waals interactions limits the CNT mats from achieving greater performance. We present an efficient approach to augment the inter-fiber interactions by introducing aramid nanofiber (ANF) links between CNTs, which forms stronger and reconfigurable interfacial hydrogen bonds and π-π stacking interactions, leading to synergistic performance improvement with failure retardation. Under supersonic impacts, strengthened interactions in CNT mats enhance their specific energy absorption up to 3.6 MJ/kg, which outperforms widely used bulk Kevlar-fiber-based protective materials. The distinct response time scales of hydrogen bond breaking and reformation at ultrahigh-strain-rate (∼10⁷-10⁸ s^-1) deformations additionally manifest a strain-rate-dependent dynamic performance enhancement. Our findings show the potential of nanofiber mats augmented with interfacial dynamic bonds─such as the hydrogen bonds─as low-density structural materials with superior specific properties and high-temperature stability for extreme engineering applications.

Hybrid Polymer Composites Used in the Arms Industry: A Review

Polymer fiber composites are increasingly being used in many industries, including the defense industry. However, for protective applications, in addition to high specific strength and stiffness, polymer composites are also required to have a high energy absorption capacity. To improve the performance of fiber-reinforced composites, many researchers have modified them using multiple methods, such as the introduction of nanofillers into the polymer matrix, the modification of fibers with nanofillers, the impregnation of fabrics using a shear thickening fluid (STF) or a shear thickening gel (STG), or a combination of these techniques. In addition, the physical structures of composites have been modified through reinforcement hybridization; the appropriate design of roving, weave, and cross-orientation of fabric layers; and the development of 3D structures. This review focuses on the effects of modifying composites on their impact energy absorption capacity and other mechanical properties. It highlights the technologies used and their effectiveness for the three main fiber types: glass, carbon, and aramid. In addition, basic design considerations related to fabric selection and orientation are indicated. Evaluation of the literature data showed that the highest energy absorption capacities are obtained by using an STF or STG and an appropriate fiber reinforcement structure, while modifications using nanomaterials allow other strength parameters to be improved, such as flexural strength, tensile strength, or shear strength.