Real Fiber Research Articles

Correction of the measurement of fiber length of short fiber reinforced thermoplastics

Short fiber reinforced thermoplastics are often made using extrusion compounding and injection moulding techniques. Fiber breakage takes place during processing. In finished fiber reinforced parts, there often exists a fiber length distribution. Measurement of fiber length is often performed on photographs of short fibers obtained from burning off or dissolving the matrix. However, relatively long fibers crossing the photographs cannot be counted, leading to underestimation of mean fiber length. In this paper, the effect of fibers intersecting the photographs is discussed on the measurement of fiber length. Correction of the measurement of fiber length is carried out and the real value of mean fiber length and the real fiber length distribution can then be obtained. An example is given to illustrate the correction of the measurement of fiber length.

On Trajectories of Analytic Gradient Vector Fields

Let f: R n ,0→ R,0 be an analytic function defined in a neighbourhood of the origin, having a critical point at 0. We show that the set of non-trivial trajectories of the equation xdot;=∇ f(x) attracted by the origin has the same Čech–Alexander cohomology groups as the real Milnor fibre of f.

A deterministic emulator for the statistical reproduction of a real fiber with accurate PMD statistics up to the third order

A novel deterministic polarization-mode dispersion (PMD) emulator, consisting of delay-sections coupled by rotators is proposed. By opportunely choosing the rotation angles, this device is shown to correctly reproduce the higher order PMD statistics with a reduced number of sections.

Single Muscle Fiber Contraction is Dictated by Inter-Sarcomere Dynamics

This paper presents first results from a study where we developed a generic framework for analysing inter-sarcomere dynamics. Our objective is to find an accurate description of a muscle as a linear motor composed of parallel and series coupled subunits. The quality of theoretical models can be tested through their ability to predict experimental observations. With the current method we have found rigorous mathematical explanations for mechanisms such as sarcomere popping, extra tension and homogenization.These phenomena have been observed for many years in single fibers experiments, yet have never been completely understood in terms of a mechanical model. Now they can be explained on a theoretical basis. Interestingly, rather simplistic descriptions of each of the various molecular components in the sarcomere (actin–myosin cross-bridges, titin and contributions from passive elastic components) are sufficient to predict these behaviors. The complexity of a real muscle fiber is addressed through rigorous coupling of the single component models in a system of differential equations.We examine the properties of the differential equations, based on a down-stripped model, which permits the derivation of analytical solutions. They suggest that the contraction characteristics of inter-connected sarcomeres are essentially dictated by the initial distribution of the sarcomeres on the force–length curve and their starting velocities.The complete model is applied to show the complexity of inter-sarcomere dynamics of activated fibers in stretch–release experiments with either external force or length control. Seemingly contradictory and unexpected observations from single fiber experiments, which have hitherto been discussed with the argument of uncontrollable biological variability, turn out to be a consistent set of possible fiber responses. They result from a convolution of multiple relatively simple rules each of them defining a certain characteristics of the single sarcomere.

Statistical correlation between first and second-order PMD

We investigate the statistical correlation between first- and second-order polarization mode dispersion (PMD) effects, which is important for PMD mitigation. The theoretical results are compared to numerical simulations and experimental data from a real high-PMD fiber. A new dependence between first- and second-order PMD is found. We show that the root mean square (RMS) value of the second-order PMD component, perpendicular to the PMD vector, increases with the length of the PMD vector.

Viscosity of curved fibers in suspension

In this paper, the relationship between fiber shape and relative viscosity of a fiber suspension is explored. A numerical simulation has been used to model non-Brownian curved rigid fibers in suspension under the influence of Newtonian shear flow. Curvature in the simulated fibers was taken to represent general deformities of real fibers in suspension. The simulation method was previously used by Joung et al. [J. Non-Newtonian Fluid Mech. 99 (2001) 1] to determine suspension viscosity for flexible fibers in suspension. When compared to the equivalent straight rigid fiber suspension, fiber curvature was found to contribute to a large increase in suspension viscosity. For typical semi-concentrated to concentrated suspensions, curved fibers were observed to produce viscosity increases of the order twice that of straight fiber suspensions. Results indicate that even a small bend in the fibers may cause a large bulk viscosity increase. Suspension viscosity is therefore highly dependent on the quality control measures taken during sample preparation.

Measurement of the elliptical birefringence of single-mode optical fibers

The polarization properties of single-mode optical fibers are theoretically modeled with use of the Jones formalism. The fiber is described as an elliptical birefringent plate. The properties predicted by this model are discussed and lead to the development of a simple experimental method to extract the parameters that describe a real fiber. A magneto-optic method that measures the beat length of the fiber is also presented and gives a more complete description of the fiber. The validity of the model is then clearly established. Finally, the wavelength dependence of the parameters characteristic of the fiber is experimentally investigated.

On the classification of real analytic fibre bundles

On the classification of real analytic fibre bundles

Analysis of an image processing method for fiber orientation in polymer composites

AbstractThe errors in fiber orientation distribution measurements of compression molding materials have been investigated, for generated as well as for real distributions. Because of the size of the sample, only a finite number of fibers are visible in a picture leading to a statistical error in the measurement. A method is proposed to express this error as function of the number of visible fibers and the number of subintervals the distribution is divided into. Studies of the error In a Fraunhofer/FT based fiber orientation distribution analysis have been performed, including effects of increasing number of fibers (fiber‐fiber intersections) in generated pictures and investigation of the errors in real fiber images. All steps in a fiber orientation distribution analysis of SMC/GMT kind of material are described, including suitable equipment, image enhancement methods and investigation of the errors present in analysis of a real image as well as comparisons to hand–measured data.

Time and frequency domain characteristics of polarization-mode dispersion emulators

We investigate both experimentally and theoretically a new technique to realistically emulate polarization-mode dispersion (PMD). We propose and demonstrate a PMD emulator using rotatable connectors between sections of polarization-maintaining fibers that generates an ensemble of high PMD fiber realizations by randomly rotating the connectors. It is shown that: (1) the DGD of this emulator is Maxwellian-distributed over an ensemble of fiber realizations at any fixed optical frequency; and (2) the frequency autocorrelation function of the PMD emulator resembles that in a real fiber when averaged over an ensemble of fiber realizations. A realistic autocorrelation function is required for proper emulation of higher order PMD and indicates the feasibility of using this emulator for wavelength-division-multiplexing (WDM) systems.

Bivariate Normal Thickness-Density Structure in Real Near-Planar Stochastic Fiber Networks

We present the analysis of experimental data that supports the recently presented hypothesis that the relationship between local areal density and local thickness in planar stochastic fiber networks may be described by the bivariate normal distribution. Measurements of the local averages of areal density and thickness have been made on experimental fiber networks with differing degrees of structural uniformity. The experimentally determined variance of local density at the 1 mm scale is in excellent agreement with that calculated from the theory. Also, the use of the bivariate normal distribution to describe the relationship between local areal density and local thickness measured in complete sampling schemes is appropriate for both near-random and clumped networks.

Wool-fibre Crimp. Part II: Fibre-space Curves

The results from the investigations of Part I relating fibre curvature to the differences in microfibril arrangement between the orthocortices and paracortices of a wool fibre are used to generate three-dimensional-space curves for virtual fibres. A simplification of the theory shows that it is possible to characterise the three-dimensional shape of a fibre in terms of a curvature factor and a curvature angle, which vary along the length of the fibre. Three series of fibres are generated, each series making a different assumption regarding the fibre cross-sectional geometry. The fibres generated show that the proposed fibre-curvature mechanism is capable of producing fibre-space curves that are qualitatively equivalent to real wool fibres.

An investigation into the relationship between internal stress distribution and a change of poly‐ p ‐phenylenebenzobisoxazole (PBO) fiber structure

This study concerns stress distribution induced by external force in individual poly-p-phenylenebenzobisoxazole (PBO) molecules in fiber. In reality, there are no fibers having an ideal structure (i.e., composed of infinitely long complete crystal elongated parallel to the fiber axis without defects that disconnect stress transfer in the crystal structure). Normally, real fiber structure has some structural incompletion, such as molecular ends, molecular misorientation, and density fluctuation (inhomogeneity) along the fiber axis. They play the role of heterogeneous stress distribution and reduction of fiber modulus in the fiber under tensile deformation. To carry out such analysis, meridional X-ray diffraction peaks of the PBO fiber under stress were measured and discussed. Distribution of the diffraction peak profile (half-height width of the diffraction profile) was especially considered. Change of the molecular orientation induced by external stress to the fiber was also estimated by measuring distribution of equatorial spots along the Debye ring. It was found that the distribution of the meridional diffraction spots became wider in the meridian, while the peak profile along the azimuthal direction became narrower as external stress was added for all three fibers. The degrees of response against stress came in this order: AS (180 GPa ) > HM (280 GPa) > HM+ (360 GPa). Hosemann's analysis was adopted to analyze real crystallite size and disorder parameter (g) of crystallites. It indicated that the crystalline size does not vary but the ordering of periodicity in the crystal lattice starts to loosen as applied stress to the fiber is increased. The stress seems to affect only local micro regions in the crystal structure.

Hepatic microvascular features in experimental cirrhosis: a structural and morphometrical study in CCl 4-treated rats

Background/Aims: In this study, a detailed morphometrical analysis of the hepatic microvasculature in the different zones of hepatic parenchyma was performed in normal and cirrhotic rat liver (CCl 4-induced). The aims were to detect, in CCl 4-induced cirrhosis, the real presence of the“capillarization” of hepatic sinusoids and to assess alterations of the sinusoid/parenchyma ratio within the nodule. Methods: Cirrhosis was promoted by controlled intragastric CCl 4 administration. Scanning electron microscopy of the vascular corrosion cast technique associated with light microscopy and transmission electron microscopy were used. Results: Evidence of connective tissue in the space of Disse was found only in sinusoids located near portal tracts or large fibrotic areas, and this was also confirmed by laminin immunohistochemistry. In contrast, all the intranodular sinusoids lacked real basal membrane and connective fibers in the space of Disse and, displayed normal fenestrations. The parenchymal area, sinusoidal area, mean sinusoidal area, sinusoidal perimeter, hepatocyte area and the reciprocal ratios were all considered in the morphometrical analysis. The sinusoids were of uniform size in the periportal, periseptal and pericentral areas of the cirrhotic liver without the typical zonal differences of the normal liver. The areas occupied by sinusoids per unit of parenchyma and the sinusoid/hepatocyte interfaces disposable for metabolic exchanges were markedly smaller ( p<0.01) in cirrhotic than normal liver. Conclusion: Our findings indicate that capillarization of hepatic sinusoids occurs only in very limited regions of the cirrhotic parenchyma, and thus this phenomenon does not have relevant functional consequences. Furthermore, the cirrhotic parenchyma appears not to be supplied by sinusoids and lacks features of zonation, which is a condition that could play a major role in the development and progression of liver failure.

Hepatic microvascular features in experimental cirrhosis: a structural and morphometrical study in CCl4-treated rats

In this study, a detailed morphometrical analysis of the hepatic microvasculature in the different zones of hepatic parenchyma was performed in normal and cirrhotic rat liver (CCl4-induced). The aims were to detect, in CCl4-induced cirrhosis, the real presence of the "capillarization" of hepatic sinusoids and to assess alterations of the sinusoid/parenchyma ratio within the nodule. Cirrhosis was promoted by controlled intragastric CCl4 administration. Scanning electron microscopy of the vascular corrosion cast technique associated with light microscopy and transmission electron microscopy were used. Evidence of connective tissue in the space of Disse was found only in sinusoids located near portal tracts or large fibrotic areas, and this was also confirmed by laminin immunohistochemistry. In contrast, all the intranodular sinusoids lacked real basal membrane and connective fibers in the space of Disse and, displayed normal fenestrations. The parenchymal area, sinusoidal area, mean sinusoidal area, sinusoidal perimeter, hepatocyte area and the reciprocal ratios were all considered in the morphometrical analysis. The sinusoids were of uniform size in the periportal, periseptal and pericentral areas of the cirrhotic liver without the typical zonal differences of the normal liver. The areas occupied by sinusoids per unit of parenchyma and the sinusoid/hepatocyte interfaces disposable for metabolic exchanges were markedly smaller (p<0.01) in cirrhotic than normal liver. Our findings indicate that capillarization of hepatic sinusoids occurs only in very limited regions of the cirrhotic parenchyma, and thus this phenomenon does not have relevant functional consequences. Furthermore, the cirrhotic parenchyma appears not to be supplied by sinusoids and lacks features of zonation, which is a condition that could play a major role in the development and progression of liver failure.

Residual Compression Stress Profile in High-Modulus Carbon Fiber Embedded in Isotactic Polypropylene by Micro-Raman Spectroscopy

Raman spectroscopy was used to investigate the compressive fragmentation process and the interface behavior in ultra high modulus (UHM) (750 GPa Modulus) pitch-based graphite/polypropylene composites upon cooling from processing temperature to room temperature. It is found that bulging is the primary mechanism of failure in these fibers, and Raman peak position measurements show that not all visually detected features represent real fiber failure. However, at real break locations, the fiber strain is found to drop to zero.

Multi-parameter observation of environmental asbestos pollution at the Institut de Physique du Globe de Paris (Jussieu Campus, France)

An original multi-parameter system has been used to study the nature of dust in the ambient air, particularly the total fibers and asbestos fibers, in eight areas of the Institut de Physique de Globe de Paris (France). These analyses provide a detailed case study of environmental pollution by asbestos fibers at low levels. The levels of total fibers with a length greater than 3 μm, measured with a real time fiber analyser monitor (FAM), give a baseline of 2.5 fibers per l., throughout the duration of sampling. The same levels, calculated during periods of effective presence of staff, are smaller than 10 fb per l. During these periods, the instantaneous value can show high peaks, reaching a maximum of 60 fb per l., but more often of about 5 to 10 fb per l. A direct cause and effect relationship exists between fiber concentrations and the presence of people, and indirectly with the variation of the other environmental parameters (temperature, humidity, air velocity). The baseline concentration of asbestos fibers, determined by analytical transmission electron microscopy (ATEM), is about 10−1 fb per l., with a mean value during the presence of people always less than 1.5 fb per l. The low levels of asbestos fibers do not allow us to establish a precise correlation between the concentration of total fibers and the asbestos concentration, but a rough estimate suggests that asbestos could represent 10–20% of the airborne fibers monitored with the FAM. The statistical study of fiber sizes shows that 70 and 55% of analyzed chrysotile and amosite fibers respectively are smaller than 5 μm. These numbers are 40 and 35% for fibers smaller than 3 μm, which are undetected by the FAM. Amosite, which characterizes most of the asbestos-containing materials (ACM) in the analyzed areas, is detected in the ambient air in quantities ten times less important than chrysotile. The low asbestos levels and the difference between the nature of building asbestos and airborne fibers, show that the mean measured asbestos contents in the ambient air represent the geochemical background of chrysotile asbestos fibers in the Parisian air.

Magnetic and electrical stimulation of undulating nerve fibres: a simulation study.

Mathematical models of myelinated nerve fibres are highly stylized abstractions of real nerve fibres. For example, nerve fibres are usually assumed to be perfectly straight. Such idealizations can cause discrepancies between theoretical predictions and experimental results. One well-known discrepancy is that the currently used models predict (contradictory to experimental findings) that an activation of nerve fibres is not possible with a pure transverse electric field. This situation occurs when a magnetic coil is placed symmetrically above a straight nerve fibre for magnetic nerve stimulation, or when an anode and a cathode are placed equidistantly on a line perpendicular to the fibre in the case of electrical stimulation. It is shown that this discrepancy does not occur if the physiological undulation of peripheral nerve fibres is included in the models. Even for small undulation amplitudes (e.g. 0.02 mm), it is possible to activate the fibre in these positions. For physiological undulations, as found in the literature, and favourable (off-centre) positions, the typical reduction of the thresholds is in a range between one and five, compared with perfectly straight fibres.

Multi-parameter observation of environmental asbestos pollution at the Institut de Physique du Globe de Paris (Jussieu Campus, France)

An original multi-parameter system has been used to study the nature of dust in the ambient air, particularly the total fibers and asbestos fibers, in eight areas of the Institut de Physique de Globe de Paris (France). These analyses provide a detailed case study of environmental pollution by asbestos fibers at low levels. The levels of total fibers with a length greater than 3 microns, measured with a real time fiber analyser monitor (FAM), give a baseline of 2.5 fibers per l., throughout the duration of sampling. The same levels, calculated during periods of effective presence of staff, are smaller than 10 fb per l. During these periods, the instantaneous value can show high peaks, reaching a maximum of 60 fb per l., but more often of about 5 to 10 fb per l. A direct cause and effect relationship exists between fiber concentrations and the presence of people, and indirectly with the variation of the other environmental parameters (temperature, humidity, air velocity). The baseline concentration of asbestos fibers, determined by analytical transmission electron microscopy (ATEM), is about 10(-1) fb per l., with a mean value during the presence of people always less than 1.5 fb per l. The low levels of asbestos fibers do not allow us to establish a precise correlation between the concentration of total fibers and the asbestos concentration, but a rough estimate suggests that asbestos could represent 10-20% of the airborne fibers monitored with the FAM. The statistical study of fiber sizes shows that 70 and 55% of analyzed chrysotile and amosite fibers respectively are smaller than 5 microns. These numbers are 40 and 35% for fibers smaller than 3 microns, which are undetected by the FAM. Amosite, which characterizes most of the asbestos-containing materials (ACM) in the analyzed areas, is detected in the ambient air in quantities ten times less important than chrysotile. The low asbestos levels and the difference between the nature of building asbestos and airborne fibers, show that the mean measured asbestos contents in the ambient air represent the geochemical background of chrysotile asbestos fibers in the Parisian air.

The breaking strength of imperfect (real) polymer fibers

The thermodynamic fusion theory of strength of perfect polymer fibers of finite molecular weight is extended to include imperfect (i.e. real) fibers of incomplete crystallinity and orientation. Approximate equations for failure strength, strain, and work of failure are derived by extracting from the real visco-elastic fiber an equivalent reversible component suitable for thermodynamic analysis. This is facilitated by an explicit relationship between fiber breaking stress, σ*, and breaking strain, ε*, which is shown to be σ*=0.632Kε* (K=modulus) for constant strain-rate deformations. It is shown that fiber breaking time is equivalent to the fiber visco-elastic mechanical relaxation time. Experimental data shows that the activation energy of rupture of polyethylene fibers is not the activation energy of covalent bond rupture. Instead it agrees with the activation energy expected of crystal melting in accordance with the fusion theory of rupture. The activation volume of the polyethylene fibers also agrees with the value expected from this theory.