bluuebunny/crossref_metadata_2025_split huggingface dataset:
Compaction of textile reinforcements for composites manufacturing. III: Reorganization of the fiber network
Authors: Robitaille François , Gauvin Raymond 
Published: April 2004

AbstractThe objectives of this series of papers are to describe the mechanical behavior of textile reinforcements under normal load and to quantify the effects of diverse processing parameters on that behavior. In the first and second papers of the series, experimental compaction and relaxation results were reported; general trends were identified and the effects of changes in the processing parameters were analyzed. In this paper, the results of sequences of successive compaction cycles applied to dry textiles and to textiles saturated in distilled H2O and silicone oil are presented. The reinforcements investigated are produced by assembling tows or rovings following different patterns; it is shown that the resulting heterogeneity, or regular variation of the local fiber volume fraction, can be associated to some particular elements of the mechanical behavior of the reinforcements. The reorganization of the fiber network and the effect of friction at the fiber contacts are demonstrated. Different stages in the reorganization process are identified; each stage is controlled by different parameters and corresponds to a precise behavior. Successive compaction cycles applied to a preform can reduce the void content of the final part.
Novel, low‐cost jute‐polyester composites. Part 1: Processing, mechanical properties, and SEM analysis
Authors: Dash B. N. , Rana A. K. , Mishra H. K. , Nayak S. K. , Mishra S. C. , Tripathy S. S. 
Published: April 2004

AbstractThe development of high performance composites from a cheap natural fiber, jute, as reinforcement is particularly significant from an economic point of view. In this work, jute fiber‐unsaturated polyester(GP) composites having appreciable mechanical properties were prepared by using solution impregnation and hot curing methods. Both unbleached (control) and bleached jute slivers with various percentages of fiber loadings were used to prepare the composites and were named JPH (C) i.e., Jute Polyester Hot Curing (control), and JPH (B) i.e., Jute Polyester Hot Curing (bleached), respectively. Mechanical properties such as tensile and flexural strain, toughness, and moduli of both the grades have been compared. Composites having 60 wt% of jute fiber yielded the best results. JPH (B) showed much better flexural properties than JPH (C), although the tensile properties of the latter were better. The inter‐laminar shear strength (ILSS) of the JPH (B) was found to be higher than JPH (C). The nature of fiber‐resin bonding was studied from scanning electron micrographs of the specimens subjected to tensile and flexural fracture. Dynamic mechanical properties were found to be very high, superior even to those of glass fiber reinforced composites. The flexural storage modulus was found to be 12.3 GPa at 30°C and to decrease slowly with temperature. The major finding in this work is the attainment of high mechanical properties of composite specimens with 60 wt %fiber loading. On a weight and cost basis, bleached jute fibres were found to be better reinforcements than other fibers with usual surface modification by coating or grafting processes.
Stochastic analysis of isothermal cure of resin systems
Authors: Padmanabhan S. K. , Pitchumani R. 
Published: April 2004

AbstractCuring of catalyzed resin systems is an important and critical processing step in the fabrication of reinforced thermosetting composite materials. Strong uncertainties inherent in the associated process and material parameters, however, pose a stiff challenge to robust commercial manufacturing of quality composites in practice. Although deterministic models have been developed over the years to simulate the cure process, analysis of the effects of the parameter uncertainties on the process performance and the product quality variabilities has been the subject of little attention, and forms the focus of this study. This paper presents a methodology for a systematic analysis of the effects of the process and material parameter uncertainties on the isothermal curing of thermosetting resin systems. A stochastic model is developed, and parameteric studies are presented to systematically examine the effects of the uncertainties in the processing temperature and the kinetic parameters on the process output variabilities. Optimum parameter spaces that minimize the variance of the output parameters are identified, as a first step towards robust manufacturing of composites.
Determinant assembled stowage bins—a case study
Authors: Button Scott D. 
Published: April 2004

AbstractMost commercial aircraft interior stowage bins are assembled using jigs. These assembly jigs are built to strict tolerances to ensure that the assemblies created in them will perform properly. Over the past decade, commercial aircraft structures assembly has been in transition from a method of assembly jig location to a method of part to part indexing, also known as Determinant Assembly. This method is now being investigated for accurate location of composite sandwich panels and metal attachments for commercial aircraft interiors. A background on Determinant Assembly (DA) as it has developed in structures is introduced. Several methods of coordinating composite sandwich panels to metal parts are discussed. Data that substantiates the use of these methods to maintain the prescribed tolerances is presented graphically. The results of building prototype parts using these techniques are presented. The process capability for DA assembled stowage bins is predicted using Variation Simulation Analysis, and those predictions are compared to results obtained with the current assembly jig method.
Mechanical properties of composites using ultrafine electrospun fibers
Authors: Kim Jong‐sang , Reneker Darrell H. 
Published: April 2004

AbstractThe objective of this research was to show the reinforcing effects of nanofibers in an epoxy matrix and in a rubber matrix using electrospun nanofibers of PBI (polybenzimidazole). The average diameter of the electrospun fibers was around 300 nanometers, which is less than one tenth the diameter and 1/100 the cross sectional area of ordinary reinforcing fibers. The ultrafine fibers provide a very high ratio of surface area to volume. The nanofibers toughened the brittle epoxy resin. The fracture toughness and the modulus of the nanofiber (15 wt%)‐reinforced epoxy composite were both higher than for an epoxy composite made with PBI fibrids (17 wt%), which are whisker‐like particles. In an elastomeric matrix, The Young's modulus and tear strength of the chopped nanofiber‐reinforced styrene‐butadiene rubber (SBR) were higher than those of the pure SBR. Micrographs of the fracture surfaces were obtained by scanning electron microscopy (SEM).
A process for prestaging thermosetting towpreg
Authors: Beck R. W. , Colton J. S. 
Published: April 2004

AbstractA method for prestaging thermosetting towpreg consisting of passing the material through a tunnel oven was developed to address the difficulties inherent in making thick‐walled thermosetting composite parts: aging, moisture uptake, and low resin viscosity during lay‐up; and residual stresses, warping, thermal degradation, resin gradients, and excessive void nucleation during the final cure. AS‐4 carbon fiber in a 3501‐6 epoxy matrix was used to test the continuous prestaging process. With prestaging, significant reductions in towpreg bulk, voids, and total enthalpy were achieved. Cure shrinkage also was achieved. The final towpreg product had good drape and greatly reduced tack. These changes addressed many of the aforementioned difficulties. A relation between residence time at 200°C (the process temperature) versus percent degree of cure (%DOC) was developed. Manufacturing characteristics such as drape, tack, and bulk were related to %DOC. A processing window of 15 to 22 %DOC yielded towpreg with optimal characteristics. Prestaged towpreg would be well suited to manufacturing with advanced fiber placement (AFP) type equipment. Initial trials in industry have been promising.
Low velocity impact behavior of glass/epoxy cross‐ply laminates with different fiber treatments
Authors: Kessler Andreas , Bledzki Andrzej K. 
Published: April 2004

AbstractThis paper deals with the influence of the fiber/matrix adhesion quality on the impact behavior of cross‐ply glass/epoxy laminates. Glass fibers with two different treatments (one to promote and one to prevent adhesion to the matrix) were embedded in epoxy matrix systems and subjected to low velocity impacts at energies below perforation energy. It will be shown that the laminates with good fiber/matrix adhesion are significantely more damage resistant than the plates with poor adhesion. It will be pointed out that the composites with the more brittle matrix system show the lower damage resistance. For all materials, the absorbed energy correlates well with the amount of impact induced damage. Furthermore, an experimental/mathematical model is introduced that gives the possibility of predicting the maximum deflection and maximum force for any given impact energy. Only one experiment is needed for each material to identify the model parameters. These parameters describe the real material behavior and can be used as characteristic values to classify materials with respect to their impact stiffness and damage resistance.
Grip point spacing along the edges of an anisotropic fabric sheet in a biaxial tensile test
Authors: Bassett Richard J. , Postle Ron , Pan Ning 
Published: April 2004

AbstractThe technique of gripping fabric edges using pin grips has been applied in several studies of biaxial mechanical behavior of fabrics. This paper presents a theoretical study of the nonuniform stress distribution caused by the spacing of the grip points. The theory leads to expressions of the shear strain in the fabric specimen and the displacement of the grip points by which the tensile stress nonuniformity caused by the grip method can be calculated. The analysis reveals important factors affecting the stress distribution in a fabric specimen and provides design criteria for new instrument development.
Characterization of mixed fiber nylon composites incorporating composite scrap
Authors: Licea‐claveríe A. , Carrillo F. J. U. , Alvarez‐castillo A. , Castaño V. M. 
Published: April 2004

AbstractRecycling of engineering thermoplastics and their composites represents both a challenge and an opportunity in today's material science. A study on nylon 6,6 based composites with mixed glass‐fiber and carbon‐fiber reinforcement, including nylon composite scrap in their formulation, is reported. Several formulations were prepared by injection molding and were characterized by stress‐strain‐measurements, impact testing, simultaneous differential thermal analysis and thermogravimetry (DTA‐TG), density measurements and scanning electron microscopy (SEM). No dependence on mechanical properties due to increasing amounts of scrap in the composites was found up to 10.4 wt%. The generated recycled composites generally showed lower mechanical properties as compared with the virgin composite because of a poor matrix‐fiber adhesion.
Measurement of principal permeability with the channel flow experiment
Authors: Weitzenböck J. R. , Shenoi R. A. , Wilson P. A. 
Published: April 2004

AbstractA framework for channel flow permeability measurement in resin transfer molding (RTM) is developed in this paper. For the channel flow experiment, five possible experimental configurations are identified, of which two have not yet been mentioned in the literature. Starting from effective permeability, the entity measured in the experiment, explicit formulas for principal permeability and its orientation in two and three dimensions are developed. These formulas are applied to (published) experimental results that demonstrate their validity. The practical problems that prevent three‐dimensional permeability measurement are discussed. Next, a framework for two‐dimensional channel flow permeability measurement is proposed. All known channel flow permeability measurement methods are classified according to this new framework, and where appropriate, differences are discussed. An important finding emerging from this comparison is that two different definitions of Darcy's law are used today in permeability measurement.
Processing and properties of new high‐temperature, lightweight composites based on foam polyimide binder
Authors: Yudin V. E. , Otaigbe J. U. , Artemieva V. N. 
Published: April 2004

AbstractWe report a method for making novel, lightweight (ρ = 0.3–1.1 kg/dm3) polymer composites based on high‐temperature foam polyimide binder, carbon fibers, and organic fibers. The density and mechanical properties of the foam composite can be varied over a relatively wide range, depending on the volume contents of the fiber and air pores. The resin's high glass transition temperature of 260°C, coupled with the high thermal stability of carbon or polyimide fibers, contributes to its excellent retention of mechanical properties at elevated temperatures. The temperature at the beginning of weight loss is not lower than 570°C and depends on the kind of fiber felt. The combination of excellent thermal and specific mechanical properties of foam composites together with exceptional thermal stability and processability on conventional molding equipment can provide unusual performance for the new design of advanced materials and structures.
Mechanical and thermal properties of environment‐friendly “green” composites made from pineapple leaf fibers and poly(hydroxybutyrate‐co‐valerate) resin
Authors: Luo S. , Netravali A. N. 
Published: April 2004

AbstractThis paper presents the mechanical and thermal properties of unidirectional, degradable, environment‐friendly “green” composites made from pineapple fibers and poly(hydroxybutyrate‐co‐valerate) (PHBV) resin. Tensile and flexural properties of the “green” composites with different fiber contents were measured in both longitudinal and transverse directions. Compared to those of virgin resin, the tensile and flexural strengths of “green” composites are significantly higher in the longitudinal direction while they are lower in the transverse direction. However, the mechanical properties are lower than those predicted by simple models. Scanning electron microscope (SEM) photomicrographs of the tensile fracture surfaces demonstrate fibers being pulled out from the matrix, the interfacial failure, fiber fibrillation, and the nonunidirectional nature of the “green” composites. The thermal behavior of the “green” composites, studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), showed that the presence of pineapple fibers does not affect the nonisothermal crystallization kinetics, crystallinity, and thermal decomposition of PHBV resin.
Copolymerization kinetics of styrene/vinyl‐ester systms: Low temperature reactions
Authors: Dua S. , McCullough R. L. , Palmese G. R. 
Published: April 2004

AbstractVinyl‐ester (VE), synthesized by the addition reaction of methacrylic acid and diglycidyl ether of bis‐phenol A (DGEBA) epoxy, and styrene react via bulk free radical chain growth copolymerization to form a crosslinked network polymer. Vital clues regarding the development and the structure of the network were obtained from the study of copolymerization kinetics of styrene/VE systems. Fourier transform infrared (FTIR) spectroscopy was used to obtain the individual fraction conversion rates of both the monomers. The conversion versus time data for both styrene and VE was fit to an autocatalytic kinetic model. The autocatalytic model was found to adequately replicate the kinetic data over the entire life of cure. In this investigation, the effects of styrene concentration, temperature, catalyst concentration, and initiator concentration on cure kinetics of styrene/VE systems were studied. The conversion profiles of both styrene and VE were used to obtain the reactivity ratios of the two monomers. The reactivity ratios were evaluated to be close to zero, suggesting that initially alternating copolymerization is favored over homopolymerization. The cure behavior of vinyl‐ester resins is affected not only by the chemical reactivity of the monomers toward the free radicals, but also by diffusion effects, phase separation, and microgel formation. The interplay of these factors controls the kinetics of cure, thereby affecting the physical and chemical properties of the resulting polymer.
Tensile properties and morphology of PP/EPDM/glass bead ternary composites
Authors: Liang J. Z. , Li R. K. Y. , Tjong S. C. 
Published: April 2004

AbstractThe tensile properties of three types of injection molded glass bead (GB) filled polypropylene (PP)/ethylene‐propylene‐diene monomer (EPDM) ternary composites have been determined at room temperature by using an Instron materials testing machine. The effects of the filler surface treatment, the glass bead (GBI) pretreated with a silane coupling agent and the EPDM (EPDM‐MA) modified with a maleic anhydride, and the filler content on the tensile mechanical properties of the ternary PP composites have been investigated. The Young's modulus (Ec) increases while the yield stress (σyc) and tensile fracture strength (σbc) of the composites decrease with increasing the volume fraction of glass beads (ϕg) when the volume fraction of EPDM is constant (ϕe = 10%). The (Ec) values of PP/EPDM/GBI and ϵbc for PP/EPDM‐MA/GB2 (no surface pretreated) systems are the highest at the same ϕg. The tensile fracture energy (Ebc) and tensile fracture strain (ϵbc) of PP/EPDM/GBI and PP/EPDM/GB2 systems appear to peak at ϕg = 25%. However, the Ebc and ϵbc of PP/EPDM‐MA/GB2 system show little changes with increasing ϕg. The fracture surfaces of ternary composites have been examined in a scanning electron microscope. The correlation between the tensile properties and morphologies of these materials have been discussed.
Electrochemical synthesis and characterization of polypyrrole‐poly(styrene sulfonate) composite coatings on carbon fibers
Authors: Iroh Jude O. , Chen Yan 
Published: April 2004

AbstractPolypyrrole‐polystyrene sulfonate composite coatings have been formed on carbon fibers by an aqueous electrochemical process. The effects of process parameters such as applied current density, monomer concentration, electrolyte concentration, and the reaction time, on the electrochemical polymerization of pyrrole onto carbon fibers were investigated. The rate of formation of the coatings increased with the current density and pyrrole concentration. It was, however, independent of electrolyte concentration, especially for polystyrene sulfonate concentration [PsSNa] of 0.05–0.25 M. At higher electrolyte concentration [PsSNa] ≥ 0.30 M, the rate of coatings formation increased with electrolyte concentration. The order of the rate of polymerization with respect to the electrolyte concentration was shown to be 0 and 1.0 at low and high electrolyte concentration, respectively. The polymerization potential, Ep, increased with the current density and decreased with pyrrole concentration. SEM micrographs showed that the morphology of coatings varied with the electrolyte concentration. At low electrolyte concentration, the coatings were rough and granular; however, at higher electrolyte concentration the coatings were smooth and uniform. The doping of polypyrrole films by polystyrene sulfonate ion was confirmed by infrared spectroscopy.
Biologically degradable fiber‐reinforced urethane composites from wheat straw
Authors: Borda Jenö , Tesléry Beáta , Zsuga Miklós 
Published: April 2004

AbstractUrethane type adhesive mixtures containing poly(MDI) were used to prepare biodegradable urethane type composites containing wheat stalks. According to the mechanical properties, i.e., tensile strength, bending strength, and hardness of the composites, the ratio of wheat stalks to sticking mixtures, the technological pressure used, and the size of the wheat stalks were optimized. The mechanism of the possible chemical reaction is also discussed.
Effect of degree of cure and fiber content on the mechanical and dynamic mechanical properties of carbon fiber reinforced PMR‐15 polyimide composites
Authors: Labronici Marcos , Ishida Hatsuo 
Published: April 2004

AbstractA unidirectional continuous carbon fiber reinforced polyimide composite is fabricated using the PMR‐15 polyimide as a matrix. Mechanical and dynamic mechanical properties of the composite are studied. The effect of variation of the fiber content ranging from 55% to 70% by volume on the properties of the composite is determined. The effects of the laminate thickness and degree of curing of the matrix on the Izod impact strength are examined. The effect of the degree of curing of the matrix on the dynamic mechanical spectrum is studied. Finally, variables such as humidity, environment temperature, vacuum, and pressure during laminate processing, and variation of monomer composition are discussed in terms of change in matrix structure, which is reflected in a variation of Tg between batches.
Rheological behavior of low molecular weight polystyrene composites containing monodisperse crosslinked polystyrene beads
Authors: Park M. , Salovey R. 
Published: April 2004

AbstractSteady shear viscosities and dynamic moduli of polymer composites, consisting of crosslinked polystyrene beads and low molecular weight polystyrene matrix, were measured in a cone‐and‐plate rheometer at different temperatures. Viscosities and dynamic moduli were found to be very sensitive to filler loading and measurement temperature. Steady shear viscosities of 30% and 40% loaded low molecular polystyrene composites showed a power‐law behavior over the entire range of shear rates. Storage and loss moduli were initially linear with frequency on double logarithmic plots, with limiting slopes of 0.3 and 0.1. At high concentration of filler particles, they showed a flat plateau at low frequencies, indicating that these systems exhibit a yield behavior. A 20% PS composite loaded with beads of high crosslink densities resulted in poor dispersion of beads as a result of poor dispersion of particles. PS beads 1.16 μm in diameter showed a higher viscosity. It is due to the apparent increase in loading resulting from broken particles. At low measurement temperature, filler effects were suppressed by high viscosity matrix and showed a similar rheological behavior to high molecular weight by PS matrix. We suggest that rheological behavior reflects the state of dispersion of beads in the matrix.
Processing and composition dependence of the structure and mechanical properties of polycarbonate/ultrax blends
Authors: De Gauna B. E. Ruiz , Gaztelumendi M. , Nazábal J. 
Published: April 2004

AbstractPolycarbonate (PC)/Ultrax blends were obtained by injection molding changing both the Ultrax content and the injection temperature, speed and pressure. The change of injection speed or pressure did not lead to significant change of morphology or properties. An injection temperature of 300°C allowed some reaction to take place between the components and the presence of some reacted Ultrax in the PC‐rich phase, but the mainly spherical morphology obtained lead to poor mechanical properties. At a lower injection temperature of 280°C, however, reactions were almost not detected, but fibrillar structures were produced, mainly because of the higher matrix viscosity. This gave rise to important increases not only in modulus and tensile strength but also in flexure properties and creep dimensional stability.