bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical simulation of three‐dimensional fiber orientation in injection molding including fountain flow effect
Authors: Han Kyeong‐Hee , Im Yong‐Taek 
Published: April 2004

AbstractIt is essential to predict the nature of flow field inside mold and flow‐induced variation of fiber orientation for effective design of short fiber reinforced plastic parts. In this investigation, numerical simulations of flow field and three‐dimensional fiber orientation were carried out in special consideration of fountain flow effect. Fiber orientation distribution was described using the second‐order orientation tensor. Fiber interaction was modeled using the interaction coefficient CI. Three closure approximations, hybrid, modified hybrid, and closure equation for CI=0, were selected for determination of the fiber orientation. The fiber orientation routine was incorporated into a previously developed program of injection mold filling (CAMPmold), which was based on the fixed‐grid finite element/finite difference method assuming the Hele‐Shaw flow. For consideration of the fountain flow effect, simplified deformation behavior of fountain flow was employed to obtain the initial condition for fiber orientation in the flow front region. Comparisons with experimental results available in the literature were made for film‐gated strip and centergated disk cavities. It was found that the orientation components near the wall were were accurately predicted by considering the fountain flow effect. Test simulations were also carried out for the filling analysis of a practical part, and it was shown that the currently developed numerical algorithm can be effectively used for the prediction of fiber orientation distribution in complex parts.
Axial impregnation of a fiber bundle. Part 2: Theoretical analysis
Authors: Amico S. C. , Lekakou C. 
Published: April 2004

AbstractThis paper considers the numerical simulation of the axial capillary infiltration of an aligned fiber bed and the assessment of the input permeability and capillary pressure data by validating the simulation results with experimental data from Part 1 (1) of this study. Theoretical predictions of capillary pressure are close to the capillary pressure value determined from a long‐term experiment and are used as input data in the infiltration simulations. The Carman‐Kozeny equation is recommended for the prediction of permeability and the validation of the numerical simulations with experimental data for two infiltrating liquids, silicone oil and epoxy, yields recommended values for the empirical Kozeny constant for different ranges of fiber volume fraction.
Compaction of fiber reinforcements
Authors: Batch Gibson L. , Cumiskey Sean , Macosko Christopher W. 
Published: April 2004

AbstractIn resin transfer molding, dry fiber reinforcements are compacted as the mold closes before injection of a curable resin matrix. This paper presents experimental data of compaction pressure as a function of fiber volume fraction. Data are presented for woven roving mats, random fiber mats, loose fiber rovings for pultrusion, and uniaxial or biaxial roving mats. These data are fit to a mathematical model derived in an Appendix. Experimental data are also given for six combinations of reinforcements. We use the compaction model of each constituent layer to predict the average volume fraction assuming that fiber layers do not interact. However, we see that most combinations of reinforcements have fiber volume fractions greater than expected at pressures under 50 psi, indicating a synergistic packing between the layers of different composition.
An optimization procedure for the pultrusion process based on a finite element formulation
Authors: Coelho R. M. L. , Calado V. M. A. 
Published: April 2004

AbstractComposite materials are manufactured by different processes. In all, the process variables have to be analyzed in order to obtain a part with uniform mechanical properties. In the pultrusion process, two variables are the most important: the pulling speed of resin‐impregnated fibers and the temperature profile (boundary condition) imposed on the mold wall. Mathematical modeling of this process results in partial differential equations that are solved here by a detailed procedure based on the Galerkin weighted residual finite element method. The combination of the Picard and Newton‐Raphson methods with an analytical Jacobian calculation proves to be robust, and a mesh adaptation procedure is presented in order to avoid integration errors during the process optimization. The two earlier‐mentioned variables are optimized by the Simulated Annealing method with some constraints, such as a minimum degree of cure at the end of the process, and the resin degradation (the part temperature cannot be higher than the resin degradation temperature at any time during the whole process). Herein, the proposed objective function is an economic criterion instead of the pulling speed of resin‐impregnated fibers, used in the majority of papers.
Effect of hydrothermal aging on the thermo‐mechanical properties of a composite dental prosthetic material
Authors: Pegoretti Alessandro , Migliaresi Claudio 
Published: April 2004

AbstractThe aim of this investigation was to evaluate the long‐tern effects of aging in water on the physical properties of a new class of commercially available dental polymer composites. The selected product consists of a bisphenol a glycidyl methacrylate (Bis‐GMA) resin diluted with triethylene glycol dimethacrylate (TEGDMA) and reinforced with long E‐glass fibers, specifically developed for prosthetic dental bridges. Samples were prepared according to a standard procedure suggested by the producer, and aged in water at 37°C and 70°C up to 32 weeks. Samples were periodically tested in order to assess their mass variation, static flexural modulus and strength, fatigue resistance, and dynamic mechanical thermal behavior. Experimental results evidenced that aging caused two simultaneous phenomena, having opposite effects on the specimen mass. In fact, composites absorbed a certain amount of water (up to 0.8 wt% at 37°C and 1.2 wt% at 70°C) but at the same time a mass loss was detected, which could be attributed to a release of unreacted monomeric species and fragments generated by polymer chain degradation (especially at 70°C). Flexural strength strongly decreased during aging in water, reaching 80% and 45% of the initial value for samples aged for 32 weeks at 37 and 70°C, respectively. Aging practically does not affect flxural modulus, while a sensible reduction of the material fatigue life was observed. Glass transition temperature and the relative activation energy were markedly influenced by the aging in water with effects related to the water uptake and mass loss phenomena.
Mechanical properties of carbon woven reinforced epoxy matrix composites. A study on the influence of matrix modification with polysulfone
Authors: Mujika F. , De Benito A. , Fernández B. , Vázquez A. , Llano‐Ponte R. , Mondragon I. 
Published: April 2004

AbstractAn experimental investigation has been carried out to study the influence of thermoplastic addition on the mechanical properties of woven carbon fiber/epoxy matrix composites. As toughening agent bisphenol‐A polysulfone, PSu, has been added to the epoxy matrix. Flexural tests haved been performed to characterize the mechanical behavior of unmodified and PSu‐modified bulk tetra‐ and bifunctional epoxy matrices and also for the corresponding woven carbon fiber, CF, composite materials. Three‐point notched flexural tests been used to investigate the influence of polysulfone addition in the mode‐I fracture properties of the bulk epoxy matrices, relating them to their microstructural features investigated by atomic force microscopy (AFM). The double‐cantilever bea (DCB) and the end‐notched flexural (ENF) tests have been applied to characterize the interlaminar fracture toughness of the corresponding composites. For composites, the flexural properties were simmilar independent of the funcetionality of the epoxy matrix and of the thermoplastic content. Nevertheless, PSu addition to the epoxy matrix celarly enhanced the ode‐I and II interlaminar fracture toughness of the corresponding composites, the immprovement being higher for the composites manufactured with the bifunctional epoxy matrix at every thermoplastic content because of the lower crosslink density of the epoxy matrix.
Surface modification of fique fibers. Effect on their physico‐mechanical properties
Authors: Gañán Piedad , Mondragon Iñaki 
Published: April 2004

AbstractA study has been performed to assess the possibilities of fique fibers (a Colombian native fiber) as reinforcement for polymeric matrices. The fique fibers were treated using different chemical surface treatments. The effect produced on the physico‐mechanical properties of fique fibers have been investigated. The applied surface treatments have been mercerization, and/or chemical agents such as maleic anhydride and acrylic acid, and also silanization. In order to analyze the chemical changes in the treated fibers, Fourier Transform infrared, FTIR, spectroscopy was used along with two related techniques: Attenuated Total Reflection (ATR) and Coupled Microscopy. Additionally, physical and mechanical properties of untreated and treated fique fibers have been studied. A wettability study using contact angle measurements has also been performed for surface free energy determination. The thermal stability of the fibers has been investigated by thermogravimetrycal analysis.
Initial dispersion mechanisms of chopped glass fibers in polystyrene
Authors: Kuroda Melody M. H. , Scott Chris E. 
Published: April 2004

AbstractUnderstanding the mechanisms contributing to the initial stage of dispersion for individual fibers from chopped glass bundles is important for optimizing process conditions and obtaining fiber composites with optimal properties. These studies have shown that under model flow conditions, bundles have two separation modes, rupture and erosion. Both of these occur in a stochastic manner and are dependent upon the internal structure of the bundles. Under chaotic flow, both strain rate and total strain to which the material is exposed are important, though the effect of increasing strain rate decreases at higher total strains. To Obtain consistent minimal dispersion in model flows, the maximum nominal stresses required are higher than 104 Pa for simple shear and 106 Pa for squeezing flows. In contrast, stress levels around 104 Pa yield good dispersion under chaotic flow, implying the flow field is a more significant factor than the stresses imposed.
The effect of moisture and loading rate on the interfacial fracture properties of sandwich structures
Authors: Scudamore R. J. , Cantwell W. J. 
Published: April 2004

AbstractThe skin‐core interfacial fracture properties of a number of dry and moistureconditioned sandwich structures have been investigated over a range of crosshead displacement rate using the three point bend sandwich (TPBS) structure. It has been shown that the interfacial fracture toughness, Gc, of a crosslinked PVC system decreases rapidly with loading rate, whereas the toughness of a linear PVC remains roughly constant. In contrast, the interfacial fracture toughness of the balsa core material increased steadily with increasing crosshead displacement rate, an effect that was attributed to the rate dependent properties of the glass fibers in the wake of the primary crack. Prolonged seawater exposure in an aluminum honeycomb structure was found to attack the bond between the epoxy matrix and the aluminum core, facilitating crack advance along the skin‐core interface. Finally, it is concluded that great care should be exercised before selecting sandwich structures for hostile marine environments.
An analysis of stretch forming of thermoplastic composites
Authors: Lee J. H. , Vogel J. H. , Rhee K. Y. 
Published: April 2004

AbstractThermoplastic composite sheet materials have found an increasing number of applications through the use of matched‐die compression molding. The combination of high strength, low weight and moderate manufacturing costs makes the material an attractive alternative to sheet metal stampings in a number of applications. However, a significant range of conventional sheet forming techniques may also prove suitable for these materials, provided the effects of strain rate and temperature can be properly understood and exploited, leading to a further reduction of manufacturing costs and an increasing number of potential applications. In this work, limiting strains in biaxial stretch forming were explored using the hemispherical stretch forming test. The materials tested contain 20, 35, and 40 percent by weight of randomly oriented glass fiber in a polypropylene matrix. The forming tests were performed at temperatures ranging from 75°C to 150°C and at punch speeds of 0.01cm/sec, 0.1cm/sec, and 1cm/sec. A rotationally symmetric, anisotropic material model with rate sensitivity was developed and incorporated into an axisymmetric finite element model of the stretch‐forming process. The model parameters were temperature‐dependent, though the temperature distribution in the formed part was assumed to be uniform. Strain distributions in the formed parts are compared to finite element method results, and the results are good up to the point when localized necking begins to dominate the strain distribution. These forming limit strains are compared with predictions based on Marciniak's imperfection theory, with good results.
Lead—Natural rubber composites as gamma radiation shields. II: High concentration
Authors: Gwaily S. E. , Madani M. , Hassan H. H. 
Published: April 2004

AbstractNatural rubber composites were prepared by the incorporation of different lead concentration, namely: 100, 300, 500, 1000, 1500 and 2000 phr to be used as gamma radiation shields. A non‐linear dependence of the attenuation coefficient upon the lead concentration was observed for both 60Co and 137Cs as gamma radiation sources. Sample containing the ultimate lead concentration (2000 phr) and thickness 1 mm was found to have 0.336 mm and 0.383 mm lead equivalent for 60Co and 137Cs respectively. Electrical and mechanical properties of the investigated composites were also measured.
Investigation of the influence of textile compression on the out‐of‐plane permeability of a bidirectional glass fiber fabric
Authors: Endruweit Andreas , Luthy Thierry , Ermanni Paolo 
Published: April 2004

AbstractIn Liquid Composite Molding (LCM) processes, the out‐of‐plane component of the textile permeability varies with the applied injection pressure because of compression of the textile. A correlation of the compressibility measured on a testing machine and the behavior in a flow channel gives information about the compression for dry and wet preforms in the LCM mold during resin injection. The permeability for injection pressure values between 0.1 MPa and 0.5 MPa has been measured for various initial porosity values with five pressure cycles each. A steady state permeability value has been defined, averaging the permeability values in the pressure range of 0.1 MPa to 0.5 MPa excluding the hysteresis effect of the initial pressure cycle. A relation between this steady permeability and the given initial porosity and injection pressure has been found, replacing the Kozeny‐Carman formula for the description of the permeability of compressed textiles. Based on the same idea, a formula for description of the variations in permeability for increasing pressure in the first pressure cycle has been found. In this empirical formula, the term describing the influence of the injection pressure varies from the one found for the steady state permeability.
A comparison between the static and fatigue properties of glass‐fiber and carbon‐fiber reinforced polyetherimide composites after prolonged aging
Authors: Viña J. , Castrillo M. A. , Argüelles A. , Viña I. 
Published: April 2004

AbstractThe static and fatigue behavior of two fiber‐reinforced composites was characterized after samples were subjected to both natural and accelerated aging. The composites consisted of a thermoplastic matrix (PEI: polyetherimide) reinforced with glass or carbon fabric. Natural aging involved exposing samples to the elements over a period of two years, while accelerated aging was conducted in a saline solution during 200 days. Subsequently, static (tensile and interlaminar shear) and fatigue tests were carried out with the aim of determining the mechanical properties of the materials after exposure. A negligible decrease in the value of these properties was observed, while different behavior was detected depending on the type of aging of the material.
Short fibers as reinforcement of rubber compounds
Authors: López Manchado M. A. , Arroyo M. 
Published: April 2004

AbstractThe effect of aramid, glass and cellulose short fibers on the processing behavior, crosslinking density and mechanical properties of natural rubber (NR), ethylene‐propylene‐diene terpolymer rubber (EPDM) and styrene‐butadiene rubber (SBR) has been investigated. Two fiber percentages (10 and 20 phr) were added to the rubber. The results have shown that the above‐mentioned fibers, especially aramid fibers, are effective reinforcing agents for these rubbers, giving rise to a significant increase in mechanical properties, such as tensile modulus and strength, and tear and abrasion resistance. Moreover, a significant decrease in the time to reach 97% of curing, t′c (97) is observed, which indicates that the fibers tend to increase the vulcanization rate, regardless of the rubber used. Fibers give also rise to an increase in crosslinking, especially the aramid fibers.
Recycling of the fibrous fraction of reinforced thermoset composites
Authors: Kouparitsas C. E. , Kartalis C. N. , Varelidis P. C. , Tsenoglou C. J. , Papaspyrides C. D. 
Published: April 2004

AbstractWe investigate the feasibility of reusing short fibers recovered from recycled thermoset composites for the production of new composites. Glass fibers were recovered from glass‐polyester composites, and carbon and aramide fibers from epoxy based composites. From the different fractions obtained after grinding, a specific fibrous fraction was selected for reuse. This recycled fraction was first characterized in terms of length and residual matrix content, and then incorporated into virgin polymer matrices to prepare new thermoplastic composites. To evaluate the performance of these composites, tensile tests were initially carried out, and the results were compared with similar measurements performed on pristine composites containing short unused fibers of similar length. In most cases examined, recycling does not adversely affect the mechanical performance of the new composite. This overall behavior is explained in terms of fiber length preservation, fiber dispersion mechanism and fiber‐matrix adhesion.
Self‐reinforced polypropylene/LCP prepregs and laminates
Authors: Liang Y. C. , Isayev A. I. 
Published: April 2004

AbstractPolypropylenes (PPs) of various molecular weights were mixed with a thermotropic liquid crystal polymer (LCP) to prepare unidirectional sheets (prepregs), quasi‐isotropic and unidirectional laminates. The mechanical properties and the morphology of the prepregs and the laminates at 0° and 90° with respect to the machine direction were investigated as a function of draw ratio, LCP concentration and molecular weight of the PP. The results for prepregs and laminates showed that both drawing and LCP concentration generally enhanced modulus and tensile strength in machine direction. The morphology of LCP changed from spherical or ellipsoidal droplets to elongated fibrils as the draw ratio increased. The diameter of LCP fibrils decreased with increasing molecular weight of the PP matrix, indicating more effective droplet breakup and better mixing in the case of high molecular weight PP.
The influence of cooling rate on the fracture properties of a glass reiforced/nylon fiber‐metal laminate
Authors: Guillén J. F. , Cantwell W. J. 
Published: April 2004

AbstractThe effect of varying cooling rate on the microstructure and resulting mechanical properties of a novel fiber‐metal laminate (FML) based on a glass fiber‐reinforced nylon composite has been investigated. Polished thin sections removed from plain glass fiber/nylon composites and their corresponding fiber‐metal laminates indicated that the prevailing microstructure was strongly dependent on the rate of cooling from the melt. Mode I and Mode II interlaminar fracture tests on the plain glass fiber reinforced nylon laminates indicated that the values of GIc and GIIc averaged approximately 1100 J/m2 and 3700 J/m2 respectively at all cooling rates. The degree of adhesion between the aluminum alloy and composite substrates was investigated using the single cantilever beam geometry. Here, the measured values of Gc were similar in magnitude to the Mode I interlaminar fracture energy of the composite, tending to increase slightly with increasing cooling rate. The tensile and flexural fracture properties of the plain composites and the fiber metal laminates were found to increase by between 10% and 20% as the cooling rate was increased by two orders of magnitude. This effect was attributed to over‐aging of the aluminum alloy plies at elevated temperature during cooling. Finally, fiber metal laminates based on glass fiber/nylon composites were shown to exhibit an excellent resistance to low velocity impact loading. Damage, in the form of delamination, fiber fracture, matrix cracking in the composite plies, and plastic deformation and fracture in the aluminum layer, was observed under localized impact loading. Here, the fast‐cooled fiber metal laminates offered superior post‐impact mechanical properties at low and intermediate impact energies, yet very similar results under high impact energies.
Effects of temperature and strain rate on the tensile behavior of short fiber reinforced polyamide‐6
Authors: Wang Zhen , Zhou Yuanxin , Mallick P. K. 
Published: April 2004

AbstractTensile behavior of extruded short E‐glass fiber reinforced polyamide‐6 composite sheet has been determined at different temperatures (21.5°C, 50°C, 75°C, 100°C) and different strain rates (0.05/min, 0.5/min, 5/min). Experimental results show that this composite is a strain rate and temperature dependent material. Both elastic modulus and tensile strength of the composite increased with strain rate and decreased with temperature. Experimental results also show that strain rate sensitivity and temperature sensitivity of this composite change at a temperature between 25°C and 50°C as a result of the glass transition of the polyamide‐6 matrix. Based on the experimental stress‐strain curves, a two‐parameter strain rate and temperature dependent constitutive model has been established to describe the tensile behavior of short fiber reinforced polyamide‐6 composite. The parameters in this model are a stress exponent n and a stress coefficient σ*. It is shown that the stress exponent n, which controls the strain rate strengthening effect and the strain hardening effect of the composite, is not only strain rate independent but also temperature independent. The stress exponent σ*, on the other hand, varies with both strain rate and temperature.