bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nonconforming Meshes and Adaptivity
Authors: Oestmann S. , Maischak M. , Stephan E. P. 
Published: December 2004

AbstractWe consider nonconforming meshes for adaptive refinements in the coupling of finite elements and boundary elements. In order to enable a good approximation of 3d problems with hexahedral elements, irregular (hanging) nodes are necessary. We use the one‐irregularity condition where only single‐constraint nodes on an edge or face are allowed. We give an a posteriori error estimate. Numerical experiments show the efficient use of nonconforming meshes. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Model Reduction Methods for Solving Symmetric Rational Eigenvalue Problems
Authors: Blömeling Frank , Voss Heinrich 
Published: December 2004

AbstractWe consider large and sparse rational eigenproblems where the rational term is of low rank compared to the dimension of the problem. Exploiting model‐order reduction techniques the dimension can be reduced considerably, and problems of this type can be solved very efficiently. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ein neuer Eigenlöser für Polynommatrizen
Authors: Falk S. , Wagner N. 
Published: December 2004

AbstractFür Polynommatrizen mit regulärer Leitmatrix wird ein neuer Eigenlöser vorgestellt. Dies geschieht über den Algorithmus ECP. Kennzeichnendes Merkmal des Algorithmus ist die Parallelrechnung. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Runge‐Kutta‐Nyström Methods with Maximized Stability Domain for Problems in Strutural Mechanics
Authors: Lunk Christoph 
Published: December 2004

AbstractStructural dynamics applications feature a particular type of second order stiff equations, often in combination with low smoothness of the right hand side, large dimension and non‐linear force terms. As alternative to implicit schemes, explicit Runge‐Kutta‐Nyström methods are analysed, with focus on low order and maximized stability domain since spurious high frequency oscillations need not be resolved. It turns out that it is possible to construct methods with a stability domain that stretches up to hω = 2s on the imaginary axis where h is the stepsize, ω the largest frequency in the system, and s the stage number. Some numerical examples show the competitiveness of the proposed methods. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Solving Diffusion Problems on Rough Surfaces with a Hierarchical Multiscale FEM
Authors: Abdulle Assyr 
Published: December 2004

AbstractDiffusion on rough surfaces is a basic problem for many applications in engineering and the sciences. Solving these problems with a standard finite element method is often difficult or even impossible, due to the computational work and the amount of memory needed to triangulate the whole surface with a mesh which resolves its oscillations. We discuss in this paper a hierarchical Finite Element Method of “heterogeneous multiscale” type, which only needs to resolve the surface's fine scale on small sampling domains within a macro triangulation of the underlying smooth surface. This method converges, for periodic surface roughness and sufficiently small amplitude, at a robust (i.e. scale independent) rate, to the homogenized solution. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Posteriori Control of Dimension Reduction Errors on Long Domains
Authors: Repin Sergey , Sauter Stefan , Smolianski Anton 
Published: December 2004

AbstractIn this work, we consider linear elliptic problems posed in long domains, i.e. the domains whose size in one coordinate direction is much greater than the size in the other directions. If the variation of the coefficients and right‐hand side along the emphasized direction is small, the original problem can be reduced to a lower‐dimensional one that is supposed to be much easier to solve. The a‐posteriori estimation of the error stemming from the model reduction constitutes the goal of the present work. For general coefficient matrix and right‐hand side of the equation, the reliable and efficient error estimator is derived that provides a guaranteed upper bound for the modelling error, exhibits the optimal asymptotics as the size of the domain tends to infinity and correctly indicates the local error distribution. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermal conductivity, electrical resistivity, mechanical, and rheological properties of thermoplastic composites filled with boron nitride and carbon fiber
Authors: Ng Hsiao Yen , Lu Xuehong , Lau Soo Khim 
Published: December 2004

AbstractHybrid composites consisting of boron nitride (BN) platelets and carbon fibers (CF) in a polybutylene terephthalate (PBT) matrix were melt‐compounded, and their thermal and electrical conductivity, tensile, and rheological properties were investigated. While it does not lead to an enhancement in thermal conductivity with respect to PBT/BN composites, the results indicate that a combination of BN and CF in PBT can significantly reduce electrical conductivity of the composites compared to that of PBT/CF composites. The relative low thermal conductivity of the hybrid composites is attributed to CF breakage that occurred during the extrusion and alignment of CF in melt flow direction, which is normal to the heat flow encountered during the thermal conductivity tests induced by injection molding. The hybrid composites were, however, found to have better tensile properties and processibility than PBT/BN composites at the same total filler content. POLYM. COMPOS., 26:66–73, 2005. © 2004 Society of Plastics Engineers
Lower‐curing‐Temperature PMR polyimides
Authors: Delvigs Peter 
Published: December 2004

AbstractStudies were performed to achieve lower‐curing temperature PMR (polymerization of monomer reactants) polyimides. Partial substitution of a p‐aminostyrene end‐cap for the monomethyl ester of 5‐norbornene‐2,3‐dicarboxylic acid lowered the final cure temperature of typical PMR resins from 600 to 500°F. The weight‐loss characteristics of neat resins and graphite fiber composites prepared by using the mixed end‐cap approach were determined at 600°F. The room temperature and short‐term elevated temperature mechanical properties of the composites at 550°F and 600°F were determined. The mechanical‐property‐retention characteristics of the composites at 550°F and 600°F are also discussed.
Dielectric relaxation spectroscopy of sheet molding compound
Authors: Venkataswamy K. , Stephens K. E. , Hughes H. , Beatty C. L. 
Published: December 2004

AbstractDielectric relaxation spectroscopic studies of sheet molding compound from 400 Hz to 100 kHz reveal the relaxation processes that exist in this material. The frequency dependence of SMC is presented and analyzed in terms of different relaxation process models. A transition map of SMC is presented.
Reinforced nylon 6 block copolymers
Authors: Gabbert J. D. , Garner A. Y. , Hedrick R. M. 
Published: December 2004

AbstractNylon block copolymers (NBC), a family of reaction injection molding (RIM) resins commercially introduced during the past year, offer new and valuable balances of properties. The polymers are comprised of alternating blocks of soft rubber segments and hard nylon 6 blocks which are chemically bound together and form discrete, incompatible phases. Glass reinforcement afforded increased resistance to expansion from moisture absorption and thermal changes, along with decreased temperature‐modulus response and increased heatsag resistance. Losses in impact strength from reinforcement addition were shown to be partially restored by moisture absorption and/or changes in resin matrix formulations.
A novel technique for the study of coupling agent phenomena
Authors: Garton Andrew 
Published: December 2004

AbstractA modification of the Internal Reflection Spectroscopy (IRS) technique for infrared (IR) spectroscopy is described, where the surface of the IRS element is modified by a thin (100 to 1000 å) layer of metal oxides, silanes or Kevlar so as to model the surface of reinforcements in composite materials. The modified IRS element is then brought into contact with the matrix material and chemical changes in the first 2000 to 3000 å of matrix examined by IR spectroscopy. Examples of the technique include a study of the effect of various surfaces on the crosslinking of an anhydride‐cured epoxy resin. The kinetics of the crosslinking process and the final ester crosslink concentration are shown to be significantly affected by, for example, a silica or Kevlar surface. The advantages and limitations of this modified IRS technique are discussed relative to other surface characterization techniques.
Damping of composite materials
Authors: Hoa S. V. , Ouellette P. 
Published: December 2004

AbstractA rule of mixture for the prediction of the loss factor of hybrid laminates of graphite/epoxy and kevlar/epoxy composite materials is developed. The theoretical values agree reasonably with the experimental values for ten samples. An optimal laminate having the modulus of aluminium and twice the loss factor of graphite/epoxy laminates is achieved.
The optimum property concept—part II the relative order in failure property maxima with increasing filler levels
Authors: Lautenschlaeger F. K. 
Published: December 2004

AbstractProperties are identified which pass through a maximum when the filler loading in a polymer is increased; all are failure properties. Under standard test conditions of strain rate and temperature, the order of the failure property maxima with increasing filler loadings is identical in different polymers. The optimum level for maximum tear strength is higher than the optimum level for tensile strength. In general, the optimum level is even higher for abrasion resistance. The order in which these maxima develop is different when the degree of crosslinking is increased. The optimum level depends on characteristics of the polymer, e.g., the glass transition temperature. It can be shown that an increase in the pore volume of silica fillers, or an increase in the length of the crystalline segment in thermoplastic elastomers, leads to similar property trends as increased filler levels. Thus, the property trend which was established for increasing filler levels provides a scheme against which polymer or compound modifications can be assessed. The implications of the observed property trends on several generalizations in the literature are assessed.
Effect of compounding on the properties of short fiber reinforced injection moldable thermoplastic composites
Authors: Bigg D. M. 
Published: December 2004

AbstractThe mechanical properties of short‐fiber‐reinforced thermoplastic composites depend on the degree of interfacial bond strength between the fibers and polymer matrix. This interfacial bond strength can be increased by appropriate coupling agents. This study shows, for example, that an amino silane coupling agent improves the bond strength of nylon‐aluminum fiber composites, but not polycarbonate‐aluminum fiber composites. For cases where appropriate coupling agents are not available it is important to maintain as high a fiber aspect ratio as possible in a molded part. This study shows that a single screw compounder does less damage to glass or carbon fibers than a twin screw compounder under similar processing conditions when the polymer is in the form of pellets. When the polymer is supplied as a powder, satisfactory dry blends can be produced and the twin screw compounder does less damage to the fibers. In both cases, however, fibers initially 6 mm long are reduced to an average length less than 0.5 mm. The greatest degree of fiber size retention was observed when extrusion coated fiber pellets were used in the injection molding machine. The relationship between a fiber's tensile strength and the interfacial shear strength between a fiber and matrix yields a critical fiber aspect ratio below which the maximum reinforcing capability of the fibers are not being utilized. For the polymers investigated in this program, the critical aspect ratio for carbon fibers was found to be between 16 and 25 to 1. The polymers investigated include flame‐retardant grades of acrylonitrile‐butadiene‐styrene (ABS) and poly(phenylene oxide)/polystyrene blend, nylon 6/6 and poly(phenylene sulfide).
Theory of coalescence in immiscible polymer blends
Authors: Fortelný I. , Kovář J. 
Published: December 2004

AbstractThe theory of coalescence in melts of polymer blends was derived on the basis of the Smoluchowski theory for colloid systems. An approximation for a flux of particles used for solutions of colloids in water was analyzed. It is shown that this approximation cannot be used for polymer blends, and an approximation is suggested that could be justifiably used for them. A system of equations was derived for the time dependence of the number of individual i‐mers, using the relation suggested for the diffusion flux of particles. In an approximation of the uniform increase in particle size, equations were found for the time dependence of the number of particles, the average radius of the particle, and the interface area in the volume unit of the blend. The suggested theory predicts measurable coalescence in considerably more viscous systems than mechanically applied relations of the Smoluchowski theory for aqueous colloid solutions.
PEEK/carbon fiber composites: Experimental evaluation of unidirectional laminates and theoretical prediction of their properties
Authors: Cervenka A. 
Published: December 2004

AbstractComparison of tensile characteristics (modulus, strength) measured for bought‐in laminates and also laminates manufactured in‐house with published data has proved the testing procedure to be sound and compression molding to give composites of good quality. In the theoretical domain, the micromechanical approach was used to predict engineering constants such as the longitudinal, transverse and shear moduli that characterize the laminate in its principal directions. For the off‐axis loading, macro‐mechanical abstraction was applied and the angular dependencies of the above composite parameters were further supplemented by those for the Poisson ratio and the ultimate strength. Regardless of the theoretical approach used, the error of the predictions relative to the experimental data does not exceed 10 percent.
Mechanical properties and morphology of polypropylene composites. III. Short glass fiber reinforced elastomer modified polypropylene
Authors: Stamhuis J. E. 
Published: December 2004

AbstractThe impact strength and rigidity of polypropylene composites can be significantly improved by application of short glass fibers instead of mineral fillers in elastomer‐modified polypropylene. The properties of such composites are strongly dependent on the adhesive forces at the fiber‐matrix interface. Poor adhesion results in interfacial fracture solely by fiber‐matrix debonding, as evidenced by scanning electron microscopy on the fracture surfaces. This is accompanied by relatively low impact strengths. By contrast, increased adhesion leads to fracture not only by fiber‐matrix debonding, but also by crack propagation through the elastomeric phase at the fiber surface. This mechanism is thought to be responsible for a remarkable increase of the impact strength. Appropriate compositions of polypropylene, glass fiber, and elastomer resulted in composite properties similar to, or even better than, those of a typical acrylonitrile‐butadiene‐styrene copolymer. The lengths of the fibers recovered from the test specimens were somewhat smaller than the critical fiber lengths as calculated by simple shear lag theory. The properties of the present composites should thus be regarded as minima, rather than as potential maxima. This suggests that current composites may be suitable for engineering applications.
Structure and properties of oil extended styrene butadiene block copolymers
Authors: Polizzi S. , Stribeck N. , Zachmann H. G. , Bordeianu R. 
Published: December 2004

AbstractThe relationships between mechanical properties and structure of rapidly spin cast styrene‐butadiene‐styrene (SBS) block copolymers diluted with two different types of mineral oil are discussed. Small angle X‐ray scattering (SAXS) measurements indicate that both oils go mainly into the rubbery polybutadiene phase. While during rapid spin casting the paraffinic oil improves the phase separation of polystyrene (PS) and polybutadiene (PB), the opposite is true for the aromatic oil. The measurements also suggest that the oils cause a preferential swelling of the superstructure along the longitudinal direction of the cylindrical PS domains. From this, it can be concluded that a larger number of interconnecting PB chains is present in the cross direction than in the longitudinal one. With increasing oil content, a further decrease of interconnecting chains in the latter direction may be the reason for the decrease of the tensile modulus. Furthermore, above a critical value of dilution (33 wt percent for paraffinic oil, 50 wt percent for the aromatic one), more and more spherical domains are formed instead of the cylindrical ones. This morphological transition explains the step present in the double logarithmic plot of the large strain tensile modulus as a function of oil dilution.
Some studies on glass fiber‐reinforced polypropylene. Part II: Mechanical properties and their dependence on fiber length, interfacial adhesion, and fiber dispersion
Authors: Gupta V. B. , Mittal R. K. , Sharma P. K. , Mennig G. , Wolters J. 
Published: December 2004

AbstractTwo commercial grades of glass fiber‐reinforced polypropylene granules, one containing short fibers of average length around 0.5 mm with a coupling agent and the other containing relatively much longer fibers mostly around 9 mm, but no coupling agent, were injection‐molded into dumbbells and tested in tension between −43 and 90°C. There is considerable fiber attrition during injection molding; the fiber lengths are reduced to average values of 0.4 to 0.8 mm for thses two samples. Also during injection molding of the test sample, partial molecular alignment of the matrix (polypropylene) occurs which supplements the reinforcement of the matrix due to the aligned glass fibers (30 percent by weight) present in the composite sample. The stiffness and strength of these samples do not reflect the effects of fiber lengths since most of the fibers are of very small length in the molded specimen and also since the sample with longer fibers has a non‐uniform distribution of fibers. While the interfacial shear strength does not appear to play a significant role in determining stiffness, it turns out to be extremely important in controlling strength, particularly at the higher test temperatures. The room temperature impact strength is high for the sample containing relatively longer fibers of average length around 0.8 mm in which fiber dispersion is non‐uniform and fiber agglomerates are present. Acoustic emission data shows that debonding and fiber pull‐out are the main contributors to sample toughness; this observation is supported by scanning electron micrographs of the fracture surfaces.
A simple illustration of structure‐properties relationships for short fiber‐reinforced thermoplastics
Authors: Doshi S. R. , Charrier J.‐M. 
Published: December 2004

AbstractIn this paper, a simple theoretical model for elastic properties of short fiber‐reinforced thermoplastic (SFRTP) composite systems is described, which considers the effect of two important structural parameters, viz., fiber aspect ratio distribution and fiber orientation distribution. An experimental technique for producing SFRTP samples featuring a fairly uniform fiber orientation is described, and a broad set of experimental results on the mechanical properties of SFRTP systems based on polystyrene (PS) and polyethylene (PE) resins with several fiber loadings is presented. The use of the simple theoretical model to analyze the experimentally‐determined elastic properties is discussed.
Fracture of ultrafine calcium carbonate/polypropylene composites
Authors: Levita G. , Marchetti A. , Lazzeri A. 
Published: December 2004

AbstractThe strength and fracture properties of a polypropylene filled with ultrafine calcium carbonate (0.07 μm) have been studied in the composition range of 0 to 40 percent by volume. Untreated and surface treated (with stearic acid and a titanate coupling agent) grades have been considered. The untreated filler caused a decrease of toughness whereas a maximum, at ∼10 percent, was observed for the treated filler. The fracture energy was analyzed in terms of the crack pinning model. Due to the very small size of particles the pinning contribution proved to be negligible.
Simulating fiber distribution in thin sheets
Authors: Chalifoux J.‐P. , Sanschagrin B. , Roche F. , Benkirane A. 
Published: December 2004

AbstractA model is presented that simulates on a microcomputer the fiber distribution in a planar arrangement applicable to thin sheets of composites. Although it does not take into account spatial fiber interference, the software allows one to investigate a number of important design parameters. The inputs used in the simulation are: thickness of the composite sheet, diameter and volume fraction of fibers along with fiber length, and angular position which can be specified in a number of ways. The program utilizes the internal random function to depict each fiber, as it is generated, in a “simulation window” of the monitor while the mathematics of the system are being done simultaneously within the smaller “valid window”. The procedure prescribes that the center of gravity of all fibers be uniformly distributed over the simulation window area. For that reason and because the 2D model is extended to simulate a three‐dimensional sheet, results will represent the ideal configuration or upper bonds of a corresponding practical case. Graphical representations and statistics are thus produced to quantify the geometric pattern of the system. One use of the model is, for instance, to see how the geometric patterns and their associated statistical parameters compare at a given volume fraction when the fiber length is fixed or when fiber length can be modeled as a normal, a uniform, or another specific distribution.
Room temperature aging of Narmco 5208 carbon‐epoxy prepreg. Part I: Physicochemical characterization
Authors: Cole K. C. , Noël D. , Hechler J.‐J. , Chouliotis A. , Overbury K. C. 
Published: December 2004

AbstractSamples of Narmco Rigidite 5208/WC3000 carbon‐epoxy prepreg were exposed to ambient temperature (22°C) and 50% relative humidity for different periods up to 66 days. They were analyzed in depth using various techniques to determine the extent of the chemical changes occurring. The physicochemical techniques used were Fourier transform infrared spectroscopy (transmission, attenuated total reflection, diffuse reflection), liquid chromatography (reverse‐phase, high‐speed reverse‐phase, and high‐performance size‐exclusion), thermal analysis (differential scanning calorimetry and thermogravimetric analysis), and pyrolysis‐gas chromatography. All showed evidence of significant changes, the most sensitive being Fourier transform infrared spectroscopy (FT‐IR) and reversephase liquid chromatography (RPLC). FT‐IR showed that the number of unreacted epoxy groups decreases steadily at a rate of 0.34% per day, based on the initial amount. At the same time, the number of free amine‐hardener molecules, as monitored by RPLC, drops at a rate of 1.05% per day. RPLC also showed that the amount of initial epoxy‐amine reaction product increases significantly over the first 30 days, but then declines as it undergoes further reaction to give higher‐molecular‐weight products. The heat of polymerization of the resin, measured by thermal analysis, decreased by 0.26% per day from its initial value of 561 J/g.