Fiber Cross-sectional Shape Research Articles

Fiber Cross-Section Shape Effect on Rate-Dependent Behavior of Polymer Matrix Composites with Fiber Bragg Grating Sensors

A strain measurement system with fiber Bragg grating (FBG) sensors is developed to monitor the quasistatic/dynamic strain in a glass/epoxy for the experimental analysis of the rate-dependent behavior of polymer matrix composites (PMCs). The rate-dependent inelastic constitutive relationship of epoxy is built using an internal state variable viscoplasticity model with experimental responses. The micromechanical investigation of fiber shape effect on the rate-dependent behavior of glass/epoxy for various off-axis angles is performed at 10–5 and 1/s. The results indicate that a higher strain rate causes a greater flow stress in PMCs. The fiber shape evidently affects the inelastic deformation at large off-axis angle with the biggest stiffness provided by the square fiber, but has little impact on the elastic deformation for all off-axis angles. The effect of fiber shapes on overall responses is enhanced with increasing off-axis angles but weakens with increasing strain rate.

Transverse permeability determination of dual-scale fibrous materials

Transverse flow through aligned yarns with two length scales is theoretically studied. Darcy’s law and Stokes equation are employed to describe flow behaviors inside the porous yarns and in the open channels between yarns, respectively. Beavers and Joseph’s semi-empirical model and Brinkman’s extension of Darcy’s law are used to characterize the jump-velocity and continuum-stress boundary condition at the interface layer between the clear fluid and the porous yarn. The analytical model for predicting permeability is developed as a function of porosity, fiber radius, fiber cross-sectional shape, and fiber packing pattern, which would help improve the physical understandings of dual-scale flows in fibrous media. Additionally, a simple but effective semi-analytical model is provided for easy use. Permeability predictions calculated from our model agree fairly well with experimental and numerical results in literature.

Effect of pile fiber cross section shape on compression properties of polypropylene carpets

Fiber cross section shapes, which have a direct influence on the physical properties of textile surfaces, are becoming more and more complex recently. There are also many important properties of the carpets such as luster, resilience, abrasion resistance which are impacted by the shape of the fiber cross sections. In this present paper, the influence of pile fiber cross section shape on compression properties of carpets was experimentally investigated under short and long-term static loadings. The material used was polypropylene carpets having two different pile fiber shapes: trilobal and hollow. The experimental results indicate that percentage thickness loss of carpets having hollow piles is slightly higher than carpets with trilobal piles in both short- and long-term static loadings. However, in the case of percentage recovery, similar values were obtained for the samples used in this study.

Compression creep behaviour of polyester needle-punched nonwoven fabrics

This present study deals with the compression creep behaviour of polyester needle-punched nonwoven fabrics. Polyester fibres of three different cross-sectional shapes (round, circular hollow and trilobal) have been selected for this study. An instrument has been designed and fabricated to measure the compression creep property of needle-punched fabrics. The effect of duration of compression load, fabric weight, fibre cross-sectional shapes and reinforcing material on percentage compression creep has been studied. It has been observed that initially, compression creep decreases rapidly and with increase in time, decrease of percentage creep becomes minimal. After about 8500 min of application of the same compression load, no change in compression creep is noticed. The percentage compression creep decreases with the increase in fabric weight irrespective to fibre cross-sectional shapes of polyester needle-punched nonwoven fabrics. Trilobal cross-sectional fabric shows maximum amount of percentage compression creep at all levels of fabric weight followed by round and hollow cross-sectional polyester samples, respectively. The percentage compression creep is higher in case of fabric samples made without reinforcing material compared to the samples with reinforcing material. Hollow cross-sectional polyester fibre can be successfully used as raw material for the preparation of needle-punched nonwoven fabrics with or without reinforcing material carpet or floor mats. However, normal round cross-sectional polyester fibre only with reinforcing material can be used for the said application. Compression creep values of these selected polyester needle-punched fabric samples are much lesser in comparison with commercial market polypropylene needle-punched carpet samples.

Effect of viscosity and electrical conductivity on the morphology and fiber diameter in melt electrospinning of polypropylene

The feasibility of fabricating polypropylene (PP) nanofibers has been explored by using different additives, such as sodium oleate (SO), poly(ethylene glycol) (PEG) and poly(dimethyl siloxane) (PDMS), during melt electrospinning. PP of high melt flow index (1000) was used with PEG and PDMS for the reduction of the melt viscosity; and it was used with SO for improving the electrical conductivity during melt electrospinning. It was observed that all the additives used in this study helped to reduce the fiber diameter. The most promising additive, SO, was effective in reducing the fiber diameter to the nanometer scale due to the increase in the electrical conductivity. The fiber diameter was decreased by the addition of PEG and PDMS due to the decrease in the melt viscosity. The effect of die shape on the fiber cross-sectional shape was analyzed and an interesting finding is that the die shapes did not have an effect on the cross-sectional shape of the fibers. That is, irrespective of the die shapes (i.e. trilobal, tetralobal, multilobal and circular) used in this study, the cross-sectional shapes of melt electrospun fibers were circular. The distribution of the additives in the fiber was analyzed by energy-dispersive X-ray analysis and was found to be uniform. Tensile tests were performed on single nanofibers with limited success, due to the problems in preparing fiber samples and successfully holding them in the jaws of the testing machine without slippage.

Effect of polypropylene fiber cross sectional shapes on some structural/mechanical fiber properties and compressibility behaviour of plain knitted fabrics

Synthetic fibers are generally produced with circular cross sectional shapes. Other cross sectional shaped fibers such as trilobal, triangular, hollow and pentagonal fibers are also produced to improve some properties of fibers and fabrics such as lustre, handle, wicking rate, strength, stiffness and bulkiness. In this research we aimed to investigate compressional behaviours of fabrics knitted from polypropylene fibers having three different cross sectional shapes; namely circular, trilobal and triangular. Morphological, structural and mechanical properties of produced fibers were evaluated by using scanning electron microscopy, X-ray diffractometry, differential scanning calorimetry and tensile tester, respectively. In terms of structural and mechanical properties, no significant differences were found related to fiber cross sectional shapes. Then, plain knitted farbrics were produced and compressional properties of these fabrics were investigated. Fabrics knitted from trilobal fibers showed the highest compressibility properties and it is followed by fabrics which are produced from triangular and circular fibers.

Optimizing fiber cross-sectional shape for improving stability of air–water interface over superhydrophobic fibrous coatings

In this letter, a mathematical force-balance formulation is developed that can be used to predict the critical pressure, the hydrostatic pressure above which the surface starts to depart from the non-wetting state, for superhydrophobic surfaces comprised of highly aligned fibers (e.g., biased AC-electrospun coatings) with arbitrary cross-sectional shapes. We have also developed a methodology for optimizing the fiber cross-sections to maximize the critical pressure of the surface, using the Euler–Lagrange equation. A case study is presented to better demonstrate the application of our method.

Automated 3D measurement of fiber cross section morphology in handsheets

Abstract We present a method for 3D measurement of fiber cross sectional morphology from handsheets. An automated procedure is used to acquire 3D datasets of fiber cross sectional images using an automated microtome and light microscopy. The fiber cross section geometry is extracted using digital image analysis. Simple sample preparation and highly automated image acquisition and image analysis are providing an efficient tool to analyze large samples. It is demonstrated that if fibers are tilted towards the image plane the images of fiber cross sections are always larger than the true fiber cross section geometry. In our analysis the tilting angles of the fibers to the image plane are measured. The resulting fiber cross sectional images are distorted to compensate the error due to fiber tilt, restoring the true fiber cross sectional shape. We use an approximated correction, the paper provides error estimates of the approximation. Measurement results for fiber wall thickness, fiber coarseness and fiber collapse are presented for one hardwood and one softwood pulp.

Performance Study of Jutecell Fiber and Yarn

As a starting point of the subject, the basic performances of Jutecell fiber and yarn were studied, the fiber cross-sectional shape, composition and mechanical properties of Jutecell fiber were first tested and analyzed systematically. In process of evaluating the quality of the yarn , its fineness , evenness, twist, strength, moisture content , hairiness properties were taken for the important reference parameters to carry on test and analysis. The blended yarn of Jutecell fiber and cotton fiber[1], with the blended rate of 50/50, Yarn fineness of 22.6tex, Fiber specification of 1.33dtex*38mm, were used in the research of the subject.

Three-dimensional microlasers based on polymer fibers fabricated by electrospinning

We report three-dimensional mirror-less lasing from non-cylindrical dye doped polystyrene fibers drawn using an electrospinning procedure where the fiber cross-sectional shape and dimension could be controlled. Signatures of three dimensional etalon like modes were observed corresponding to the transverse and axial quantization of the wave vector. Low lasing thresholds of the order of 200 nJ were achieved along with moderate Q factors.

Micromechanical analysis of off-axis loading of fiber reinforced composites with imperfect interface bonding

A micromechanical method based on generalized method of cells for investigating elastic and plastic response of composites subjected to off-axis loading is presented. Through implementing the formulas of interfacial displacement into average displacement continuity, the relationship between sub-cell strain rate and macro-strain rate is constructed in the condition of composites with wake interface bonding. On this basis, microstructure parameters, such as fiber cross-section shape, fiber volume fraction, are considered. Numerical results indicate that increasing fiber volume fraction will decrease the flow stress of composites in the condition of weak interfacial bonding. While the tendency is independent on fiber cross-section shape. Also, the effect of off-axis tensile strength tends to be weakened with the increase of off-axis angle in the condition of weak interfacial bonding. However, square fiber always provides more flow stress than circular fiber in both perfect interfacial binding and weak interfacial bonding.

Studies on compression properties of polyester needle-punched nonwoven fabrics under dry and wet conditions

In this article, the effects of fabric weight, fiber cross-sectional shapes (round, hollow, and trilobal), and presence of reinforcing material on the compression properties (initial thickness, percentage compression, percentage thickness loss, and percentage compression resilience) under dry and wet conditions of polyester needle-punched industrial nonwoven fabrics are presented. It has been found that initial thickness of the fabric decreases under wet condition for both with and without reinforcing materials. The percentage thickness loss values are higher under wet condition in case of samples with reinforcing material compared to samples without reinforcing material. In the presence of reinforcing material, the trilobal cross-sectional fabric samples show the highest increase in thickness loss under wet condition followed by round and hollow cross-sectional polyester needle-punched nonwoven samples. Compression resilience is the highest in case of round cross-sectional fabric without reinforcing material under wet condition than fabric with reinforcing material. The initial thickness increases, and percentage compression and thickness loss decrease with the increase in fabric weight irrespective of fiber cross-sectional shapes both in dry and wet conditions. The initial thickness, percentage compression, and percentage compression resilience of the fabric decrease but percentage thickness loss increases under wet condition compared to the dry condition irrespective of the fiber cross-sectional shape. Compared to other cross-sectioned polyester samples, the hollow cross-section samples undergo very less consolidation under wet condition due to their consolidated structure. There is a drastic drop in compression resilience and increase in thickness loss under wet condition than in dry state irrespective of the fiber cross-sectional shape.

Influence of Polyester Fibre Fineness and Cross-Sectional Shapes on Tensile Properties of Yarns

Mechanical properties of 100% polyester and polyester-viscose (P/V) blended yarns produced from polyester fibres which vary in denier and cross-sectional shape have been analyzed. It is observed that fibre fineness and cross-sectional shape play a significant role in the translation of fibre properties to the respective yarn properties. As the fibre linear density decreases, fibre strength translation efficiency increases. In the case of trilobal fibre, translation efficiency is observed to be lower, but yarn breaking elongation is higher in comparison to the corresponding circular fibre. Scalloped oval fibre contributes more towards yarn strength and elongation versus the equivalent circular and tetraskelion fibres. In the P/V blended form, a decrease in yarn tenacity does not affect fibre fineness, but is substantially influenced by changes in the fibre profile. Contribution of broken viscose fibres (comparatively weaker component) at the point of actual breaking of yarn, i.e. Z-value, is altered depending on the polyester fibre profile, which is higher in trilobal and scalloped oval fibres in comparison to the corresponding circular ones, but the role of fibre linear density in this regard is rendered insignificant.

Strength variability of single flax fibres

Due to the typical large variability in the measured mechanical properties of flax fibres, they are often employed only in low grade composite applications. The present study aims to investigate the reasons for the variability in tensile properties of flax fibres. It is found that an inaccuracy in the determination of the cross-sectional area of the fibres is one major reason for the variability in properties. By applying a typical circular fibre area assumption, a considerable error is introduced into the calculated mechanical properties. Experimental data, together with a simple analytical model, are presented to show that the error is increased when the aspect ratio of the fibre cross-sectional shape is increased. A variability in properties due to the flax fibres themselves is found to originate from the distribution of defects along the fibres. Two distinctive types of stress–strain behaviours (linear and nonlinear) of the fibres are found to be correlated with the amount of defects. The linear stress–strain curves tend to show a higher tensile strength, a higher Young’s modulus, and a lower strain to failure than the nonlinear curves. Finally, the fibres are found to fracture by a complex microscale failure mechanism. Large fracture zones are governed by both surface and internal defects; and these cause cracks to propagate in the transverse and longitudinal directions.

Effects of thermal stress and imperfect interfacial bonding on the mechanical behavior of composites subjected to off-axis loading

Metal matrix composites exhibit inelastic response due to the viscoplasticity of matrix, and imperfect interfacial bonding will decrease the flow stress sharply. The present study develops the generalized model of cells (GMC) to predict mechanical behavior of unidirectional metal matrix composites with imperfect interfacial bonding, which is subjected to off-axis loading. The model incorporates viscoplastic model for the matrix and interfacial debonding model for the fiber/matrix interface. The effects of fiber volume fraction and thermal residual stress on stress–strain response of composites are also discussed. Results show that stress–strain response influenced by fiber cross-section shape becomes more evident with the increase of fiber off-axis angle. Similar stress–strain response can be found in the early stage of loading regardless of the thermal residual stress. However, the effect of thermal residual stress on the stress–strain behavior of composites with imperfect interfacial bonding is closely dependent on fiber off-axis angle in the plastic stage.

A study on thermophysiological comfort properties of fabrics in relation to constituent fibre fineness and cross-sectional shapes

The present study reports the effect of linear densities and profiles of polyester fibres on the physiological properties of their fabrics. Four different polyester fibre finenesses along with microdenier and four cross-sectional shapes (circular, scalloped oval, tetrakelion and trilobal) were selected to produce two sets of 2/1 twill fabrics; one composed of 100% polyester and the other 67:33 P/V blends. In studying the thermophysiological component of the clothing comfort, heat, air and moisture transmission characteristics of the fabrics were assessed. The principal thermal properties, such as thermal absorptivity, thermal resistance and thermal conductivity, were experimentally evaluated, using the Alambeta instrument. The study of the obtained results established the fabrics of non-circular cross-sections as against circular ones, and increase in the linear density results in higher thermal resistance, lower thermal conductivity and lower thermal absorptivity. Wicking behaviour of fabrics was studied under two conditions–wicking from an infinite liquid reservoir (transverse wicking) and wicking from a finite liquid reservoir (single drop wicking into the fabrics). Increase in fibre linear density enhances transplaner wicking but slows down the spreading speed of water drops. Air permeability and moisture vapour permeability are found to be positively correlated with fibre decitex. The role of fibre cross-sectional shapes in influencing mass-flow characteristics is quite considerable. Use of non-circular polyester in place of a circular one augments the wickability of liquid water along with the permeability of air and moisture vapour through the fabrics, revealing their high porosity, which assists air and moisture to propagate. Mixing viscose into polyester brings down the air permeability and moisture vapour transmission rate (MVTR) of fabrics. Results show that moisture absorption of viscose is an important factor in influencing the moisture transport characteristics including both wickability and MVTR of 100% viscose and P/V-blended fabrics.

Growth mechanism of carbon microcoils with changing fiber cross-section shape

Growth mechanism of carbon microcoils with changing fiber cross-section shape

Compression Properties of Polyester Needlepunched Fabric

In the present paper, a study of the effects of fabric weight, fiber cross-sectional shapes (round, hollow and trilobal) and presence of reinforcing material on the compression properties (initial thickness, percentage compression, percentage thickness loss and percentage compression resilience) of polyester needle punched industrial nonwoven fabrics is presented. It was found that for fabrics with no reinforcing material, the initial thickness, compression, and thickness loss were higher than fabrics with reinforcing material, irrespective offiber cross-section. Compression resilience data showed the reverse trend. Initial thickness for trilobal cross-sectional fabric sample was highest followed by round and hollow cross-sectioned polyester needle punched fabrics. The polyester fabric made from hollow cross-sectioned fibers showed the least percentage compression at every level of fabric weights. The trilobal cross-sectioned polyester fabric sample showed higher thickness loss followed by round and hollow cross-sectioned polyester fabric samples respectively. The hollow cross-sectioned polyester fabric samples showed maximum compression resilience followed by round and trilobal cross-sectioned polyester samples irrespective of fabric weights. The initial thickness increases, but percentage compression, thickness loss and compression resilience decreases with the increase in fabric weight irrespective of fiber cross-sectional shapes.

Growth mechanism of carbon microcoils with changing fiber cross-section shape

Carbon microcoils (CMCs) with a fiber cross-section changing from flat to circular along with a coil diameter changing from 4.2 to 6.0 μm, which may develop a novel spring for micromechanical systems, were obtained by controlling the acetylene flow rate using Ni catalyst at a temperature of 1 013–1 053 K. A growth model for these changes was proposed in which catalytic anisotropy is considered to be the possible factor changing the fiber cross-section shape of the CMCs. Owing to the change of catalytic anisotropy caused by reaction conditions, the same slender catalyst can produce both flat CMCs and circular CMCs depending on its relative orientation to the fiber axis. A cubic Ni catalyst can only produce a circular CMC, and can only change the coil diameter upon changing the reaction conditions. The model will give more insight into the formation of CMCs and provide information on the controlled synthesis of CMCs and carbon fibers.

Shaped Fiber Identification Using a Distance-Based Skeletonization Algorithm

Fiber cross-sectional shapes can influence many physical properties of fibers. Automated identification of shaped fibers is critically important for fiber quality inspection. This paper presents a distance-based skeletonization algorithm used for reliable identification of shaped fibers. The skeleton of a fiber cross section, which is generated from fiber distance maps and maximal disks, is ensured to be continuous and insensitive to edge noise, and therefore can be used as abstract representations of fiber topology for shape analysis. A set of shape descriptors are defined from fiber skeletons and a support vector machine method is used to classify fibers based on the shape measurements. The experimental results show that the presented approach can be used to recognize shaped fibers based on the analysis of skeleton structures.