Calculated stresses in dual coated optical fibers

We examine several practically important problems, related to the mechanical behavior of dual coated optical fibers: low temperature microbending, evaluation of spring constant due to coating layers, strength of the end portions of fibers clamped in terminal fixtures, and prediction of stresses caused by the misalignment of the openings in the frame and in the terminal fixture. The developed formulas are simple, easy-to-use, and clearly indicate the role of the major factors affecting the mechanical behavior of the fibers. The obtained results can be of help in physical design of dual coated fibers and optical interconnections.     

Longitudinal variation in the stress–strain properties of wool fibers

In order to obtain information on possible end-to-end differences in the physical properties of wool caused by weathering of the more exposed portions, a comparison has been made of the stress–strain characteristics of the tip and root halves of fibers taken from the midback region of sheep reared outdoors over a 6-month summer to winter period. The results were further compared with the tip and root halves of fibers taken from animals reared indoors under conditions of essentially continuous darkness. When 11 features of the stress–strain curves were compared, it was found that for the outdoor wools the tip halves had lower initial moduli, higher yield strains, and lower yield moduli than the root halves. In contrast, the dark grown wools showed no end-to-end differences. The greater ease of extension of the tip halves of outdoor wools may be attributed to light-induced diminution in the levels of crosslinking within the keratin structure. The results show that normal environmental influences caused end-to-end differences and that longitudinal variations in physical properties may be a typical characteristic of all field grown wools at the time of harvesting.     

Stress–strain optical study of styrene–butadiene and ethylene–propylene rubbery copolymers

Birefringence–temperature behavior at constant stress during cooling and heating of styrene–butadiene and ethylene–propylene copolymers between ?120°C and +60°C was investigated. Copolymer composition, thermal treatment, and stress levels were shown to have a pronounced effect on the photoelastic properties.     

Electrically conductive composites based on epoxy resin containing polyaniline–DBSA‐ and polyaniline–DBSA‐coated glass fibers

Four kinds of polyaniline (PANI)‐coated glass fibers (GF–PANI) combined with bulk PANI particles were synthesized. GF–PANI fillers containing different PANI contents were incorporated into an epoxy–anhydride system. The best conductivity behavior of the epoxy/GF–PANI composites was obtained with a GF–PANI filler containing 80% PANI. Such a composite shows the lowest percolation threshold at about 20% GF–PANI or 16% PANI (glass fiber‐free basis). The PANI‐coated glass fibers act as conductive bridges, interconnecting PANI particles in the epoxy matrix, thus contributing to the improvement of the conductivity of the composite and the lower percolation threshold, compared with that of a epoxy/PANI–powder composite. Particularly, the presence of glass fibers significantly improves the mechanical properties, for example, the modulus and strength of the conductive epoxy composites. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1329–1334, 2004     

Thermally induced double‐positive temperature coefficients of electrical resistivity in combined conductive filler–doped polymer composites

Polymer composites of low‐density polyethylene/polypropylene/graphite/vanadium dioxide (LDPE_0.8/PP_0.2/Gr_0.4/VO₂) are prepared by classical melt‐mixing technology and show a notable double positive temperature coefficient of electric resistivity (PTC), which originates from the combined effect of highly conductive Gr and VO₂ with a thermal phase transition. When the weight ratio of VO₂ is 8 wt %, the positive temperature coefficient intensity (PTCI) for the composites reaches 3.85 orders of magnitude. The model system demonstrates the reason for the improvement in the PTC performance of the polymer composites by analyzing the construction of the conductive networks. Therefore, the addition of phase‐transition compounds may be a promising path to improving PTC materials. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44876.     

Effects of static axial strain on the tensile properties and failure mechanisms of self-assembled collagen fibers

Collagen fibers form the structural units of connective tissue throughout the body, transmitting force, maintaining shape, and providing a scaffold for cells. Our laboratory has studied collagen self-assembly since the 1970s. In this study, collagen fibers were self-assembled from molecular collagen solutions and then stretched to enhance alignment. Fibers were tested in uniaxial tension to study the mechanical properties and failure mechanisms. Results reported suggest that axial orientation of collagen fibrils can be achieved by stretching uncrosslinked collagen fibers. Stretching by about 30% not only results in decreased diameter and increased tensile strength but also leads to unusual failure mechanisms that inhibit crack propagation across the fiber. It is proposed that stretching serves to generate oriented fibrillar substructure in self-assembled collagen fibers. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1429–1440, 1997     

Bioinduced changes in the colored nitrocellulose‐coated cellophane films,induced by the Shewanella J18 143 strain

Two types of the nitrocellulose (NC)‐coated cellophane films, denoted 335 MS films (uncolored) and 335 MSC films (dyed with C.I. Direct Red 81), were incubated with Shewanella J18 143 for a period of 1 month at 50°C. The colored films were decolorized by Shewanella strain throughout this process. Changes in the NC coating of the films were studied by FTIR analysis, by determination of the surface wettability, and by ESEM evaluations. The colored films that were exposed to the Shewanella culture and decolorized, lost a significant amount of nitrate groups and became enriched in the hydroxyl group content. Moreover, the critical surface tension of the colored NC‐coated cellophane films increased, from 18.7 mN/m, for the original films, to 33.1 mN/m, for the film that was treated by the Shewanella strain. Unlike the colored film, the uncolored NC‐coated films did not give any considerable changes in their NC coating when exposed to the Shewanella culture, for the same time period. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Tensile stress–strain and recovery behavior of Indian silk fibers and their structural dependence

The tensile stress–strain and recovery behavior of all the four commercial varieties of Indian silk fibers, namely Mulberry, Tasar, Eri, and Muga, have been studied along with their structures. Compared to the non‐Mulberry silk fibers, Mulberry silk fiber is much finer and has crystallites of smaller size, higher molecular orientation, and a more compact overall packing of molecules. These structural differences have been shown to result in (1) the presence of a distinct yield and a yield plateau in non‐Mulberry silk and their absence in Mulberry silk, and (2) relatively higher initial modulus and tenacity along with lower elongation‐to‐break and toughness and superior elstic recovery behavior of mulberry silk compared to non‐Mulberry silk. It is also observed that fine silk fibers have a relatively more ordered and compact structure with higher orientation compared to their coarse counterparts, and this gives rise to higher initial modulus and higher strength in the finer fibers. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2418–2429, 2000     

关于自增强残余应力松弛规律的研究

以高压聚乙烯量式反应器为侧．对自增强废余应力松弛规律进行研究,分析自增强残余应力的松弛特点、原因和机理，着重研完自增强废余应力松弛的影响因素茛其对友余应力的影响情况。     

关于自增强残余应力松弛规律的研究

以高压聚乙烯管式反应器为例,对自增强残余应力松弛规律进行研究,分析自增强废余应力的松弛特点、原因和机理,着重研究自增强残余应力松弛的影响因素及其对发余应力的影响情况.     

Theoretical analysis of the thermally induced delamination of polymeric coatings in double-coated optical fibers

To maintain its mechanical strength, the glass fiber of optical fibers is coated by polymeric materials during the fabrication process, However, when the thermally induced shear stress at the interface of the glass fiber and primary coating is larger that its adhesive stress, the adhesive bond between the glass fiber and primary coating will be broken. When the polymeric coatings are delaminated from the glass fiber, the optical fiber will lose its mechanical strength. In this article, the thermally induced delamination of polymeric coatings in double-coated optical fibers is investigated. To minimize the coating's delamination, the thermally induced shear stress at the interface of the glass fiber and primary coating should be reduced. The method to minimize such a shear stress is to select suitable polymeric coatings as follows: The thickness and Poissòn's ratio of the primary coating should be increased, but the Young's modulus of the primary coating and the thickness, Young's modulus, and thermal expansion coefficient of the secondary coating should be decreased. Finally, the optimal design of commercialized double-coated optical fibers to minimize the thermally induced coating's delamination is also discussed.     

Modified resistivity–strain behavior through the incorporation of metallic particles in conductive polymer composite fibers containing carbon nanotubes

Eutectic metal particles and carbon nanotubes are incorporated into a thermoplastic polyurethane matrix through a simple but efficient method, melt compounding, to tune the resistivity–strain behavior of conductive polymer composite (CPC) fibers. Such a combination of conductive fillers is rarely used for CPCs in the literature. To characterize the strain‐sensing properties of these fibers, both linear and dynamic strain loadings are carried out. It is noted that a higher metal content in the fibers results in higher strain sensitivity. These strain‐sensing results are discussed through a morphological study combined with a model based on the classic tunneling model of Simmons. It is suggested that a high tunneling barrier height is preferred in order to achieve higher strain sensitivity. Copyright © 2012 Society of Chemical Industry     

Resistivity of conductive polymer–coated fabric

Preparation of conductive polymer–coated fabrics was carried out by admicellar polymerization. By this method, a thin layer of conductive polymers (polypyrrole, polyaniline, and polythiophene) was formed on cotton and polyester fabrics by a surfactant template. The effects of monomer concentration, oxidant to monomer ratio, and addition of salt on the resistivity of the resulting fabrics were studied. The results showed that the apparent surface and volume resistivity decreased with an increase in monomer concentration in the range 5–15 mM, but was not strongly dependent on the oxidant to monomer ratio over the range of 1 : 1 to 2 : 1. Addition of 0.5M salt was found to reduce the resistivity significantly. The lowest resistivity obtained was with polypyrrole‐coated fabric, with resistivity around 10⁶ ohm. SEM micrographs of the treated fabric surface showed a filmlike polymer coating, confirming that the fabrics were successfully coated by admicellar polymerization. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2629–2636, 2004     

Relaxation phenomenon in epoxy glass aged under post‐yield strain

Relaxation phenomenon in epoxy glass aged under shear strain larger than an upper yield point was studied. After aged under post‐yield strain for various aging periods, cylindrical specimens of epoxy glass were twisted clockwise (in the same direction as the prestrain) or counterclockwise (the opposite direction to the direction of the prestrain). The evolution of yield points was significantly different from that of the specimens aged under preyield strain. There exist two knee‐like yield points on stress–strain curves of specimens twisted counterclockwise: one evolved toward to an upper yield point and merged the other knee‐like yield point whose stress value was almost independent of aging time. On the basis of the experimental results, we proposed a combined relaxation model of two relaxation mechanisms: one is relaxation results in an isotropic structure whose center in stress space is the stress value in the terminal zone and the other is kinetic relaxation of the isotropic center. The combined relaxation indicated the possibility of phase transition caused by postyield strain, and therefore the higher yield stress than that of an annealed specimen was not resulted from strain‐accelerated aging, but presumably resulted from a structural change under postyield strain. POLYM. ENG. SCI. 46:630–634, 2006. © 2006 Society of Plastics Engineers     

Double coated optical fibers undergoing temperature variations: The influence of the mechanical behavior on the added transmission losses

A model to predict the temperature-induced added loss in dual-coated optical fibers is presented. Longitudinal and lateral temperature-induced forces, originating from fiber irregularities and from the mismatch among the expansion coefficients of the glass fiber and of the coatings, are consistently included in the model. Both the bendings of the glass fiber and of the coating are considered. Transmission losses are explicity computed according to Petermann's theory on the microbending of single-mode fibers.     

Infrared spectroscopy measurements of residual stresses in polypropylene fibers

Average residual stresses in polypropylene fibers, produced in a full-scale short-spin line, are estimated from the shift of the IR absorption peak at 975 cm^-1. Linearly polarized incident IR radiation is used to separate between stress components parallel and perpendicular to the fiber axis. For all the fibers in this study, the axial stress component is larger than the average stress perpendicular to the fiber axis. Axial and perpendicular stresses are correlated with draw ratio and polydispersity index. For narrow molecular weight distributions (M_w/M_n < 4–5), the axial stress increases with increasing draw ratio. Average stress perpendicular to the fiber axis decreases with increasing draw ratio for all the molecular weight distributions in this study (M_w/M_n = 3–6). Measurements of residual stresses are consistent with other results characterizing molecular structure and mobility. An expression for estimating the stored deformation energy is discussed. © 1993 John Wiley & Sons, Inc.     

Swelling of cotton fibers in ethylenediamine–morpholine mixtures

Cotton fibers were treated with anhydrous mixtures of ethylenediamine and morpholine of varying proportions to study the changes in accessibility (X-ray crystallinity index, swelling by propanol-2 retention, formylaiton, and dyeability) as well as lattice conversions from cellulose I to cellulose II and cellulose III. Positive synergistic influence of the highest order was noticed at 70:30 (molar proportion 3:1) ethylenediamine–morpholine mixture as judged from accessibility and lattice conversion from cellulose I to cellulose II. The same critical proportion was found to give the highest order of negative synergistic effect in the lattice conversion of cellulose I into cellulose III. These opposing trends have been explained on the basis of the different mechanisms associated with the lattice conversions of cellulose I into cellulose II and cellulose III.     

Structure–property relation in varieties of silk fibers

Crystallite shape ellipsoid in different varieties of silk fibers namely (i) Chinese (ii) Indian, and (iii) Japanese, has been computed using wide‐angle X‐ray data and Hosemann's one‐dimensional paracrystalline model. The estimated microcrystalline parameters are correlated with the observed physical property of the silk fibers. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1979–1985, 2001     

High-strength–high-modulus polyimide fibers II. Spinning and properties of fibers

The polyimides based on 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) described in Part I of this series were dissolved in p-chlorophenol and spun into fibers using a coagulating bath of ethanol. The fibers as spun had in general low tenacities and low moduli, but a heat treatment at 300–500°C under tension produced a remarkable increase in strength and modulus, and fibers with a tensile strength of 26 g/den (3.1 GPa) and an initial modulus higher than 1,000 g/den (120 GPa) could be obtained. Thus, the annealed fibers of polyimides are comparable to aramid fibers in mechanical properties. To heating in air and in the saturated steam, the polyimide fibers showed higher resistance than the aramid fibers. The polyimide fibers surpassed the aramid fibers in resistance to acid treatment and ultraviolet (UV) irradiation, but were inferior in resistance to alkali treatment. The annealed fibers of polyimides displayed distinct X-ray diffraction patterns. The chain repeat distance of 20.5 Å determined on the fibers of polyimide prepared from BPDA and o-tolidine, and 20.6 Å determined on the fibers of polyimide derived from BPDA and 3,4′-diaminodiphenyl ether are reasonable when the dimensions of monomeric units and the shapes of the molecular chains are considered. The X-ray reflections of both polyimide fibers were indexed satisfactorily on the basis of postulated unit cells.     

Stress–strain properties of polyurethane–polyacrylate interpenetrating polymer networks

Two-component interpenetrating polymer networks (IPN) of the SIN type (simultaneous interpenetrating networks) were prepared from two different polyurethanes (a polyester type and a polyether type) and a polyacrylate of two different crosslink densities. The linear polymers and prepolymers were combined in solution, together with crosslinking agents and catalysts, films cast, and subsequently chain extended and crosslinked in situ. In all cases, maxima in tensile strengths significantly higher than the tensile strengths of component networks occurred. This was explained by an increase in crosslink density due to interpenetration.