bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analysis of dynamic flows through porous media. Part I: Comparison between saturated and unsaturated flows in fibrous reinforcements
Authors: Bréard Joël , Henzel Yann , Trochu François , Gauvin Raymond 
Published: April 2004

AbstractThis article presents a general approach to model flows through unsaturated porous media as they occur in Liquid Composite Molding (LCM). Saturated and unsaturated flows will be studied here both from the experimental and theoretical points of view. It is indeed important to distinguish between these two flow behaviors in order to understand the interactions between the three phases that coexist in a fibrous reinforcement: the solid and fluid phases on one hand, and the air content on the other. The experimental work presented here includes the study of permanent and transient flow regimes, both for saturated and unsaturated porous media. The dynamic effects that occur during fluid injection through fibrous reinforcements highlight the double scale, structure of their pore volume. The ratio between saturated and unsaturated permeabilities appears to be connected to the degree of saturation and to the porosity of the part. Given the importance of permeability as a key input parameter in process simulation, this article proposes to introduce the degree of saturation in the equations that govern the flow in order to increase the accuracy of numerical predictions. This will not only provide a better understanding of the underlying physical phenomena during the fluid impregnation of a fibrous preform, but will also ultimately allow the study of air entrapment mechanisms that govern the quality of composite parts.
Morphology and mechanical properties of crosslinked PE/PE composite materials
Authors: Ratner S. , Weinberg A. , Marom G. 
Published: April 2004

AbstractNovel peroxide‐crosslinked composite materials based on ultra high molecular weight polyethylene fibers were studied in comparison with their non‐crosslinked homologues. Two material types were prepared, either by embedding the fibers in a low‐density polyethylene matrix, or by compacting neat fibers. The resulting composites were analyzed by differential scanning calorimetry, focusing on the typical double‐melting endotherm of the PE fibers, and by X‐ray diffraction, concentrating on the characteristic weak 010 reflection of the triclinic phase in the fiber. Mechanical testing of unidirectional composites showed crosslinking to be highly advantageous, yielding significant property enhancement, e.g., increasing the flexural modulus from 28 to 33 GPa in the compacted fiber composite. The advantage results from the crosslinking mechanism, entailing only partial melting that is confined to the fiber skin, while retaining a significant degree of crystallinity in the fiber.
Studies on bamboo polymer composites with polyester amide polyol as interfacial agent
Authors: Saxena Mohini , Gowri V. Sorna 
Published: April 2004

AbstractThe effect of surface treatment on the properties of bamboo/epoxy, bamboo/polyester composites was investigated. An improvement in the properties was observed when the surfaces of the bamboo fibers were modified with polyesteramide polyol (PEAP). The performance of surface treated bamboo composites in terms of water resistance is significantly better than that of untreated bamboo composites. Polyester amide polyol treated bamboo composites exhibited better mechanical strength properties. Fractographic evidence such as fiber breakage/splitting and matrix adherence on the pulled‐out fiber surface explains such behavior.
Drop weight impact and work of fracture of short glass fiber reinforced polypropylene composites toughened with elastomer
Authors: Tjong Sie Chin , Xu Shi‐Ai , Mai Yiu Wing 
Published: April 2004

AbstractShort glass fiber (SGF) reinforced polypropylene composites toughened with styrene‐ethylene butylene‐styrene (SEBS) or maleated SEBS (SEBS‐g‐MA) triblock copolymer were injection molded. Charpy drop‐weight impact properties and the impact essential work of fracture (EWF) of the SGF/SEBS/PP and SGF/SEBS‐g‐MA/PP hybrids were investigated. Drop‐weight impact results revealed that the SGF/SEBS/PP hybrid exhibits higher impact strength than the SGF/SEBS‐g‐MA/PP hybrid at low impact speeds. This was derived from the pull‐out of fibers from the SGF/SEBS/PP hybrid. At high impact speeds, the impact strength of the SGF/SEBS‐g‐MA/PP hybrid was slightly higher than that of the SGF/SEBS/PP hybrid. Impact EWF measurements showed that the hybrids only exhibit specific essential work (We) at a high impact speed of 3 ms−1. The non‐essential work does not occur in the hybrids under high impact rate loading conditions. Moreover, SEBS or SEBS‐g‐MA addition was beneficial in enhancing the high‐rate specific essential work of the SGF/SEBS/PP and SGF/SEBS‐g‐MA/PP hybrid composites.
Mechanical behavior of cold plasma–treated sisal and high‐density polyethylene composites
Authors: Martin Adriana R. , Denes Ferencz S. , Rowell Roger M. , Mattoso Luiz H. C. 
Published: April 2004

AbstractSisal fibers and finely powdered high‐density polyethylene were surface functionalized with dichlorosilane on a RF(radio frequency)‐plasma reactor. Composites made from sisal and high‐density polyethylene were compounded using a thermokinetic mixer. The discharged mass was cooled, granulated, and injected molded into composite specimens for testing. The mechanical behaviors (tensile, impact and thermal dynamical mechanical properties) of composites made from cold plasma‐treated and untreated components are compared and discussed. The best mechanical performance was generally obtained for composites where only the inert thermoplastic matrix was plasma‐functionalized. Plasma treatment of lignocellulosic fibers seems to induce decomposition processes of the surface layers structures exposed to the plasma that generally does not contribute to significant improvement on the mechanical behavior of the composite.
Interfacial shear strength and wettability between glass fiber and PC/SAN/SMA blends
Authors: Nam G. J. , Kim H. , Lee J. W. 
Published: April 2004

AbstractThe two important factors affecting the mechanical properties of fiber‐reinforced composite materials are the interfacial shear strength (IFSS) and wettability. The IFSS and wettability of glass fiber in a polycarbonate (PC)/styrene‐co‐acrylonitrile (SAN) blend system were measured by the single fiber fragmentation test (SFFT) and the Wilhelmy method, respectively. Styrene‐co‐maleic‐anhydride (SMA) was used as a compatibilizer and the glass fiber was surface‐treated with organosilane coupling agents to induce chemical bonding between maleic anhydride and silanol. The IFSS was found to increase with the content of SMA copolymer and then level off: There was an optimum level of the SMA content for a given silanol content. The IFSS and wettability increased with increasing SAN content, and the wettability showed quite similar behavior to the case of the IFSS with respect to SAN content. The effect of the miscibility of SAN/SMA blends on the IFSS was also investigated. The IFSS was greatly affected by the miscibility of SAN/SMA blends, which is mainly dependent on the copolymer compositions of SAN and SMA. Higher IFSS was obtained when the SAN/SMA blend was miscible.
Polymerization compounding composites of nylon‐6,6/short glass fiber
Authors: Feng Wei , Ait‐Kadi Abdellatif , Brisson Josee , Riedl Bernard 
Published: April 2004

AbstractNylon‐6,6 was grafted onto the surface of short glass fibers through the sequential reaction of adipoyl chloride and hexamethylenediamine onto the fiber surface. Grafted and unsized short glass fibers (USGF) were used to prepare composites with nylon‐6,6 via melt blending. The glass fibers were found to act as nucleating agents for the nylon‐6,6 matrix. Grafted glass fiber composites have higher crystallization temperatures than USGF composites, indicating that grafted nylon‐6,6 molecules further increase crystallization rate of composites. Grafted glass fiber composites were also found to have higher tensile strength, tensile modulus, dynamic storage modulus, and melt viscosity than USGF composites. Property enhancement is attributed to improved wetting and interactions between the nylon‐6,6 matrix and the modified surface of glass fibers, which is supported by scanning electron microscopy (SEM) analysis. The glass transition (tan δ) temperatures extracted from dynamic mechanical analysis (DMA) are found to be unchanged for USGF, while in the case of grafted glass fiber, tan δ increases with increasing glass fiber contents. Moreover, the peak values (i.e., intensity) of tan δ are slightly lower for grafted glass fiber composites than for USGF composites, further indicating improved interactions between the grafted glass fibers and nylon‐6,6 matrix. The Halpin‐Tsai and modified Kelly‐Tyson models were used to predict the tensile modulus and tensile strength, respectively.
Evaluating the mechanical performance of supercritical CO2 fabricated polymide 6,6/PMMA, fiber reinforced composites
Authors: Caskey Terrence C. , Lesser Alan J. , McCarthy Thomas J. 
Published: April 2004

AbstractRecent advancements in SC CO2 mediated synthesis and material processing have led to polymer‐polymer blends and composite materials with complex morphologies, exhibiting long‐range order and orientation on multiple length‐scales from the nanometer to the centimeter scale. The material under consideration in this work is a polyamide 6,6 (nylon)/poly (methyl methacrylate) (PMMA) fiber‐reinforced composite that was fabricated in a unique SC CO2 assisted process. The tensile and flexural properties of these unique composites are studied and the evolution of damage and energy dissipation are monitored through cyclic loading and microscopic analysis of post‐stressed composite cross sections. It is shown that this morphology leads to improved flexural modulus and increased ultimate strength with only a small decrease in tensile modulus. These composites also exhibited significant improvements in stress distribution and load transfer without the use of fiber sizing agents for fiber/matrix compatibilization.
Enhanced strength of portland cement products via reinforcing polypropylene/fiberglass structures obtained from a novel processing technique
Authors: Zhang Yuanheng , Jacob George C. , Fellers John F. , Sayre Jay , Pope A. E. 
Published: April 2004

AbstractAn uninterrupted filament winding process was used to fabricate structures made of polypropylene and glass fiber that provide superior reinforcement to Portland cement structures. Fabricated polypropylene/fiberglass composite tubes were filled with a cement mixture and some were reinforced with internal tapes. Three‐point bending experiments, microscopic observation, and image analysis were used as tools to study various processing variables and their effect on the mechanical properties of the tubes. The temperature of the mandrel and wetting strongly affected the composite's mechanical properties. Increased temperatures diminished the void content within the composite and produced a unique “fuzzy” inner surface for the cylindrical tube. The development of this “fuzzy” inner surface improved the strength and fatigue properties of the cement filled composite tube by providing efficient load transfer to the glass fibres. Also the surface to volume ratio of the steel rebar geometry when compared to that of the polypropylene/fibreglass structure explains the superior load transfer to the glass. It was found that a tube reinforced with 15 internal tapes filled with a cement mixture recorded a maximum tensile stress of 71 MPa (10,000 psi) with excellent damage tolerance, more than a 10‐fold increase over the upper bound value for steel reinforced cement obtained from the rule of mixtures. The tube continued to be load bearing to strains of 0.4, which is more than 40 times the failure strain of glass. These large failure strains are the result of the shear yielding of polypropylene that coats the glass fibres and allows them to move within the cement.
Effects of nano‐fillers and process conditions on the microstructure and mechanical properties of microcellular injection molded polyamide nanocomposites
Authors: Kharbas Hrishikesh , Nelson Paul , Yuan Mingjun , Gong Shaoqin , Turng Lih‐Sheng , Spindler Rick 
Published: April 2004

AbstractThis paper presents the effects of process conditions and nano‐clay fillers on the microstructure (namely, size, density, and distribution of microcells within samples) and the resulting mechanical properties of microcellular injection molded polyamide‐6 (PA‐6) nanocomposite and its neat‐resin counterpart. Based on the design of experiments (DOE) matrices, samples were molded at various supercritical fluid (SCF) levels, melt temperatures, shot sizes, melt plastication pressures (MPP), and injection speeds. These samples were then subjected to scanning electron microscope (SEM) analysis, tensile testing, and impact testing. For both materials, the microstructure and the mechanical properties of the molded samples were found to be dependent on the process conditions and presence of nano‐clay, which could serve as microcell nucleating agent. At higher weight reductions, the nanocomposite samples exhibit much smaller microcells and higher cell densities than those obtained in the neat‐resin samples. The SEM micrographs reveal noticeable differences in microcell surface roughness between the nanocomposite and the neat resin. A statistical design analysis was used to identify the optimal process conditions that would result in desirable cell size and density and, thus, better mechanical properties. For example, the highest tensile strengths have been observed at the highest levels of shot size, MPP, injection speed, and SCF level, and at the lowest level of melt temperature.
A comparative study of vacuum‐assisted resin transfer molding (VARTM) for sandwich panels
Authors: Dai J. , Pellaton D. , Hahn H. T. 
Published: April 2004

AbstractVacuum‐assisted resin transfer molding (VARTM) of sandwich panels can be facilitated by using high permeability layers (HPL) over the skins or adding channels in the surfaces of the core (CIC). The present paper investigates the advantages and disadvantages of both methods in terms of manufacturing cost and time through simulations and experimental observations. A cost model is developed, and the resin infusion time for each method was minimized through simulations. The design parameters are the number of high‐permeability layers and the number and size of channels. A penalty function with equal weight on cost and time is used to find the optimum values of the design parameters. Under the conditions studied, the optimal HPL method is found to be better than the optimal CIC method. While the conclusion is limited to the present study, the proposed approach can be used to optimize manufacturing processes for larger sandwich panels under different conditions.
Processability, morphology and mechanical properties of glass fiber reinforced poly(ether sulfone) modified by a liquid crystalline copolyester
Authors: García M. , Eguiazábal J. I. , Nazábal J. 
Published: April 2004

AbstractTernary composites based on glass fiber reinforced polyethersulfone (gPES) modified by a liquid crystalline copolyester (R5) were obtained by injection molding at different nozzle temperatures and at LCP contents up to 20%. The blends showed two pure amorphous phases. The ability of R5 to improve processing was seen mainly in the increase in the MFI of the blends on 5% LCP addition, which was more than 75% and 16% with respect to that of pure gPES and PES, respectively. The best processing temperature appeared to be 330°C, as it led to the maximum skin fibrillation and provided both the best small strain and fracture mechanical properties. The blend processed at 330°C with 5% R5 showed the best balance of properties because, besides the highest relative processability increase, it led to maximum values in all mechanical properties measured. This was due to both the overall fibrillation of the skin and to its having the highest ductility.
New Test method for determining energy absorption mechanisms in polymer composite plates
Authors: Jacob George C. , Starbuck J. Michael , Simunovic Srdan , Fellers John F. 
Published: April 2004

AbstractIn passenger vehicles the ability to absorb energy due to impact and be survivable to the occupant is called the “crashworthiness” of the structure. To identify and quantify the energy absorbing mechanisms in candidate automotive composite materials, test methodologies were developed for conducting progressive crush tests on composite plate specimens. The test method development and experimental setup focused on isolating the damage modes associated with frond formation that occurs in dynamic testing of composite tubes. A new test fixture was designed to progressively crush composite plate specimens under quasi‐static test conditions. Features incorporated into the design include an observable crush zone, long crush length, interchangeable contact profile, frictionless roller for contact constraint, and out of plane roller supports to prevent buckling. Preliminary results are presented under a sufficient set of test conditions to validate the operations of the test fixture. The activation of different damage mechanisms was demonstrated by the validation tests on the representative composite material systems. The experimental data, in conjunction with test observations will be used in future work to identify the characteristic damage and failure modes, and determine the energy absorption capability of candidate automotive composite material systems.
Effect of water absorption on the izod impact energy of crosslinked poly(methyl methacrylate‐acrylic acid) and their composites
Authors: Abusafieh Abdel , Kalidindi Surya R. 
Published: April 2004

AbstractCrosslinked poly(methyl methacrylate‐acrylic acid) and composites using this crosslinked copolymer as the matrix have been synthesized and evaluated for their potential as bioimplantable materials in design of a new class of bone anchors. The low‐velocity impact energy absorption properties of this slightly hydrophilic class of materials were examined by Izod impact testing. In particular, the influence of swelling (by absorption of water) on the impact resistance of the crosslinked copolymer and composites based on this copolymer was investigated. Also, the influence of fiber type and preform architecture on the impact resistance of the composite, in both the dry and swollen states, was investigated. The fracture surfaces and the modes of failure in these tests were examined using scanning electron microscopy. The results indicated that absorption of water leads to about a threefold increase in the impact resistance of the copolymer. However, the increase in the impact resistance of the composite samples after water absorption varied considerably, depending on the type and form of fibrous reinforcement. These results and our understanding of the role of water absorption on the impact resistance of these novel systems are presented.
On phase connectivity descriptions in modeling viscoelasticity of fiber or sphere reinforced composites
Authors: Franciosi P. , Gaertner R. 
Published: April 2004

AbstractWe consider composites exhibiting different scales of heterogeneities and some hierarchical phase connectivities, referred to as “composites of composites.” Following literature suggestions, and as an alternative to the use of complicated pattern‐based models, effective elastic or viscoelastic moduli of such structures, with spherical (isotropic) or fiber‐like (transverse isotropic) symmetry are estimated following a stepwise homogenization procedure. The steps are chosen according to the successive identified heterogeneity scales, making use, at each step, of the simplest n‐layered (n=3 or 4) sphere or fiber inclusion model accounting for the scale dominant connectivity features. We quantitatively check the sensitivity of such an estimate process to the chosen simplifications for the morphology description, on comparing different choices for morphologies typical of nonuniformly reinforced matrices. The comparison first investigates, in elasticity, the effects of volume fractions of phases and of stiffnesses ranging over several orders, as well as phase connectivity permutations for 3‐phase arrangements. One then compares several estimates obtained for the effective complex longitudinal modulus of a typical fiber reinforced polymer morphology using the correspondence principle for its viscoelasticity. The material description is compared to experiment, which for the morphological characteristics is the most important.
Cowoven polypropylene/glass composites with polypropylene + polymer liquid crystal interlayers: Dynamic mechanical and thermal analysis
Authors: Own Christopher S. , Seader Darin , D'Souza Nandika Anne , Brostow Witold 
Published: April 2004

AbstractSimultaneous macroscopic and molecular reinforcement of polypropylene with glass fibers and Polymer Liquid Crystals (PLCs) is evaluated. Interlayers of polypropylene (PP) + poly(ethylene terephthalate) /0.6 p‐hydroxybenzoic acid PLC blends are introduced between the cowoven polypropylene + glass fiber plies. Analysis was conducted using Dynamic Mechanical Thermal Analysis (DMTA), Differential Scanning Calorimetry (DSC), and Thermogravimetric Analysis (TGA). The results indicate that low fractions of PLC material in the composite have dual benefits of increased rigidity and toughness. The crystallization kinetics are influenced by the dual nucleating effects of both reinforcing agents. A decrease in crystallinity is associated with increasing PLC presence. Degradation kinetics of the composites demonstrate only one kinetic step in contrast to the interlayers alone.
The effect of preparation methods on the thermal properties of poly(acrylic acid) / alumina composites
Authors: Çaykara Tuncer , Güven Olgun 
Published: April 2004

AbstractPoly(acrylic acid) ‐ alumina composites have been prepared by two different methods and thermally characterized. The glass transition temperatures (Tg) of the PAA/Al2O3 systems prepared by mixture and polymerization method were found to be 126°C and 130°C, respectively, irrespective of the alumina amounts involved in this work. The composites prepared by mixture and polymerization method have been investigated by using thermogravimetry (TGA) to follow the kinetics of anhyride formation and thermal degradation reactions. The activation energy of thermal anhydride formation and thermal degradation reaction was not found to change very much with the ratio of PAA/Al2O3 when the composites were prepared by simple mixing. For the composites prepared by the polymerization method, the activation energy of anhyride formation and thermal degradation reaction were observed to change with percentage conversion.
Key issues in numerical simulation for liquid composite molding processes
Authors: Gauvin Raymond , Trochu François 
Published: April 2004

AbstractPolymer‐based composites have a great potential for the manufacture of energy‐efficient vehicles. Because of this growing usage and also because mold cost increases with part complexity, numerical simulation of Liquid Composite Molding Processes such as Resin Transfer Molding (RTM) and Structural Reaction Injection Molding (SRIM) are becoming more important. To succeed in that venture, reliable input data as well as a numerical model able to simulate specific molding difficulties and complex shapes must be used. In this paper, several issues are discussed and a computer software is presented. Among them, permeability measurement is discussed. Concerning specific molding difficulties, simulation results compared with experimental data are presented for edge effects, flow in multilayers and flow in ribbed structures. Finally, nonisothermal filling is discussed. Experimental data showing how the temperature boundary layer is developed during the filling of a heated mold are presented.