Interfiber Friction Research Articles

N-Like rheograms of suspensions of magnetic nanofibers

Rheograms of suspensions of single-domain magnetic nanofibers in the presence of an applied magnetic field display an N-like shape. Namely, the shear stress initially increases with the shear rate, reaching a maximum at values of the shear rate of the order of 10 s−1, then decreases to a minimum and, finally, increases monotonically as the shear rate is further increased. In this paper we present a theoretical model that explains this shape of the rheograms from a microscopical viewpoint. Our model considers that two types of nanofiber aggregates of ellipsoidal shape are built upon magnetic field application, depending on the strength of solid friction between nanofibers in each type of aggregate. In the first type of aggregate, interfiber friction is not very strong and nanofibers could reorganize as the aggregate is tilted by the shear flow, giving rise to a “paramagnetic” aggregate with changeable magnetization. In the second type of aggregate, interfiber friction is so strong that nanofiber orientations are fixed and, thus, the magnitude and direction (along the aggregate main axis) of the magnetization of the aggregate are fixed too. This model is a simplification of the real situation in which a more or less continuous distribution of the aggregates over the friction forces is expected. In spite of this simplification, the predictions of our model agree qualitatively and quantitatively with experimental results.

The Effect of the Sliver Fiber Configuration on the Cotton Inter-fiber Frictional Forces

Fiber surface properties have a significant effect on yarn spinning. The frictional behavior of fibers greatly influences their processing, their performance and the performance of the final product. In order to investigate the effect of fiber surface properties and inter-fiber friction during spinning process, card slivers are taken and subjected to three drawing passages. Card and drawing frame slivers are then tested by the Static Friction Tester (SFT), which has been developed earlier. Fiber fineness, maturity and fiber length are measured by using different testing instruments. Hook content is calculated by utilizing fiber length data. The statistical analysis of results shows the same trend for the different cotton fibers tested.

A constitutive model for the in-plane mechanical behavior of nonwoven fabrics

A constitutive model is presented for the in-plane mechanical behavior of nonwoven fabrics. The model is developed within the context of the finite element method and provides the constitutive response for a mesodomain of the fabric corresponding to the area associated to a finite element. The model is built upon the ensemble of three blocks, namely fabric, fibers and damage. The continuum tensorial formulation of the fabric response rigorously takes into account the effect of fiber rotation for large strains and includes the nonlinear fiber behavior. In addition, the various damage mechanisms experimentally observed (bond and fiber fracture, interfiber friction and fiber pull-out) are included in a phenomenological way and the random nature of these materials is also taken into account by means of a Monte Carlo lottery to determine the damage thresholds. The model results are validated with recent experimental results on the tensile response of smooth and notched specimens of a polypropylene nonwoven fabric.

Mechanics of three-dimensional, nonbonded random fiber networks

The mechanical behavior of an ensemble of athermal fibers forming a nonbonded network subjected to triaxial compression is studied using a numerical model. The response exhibits a power law dependence of stress on the dilatation strain and hysteresis upon loading and unloading. A stable hysteresis loop results after the first loading and unloading cycle. In the early stages of compaction, strain energy is associated primarily with the bending of fibers, while at higher densities, it is stored primarily in the axial deformation mode. It is shown that the exponent of the power law, and the partition of energy in the axial and bending modes depends on the ratio of the bending to axial stiffness of the fibers. Accounting for interfiber friction does not change the functional form of the stress-strain relationship or the exponent. The central feature that distinguishes the mechanics of this system from that of bonded random networks is the relative sliding at contacts and the ensuing fiber rearrangements. We show that suppressing sliding leads to a much stiffer response. The results indicate that the value of the exponent of the stress-strain power law is determined not only by fiber bending and the formation of new contacts, but also by the relative sliding and axial deformation of fibers.

Consequences of immature fiber on the processing performance of Upland cotton

Immature cotton fiber will negatively impact textile processing. Three field experiments were undertaken that applied chemical harvest aids to upland cotton ( Gossypium hirsutum L.) crops at varying times with the intention of manipulating the maturity of bolls and fibers. The aim was to quantify the effects of these treatments on the textile performance of the harvested cotton and relate these differences to the status of the crop at the time of treatment application. Although earlier treatments produced less mature fiber that was lower in linear density, yarn and fabric strength was not affected. However less mature cotton from a cooler growing season produced stronger yarns (by 3 cN tex −1) and fabric (by 0.39 N (g m −2) −1) which was partly attributed to the smaller ribbon width of this fiber affecting more fiber packing density and inter-fiber friction. Yarns made from this immature cotton also contained more neps. Micronaire and linear density were equally well related, and more strongly related than maturity ratio, to dyed fabric color dimensions, which were greatly influenced by treatments. Percent immature bolls at the time of harvest aid application related well to changes in the degree of fabric blueness ( R 2 = 0.89). Knowing the status of a crop in the final stages of production will help cotton producers and the supply chain to predict some of the processing performance aspects of harvested fiber.

Objective evaluation of artificial furs for tactile comfort

The resistance of piles when fingers move on artificial furs is important for tactile comfort. To evaluate the resistance of piles, a simple device for measuring the horizontal force FH of artificial furs was developed and attached to a KES-SE surface tester. The horizontal force (FH) generated when a bar moves on the surface was measured at different vertical displacements from the base for samples with different pile lengths. A hand evaluation test was carried out to find the relationship between FH and subjective parameters, namely, smoothness, comfort and ‘shittori’. Subjective hand evaluations showed that fur mobility was directly related to the sensations of smoothness and comfort. The average horizontal force included the interfiber friction force caused by changing the pile density during bar movement. FH is related to fur mobility and is one of the useful indicators of the tactile comfort of furs.

Digital element approach for simulating impact and penetration of textiles

A micro-scale computational tool, based upon an explicit digital element method (DEM), has been developed for numerical simulation of ballistic impact and penetration of textile fabrics. In this approach, each yarn is digitized as an assembly of digital fibers. Each digital fiber is further digitized into a short digital rod element chain connected by frictionless pins (nodes). A search is conducted to find contacts between adjacent digital fibers. If a contact is detected, compressive and frictional forces between fibers will be determined, based upon contact stiffness and friction coefficient. Nodal forces are calculated for each time step. Nodal displacements are determined using an explicit procedure. Because the digital element approach operates on a sub-yarn micro-scale, one can determine textile penetration resistance based upon sub-yarn scale properties, such as inter-fiber compression, friction, and fiber strength. Research presented in this paper includes three parts. First, the explicit digital element algorithm used in dynamic simulation is explained. Second, the approach is used to generate 2-D woven fabric micro-geometries and to simulate ballistic penetration processes. Third, numerical results are compared to high resolution experimental impact and ballistic test data.

Measurement of interfiber friction force for pulp fibers by atomic force microscopy

Interfiber friction in paper exists in fiber suspensions, fiber flocs, and fiber networks. The interfiber friction force is, therefore, important both in papermaking and in the use of paper. The objective of this research is to develop a methodology using atomic force microscopy (AFM) for the direct measurement of the friction force between pulp fibers. Different factors such as AFM scanning velocity, contact area, and fiber surface roughness were investigated. The results show that AFM is an effective tool for measuring micro-scale interfiber friction forces. Both AFM scanning velocity and fiber surface roughness affect the measured results. The coefficient of friction increases, but the initial adhesion force decreases, with increasing fiber surface roughness.

Friction in textile fibers and its role in fiber processing

Textile fibers are characterized by many parameters, used by both researchers and industrial users. Many studies focus on the effect of fiber length, fineness, maturity (only for cotton), tensile properties, etc. on the properties of intermediate products and yarns. Contrary, few studies concerning the fiber surface properties, especially the inter-fiber friction, appear in the scientific literature. A new and simple device is designed and used in this. It enables the measurement of inter-fiber friction force during the dissociation of an ordinary sliver. Contrary to what has previously been mentioned in the scientific literature, the study of a set of different cottons shows that the inter-fiber friction seems to obey the Amontons’ law rather than a more complex power law model. The calculated inter-fiber friction coefficient helps to differentiate the different types of cotton and to bring to the fore the non-negligible effect of the friction on yarn irregularity and imperfections, affecting the yarn tenacity indirectly. Meanwhile, this work has revealed a curious grouping of different types of cotton, which is not observed before. This phenomenon is undoubtedly due to the surface properties of fibers.

Magnetorheology of fiber suspensions. II. Theory

This paper reports the first predictions of the yield stress of suspensions of non-Brownian magnetic fibers in the presence of uniform magnetic fields. The quasistatic regime of the shear deformation (before the flow onset) of the suspension is studied. Four different structures of the magnetic fiber suspensions are considered—column, zigzag, three-dimensional stochastic and near-planar stochastic structures—and the yield stress is attributed to the failure of the given structure at a critical strain. The main contributions to the yield stress are found to come from the restoring magnetic torque acting on each fiber and from the solid friction between fibers. The enhanced magnetorheological effect of magnetic fiber suspensions observed experimentally [M. T. López-López et al., J. Rheol. 53, 115–126 (2009)] is explained and quantified in terms of interfiber friction. Surprisingly, the dipolar magnetic interactions between fibers do not affect significantly the yield stress. The lowest yield stress is obtained for the zigzag structure and the highest one for the column structure. A reasonable agreement with the experiments is obtained for 5% and 7% fiber volume fractions in the frame of the more realistic model of near-planar stochastic structures.

Statistical strength of a twisted fiber bundle: an extension of daniels equal-load-sharing parallel bundle theory

In this work, we extend the statistical strength model of Daniels for a parallel fiber bundle to a twisted bundle with an ideal helical structure. The bundle is clamped at each end in such a way that it has no slack fibers in the unloaded state. The fibers are linearly elastic and continuous, and have random strengths following a Weibull distribution with Weibull shape parameter . We calculate the stress redistribution from failed to surviving fibers according to a twist-modified equal load sharing (TM-ELS) rule, introduced here. The effect of the twist is modeled analytically by two approaches, one called geometrical averaging, in which the fiber helix angles are averaged, and the other called statistical averaging, in which the fiber failure probabilities are averaged. In both probability models, the bundle strength distributions remain asymptotically Gaussian, as in Daniels’ original model; however, the associated mean and standard deviation are additionally altered by the surface twist angle. To validate these theories, a Monte Carlo model is developed to simulate fiber break initiation and progression within a cross-sectional plane under tension. For all values of surface twist angle s, and bundle size studied, the simulated strength distributions are shown to be strongly Gaussian. Transitions in failure mode from diffuse, across the bundle cross-section, to localized near the center of the bundle occur when s and increase and the bundle size decreases, in spite of application of a diffuse-type loading sharing rule, TMELS. Both analytical models provide similar results which are in excellent agreement with the simulated results. For the most part, we consider the bundle to be short enough that interfiber friction plays no role in the stress redistribution. However, to demonstrate its importance in long bundles, we mimic the effects of interfiber friction by considering a chain of such bundles where the bundle length is chosen to approximate the characteristic length of unloading around breaks.

Rheology of sheared flexible fiber suspensions via fiber-level simulations

We employ a particle-level simulation technique to investigate the rheology of non-Brownian, flexible fiber suspensions in simple shear flow. The model incorporates a variety of realistic features including fiber flexibility, fiber deformation, and frictional contacts. The viscosity of fiber suspensions is strongly influenced by the fiber equilibrium shape, interfiber friction, and fiber stiffness. The viscosity of the suspension increases as the fiber curvature, the coefficient of friction, or the fiber stiffness is increased. The yield stress of fiber suspensions scales with the volume fraction in a manner similar to that observed experimentally. Fiber suspensions that flocculate exhibit a shear thinning regime that extends to shear rates lower than those observed for homogeneous suspensions.

Effects of Silicone Treatments on the Dimensional Properties of Wool Fabric

This study evaluates the effects of silicone softeners on the dimensional properties of wool fabric. Samples are treated with a simple pad-dry-cure process in an aqueous bath with aminofunctional and epoxyfunctional silicone softeners. The results indicate that dimensional stability and performance properties improve. The maximum effect is obtained with a 1:1 proportion of aminofunctional and epoxyfunctional silicone softeners, probably due to the synergistic effect of both softeners by the catalyzing reaction of the amine group. A hydrophilic epoxyfunctional silicone softener seems to increase fiber swelling and prevents the reduction of hygral expansion. As for the other properties, there are no significant variations when different kinds of epoxyfunctional silicone softeners are used. The most significant effect of the softeners is the surface coating, which reduces interfiber or interyarn friction.

Measuring Deformations of Limp Fabrics for Material Handling

There is an increasing focus on automating the textile industry, particularly labor- intensive tasks such as fabric manipulation and assembly. The highly flexible nature of these materials makes automation very challenging. Not only are fabrics difficult to manipulate, but their geometric characteristics are difficult to measure with conventional instruments. Accurate ways of measuring the state of the workpiece are needed to provide feedback for system control. This paper proposes a system for measuring the shape and range of locations for a wrinkle along the length of a fabric strip, based on a measurement of the difference between its total unwrinkled length and total wrinkled length Δ Ltotal. A relationship can be established between ΔLtotal and the forces necessary to sustain the wrinkle that corresponds to Δ Ltotal using Clapp's model for the fabric elastica and a model of the flat fabric lying on the table. Force balances that include the frictional force required to support the wrinkle provide the basis for locating it along a spatial length. A nondi mensional variation of Clapp's model shows many possible solutions or modes for a wrinkle shape corresponding to one value of Δ Ltotal, although the boundary forces will be different for each mode. Each wrinkle shape is unique in the number of "humps" it contains. This variation of the model also shows that as the wrinkle gets taller, an effect similar to an inverted pendulum occurs when the simulated wrinkle tends to lean to one side or the other. These results can be observed experimentally with actual fabrics, although heavier weight fabrics have poorer comparisons to their modeled simulations. One explanation is that heavier fabrics are prone to interfiber friction that creates material memory, which was not included in the mathematical model analysis. This system provides a useful measuring tool for industry. The general solution provided by the nondimensional model defines important relationships between the wrinkle's boundary forces and Δ Ltotal. Finding the material parameters of a fabric, which costs only a small initial time investment, provides information the general model needs to predict a shape and range of locations for a wrinkle in a high-speed industrial environment.

Tribology of Sized Glass Fibers

Lateral force microscopy (LFM) and an electronic microbalance method are used for a friction force analysis of sized glass fibers, which are generally used to reinforce com posite materials. Friction coefficients of glass fibers A and E, coated with sizes containing a starch and an epoxy film former, respectively, are determined. Friction force values measured between a scanning Si3 N4 microtip and the fiber's surface are smaller than those evaluated between two sliding glass fibers. Important variations of lateral force signals by the LFM reveal the chemical heterogeneity of the sized glass fiber A, while for fiber E, plowing effects and variations of the friction coefficient from one fiber to another as well as a greater friction coefficient than fiber A are detected. With the second technique, there is a large distribution of friction coefficient values due to chemical and/or physical heterogeneities of the fiber surface. Statistical methods are used to interpret the results. Interfiber friction values are correlated to the friction values obtained by lateral force microscopy. The overall results show that these two methods are very effective in determining tribological properties of sized glass fibers.

Simulations of fiber flocculation: Effects of fiber properties and interfiber friction

Non-Brownian fibers commonly flocculate in flowing suspensions at relatively low concentrations (<1% by weight). We have developed a particle-level simulation technique modeling fibers as chains of rods connected by hinges to probe fiber flocculation. The model incorporates fiber flexibility, irregular fiber equilibrium shapes, and frictional fiber interactions. Model fibers reproduce known orbits of isolated rigid and flexible fibers in shear flow. Simulation predictions of first normal stress differences in homogeneously dispersed, dilute flexible fiber suspensions agree with experimental data. Fiber features such as flexibility and irregular equilibrium shapes strongly impact single fiber and suspension behavior. Fibers aggregate in simulations with interfiber friction, in the absence of attractive forces between fibers. Strong flocculation is observed in suspensions of stiff fibers with irregular equilibrium shapes. Flocs contain many fibers with three or more contact points, and derive cohesiveness from elastic energy held in fibers—consistent with the elastic interlocking mechanism of flocculation. At higher concentrations (nL3≈100, where n is the fiber number density and L is the fiber length), coherent fiber networks form in simulations. Average numbers of contacts per fiber and contact force magnitudes in sheared and static networks are compared with existing fiber network theory predictions.

Properties of Fiber Flocs with Frictional and Attractive Interfiber Forces

Theory and experiment suggest that the flocculation of non-Brownian, flexible fibers in flowing viscous media arises from the mechanical entanglement of fibers. We probe the role of frictional and attractive interfiber forces on fiber entanglement using a recently developed particle level simulation technique. With frictional and repulsive interparticle forces only, simulations capture flocculation in 0.125% by volume suspensions of fibers with properties similar to those of softwood pulp fibers. Here, model fibers elastically interlock—flocculation tendency and floc coherency are directly linked to elastic energy storage in fibers. By applying only repulsive and attractive interparticle forces of various strengths, sheared suspensions attain similar degrees of aggregation, and similar floc strengths, as in suspensions with interfiber friction. However, in the absence of interfiber friction, model fibers do not elastically interlock. We find friction to be an essential element in elastic entanglement of fibers. Simulations suggest that effective formation aids in papermaking should reduce interfiber friction under normal force loadings of 1–10 μN.

Mathematical Simulation of Fabric Bagging

A mathematical model is developed to simulate the rheological behavior of fabric bagging. The model is based on the assumption that stress-strain relationships in fabric consist of three essential components: elastic deformation and viscoelastic deformation of fibers and the friction between fibers and yarns within the fabric structure. The nonlinear strain of the fabric, the elastic and viscoelastic deformation of fibers, and interfiber friction during the bagging process have been taken into account in the model. By specifying the fundamental parameters of fiber mechanical properties and yarn-fabric structural features, the model is able to predict fabric bagging behavior under test conditions, such as loading and unloading processes in each cycle, change of bagging force with cycles, relative contributions of the three components (elasticity, viscoelasticity, and frictional forces) in each cycle, and residual bagging height in each cycle. A comparison of theoretical predictions with experimental measurements for two wool fabrics with different structures reveals good agreement between them. The results indicate that the mathematical model is able to quantitatively simulate fabric bagging rheological behavior and predict fabric bagging performance by specifying basic fiber mechanical properties and yarn-fabric structural parameters.

Effects of Softener Treatment on Hand, Thermal and Moisture Transport, and Wear Comfort of Knitted Fabrics.

Knitted fabrics were treated with household softeners. The mechanical and surface properties as well as the thermal and moisture transport properties of the fabrics were measured. The use of softeners decreased the friction between fibers, the fabrics treated with softeners became softer and the primary fabric hand values (NUMERI, FUKURAMI, SOFUTOSA) increased slightly. Therefore, the wearing comfort on winter of these fabrics seemed to increase. But cotton fabric exhibited polyester fabric-type hydropyobic properties and the wearing comfort on summer seemed to decrease. In the case of washing with detergent that contains softener, the softener did not adequately reduce the inter-fiber friction that increases when a fabric is washed by detergent alone, indicating that it is most effective to add softener after the wash cycle.

Mechanism of Yarn Failure

The importance of interfiber friction in determining yarn strength has been acknowledged by several authors. Studies of the effect of friction on yarn strength were often based on determining the influence of twist level, a structural factor, to change the level of friction. To our knowledge, no study is available in which varying fiber frictional characteristics are introduced into a constant yarn structure ( i.e., the same twist, fiber type, fiber length, etc.). This effect has been accomplished through a surface treatment that changes the level of interfiber friction, and subsequent yarn testing provides useful and interesting information about how fiber interaction contributes to yarn strength. The results presented here show that interfiber friction can (under certain circumstances) be the dominant factor in determining the tensile properties of a ring spun staple yarn. Friction and yarn strength results show that moderate changes in the interfiber friction can produce large changes in yarn strength. We suggest that interfiber friction should receive more attention as a determinant of yarn properties, particularly strength.