Shear Thickening Fluid Impregnation Research Articles

A hybrid approach of NiP coating and STF impregnation of UHMWPE fabric for conductive soft body armor

To enhance the ballistic impact performance and impart electrical conductivity into soft armor material made up of UHMWPE fabric, a novel hybrid technique has been devised and incorporated. Initially, the NiP layer was deposited on the UHMWPE fabric surface through the electroless process, subsequently, it was impregnated in the shear thickening fluid (STF) based on nano-silica (40 wt%). The morphology, functional groups, phase structure, thermal stability, breaking load, inter-yarn friction, electro-heating, and ballistic impact performance of the neat (UHM), STF impregnated (UHM-STF), NiP coated(UHM/NiP), and NiP coated STF impregnated (UHM/NiP-STF) fabrics are detailed. The NiP coating enhanced the ballistic impact performance, and thermal stability, and became electrically conductive compared to neat fabric. The ballistic impact test confirmed the enhancement in the energy absorption of UHM-STF (30.84%), UHM/NiP(18.37%), and UHM/NiP-STF(54.82%) compared to UHM. The hybrid technique (UHM/NiP-STF) exhibited higher inter-yarn friction (53.79%) and ballistic impact energy absorption (18.43%) compared to UHM-STF. The significant rise in the impact energy absorption of the UHM/NiP-STF can be ascribed to the synergetic effect of enhanced inter-yarn friction induced by the NiP-coated layer and the shear thickening behavior exhibited by STF. The NiP-coated and STF-impregnated fabrics present a promising prospect for the advancement of soft body armor materials with multifunctional ability.

Determination of Energy Absorption Capabilities of Shear Thickening Fluid Impregnated Aramid Fiber Fabrics for Ballistic Applications

Low velocity impact behavior of shear thickening fluid (STF) impregnated aramid fabric having different number of layers had been investigating throughout this study to determine a relationship between number of layers and perforation energy. Firstly, STF solutions including polyethylene glycol, silica nanoparticles and ethanol were prepared by mixing a homogenizer. Solutions containing 20% silica nanoparticles by weight were used in this study. Rheological analysis was performed to observe thickening behavior of solution. After thickening behavior and critical shear rate was determined from rheological analysis, solution was impregnated into aramid fabric. Then, specimens having different number of layers from 1 to 8 were prepared for low velocity impact experiments. A drop weight impact test was applied at different energy levels and perforation energy was determined. Finally, a curve fitting equation was found to use it for potential energy absorption applications such as ballistic impact.

High-impact resistant hybrid sandwich panel filled with shear thickening fluid

This study developed a hybrid aluminium sandwich panel (ASP) with aluminium/Kevlar fabric facings filled with a concentrated shear thickening fluid (STF) for high impact resistance. Local puncture failure mode was dominant in pristine ASP after low-velocity impact, whereas global energy absorption behaviour was achieved after the addition of Kevlar fabrics and STF. The impact resistance of hybrid ASPs was greatly enhanced with increased core thickness. Micro-CT analysis after impact revealed that the excellent impact resistance of the hybrid sandwich panels was attributed to the synergistic effect of STF’s high energy absorption, Kevlar fabrics’ increased in-plane stiffness after STF impregnation and confinement of aluminium cells on the STF fillings. The energy absorption mechanism after the addition of Kevlar fabrics and STF are discussed in detail.

Ballistic impact performance of UHMWP fabric impregnated with shear thickening fluid nanocomposite

In the present study, an attempt is made to improve the ballistic performance of unidirectional (UD) ultra-high molecular weight polyethylene (UHMWP) fabrics through shear thickening fluid (STF) impregnation. Impact tests in the range of 250–700 m/s were conducted using an aero-ballistic range. It was observed that the ballistic limit (V50) and the energy absorption of STF treated UD-UHMWP fabrics can be improved up to 5% and 13% respectively, corresponding to their neat ones. Increased energy absorption of STF treated fabric is attributed to the enhancement in the friction between layers of the STF-UHMWP fabric and the shear thickening effect. The effect of sample thickness of STF treated panels on the energy absorption, failure mechanism, and back face signature (BFS) is evaluated and compared with their neat counterparts. The damage was localized in the thinner panels (5 and 10 layers), and the layers were perforated through shear plugging near the impact region. The failure mode of thicker panels (20 and 30 layers) is accompanied by the tensile fracture of high tenacity fibres. It is concluded that the STF impregnation improves the ballistic resistance of UD-UHMWP fabric without affecting the flexibility and adding weight penalty.

Investigation of the Low Velocity Impact Behaviour of Shear Thickening Fluid Impregnated Kevlar, Hybrid (Kevlar/Carbon) and Carbon Fabrics

Investigation of the Low Velocity Impact Behaviour of Shear Thickening Fluid Impregnated Kevlar, Hybrid (Kevlar/Carbon) and Carbon Fabrics

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

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

Interplay of fabric structure and shear thickening fluid impregnation in moderating the impact response of high-performance woven fabrics

The beneficial effect of STF impregnation in enhancing the impact resistance of high-performance fabrics has been extensively reported in the literature. However, this research work reports that fabric structure has a decisive role in moderating the effectiveness of STF impregnation in terms of impact energy absorption. Plain woven fabrics having sett varying from 25 × 25 inch−1 to 55 × 55 inch−1 were impregnated with STF at two different padding pressures to obtain different add-ons. The impact energy absorption by STF impregnated loosely woven fabrics was found to be higher than that of their neat counterparts for both levels of add-on, while opposite trend was observed in case of tightly woven fabrics. Further, comparison of tightly woven plain, 2/2 twill, 3/1 twill and 2 × 2 matt fabrics revealed beneficial effect of STF impregnation, except for the plain woven fabric, establishing that there exists a fabric structure-STF impregnation interplay that tunes the impact resistance of woven fabrics.

High-velocity impact onto a high-frictional fabric treated with adhesive spray coating and shear thickening fluid impregnation

The ballistic performance of a bullet-proof fabric can be increased by an increment in the friction between fibres. For enhancement of this performance, numerous studies on the shear thickening fluid (STF)-impregnated fabric have been conducted. The STF as a fluid, however, has inherent shortcomings. Our research aim is to understand and compare experimentally two different bullet-proof fabrics treated with a simple spray coating and STF impregnation. In this study, 71 single yarn pull-out and 90 high-velocity impact experiments were carried out. It was remarkable that the newly proposed Heracron fabric coated with a commercial coating spray increased by more than 90% the energy absorption before penetration, with only less than 15% of add-on weight. It was found that the polymeric anchors created on the fibre produce an exceptionally high level of friction between fibres, according to a microscopic morphological analysis and the single-yarn pull-out experiment. This study revealed the physical explanation of this coating method, showed its feasibility, and considered its effectiveness with excellent results.

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

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

Evaluation of ballistic performance of STF impregnated fabrics under high velocity impact

Shear thickening fluid (STF) impregnated fabrics offer improved ballistic performance against impacts, but the effect becomes not obvious at high impact velocity (e.g. 300 m/s) as reported by some. This paper presents findings from an investigation of STF-impregnated fabric panels against ballistic impact, and attempts to identify the failure mechanisms of such panels under high velocity impact, which will shed light on effects of STF-impregnated fabrics for low and high velocity impacts. Single-ply and 10-ply neat and STF-impregnated aramid fabric panels were experimented on at impact velocities around 500 m/s. The results indicated that the specific energy absorption of the single-ply and 10-ply STF impregnated fabric panels was 44.8% and 64.1% lower than that of their neat counterparts respectively. The mechanisms were studied theoretically and morphologically. It was found that the projectile velocities perforating the fabrics were decreased by STF impregnation due to the total movement constraint of the primary yarns. This changes the failure mode from tensile dominant to shear dominant, increases the possibility of earlier damage and failure of the primary yarns, and reduces the pull out distance, causing decrease in the energy absorption. The findings are significant for guiding further design of STF impregnated fabric panels for ballistic protection.

An investigation on composite laminates including shear thickening fluid under stab condition

Shear thickening fluids have been extensively utilized in composite laminate structures to enhance the impact resistance in the last decade. Despite the contribution of shear thickening fluids to the protective systems, the mechanism behind the energy absorption behavior of shear thickening fluids is not fully understood. In the present study, various configurations of composite laminates were prepared and these structures were investigated under low velocity stab conditions. Contrary to the common idea of shear thickening fluid impregnation for fabrics, shear thickening fluids were used in bulk form and by means of this, pure contribution of shear thickening behavior to the energy absorption was investigated. To hold the bulk shear thickening fluids in the composite laminates, Lantor Soric SF honeycomb layers were filled with shear thickening fluids and Twaron fabrics were plied in the structures as the reinforcement. As a result of this study, it is stated that shear thickening behavior is insufficient to effectively improve the energy absorption performance of composite laminates; however, shear thickening fluids are beneficial to fabric based composites because the inter-yarn friction of fabrics is enhanced using shear thickening fluids as an impregnation agent rather than a bulk form.

Experimental and numerical analysis of high and low velocity impacts against neat and shear thickening fluid (STF) impregnated weave fabrics

This investigation aims to study the efficiency of STF impregnated plain-weave fabric made of Kevlar under high and low velocity impact conditions. The shear thickening fluid (STF) was prepared by ultrasound irradiation of silica nanoparticles (diameter ≈30 nm) dispersed in liquid polyethylene glycol polymer. STF impregnation effect was determined from single yarn pull-out test and penetration at low velocity using drop weight machine equipped with hemi-spherical penetrator and dynamic force sensor. Force-displacement curves of neat and impregnated Kevlar were analysed and compared. Also, the STF impregnation effect on Kevlar multilayers was analysed from high velocity impact tests using 9mm FMJ bullet at 390 m/s. After impact, Back face deformation (BFD) of neat and impregnated Kevlar layers were measured and compared. Results showed that STF impregnated fabrics have better energy absorption and penetration resistance as compared to neat fabrics without affecting the fabric flexibility. When relative yarn translations are restricted (e.g. at very high levels of friction), windowing and yarn pull-out cannot occur, and the fibres engaged with the projectile fail in tension that leads to fabric penetration. Microscopy of these fabrics after testing have shown pitting and damage to the Kevlar filaments caused by the hard silica particles used in the STF. Mesoscopic 3D Finite Element models were developed using explicit LS-DYNA hydrocode to account for STF impregnation by employing the experimental results of yarn pull-out tests, low and high velocity impacts. It was found that friction between fibers and yarns increase the dissipation of energy upon impact by restricting fiber mobility, increasing the energy required for relative yarn translations and transferring the impact energy to a larger number of fibers.

Tuning the structure of 3D woven aramid fabrics reinforced with shear thickening fluid for developing soft body armour

Soft body armour panels have been developed by tuning the structure of 3D woven orthogonal aramid fabrics and reinforcing them with shear thickening fluid (STF). Five 3D woven orthogonal aramid fabric structures were prepared by changing the ratio of stuffer (X direction) to binder (Z direction) yarns and also by changing the relative position of the latter. Two types of ballistic evaluations, namely energy absorption against low velocity (165±10 ms−1) bullets and back face signature (BFS) against high velocity (430±10 ms−1) bullets were carried out for neat and STF impregnated 3D fabrics and their panels. STF impregnation improved impact energy absorption by 3D woven aramid fabrics. Increasing the ratio of stuffer to binder yarns was found to be beneficial in terms of impact energy absorption and resistance against bullet penetration. STF impregnated 3D fabrics having 4:1 stuffer to binder ratio performed the best in ballistic evaluations. Synergistic effect of 3D woven fabric structure and reinforcement of STF was found to be the key for successful design of soft body armour.

Impact Response of Shear Thickening Fluid (STF) Treated High Strength Polymer Composites – Effect of STF Intercalation Method

Modern and sophisticated ammunition systems have necessitated the development of advanced ballistic protection personal armour systems that are damage resistant, flexible, light-weight and possess high energy absorbing/dissipating capacity. Although, exhaustive studies are available which show the improvement in impact resistance of STF-treated high performance fabrics, but there are limited studies which explore the efficacy of STF impregnation method. In this study, an attempt is made to understand this aspect. The low velocity impact studies were conducted on drop tower machine, while high velocity impact studies were accomplished on Split Hopkinson Pressure Bar (SHPB). High impact Poly Propylene Co-polymer (CO15EG) and UHMWPE variants Gold Shield® and Spectra Shield® were chosen for this study. It was observed that when STF was kept in liquid form between layers of ballistic fabrics, the composite exhibited reduced performance, whereas, when STF was impregnated in a ballistic fabric it had a synergistic effect to enhance the impact toughness of ballistic composite.

Stabbing resistance of body armour panels impregnated with shear thickening fluid

This paper presents an investigation on the use of shear thickening fluid (STF) to improve stabbing resistance of soft ballistic body armour. STFs were produced from polyethylene glycol and silica nanoparticles. The effects of silica nanoparticle sizes and silica nanoparticle weight fraction were studied and STFs made with the different compositions were used to impregnate the Twaron® woven fabrics. Systemic investigations into rheological behaviour of STF were carried out experimentally on STFs with different compositions. STF impregnated woven fabric panels were created and tested for stabbing resistance. Stabbing impact tests were conducted on 6 different types of STF impregnated fabric panels against 2 untreated fabric panels, and the results were studied against the benchmark fabrics without STF impregnation. Based on the same number of layers of fabric, the STF impregnation improves the stabbing resistance notably. For same panel areal density, the STF impregnated panels outperform the untreated fabric panel. The results of this research indicate the possibility of lighter ballistic panel materials for higher stabbing protection. It was also found that higher nanoparticle weight fraction and larger nanoparticle size of silica leads to better stabbing resistance performance among the STF impregnated panels.

Effects of fabric construction and shear thickening fluid on yarn pull-out from high-performance fabrics

Yarn pull-out is one of the major modes of fabric failure during an event of impact. In this article, the effects of weave and fabric sett on yarn pull-out force have been investigated for untreated and shear thickening fluid (STF) treated p-aramid fabrics. Further, the effect of different fluid treatments on yarn pull-out behavior has been analyzed using p-aramid and ultra-high molecular weight polyethylene (UHMWPE) fabrics. For all levels of fabric sett, plain woven fabrics exhibited higher yarn pull-out force compared to twill, matt and satin weaves. STF impregnation increased the yarn pull-out force considerably for p-aramid and UHMWPE fabrics and this was found for all the weaves in the case of the former. However, increase in fabric sett beyond a threshold level caused yarn breakage before yarn pull-out in case of STF-treated plain woven p-aramid fabrics. Yarn pull-out force was found to have good association with the energy absorption by the high-performance fabrics during low-velocity impact (6 m s–1). The normalized yarn pull-out force was higher for two consecutive yarns than for two yarns with a single gap.

Empirical study of the high velocity impact energy absorption characteristics of shear thickening fluid (STF) impregnated Kevlar fabric

The application of shear thickening fluids (STF) allows further enhancement of ballistic resistance without hindering flexibility by the fabric impregnation process. Studies on the effect of STF impregnation on fabric ballistic performance have been limited to the impact velocity range of below 700 m/s. Considering the muzzle velocity of modern rifles with high performance cartridges, investigation of the high velocity impact energy absorption characteristics of neat and STF impregnated Kevlar fabric specimens was conducted in this study. 100 nm diameter silica nanoparticles were dispersed in a solution of polyethylene glycol (PEG) and diluted with methanol for effective impregnation to the Kevlar fabric. High velocity impact experiments with projectile velocities between 1 and 2 km/s were conducted using a 2-stage light gas gun. The experiments revealed that the STF impregnation provides substantial energy absorption enhancement in terms of volume, areal density, and fabrication material cost. Thinner shielding configurations with equivalent energy absorption performance was found to be possible through STF impregnation as the 5 layer STF impregnated Kevlar configuration showed the same energy absorption as the 8 layer neat Kevlar while the energy absorption normalized for areal density and thickness revealed that the STF impregnated Kevlar provides an approximately 70% enhanced specific energy absorption performance over neat Kevlar.

High Velocity Impact Characteristics of Shear Thickening Fluid Impregnated Kevlar Fabric

The development of high performance fabrics have advanced body armor technology and improved ballistic performance while maintaining flexibility. Utilization of the shear thickening phenomenon exhibited by Shear Thickening Fluids (STF) has allowed further enhancement without hindering flexibility of the fabric through a process of impregnation. The effect of STF impregnation on the ballistic performance of fabrics has been studied for impact velocities below 700 m/s. Studies of STF-impregnated fabrics for high velocity impacts, which would provide a transition to significantly higher velocity ranges, are lacking. This study aims to investigate the effect of STF impregnation on the high velocity impact characteristics of Kevlar fabric by effectively dispersing silica nanoparticles in a suspension, impregnating Kevlar fabrics, and performing high velocity impact experiments with projectile velocities in the range of 1 km/s to compare the post impact characteristics between neat Kevlar and impregnated Kevlar fabrics. 100 nm diameter silica nanoparticles were dispersed using a homogenizer and sonicator in a solution of polyethylene glycol (PEG) and diluted with methanol for effective impregnation to Kevlar fabric, and the methanol was evaporated in a heat oven. High velocity impact of STF-impregnated Kevlar fabric revealed differences in the post impact rear formation compared to neat Kevlar.

Computational analysis of shear thickening fluid impregnated fabrics subjected to ballistic impacts

The impregnation of shear thickening fluid (STF) into high-tenacity fabrics has drawn research attention, because it enhances the ballistic performance of fabrics without inducing loss of flexibility in the fabrics. The performance enhancement provided by the STF is suspected to be due to the increased frictional interaction between yarns in impregnated fabrics. In order to explore the mechanism of this enhanced energy absorption, a computational analysis has been performed to consider the effect of STF impregnation on the ballistic performance of STF impregnated fabrics, and the results are reported here. The computational model to account for STF impregnation was implemented into the explicit analysis code LS-DYNA by employing the experimental results of yarn pull-out tests to characterize the frictional behavior of the STF impregnated fabric. The results of a ballistic impact test were used to validate the computational model that takes into account STF impregnation effect. The computational analysis model proposed here to account for the effect of STF impregnation on the ballistic performance of STF impregnated high-tenacity fabrics is shown to reflect the experimental observations of STF impregnated fabrics subjected to ballistic tests.

Investigation of impact resistance of multilayered woven composite barrier impregnated with the shear thickening fluid

Dynamic properties of the Shear Thickening Fluid (STF) are studied. Two series of tests by the Split Hopkinson Pressure Bar method were carried out to determine the dynamic bulk and shear properties of STF. The hypothesis about the possibility to describe STF behavior by a Newtonian fluid model in the characteristic range of strain rates is confirmed. A simplified mathematical model of the STF is then formulated for the use in computer simulation of ballistic impact tests of multilayered composite protective shells. The effectiveness of the STF impregnation for improvement of ballistic impact characteristics of Kevlar woven fabrics is confirmed. It is concluded that the role of the contact conditions between STF and Kevlar basis in the process of increasing the energy absorption capacity of Kevlar-STF barrier is significant, noting that the mechanism of contact interaction between STF and Kevlar basis can be described by viscous friction law, i.e., the STF behaves almost as a rigid body during the interactions with the solids, while it normally behaves as a fluid. It is also established that the STF impregnation of protective shells with titanium framework not only increases the absorption capacity of the whole package but also reduces the deflection of the metal base.