Showing papers on "Fiber published in 1993"

Mechanical Properties of Polymers and Composites

Abstract: Mechanical Tests and Polymer Transitions * Elastic Moduli * Creep and Stress Relaxation * Dynamical Mechanical Properties * Stress-Strain Behaviour and Strength * Other mechanical Properties * Particulate-Filled Polymers * Fiber- Filled Composites and Other Composites.

Preparation of poly(glycolic acid) bonded fiber structures for cell attachment and transplantation.

Abstract: A novel method was developed to prepare three-dimensional structures with desired shapes used as templates for cell transplantation. The produced biomaterials are highly porous with large surface/volume and provide the necessary space for attachment and proliferation of the transplanted cells. The processing technique calls for the formation of a composite material with nonbonded fibers embedded in a matrix followed by thermal treatment and the selective dissolution of the matrix. To evaluate the technique, poly(glycolic acid) (PGA) fiber meshes were bonded using poly(L-lactic acid) (PLLA) as a matrix. The bonded structures were highly porous with values of porosity up to 0.81 and area/volume ratios as high as 0.05 micron-1.

Electrospinning process and applications of electrospun fibers

Abstract: An electric field is used to create a charged jet of polymer solution. As this jet travels in air, the solvent evaporates, leaving behind a charged fiber that can be electrically deflected or collected on a metal screen. Fibers with a variety of cross-sectional shapes and sizes were produced from different polymers. These fibers had diameters in the range of 0.05 to 5 microns. The authors describe the electrospinning process, the processing conditions, fiber morphology, and some possible uses of electrospun fibers. >

Anisotropic Actuation with Piezoelectric Fiber Composites

Abstract: An investigation was made into the field of planar structural actuation with anisotropic active materials. The mechanisms for creating anisotropic actuators were discussed, and the impact of anisotropy was shown at the individual lamina level and at the laminated structure level. Models for laminated structures were developed using an augmented Classical Laminated Plate Theory incorporating induced stress terms to accommodate anisotropic actuator materials. A twistextension coupled laminate was used to exemplify how twist can be directly induced into isotropic host structures using anisotropic actuation. Four anisotropic actuators with different material anisotropies were compared using this example. Finally, a laminate incorporating piezoelectric fiber composite actuators was manufactured and tested. Excellent agreement was found between the predicted and experimental response.

Polymeric materials formed by precipitation with a compressed fluid antisolvent

Abstract: Polymer microspheres and fibers are formed with a versatile new process, precipitation with a compressed fluid antisolvent. By spraying a 1 wt. % polystyrene in toluene solution into CO2 through a 100-μm nozzle, microspheres are formed with diameters from 0.1 to 20 μm as the CO2 density decreases from 0.86 to 0.13 g/cm3. The uniform submicron spheres produced at high CO2 density are due in part to the rapid atomization produced by the large intertial and low interfacial forces. Fibers, with and without microporosity, are obtained at higher polymer concentrations where viscous forces stabilize the jet. The effect of CO2 density and temperature on the size, morphology and porosity of the resulting polymeric materials is explained in terms of the phase behavior, spray characteristics, and the depression in the glass transition temperature.

Gas absorption studies in microporous hollow fiber membrane modules

Abstract: A comprehensive experimental investigation of gas-liquid absorption in a shell-and-tube type microporous hydrophobic hollow fiber device in a parallel flow configuration was carried out. Two modes of countercurrent gas-liquid contacting were studied, the wetted mode (absorbent liquid filled pores) and the nonwetted mode (gas-filled pores). The absorbent flowed through the fiber bore in most of the experiments. The systems studied include pure CO[sub 2], pure SO[sub 2], CO[sub 2] - N[sub 2] mixtures and SO[sub 2] - air mixtures. The absorbent was pure water. The absorption process was simulated for each case with a numerical model for species transport with and without chemical reaction. Laminar parabolic velocity profile was used for the tube-side flow, and Happel's free surface model was used to characterize the shell-side flow. The model simulations agreed well with the experimental observations in most cases. SO[sub 2] removals as high as 99% were obtained in small compact contactors. High K[sub L]a and low height of transfer unit (HTU) values were obtained with hollow fiber contactors when compared to those of conventional contactors. The applications of direct interest here are those for acid gas cleanup.

Fibers of polyolefin polymers

Abstract: Fiber with unique elastic properties comprising copolymer of ethylene and comonomer, having density in the range of about 0.86 to about 0.91 g/cm3, MWD in the range of about 2 to about 3.5, melt index in the range of about 4 to about 1000, and SDBI less than about 28 °C.

Vasoocclusion device containing radiopaque fibers

Abstract: This invention relates to a vaso-occlusive device (110) to be surgically implanted within a patient vessel (102) in order to block the flow of blood through the vessel (102) or to form a clot within an aneurysm stemming from the vessel (102). The vaso-occlusive device (110) is formed of a woven tubular braid (126) having at least one radiopaque fiber (128) so that the braid location may be observed. The braid (126) may also be partially woven from radio-lucent fibers (130). Optionally, the device may contain a fibrous center (156) or wick in its interior. The device may be continuous or segmented and a fibrous covering or element (152) may be attached.

A method for dynamic simulation of rigid and flexible fibers in a flow field

Abstract: A method is proposed for simulating the dynamic behavior of rigid and flexible fibers in a flow field. The fiber is regarded as made up of spheres that are lined up and bonded to each neighbor. Each pair of bonded spheres can stretch, bend, and twist, by changing bond distance, bond angle, and torsion angle between spheres, respectively. The strength of bonding, or flexibility of the fiber model, is defined by three parameters of stretching, bending, and twisting constants. By altering these parameters, the property of the fiber model can be changed to be rigid to flexible. The motion of the fiber model in a flow field is determined by solving the translational and rotational equations for individual spheres under the hydrodynamic force and torque exerting on. This method was applied to simulate rotational motions with and without bending deformation of the fiber in a simple shear flow under the conditions of infinitely dilute system, no hydrodynamic interaction and low Reynolds number of a particle. For the rigid fiber, the computed period of rotation and the computed distribution of orientation angle agree with those calculated by Jeffery’s equation with an equivalent ellipsoidal aspect ratio. For the flexible fiber, the period of rotation decreases rapidly with the growth of bending deformation of the fiber and rotation orbits deviate from a circular one of the rigid fiber. These tendencies are similar to experimental ones described by Forgacs and Mason. These results show that the proposed method using bonded spheres’ model can reproduce the dynamic behavior of rigid and flexible fibers in a flow field successfully.

Carbon fibers and method for their production

Abstract: The present invention relates to hollow carbon fibers having a cylindrical wall comprising a single layer of carbon atoms and a process for the production of these fibers.

Soliton pulse compression in dispersion-decreasing fiber

Abstract: We investigate the adiabatic compression of picosecond and subpicosecond soliton pulses from all-fiber, passively mode-locked, erbium-doped fiber soliton lasers operating at 1550 nm in dispersion-decreasing fibers (DDF's). High-quality soliton compression from 630 down to 115 fs in a 100-m DDF and from 3.5 down to 230 fs in a 1.6-km DDF is obtained. The effects of third-order dispersion and Raman self-scattering on the compression process are observed and discussed.

Fiber orientation and mechanical properties of short‐fiber‐reinforced injection‐molded composites: Simulated and experimental results

Abstract: A numerical simulation is presented that combines the flow simulation during injection molding with an efficient algorithm for predicting the orientation of short fibers in thin composite parts. Fiber-orientation state is represented in terms of a second-order orientation tensor. Fiber-fiber interactions are modeled by means of an isotropic rotary diffusion. The simulation predicts flow-aligned fiber orientation (shell region)near the surface with transversely aligned (core region) fibers in the vicinity of the mid-plane. The effects of part thickness and injection speed on fiber orientation are analyzed. Experimental measurements of fiber orientation in plaque-shaped parts for three different combinations of cavity thickness and injection speed are reported. It is found that gapwise-converging flow due to the growing layer of solidified polymer near the walls tends to flow-align the fibers near the entrance, whereas near the melt front, gapwise-diverging flow due to the diminishing solid layer tends to lign the fibers transverse to the flow. The effect of this gapwise-converging-diverging flow is found to be especially significant for thin parts molded at slower injection speeds, which have a proportionately thicker layer of solidified polymer during the filling process. If the fiber orientation is known, predictions of the anisotropic tensile moduli and thermal-expansion coefficients of the composite are obtained by using the equations for unidirectional composites and taking an orientation average. These predictions are found to agree reasonably well with corresponding experimental measurements.

Application of dynamic mechanical analysis for the study of the interfacial region in carbon fiber/epoxy composite materials

Abstract: The application of dynamic mechanical analysis (DMA) for quantifying interfacial interactions in composites is briefly reviewed. Carbon fiber/epoxy composites with fiber volume fractions of 12, 17, 38 and 61 vol% were subjected to flexural deformation on a Dupont DMA 983 instrument. The dependencies of dynamic mechanical properties of the composites on experimental parameters such as oscillation mode, amplitude, frequency, and temperature were investigate. As opposed to the storage modulus, the loss modulus is found to be sensitive to all parameters. In a fixed multiple frequency mode, the loss modulus of the composites increases with oscillation amplitude and decreases with frequency and the number of tests. The information produced in the resonant mode is more reproducible. An additional damping at the interfaces, apart from those of the constituents, suggests a poor interface adhesion in these composites. A linear relationship between the excess damping at the interfaces and the fiber volume fraction shows a similar interface quality for these composites having different fiber volume fractions. The detection of interfacial properities was found to be more sensitive in the flexural deformation mode than in the torsional mode. At temperatures higher than the glass transition temperature of the matrix, the effective volume fraction of the matrix is reduced. Such a reduction can be interpreted from the mismatch of thermal expansion of the matrix and the fibers.

Properties of polypropylene fiber reinforced concrete

Abstract: An experimental research investigation of the fresh and hardened material properties of the fibrillated polypropylene fiber reinforced concrete is reported. Fiber lengths were 1/2 and 1/4 inch, and volume fractions were 0.1, 0.3, and 0.5%. Fiber effects on concrete properties were assessed. Properties studied were slump, inverted slump cone time, air content, compressive and flexural behaviors, impact resistance and rapid chloride permeability, and volume percent of permeable voids. An innovative method of characterizing the flexural behavior of fibrillated polypropylene fiber concrete was proposed. The new method was dependent on the post-peak flexural resistance of concrete. For impact resistance and flexural behavior, it was concluded that 1/4-inch-long fibers were more effective than 1/2-inch-long fibers for volumes of 0.3% or less, while 1/2-inch-long fibers were more effective for 0.5% volume.

Effects of thermal residual stresses and fiber packing on deformation of metal-matrix composites

Abstract: The combined effects of thermal residual stresses anmd fiber spatial distribution on the deformation of a 6061 aluminum alloy containing a fixed concentration unidirectional boron fibers have been analyzed using detailed finite element models. The geometrical structure includes perfectly periodic, uniformly spaced fiber arrangements in square and hexagonal cells, as well as different cells in which either 30 or 60 fibers are randomly placed in the ductile matrix. The model involves an elastic-plastic matrix, elastic fibers, and mechanically bonded interfaces. The results indicate that both fiber packing and thermal residual stresses can have a significant effect on the stress-strain characteristics of the composite. The thermal residual stresses cause pronounced matrix yielding which also influences the apparent overall stiffness of the composite during the initial stages of subsequent far-field loading along the axial and transverse direction. Furthermore, the thermal residual stresses apparently elevate the flow stress of the composite during transverse tension. Such effects can be traced back to the level of constraint imposed on the matrix by local fiber spacing. The implications of the present results to the processing of the composites are also briefly addressed.

Frameless array of hollow fiber membranes and method of maintaining clean fiber surfaces while filtering a substrate to withdraw a permeate

Abstract: A frameless array unconfined in a modular shell, proves to be a surprisingly effective membrane device for withdrawing permeate from a substrate, the flux through the membranes reaching an essentially constant relatively high value because of the critical deployment of fibers of the array as a skein, arching in a buoyantly swayable generally parabolic configuration within the substrate, above at least one of the array's headers in which the terminal end portions of the fibers are potted. The length of each fiber must be greater than the direct center-to-center distance between the array's pair of headers. For use in a large reservoir, an assembly of the array and a gas distributor means has fibers preferably >0.5 meter long, which together provide a surface area >10 m2. The terminal end portions of fibers in each header are substantially free from fiber-to-fiber contact. When used in a tank from which the permeate is withdrawn at a location low enough to overcome the transmembrane pressure differential of the fibers, the permeate is withdrawn under a vacuum induced by gravity. To increase flux, a pump may be used which provides a suction less than 75 cm of Hg. When used in combination with a gas-distribution manifold disposed beneath the skein so as to flow bubbles through it, the surfaces of the fibers are surprisingly resistant to being fouled by build-up of deposits of inanimate particles or microorganisms in the substrate. Membranes with high transmembrane pressure differential may be used, if desired, and permeate removed with a vacuum pump.

Preparation of bonded fiber structures for cell implantation

Abstract: A novel processing technique is reported to bond non-woven fibers and, thus, prepare structural interconnecting fiber networks with different shapes for organ implants. The fibers are physically joined without any surface or bulk modification and have their initial diameter.

Enhanced Mechanical Properties of TiNi Shape Memory Fiber/Al Matrix Composite

Abstract: A design concept of shape memory TiNi fiber reinforced/Al metal matrix composite (SM-MMC) was proposed. Mechanical tensile properties such as stiffness and yield strength, were improved by the strengthening mechanisms: back stress in the Al matrix induced by stiffness of TiNi fibers and the compressive stress in the matrix caused by shape memory shrinkage of TiNi fibers. Damping capacity of the composite was also increased. These results suggest that this composite with prestrain can be applicable and is suitable for machinery, especially engine components where the material becomes stronger at higher temperatures owing to the shape memory effect

Passive smart self-repair in polymer matrix composite materials

Abstract: An investigation was made into the feasibility of developing a smart polymer matrix composite which has the ability to self-repair internal microcracks due to thermo-mechanical loading. The investigation focuses on the controlled cracking of hollow repair fibers dispersed in a composite and the subsequent timed release of chemicals which results in the sealing of matrix microcracks and the rebonding of damaged interfaces. In this preliminary work, the mechanisms of chemical release from a single repair fiber embedded in a polymer matrix were investigated using experimental analyses. It was found that controlled cracking of the repair fiber and subsequent release of the repair chemicals could be achieved by applying a polymer coating to the surface of the repair fibers. Release of chemicals into cracks was observed using optical microscopy and photoelasticity. Fiber pull-out and impact tests were performed to examine the ability to rebond fibers and fill cracks, respectively.

Optical Fiber Amplifiers: Design and System Applications

Abstract: Manufacturing of active fibers properties of rare-earth ions in glass host materials characterization measurements for rare-earth-doped fibers basics of 1550-nm fiber amplifiers optimization of er-doped fiber pump wavelength choice for 1550-nm amplifiers improved 1550-nm amplifiers in advanced configurations the 1300-nm amplifiers in advanced configurations the 1300-nm fiber amplifier fiber amplifiers in digital direct detection systems distributed fiber amplifiers amplifiers for AM-modulated systems

Controlled interactions in cellulose‐polymer composites. 1: Effect on mechanical properties

Abstract: The surface properties of cellulose fibers have been modified by heat treatment, by silane coupling agents, and by maleated polypropylene grafts. The effectiveness of these methods has been evaluated by electron spectroscopy (ESCA), by contact angle measurements, and by inverse gas chromatography. The latter analyses yielded information on the fibers' acid/base interaction potential. Cellulose was found to be amphoteric, with prevalent acidic properties. Heat and chloro-silane treatments accentuated acidity, while amino-silane treatment produced net basicity in the fiber surface. Modification with maleated polypropylene reduced specific interactions and converted the fiber to a predominantly dispersion-force solid. The modified fibers were used in composites with polypropylene (neutral), polystyrene (base), and chlorinated polyethylene (acid) as matrix. Stress/strain and dynamic mechanical parameters were found to vary with acid/base interactions between polymer and fiber, significant improvements being noted in elastic and storage moduli, in tensile strength and elongation. In polypropylene, properties were unaffected by acid/base considerations. Acid/base forces, not necessarily dominant, merit consideration in the design of surface modification strategies intended to optimize composite mechanical properties.

Oil sorption behavior of various sorbents studied by sorption capacity measurement and environmental scanning electron microscopy.

Abstract: Oil sorption capacities of various natural and man-made fibrous sorbents were compared in a simulated seawater bath containing oil. Natural sorbents such as milkweed, kapok, cotton, and wool showed higher sorption capacities than man-made sorbents such as polyester, polypropylene, viscose rayon, nylon 6, nylon 66, and acetate. Sorption capacities of the natural sorbents were over 30 g oil/g fiber. No definite advantages were observed using man-made bicomponent and biconstituent fibers over regular man-made fibers with respect to their sorption capacity. Analyses of sorption mechanisms using an environmental scanning electron microscope revealed that an oil deposit disappeared from the fiber surface after a certain time interval in milkweed, kapok, and cotton. This suggested that the sorption of oil in these fibers occurred through capillary action, probably due to their hollow lumens. Contrarily, adsorption, a surface phenomenon, would be the most prominent mechanism for oil sorption of wool fibers due to large amounts of surface wax, irregular scaly surfaces, and crimp. Effects of both adsorption and absorption were shown in the oil sorption of man-made fibers, depending upon the type and shape of the sorbent. Dumbbell-like oil deposits were seen on the fiber surface in certain oleophilic man-made fibers, because of a partial wetting of oil on the fiber surface. For some hydrophilic man-made fibers such as polyvinylalcohol and copolymer of isobutylene-maleic anhydride, the physical configuration of the fiber was a decisive factor in determining oil sorpton capacity of the sorbents. © 1993 Wiley-Liss, Inc.

A Modified Analysis of the Microstructural Characteristics of General Fiber Assemblies

Abstract: A critical problem in the study by Komori and Makishima about the microstructural characterization of general fiber assemblies is analyzed, and a modified approach is presented in this paper. The modified theory is able to predict satisfactorily such , parameters as the mean values of the number of fiber contacts and fiber segments between contacts in an unbonded fiber system. For a bonded fibrous structure like a nonwoven material, the relative proportions, the distributions of the bond lengths, and the free fiber lengths are also provided based on the modified theory. The theory has been applied to three typical fibrous systems to calculate the microstructural pa rameters that are believed useful for further studies of these systems.

Effects of concentration and clusters in erbium-doped fiber lasers.

Abstract: We report a low-threshold, high-conversion-efficiency erbium-doped fiber laser in a 100-parts-in-106 fiber pumped at 1.48 μm. The threshold and efficiency are found to deteriorate noticeably as the erbium concentration is increased. We propose that this is due mostly to rapid cross relaxation between ion pairs or clusters, and through modeling we show that the cluster content increases with concentration.

Behavior of Fiber-Reinforced Cemented Sand Under Static and Cyclic Loads

Abstract: Triaxial static compression, cyclic compression, and splitting tension tests were performed to evaluate the effect of randomly distributed fiber reinforcement on the response of cemented sand to load. Test results indicated that fiber reinforcement significantly increases the compressive and splitting tensile strength of cemented sand. An increase in the compressive and tensile strength was found to be more pronounced at higher fiber contents and longer fiber lengths. Peak strength envelopes in compression indicated that both the friction angle and cohesion intercept of cemented sand were increased as a result of fiber inclusion. Inclusion of fibers also contributed to increased brittleness index of cemented sand while increasing its total energy absorption capacity. Fiber reinforcement also affected the response of cemented sand to cyclic load by significantly increasing the number of cycles, and the magnitude of cyclic strain needed to reach failure.

Buckling response of laminates with spatially varying fiber orientations

Abstract: The buckling response of a symmetrically laminated composite panel with a spatially varying fiber orientation has been analyzed. Variation of the fiber orientation angle as a function of the position in the panel results in a composite laminate with stiffness properties that are functions of the panel coordinates. The laminates are therefore termed variable stiffness panels. The fiber orientation is assumed to vary only in one spatial direction, although the analysis can be extended to fiber orientations that vary in two spatial directions. The Ritz Method has been used to find the buckling loads and buckling modes for the variable stiffness panels for two different cases. In one of the cases the fiber orientation is assumed to change in the direction of the applied load. The other case is the one in which the fiber orientation varies in a direction perpendicular to the loading direction. Improvements in the buckling load of up to 80 percent over straight fiber configurations were found. Results for three different panel aspect ratios are presented.

From dopyballs to nanowires

Abstract: Consideration of the factors involved in the production of fullerene nanotubes in carbon arcs leads to the notion that a high electric field may be the critical factor that causes the tubes to grow. This thought then leads to a suggestion that it may be possible to grow continuous fullerene fibers many centimeters in length by an electric-field-and-laser induced pyrolysis of gas phase hydrocarbons of fullerenes on the tip of the growing fiber as it extends out from its place of attachment on a high voltage needle. Use of metal- or boron-doped fullerenes (dopyballs) in such an apparatus may lead to the production of doped fullerene fiber nanowires of high strength and conductivity.

Resistant Starch in Foods: Modified Method for Dietary Fiber Residues

Abstract: In a modified method for measuring Resistant Starch (RS) in dietary fiber residues all operations for obtaining fiber residues and determination of RS were performed in a 50 mL centrifugation tube. This minimized error sources and simplified previous methodology.

Skeletal muscle fiber hyperplasia.

Abstract: Skeletal muscle enlargement in adult animals has been ascribed primarily to changes in fiber cross-sectional area (ie, fiber hypertrophy); however, recent evidence from several laboratories suggests strongly that fiber hyperplasia contributes to muscle mass increases in adult animals and possibly human athletes Scientists have used three models to study the cellular mechanisms of muscle enlargement: compensatory hypertrophy, stretch, and exercise Each of these models has provided direct as well as indirect evidence supporting the occurrence of muscle fiber hyperplasia Direct counts of muscle fibers using nitric acid digestion techniques have shown that both exercise and stretch overload result in significant increases (range = 9-52%) in fiber number Indirect fiber counts using histological cross-sections have suggested fiber hyperplasia (range = 10-82%) in all three models Additionally, the expression of embryonic myosin isoforms have provided indirect evidence for new fiber formation in stretch overloaded muscle Furthermore, satellite cells have been shown to be involved in muscle fiber hyperplasia in stretch and exercise