bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of interface modification on the mechanical properties of polystyrene‐sisal fiber composites
Authors: Nair K. C. Manikandan , Thomas Sabu
Published: April 2004

The effect of interface modification on the mechanical (tensile, impact and flexural) properties of polystyrene–sisal fiber composites was investigated. The interface modification was performed by treatment of sisal fibers with benzoyl chloride, polystyrene maleic anhydride (PSMA), toluene diisocyanate (TDI), methyl triethoxy silane and triethoxy octyl silane. These interface modifications improve the compatibility of hydrophilic sisal fiber with a hydrophobic polystyrene matrix and change the tensile, impact and flexural properties of the composite, but to varying degrees depending on the fiber modification. The treated fibers were analyzed by spectroscopic techniques. Scanning electron microscopy was used to investigate the fiber surface, fiber pullout, and fiber‐matrix interface.
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

This 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

Novel 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

The 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

Short 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

Sisal 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

The 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

Nylon‐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

Recent 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

An 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

This 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

Vacuum‐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

Ternary 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

In 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

Crosslinked 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

We 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

Simultaneous 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

Poly(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

Polymer‐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.
Experimental analysis and simulation of flow through multi‐layer fiber reinforcements in liquid composite molding
Authors: Diallo M. L. , Gauvin R. , Trochu F.
Published: April 2004

Liquid composite molding (LCM) is a process in which a reactive fluid is injected into a closed mold cavity with preplaced reinforcement. Combined layers of different permeabilities are often used in LCM, which creates through thickness and inplane porosity and permeability variations. These inhomogeneities may influence the flow front profile in the thickness direction. To investigate the effect of the through thickness inhomogeneities, mold filling experiments were performed using preforms containing layers of two different fiber architectures. Aqueous corn syrup solutions were injected into a tempered glass mold containing the reinforcement stack. The progress of the flow front at various locations within the reinforcement was measured by an electrical conductivity technique based on the insertion of small wires between the reinforcement layers. Experimental data reveal the details of the flow front shape as the fluid penetrates the preform. Using these data, a model is proposed to calculate the overall in‐plane permeability of the preform. Numerical simulations of the flow front progression performed with the computer software RTMFLOT developed in our laboratory are compared to the experimental flow front for various stacking arrangements. Results show good agreement between simulations and experiments and demonstrate the capability of the software to simulate multi‐layer flow process.
Inverse gas chromatography as a tool to characterize ligno‐cellulosic fibers modified for composite applications
Authors: Coupas A.‐C. , Gauthier H. , Gauthier R.
Published: April 2004

Inverse gas chromatography (IGC) was used to characterize ligno‐cellulosic fiber modified for composite applications. The surface properties of the paper fiber was modified by solution grafting of maleic anhydride functionalized polypropylene (PPgMA): We have investigated the influence of the maleic anhydride content and the chain length of the PPgMA on the surface modifications involved in the solution grafting process. Using IGC at infinite dilution, the evolution of the dispersive component of surface energy with such treatments and the variation of the paper fiber acid/base behavior was determined. The treatment by PPgMA was found to reduce the acidic character of the paper fiber and to enhance its basic character. Moreover, increasing the chain length of the PPgMA resulted in a reduction of both the hydrophilic character of the fiber and its acidic character, while increasing the anhydride content of the PPgMA enhanced the basic character of the fiber. Finally, using IGC at finite concentration, it is observed that reducing the chain length of PPgMA contributes to reducing the specific area of the paper fiber.
The relationship between zeta‐potential and pull‐out shear strength on modified UHMWPE fiber reinforced epoxy composites
Authors: Chiu Hsien‐Tang , Wang Jyh‐Horng
Published: April 2004

UHMWPE fiber exhibits high performance, featuring high tensile strength and modulus, because of its extended chain structure. However, this fiber demonstrates some defects, such as low melting point, creep, and poor interfacial bonding with resin. Therefore, it is still not widely applied in composites. This research attempted to improve the performance by applying interfacial treatment to the fiber, using polypyrrole (PPy) synthesized through oxidation. The interfacial shear strength was evaluated using the results of a pull‐out test and a Zeta Potential. The UHMWPE fiber was exposed to PPy treatment at various temperatures. The PPy‐modified fiber was then impregnated with epoxy to generate the composites. The effects of the modification were also examined. The performance of the composites was determined by the Zeta Potentials of the fiber and resin, using an EKA electrokinetic analyzer. The interfacial shear strength was determined by the pull‐out test. The morphology of fiber was observed by SEM. Results show that the shear strength of the interface between the PPy‐treated UHMWPE fiber and epoxy increased 215%. The correlation between the Zeta Potential and the interfacial shear strength was also observed.
Fabrication and mechanical response of commingled GF/PET composites
Authors: Svensson Niklas , Shishoo Roshan , Gilchrist Michael
Published: April 2004

The mechanical properties and the response to mechanical load of continuous glass fiber reinforced polyethylene terephthalate (GF/PET) laminates have been characterized. The laminates were manufactured by compression molding stacks of novel woven and warp knitted fabrics produced from commingled yarns. The laminate quality was examined by means of optical and scanning electron microscopy. Few voids were found and the laminate quality was good. Resin pockets occurred in the woven laminates, originating from the architecture of the woven fabric. The strength of the fiber/matrix interface was poor. Some problems were encountered while manufacturing the laminates. These led to fiber misalignment and consequently resulted in tensile mechanical properties that were slightly lower than expected. Flexural failures all initiated as a result of compression, and it is possible that the compression strength of the matrix material, rather than its tensile strength, might limit the ultimate mechanical performance of the composites. Flexural failures for both materials were very gradual. The warp knitted laminates were stronger and stiffer than the woven laminates. The impact behavior was also investigated; the woven laminates exhibited superior damage tolerance compared with the warp knitted laminates.
Forming limit measurements for random‐fiber mats
Authors: Dessenberger Richard B. , Tucker Charles L.
Published: April 2004

In resin transfer molding, the fabrication of the fiber preform is critical to both part quality and production efficiency. The deformation induced by preforming introduces porosity and permeability variations, which affect mold filling, and may result in defects (tears and wrinkles) in the preform. In this study we develop an experimental method for determining the formability of thermoformable random‐fiber mats, and provide a mathematical framework for expressing the results. We characterize formability of random‐fiber mats using a forming limit diagram, similar to the diagrams used for sheet metal. This diagram maps the combinations of principal stretch ratios λ1 and λ2 that cause the material to fail. The maximum load during constant‐rate extension provides the failure criterion in forming limit tests. The experiments combine uniaxial and constrained tests. The uniaxial tests reveal behavior when the sample is free to contract in the lateral direction, and also help determine the strains that cause wrinkling in the sheet. The constrained tests give data when lateral contraction is prohibited. Biaxial data is acquired by conducting a sequence of two constrained tests on a single sample, rotating the sample by 90° between the tests. Forming limit data is presented for CertainTeed's U750 thermoformable random‐fiber mat. The results are expressed mathematically in a formability function W (λ1, λ2), in which the forming limits are incorporated through a quadratic penalty function. This type of data can be used in an ideal forming theory to determine the feasibility of forming any given shape from a random‐fiber mat.
Thermoplastic composites reinforced with long fiber thermotropic liquid crystalline polymers for fused deposition modeling
Authors: Gray R. W. , Baird D. G. , Bøhn J. H.
Published: April 2004

This work is concerned with preliminary studies on developing thermoplastic composites for use in fused deposition modeling (FDM). Polypropylene (PP) strands reinforced with thermotropic liquid crystalline polymer (TLCP) fibrils were generated in a novel dual extruder process. The process allowed the reinforcement of PP with a melting point (Tm) of 165°C with continuous fibrils of a high melting (283°C) TLCP (Vectra A950). The strands were then re‐extruded in a capillary rheometer forming monofilaments to simulate piston actuated FDM. The effects of the thermal and deformation histories on the mechanical properties of the re‐extruded strands were evaluated. It was found that tensile properties of the strands improved with draw ratio and that the maximum modulus of the composite strands was similar to that predicted by composite theory. Strands were consolidated uniaxially via compression molding at temperatures just above the melting point of the matrix to determine the effect of thermal history. This resulted in a ∼20% reduction in tensile modulus relative to the modulus of the strands. Monofilaments were extruded from a capillary rheometer in which long fiber strands were used as feedstock to study the effects of deformation history on the tensile properties. It was found that the tensile properties of the monofilaments were dependent on capillary diameter, capillary L/D, and apparent shear rate due to fibril alignment.
Physical and numerical modeling of mold filling in resin transfer molding
Authors: Golestanian Hossein , El‐Gizawy A. Sherif
Published: April 2004

Finite element modeling and experimental investigation of mold filling in resin transfer molding (RTM) have been performed. Flow experiments in the molds were performed to investigate resin flow behavior into molds of rectangular and irregular shapes. Silicone fluids with viscosity of 50 and 100 centistoke as well as EPON 826 epoxy resin were used in the mold filling experiments. The reinforcements consisted of several layers of woven fiberglass and carbon fiber mats. The effects of injection pressure, fluid viscosity, type of reinforcement, and mold geometry on mold filling times were investigated. Fiber mat permeability was determined experimentally for the five‐harness and eight‐harness woven mats. Resin flow through fiber mats was modeled as flow through porous media. Pressure distributions inside both types of molds were also determined numerically. In the case of resin flow into rectangular molds, numerical results agreed well with experimental measurements. Comparison between the experimental and numerical results of the resin front position indicated the importance of edge effects in resin flow behavior in small cavities with larger boundary areas. Reducing the resistance to resin flow at the edge region in the numerical model allowed for good agreement between the numerical simulation and the physical observations of the resin front position and mold filling time.
Effects of time and temperature on the tension‐tension fatigue behavior of short fiber reinforced polyamides
Authors: Jia Nanying , Kagan Val A.
Published: April 2004

To support the fatigue design of the cyclically stressed plastics parts, such as automotive under‐the‐hood and exterior components, we analyzed the short‐term and long‐term mechanical performance (tensile strength, fatigue strength, and fatigue life) of short glass fiber reinforced polyamides PA 6 and PA 66. Comprehensive tension‐tension fatigue tests were conducted with reference to the latest ASTM, ISO, and Japanese industrial standards for plastics, at temperatures from −40°C to 121°C, on materials aged at 121°C for 0, 100, 500, and 1000 h. Tests were conducted at a loading frequency f = 5 Hz, stress ratio R = 0.1, and in a wide range of cycles to failure from 2 × 103 to 2 × 106. Without aging and for both PA 6 and PA 66, the highest fatigue strength or fatigue life was found at −40°C; it decreased significantly at 23°C, and decreased further at 121°C. The fatigue strength of PA 6 was found to be higher than that of PA 66 at −40°C, but the reverse was seen at 23°C. At 121°C, the fatigue strengths of PA 6 and PA 66 were virtually the same. Aging at 121°C improved the tensile strength of PA 6 and PA 66 as aging time increased from 100 to 1000 h, and this process seemed to be more influential for PA 6.
Modeling and rheology of HTPB based composite solid propellants
Authors: Erişken Cevat , Göçmez Ahmet , Yilmazer Ülkü , Pekel Fikret , Özkar Saim
Published: April 2004

The propellant with the minimum viscosity required for a defect‐free casting can be obtained by proper selection of the size and fractions of solid components leading to maximum packing density. Furnas' model was used to predict the particulate composition for the maximum packing density. Components with certain size dispersions were combined to yield a size distribution that is closest to the optimum one given by Furnas for maximum packing. The closeness of the calculated size distribution to the optimum one was tested by using the least square technique. The results obtained were experimentally confirmed by viscosity measurement of uncured propellants having HTPB binder and trimodal solid part accordingly prepared by using aluminum (volumetric mean particle diameter of 10.4 μm) and ammonium perchlorate with four different sizes (volumetric mean particle diameters: 9.22, 31.4, 171, and 323 μm). The experimental measurements showed that the compositions for the minimum viscosity are in good agreement with those predicted by using the model for maximum packing. The propellant consisting of particles with mean diameters of 10.4, 31.4, and 323 μm was found to yield the minimum viscosity. This minimum viscosity was observed when the fraction of the sizes with respect to total solids was 0.141, 0.300, and 0.559, respectively.
Mechanical characterization of triaxially braided hybrid composites
Authors: Savino Vincenzo , Chou Tsu‐Wei
Published: April 2004

The use of advanced composites has been expanded to the oil and gas industry. One of the newly developed technologies is in composite coiled tubing that offers the potential of exceeding the performance of metallic tubings. The high strains due to bending and the complex state of stress in these tubes necessitate the better understanding of the correlation between fiber architecture and tube performance. Braided composites can withstand high bending deformation without severe degradation of properties. In this study, braided hybrid composites are presented as an option for achieving high performance coiled tubing under tensile and flexural loads. The effects of material and fabric microstructural parameters on the mechanical behavior of braided hybrid composites are studied. The mechanical characterization of triaxially braided composites has identified the influence of the mechanical properties of the axial yarn, the axial yarn volume fraction, and the braid angle. Overall, this study provides a sound knowledge base for the design, fabrication, and characterization of triaxially braided composites for coiled tubing applications in the petroleum industry.
Practical use of the statistically modified laminate model for injection moldings. Part 1: Method and verification
Authors: Saito Makoto , Kukula Stefan , Kataoka Yasuto
Published: April 2004

The fibers in injection molded FRP provide the material's strength and stiffness; however, they also supply many of the problems. Preferential orientation of fibers during molding can reduce strength and stiffness below expected values in critical directions, or induce warpage in thin walled sections. Makers of short fiber reinforced injection molded products typically use computer aided engineering packages to optimize product performance and manufacturing variables. However, the reliability of the fiber orientation simulation can be limited, and the method is not easily understood, making an assessment of accuracy for a given situation difficult. In addition, the structural module of flow analysis packages is often a basic package with many features missing. This paper presents a structural analysis system for injection molded parts made of short fiber reinforced plastics. A full‐featured commercial structural analysis code is interfaced with a flow analysis program using a practical material model that takes into account the effects of local fiber orientation. The system is completely open to the user, and can be modified as required.
Sliding mode interlaminar fracture toughness of interply hybrid composite materials
Authors: Hwang Shun‐Fa , Huang Chih‐Ching
Published: April 2004

To measure the sliding mode interlaminar fracture toughness of interply hybrid composites, end notched flexure (ENF) specimens with three different types of stacking sequence have been utilized. Finite element analysis is applied to separate the contribution from different modes on the strain energy release rate. In addition, the methods of beam theory, compliance, and compliance calibration to calculate the GC values are compared. The effects of interface friction, crack length, and specimen width are also discussed. The results show that the crack growth in the three types of specimens is dominated by the sliding mode and the Mode II interlaminar fracture toughness can be approximated. The compliance method is not recommended for hybrid ENF specimens and the effects of interface friction can be neglected. To get rid of the edge effect, the specimen width must be carefully chosen, while the fracture toughness does increase with the initial crack length.
Flow channels/fiber impregnation studies for the process modeling/analysis of complex engineering structures manufactured by resin transfer molding
Authors: Mohan R. V. , Shires D. R. , Tamma K. K. , Ngo N. D.
Published: April 2004

The success of resin transfer molding (RTM) depends upon the complete wetting of the fiber preform. Effective mold designs and process modifications facilitating the improved impregnation of the preform have direct impact on the successful manufacturing of parts. Race tracking caused by variations in permeabilities around bends, corners in liquid composite molding (LCM) processes such as RTM have been traditionally considered undesirable, while related processes such as vacuum assisted RTM (VARTM) and injection molding have employed flow channels to improve the resin distribution. In this paper, studies on the effect of flow channels are explored for RTM through process simulation studies involving flow analysis of resin, when channels are involved. The flow in channels has been modeled and characterized based on equivalent permeabilities. The flow in the channels is taken to be Darcian as in the fiber preform, and process modeling and simulation tools for RTM have been employed to study the flow and pressure behavior when channels are involved. Simulation studies based on a flat plate indicated that the pressures in the mold are reduced with channels, and have been compared with experimental results and equivalent permeability models. Experimental comparisons validate the reduction in pressures with channels and validate the use of equivalent permeability models. Numerical simulation studies show the positive effect of the channels to improve flow impregnation and reduce the mold pressures. Studies also include geometrically complex parts to demonstrate the positive advantages of flow channels in RTM.
Compaction of textile reinforcements for composites manufacturing. II: Compaction and relaxation of dry and H2O‐saturated woven reinforcements
Authors: Robitaille François , Gauvin Raymond
Published: April 2004

Previous analysis of published experimental results on compaction and relaxation of textile reinforcements allowed the effects of some processing parameters on the mechanical behavior of the reinforcements to be identified. However, a limited number of relaxation results are available; also, the effect of some parameters on compaction received limited attention, and the behavior observed with fluid‐saturated reinforcements has not been investigated. In this paper, the results of a structured experimental program of compaction and relaxation performed on three woven reinforcements are reported. In half the trials, a relaxation period was imposed on the samples. In the other half, samples saturated with distilled H2O were compacted. The selection of the processing parameters was found to be as important as the selection of the reinforcement itself for the definition of a manufacturing operation. The processing parameters governing the compaction and relaxation were seen not to be the same, and the fiber reorganization that occurs during the compaction phase was found to have a different effect on successive compaction cycles than the reorganization occurring during the relaxation.
Polymerization of styrene‐isoprene on glass cloth for use in composite manufacture
Authors: Grady Brian P. , O'Rear Edgar A. , Penn Lynn S. , Pedicini Angelo
Published: April 2004

The evaluation of a new process for promoting the adhesion of thermosetting resins to a reinforcing fiber is described. In this process, termed admicellar polymerization, monomers are polymerized inside a surfactant bilayer adsorbed on a surface. Admicellar polymerization is essentially a surface analogue of emulsion polymerization. This technique can place a variety of polymers at the surface of the reinforcing agent, so that the interfacial layer can be tailored at will. In this study, a styrene‐isoprene copolymer was polymerized on the surface of glass mats. Epoxy‐matrix composites made with untreated cloth, silane‐treated cloth, and admicellar‐treated cloth were evaluated via three‐point bend tests and single filament pull‐out tests. The epoxy‐matrix composites made from admicellar‐treated and silane‐treated cloth gave significantly higher strengths in three‐point bend tests than composites made from untreated cloth. Single filament pull‐out tests, which measure fiber‐matrix adhesion directly, and scanning electron micrographs of the failure interface gave results consistent with three‐point bend tests. This paper indicates that admicellar polymerization deserves further study as an alternative to silane coupling agents in structural composites.
Effect of fiber architecture on permeability in liquid composite molding
Authors: Shih Chih‐Hsin , Lee L. James
Published: April 2004

This study investigates the effect of fiber architecture on the permeability in liquid composite molding. The in‐plane permeabilities of several glass fiber mats with different architectures were measured. A conceptual model based on the observed micro‐scale flow pattern is proposed to explain the measured permeability results. It is found that the size of the pores outside the fiber tows and how these pores are connected determine the permeability of a fiber reinforcement.
Evaluation of dynamic mechanical properties of unidirectional composites in relation to their morphology
Authors: Gauthier C. , Khavandi A. , Franciosi P. , Perez J. , Gaertner R.
Published: April 2004

We were interested in the dynamic mechanical behavior of unidirectional composites from E‐glass fibers and an epoxy matrix with several glass fiber contents ranging from 43% to 68%. A method is proposed for the determination of the viscoelastic response of such reinforced material, based on successive applications of the three‐phase self‐consistent analysis proposed by Christensen and Lo. When we apply this model in consecutive steps, we can take into account some morphological features including nonuniform arrangement of the fibers in the transverse plane with clustering or connecting arrangements as well as particular strengthening effects of the polymer in the interphase.