bluuebunny/crossref_metadata_2025_split huggingface dataset:
Crack tip damage analysis in fatigue fracture of epoxy resin
Authors: Wang X. , Sehanobish K. , Moet A. 
Published: December 2004

AbstractThe application of the crack layer theory to fatigue crack propagation (FCP) in epoxy is discussed. A crack tip damage evolution coefficient μ is introduced to assess the extent of damage as a fraction of the damage associated with critical crack propagation. The results can be expressed in the form

where dl/dN is the rate of FCP, G1 is the energy release rate whose critical value is G1c, and β is a phenomenological constant. Although no damage was detected from microscopic analyses, μ increases fivefold during stable crack propagation. Fractal analysis of fracture surface profiles provides a quantitative measure of the roughness associated with crack advance. The fractural measure d is found to evolve in a similar fashion as μ, suggesting the applicability of d to quantify crack tip damage evolution.
Some effects of surface‐controlled reactions of Kevlar 29 on the interface in epoxy composites
Authors: Penn L. S. , Tesoro G. C. , Zhou H. X. 
Published: December 2004

AbstractSurface energetics and adhesion to epoxy resin were investigated in the laboratory for Kevlar 29 fiber modified by a surface‐controlled nitration reaction and by a nitration/reduction sequence. Results show that at the level of modification studied, the presence of functional groups on the fiber surface does not alter surface energy. On the other hand, interfacial adhesion is significantly increased for the modified as compared with untreated fiber.
The contribution of thermal stresses to the failure of Kevlar fabric composites
Authors: Deteresa S. J. , Nicolais L. 
Published: December 2004

AbstractThe mismatch in thermoelastic properties between fiber and matrix in Kevlar 49 fabric‐epoxy composites is shown to result in significant thermal stresses with cool down from processing temperatures. Cooling generates local transverse tensile stresses that can potentially initiate microcracking at ambient conditions. A temperature reduction also places the curved fiber in the fabric composite in axial compression. This compression adds to the bending strain in the fiber, resulting in significant local reduction of its inherently low compressive load‐bearing capability. The combination of thermal stresses and external compressive loads that are below ultimate values can cause local compressive failure of the fiber. The kink bands formed as a result of compressive failure of Kevlar fiber are expected to cause debonding between fiber and matrix and, therefore, are also potential sites for crack initiation. Thus, thermal stresses can contribute to the initiation of at least two damage mechanisms that may severely limit the compressive and flexural fatigue strength of Kevlar fabric composites at and below ambient temperature.
Measuring spatial orientation of short fiber reinforced thermoplastics by image analysis
Authors: Fischer Günther , Eyerer Peter 
Published: December 2004

AbstractA computer based measuring strategy to determine spatial orientation of short glass fibers from the cross‐section of single fibers is presented. A practicable way of correcting the inclination‐dependent probability of hitting a fiber is shown as well as the correction of fiber‐end intersections. The latter is done by pattern recognition and application of a set of FORTRAN subroutines. A simple model allows the approximate calculation of thermal expansion as a function of volume content and fiber orientation. This serves as an applicability test for the measuring system.
Scanning electron microscopy and X‐ray fluorescence analysis of a polymer blend, glass fiber composite
Authors: Saini D. R. , Schultz J. M. 
Published: December 2004

AbstractThis paper explores the possibility of using X‐ray micro‐analysis for studying the morphology of the polymer blend composite PPS(GF)/HDPE (glass‐filled poly(phenylene sulfide)/high density polyethylene) system and the characterization of filler and polymer dispersion in the system.
Stamping of thermoplastic matrix composites
Authors: Bigg D. M. , Preston J. R. 
Published: December 2004

AbstractThe recent growth in the use of polymer composites has resulted in the need for higher productivity manufacturing processes than are currently used in most thermoset composite production. One of the ways to provide increased productivity in composite manufacturing is to use thermoplastic matrix sheet composites. In this investigation the part forming characteristics of several thermopolastic composites were investigated. Glass fiber reinforced composites based on polypropylene, nylon 12, poly(butylene terephthalate), poly(ethylene terephthalate), poly(phenylene sulfide), and poly(etheretherketone) were examined. The processing conditions required for solid‐state stamping of these composites were determined. A temperature process window for stamping each of these composites was determined, and found to correlate with the melting and re‐crystallization peaks from differential scanning calorimetry (DSC) scans.
Thermoforming of advanced thermoplastic composites. I: Single curvature parts
Authors: Dutta A. , Niemeyer M. , Cakmak M. 
Published: December 2004

AbstractThermoforming has been studied for a single curvature part made from various advanced thermoplastic matrix composite prepregs. For parts with acceptable shape conformity, preheating of the composite laminates to a processing temperature of 350 to 400°C is necessary prior to forming with molds maintained at 200°C. However, only PEEK/carbon fiber prepreg tapes yielded parts with acceptable microstructural integrity and a matrix crystallinity level of about 30 percent. Amorphous matrix based PXM 8505/T500 fabric prepregs also result in lamination and void free parts, but fiber matrix distribution in this case was rather poor. Parts thermoformed from other prepreg laminates contained voids and/or were delaminated, thereby indicating the need for higher mold temperature and forming pressure than that afforded by the present study, in which a standard lab‐scale thermoforming machine was used.
The electrical conductivity of polypropylene and nickel‐coated carbon fiber composite
Authors: Ahmad M. S. , Zihilif A. M. , Martuscelli E. , Ragosta G. , Scafora E. 
Published: December 2004

AbstractThe effect of filler content, temperature, and frequency of the applied electric field on DC and AC electrical conductivities of composites of nickel‐coated carbon fibers and polypropylene are considered. The impedance behavior and the dielectric properties of these composites were studied in the low frequency range 10 Hz–30 kHz. It was found that the volume electrical resistivity shows filler content and temperature dependence. The calculated activation energy of the thermal rate‐process decreases with the filler concentration, while the shielding effectiveness increases. The overall observed permittivity of the composites increases with the filler concentration, and the dielectric behavior is discussed in terms of the space charge, electronic and interfacial polarization within the covered frequency range. It was observed that the AC conductivity is nearly independent of the frequency below 100 Hz and increases with frequency above this range. Finally, it was concluded that addition of nickel‐coated carbon fibers could alter the electrical conduction mechanism and the polarization process of the polymeric matrix.
The large deformation elastic response of woven kevlar fabric
Authors: Warren William E. 
Published: December 2004

AbstractThe large deformation elastic response of a plane woven Kevlar fabric is investigated analytically and experimentally. The analysis assumes the undeformed geometry to be a sequence of interlaced arcs of circles that reverse at each yarn midpoint, and each yarn is modeled as an extensible elastica subject to certain compatibility conditions. Deflection‐force relations for the fabric are determined in terms of the initial weave geometry and the elastic properties of the individual yarns. The theoretical results agree well with the results of experiments performed on a fabric woven from 400 denier Kevlar yarns under conditions of uniaxial loading in both warp and fill directions.
Tin‐Lead flake poly (ether sulfone) composite formed by in‐situ melt processing of tin‐lead particles
Authors: Li Lin , Chung D. D. L. 
Published: December 2004

AbstractTin‐lead (60Sn‐40Pb) flake poly(ether sulfone) (PES) composites in which the flakes were partially interconnected and of average thickness 2 μm were prepared by hot pressing molten Sn‐Pb particles in a matrix of PES at a temperature above the melting temperature of Sn‐Pb and above the glass transition temperature of PES. Hot pressing at 240°C and 6.51 Mpa resulted in a 15 vol% Sn‐Pb composite of lower electrical resistivity and higher electromagnetic interference shielding effectiveness than a PES composite containing 15 vol% aluminum flakes that were not formed in‐situ. The electrical properties of the in‐situ PES/Sn‐Pb flake composites were much better than those of PES/Sn‐Pb flake composites were fabricated by hot pressing at 310°C (the manufacturer‐suggested fabrication temperature), though the mechanical properties were not as good.
Fiber orientation and mechanical properties of short‐fiber‐reinforced injection‐molded composites: Simulated and experimental results
Authors: Gupta Mahesh , Wang K. K. 
Published: December 2004

AbstractA numerical simulation is presented that combines the flow simulation during injection molding with an efficient algorithm for predicting the orientation of short fibers in thin composite parts. Fiber‐orientation state is represented in terms of a second‐order orientation tensor. Fiber‐fiber interactions are modeled by means of an isotropic rotary diffusion. The simulation predicts flow‐aligned fiber orientation (shell region)near the surface with transversely aligned (core region) fibers in the vicinity of the mid‐plane. The effects of part thickness and injection speed on fiber orientation are analyzed. Experimental measurements of fiber orientation in plaque‐shaped parts for three different combinations of cavity thickness and injection speed are reported. It is found that gapwise‐converging flow due to the growing layer of solidified polymer near the walls tends to flow‐align the fibers near the entrance, whereas near the melt front, gapwise‐diverging flow due to the diminishing solid layer tends to lign the fibers transverse to the flow. The effect of this gapwise‐converging‐diverging flow is found to be especially significant for thin parts molded at slower injection speeds, which have a proportionately thicker layer of solidified polymer during the filling process. If the fiber orientation is known, predictions of the anisotropic tensile moduli and thermal‐expansion coefficients of the composite are obtained by using the equations for unidirectional composites and taking an orientation average. These predictions are found to agree reasonably well with corresponding experimental measurements.
Application of dynamic mechanical analysis for the study of the interfacial region in carbon fiber/epoxy composite materials
Authors: Dong S. , Gauvin R. 
Published: December 2004

AbstractThe application of dynamic mechanical analysis (DMA) for quantifying interfacial interactions in composites is briefly reviewed. Carbon fiber/epoxy composites with fiber volume fractions of 12, 17, 38 and 61 vol% were subjected to flexural deformation on a Dupont DMA 983 instrument. The dependencies of dynamic mechanical properties of the composites on experimental parameters such as oscillation mode, amplitude, frequency, and temperature were investigate. As opposed to the storage modulus, the loss modulus is found to be sensitive to all parameters. In a fixed multiple frequency mode, the loss modulus of the composites increases with oscillation amplitude and decreases with frequency and the number of tests. The information produced in the resonant mode is more reproducible. An additional damping at the interfaces, apart from those of the constituents, suggests a poor interface adhesion in these composites. A linear relationship between the excess damping at the interfaces and the fiber volume fraction shows a similar interface quality for these composites having different fiber volume fractions. The detection of interfacial properities was found to be more sensitive in the flexural deformation mode than in the torsional mode. At temperatures higher than the glass transition temperature of the matrix, the effective volume fraction of the matrix is reduced. Such a reduction can be interpreted from the mismatch of thermal expansion of the matrix and the fibers.
Synthesis and characterization of a new class of thermosetting resins: Allyl and propargyl substituted cyclopentadiene derivatives
Authors: Mathias Lon J. , Muthiah Jeno 
Published: December 2004

AbstractA series of all‐hydrocarbon resins were synthesized by reacting cyclopentadiene allyl chloride, propargyl chloride, or a mixture of allyl chloride and propargyl ide, under phase transfer conditions. Phase transfer reactions with and without added solvents, and with either quaternary ammonium or crown ether catalysts, yielded similar products consisting of a mixture of 1,1‐disubstituted cyclopentadiene (minor amount) and 2‐3 isomers each of tri‐, tetra‐, penta‐, and hexa‐substituted derivatives. No further reaction of each these components possible. The overall substitution pattern varied little with changes in reaction conditions although limiting the allyl chloride content led to still reactive, partially substituted products. Incorporation of all‐propargyl and high propargyl‐to‐allyl mixed functionalities on cyclopentadiene yielded products whose stability was very hindering their thorough characterization. Preliminary evaluation was there‐carried out for mixed resins with lower propargyl functionality. The allyl substituted resin (allylated cyclopentadiene, ACP) underwent thermal cure lout initiator at around 200°C while allyl/propargyl substituted resin (7:1 ratio, APCP) showed a faster, lower temperature cure at around 120°C. Cationic cure of ACP was also initiated by a novel sulfonium salt at around 100°C. Neat resin when cured at 200°C gave material with a flexural storage modulus 2 of about 300 MPa. Further cure at 250°C raised the modulus to 1.2 GPa. resin gave composites with excellent properties when used with glass and on fibers. Flexural modulus values (by DMA) of ∼ 66 GPa were obtained for ACP/carbon fiber composites compared with 42 GPa for epoxy/carbon composites made in our laboratories using commercially available materials. The modulus values at 300°C dropped to 10% of the room temperature value for the epoxy composites, while the ACP/carbon composite maintained 60% of its room temperature value at 300°C. When brought back to ambient temperature, the modulus of latter sample had increased to 80 GPa and that of the epoxy composite dropped to 23 GPa. Glass fiber ACP composites performed similar to an epoxy composite up to 200°C but maintained properties up to 300°C while those of the epoxy were drastically reduced. TGA analysis of both cured ACP resin and its composites showed decomposition beginning at 375°C. Three‐point‐bending tests indicated very high modulus with brittle failure for ACP composites. Scanning electron micrographs showed moderate bonding of the new resin to both carbon glass fiber surfaces. This new class of thermosetting resins offers excellent potential for application in low‐cost glass and carbon composites with good thermal and physical properties.
Determining fiber strength vs. gage length
Authors: Curtin W. A. 
Published: December 2004

AbstractThis paper concerns the gage length dependence of fiber strength as established by measuring the fiber fracture stress vs. fragment length in the succession of fragments, which occur in tension testing of a single‐fiber composite (s.f.c.). For fibers with a strength distribution described by a Weibull modulus m, a plot of In (fragment fragment fracture stress) vs. ln (actual fragment length) leads to the deduction of an apparent Weibull modulus mapp ⋍ 0.63 m, whereas the apparently less drigorous procedure of plotting In (fragment fracture stress) vs. ln (average fragment length) allows for accurate assessment of the true Weibull modulus. The mapp < m behavior arising from the use of actual fragment lengths occurs because fragments in the s.f.c. are not random sections of the fiber, but rather sections which have effectively been proof‐tested at a stress corresponding to the strength of last fiber breaking stress occurring in the entire sample length. Hence, the individual fragments appear stronger than random fiber sections, leading to an apparently smaller Weibull modulus. Such complications do not arise if only the average fragment length, or equivalently the location‐independent total number of breaks, is considered. Computer simualtions of the fragmentation process verify analytic estimates of the ratio of mapp/m, and demonstrate the accuracy of using the average fragment length to assess fiber Weibull modulus.
Viscoelasticity of porous composite materials: Experimentals and theory
Authors: Alberola N. D. , Lesueur D. , Granier V. , Joanicot M. 
Published: December 2004

AbstractThe viscoelasticity of latex/PS beads composites, having the same volume content of latex and PS beads, but various porosity ratios and specific surfaces of particles has been investigated in the glass temperature range of the latex matrix. In order to give evidence for the main factors governing the viscoelastic properties, data were compared to numerical simulations based on the Christensen and Lo model and Skorokhod's approach. Such modelings were performed by considering either the latex matrix of the PS beads as the continuous phase. It was concluded that the glassy modulus is mainly governed by the volume fraction of porosity, while the rubbery modulus is controlled by both the interactions between phases and the void volume content. The location of the mechanical relaxation seems to be governed by the mechanical coupling between phases, which implies some local phase inversion. The magnitude of the mechanical relaxation depends not only on the chemical coupling induced by the interactions between phases, but also on the mechanical coupling.
Swelling and dissolution rates of glass fiber sizings in matrix resin via micro‐dielectrometry
Authors: Larson B. K. , Drzal L. T. , Van Antwerp J. 
Published: December 2004

AbstractComplex fiber‐matrix interactions occur in the processing of glass fiber reinforced polymeric composites, because of the proprietary, complex composition of commercial sizings applied to the glass fiber surface. Research involving a vinyl ester resin system and three model commercial glass fiber sizings, having varying levels of solubility in the resin, has shown that micro‐dielectrometry can provide important information about interactions and may be useful as a tool in optimizing sizing‐matrix resin interactions. Two distinct types of interactions may be monitored by micro‐dielectrometry: The initial resin swelling of the sizing, as well as the dissolution of the sizing into the resin. An estimate of the times associated with swelling and dissolution of the sizing into the matrix resin can be made from micro‐dielectric measurements to optimize composite processing.
Effect of stress on nucleation and crystallization in polymers
Authors: Lindenmeyer P. H. 
Published: December 2004

AbstractPolymer crystallization is recognized as a non‐equilibrium process and the postulate of local equilibrium is combined with the formalism of small systems thermodynamics to provide a general method of relating structure, kinetics and thermodynamics. In this method a single polymer molecule is assumed to be in equilibrium with its environment and the appropriate partition function is factored into the bulk free energy and the remaining factors which are important only in small systems.
Extended‐chain and folded‐chain crystallite formation during the crystallization of stretched crosslinked rubbers
Authors: Wu W. 
Published: December 2004

AbstractThe strain‐induced crystallization phenomenon of a crosslinked polymer network was studied using statistical, thermodynamics. The basic approach was essentially that used by Flory (1), but in this work Flory's assumption of only a single crystalline phase (the extended‐chain crystalline structure with chain parallel to stretch direction) was abandoned. The dimension of the crystalline vector‐which is assumed to be parallel to the stretch direction and the percent crystallinity is taken as two independent variables instead of being treated as one single variable. A single variable treatment is inherent in the assumption of a single extended‐chain crystallite. By use of the present approach, either the folded‐chain crystallite or the extended‐chain one is found to be thermodynamically stable depending on temperature, stretch ratio and molecular weight. The retractive force of a crystallized polymer network has been calculated. It is shown theoretically that the formation of an extended‐chain crystallite will cause the retractive force to decrease, and that the formation of a folded‐chain crystallite will cause the retractive force to increase in a reversible crystallization process.
Stress‐induced crystallization of branched polyethylene terephthalate films
Authors: Hennessey W. J. , Spatorico A. L. 
Published: December 2004

AbstractPolyethylene terephthalate (PET) prepolymer containing 0.0 to 0.3 mole percent pentaerythritol was polymerized to an inherent viscosity of 0.63‐0.70 dl/gm by the fluidized bed technique. Rheological studies and gel permeation chromatography (GPC) examination showed the samples to be branched in character. Amorphous films were stretched at 82 and 93°C at elongation rates of 54, 161 and 267 percent‐s−1 using the T. M. Long machine. The extent of stress‐induced crystallization was established by a density determination. The branched samples behaved very similarly to the linear PET material in crystallization and birefringence studies. Neither the percent crystallinity nor the birefringence appears to be a strong function of strain rate over the range 54‐267 percent‐s−1. A cursory examination of the crystallization kinetics of the oriented samples suggests that extent of branching in our samples does not markedly reduce the crystallization rate at annealing temperatures of 180 and 220°C.