bluuebunny/crossref_metadata_2025_split huggingface dataset:
Robust design of a composite air spindle
Authors: Chang Seung Hwan , Lee Dai Gil 
Published: April 2004

AbstractIf the spindle shaft of an spindle system is made of high‐stiffness carbon fiber composite material, the spindle system will be dynamically robust because the maximum rotating speed of a spindle (or rotor) system is usually restricted by the critical whirling vibration frequency of the spindle shaft, which is proportional to (EI/m)0.5 (E: Young's modulus, I: 2nd moment of inertia of shaft cross section, and m: mass per unit length of spindle). In this paper, a composite air spindle system composed of a high‐modulus carbon fiber composite shaft, powder‐containing epoxy composite squirrel cage rotor, and aluminum tool holder is introduced. For the optimal design of the composite air spindle system, the stacking sequence and thickness of the composite shaft were determined by considering the fundamental natural frequency and deformation of the system. Then the dynamic characteristics of the composite spindle system were compared with those of a conventional steel air spindle system.
Preformed particle toughening of epoxy‐based film adhesive systems: The effect of particle size and chemistry
Authors: Hayes Brian S. , Seferis James C. 
Published: April 2004

AbstractA new family of particulate modifiers was incorporated into an epoxy‐based model film adhesive system and the performance was evaluated. The particulate modifiers were selected to include a range of particle sizes, chemistry, and functionality. Thermal analysis, lap shear, and fracture energy tests were performed to characterize the performance of the adhesives. The mechanisms of failure for the adhesives were analyzed in relation to the particle modifier characteristics. Significant differences were found for mode I fracture energy when comparing adhesively joined composite specimens in cocured and bonded situations. Large preformed particle modified adhesives had nearly the same GIC values for both cocured and bonded applications, while the GIC values for the much smaller core‐shell particle modified adhesives differed significantly. All particle modified adhesives provided an improvement in mode II fracture toughness over that of the control such that the laminates failed either in compression (through‐thickness direction) or through delamination of the prepreg plies.
All‐Plant fiber composites. I: Unidirectional sisal fiber reinforced benzylated wood
Authors: Lu Xun , Zhang Ming Qiu , Rong Min Zhi , Shi Guang , Yang Gui Cheng 
Published: April 2004

AbstractBenzylation of sawdust from China fir was carried out to prepare plastics based on natural resources. It was found that thermoplasticity and mechanical properties of the chemically modified wood flour changed with the substitution reaction conditions. By compounding sisal fibers and the plasticized fir sawdust, unidirectional laminates were manufactured in a method similar to conventional thermoplastic composites. Such an all‐plant fiber composite material is characterized by easy processing, environmental friendliness, and low cost. Instead of chemical heterogeneity of conventional composites, physical heterogeneity of the current natural fiber composite should be favorable for interfacial interaction. However, the reinforcing sisal fibers were not well impregnated by the matrix because of the relatively high viscosity of the benzylated fir sawdust. Further efforts should be made in this area on the basis of the current preliminary work in order to improve mechanical properties of the composites.
Interface modification and characterization in linear low‐density polyethylene highly loaded with aluminium hydroxide
Authors: Wang Genlin , Jiang Pingkai , Zhu Zikang 
Published: April 2004

AbstractFire‐retardant linear low‐density polyethylene (LLDPE) composites were prepared by combining this polymer with uncoated and surface treated forms of aluminum hydroxide (Al(OH)3). The poor toughness and ductility of polyethylene highly filled with Al(OH)3 can be significantly improved by addition of a small amount of silicon oil. It is found that silicon oil improves elongation at break of the composite remarkably, but this is accompanied by the deterioration of tensile strength. Silane crosslinked polyethylene substituting for polyethylene as the matrix in Al(OH)3‐filled polyethylene improves the tensile strength of the composite. Fractured surface analysis and limiting oxygen index (LOI) of the composites were also studied. Possible mechanisms accounting for these effects are discussed.
Empirical nonlinear viscoelastic model for injection molded thermoplastic composite
Authors: Hadid M. , Rechak S. , Zouani A. 
Published: April 2004

AbstractInjection molded components made from fiber reinforced thermoplastics exhibit strong viscoelastic behavior. In the present study, the bending creep tests show that the 43‐wt% glass fiber reinforced polyamide 66 is highly stress‐dependent and requires a nonlinear viscoelastic representation. However, such representation is complex for isotropic materials and is even more arduous for composite materials. In order to overcome this complexity, an empirical approach is used herein to develop a viscoelastic model based on a simple power law with stress‐dependent parameters. The proposed model demonstrates high stress sensitivity and agrees with experimental data over a wide range of applied stress.
Blade geometry effects on initial dispersion of chopped glass fibers
Authors: Kuroda Melody M. H. , Scott Chris E. 
Published: April 2004

AbstractThe effects of blade geometry on the initial dispersion of chopped glass fiber bundles in polystyrene during batch mixing are investigated. Roller, banbury, cam, and sigma blades are evaluated for dispersive efficiency and differences in mechanism. Processed samples are characterized by image analysis to focus upon the initial stages of dispersion. Sigma blades are found to be the most effective blades for initial chopped glass dispersion, while banbury blades prove the least effective. Analytical treatment based on the average time for a volume to pass through high stress regions does not explain the results; chopped glass fiber dispersion does not depend solely upon passage through narrow‐gap, high‐stress regions.
Surface characterization of flax, hemp and cellulose fibers; Surface properties and the water uptake behavior
Authors: Bismarck Alexander , Aranberri‐Askargorta Ibon , Springer Jürgen , Lampke Thomas , Wielage Bernhard , Stamboulis Artemis , Shenderovich Ilja , Limbach Hans‐Heinrich 
Published: April 2004

AbstractThe surface characteristics of several natural fibers—flax, hemp and cellulose—were investigated using scanning electron microscopy, BET‐surface area and zeta (ζ‐) potential measurements. ζ‐Potential measurements using the streaming potential method were performed in order to study the water uptake behavior as well as the surface properties of several natural fibers. The influence of different flax‐fiber separation methods and several modifications, like industrial purification, and such a treatment followed by alkaline purification as well as polypropylene grafting on the fiber surface morphology, surface area and time‐ and pH‐depending ζ‐potentials were studied. The time‐dependence of the ζ‐potential, measured in 1 mM KCl solution, offeres and alternative possibility to estimate the water uptake behavior for nearly all investigated natural fibers. The water uptake data derived from the ζ‐potential measurements (ζ = f(t)) were compared with data from conventional water adsorption studies for some chosen examples.
Flow‐enhancing layers in the vacuum infusion process
Authors: Andersson H. M. , Lundström T. S. , Gebart B. R. , Långström R. 
Published: April 2004

AbstractThe current trend towards increased use of vacuum infusion molding for large surface‐area parts has increased the interest in an advanced modeling of the process. Because the driving pressure is limited to 1 atmosphere, it is essential to evaluate possible ways to accelerate the impregnation. One way of doing this is to use layers of higher permeability within the reinforcing stack, i.e. flow‐enhancing layers. We present an experimental investigation of the flow front shape when using such layers. The through‐thickness flow front was observed by making a number of color marks on the glass‐mats forming the reinforcing stack, which became visible when the resin reached their position. The in‐plane flow front was derived from observations of the uppermost layer. It turned out that existing analytical models agree very well with the experiments if effective permeability data is used, that is, permeability obtained from vacuum infusions. However, the fill‐time was nearly twice as long as predicted from permeability data obtained in a stiff tool. This rather large discrepancy may be due to certain features of a flexible mold half and is therefore a topic for further research. The lead‐lag to final thickness ratio is dependent on the position of the flow front and ranges form 5 to 10 for the cases tested. Interestingly the lead‐lag has a miximum close to the inlet.
Optimization of tubular double lap‐joint configuration
Authors: El‐Hady Faissal Abd , Kandil Naglaa 
Published: April 2004

AbstractThe potential of using composite materials with a polymer base in the automotive industry has grown rapidly. However, one of the main problems encountered is bonding the composite part to metal conventional parts. This paper studies a proposed tubular double lap joint to bond a composite shaft to a metallic end. The automotive driveshaft will be taken as an application throughout this paper. A mathematical model of this joint is presented and a finite element solution has been carried out in order to validate the mathematical model. The optimization objective is to minimize the shear stress level in the adhesive layer. The results show that one can obtain up to 50% reduction in the level of adhesive shear stress. This can be achieved through an optimum selection of lap geometry.
Scratch behavior of nanoparticle Al2O3‐filled gelatin films
Authors: Li Tao , Chen Quan , Schadler Linda S. , Siegel Richard W. , Mendel John , Irvin Glen C. 
Published: April 2004

AbstractNanoscale alumina/protein gel composite films with 10–50 wt% filler were subjected to scratch testing and compared to micron‐scale alumina/protein gel composites. Atomic force microscopy (AFM) was employed to examine the width, depth, and morphology of the as‐produced scratches. The results show that the scratch depth in gelatin films and the tearing within the scratch decrease dramatically with the addition of the nanoscale (average particle size, 13 nm) alumina fillers. It was found that refining the particle size distribution of the Al2O3 powder (average particle size, 10 nm, with no particles larger than 70 nm) further reduced the scratch depth and width, while improving the dimensional integrity and surface roughness of the nanocomposites. Aging of the gelatin films improved the intrinsic scratch resistance of both filled and unfilled gelatin films. In comparison, micron‐size Al2O3 filler not only increased the scratch width, but also resulted in poor particle dispersion and low transparency of the films. The optical clarity of the nanofilled composites was much higher than that of the composites with micron‐size filler.
The role of fiber bundle interaction forces in non‐isothermal compression molding of thermoplastic composites
Authors: Törnqvist Ronnie , Servais Colin , Ebinger Jean‐Christophe , Månson Jan‐Anders E. 
Published: April 2004

AbstractThe non‐isothermal flow during compression molding of thermoplastic‐based composites having a planar, randomly oriented fiber structure has been investigated. Local interactions at the bundle‐bundle level were measured and a constitutive equation was derived to describe the shear and squeeze flow of the composites. This equation contains only micro‐mechanics‐related variables, and accounts for the temperature dependence of the interaction forces. The flow of the material under industrial processing conditions can thus be related to the deformation mechanisms of the reinforcement structure at the scale of the individual fibers Good agreement was obtained between the predicted and experimentally observed theological behavior of the composites in both shear and squeeze flow. The use of this approach to analyze the industrial molding of complex‐shaped parts is dis cussed.
Effects of glass fibers and polypropylene/glass fiber hybrid fibers on the kinetics and mechanical properties of epoxy composites
Authors: Punchaipetch Prakaipetch , D'Souza Nandika Anne , Brostow Witold , Akinay Ali E. , Reed Jonathan 
Published: April 2004

AbstractCuring reactions of diglycidyl ether of bisphenol F (DGEBP‐F) and pre‐catalyzed methyltetrahydrophthalic anhydride (MTHPA) with benzyl triethyl ammonium chloride (BTEAC) were studied and effects of glass fibers evaluated. The influence on the kinetics of glass fibers and a hybrid blend of maleated polypropylene + glass fibers is studied. Isothermal and dynamic kinetic parameters are determined by differential scanning calorimetry (DSC). Applicability of the autocatalytic model is investigated. The model serves well in the range of degrees of conversion between 25 and 80%. At high conversion rates the diffusion control becomes apparent. Glass fibers accelerate the curing, shortening the time needed to reach the maximum reaction rate; this is reflected in lower activation energies for curing in comparison to the neat resin. The effects observed can be explained by a reaction between the amine group present on the fiber surfaces and the epoxy glycidyl groups. The result of both isothermal and non‐isothermal curing of resin + glass fibers commingled with polypropylene are close to those for the neat resin. The reinforcement increases the elastic modulus 12 times, the tensile strength 2 times, and the impact strength 285 times. The glass fibers + commingled polypropylene reinforcement provides comparable mechanical properties as glass fibers alone when normalized with respected to the density fraction of the fibers.
Influence of chemical structure of polyimide prepolymer on rheo‐mechanical properties of polyimide foam composites
Authors: Otaigbe J. U. , Yudin V. E. , Artemieva V. N. 
Published: April 2004

AbstractA study is reported of the effect of varying chemical composition of foam polyimide prepolymers (H‐complex) on the structure and properties of foam polyimide resins and their composites with aromatic polyimide fiber felt. The melt rheological behavior of the H‐complex was found to be strongly dependent on its chemical composition and structure reorganization in the melt which is akin to mesophasic structural transition states in liquid crystal polymers. Changing the diamine part of the H‐complex from 4,4‐methylene dianiline to 1,3‐diaminobenzene led to decreased steady shear viscosity at temperatures and shear rates ranging between 95° and 105°C and 0.01 and 1 s−1, respectively. Additionally, changing the dialkyl moiety from dimethyl to diethyl in 3,3′,4,4′‐benzophenonetetracarboxylic dialkyl ester (precursor to the H‐complex) increased gelation time of the H‐complex, enhancing processibility of the foam polyimide composites. The results indicate that novel, lightweight foam polyimide composites with enhanced thermomechanical properties for beneficial uses can be prepared through chemical modification of the H‐complex prior to its thermal imidization in the presence of the aromatic polyimide fiber felt.
Structure and properties of PP/SBS/glass fiber hybrid composites. Part I: Crystallization behavior and morphology
Authors: Saujanya C. , Sainkar S. , Radhakrishnan S. 
Published: April 2004

AbstractThe structure development, crystallization behavior and morphology were studied in hybrid composites made with polypropylene/styrene‐butadiene‐styrene (PP/SBS) containing glass fibers (GF). The techniques applied include optical polarizing microscopy, X‐ray diffraction and scanning electron microscopy (SEM). The isothermal crystallization studies of PP/SBS/GF revealed that SBS as well as GF could act as good nucleating agents for PP. However, the nucleation efficiency of GF is much higher than that of the SBS. At high concentrations of SBS (> 30%), the crystallization rate decreases even in the presence of GF. This was attributed to the strong bonding between SBS and glass, giving rise to an intermediate layer of SBS between PP and GF, which was confirmed from the SEM of the fractured morphology of the injection molded hybrid composite. The orientation of GF was observer in the injection molded samples for certain compositions, and this was accompanied by an increase of intensities of particular diffraction peaks in the XRD.
In‐plane compression of constrained preforms
Authors: Norman David A. , Kim Jae‐Ho , Robertson Richard B. 
Published: April 2004

AbstractPreforms constructed from a plain‐weave, glass fabric were compressed in‐plane within a fixture that mimicked the constraints of a closed mold. Typically, a gap was left between the bottom of the preform and the floor of the fixture; upon Initial compression, the preform slid within the fixture, which allowed the friction between the preform and the fixture wall to be measured. The preform began to compress as it contacted the floor of the fixture. The deformation was proportional to the applied stress until a critical stress was reached. Above this stress, the preform sustained damage in the form if localized buckling and a corresponding decrease in mechanical integrity. The in‐plane compressive behavior varied with system parameters, such as preform geometry, fabric orientation, and clamping stress and was shown to be strongly dependent on friction of the preform against the fixture wall. A model was developed to describe the contribution of preform friction with the fixture wall to the in‐plane compressive behavior of constrained preforms.
Detecting sub‐surface cracking in laminated membranes using infrared imaging
Authors: Mackin Thomas J. , Vernon Paul J. 
Published: April 2004

AbstractThis paper presents a new experimental method that utilizes the thermoelastic effect to detect sub‐surface cracks in a laminated polymer membrane. A highly accurate infrared camera is used to measure the thermoelastic and dissipational heat signatures associated with bi‐axial fatigue loading of membranes. Changes in these thermal signatures arise whenever cracks form in any layer of the laminate, including fully embedded layers, thereby providing a novel method for experimentally measuring the initiation and growth of damage in sub‐surface layers. The proposed method is illustrated using a model 3‐layer system of EVOH sandwiched between two polyurethane layers. Bi‐axial fatigue loading was used to initiate cracking in the central EVOH layer without damaging the outer polyurethane layers. Cracking in the central layer resulted in a distinct thermal signature that was plainly visible using the proposed method.
A T spin lattice relaxation study of the molecular motions of a semicrystalline polyimide matrix
Authors: Russell Vernon M. , Koenig Jack L. 
Published: April 2004

AbstractThe kHz molecular motion of a semicrystalline polyimide was studied through 13C solid state NMR spectroscopy. Variable temperature T experiments were performed on a Bruker msl‐300 spectrometer for various B1 applied radio frequency fields. Similar activation energies of motion for different carbon atoms in the flexible spacer gave evidence of a group motion of this molecular segment. It was also found that aromatic activation energies were higher than those of aliphatic carbons.
Novel isocyanate‐based matrix resins for high temperature composite applications
Authors: Sendijarevic Vahid , Sendijarevic Aisa , Frisch Kurt C. , Reulen Paul 
Published: April 2004

AbstractPolyoxazolidone composites were prepared from polymeric isocyanate (PAPI 901) and epoxides (Epon 828 and DEN 431) in the presence of an oxazolidone‐forming catalyst, triphenylantimony iodide. The effects of isocyanate to epoxide equivalent ratio, type of epoxide, and amount of fiberglass reinforcement on the composite properties were studied as well as the effects of post‐curing temperature and time. Increasing the fiberglass content of the polyoxazolidone composites resulted in an improvement of the thermal and mechanical strength properties. The heat deflection temperature of all polyoxazolidones was > 250°C. The retention of the tensile strength at 150°C was excellent, ∼90% or higher. Polyoxazolidone composites based on DEN 431 at 1.2 isocyanate to epoxide equivalent ratio with 70 wt.% of fiberglass and post‐cured at 150°C for 48 h exhibited the best properties. According to the results of DMA, TMA and DSC, the maximum operating temperature for polyoxazolidone composites is around 200°C. The TGA data showed that the decomposition temperature was ∼330°C.
Emergence of fibrillar composites due to chaotic mixing of molten polymers
Authors: Liu Y. H. , Zumbrunnen D. A. 
Published: April 2004

AbstractA technique is presented in which fine fibers (2 μm–20 μm) emerge within a cavity containing randomly distributed molten pellets of low‐density polyethylene (LDPE) and poly(ethylene‐stat‐vinyl acetate) (EVA) or polystyrene (PS) and LDPE as a result of three‐dimensional chaotic mixing. Initially coarse mixtures processed with this technique adopted fibrillar morphologies because of the interaction of interfacial tension and flow structures that are characteristic of chaotic mixing. Similar fibrillar structures were obtained for inverse viscosity ratios and different interfacial tensions, suggesting that chaotic mixing is a robust process to produce fibrillar composites. Mechanisms for the emergence of fibrils during chaotic mixing are presented. The unique characteristics of this novel technique are highlighted and possible applications in the polymer processing industry are discussed.
Acousto‐ultrasonic evaluation of carbon‐carbon composites at different processing stages
Authors: Raju P. K. , Vaidya U. K. 
Published: April 2004

AbstractThe final form of a carbon‐carbon (C/C) composite is a consequence of a series of complex processing stages, during which significant changes occur in material microstructure and properties (thermal, physical, and mechanical). Owing to the uncertainties in the processing steps, material integrity and quality assurance is a matter of concern. The present study focuses on acousto‐ultrasonic (AU) evaluation of plain and eight‐harness (8H) satin weave fabric reinforced C/C composites. Studies pertaining to ex‐situ AU testing of C/C composites at various stages of processing are presented. The sensitivity of AU in identifying such defects as fiber breakage and misaligned fibers is also considered. AU signatures were interpreted in the time and frequency domains through well‐known approaches, such as measurement of stress wave factor (SWF) and spectral moment computation. The results indicated strong qualitative and quantitative correlations between the parameters obtained from time and frequency domain features of the AU signal and the evolving microstructure of carbon‐carbon at various processing stages. An important application of this work will be in the establishment of AU for in‐situ process monitoring of C/C composites.