bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modeling the deformation of thermoformable random fiber reinforcements during preform manufacture
Authors: Long A. C. , Rudd C. D. , Middleton V. 
Published: April 2004

AbstractLiquid molding processes have been identified by the automotive and aerospace industries as having potential for structural and semistructural applications. Of the several obstacles to their more widespread use, the major drawback is the lack of an automated and reliable technology for producing reinforcement preforms. Current preform technology is usually based on the forming of continuous fiber mats or fabrics between matched molds. This can result in defects within the fiber structure including wrinkling, thinning, and, in extreme cases, tearing. To understand and eliminate these defects, it is necessary to develop a simulation of the preforming process. This paper is aimed at developing a mathematical model of the deformation of thermoformable continuous filament random mat. The analysis presented is based on plasticity theory, suitably modified to describe the behavior of fiber reinforcements. This is demonstrated for the stretch‐forming of reinforcement using arbitrary axisymmetric punch and die profiles. Experimental work is included to demonstrate the effect of varying a range of process parameters, including rate of forming, reinforcement temperature, and stack thickness. The Validity of the model is demonstrated for a number of punch geometries.
Charaterization of UHMWPE fiber/matrix adhesion by dynamic mechanical spectrometry
Authors: Arnold J. J. , Zamora M. P. , Brennan A. B. 
Published: April 2004

AbstractThe tensile and dynamic mechanical properties of polystyrene and a poly(styrene‐co‐buty1 acrylate‐co‐cyclohexy1 methacrylate) statistical terpolymer (terpolymer) reinforced by randomly oriented, discontinuous ultra‐high molecular weight polyethylene (UHMWPE) fibers are presented in terms of the fiber/matrix interfacial properties. Using a thermomechanical block model based on the parallel rule of mixtures, the adhesion characteristics of poly(butyl acrylate) (PBA) and poly(cyclohexyl methacrylate) (PCHM) grafted, plasma treated, and untreated fibers were determined. The model successfully predicts the tan δ response of the composites including peak height variations and the development of additional loss dispersions associated with the interphase. Moreover, the model yields a fiber reinforcement efficiency factor, K, which gives a quantitative measure of adhesion. The contact angle of PBA and PCHM grafted high density polyethylene (HDPE) films are also included and are compared to the contact angle of plasma treated fibers. The results indicate that PBA and PCHM grafts enhance adhesion through polymer graft/matrix interactions, not simply by improved wetting.
Time‐implicit fixed and deforming grid solutions for compression mold filling
Authors: Chen Y. F. , Voller V. R. , Stelson K. A. 
Published: April 2004

AbstractA general governing equation for tracking the filling free surface during compression molding is derived. From this equation, with appropriate choice of parameters, a time‐implicit fixed grid solution and a time‐implicit deforming grid solution are obtained. Numerical results of several test problems reveal that both solutions reach the same level of accuracy. The fixed grid scheme, however, is more robust and can solve problem with complex geometrical features.
The modulus of shear‐induced fibers from a thermotropic liquid crystalline polymer in a thermoplastic matrix
Authors: Yi Xiao Su , Shi Fang , Michaeli Walter 
Published: April 2004

AbstractA morphological study was performed to determine the volume fraction and the aspect ratio of shear‐induced fibers from a thermotropic liquid crystalline polymer (LCP) in a polycarbonate (PC) matrix. A set of micromechanical models was then applied to estimate the elastic modulus of LCP fibers (Eƒ) in a LCP(20 wt%)/PC blend. The dependence of the composite modulus (Et) of the blend on sample dimensions was predicted. The effects of different injection molding conditions on fiber aspect ratio, Et and Eƒ, were examined.
Effects of thermal history on mechanical behavior of PEEK and its short‐fiber composites
Authors: Sarasua J. R. , Remiro P. M. , Pouyet J. 
Published: April 2004

AbstractThe effect of crystallinity differences induced by mold wall temperature and annealing on mechanical behavior is evaluated for poly(etheretherketone) (PEEK) resin and its composites. The systems investigated were neat PEEK, glass fiber (GF) reinforced PEEK, and carbon fiber (CF) reinforced PEEK. Both composite systems were reinforced with 10, 20, and 30 wt% fiber. The degree of crystallinity (Xc) of PEEK was found to increase by processing at higher mold temperatures, by annealing, and by fiber length reductions, which appears to indicate the ability of short fibers to nucleate the crystallization of PEEK under favorable thermal conditions. Improvements in Young's modulus and strength together with ductility reductions are generally obtained as crystallinity increases in both neat PEEK and its composites. The contribution of crystallinity to mechanical behavior is significant only for neat PEEK and PEEK reinforced by 10% fiber. SEM micrographs reveal that this is due to a change in failure mode. When PEEK is reinforced by carbon fibers or by 20–30% glass fibers, a macroscopic brittle mode of failure is observed irrespective of matrix crystallinity, and mechanical behavior is principally determined by the nature and content of the reinforcing fibers.
Analysis of pultrusion processing of composites of unsaturated polyester resin with glass fibers
Authors: Moschiar S. M. , Reboredo M. M. , Kenny J. M. , Vázquez A. 
Published: April 2004

AbstractAn analysis of the principal processing variables of pultrusion of a thermosetting matrix composite is presented. A fundamental study of the changes of temperature, degree of reaction, and resin viscosity is performed through the application of transfer phenomena principles. Moreover, the development of pressure in the die and the required pulling force are modeled and compared with experimental results reported previously by other authors on the pultrusion of unsaturated polyester matrix‐glass fiber composites. The modeling approach discussed here integrates several sub‐models, reported previously, to obtain a complete description of the basic aspects of the pultrusion process. The application of the mathematical model allows a better understanding of the relationship between processing conditions and material behavior leading to the determination of the processing window for a given system.
Recyclability of a glass fiber poly(butylene terephthalate) composite
Authors: Chu J. , Sullivan J. L. 
Published: April 2004

AbstractThe recyclability of a fiber‐reinforced poly(butylene terephthalate) (PET) composite has been studied. After treatment with a suitable silane, processed regrind composites are successfully recycled, with mechanical properties as good as a comparable, commercial composite. The three processing techniques investigated are injection molding, extrusion compression molding and compression molding. As expected, processing technique and processing parameters are important in determining the mechanical properties of the molded regrind. Our results show that injection‐ and extrusion‐compression‐molded regrind composites have good fiber bundle dispersion and fiber alignment, resulting in tensile properties better than the compression‐molded samples. On the other hand, compression‐molded samples, which show random fiber orientation and low fiber bundle dispersion, have lower tensile properties, but better impact strength than injection‐ and extrusioncompression‐molded composites.
Mechanical and physical properties of isothermally aged carbon fiber‐epoxy composites
Authors: Chifu A. F. , Iroh J. O. 
Published: April 2004

AbstractIsothermal aging of continuous carbon fiber‐epoxy resin composites containing epoxy resin derived from diglycidyl ether of bisphenol‐A (DGEBA) and methylene dianiline (MDA) and 64 vol% of carbon fibers with orientation angles of 0°, 45°, 90° and crossply fibers was performed in vacuum, air and nitrogen atmosphere. The impact strength of the 45° ply composites increased from 149 kJ/m2 to 15.5 × 102 kJ/m2 after isothermal aging in vacuum at 200°C for 13 h. The interlaminar shear strength (ILSS) of the 90° ply composites increased from 3 to 4 MPa after isothermal aging at 184°C for 336 h in nitrogen atmosphere. The flexural strength of the 90° ply composites, however, remained unchanged (∼80 MPa) after isothermal aging in nitrogen at 184°C for 336 h. The impact strength of the 90 degree ply composites decreased by 20% (∼15 kJ/m2 to 12 kJ/m2) and 80% (∼15 kJ/m2 to 3 kJ/m2) after isothermal aging in nitrogen atmosphere at 184°C for 336 h and in air at 200°C for 336 h, respectively.
Tough low profile additives in sheet molding compound
Authors: Chan‐Park Mary B. , McGarry Frederick J. 
Published: April 2004

AbstractThermosetting polyester in a sheet molding compound (SMC) shrinks by 7 to 10% and causes fiber show‐through and poor surface quality. Adding certain thermoplastics results in zero shrinkage and smooth surfaces; these are called low‐profile additives (LPA). Poly(vinyl acetate) (PVAc), a highly effective LPA, decreases the fracture energy from 66.3 to 35.1 J/m2 when present as 14 wt% of the matrix, even though the PVAc is tough. It produces a nodular three dimensional network; the crosslinked polyester nodules are interconnected by weak polyester bridges and the PVAc forms a thin coating on each nodule. The macroscopic crosslinking shrinkage is offset by void formation in the PVAc phase. Crack follows the void structure and cleaves the bridges between the nodules. Low matrix fracture toughness leads to high microcracking and early gross failure of the SMC. This paper presents alternative low profile additives that give excellent low profile effect with improved matrix fracture energy and SMC strength. Commercially available styrene‐butadiene block copolymers were studied. These are less polar and form discrete cavitated domains of a few 100 μm in the solid polyester matrix. With this morphology, good low profile and toughening usually are contradictory, since the former requires small LPA particles for smooth surfaces and the latter requires large particles for crack bridging by the rubber. However, a good compromise was found in Epoxidized Kraton D1300X (a 50% diblock and 50% triblock copolymer of styrene and butadiene) with the compatibilizer Ricon 131MA17 (a maleic anhydride‐polybutadiene adduct). This produces a low profile effect equivalent to PVAc, but with a higher matrix fracture energy of 70.7 J/m2 and higher matrix modulus. With the epoxidized rubber, the flexural strength of the SMC increases by 13% over that with PVAc, with no sacrifice of the modulus or strain‐to‐failure.
Mesostructure development during molding of sheet molding compounds
Authors: Mei T. , Piggott M. R. 
Published: April 2004

AbstractExperiments have been carried out with sheet molding compounds in which the amount of shear developed during molding was varied by changing the charge size. The effects of pressure and temperature were also investigated. The moldings were characterized by their mesostructures and the influence of the mesostructures on the Izod toughness and flexural strength was examined. It was found that high degrees of shear resulted in fiber orientation and the spreading of the fiber bundles. However, this did not improve properties, and it was concluded that for optimum properties, small amounts of shear were desirable.
A simple technique for grafting poly(methyl methacrylate) onto glass fabric
Authors: Sailaja R. R. N. , Kumar Anil 
Published: April 2004

AbstractWe have developed a two‐step technique for synthesizing dichlorosuccinyl peroxide at room temperature, starting from succinic anhydride. It reacts with silanated glass fabric or beads at room temperature. The macroinitiator thus formed can be used for the polymerization of methyl methacrylate, MMA. We show that the MMA is grafted to the surface of glass giving a chemically bonded ultrathin coating, as confirmed by the FTIR analysis and electron micrography.
Development and characterization of high‐performance polybenzoxazine composites
Authors: Shen Shyan Bob , Ishida Hatsuo 
Published: April 2004

AbstractTo develop high‐performance composites with high temperature resistance, two newly synthesized polybenzoxazines were successfully cured with carbon fiber to obtain composites with 60 vol% fiber. Results from differential scanning calorimetry studies were used to modify the benzoxazine monomers to improve processability in terms of melting point and solubility. The density and void content of these composites were measured. Dynamic mechanical tests were performed to determine the glass transition temperature (Tg) and the activation enthalpy of the glass transition process for these two composites. The effect of cure temperature on the Tg of the composites was investigated. Thermal characteristics were studied by means of dynamic mechanical analysis in terms of isothermal aging, decomposition temperature from thermogravimetric analysis, and storage moduli change at high temperatures. Mechanical evaluations of these composites were conducted by flexural and interlaminar shear tests. The mechanical and thermal properties of these two composites exceed bismaleimide composites and compete with polyimide composites, while exhibiting easier processability than polyimides.
Development and hot‐melt impregnation of a model controlled flow prepreg system
Authors: Hayes Brian S. , Seferis James C. , Chen Judy S. 
Published: April 2004

AbstractA controlled‐flow epoxy‐based model prepreg resin system was developed. The formulation of the model controlled‐flow resin was designed from performance information obtained from a commercially available controlled‐flow resin, presently used in the aircraft industry. Thermoanalytical techniques including rheometry were used to provide the necessary information to develop the model system along with a formulation methodology developed by Seferis and co‐workers. The model resin formulation, which was a combination of tetraglycidyl ether of methylenedianiline (TGMDA), diglycidyl ether of bisphenol‐A (DGEBA), carboxyl‐modified butadiene/acrylonitrile rubber (CMBN), carboxyl‐terminated butadiene/acrylonitrile rubber (CTBN), bisphenol‐A (BPA), diaminodiphenyl sulfone (DDS), and dicyandiamide (DICY), was hot‐melt impregnated into unidirectional carbon fibers on a laboratory scale hot‐melt prepreg machine. A two‐parameter, three‐level design of experiments was performed on the prepreg processing parameters in which impregnation temperature and pressure were varied. Thus, a total of nine different experimental prepregs were produced and characterized by resin content, extent of impregnation, and tack. The results from the characterization of the nine experimental prepregs are compared with the effects of the prepreg processing conditions. These results are also compared with the results generated for the commercial controlled‐flow resin. Collectively, this work provides a fundamental basis by which the analysis and rational utilization of controlled‐flow matrix prepregs can be effected.
Evaluation of interlaminar‐toughened poly(etherlmide)‐modified epoxy/carbon fiber composites
Authors: Woo E. M. , Mao K. L. 
Published: April 2004

AbstractAmorphous poly(ether imide) has been used as interlaminar toughening particulate agent in laminated carbon fiber/epoxy composites. Mode I and Mode II delamination fracture toughness was characterized using the double cantilever beam (DCB) and end‐notched flexure (ENF) specimens. The delamination surface was examined using a scanning electron microscopy (SEM) to investigate relationships between the morphology and properties. The results revealed that the PEI‐modified composites exhibited a significantly increased fracture toughness, which increased with the PEI content.GICwas improved from 165 to 540 J/m2(at 1 mm/min crosshead speed).GIICwas improved more significantly from 290 to 1300 J/m2. It is believed that these values could be further improved if the processing cycle were to be optimized.
Phthalonitrile‐carbon fiber composites
Authors: Sastri Satya B. , Armistead James P. , Keller Teddy M. 
Published: April 2004

AbstractPhthalonitrile polymers offer promise as matrix materials for advanced composite applications. The phthalonitrile monomer is readily converted to a highly crosslinked thermosetting polymer in the presence of thermally stable organic amine catalysts. Rheometric studies were conducted to elucidate the optimum amine concentration for composite formulations. High quality composite panels were processed in an autoclave using unsized IM7 carbon fibers. Mechanical properties of the phthalonitrile/carbon composite are either better than or comparable to the state‐of‐the‐art PMR‐15 composites. Dynamic mechanical analysis reveal that samples postcured at elevated temperatures (375°C) do not exhibit a glass transition temperature up to 450°C and also retain °90% of their initial modulus at 450°C. Flame resistance of phthalonitrile/carbon composites, evaluated by cone calorimetric studies, excels over that of other polymeric composites for marine applications. The composites also show low water uptake, <1% after exposure to water for 16 months.
Pultrusion of epoxy matrix composites: Pulling force model and thermal stress analysis
Authors: Moschiar S. M. , Reboredo M. M. , Larrondo H. , Vazquez A. 
Published: April 2004

AbstractPultrusion processing for epoxy resin with glass, carbon, and DuPont Kevlar fibers has been modeled. The model has three submodels: heat transfer, pressure, and force. The validity of the model was verified by comparison of results obtained on the glass fiber/epoxy system with experimental values in the literature. The application of the model permitted an explanation of the difference in behavior between polyester and epoxy resins. Different process variables were studied. Increasing the pulling velocities increases force values. The influence of the fiber content was analyzed. Different wall temperature profiles were used and the residual thermal stresses were calculated. The use of different fibers (glass, carbon, and Kevlar) was simulated under the same process conditions. The higher pulling force was obtained for composites with carbon fibers.
Coupled analysis of injection molding filling and fiber orientation, including in‐plane velocity gradient effect
Authors: Chung S. T. , Kwon T. H. 
Published: April 2004

AbstractOn injection molding of short fiber reinforced plastics, fiber orientation during mold filling is determined by the flow field and the interactions between the fibers. The flow field is, in turn, affected by the orientation of fibers. The Dinh and Armstrong rheological equation of state for semiconcentrated fiber suspensions was incorporated into the coupled analysis of mold filling flow and fiber orientation. The viscous shear stress and extra shear stress due to fibers dominate the momentum balance in the coupled Hele‐Shaw flow approximation, but the extra in‐plane stretching stress terms could be of the same order as those shear stress terms, for large in‐plane stretching of suspensions of large particle number. Therefore, a new pressure equation, governing the mold filling process, was derived, including the stresses due to the in‐plane velocity gradients. The mold filling simulation was then performed by solving the new pressure equation and the energy equation via a finite element/finite difference method, as well as evolution equations for the second‐order orientation tensor via the fourth‐order Runge‐Kutta method. The effects of stresses due to the in‐plane velocity gradient on pressure, velocity, and fiber orientation fields were investigated in the center‐gated radial diverging flow in the cases of both an isothermal Newtonian fluid matrix and a nonisothermal polymeric matrix. In particular, the in‐plane velocity gradient effect on the fiber orientation was found to be significant near the gate, and more notably for the case of a nonisothermal polymer matrix.
Fiber/Matrix mechanical interaction in carbon fiber/bismaleimide model composites
Authors: Favre J.‐P. , Auvray M.‐H. , Chéneau‐Henry P. , Galiotis C. , Vlattas C. , Paipetis A. , Pegoraro M. , Severini F. , Di Landro L. , Yuan Liju 
Published: April 2004

AbstractThe fiber/matrix interaction of high modulus (M40) and intermediate modulus (T800) carbon fibers with a bismaleimide resin has been studied by means of three micromechanical techniques involving a single fiber, namely, fragmentation, Raman spectroscopy, and pullout. A number of chemical treatments aimed at improving the fiber/matrix stress transfer at elevated temperature were tested. The stress transfer proved to be reduced by the temperature in the same way for all interfacial conditions. The limitations to the micromechanical characterization of model composites in temperature are emphasized.
Control of polymer properties by melt vibration technology: A review
Authors: Ibar J. P. 
Published: April 2004

AbstractThis paper reviews the technology of melt vibration (more specifically at low frequency) to reduce viscosity during processing of plastics and to enhance mechanical performance of the solidified parts. The effect of vibration frequency and amplitude on melt viscosity is explained in terms of shear‐thinning criteria. The effect of pressure and temperature on shear thinning is also reviewed to predict how these variables interfere with melt vibration. Practical applications of the principles of melt vibration are provided in injection molding, extrusion and compression molding/thermoforming, from reduction of viscosity to lowering processing temperature and pressure to the elimination of melt defects and weld lines, to the enhancement of mechanical properties, stiffness and strength, by modification of the amorphous and semicrystalline texture and orientational state. Commercially available equipments are reviewed. Results showing the effect of melt vibration during processing for two classical polymers, polystyrene and polypropylene, are discussed. The paper concludes on the remaining challenges to bring the benefits of the new technology to full commercialization.
3D finite element method for the simulation of the filling stage in injection molding
Authors: Hétu J.‐F. , Gao D. M. , Garcia‐Rejon A. , Salloum G. 
Published: April 2004

AbstractDuring the molding of industrial parts using injection molding, the molten polymer flow through converging and diverging sections as well as in areas presenting thickness and flow direction changes. A good understanding of the flow behavior and thermal history is important in order to optimize the part design and molding conditions. This is particularly true in the case of automotive and electronic applications where the coupled phenomena of fluid flow and heat transfer determine to a large extent the final properties of the part. This paper presents a 3D finite element model capable of predicting the velocity, pressure, and temperature fields, as well as the position of the flow fronts. The velocity and pressure fields are governed by the generalized Stokes equations. The fluid behavior is predicted through the Carreau Law and Arrhenius constitutive models. These equations are solved using a Galerkin formulation. A mixed formulation is used to satisfy the continuity equation. The tracking of the flow front is modeled by using a pseudo‐concentration method and the model equations are solved using a Petrov‐Galerkin formulation. The validity of the method has been tested through the analysis of the flow in simple geometries. Its practical relevance has been proven through the analysis of an industrial part.