Yarn Pull-out Tests Research Articles

Improvement of spall liner performance with smart fluid applications

Shear thickening fluid (STF) treated textiles have been widely used in anti-impact structures in recent years. STF treatment provides an enhanced energy absorbing capacity for textiles due to increased yarn interactions within the structures. Adjacent yarns around the impact point contribute to energy distribution to far-fields. STF treated textiles show great efficiency in terms of protection even being hit at single point. From this viewpoint, these structures are expected to exhibit higher efficiencies under multi-point impacts because of their energy dissipation capabilities by the contribution of far-fields. On this basis, STF treated aramid fabrics were adapted to a secondary protective structure, namely spall liner for the first time in this study. Spall liner restrains emission of spalling pieces inside an armored vehicle and being subjected to multi-point impacts when armor is perforated by an impacting threat. In this work, STF rheology was investigated in rheological measurements. Yarn pull-out tests were carried out to investigate the effect of STF treatment on yarn interactions. To increase the yarn coupling in textiles, various amounts of silicon carbide (SiC) particles were also included in the STF treatments. A metal plate, which was impacted by a projectile in ballistic testing, was used in front of the spall liners to produce spalling pieces. The performance of the spall liners was evaluated by measuring the angle of spall emissions at the back face of the spall liners. According to the results, STF treatments enhanced yarn interactions within the spall liners. Carbide additives led to a further increase in this mechanism. For this reason, angle of spall emission was reduced from 16.9° to 10.5° by treating neat textiles with STF. This metric was restricted to 8.8° in the carbide included spall liners. By designing a 90 mm gap between the spall liner and metal plate, emission angle was lowered to 5.7°.

Mechanical properties of polytetrafluoroethylene coated glass fabrics: Influence of weave pattern and coating percentage

The present study reports the mechanical performance of polytetrafluoroethylene (PTFE) coated fabrics. Glass fabrics with two weave structures, three dimensional plain-woven knitted (3D) and satin weave (SW) were tested. These fabrics were coated with PTFE in different weight percentages (30% and 60%). Mechanical tests included uniaxial tensile, tear (double tongue and pendulum tear), puncture, yarn pull-out and low-velocity impact (LVI) tests. The influence of weave pattern and PTFE coating on these mechanical properties was investigated. In the case of yarn pull-out and tensile tests, 60% PTFE coated glass fabrics exhibited better performance due to the increased adhesive bonding and inter-yarn friction. However, the 30% PTFE coated glass fabrics exhibited better performance for tear, puncture, and LVI tests. The SW fabrics exhibited superior performance to the 3D fabrics in all the mechanical tests performed. Overall, the results indicate that SW fabrics offer better mechanical performance than 3D fabrics under different loading conditions. In terms of coating percentage, 30% PTFE coated fabrics exhibited better mechanical performance than the 60% coated ones.

Parametric study on the ballistic performance of seamed woven fabrics

The ballistic perforation response of composite fabrics made by combining plain weaves with seaming technology is reported and compared with conventional unseamed plain fabrics. The effect of the seaming technique on the ballistic resistance of aramid plain fabrics is investigated by varying the seaming process. The ballistic experiment uses 8 mm diameter spherical projectiles to impact different fabric sample targets with velocities of 230 m/s and 400 m/s. The ballistic performance of seamed and unseamed fabrics is characterized by the specific energy absorption (SEA) values of the fabrics. The results show that the seamed fabric has a better energy absorption capacity than the unseamed fabric, e.g., the SEA of sample 5 (seaming lines on every four yarns in a single-ply fabric system) is 135% of sample 1 (plain weave without thread seaming). In the single-layer system, the effect of the seaming technique on the energy absorption of the fabric in significant when considering seaming density, seaming orientation, seaming distance, and seaming material on the plain fabric; In addition, it is found that in multi-layer systems, seamed panels (e.g., sample 7) exhibit better ballistic performance than multi-layer fabrics (e.g., sample 2), and the specific energy absorption of sample 7 is approximately 156% and 200% of sample 6 and sample 2, respectively. Meanwhile, the energy absorption of the fabric decreases with the increase of impact velocity, which is related to the energy absorption mechanism of the soft fabric system at high impact velocities. The yarn pull-out tests shows that the constraint provided by the seaming thread increases the friction between the fabric-forming yarns. However, when the constraint exceeds a certain level, it is detrimental to the energy absorption of the fabric, which may be due to the over-constraint of yarn mobility.

The responses of stitched ultra-high-molecular-weight polyethylene woven fabrics upon ballistic impact

This paper investigates the influence of thread stitching on the ballistic performance of plain weaves made of ultra-high-molecular-weight polyethylene multi-filament yarns. The inter-yarn friction is increased due to the constraint imparted by the sewing thread. The yarn pull-out test shows that the peak-load force of the sample with one stitching line is almost 10 times greater than that of the unstitched plain weave, and the maximum pull-out force increases with the loading rate. Ball-bearing impact tests are performed to characterize the ballistic performance of the stitched and the unstitched samples, and finite element simulation is used to study the underlying mechanisms of energy absorption. The ballistic penetration tests show that the stitched fabrics outperform the plain weave in terms of energy absorption. The most significant improvement in ballistic performance is observed in stitched panels where sample SL2T (a triple-ply plain fabric system stitched on every two yarns) exhibits a specific energy absorption over two times greater than that of multi-ply systems consisting of plain weaves. It is also found from the high-speed photography that thread stitching constrains the yarn displacement and therefore eliminates the possibility of yarn pull-out, enabling the primary yarns to be well-engaged with the projectile at low impact velocities and to be stretched to fail at high impact velocities. Numerical predictions show that thread stitching enlarges the area of stress distribution and widens the transverse deflection, making the stitched systems absorb more energy than the unstitched system shortly after impact.

On the possibility of using Ramie – A natural material in cost-effective low threat body armours

Low intensity clashes have become the emerging crisis in society. In such situations, the protective vests worn by the law enforcing personnel are generally exposed to stabbing and low velocity impact from splinters. The present study is an attempt to explore the potential of Ramie, a natural fibre, to be used in body armours designed for relatively lesser threat (compared to military operations) encountered in low intensity conflict areas. Cultivation of Ramie plant to the preparation of Ramie fabric – the entire process is performed in a laboratory setup. Experiments (uniaxial tension test, direct shear test, yarn pull-out test, etc.) are conducted to characterize the stress–strain behaviour and inter-yarn friction of Ramie. The ballistic responses of single and multi-layered Ramie fabric targets are numerically investigated via FEM. In order to understand where Ramie stands with respect to Kevlar (a commonly used para-aramid synthetic fabric), the response of a single layer Kevlar target under similar circumstances (i.e. target size, boundary conditions, projectile types and impact velocities) is taken as the benchmark. Through the series of numerical simulations, the advantage and limitations of Ramie vis- a´- vis Kevlar are brought to an extent.

Internal friction properties of carboxylated cellulose nanofibers (CNF-C) modified aramid woven fabrics

The internal friction properties of the aramid woven fabrics modified by carboxylated cellulose nanofibers (CNF-C) were studied, in order to better investigate the effect of CNF-C on the internal friction properties of the aramid woven fabrics, the yarn pull-out force of the modified aramid fabrics were tested by single yarn pull-out test. The chemical structure and surface morphology of the aramid fibers were characterized by Fourier Transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The results show that the strong hydrogen bond between CNF-C and aramid fiber and the dipole–dipole interaction between the polar groups of the fiber (such as –NH, –C = O) and hydroxyl groups are the bond mechanism. Compared with the untreated fabrics, the yarn pull-out force and fiber surface roughness of the CNF-C modified aramid fabrics are significantly improved. When the impregnation time is 0.5 h and the CNF-C concentration is 1 wt%, the yarn pull-out force reaches the maximum of 13.3 N, which is increased by 133.3% compared with the untreated aramid fabrics. The internal friction properties of the aramid woven fabrics are obviously increased by modification.

Ballistic performance of the structure-modified plain weaves with the improved constraint on yarn mobility: Experimental investigation

This paper investigates the possibility of constraining yarn mobility and consequently improving the ballistic performance by modifying the structure of the plain weaves. The constraint on yarn mobility was characterized by the increase in the inter-yarn frictional force, which was confirmed by the yarn pull-out test. Ballistic penetration tests were performed to study the performance of plain weave and the structure-modified fabrics at impact velocities from the ballistic limit up to 400 m/s. It was found that the ballistic performance of structure-modified fabrics outperformed the plain weave significantly, showing a 21.7% and 50% increase in ballistic limit and energy absorption, respectively. Images obtained from the high-speed camera revealed that the secondary deformation was generated in the vicinity of the crossovers of the primary warp yarns and the gripping lines, serving to mitigate the stress concentration and to assist in energy dissipation during a ballistic event. It was also found that the structure-modified fabrics exhibit inferior energy absorption capability when the projectile impacts the gripping insertions. The observed improvements in performance could have been offset by the lines of weakness.

Ballistic performance of B4C/STF/Twaron composite fabric

This work proposes a new type of bullet-proof composite fabric, which is made of B4C modified shear thickening fluid (STF) and Twaron aramid fabric. We conducted yarn pull-out test, ballistic impact test and finite element analysis (FEA) to investigate the ballistic performance of this new type of composite fabric. Based on the yarn pull-out test, it is found that the inter-yarn friction is greatly increased after the aramid fabric is impregnated with the B4C modified STF. The ballistic test shows that the ballistic limit velocity of single-layer neat Twaron fabric can be improved from 114 m/s to 160 m/s by using pure STF while 179 m/s by using the B4C modified STF where 10% B4C of particle size W3.5 was added into the STF. For multiple layers of fabrics, the ballistic performance of 3-layer B4C/STF/Twaron composite fabric is better than 3-layer neat Twaron whereas worse than 4-layer neat Twaron (which is of similar areal density to 3-layer composite). In order to study the ballistic properties of the composite fabric composed of fabric impregnated with B4C modified STF and neat fabric, the ballistic performance of 6-layer fabric was studied. By optimizing the combination of fabrics, we found putting 1 layer of B4C/STF/Twaron composite fabric in front of 5 layers of neat Twaron fabrics can maximize the overall ballistic resistance of the structure with the similar areal density. The simulation results agree well with the experimental results, which shows the path stress wave propagates and further emphasizes that the friction coefficient between yarns has a significant impact on the anti-impact property of fabric.

Characterization of the rheological behaviors and mechanical properties of fabrics impregnated by different shear thickening fluids at changing temperatures

Liquid armor prepared with shear thickening fluid (STF) and high-performance fiber fabric is a novel body protection material which possesses both anti-impact performance and improved wearing comfort. In this work, the rheological behaviors of STFs with different features and mechanical properties of STF impregnated fabrics at different temperatures were characterized. Three kinds of STFs were prepared by mixing silica particles and polyethylene glycol with different particle concentrations and/or particle-fluid interaction. Their rheological behaviors show remarkable differences in viscosity, loss modulus and storage modulus. High solid concentrations and strong particle-fluid interaction are considered to be important factors to obtain high viscosity and high modulus. The rheological properties of STFs are also very sensitive to temperature, as we have found that the viscosity and the modulus values at −40 °C are three orders of magnitude higher than those at 55 °C. However, the mechanical properties of the aramid fabrics impregnated with these STFs do not change significantly with the STF types and temperature. Yarn pull-out and dynamic impact tests results show that fabrics impregnated with STFs possess excellent energy absorption effects, but the friction resistance and energy absorption capacity of the fabrics are not positively related to the STF viscosity and modulus. Our findings will provide guidance to the design of STF composites in the field of low-speed impact.

Improving ballistic performance of Kevlar fabrics by resin treatment

The aims of our investigation are to increasing inter-yarn friction by using polyurethane resin for superior ballistic protection without affecting the weight. In our concentration, we have used three different resin impregnated (25 × 25 cm) (Type-A), (4.5 × 4.5 cm) (Type-B), (9 × 9 cm) (Type-C) structure to treat our Kevlar fabrics and 12% wt. PU solution as resin. Grounded on our three different resin-impregnated fabric, we have been evaluated the weight increase percentage to analyze our core objectives maintaining the less weight escalation ratio with better ballistic performance. As the resin impregnation amount increases, the yarn or fiber dimensions lead to fabric stiffness. Later on, the yarn pull-out installation was created and the yarn (single and multiple) pullout tests were performed on both plain and resin impregnated structures to find the differentiation. The result of the investigation shows high-density resin-impregnated fabric indicates a higher pull-out force contrasted with those of low-resin impregnated fabric structure. Fabric displacement at max. Force during multiple-end pull-out indicated a higher fabric displacement (mm) rate contrasted with that of the single pull-out. Optical microscopic examination is done to observe the progressions on pulled out regions. During our observation, no implication variety was found in the surface at a specified loading rate except adjacent yarn displacement grounded on the amount of yarn pulled out. Utilization of resin impregnation builds the commitment of more yarns as the slippage of yarns is limited thus leads to the higher energy required rate. Finally, by ballistic perforated impact parameters, it is affirmed that expanding inter-yarn friction can improve ballistic performance of fabrics. Ultimately, it is concluded in the way that these new ballistic resin-impregnated structures come up with higher inter yarn friction, low expense, less weight, considerable stiffness of the fabric and the reliable ballistic performance on the finished result.

Intralayer interfacial sliding effect on the anti-impact performance of STF/Kevlar composite fabric

The influence of intralayer interfacial sliding among yarns on the enhancement of anti-impact and energy absorption was investigated in this work. Firstly, the rheological test and yarn pull-out test were conducted to analyze the relationship between the state of shear thickening fluid (STF) and the interfacial sliding among yarns. Then, the influence of impact velocity and constraint conditions on the interfacial sliding were studied by drop hammer and ballistic tests. The results showed that the impact speed and constraint conditions would affect the relative interfacial sliding rate among yarns, which would affected the rheological state of STF and the anti-impact performance of fabric. Besides, the mathematical model of the relationship between projectile velocity and fabric kinetic energy under the strong constraints was given by combining with the results of finite element analysis (FEA) of ballistic impact. This work provided a design idea for the body armor with high protective performance.

Effect of nano-solid particles on the mechanical properties of shear thickening fluid (STF) and STF-Kevlar composite fabric

To analyze the effect of nano-solid particles on the mechanical properties of shear thickening fluid (STF) and its Kevlar composite fabric. In this study, nano-silica and polyethylene glycol (PEG 200) were used as dispersed and continuous phases. Nano-graphite and nano-diamond particles were used as additives to prepare STF and Kevlar composite fabric. Study the friction characteristics and rheological characteristics of STF at different temperatures. Explore the STF’s mechanical response under transient high-speed impact conditions through the split Hopkinson pressure bar experiment. The mechanical properties of STF-Kevlar fabric are studied through yarn pull-out test and burst experiments. The experimental results show that the intermolecular repulsive force of STF is enhanced under a high-temperature environment, and shear thickening effect is reduced. Nano-diamond particles strengthen the contact coupling force and contact probability between the particle clusters, so that the maximum viscosity of the system reaches 1679 Pa s, the thickening ratio reaches 318 times, and the rheological properties of the shear thickening fluid are improved. The results of the SHPB experiment show that the STF can complete a dynamic response within a 50–75 µs time range, and the maximum stress can reach 78 MPa. The bullet’s incident kinetic energy is not only transformed into thermal energy and phase change energy of solid-liquid conversion, but also into frictional energy between particles. The mechanical experiments of STF-Kevlar composite fabrics show that the tensile force value of STF5-Kevlar is the largest (10.3 N/13.5 N), and the tensile force of neat Kevlar was the smallest (4.3 N/4.9 N). The maximum bearing capacity (0.3 kN) and absorption energy (51.8 J) of Neat Kevlar are less than those of STF1-Kevlar (3.2 kN, 116.7 J) and STF3-Kevlar (1.9 kN, 88.2 J), and STF5-Kevlar (4.7 kN, 143.3 J). Fabric’s failure mode is converted from partial yarn extraction to overall deformation and rupture of the fabric. Therefore, by changing the solid additives’ parameters, the STF and the composite fabric’s mechanical properties can be effectively controlled, which provides a reference for preparing the STF and fabric composite materials.

Facile fabrication and mass production of TPU/Silica/STF coated aramid fabric with excellent flexibility and quasi-static stab resistance for versatile protection

Stab-resistant materials with lightness and softness have received increasing attention with the progress and development of society. In this paper, we have fabricated excellent flexibility and quasi-static stab resistance fabric by coated thermoplastic polyurethanes (TPU)/Silica /Shear thickening fluid (STF) on the aramid fabric, which can be facile fabrication and mass production. Several tests, including quasi-static stab test, quasi-static puncture test, yarn pull-out test, and interlayer peeling test were conducted to evaluate the bonding fastness between TPU film and the stab resistance of the coated fabric. The results showed that the quasi-static stab resistance, puncture resistance, and yarn pulling-out performance of TPU-coated fabrics were improved greatly compared to neat fabrics. Coated fabrics had lower quality increase and less flexibility decrease as compared with neat fabrics. The stab resistance of the fabric treated with TPU coating solution with silica additive was also improved. Meanwhile, the aramid fabric coated with a coating solution containing 3 % fumed silica had the best performance in terms of knife stab and puncture force performance (135.98% higher for P1 knife blade stabbing, 127.21 % for S1 knife blade stabbing and 129.48 % for spike punching) as compared with neat fabrics.

Yarn dynamic tensile behavior and meso-scale numerical simulation method for STF-Kevlar fabrics

Shear thickening fluids (STFs) were found to be effective at enhancing the energy absorption capacity of Kevlar fabrics, which is promising in the area of soft-wall containment casings. In the current study, an improved mesoscale numerical simulation method for the yarn level was developed to predict the properties of STF-Kevlar fabrics with various STF concentrations. In addition, quasi-static and dynamic tensile tests as well as yarn pull-out tests were performed. Based on the dynamic tensile behavior and friction between yarns, a mesoscale numerical simulation method was proposed for STF-Kevlar fabrics. Combined with a ballistic impact test, the numerical simulation method based on the yarn tests was verified. It was found that the STF generates a strain-rate strengthening effect due to its shear thickening behavior during quasi-static tensile tests conducted at 0.0001 and 0.001 s−1. The initial elastic modulus, tensile strength, and failure strain of the yarn were obtained from dynamic tensile tests using a split-Hopkinson tension bar (SHTB) apparatus. The yarn pulling process includes the yarn straightening stage and yarn translation stage. The pull-out force decreased with the pull-out rate for the STF-treated yarn. The pull-out force of the STF-treated fabric increased by up to 213.2% compared with the neat fabric at the same pull-out rate. Based on the yarn pull-out testing results, the friction coefficient between the weft and warp yarns was estimated. Mesoscale numerical simulations were performed based on the dynamic tension behavior and friction behavior of the yarn, which were verified through ballistic impact test. Although the friction characteristics of the three STF fabrics were not significantly different, the energy absorption of the STF-treated fabrics differed considerably. As the tensile strength increased, the energy absorption characteristics of the fabric improved considerably.

Ballistic impact performance of multi-phase STF-impregnated Kevlar fabrics in aero-engine containment

The current study focus on the multi-phase Shear thickening fluid (STF) treated high-strength fabrics which is an promising material for soft-wall containment casing. Three types of multi-phase STF were manufactured by adding graphene oxide (GO) and carbon nanotubes (CNTs) to a nanosilica suspension system. Steady rheological property tests and yarn pull-out tests were conducted to determine the shear thickening behavior of the multi-phase STFs and inter-yarn friction of their compound fabrics. Ballistic impact tests were conducted using titanium blade-like projectiles. The energy absorption, deformation evolution and damage patterns were investigated. Tests show that the addition of GO and CNTs resulted in a higher initial viscosity, a lower shear rate for onset of shear thickening and a lower thickening ratio. The enhancement of the frictional force is more striking for multi-phase STFs. The GO additives have the highest deformation in the ballistic impact tests, corresponding to the greatest energy absorption with a ballistic performance index 78.3% higher than that of neat fabrics. The results show great potential for reducing the weight of containment casing.

Influence of surface polymer coating on ballistic impact response of multi-layered fabric composites: Experimental and numerical study

Composites based on aramid fibres are widely used to protect people and vehicles from high-velocity impact threats. Currently, quite a lot of attention is paid to methods for increasing the efficiency of such structures without a significant increase in areal density. The article demonstrates the results of experimental and computational studies of two types of multilayer fabric systems based on Twaron® 709. The first system consisted of dry fabric layers, and the second one was based on the fabric layers with polyvinyl acetate (PVA) surface coating. Experimental studies included quasi-static yarn pull-out tests, high-velocity impact tests of specimens without backing support, and tests on a plasticine block to assess the back face bulging. The results of the experiments showed that thin coatings of PVA contributed to a significant pull-out force increase due to polymer connections between the yarns. This effect led to the fact that specimens based on coated fabrics had a ballistic limit twice as much and showed a three-fold decrease in the depth of the dent on plasticine in comparison with dry fabrics. The total increase in surface density did not exceed 6% while maintaining high flexibility of the package. Also, numerical simulations were used to confirm the results of experiments. It was shown that mesoscale yarn-level models allow to predict plasticine indentation depths of the dry and coated multilayer fabric targets.

Mechanical behavior of 3D GFRP composite with pure and treated shear thickening fluid matrix subject to quasi-static puncture and shear impact loading

In this study, a new low-velocity shear impact test was introduced to carefully investigate the resistance of 3D E-glass fiber reinforced polymer composites with shear thickening fluid matrix. The shear thickening fluids were prepared by dispersing silica nano-particles in polyethylene glycol. Pure shear thickening fluid was modified by treating the silica surface with (3-Aminopropyl) triethoxysilane. Despite the low-velocity shear impact test, various experimental tests such as yarn pull-out, quasi-static puncture, flexibility and thickness tests were carried out to study the mechanical behavior of the composites. Results revealed the treated shear thickening fluid up to 60 wt% improves the performance of the impregnated samples against the yarn pull-out and puncture tests by 353% and 45%, respectively, and their shear impact resistance by 130% compared to the neat cases without noticeably affecting the fabric flexibility.

The influences of rheological property on the impact performance of kevlar fabrics impregnated with SiO2/PEG shear thickening fluid

Abstract Shear thickening fluids (STFs) have been proven promising in enhancing the anti-impact performance of woven fabric, which can be incorporated into soft-wall containment casing in aero-engine applications. In the current study, STFs having distinct different shear thickening behaviors were investigated through yarn pull-out and ballistic impact tests to understand the relationship between the rheological behavior of STFs and their effect in enhancing impact resistance, which provide insight into the design of STF-treated soft-wall casing. Spherical SiO2 particles of diameters 100 and 650 nm were employed to prepare the STFs, which were referred to as a-system (100 nm particles) and b-system (650 nm particles). The rheological properties were investigated for two STF system series. The critical shear rate is 0.6–3.2 s−1 for a suspension system composed of 650 nm silica particles, whereas the critical shear rate is 169–627 s−1 for that of 100 nm particles. Kevlar fabrics were impregnated with STFs, and ballistic impact tests were conducted on different types of STF–Kevlar and neat Kevlar fabrics using titanium blade-like projectiles to evaluate their impact resistances in aero-engine containment applications. Energy absorption characteristics, deformation features, and damage patterns are analyzed. Impact test results show that the STF made of 100 nm SiO2 improved the anti-impact performance of the Kevlar fabric and increased the energy absorption up to 56.6%, whereas it decreased in the treatment by STFs made of 650 nm SiO2. The different trends of the two suspension systems are attributed to the specific value of shear rate with critical shear rate. The maximum deformation is estimated and compared with the pyramid deformation formed in the fabric. The STF–Kevlar fabrics under impact are more compact and act as an integrated structure compared with the loose structure of neat Kevlar fabrics. Owing to the increased interyarn friction action after the STF treatment, less yarn slippage occurred during the impact. For fabrics treated with the a-system STF, primary yarns were stretched and pulled out from the overlap structure of the woven fabric, forming perpendicular strip areas with failure modes involving unraveled yarns. The perforated damage of the b-system-STF-treated fabrics is concentrated at the area directly in contact with the blade projectile, in which a small amount of yarns fractured and pulled out.

Shear and yarn pull-out grip for testing flexible sheets by universal load machines

The purpose of this research was to develop a novel, multifunctional apparatus that makes possible to carry out two common tests of woven fabrics and flexible sheet-like materials, namely the shear and the yarn-pull out test. We designed an apparatus that can be mounted on a universal load machine and makes possible to test the materials rapidly and precisely.In this paper we introduce the apparatus and the related simple shear and yarn pull-out test methods, as well as the accuracy and reproducibility of the test results obtained. We carried out cyclic shear and yarn pull-out tests on plain and panama weave materials. We found that the relative deviations of the common shear (G, 2HG, 2HG5) and yarn pull-out parameters were around 5–9% in most cases that confirms the repeatability of the test method. With our method, one can carry out these tests without an expensive, dedicated test device.

Tuning shear thickening behavior via synthesis of organically modified silica to improve impact resistance of Kevlar fabric

In this paper, we are reporting for the first time ability to tune the shear thickening behavior of silica through synthesis of an organically modified silica. The organically modified silica having varying degree of functionalization was synthesized in a one-step procedure. The success of the preparation of organically modified silica was confirmed using a variety of techniques, for example, FT-IR, 13C solid state NMR and X-ray photoelectron spectroscopies. The morphology and particle size was studied using TEM, SEM, and DLS. The rheological behavior of organically modified and non-functionalized silica was evaluated after dispersion in poly(ethylene glycol). The organically modified silica having varying degree of functionalization showed shear-thickening behavior depending on the amount of organic functionalization/modification. Based on the results obtained, it is possible to tune the rheological behavior of organically modified silica by controlling the amount of organic functionalization which is not possible in the case of non-functionalized silica as well silica functionalized via post-modification technique. In addition, organically modified silica showed significant shear thickening at much lower loading (50 wt.%) as compared to non-functionalized silica. The organically modified silica containing the lowest amount of functionalization showed shear thickening behavior at lower shear rate due to increased inter-particle interaction through hydrogen bonding. The shear-thickening fluids (STFs) prepared using organically modified and non-functionalized silica were further applied on Kevlar fabric in order to study properties of STF impregnated fabric. For impregnated fabric, yarn pull-out and drop impact test were performed. In this case also, organically modified silica impregnated fabric showed higher force required for yarn pull-out (38–39.5 N) as compared to fabric impregnated with non-functionalized silica where the force required for yarn pull-out was 25.8 N. In the drop impact testing, average peak force (900 N) and peak energy (246 J) for Kevlar fabric impregnated with organically modified silica was higher as compared to average peak force (493 N) and peak energy (131 J) for Kevlar fabric impregnated with non-functionalized silica.