bluuebunny/crossref_metadata_2025_split huggingface dataset:
SUPG and grad‐div stabilized finite element methods for steady weakly compressible viscous flow
Authors: Bause Markus 
Published: December 2004

AbstractThe extensive application of mathematical and computational methods has become an efficient and powerful approach to the investigation and solution of many problems and processes in fluid dynamics from qualitative as well as quantitative point of view. In this work a new class of advanced numerical approximation schemes to isothermal compressible viscous flow is presented. The schemes are based on an iteration between an Oseen like problem for the velocity and a hyperbolic transport equation for the density. Such schemes seem attractive for computations because they offer a reduction to simpler problems for which highly refined numerical methods either are known or can be built from existing approximation schemes to similar equations, and because of the guidance that can be drawn from an existence theory based on them. For the generalized Oseen subproblem a Taylor–Hood finite element method is proposed that is stabilized by a reduced SUPG and grad‐div technique (cf. [1, 4]) in the convection‐dominated case. Results of theoretical investigations and numerical studies are presented. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Solution of the three‐dimension wave equation by using wave polynomials
Authors: Maciąg Artur 
Published: December 2004

AbstractThe paper demonstrates a specific power series expansion technique to solve the three‐dimensional wave equation. As solving functions, so‐called wave polynomials are used. The presented method is useful for a finite body of certain shape geometry without strength restrictions. The wave polynomials are defined. Recurrent formulas for the wave polynomials and their derivatives are obtained. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An adaptive refinement method for convection‐diffusion problems
Authors: Schamberg Thomas , Heinrichs Wilhelm 
Published: December 2004

AbstractAn adaptive finite difference method for singularly perturbed convection‐diffusion problems is presented. The method is introduced using a first‐order upwind scheme and a suitable error estimator based on the first derivatives. To obtain the grid structure needed for the cross stencil a special refinement strategy is considered. To avoid the slave points we change the stencil at the interface points from a cross to a skew one. After the convergence of the refinement algorithm we use a combination of a first order upwind and a second order central schemes to achieve higher order of convergence. Several numerical examples show the efficiency of our treatment. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Iterative Projection Methods for Sparse Nonlinear Eigenproblems
Authors: Voss Heinrich 
Published: December 2004

AbstractFor the sparse nonlinear eigenproblem T(λ)x = 0 we consider iterative projection methods where the current search space is expanded by a direction having a high approximation potential for the eigenvalue wanted next. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effects of processing on the mechanical properties of carbon short‐fiber reinforced polycarbonate
Authors: Haskell W. E. , Petrie S. P. , Lewis R. W. 
Published: December 2004

AbstractThe effects of varying the injection‐molding parameters of temperature, pressure, and injection rate on the mechanical properties of commercially obtained neat and carbon‐rein‐forced polycarbonate were investigated. The test specimens contained molded‐in and drilled holes so that the effect of a weld‐line could be investigated. The breaking‐strength and modulus‐of‐toughness values are reported. The results of the Young's moduli determinations showed that the stiffness of the neat materials was invariant and that the carbon‐reinforced material was orthotropic. Gel Permeation Chromatography (GPC) results showed that the neat resin was stable at the temperature investigated. The filled resin, however, underwent a decrease in molecular weight distribution at 650°F. At elevated temperatures, the breaking strength and modulus of thoughness of the carbon‐reinforced material showed a decrease where the properties were dependent upon the resin. Fiber orientation produced during molding significantly affected the toughness. The results agreed well with theory.
Direct determination of the orientation of short glass fibers in an injection‐molded poly(ethylene terephthalate) system
Authors: Fakirov S. , Fakirova C. 
Published: December 2004

AbstractA simple and new technique for direct determination of the short fibers orientation in polymer composites is described. It is based on the fact that the shape of the fibers' cross section in the plane perpendicular to the desired direction (e.g., orientation direction) depends on the orientation angle ϕ with respect to this direction. For an eliptical shape with minor and major radii r and R, the cosϕ = r/R. Using micrographs from the polished samples' cross section and assuming a planar fiber distribution, it is possible to calculate for a part or entire cross section area: (i) the ϕ‐values; (ii) the orientation parameter fp; (iii) the angular distribution (by histograms); and (iv) the number and the sizes of the layers with more uniform fiber orientation as well as the transition zones between them. It is demonstrated for commercial poly(ethylene terephthalate) (PET) reinforced with 45 percent (by weight) short E‐glass fibers (Rynite®) that each surface layer (A) takes ca. 3/16 of the sample thickness (b), the core (C)—3/16b and the boundary (B) between them occupies 3/16b. These layers are characterized, respectively, by <ϕ>A = 28°, <ϕ>B = 38°, <ϕ>C = 64°, and f = 0.51, f = 0.18, f = −0.15. For the entire thickness (A + B + C) the <ϕ>A+B+C = 44° and f = 0.17. The method described is applicable to any kind of fiber‐reinforced composites from which it is possible to obtain micrographs of a desired cross section. The thickness of the cross section studied, as well as the number of the layers, does not affect the efficiency of the method.
Thermal properties of composites with bismaleimide‐vinyl poly(styrylpyridine) blends
Authors: Kourtides D. A. 
Published: December 2004

AbstractFlammability, thermal properties, and selected mechanical properties of composites fabricated with epoxy and other thermally stable resin matrices are described. Properties measured included limiting‐oxygen index, smoke evolution, thermal degradation products, total‐heat release, heat‐release rates, mass loss, flame spread, ignition resistance, thermogravimetric analysis, and selected mechanical properties. This paper describes the properties of eight different graphite composite panels fabricated using four different resin matrices and two types of graphite reinforcement. The resin matrices included: XU71775/H795, a blend of vinyl poly(styrylpyridine) and bismaleimide; H795, a bismaleimide; Cycom 6162, a phenolic; and PSP 6022M, a poly(styrylpyridine). The graphite fiber used was AS‐4 in the form of either tape or fabric. The properties of these composites were compared with those of epoxy composites. It was determined that the blend of vinyl poly(styrylpyridine) and bismaleimide (XU71775/H795) with the graphite tape was the optimum design giving the lowest heat release rate.
Properties and processing characteristics of dielectric‐filled epoxy resins
Authors: Zee R. H. , Huang Y. H. , Chen J. J. , Jang B. Z. 
Published: December 2004

AbstractA family of casting composites, epoxy resins with mineral fillers, having a range of electrical properties, are being developed. In such composites, the dielectric constant is controlled primarily by varying the filler material in composition and proportions. The present work reports on the mechanical properties of composites made with two types of filler, an alumina powder (XA3500 from ALCOA) and a BaTiO3/TiO2 ceramic powder (ATD‐50 from Ampex). Dependence of mechanical properties on curing agents was also determined. Filler contents from 0 to 40 percent volume were used. Epoxy systems contained single epoxy resin with both amine and anhydride hardeners. Processing of the anhydride‐cured systems was easier than that of the amine‐based systems because of their lower viscosity and longer gel time of the former. However, the anhydride‐cured systems required higher processing temperatures. Curing kinetics and molecular bonding were investigated using a combination of differential scanning calorimetry, dynamic mechanical thermal analysis, and scanning electron microscopy. Activation energies of 11.2 kcal/mole and 12.1 kcal/mole were obtained for the curing of the amine‐based and the anhydride‐based composites respectively, and a small difference in the glass transition temperature was also observed. These effects can be attributed to the difference in the structure of the curing agents. The epoxy resin cured with NMA is less ductile compared with those cured with MTHPA or MHHPA due to slight chemical modification on the ring structures. This dependence of ductility on curing agent was observed in specimens with different filler contents. Although the presence of the filler materials was found to enhance the mechanical properties of the epoxy, the fracture mode in these materials is still brittle.
Delamination shape effects in aramid‐epoxy‐aluminum (ARALL) laminates with fatigue cracks
Authors: Macheret J. , Teply J. L. , Winter E. F. M. 
Published: December 2004

AbstractAn aramid reinforced aluminum‐epoxy‐laminate, ARALL, which contains a fatigue crack and a delamination zone is analyzed. It is assumed that the interlaminar shear forces between the aluminum and aramid/epoxy layers are transmitted along the delamination boundary. The aramid/epoxy layer of the laminate is considered a series of linear springs. The tensile stress in the aramid/epoxy layer and the stress intensity factor in the aluminum layer are found for various experimentally observed delamination shapes. A residual strength criterion based on the maximum tensile stress in the aramid/epoxy layer is applied and the analytical results are correlated with the available experimental data.
Investigation of composite interphase using dynamic mechanical analysis: Artifacts and reality
Authors: Thomason J. L. 
Published: December 2004

AbstractThe fiber‐matrix interface is an important factor determining the overall mechanical properties of composites. This interface is no longer regarded as a sharp boundary, but is now considered to be an „interphase,”︁ i.e., a region surrounding the fiber where properties differ from those of the bulk matrix. Although the concept of the interphase is rapidly gaining acceptance, its in situ detection and characterization remains a largely unsolved problem. Dynamic mechanical analysis (DMA) is a technique known for its sensitivity in the detection of inhomogeneity in polymer morphology. Recent publications have claimed that the interphase in unidirectional fiber‐reinforced composites is detectable using DMA. We have been evaluating a Du Pont 982 DMA on its uses in characterization of composites and their individual components. We have found that using heating rates higher than 2°C/min produces an artificial peak in the DMA loss spectrum of glass‐fiberreinforced epoxy composites at temperatures above the matrix glass‐transition temperature (Tg). This peak was not present in the data from the unreinforced matrix nor in data from carbon‐fiber‐reinforced samples. This artifact could be interpreted as evidence of an interphase. However, our investigations revealed that it is in fact due to a complex interaction of the instrument, the thermal conductivity of the sample, the heating rate, and the sample modulus above Tg. Despite this artifact, the high sensitivity of the Du Pont 982 DMA enables detection of inhomogeneities in the composite matrix that are attributable to an interphase.
Room‐temperature aging of Narmco 5208 carbon‐epoxy prepreg. Part II: Physical, mechanical, and nondestructive characterization
Authors: Cole K. C. , Noël D. , Hechler J.‐J. , Cielo P. , Krapez J.‐C. , Chouliotis A. , Overbury K. C. 
Published: December 2004

AbstractSamples of Narmco Rigidite 5208/WC3000 carbon‐epoxy composite prepreg were exposed to ambient temperature (22°C) and 50 percent relative humidity for different periods up to 66 days. The aging has a significant effect on prepreg physical properties such as tack, volatiles content, and gel time. A set of 4‐ply laminates made from aged prepreg was subjected to tensile testing, ultrasonic inspection, and optothermal inspection. No relationship could be discerned between laminate properties and prepreg aging time. However, variations in panel homogeneity were observed, and these correlated with thermal diffusivity and tensile modulus measurements, but not with ultimate tensile strength or elongation. A set of 6‐ply laminates was used to measure compressive properties, interlaminar shear strength, and physical properties. These panels also showed variations in porosity, again unrelated to aging, but in addition, the fiber/resin ratio was observed to decrease with aging time. Both factors were found to affect mechanical properties. The implications concerning the importance of monitoring the aging by physicochemical methods are discussed.
Continuous monitoring of the fragmentation phenomenon in single fiber composite materials
Authors: Yavin B. , Gallis H. E. , Scherf J. , Eitan A. , Wagner H. D. 
Published: December 2004

AbstractA continuously monitored single‐filament composite (CM‐SFC) test was conducted to measure the stress at which successive fiber breaks occur in the single fiber fragmentation process. This exercise was performed with a limited number of samples of various types. The purpose was to explore the possibility of using this test as a simple alternative means of (i) measuring the size effect in single fibers, (ii) calculating the Weibull shape and scale parameters for fiber strength, (iii) calculating the fiber/matrix interfacial shear strength from the extrapolated value of fiber strength using the loading history of a single fragmentation test, rather than from the value of fiber strength extrapolated from extensive testing of single fibers at various gage lengths, as is usually done. These are aspects of the SFC test that have largely been ignored so far. The results presented here confirm the possibility of using the CM‐SFC test for such purposes, with a certain degree of approximation, as discussed. Additional information supplied by this test as well as a possible effect of fiber pre‐tensioning on fragmentation results (including the value of the interfacial shear strength) are also briefly discussed.
Simulation of compression molding of long‐glass‐fiber‐reinforced thermoplastic sheets
Authors: Ducloux R. , Vincent M. , Agassant J. F. , Poitou A. 
Published: December 2004

AbstractAn isothermal two‐dimensional shear‐thinning model of the compression molding of long‐glass‐fiber–reinforced thermoplastic is presented. A transverse isotropic behavior is introduced by considering two different pairs of power‐law coefficients. First (K1, m1) is linked to the shear deformations through the thickness and to the compression deformation; second (K2, m2) is associated to the expansion motions in the plane. K2 is significantly greater than K1 because of the influence of the glass mat structure, which resists stretching in the plane of the part. These coefficients are determined by fitting the computed and experimental mold closing forces in a circular isothermal compression‐molding test. The average velocity through the thickness is obtained by a variational method. Incompressibility is ensured by penalization. A finite element method is used, with a convected mesh and remeshing technique. The agreement between this model and experimental results (shape of the sample, mold closing force, pressure) performed on a rectangular mold is good.
Random glass mat reinforced thermoplastic composites. Part V: Statistical characterization of the tensile modulus
Authors: Bushko W. C. , Stokes V. K. 
Published: December 2004

AbstractRandom glass mat thermoplastic composites (GMT), which can be thermostamped to form complex deep‐drawn parts with ribs and boxes, are complex material systems in which the local elastic modulus and local strength vary widely and randomly across the material (the tensile modulus can vary by a factor of two over a 12.7‐mm length scale). And the values of these local properties depend on the length scale of measurement. The random, large‐scale point‐to‐point variations in their properties cannot be described by a single number. The broad distribution of elastic moduli in GMT has been modeled by a four‐parameter probability density function. Moments of this distribution function provide numerical measures that can be used for comparing data sets representing properties of different material samples. This statistical characterization is used to establish the consistency and the random nature of previously obtained elastic moduli data sets. The framework is also used to predict the effect of the gage length used to measure the local elastic modulus on the shape of the modulus probability density function.
Flow behavior of stampable sheet with a rib part
Authors: Hamada H. , Shonaike G. O. , Yamaguchi S. , Sato T. , Maekawa Z. , Koshimoto M. 
Published: December 2004

AbstractThe effect of die design on the flow characteristics of compression molded three‐layer long glass fiber reinforced polypropylene composite, known as “stampable sheet,” was investigated. The flow behavior of each layer was observed by optical and soft X‐ray photographs. The fiber flow length into the rib part was measured by an image processing system. The results showed that during compression resin exudation occurred and that this depended on the die's rib width. Thus, the larger the rib width, the lower the amount of resin exuded. Resin exudation was found to occur earlier in a die with zero fillet radius. The fiber flow length into the rib part was enhanced by using a die with a large fillet radius. The results were confirmed by a short‐shot molding process. In this process, the stamping operation was stopped short of making a complete part.A finite element method was used to study the flow process. The results agree with the experimental results confirmed by short‐shot molding.
Hydrothermal effects on mechanically fastened glass/polypropylene composite joints
Authors: Morii Ohru , Hamada Hiroyuki , Maekawa Zen‐Ichiro , Tanimoto Toshio 
Published: December 2004

AbstractThis study deals with the hydrothermal effects on mechanically fastened glass fiber mat/polypropylene composite joints with different joint geometry. Three kinds of joint geometries were adopted; hole diameter was 6 mm, the length from top edge to the hole center was 18 mm (3e) and the specimen width was 12 (2w), 18 (3w), and 30 mm (5w). The joints were immersed in hot water at 60 and 80°C. The effect of water temperature on the failure load appeared clearly in 2w3ejoints. The higher water temperature induced more strength reduction. The dominant failure mode changed from the net‐tension to the bearing for the original dry joints for wider specimens. The failure mode changed from multiple to net‐tension only for 3w3ejoints, because of a remarkable tensile strength reduction. The failure strength and the failure mode were predicted by the macroscopic failure criterion, and the characteristic experimental curves, and the FEM analysis. The predicted results agreed with experiment.
Unsteady flow of dilute fiber suspensions using a Generalized Eulerian Lagrangian approach
Authors: Alexanurou Andreas N. , Aiimed Alauddin 
Published: December 2004

AbstractIn recent years the emphasis on the development of fiber reinforced plastics has experienced an unprecedented expansion. One of the most commonly used methods in manufacturing of plastic products is injection molding. In this work we are using a Generalized Eulerian Lagrangian (GEL) formulation to study the unsteady flow of dilute fiber suspensions in injection molding. This formulation combines the advantages of both formulations: in the same flow problem but different regions the GEL formulation allows the selective application of an Eulerian, Lagrangian or a mixture of the two formulations. The suspending fluid is considered to be Newtonian and the contribution of the fibers to the local stress tensor is obtained using a volume averaging theory. The fiber distribution tensor is expressed in terms of a second order tensor with a quadratic closure approximation. Results are shown and discussed for the filling of a cavity from a single gate under different process conditions fibers aspect ratio and content.
Elastic constants and thermal expansivity of gel‐spun polyethylene fiber and its composites
Authors: Choy C. L. , Kwok K. W. , Ma H. M. 
Published: December 2004

AbstractThe five independent stiffness constants, C11, C33, C44, C66, and C13, and the axial and transverse thermal expansivity of unidirectional gel‐spun polyethylene fiber reinforced composites have been measured as functions of fiber volume fraction Vf. The axial extensional modulus C33 and axial Poisson's ratio v13 follow the rule of mixtures, while the axial shear modulus C44, transverse shear modulus C66, and transverse plane‐strain bulk modulus Ct ( = C11 − C66) obey the Halpin‐Tsai equation. Extrapolation to Vf = 1 gives the five stiffness constants of gel‐spun polyethylene fiber. The tensile property of the fiber is highly anisotropic, with the axial Young's modulus about 40 times higher than the transverse Young's modulus. In contrast, the axial shear modulus exceeds the transverse shear modulus by only 5%. A similar treatment of the thermal expansivity data in terms of the Schapery equations gives an axial thermal expansivity of −1.25 × 10−5 K−1 and a transverse thermal expansivity of 11.7 × 10−5 K−1 for the fiber.
Torque rheometer evaluation of polypropylene process stability
Authors: Goodrich J. E. 
Published: December 2004

AbstractA new method of treating torque rheometer test data has been developed. First, it involves converting the torque values measured over a range of temperatures to torques corresponding to a constant reference temperature. Then the log of the calculated torques is plotted against time. The method has been applied to several polypropylene grades, and the effects of numerous test variables have been explored. Correlations have been developed between torque rheometer data and fundamental polymer properties of viscosity and molecular weight. The method should also be applicable to polymers other than polypropylene.
Isothermal kinetic studies using a thermomechanical analyzer II. Rates of penetration of a polymer by a spherical indenter
Authors: Machin D. , Rogers C. E. 
Published: December 2004

AbstractThe use of a commercially available thermomechanical analyzer (TMA) operated in its isothermal mode is illustrated for studies of penetration of a hemispherically‐tipped probe into a material sample. Two amorphous copolymers were studied at various temperatures above their softening points. Kinetics of penetration are compared with tensile creep measurements for these viscoelastic materials. A simple semi‐empirical relationship between creep and penetration at small strains is applied and found to yield approximate although not exact agreement with experiment. It is thus possible that for homogeneous materials of this type creep data might be easily predicted with a fair degree of accuracy from penetration data and vice versa. Experimental problems involved in the TMA penetration technique are discussed.