Optimal designing of soft body armour materials using shear thickening fluid

This paper deals with the optimal design of soft body armour materials by treating Kevlar (para-aramid) fabrics with silica nano-particle based shear thickening fluid (STF). Box and Behnken design of experiment (DOE) plan in conjunction with contour analysis has been used to study the effect of silica concentration, padding pressure and diluent: STF ratio (solvent ratio) on STF add-on% and impact energy absorption. Silica concentration, solvent ratio and square of solvent ratio were found to be statistically significant terms influencing the STF add-on% on Kevlar fabrics. On the other hand, silica concentration, padding pressure and the square of solvent ratio were the statistically significant terms influencing the impact energy absorption. Higher padding pressure enhances the impact energy absorption by the STF treated Kevlar fabrics although it does not influence the STF add-on% significantly. Higher STF add-on% is a necessary but not the sufficient condition for improving the impact resistance performance of Kevlar fabrics.     

Numerical simulation of the impact behaviors of shear thickening fluid impregnated warp-knitted spacer fabric

The impact behavior of warp-knitted spacer fabrics (WKSFs) impregnated with shear thickening fluid (STF) under low-velocity impact loadings have been investigated from experimental and finite element analyses (FEA) approaches. From the experimental approach, the impact load–displacement curves have been obtained. It was observed that the WKSF impregnated with the STF composite material (the WKSF/STF composite) shows a higher stiffness and lower peak force than those of the WKSF under the same impact loadings. In FEA approach, the geometrical models of the WKSF and the WKSF/STF composite material were established based on the WKSF fabric architectures. The dynamic responses including the impact load–displacement curves and impact deformation of the samples were predicted based on finite element analyses at the microstructure level. It was found that the STF and the coupling effect between the STF fluid and fiber tows are the key factors which influence the cushioning behaviors of the composite. The energy absorption mechanisms include the buckling of the spacer finer tows and the thickening effect of the STF under impact loading. The WKSF/STF composite could be expected as a damping or energy-absorptive materials under impact loading.     

Low-velocity penetration damage of Kevlar woven fabrics impregnated with shear thickening fluid penetrated with different tups

Abstract

Low-velocity penetration damage behaviors of Kevlar woven fabrics impregnated with shear thickening fluid (STF) were investigated. Cone-shaped tup (CST) and hemispheric tup (HST) were employed to penetrate fabric/STF composites with the velocities of 1.5 m/s and 3.0 m/s under drop-weight tests. The fabric impregnated with 3:1 diluted volume ratio has the highest energy absorption and the lowest deformation. The peak load and energy absorption under HST penetration at 3.0 m/s are 2.0?kN and 36.7 J, which are higher than the CST penetration. Energy absorption increment under HST penetration at 3.0 m/s is 61.76% while 117.88% for CST penetration.     

Design of composite materials with improved impact properties

Composites have been widely used in applications where there is a risk of impact, due to the excellent properties these materials display for absorbing impact energy. However, composites during impact situations typically generate an enormous number of small pieces, due to the energy absorption mechanism of these materials, a mechanism which does not include plastic deformation. This can prove dangerous in sports competitions, where the small fragments of the original structure may harm competitors.This study was designed to explore the possibility of incorporating a material which, whilst maintaining a high level of energy absorption without any plastic deformation mechanism, was able to maintain its original form, or at least significantly reduce the number of pieces generated after impact.The addition of a polyamide layer, NOMEX^®, to a monolithic fabric laminate was investigated in this paper. The process of fabrication is described and the different properties of the material under consideration: interlaminar fracture toughness energy (G_IC), indentation (id) and delamination after impact (A_i) and compression after impact (σ_CAI), were measured and compared with those of the original monolithic fabric.     

Evaluation of the mechanical behavior of epoxy composite reinforced with Kevlar plain fabric and glass/Kevlar hybrid fabric

In this study, composite plates were manufactured by hand lay-up process with epoxy matrix (DGEBA) reinforced with Kevlar fiber plain fabric and Kevlar/glass hybrid fabric, using to an innovative architecture. Results of the mechanical properties of composites were obtained by tensile, bending and impact tests. These tests were performed in the parallel direction or fill directions of the warp and in a 90° direction. FTIR was used in order to verify the minimum curing time of the resin to perform the mechanical tests, and scanning electron microscopy was used to observe reinforcement and matrix fractures. Composites with Kevlar/glass hybrid structure in the reinforcing fabric showed the better results with respect to specific mechanical strength, as well as bending and impact energy.     

Stab resistance of shear thickening fluid (STF)-treated fabrics

The stab resistance of shear thickening fluid (STF)-treated Kevlar® and Nylon fabrics is investigated and found to exhibit significant improvements over neat fabric targets of equivalent areal density. Specifically, dramatic improvements in puncture resistance (spike threat) are observed under high and low speed loading conditions, while slight increases in cut protection (knife threat) are also observed. Studies on the effect of fabric architecture indicate that STF addition provides benefits analogous to the effect of increasing fabric yarn count, with STF addition primarily reducing the mobility of filaments and yarns in the impact zone. Microscopy shows significant energy dissipation in the damage zone that includes plastic flow of the polymeric filaments, as well as deformation of the filaments due to mechanical interaction with the colloidal particles of the STF. These results indicate that these novel materials could be used to fabricate flexible body armors that provide improved protection against stab threats.     

剪切增稠液体的制备及其性能表征

研制了一种新型功能材料——剪切增稠液体（Shear thickening fluid，即STF）。采用溶胶凝胶方法制备纳米二氧化硅作为分散相，极性溶剂作为分散介质。用流变仪测量了二氧化硅质量分数分别为30％、40％、50％、60％和70％的体系稳态和动态粘度曲线，结果表明，在低剪切速率下，出现剪切变稀现象，在高剪切速率下，出现剪切增稠现象。从实验角度证明了剪切增稠的可逆性。并对不同固相含量的剪切增稠液体的性能进行了分析比较。     

不同分子量PEG对剪切增稠液体流变性能的影响

将两种不同分子量的聚乙二醇(PEG200,PEG600)作为剪切增稠液体的分散介质,按不同比例进行复配,制备剪切增稠液并在透射电镜中进行观察,同时对几种不同的剪切增稠液进行流变性能测试。比较了不同分子量的分散介质对剪切增稠液流变性能的影响,包括稳态流变性能以及动态流变性能。研究得出,分散相粒子质量分数相同的情况下,适当提高分散介质的分子量对剪切增稠液体的流变性能有积极的影响,在较小的冲击力下,STF体系便能发生剪切增稠效应。     

Enhanced wear resistance of hybrid PTFE/Kevlar fabric/phenolic composite by cryogenic treatment

Hybrid PTFE/Kevlar fabric was treated by cryogenic approach. The untreated or cryo-treated fabric was incorporated into fabric/phenolic composite for friction and wear tests. It was found that the wear resistance of the fabric/phenolic composite was improved after cryo-treatment, although the friction coefficient increased to a certain extent. SEM observations showed that the roughness of hybrid fabric increased by cryo-treatment, which may enhance the mechanical interlocking of the phenolic resin on the fiber surface. Enhanced fiber/resin adhesion was considered to contribute to the improved wear resistance of cryo-treated fabric/phenolic composite.     

复配型剪切增稠液体对非织造织物防刺性能的影响

引入"复配"的概念,制备出不同复配方式的剪切增稠液体(STF),并将该复配型STF对超高分子量无纺布进行处理,通过对STF无纺布的复合材料进行扫描电镜形貌分析以及静态防刺实验,来对复合织物的防刺性能进行研究。主要阐述了不同分子量分散介质(PEG200、PEG600)复配后的剪切增稠液与无纺布织物复合后对复合材料防刺性能的影响,发现采用不同分子量分散介质较单一分子量分散介质的STF无纺布复合织物的防刺性能好,采用复配分散介质的方式对剪切增稠液体在防刺效果上有一定程度的改善作用,在同等单位质量的情况下,此复配方式可将复合材料的防刺性能提高7.13%。     

Progressive failure modeling of woven fabric composite materials using multicontinuum theory

Failure of composite materials often results from damage accumulation in the individual constituents (fiber and matrix) of the composite. At times, damage may even be limited to a single constituent. The ability to accurately predict not only ultimate strength values but also intermediate constituent level failures is crucial to the success of introducing composite materials into demanding structural applications.In this paper, we develop two progressive failure models for the analysis of a plain weave composite material. The formulations are based on treating the weave as consisting of separate but linked continua representing the warp fiber bundles, fill fiber bundles, and pure matrix pockets. Retaining constituent identities allows one to access constituent (phase averaged) stress fields that are used in conjunction with both a stress based and damage based failure criterion to construct a nonlinear progressive failure algorithm for the woven fabric composite material. The MCT decomposition and the nonlinear progressive failure algorithm are incorporated within the framework of a traditional finite element analysis.The constituent based progressive failure algorithm combined with both the stress based and damage based failure criteria are compared against experimental data for a plain weave, woven fabric composite under various loading conditions. The analytical results from the damage based approach show a marked improvement over the stress based predictions and are in excellent agreement with the experimental data.     

The effect of silicon carbide additives on the stab resistance of shear thickening fluid treated fabrics

Applications of shear thickening fluids (STFs) with ballistic fabrics improve the protection performance of body protective systems. This article presents an innovative view of STF-impregnated ballistic fabrics by integrating silicon carbide (SiC) particles into targets. In this study, SiC particles were added into silica-based STFs, and Twaron fabrics were impregnated with this novel suspension. The effect of the SiC particles in the STFs was investigated with rheological testing. The results show that SiC particles are able to increase the viscosity profile of the suspension. In the stab testing, two types of impactors, such as spikes and knives, were dropped on the composite targets. According to the results, SiC particles enhance the protection performance of the STF-treated ballistic fabrics while keeping the flexibility.     

Development of a novel magnesium-copper based composite with improved mechanical properties

Magnesium based composite with 17.95 wt.% of copper reinforcement was fabricated using an innovative DMD technique followed by hot extrusion. Microstructural characterization of the extruded composite samples showed fairly uniform reinforcement distribution, presence of Mg-Cu based intermetallics, good Cu_P-Mg interfacial integrity, and the presence of minimal porosity. Mechanical properties characterization revealed that the presence of copper as reinforcement lead to a significant increase in hardness, elastic modulus, 0.2% yield strength and UTS of pure magnesium while the ductility was adversely affected. An attempt is made in the present study to correlate the effect of copper as reinforcement with the microstructural and mechanical properties of magnesium.     

Crack resistance of materials with high-velocity impact

A procedure is suggested for determining critical dynamic stress intensity factors with normal separation and transverse shear from crack stopping under rear spalling conditions for specimens. Results obtained by the method suggested for three grades of steel are compared with those calculated by the Panasyuk-Andreikiv procedure. Good agreement is noted for critical stress intensity factors with normal separation.Translated from Problemy Prochnosti, No. 12, pp. 19–23, December, 1990.     

Micromechanical approach to damage mechanics of composite materials with fabric tensors

The purpose of this study is to apply continuum damage mechanics – introduced through the concept of fabric tensors – to composite materials within the framework of the theory of elasticity. A directional data model of damage mechanics for composite materials will be developed using fabric tensors. The introduction of fabric tensors into the analysis of damage of composite materials will allow for an enhanced and better understood physical meaning of damage. The micromechanical approach will be used here to relate the damage effect through fabric tensors to the behavior of composite materials. In this approach, damage mechanics is introduced separately to the constituents of the composite material through different constituents’ damage effect tensors. The damaged properties of the composite system as a whole can then be obtained by proper homogenization of the damaged properties of the constituents.

The derivation of a generalized formulation of damage evolution will be shown here in a mathematically consistent manner that is based on sound thermodynamic principles. Numerical examples will be presented to show applicability. In addition, damage evolution for the one-dimensional tension case is also illustrated.     

Low velocity impact analysis of composite sandwich shells using higher-order shear deformation theories

In the present investigation, higher-order and conventional first-order shear deformation theories are used to study the impact response of composite sandwich shells. The formulation is based on Donnell’s shallow shell theory. Nine-noded Lagrangian elements are used for the finite element formulation. A modified Hertzian contact law is used to calculate the contact force. The results obtained from the present investigation are found to compare well with those existing in the open literature. The numerical results are presented to study the changes in the impact response due to the increase of core depth from zero to some specified value and the changes in core stiffness for a particular core depth.     

The influence of transverse shear on the static flexure and Charpy impact response of hybrid composite materials

Classical laminated anisotropic plate theory, extended to include the effects of transverse shear, is applied to the three-point beam bending problem, to determine the deflections under load, hence flexural modulus, and also the energy absorbed by the beam to the point of peak load, i.e. to first failure. A standard unnotched Charpy impact specimen configuration, constructed of a multi-lamina hybrid composite material, is analysed. Transverse shear is shown to have a significant influence on the response. The analytical results are compared with experimental data, for both impact and static loadings. A definite loading rate dependence is observed.     

A numerical study on the impact resistance of composite shells using an energy based failure model

This paper presents a numerical study on the impact resistance of composite shells laminates using an energy based failure model. The damage model formulation is based on a methodology that combines stress based, continuum damage mechanics (CDM) and fracture mechanics approaches within a unified procedure by using a smeared cracking formulation. The damage model has been implemented as a user-defined material model in ABAQUS FE code within shell elements. Experimental results obtained from previous works were used to validate the damage model. Finite element models were developed in order to investigate the pressure and curvature effects on the impact response of laminated composite shells.     

Effect of CF/GF fibre hybrid on impact properties of multi-axial warp knitted fabric composite materials

The multi-axial warp knitted fabric (MWK) is a useful reinforcement for composite. Higher mechanical performance resulted from no crimp of the fibre bundle is achieved compared with the general textile composites. For the fibre bundle of MWK, only one type of reinforcement fibre among glass, carbon fibre bundle, and so on has been selected. The mechanical properties and the cost of MWK composite depend on the feature of the fibre bundle. In order to extend the applicability of composite, the concept of “fibre hybrid composite” was applied into the MWK composite. Two kinds of fibre bundle; carbon and glass, were used in the 0/90 multi-axial warp knitted fabric. As the fibre hybrid composite; the inter-layer hybrid composite in which each layer was fabricated by carbon and glass fibre bundle respectively was investigated. Impact properties of composite were investigated by using drop weight impact tests. In case of unsaturated polyester, total energy and progressive energy of inter-layer fibre hybrid composite realized the highest value in all specimens. However, in case of epoxy resin, inter-layer hybrid composite didn’t realize the highest value in all specimens. The difference in energy absorption capability could be described with the fracture mechanism.