Xueliang Xiao

Deformation behaviors of three-dimensional auxetic spacer fabrics

Auxetic spacer fabrics are a novel kind of three-dimensional (3D) fabric structure with a negative Poisson’s ratio. They have found a number of applications in functional garments, protective pads and sportive shoes due to their unusual properties. In this paper, a study on deformation behaviors of 3D spacer fabrics that could be fabricated on a large scale is reported. Through experimental observations of deformation of a basic hexagonal unit at different tensile strains, two different geometrical models are proposed for the fabric structure when extended in the course direction and wale direction, respectively. Based on the geometrical models, two semi-empirical equations between the Poisson’s ratio and tensile strain are established for both tensile directions. The study shows that the established semi-empirical equations fit well with experimental results. Therefore, they could be used in the design and prediction of 3D auxetic spacer fabrics with different values of geometrical parameters.

An analytical model for through-thickness permeability of woven fabric

Woven fabric permeability is relevant to many applications, such as airbags, textile composites processing, paper making and air and water filtration. This paper proposes an analytical model to predict through-thickness fabric permeability based on viscous and incompressible Hagen–Poiseuille flow. The flow is modeled through a unit cell of fabric with a smooth fluid channel at the center with slowly varying cross-section. The channel geometry is determined by yarn spacing, yarn cross-section and fabric thickness. The shape of the channel is approximated by a parabolic function. Volumetric flow rate (Q) is formulated as a function of pressure drop and flow channel geometry for woven fabric. The permeability (K) is calculated thereafter according to Darcy’s law. The air permeability of nine different fabrics has been measured to verify the analytical model. A sensitivity study was carried out to understand how geometric parameters influence the fabric permeability. The analytical model shows very close agreement with the experimental data: within 5% for most fabrics. The sensitivity study on permeability indicates the importance of flow channel geometry in obtaining accurate predictions.

Experimental study of dynamic air permeability for woven fabrics

Dynamic permeability is relevant to textile applications subjected to fluid/gas flow under high pressure, such as automotive airbags, wearable airbags and parachute fabrics. Dynamic permeability can be determined when a porous medium is tested under transient pressure conditions. This paper utilizes a reliable approach to measure and characterize dynamic permeability for woven fabrics. The experimental principle is based on the ideal gas law and the non-linear Forchheimer equation. Compared with static permeability measured under a constant low pressure, the dynamic permeability is an intrinsic property determined by change of fabric geometry and structure due to a high-pressure load. The pressure-induced deformation is identified, including effects on fiber and yarn arrangement, yarn porosity and fabric thickness. The level of deformation is a function of the number of fabric layers and initial pressure drop. The experimental results show that the dynamic permeability is higher than the static permeability for loose fabric, while it is lower for tight fabrics. For tight fabric, more fabric layers and a lower initial pressure can reduce the difference between the static and the dynamic permeability. Analytical models are used to explain and predict both static and dynamic permeability.

Through-thickness air permeability of woven fabric under low pressure compression

Through-thickness permeability (TTP) is one primary property of technical textiles used in air-related applications, such as filtration and protection. The TTP depends on the textile geometrical factors and usually varies according to the test conditions. In this article, the effect of low air pressure compression (LPC) on TTP of woven fabric was investigated. Nine woven fabrics were measured for the relationships of LPC and thickness, LPC and fabric in-plane dimensions, air pressure drop (APD) and air velocity, as well as LPC and fabric TTP. A dramatic decrease of woven fabric thickness was found below the APD value of 200 Pa and less decreased thickness was observed with a continued increase of APD. The variation of fabric in-planar dimensions was found to be negligible during LPC. The plot relationship of the APD and measured air velocity was presented in linearity for most fabric samples. The fabric TTP showed a linear proportion to the fabric thickness, indicating the fabric to be more permeable with the increase of thickness. A sensitivity study showed an evident difference between using fabric constant and decreased (LPC) thickness in calculating TTP, disclosing the importance of compression in fabric TTP evaluation.

Shape Memory Investigation of α-Keratin Fibers as Multi-Coupled Stimuli of Responsive Smart Materials

Like the water responsive shape memory (SM) effect of β-keratin bird feathers, α-keratin hairs either existing broadly in nature are found responsive to many types of coupled stimuli in SM behaviors. In this article, α-keratin hairs were investigated for the combined stimuli of thermo-solvent, solvent-solvent, and UV (radiation)-reductant sensitive SM abilities. The related netpoints and switches from the hair molecular networks were identified. The experimental results showed that α-keratin hairs manifested a higher ability of shape fixation under thermal stimulus followed with the stimuli of solvent and UV-radiation. Shape recovery from the hair with a temporarily fixed shape showed a higher recovery ability using solvent than the stimuli of heat and UV-radiation. The effects of coupled stimuli on hair’s shape fixation and recovery and on variations of the crystal, disulfide, and hydrogen bonds were studied systematically. A structural network model was thereafter proposed to interpret the multi-coupled stimuli sensitive SM of α-keratin hair. This original study is expected to provide inspiration for exploring other natural fibers to reveal related smart functions and for making more types of remarkable adapted synthetic materials.

Geometrical modeling of honeycomb woven fabric architecture

Honeycomb woven fabric is considered as a single layer fabric produced only using common weaving looms, but it forms a unique three-dimensional (3D) architecture with inverted pyramidal pits on the fabric surface and repeated tetrahedral-closed space inside the fabric, which is greatly different from the traditional 3D woven fabrics, such as angle-interlock and orthogonal fabrics, showing good prospect for various applications in fields such as geotextiles, medical textiles, air filter, tower packing and underclothing. This paper proposes an analytical model to characterize the geometrical shape and position of each yarn in a honeycomb fabric unit-cell and the volume of the internal space. The model is based on the assumption of fabric thickness in the sum of yarn height and the linear relationship of yarn position and fabric unit-cell dimensions. The model involves geometric parameters, including yarn width, height, spacing, crimp and the number of yarns in a fabric unit-cell. Six honeycomb woven fabrics were manufactured to verify the model. Based on the position and crimp prediction of each yarn node, the architectures of the six fabrics were simulated numerically, which shows close agreement with the observed manufactured fabrics, indicating good accuracy of the geometrical model. A sensitivity study shows that the volume of the internal space decreases with the increase of fabric density, and the application of the elastic yarns to the fabric reduces the volume significantly.

Transfer and mechanical behavior of three-dimensional honeycomb fabric

Honeycomb woven fabric is a single layer of fabric exhibiting three-dimensional (3D) cellular shape on both fabric sides due to the combination of periodic straight yarn floats and partial plain weave. In a fabric weave repeat, the triangle shape of increased yarn floats and crossed diagonal woven lines form two inverted pyramidal spaces on the fabric surfaces and a closed internal space. This particular 3D architecture is bound to influence the fabric transfer and mechanical properties. This study investigated these properties for honeycomb weaves experimentally, including air resistance, thermal conductivity, water absorption and vapor transmission rate, bending rigidity, compressional energy and tensile behavior. The typical two-dimensional plain woven fabrics with the same yarns and density were set as references and elastic yarns were considered as a factor of effect on the fabric properties. The measurements by the Kawabata Evaluation System and Instron machine show that the honeycomb woven fabric has enhanced air permeability and water absorption, as well as lower thermal conductivity compared to that of the plain woven fabric. Higher bending rigidity, compressional energy and Young’s modulus are also observed for honeycomb fabrics. The mechanical properties are found to be affected significantly by applying the elastic yarns to the honeycomb woven fabrics.

Through-thickness permeability modelling of woven fabric under out-of-plane deformation

When a woven fabric is subject to a normal uniform loading, its properties such as tightness and through-thickness permeability are both altered, which relates to the fabric out-of-plane deformation (OPD) and dynamic permeability (DP). In this article, fabric OPD is analytically modelled through an energy minimisation method, and corresponding fabric DP is established as the function of loading and fabric-deformed structure. The total model shows the permeability a decrease for tight fabric and an increase for loose fabric when the uniform loading increases. This is verified experimentally by fabric OPD, static and dynamic permeabilities. Experimental tests for both permeabilities showed good agreement with the corresponding predictions, indicating the fact that tight fabric becomes denser and loose fabric gets more porous during OPD. A sensitivity study showed that an increase of fabric Young’s modulus or a decrease of fabric test radius both lead to an increase of DP for tight fabric and opposite for loose fabric. The critical fabric porosity and thickness were found for inflexion of fabric DP trend during the OPD, which contributes to the optimum design of interlacing structure applied to protective textiles and composites.

A solution for transverse thermal conductivity of composites with quadratic or hexagonal unidirectional fibres

Abstract A solution for the transverse thermal conductivity (Ke) of unidirectional fibre arrays, quadratic and hexagonal, is developed analytically. The solution integrates the thermal conductivity of fibre (Kf) and fluid (Km) based on electricity analogy without thermal contact resistance (Rc) at the fibre/fluid interface. The expression Ke is a function of Kf and Km, as well as of the fibre volume fraction (Vf). In this article, Ke values of four composites were predicted and verified by computational fluid dynamics (CFD) simulations. The results showed good agreement when the ratio of Kf/Km is close to 1. An increase in the ratio or Vf gives poorer agreement owing to the local temperature gradient at the fibre/fluid interface. CFD simulation also showed that Ke is decreasing as the Rc value increases.

Preparation and Property Evaluation of Conductive Hydrogel Using Poly (Vinyl Alcohol)/Polyethylene Glycol/Graphene Oxide for Human Electrocardiogram Acquisition

Conductive hydrogel combined with Ag/AgCl electrode is widely used in the acquisition of bio-signals. However, the high adhesiveness of current commercial hydrogel causes human skin allergies and pruritus easily after wearing hydrogel for electrodes for a long time. In this paper, a novel conductive hydrogel with good mechanical and conductive performance was prepared using polyvinyl alcohol (PVA), polyethylene glycol (PEG), and graphene oxide (GO) nanoparticles. A cyclic freezing–thawing method was employed under processing conditions of −40 °C (8 h) and 20 °C (4 h) separately for three cycles in sequence until a strong conductive hydrogel, namely, PVA/PEG/GO gel, was obtained. Characterization (Fourier transform infrared spectroscopy, nuclear magnetic resonance, scanning electron microscopy) results indicated that the assembled hydrogel was successfully prepared with a three-dimensional network structure and, thereafter, the high strength and elasticity due to the complete polymeric net formed by dense hydrogen bonds in the freezing process. The as-made PVA/PEG/GO hydrogel was then composited with nonwoven fabric for electrocardiogram (ECG) electrodes. The ECG acquisition data indicated that the prepared hydrogel has good electro-conductivity and can obtain stable ECG signals for humans in a static state and in motion (with a small amount of drift). A comparison of results indicated that the prepared PVA/PEG/GO gel obtained the same quality of ECG signals with commercial conductive gel with fewer cases of allergies and pruritus in volunteer after six hours of wear.