Showing papers on "Fiber published in 1990"

Static Response of Sands Reinforced with Randomly Distributed Fibers

Abstract: Laboratory triaxial compression tests are performed to determine the static stress‐strain response of sands reinforced with discrete, randomly distributed fibers, and to observe the influence of various fiber properties, soil properties, and test variables on soil behavior. In addition to the experimental program, a model is developed, based on a statistical theory of strength for composites, to predict the fiber contribution to strength under static loads. Randomly distributed fiber inclusions significantly increase the ultimate strength and stiffness of sands. The increase in strength and stiffness is a function of sand granulometry (i.e., gradation and particle size and shape) and fiber properties (i.e., weight fraction, aspect ratio, and modulus). The sand‐fiber composites have either a curved linear or a bilinear failure envelope, with the break occurring at a threshold confining stress called the “critical confining stress.” The magnitude of the critical confining stress decreases with an increase i...

Mechanical properties of biodegradable polymers and composites proposed for internal fixation of bone

Abstract: The mechanical properties of biodegradable polymers and composites proposed for use in internal fixation (in place of stainless steel) are crucial to the performance of devices made from them for support of healing bone. To assess the reported range of properties and degradation rates. we searched and reviewed papers and abstracts published in English from 1980 through 1988. Mechanical property data were found for poly(lactic acid), poly (glycolic acid), poly(ϵ-caprolactone), polydioxanone, poly(ortho ester), poly(ethylene oxide), and/or their copolymers. Reports of composites based on several of these materials, reinforced with nondegradable and degradable fibers, were also found. The largest group of studies involved poly(lactic acid). Mechanical test methods varied widely, and studies of the degradation of mechanical properties were performed under a variety of conditions, mostly in vitro rather than in vivo. Compared to annealed stainless steel, unreinforced biodegradable polymers were initially up to 36% as strong in tension and 54% in bending, but only about 3% as stiff in either test mode. With fiber reinforcement, reported highest initial strengths exceeded that of stainless steel. Stiffness reached 62% of stainless steel wiht nondegradable carbon fibers, 15% with degradable inorganic fibers, but only 5% with degradable polymeric fibers. The slowest-degrading unreinforced biodegradable polymers were poly(L-lactic acid) and poly(ortho ester). Biodegradable composites with carbon or inorganic fibers generally lost strength rapidly, with a slower loss of stiffness, suggesting the difficulty of fiber-matrix coupling in these system. The strength of composites reinforced wiht (lower modulus) degradable polymeric fibers decreased more slowly. Low implant stiffness might be expected to allow too much bone motion for satisfactory healing. However, unreinforced or degradable polymeric fiber reinforced materials have been used successfully clinically. The key has been careful selection of applications, plus use of designs and fixation methods distinctly different from those appropriate for stainless steel devices.

Electrochemical Bonding of Amines to Carbon Fiber Surfaces Toward Improved Carbon‐Epoxy Composites

Abstract: Electrochemical oxidation of ω‐diamines on carbon fibers allows the bonding of these molecules to the carbon fibers. The conditions leading to this surface modification are described, and the influence of the different parameters is discussed. The structure of the bonded layer is studied by voltammetry, XPS, and SIMS. A mechanism is proposed which involves the coupling of a radical cation to the fiber. Toughness of carbon‐epoxy composites is improved when prepared from these modified fibers.

Strong nonwoven fabrics from engineered multiconstituent fibers

Abstract: The present invention provides a thermally-bonded nonwoven fabric that is made from a web which comprises from 100 to 5 percent by weight of multiconstituent fibers. Said multiconstituent fibers are composed of highly dispersed blends of at least two different immiscible thermoplastic polymers and have a dominant continuous polymer phase with at least one noncontinuous phase dispersed therein. The noncontinuous phase exists as an elongated fibrillar polymer domain oriented generally in the direction of the fiber axis. No single polymer domain cross-section of said noncontinuous phase or phases is larger than 0.1% of the cross-sectional area of said fiber. The polymer of the noncontinuous phase or phases has a Polymer Melt Temperature (PMT) at least 30°C below the PMT of the continuous phase. The fiber is configured such that said noncontinuous phase or phases occupy a substantial portion of the fiber surface. In addition to such fabrics, laminates --made by combining nonwoven fabrics made from the materials and processes as described herein with films, paper, tissue, woven fabrics, or nonwoven fabrics such as meltblowns-- are also contemplated. The fabric according to the invention readily bonds to other materials of the sorts mentioned, and is therefore suitable for use in filtration media, medical and clean room garments, CSR wrap, absorbent article backsheets, and other barrier structures.

Distribution and orientation of fibers in steel fiber reinforced concrete

Abstract: Measurements were made on the number of fibers per unit cross-sectional area in steel fiber reinforced concrete specimens incorporating various volume fractions of fibers of different types. Based on statistical evaluation of the measured values, the differences in fiber concentrations at different locations on the cross section were assessed. Theoretical expressions were derived for the number of fibers per unit cross-sectional area in fiber reinforced concrete, with due consideration given to the effects of the surrounding boundaries. The effects of vibration on reorientation of steel fibers in concrete were investigated through comparisons betwen the computed and measured values of number of fibers per unit cross-sectional area.

Fibre optic single mode rotary joint

Abstract: The invention is a rotary joint for singlemode optical fibers, having a fixed and a rotating part to permit the transmission of optical signals across a rotational interface (such as a winch or turret) with minimal insertion loss and, in particular, low reflections (good return loss). There is no need of conversion to electrical signals; the device is passive. It may be use an oil of refractive index matched to that of the glass fibers and to that of fiber tapers or lenses used to expand the beam emitted from one fiber and contract it for transmission into the other fiber. The device is bidirectional. By use foil, through precision techniques for building and mounting the optical and mechanical components, and by use of advanced bearings, both the insertion loss and unwanted reflections (return loss) can be minimized, thereby making it suitable for use with singlemode fiber. Insertion loss can be further reduced in conjunction with index-matching fluid by using optical elements (lenses, tapers, fibers) having angled or curved facets rather than perpendicular facets. Oil filling has the further advantage of pressure compensation allowing the device to operate at any ambient pressure. Lenses having curved surfaces can be accommodated by the use of fluid having a refractive index different from that of the lens material.

Composites from compounding wood fibers with recycled high density polyethylene

Abstract: The development of composites consisting of wood fibers and recycled plastics offers not only an opportunity to utilize an abundant natural resource but also a means to alleviate the serious plastics disposal problem. In this work, aspen fibers are incorporated into recycled high density polyethylene with a co-rotating inter-meshing twin-screw extruder to study processing-property relationships. Tensile, impact, and flexural strengths are measured as functions of fiber concentration. The effects of fiber pretreatment, screw configuration, and compounding temperature on the properties of composites are discussed.

Tensile properties of short fiber-reinforced SiC/Al composites: Part II. Finite-element analysis

Abstract: The tensile properties of aluminum matrix composites containing SiC whiskers or particulate were investigated analytically and compared to experimental results. Two finite-element models were constructed and used for elastoplastic analysis. In both models, the SiC fibers are represented as longitudinally aligned cylinders in a three-dimensional array. The cylinder ends are transversely aligned in one model and staggered in the other. Using the models, the sensitivity of the predicted composite properties to the deformation characteristics of the matrix alloy was examined, and the general behavior of the models was validated. It was determined that both models are necessary to predict the overall composite stress-strain response accurately. The analytic results accurately predict: the observed composite stress-strain behavior; the experimentally observed increase in Young’s modulus and the work-hardening rate with increasing fiber volume content and aspect ratio; and the decrease and subsequent increase in proportional limit as the SiC volume fraction is increased. The models also predict that the transverse material properties should be insensitive to fiber aspect ratio. In addition, the model predicts the location of initial yielding and the propagation of the plastic region. These results offer insights into the deformation mechanisms of short fiber-reinforced composites.

Fiber type composition of the human female trapezius muscle: enzyme-histochemical characteristics.

Abstract: The human trapezius muscle has an origin that is more extensive than that of any other body muscle; it has a complex macroscopic structure with fibers running in different directions. Histochemical analysis of multiple samples, obtained from different parts of the trapezius muscle from five males, showed marked differences in the distribution and the cross-sectional fiber area of the fiber types among different parts of the muscle as well as among individuals. As revealed by the mATPase activity, after different levels of alkaline and acidic preincubations, the lower third of the descending portion, the transverse, and the ascending portions of the muscle had a predominance of type I fibers (low mATPase activity at pH 9.4), whereas the most superior parts of pars descendens had a higher frequency of type II fibers (high mATPase activity at pH 9.4). The fibers of the most superior parts of the muscle were considerably smaller compared with those in all the other parts. In sections stained for NADH-TR, moth-eaten fibers were observed within parts of the descending portion. Their location and their larger fiber area, compared with that of ordinary type I fibers, may be related to frequent and/or continuous use of these fibers. In conclusion, the differences in fiber type composition between the different parts of the muscle probably reflect different functional demands on the trapezius muscle in various head, neck, and shoulder movements. We suggest that the interindividual differences in muscle fiber composition are due, at least in part, to genetic factors.

Geometric factors affecting the internal stress distribution and high temperature creep rate of discontinuous fiber reinforced metals

Abstract: The creep deformation behavior of metal-matrix composites has been studied by a continuum mechanics treatment utilizing finite element techniques. The objective of the work has been to understand the underlying mechanisms of fiber reinforcement at high temperatures and to quantify the importance of reinforcement phase geometry on the overall deformation rate. Internal stress distributions are presented for a material that consists of stiff elastic fibers in an elastic, power law creeping matrix. Results indicate that large triaxial stresses develop in the matrix, and that these stresses have a strong effect on reducing the creep rate of the composite. Reinforcement phase geometry, as measured by the fiber volume fraction, aspect ratio, separation, and overlap, greatly influences the degree of constraint on the flowing matrix material and the overall deformation rate. Theoretical predictions from this modeling are compared to experimental results of creep deformation in metal-matrix composite systems with varying degrees of agreement.

Non-woven fabric and method and apparatus for making the same

Abstract: Non-woven fabrics comprising yarn-like fiber groups of parallel and tightly compacted fiber segments, which groups include fiber segments circumferentially wrapped around at least a portion of the fiber groups. The groups are interconnected at junctures by fibers common to the plurality of such groups.

Pullout Problem: Stress versus Fracture Mechanical Approach

Abstract: The pullout of a single fiber from a brittle matrix is widely recognized as one of the basic tests to be performed to provide information about the expected behavior of a given fiber-reinforced brittle matrix composite material. Thus, it is of great importance that the pullout test be interpreted in a way that yields the true material parameters. Two approaches to the fiber/matrix debonding problem can be made: (1) The stress approach where the criterion for growth of the debonded fiber/matrix interface is expressed in terms of the interfacial stress; and (2) the fracture mechanical approach where the criterion for interfacial debonding is expressed in terms of energy equilibrium. This paper investigates these two approaches by applying both to the same model, which includes frictional stresses on the debonded interface. The debonding load-versus-crack length relationships predicted by the two approaches are compared and differences in the parametric dependency are discussed. The results predicted by the fracture mechanical approach are compared with available experimental results.

Study of the complex atomic susceptibility of erbium-doped fiber amplifiers

Abstract: A study of the complex atomic susceptibility of erbium-doped fiber amplifiers operating near the 1.53- mu m transition (/sup 4/I/sub 13/2/-/sup 4/I/sub 15/2/) developed from a semiclassical theoretical description is presented. Expressions for the emission cross section sigma /sub e/( lambda ) and absorption cross section sigma /sub a/( lambda ) of erbium:glass as a quasi-three-level laser system with Stark-split sublevel manifolds are derived. The results are used to calculate the cross sections of aluminosilicate erbium-doped fibers at low temperatures (T=4.2, 77 K) and at room temperature. It is demonstrated that an expression for the gain coefficient of the fiber amplifier can be derived from the expression of the susceptibility. Using Kramers-Kronig relations, an expression for the refractive index change in the fiber is derived. The theoretical spectral gain profile of the fiber amplifier and concurrent refractive index changes are analyzed for different pumping regimes. >

Calcium-sensitive cross-bridge transitions in mammalian fast and slow skeletal muscle fibers.

Abstract: The fundamental mechanism underlying the differing rates of tension development in fast and slow mammalian skeletal muscle is still unknown. Now, in skinned (membrane-permeabilized) single fibers it has been shown that the rate of formation of the strongly bound, force-producing cross-bridge between actin and myosin is calcium-sensitive in both fast and slow fibers and that the rate is markedly greater in fast fibers. The transition rates obtained at high calcium concentrations correlated with myosin isoform content, whereas at low calcium concentrations the thin filament regulatory proteins appeared to modulate the rate of tension development, especially in fast fibers. Fiber type-dependent differences in rates of cross-bridge transitions may account for the characteristic rates of tension development in mammalian fast and slow skeletal muscles.

Mechanical Characterization of Unnotched SCS 6 /Ti-15-3 Metal Matrix Composites at Room Temperature

Abstract: The Ti-15-3 metal matrix composites containing silicon-carbide (SCS6) fibers, in five different lay-ups, have been tested at room temperature to determine static strengths and mechanical properties. Experimental data and predicted values of the laminate properties and strengths showed good correlation. The off-axis laminate plies (that is, 90 and 45 deg) suffered fiber/matrix interface failures at stress levels as low as 20 ksi, thus significantly affecting the mechanical properties of the laminate. Edge replicas were used to verify the fiber/matrix separations. Microscopic examinations determined that the fiber/matrix failures were occurring in the titanium/silicon reaction layer. Fatigue tests were performed on unnotched specimens to determine the number of cycles to failure versus cyclic stress level. It was found that the stress in the 0 deg fiber could be used to correlate the fatigue life of different laminates containing 0 deg plies.

Evaluation of (4)I(15/2) and (4)I(13/2) Stark-level energies in erbium-doped aluminosilicate glass fibers.

Abstract: Spectroscopic measurements of fluorescence and absorption in an erbium-doped fiber permit the evaluation of the Stark-level energies of the (4)I(15/2) and (4)I(13/2) manifolds in Er:glass. The data permit the allocation of the individual laser transitions associated with the room-temperature gain spectrum of erbium-doped fiber amplifiers operating near lambda = 1.53 microm.

Dietary fiber for dogs: I. Effects of graded levels of dietary beet pulp on nutrient intake, digestibility, metabolizable energy and digesta mean retention time.

Abstract: The optimal level of beet pulp (BP) inclusion in a meat-based dog diet and the effects of graded levels of dietary BP on fecal excretion responses and mean retention time of marked fiber in the gastrointestinal tract of the dog were evaluated using 30 female English Pointers assigned to isonitrogenous diets containing 0, 2.5, 5.0, 7.5, 10.0 or 12.5% BP (DM basis). Beet pulp replaced portions of dietary cornstarch. Digestibilities of DM and OM decreased by an average of 6% when comparing diets containing BP to the control diet, and quadratic and cubic responses were noted in digestibilities of fiber constituents (lower values at the 7.5 and 10.0% levels, higher values at the 2.5, 5.0 and 12.5% levels). Digestible energy (DE) and ME intakes (kcal/d) were not affected by treatment, but when expressed as a percentage of GE, values decreased (4.8% for DE; 6.2% for ME) linearly with increasing BP levels. Wet weight of feces increased (from 117 to 374 g/d) linearly as percentage of dietary BP increased. Frequency of defecation was higher (P less than .05) for dogs fed the diet containing 12.5% BP than for dogs fed the other diets (5.2 vs mean value of 2.8/24 h). Mean retention time of marked fiber decreased linearly (high value of 23.4 h for the 2.5% BP treatment, low value of 13.0 h for the 10.0% BP treatment) with increased level of BP. Beet pulp levels up to 7.5% of diet DM appear acceptable as a dietary fiber source in a meat-based canine diet.

Hindered transport in fibrous membranes and gels: Effect of solute size and fiber configuration

Abstract: Hindered transport coefficients for a spherical macromolecule in a spatially periodic fibrous medium were calculated using two different methods. The first method is an effective medium approach based on Brinkman's equation and can be readily applied to disordered fibrous media. The second and more rigorous set of calculations makes use of generalized Taylor dispersion theory. Results from these two approaches are compared for two different spatially periodic lattices of bead-and-string fibers, which were chosen to illustrate the effects of inhomogeneity in the distribution of fibers. In addition, ratios of solute radius to fiber radius ranging from 0.5 to 5.0 were considered. Qualitative agreement between the two methods was obtained for each case studied, and quantitative agreement was obtained for volume fractions at which the hindering effects of the fibers were not too severe.

Influence of temperature on muscle recruitment and muscle function in vivo.

Abstract: Temperature has a large influence on the maximum velocity of shortening (Vmax) and maximum power output of muscle (Q10 = 1.5-3). In some animals, maximum performance and maximum sustainable performance show large temperature sensitivities, because these parameters are dependent solely on mechanical power output of the muscles. The mechanics of locomotion (sarcomere length excursions and muscle-shortening velocities, V) at a given speed, however, are precisely the same at all temperatures. Animals compensate for the diminished power output of their muscles at low temperatures by compressing their recruitment order into a narrower range of locomotor speeds, that is, recruiting more muscle fibers and faster fiber types at a given speed. By examining V/Vmax, I calculate that fish at 10 degrees C must recruit 1.53-fold greater fiber cross section than at 20 degrees C. V/Vmax also appears to be an important design constraint in muscle. It sets the lowest V and the highest V over which a muscle can be used effectively. Because the Vmax of carp slow red muscle has a Q10 of 1.6 between 10 and 20 degrees C, the slow aerobic fibers can be used over a 1.6-fold greater range of swim speeds at the warmer temperature. In some species of fish, Vmax can be increased during thermal acclimation, enabling animals to swim at higher speeds.

Method for producing molded article of fiber-reinforced thermoplastic resin

Abstract: A method for producing a molded article of a fiber-reinforced thermoplastic resin, which comprises supplying a melt mass of a thermoplastic resin (A) which is reinforced with fibers dispersed therein and having an average fiber length of not shorter than 1 mm and not longer than 50 mm as a reinforcing material in an unclosed mold in which a film or sheet made of a thermoplastic resin (B) having adhesiveness to a thermoplastic resin (A) is optionally placed, closing the mold and pressurizing and cooling it to obtain a molded article.

Fiber optic security system

Abstract: An optical security system is disclosed for one or more appliances such as a network of computers, terminals, and associated peripheral devices. The system comprises an optical fiber cable that is attached to an appliance through attachment devices that are secure from physical attack. The ends of the optical fiber are connected to a control box to form an optical fiber circuit which senses the amount of light within the fiber at any given time. The alarm device sounds if light within the fiber cable is attenuated through bending or breaking of the fiber cable in an attempted theft of the secured computer. The attachment devices comprise a two piece unit which holds the optical fiber. The first piece is a solid cone that is fastened to the computer component by a screw or adhesive. The second piece is a hollow cone that fits entirely over the solid inner cone. The cones include slots for holding the optical fiber between the cones. The fiber is held by the cones but is able to slide within the cones without breaking or bending the fiber cable. This allows the computer component to be moved without setting off the alarm. The alarm activates only when someone attempts to pry or pull the cones apart, subsequently bending the fiber cable.

Process for the co-production of ethanol and an improved human food product from cereal grains

Abstract: A process for producing a novel cereal grain food product is disclosed. This novel food product is high in fiber and protein with a complex sugars coating that renders the product good tasting and suitable for human consumption. This process involves the enzymatic conversion and removal of starch from the grain. The converted grain is separated from its liquor before the liquor is fermented to produce ethanol. The food product may be incorporated into baked goods, drinks, breakfast cereals and the like or eaten 'as is'.

Origin of Hysteresis Observed During Fatigue of Ceramic‐Matrix Composites

Abstract: Possible mechanisms for the hysteresis in stress-strain response observed during fatigue of fiber-reinforced ceramics are examined analytically. In the model developed, the microstructure of a unidirectional composite is divided into adjacent cells, each containing a single fiber. The compliance of each cell is modeled by a series of springs, with frictional sliding of fibers represented by sliding blocks. Fatigue damage is modeled by allowing fibers to debond and fracture on a random cycle-by-cycle basis. The magnitude of the interfacial shear between the fibers and matrix is shown to play a significant role in determining the extent of hysteresis observed during fatigue loading of unidirectional composites. Practical considerations, such as the influence of fiber volume fraction on macroscopic fatigue behavior, are also dis

Composites of Polyvinyl Chloride-Wood Fibers. I. Effect of Isocyanate as a Bonding Agent

Abstract: Various parameters concerning the performance of isocyanate as a coupling agent have been discovered. Greater premixing time (e.g., 20 min) leads to an improvement in the mechanical properties of the composites. the isocyanate solution is more efficient in comparison with undiluted isocyanate. Moreover, the chemical structure of isocyanate, which provides a better interaction with thermoplastics, results in superior properties. the reactivity of different isocyanates decreases in the following order: PMPPIC, TDIC, HMDIC, EIC. Again, isocyanate can act as a promoter or as an inhibitor, depending on the concentration of isocyanate used. For example, with a moderate concentration, it promotes maximum mechanical properties, while with a higher concentration, mechanical properties deteriorate. In addition, the nature of the pulp (e.g., CTMP, cotton, or sawdust) and fiber loading percentage as well as different grades of polymer supplied by different companies also play an important role in the mechani...

Potassium Nutrition Effects on Lint Yield and Fiber Quality of Acala Cotton

Abstract: Although results from in vitro ovule culture studies have demonstrated a specific K requirement for fiber growth, a direct association between the K status of the cotton (L.) plant and fiber quality has not been established under field conditions. To evaluate this relationship, a single cultivar (1985) and two cultivars (1986 and 1987) were grown with 0, 120, 240, or 480 kg K ha in 10 blocked replicates of each K level on an irrigated, vermiculitic soil. There was a significant seed-cotton yield response to applied K in each year. Lint yield, however, increased relatively more than seed yield, resulting in a greater lint percentage as plant K supply increased. The greater lint percentage reflected increased fiber length and secondary wall thickness (measured as a micronaire index) obtained from plants that received fertilizer K. For both cultivars, the fiber length, micronaire index, fiber strength and percent elongation, and fiber length uniformity ratio (dependent variables) were each positively related to (i) fiber K concentration at maturity, (ii) leaf K concentration at early bloom, and (iii) an index of soil K availability as independent variables in regression analyses. Comparison of cultivar regressions, however, indicated that fiber quality of ‘Acala GC510’ was higher than that of ‘Acala SJ2’ at low fiber, leaf, or soil K levels. We conclude that K supply to cotton fruit is an important determinant of fiber quality under field conditions, and that the K requirement for producing high lint yield with acceptable quality may differ among genotypes.

Thin Films Flowing on Vertical Fibers

Abstract: We describe annular films flowing and thinning along vertical fibers. According to the film thickness and to the radius of the fiber, two different kinds of behaviour can be observed: i) when the film is thick, drops develop because of the Rayleigh instability and flow downward. Some of them grow by swallowing the other ones, and quickly fall, leaving behind them a thick film which breaks in turn into droplets. ii) For a thin film on a large fiber, the instability cannot grow because of the flow. We present a quantitative study of the conditions under which drops do not appear, and show that these conditions are compatible with a scenario of nonlinear saturation of the Rayleigh instability.