bluuebunny/crossref_metadata_2025 huggingface dataset:
The diffusion of liquids into resins and composites
Authors: Marshall J. M. , Marshall G. P. , Pinzelli R. F.
Published: May 2005

Existing methods of assessing the resistance of a polymer to environmental attack are of only limited use. A new technique, which utilizes radiolabelled diffusants, has been developed to study the diffusion of liquids into thick sections of polymer‐and glass‐fiber‐reinforced laminates. This technique allows the construction of concentration profiles of the liquid in the polymer at any time, and diffusion coefficients can be calculated from short‐term data. The application of this method of measurement has given a clear picture of the way in which water diffuses into vinyl ester resins and their glass‐reinforced laminates. The effects of stress and damage on this diffusion pattern have been quantified. It has been found that the presence of stress enhances the diffusion, and that the diffusion coefficient is further increased by the presence of a stress concentration. No evidence has been found, however, to suggest that the liquid “wicks” along the fibers when stress concentrations are absent.
Bulk modulus and thermal expansivity of melt polymer composites: Statistical versus macro‐mechanics
Authors: Simha Robert , Jain R. K. , Jain S. C.
Published: May 2005

Physical properties of composites as a function of filler content have been described in the past through models requiring the solution of macroscopic equations of motion for an elastic continuum or, on a more empirical level, by the assumption of various compositional averaging schemes. We discuss a model drawn from our molecular mixture theory. This allows us to avoid the formal problems attending concentrated suspensions and introduces molecular filler‐medium interaction parameters. Comparisons with experimental material and empirical equations involving bulk modulus and thermal expansivity will be given. The theory opens the possibility of determining interfacial strengths from appropriate mechanical and thermal measurements and of predicting one set from another set of data.
Processing and flammability parameters of bismaleimide and some other thermally stable resin matrices for composites
Authors: Kourtides Demetrius A.
Published: May 2005

The effect of processing variables on the flammability and mechanical properties of state‐of‐the‐art and advanced resin matrices for graphite composites were studied. Resin matrices which were evaluated included state‐of‐the‐art epoxy, phenolic‐novolac, phenolic‐Xylok, two types of bismaleimides, benzyl, polyethersulfone, and polyphenylsulfone. Comparable flammability and thermochemical data on graphite‐reinforced laminates prepared with these resin matrices are presented, and the relationship of some of these properties to the anaerobic char yield of the resins is described.
Three‐phase syntactic foams
Authors: Narkis M. , Kenig S. , Puterman M.
Published: May 2005

Three‐phase syntactic foams consisting of a close‐packed microballoons bed, binding resin, and air voids are reported. Preparation methods varied from simple dry‐blending with a solid powdery resin‐to‐resin coating of spheres from polymer solutions. By holding the hollow spheres volume fraction constant and at the maximum packing, a property studied was a function of a single variable, namely, resin volume fraction, void content or density. Mechanical properties are reported as function of one of these variables. The temperature effect was investigated on polyimide based foams. The dielectric constant is shown to obey a logarithmic rule of mixtures. Modified modulus‐composition equations are shown to be applicable for prediction of moduli values of the three‐phase systems.
Continuous fiber rearrangements during the molding of fiber composites. II. Flat cloth to a rounded cone
Authors: Robertson R. E. , Hsiue E. S. , Yeh G. S. Y.
Published: May 2005

This report is the second in a series in which we attempt to develop rapid computational procedures for determining the rearrangement of continuous fibers that occurs during the molding of fiber composite components from flat precursors. This report considers the shaping of a balanced cloth into a cone with a rounded top. The numerical procedure developed predicts that a cloth can be shaped into rounded cones with all but the smallest cone angles without wrinkling. The predictions are compared with experiment for a particular cone angle, and various parameters connected with the shaping calculation are discussed.
Electrostatic phenomena and molecular motion at interfaces of glass/polymer composites
Authors: Stupp S. I. , Weldert S. C.
Published: May 2005

A boundary zone of filler‐affected polymeric network is a possible element in the microstructure of composites. The intensity of adsorption potentials for polymeric material on the filler and therefore its surface energy should be an important variable in boundary zone properties. This work has involved the modification of surface energy in a glass filler material through the introduction of externally induced electrostatic charge that is through the creation of a ‘synthetic’ zeta potential on filler particles. The interactions of charged and uncharged glass surfaces with a polymeric matrix were studied by thermally stimulated discharge (TSD), and also by contact angle measurements. The experimental system studied was an aluminosilicate glass as the filler material, and poly(tetraethylene glycol dimethacrylate) as the organic matrix. Contact angle measurements revealed enhanced wettability for the matrix‐forming monomer on glass surfaces charged negatively by electric fields. TSD analysis was also carried out on pure polymer, and composite materials containing either uncharged or bipolar filler particles (particles exposed to an external electrical potential). TSD spectra suggest a suppressed level of molecular motion in composites with fillers of high electrostatic surface energy. Also, activation energies calculated from TSD data are higher in bipolar filler composites. The higher activation energies are consistent with the possibility that a less mobile interfacial zone polymerizes around higher surface energy filler particles.
The relationships between mixing and properties of filled polymers and foams
Authors: Lee Biing‐Lin
Published: May 2005

The increased utilization of reinforced polymeric blend composite materials has prompted renewed interest in mathematical models which can explain or predict the characteristics of processing and the properties of composite materials in terms of the properties and concentration of the components. As a first step toward developing the rules for multicomponent systems we restrict our attention to the Lee‐Nielsen's model and concepts of two‐component systems with particulate inclusions embedded in a continuous matrix. The following property‐mixing relationships are then discussed: (1) reinforcement of uncured and cured rubber composites; (2) thermal expansion of polymer composites; (3) elastic modulus, and thermal conductivity of (reinforced) polymeric foam materials; and (4) heat buildup of rubber composites. Some important concepts and principles which have evolved from our experimental attempts at correlating the behavior of heterogeneous multiphase polymer materials are also discussed.
Mechanical characterization of the interfacial strength of glass‐reinforced composites
Authors: Koenig Jack L. , Emadipour Hamid
Published: May 2005

A mechanical test system using a monofilament pullout technique has been utilized to investigate the interfacial bond strength of glass monofilament‐epoxy resin composites. The factors influencing the interfacial strength and hydrothermal stability of the glass monofilament‐epoxy resin composites have been studied including: varying the amount of thickness of the N‐2‐aminoethyl‐3‐aminopropyl trimethoxysilane (AAPS) coupling agent layers between the two substrates of the composite; the debonding effect of moisture and heat as the result of long term exposure; and the partial removal of the deposited silane coupling agent on glass by water, prior to composite preparation. It is found that a critical amount of the bifunctional silane coupling agent is necessary to improve the mechanical strength and hydrothermal stability of the composite interface. Partial removal by washing of the deposited aminosilane on glass, prior to composite preparation, irrespective of its original thickness, enhances the interfacial strength of the composite.
Modification of the dynamic damping behavior of epoxy/glass fiber composites via fiber coating with functional latices
Authors: Schlund B. , Lambla M.
Published: May 2005

A series of functionalized latices were synthesized using: n‐butyl acrylate (BuA), butyl methacrylate (BuMA), and glycidyl methacrylate (GMA). The particle microstructure was controlled by a sequential addition of monomers. The glass fibers were commercially roll‐coated using a mixture of these latices and amino‐silane. The specimens were filament wound, compression molded, and cured. The effects of the morphology and reactivity of the latices were analyzed in dynamic as well as flexural modes. The uniformity of the coating as well as the nature of the latex are responsible for the mechanical behavior of the composites.
Influence of a filler on the fracture of a highly crosslinked polymer
Authors: Kalnin M. , Turner D. T.
Published: May 2005

Glassy composites were made by photopolymerization of a dimethacrylate paste containing silanated silicate particles (up to 50 μm). Minimum values of Vickers hardness number, stiffness, and yield stress were found for volume fractions of the filler in the range 0.03 to 0.05. Generally fracture surface morphology resembled classical results for inorganic glasses. In addition, tracks and features were observed of the kind reported previously for highly crosslinked organic glasses. Such morphology has been attributed to fortuitous changes in direction of the principal tensile stress just ahead of the crack tip. In the present work it was found that single tracks and features were associated with individual filler particles. This observation is consistent with the expectation that individual particles would act as stress concentrators and thereby serve to change the direction of the principal stress. Furthermore, stress concentration may be invoked to account for the minimum in mechanical properties but dewetting might also be involved.
Effect of fiber misorientation on the tensile strength of compression molded continuous fiber composites
Authors: Mallick P. K.
Published: May 2005

Resin cross‐flow during compression molding of unidirectional sheet molding compound composites, such as CSMC and XMC, may cause severe misorientation of the continuous fibers in the outer layers. The extent of fiber misorientation depends on the type of molding compound, the length of cross‐flow, and the location of the charge in the mold. The tensile strength is reduced in the direction of cross‐flow with decreasing mold surface coverage. However, since severe fiber misorientation is generally restricted to the outer layers, increasing the number of plies improves the tensile strength to the level observed with little or no misorientation.
Acoustic emission during irreversible deformation in short fiber reinforced poly(vinyl chloride) composites
Authors: Yuan J. , Hiltner A. , Baer E.
Published: May 2005

Acoustic emission (AE) during irreversible deformation in short glass fiber reinforced poly(vinyl chloride) (PVC) composites was studied using a piezoelectric crystal transducer. Compared to the well‐coupled composites, many more AE events were observed during tensile deformation in the poorly‐coupled composites, presumably due to failure at the fiber‐matrix interface. No fiber fracture was detected in the tensile tests for either well‐coupled or poorly‐coupled composites. Irreversibility of acoustic emission was observed in repeated tensile loading experiments. Unlike PVC, the short fiber composites fractured during stress relaxation at 1 percent elongation. Studies of acoustic emission behavior during stress relaxation indicated that interfacial debonding is a time‐dependent process. Relaxation fracture time was strongly increased by chemical coupling at the interface.
Quantitative estimation of matrix‐filler interactions in ferrite‐filled styrene‐isoprene‐styrene block copolymer systems
Authors: Shenoy A. V. , Saini D. R.
Published: May 2005

Quantitative estimation of matrix‐filler interaction in highly loaded ferrite filled Styrene‐isoprene‐styrene block copolymer has been attempted through dynamic viscoelastic melt studies. A correlation between the interaction parameter in the melt state and that in the solid state at comparable frequency of deformation has been shown to exist so that the matrix‐filler affinity at any temperature of interest can be estimated. Such a correlation eliminates the need for generating solid state dynamic data in order to check matrix‐filler compatibility as the results obtained in the melt could be extrapolated to the behavior in the solid state.
The influence of velocity on the impact strength of glass reinforced polypropylene
Authors: Golovoy A.
Published: May 2005

The influence of impact velocity, between 1 and 8.7 meters per second (m/s) (2.2 to 19.5 mph), on the impact behavior of polypropylene, reinforced with 20 volume percent continuous glass fibers, was investigated in a 3‐point bend test at 21 °C. The ratio of specimen span to thickness, which has a profound effect on the observed results, was varied between 5.3 and 26. An attempt to apply simple beam theory for the analysis of the initial specimen response to the high loading rate was successful, except for the lower than expected values of shear modulus. The stress to break and the tensile and shear moduli were found to increase along with velocity. The dependence of impact energy on velocity was observed to be affected by the span to thickness ratio: a positive dependency was observed at low ratios and none at high ratios. This is different from the negative dependency reported for polypropylene reinforced with short fibers, and is attributed to the influence of the continuous glass fibers on the impact behavior of the composite.
Composites containing glass spheres and fibers: II tensile, flexural, and shear strengths
Authors: Dai S. R. , Piggott M. R.
Published: May 2005

Tensile, flexural, and shear tests on glass fiber‐polyester pultrusions containing glass spheres show that the spheres reduce the tensile strengths when both rigid and flexible polyesters are used, but some increase in flexural strength is obtained with the flexible resins. Small additions of spheres increased the shear strengths, but for sphere volume fractions greater than about 0.2, the shear strength declined. A silane coupling agent on the spheres increased the strength of the rigid resin composites, but had little effect with the flexible resin. Some of the results could be due to the lack of straightness of the fibers caused by the presence of spheres having diameters greater than the fiber diameter. However, when the fibers were not present, the sphere filled matrices showed very diverse behavior. The results presented here indicate that even in the absence of fibers, simple models are unlikely to be successful in explaining the properties.
Effect of glass fiber length on the creep and impact resistance of reinforced thermoplastics
Authors: Silverman Edward M.
Published: May 2005

Impact and flexural creep testing were conducted at temperatures between −22°F (−30°C) and 250°F (121°C) to evaluate and compare the end‐use performance of continuous long glass fiber‐reinforced thermoplastic sheet composites to that of short glass fiber‐reinforced thermoplastics. The matrices studied consisted of amorphous (polycarbonate and acrylonitrile‐butadiene‐styrene) and semicrystalline (polypropylene) polymers. Data were obtained from both injection‐molded specimens (short fibers), and from specimens machine‐cut from compression‐molded test panels (continuous long fibers). The creep results of this study demonstrated that continuous long fibers are more efficient than short fibers in reinforcing the thermoplastic matrices, resulting in enhanced load‐bearing ability at elevated temperatures. The addition of continuous long glass fibers to the thermoplastic matrices led to a significant increase in the notched Izod impact strengths between the temperatures of −22°F (−30°C) and 77°F (25°C), and only slight improvement in the drop‐weight impact strengths. The lack of correlation between notched Izod impact and drop‐weight strengths is largely due to the difference in crack propagation and fracture initiation energies. Results of the Rheometrics instrumented impact test indicated a higher total fracture energy for the long glass‐reinforced thermoplastic sheet composites than for the short glass‐reinforced injection‐molded thermoplastics. The decreased ease of crack propagation in thermoplastic sheet composites is associated with the high energy‐absorbing mechanisms of fiber debonding and interply delamination. The results of this study point to the significant property improvement of continuous long fibersvs.short fibers. The creep strength of short fiber‐reinforced thermoplastics are greatly affected by the nature of the stress transfer which in turn is influenced by the critical fiber length and temperature, which is not the case for the long fiber‐reinforced thermoplastic sheet composites. Long fibers dramatically increase the impact resistance of thermoplastics. The retention of toughness at low temperatures coupled with elevated temperature performance greater than similar short glass fiber‐reinforced thermoplastics effectively extends the capabilities of thermoplastic sheet composites at both temperature extremes.
A model for resin flow during composite processing: Part 1—general mathematical development
Authors: Dave R. , Kardos J. L. , Duduković M. P.
Published: May 2005

A generalized three‐dimensional model for resin flow during composite processing has been developed. The model is based on a theory of consolidation and flow through a porous medium, which considers that the total force acting on a porous medium is countered by the sum of the opposing forces, including the force due to the spring‐like effect of the fiber network and the hydrostatic force due to the pressure of the liquid within the porous medium. The flow in the laminate is described in terms of Darcy's Law for flow in a porous medium, which requires a knowledge of the fiber network permeability and the viscosity of the flowing fluid. Unlike previous resin flow models, this model properly considers the flows in different directions to be coupled and provides a unified approach in arriving at the solution. Comparison of numerical solutions with the closed form analytical solution shows good agreement. Resin pressure profiles show that the pressure gradients in the vertical and horizontal directions are not linear, unlike the assumption of linearity made in several previous resin flow models. The effects on the resin pressure of both linear and nonlinear stress‐strain behavior of the porous fiber network were considered. The nonlinear behavior simulates a rapidly stiffening spring and the resin pressure decreases much more rapidly after a given initial period compared to the linear stress‐strain behavior.
Thermal characterization of a bis‐maleimide/bis‐cyanate/epoxy thermosetting resin for composites
Authors: Gotro J. T. , Appelt B. K. , Papathomas K. I.
Published: May 2005

The thermosetting resin investigated here was a mixture of bis‐maleimide and bis‐cyanate, frequently referred to as BT (bis‐maleimide triazine). Triazine is the reaction product of the cyclotrimerization of bis‐cyanate during curing. For circuit board applications, a brominated epoxy resin was blended with BT to impact flame resistance. Resin cure was extensively investigated using a combination of thermoanalytical techniques (thermal analysis, heated cell infrared spectroscopy, and dynamic mechanical analysis). The ultimate glass transition temperature was found to be 240°C, which could only be obtained using cure temperatures above 225°C. At lower temperatures, the reaction does not reach full conversion, since the glass transition temperature of the curing network equals or slightly exceeds the cure temperature. Differential scanning calorimetry (DSC) indicates a minimum of two separate reactions. Fourier transform infrared spectroscopy provided more detailed information on the crosslinking reactions during cure. The onset of cyclotrimerization was found to start at 150°C, correlating with one of the peaks in the DSC. At higher temperatures, the epoxide reacts with the cyanate functionality forming oxazoline ring structures. It was not possible to unambiguously assign the origins of the high temperature peaks in the DSC. These high temperature peaks may be attributed to several reactions, including epoxy homopolymerization and polymerization of bis‐maleimide. The high temperature reaction mechanisms warrant further investigation.
Fiber orientation and its effect upon thermoelastic properties of short carbon fiber reinforced poly(etheretherketone) (PEEK)
Authors: Bozarth M. Jean , Gillespie John W. , McCullough Roy L.
Published: May 2005

Experimental and analytical techniques are employed in the present study to investigate the influence of microstructure on thermoelastic properties of short carbon fiber reinforced poly(etheretherketone). The test specimen geometry is an edge gated, injection molded dogbone tensile bar. Typical of injection molded structures, three distinct layers of fiber orientation were discernable through the sample thickness. The thermoelastic properties of the surface layer (machined from the specimen) are measured for direct correlation with a micromechanics model. In addition to measuring the volume fractions and constituent properties, microstructural features such as fiber aspect ratio and the process‐induced fiber orientation distribution are quantified. Correlation of experimental data with micromechanics model predictions is found to be quite good.
Experimental and analytical procedures for flow dynamics of sheet molding compound (SMC) in compression molding
Authors: Kau Hua‐tie , Hagerman Edward M.
Published: May 2005

A package of procedures have been developed to collect and analyze the response of dynamic variables such as pressure, temperature, and mold separation during the compression molding of Sheet Molding Compound (SMC). From the dynamic responses, the molding process was found to consist of two regions: the flow and the subsequent curing reaction region. With an R‐25 formulation and a mold closing rate of 30 mm/s, these two regions are well separated and the average flow time is not significantly affected by the maturation time for the material up to 30 days. Several mechanical parameters were estimated based on relatively simple flow models. The relationship between the press force, mold separation, and mold closing rate is found to be sensitive to the restrictions of the flow.
Cryogenic failure mechanisms of fiber‐epoxy composites for energy applications
Authors: Jang B. Z. , Lieu Y. K. , Chang Y. S. , Hwang L. R.
Published: May 2005

Fiber‐reinforced composites used in the production, storage, and transport of energy are often exposed to extreme environments such as cryogenic temperatures and/or nuclear radiation. The fraction resistance of composites subjected to these conditions are of fundamental interest. A study was undertaken to examine the effects of Gammaradiation on the structure and properties of fibers, matrix and their interfacial bonding in terms of their influence on composite failure mechanisms. Also thermomechanical analysis was conducted to estimate the residual thermal stresses due to differential thermal expansion coefficients both between fiber and matrix and between two laminae. Results indicate that the impact energy of a composite laminate could be increased by 100 percent by immersing the specimen in liquid nitrogen for only five min. Samples impact‐tested at cryogenic temperatures were found to possess a great degree of delamination and crack bifurcation. Thermomechanical analysis and SEM investigation both reveal that microcracking and small‐scale delamination are promoted by differential thermal contraction. Such effects could be responsible for the observed crack branching and delamination phenomena during impact loading. Although under certain circumstances the Gammaradiation may yield a small increase in fracture resistance it generally degrades the cohesive strength of the matrix and reduces the interfacial bonding between fiber and matrix. Results of a mechanical and microscopic analysis are presented and discussed.
Cellulose fiber‐polyester composites with reduced water sensitivity (2)—surface analysis
Authors: Hua Li , Flodin Per , Rönnhult Tore
Published: May 2005

The water absorption of cellulose fibers has been reduced after the cellulose surface was treated by mono‐ ordi‐methylomelamine(DMM) resin. The wet strength of cellulose‐polyester composites was also enhanced considerably. Scanning electron microscopy, transmission electron microscopy, and electron spectroscopy for chemical analysis were used as the tools for surface analysis in this study. The surface composition and micro morphology have been characterized. Qualitative and semiquantitative results have been obtained for the cellulose fiber surfaces treated with DMM.
The effect of sand surface treatment on sand‐filled composites
Authors: Rodriguez E. L. , Newaz G. M.
Published: May 2005

Sand/unsaturated polyester composites, 50/50 composition by weight, were prepared from sand treated with different silane solutions. N‐2‐aminoethyl‐3‐aminopropyl‐trimethoxy silane (A0700) and 3‐aminopropyltriethoxy silane (A0750) were used. Water and styrene solutions were employed to treat the sand. It was found that A0750 in styrene produced better composites than other surface treatments. As the interfacial bond was improved, the tensile strength and the tensile modulus increased whereas the strain to failure decreased. The acoustic emission data was a function of the sand surface treatment where a better interfacial bond resulted in more acoustic activity. Dynamic mechanical analysis showed that the interfacial bond affects the dynamic shear modulus, the loss shear modulus, and the damping of the sand‐filled composites. The glass transition temperature (Tg) of the composite was also affected by the surface treatment. The thermogravimetric analysis did not show a well‐defined trend between the decomposition temperature and the surface treatment.
Interfacial adhesion between ionic copolymers and high‐modulus surface‐treated carbon fibers
Authors: Belfiore Laurence A. , Shah Rakesh J. , Cheng Chihmin
Published: May 2005

High‐modulus carbon‐fiber‐reinforced thermoplastic composites typically fail at the interface due to poor adhesion between fiber and matrix. To increase interfacial strength, the research described herein focuses on modifying the fiber surface (via high‐temperature acid treatment or zinc electrolysis) to facilitate chemical functional groups on the fiber that might increase fiber‐matrix inter‐actions. The thermoplastic matrix materials used in this study were random copolymers of ethylene and methacrylic acid in which the carboxyl groups in the methacrylic acid segments were neutralized with either sodium or zinc counterions. Mechanical tests were performed to determine the macroscopic effects of fiber pretreatment on the ultimate mechanical properties of the composites. Fabrication was designed such that fiber‐matrix separation provides the dominant contribution to mechanical gracture. Composites containing fibers treated with nitric acid, or a mixture of nitric and sulfuric acids exhibit a 20 to 25 percent increase in transverse (tensile) fracture stress relative to composites fabricated with as‐received fibers. Scanning electron microscopy of the fiber‐matrix interface at fracture allows one to “zoom‐in” and obtain qualitative details related to adhesion. Fracture surface micrographs of the above‐mentioned acid‐treated fiber‐reinforced composites reveal an increase in the amount of matrix material that adhered to the fiber surface relative to the appearance of the fracture surface of composites fabricated with as‐received fibers. The presence of acid functionality in the matrix, rather than the divalent nature of the zinc counterions, produces the largest relative enhancement of transverse (tensile) fracture stress in the above‐mentioned composites containing surface‐treated carbon fibers.
Analytical solutions for fiber orientation in 2‐D flows of dilute suspensions
Authors: Eduljee R. F. , Gillespie J. W.
Published: May 2005

Analytical solutions for fiber orientation in dilute solutions are presented for both 2‐D planar and axisymmetric flow. The viscosity is assumed to be independent of position along the flow direction, but varies through the thickness of the mold cavity. For the particular case of a laminate of two fluids, an analytical solution is derived. Based upon the assumption that the fluid adjacent to the mold wall exhibits reduced viscosity due to non‐isothermal considerations, the fluid kinematics simplify, and an analytical solution to Jeffery's orientation equation is derived. Since the fiber orientation analysis is based on Jeffery's equation, it is valid only for dilute suspensions, i.e. for fiber volume fraction < 1/(fiber aspect ratio)2. Qualitatively, the analytical results obtained provide superior correlation with experimental results, indicating that non‐isothermal fluid flow may play an important role in the development of the fiber orientation distribution in the molded component.
Thermal and electrical properties of some epoxy based composites
Authors: Bánhegyi György , Szaplonczay Pál , Frojimovics Gábor , Karasz Frank E.
Published: May 2005

Thermally stimulated creep compliance, differential scanning calorimetric behavior, thermal degradation, AC dielectric permittivity and loss (between 120 Hz and 100 kHz) and thermally stimulated polarization and aepolarization currents were studied in a cycloaliphatic epoxy resin (B), in a conventional bisphenol‐A‐diglycidyl ester type epoxy resin (C) and in composites consisting of: resin B/wollastonite (B/W), resin B/quartz (B/Q) and resin C/wollastonite (C/W). The filler content was 60 wt%. Resin B exhibited higher Tg and lower rubbery deformability than resin C due to its more compact structure. Fillers reduced the rubbery deformation and thermal expansion and shifted the transition temperatures by a few degrees. The shift depended on the method used. Composites B/W and C/W exhibited higher thermal stability than the corresponding pure resins, while sample B/Q was less stable than resin B. Resins B and C exhibited a low temperature β transition (in the case of resin B a doublet) and a high temperature α or glass transition. AC dielectric losses were fairly similar in samples B and B/W, while the high temperature loss of sample B/Q was determined by a space charge process probably due to the matrix/filler interface. In samples C and C/W the α transition is visible but it is superposed on a strong space charge process due to the resin/electrode interface. Thermally stimulated currents show a behavior qualitatively in agreement with the AC results but the very low effective frequency and the nonlinear field strength dependence of the space charge processes cause some minor differences.
Determination of matrix crystallinity of composites by X‐ray diffraction
Authors: Spahr D. E. , Schultz J. M.
Published: May 2005

Determination of the degree of crystallinity of the matrix of polymer matrix composites by wide‐angle X‐ray diffraction is discussed. An extensive theoretical review is given, and many of the practical difficulties are also discussed. Poly(aryl ether ether ketone)‐carbon fiber composites are used as example materials. It is shown that although wide‐angle X‐ray diffraction is potentially useful for unoriented samples, there are practical and theoretical difficulties in applying the technique to highly oriented materials.
An integrated methodology for optimizing the passive damping of composite structures
Authors: Saravanos D. A. , Chamis C. C.
Published: May 2005

A method is presented for tailoring plate and shell composite structures for optimal forced damped dynamic response. The passive damping of specific vibration modes is optimized with respect to dynamic performance criteria including placement of natural frequencies and minimization of resonance amplitudes. The method provides the capability to tailor micromechanics, laminate and structural parameters. Application studies include the optimization of laminated composite beams and composite shells with fiber volume ratios and ply angles as design variables. The results illustrate the significance of damping tailoring to the dynamic performance of composite structures and the effectiveness of the method in optimizing the structural dynamic response.
Polypropylene/low density polyethylene blend matrices and short glass fiber based composites. III: Morphology and fiber orientation
Authors: Ramos M. Arroyo , Belmontes F. Avalos
Published: May 2005

The morphology of short glass fiber reinforced composites based on polypro‐pylene/low density polyethylene (PP/LDPE) blend matrices was investigated by means of an optical microscope as a function of both matrix composition and fiber content. The influence of compounding and processing methods was also studied. The LDPE content hardly affects the morphology of the blends, at least within the range of percentages that have been investigated (5 and 10% by weight). On the other hand, glass fibers obstruct the matrix spherulitic development. The blend morphology is strongly affected by the processing method and the compression molded blends show larger spherulitic size than the injection molded ones. Scanning electron microscopy showed the fiber orientation across the injection molded composites.
Analysis of resin injection molding in molds with preplaced fiber mats. II: Numerical simulation and experiments of mold filling
Authors: Young W. B. , Rupel K. , Han K. , Lee L. James , Liou Ming J.
Published: May 2005

This work presents the results of numerical simulation and experimental visualization of the mold filling process in resin injection molding with preplaced fiber mats. The mold filling experiments were conducted with various mat stacks consisting of continuous random glass fiber mats and bidirectional stitched glass fiber mats. The use of two different mat types in the mat stack created porosity and permeability variations. The effect of these permeability variations was studied by taking flow pressure measurements and observing the progress of the flow front of a non‐reactive fluid filling a clear acrylic mold that contained the reinforcement mat stack. Numerical simulation corresponding to each experiment was also carried out. The numerical results were compared to the experimental measurements.
Processing parameters for consolidating PEEK/carbon fiber (APC‐2) composites
Authors: Colton J. , Muzzy J. , Birger S. , Yang H. , Norpoth L.
Published: May 2005

This consolidation of unidirectional APC‐2 was studied experimentally to determine the effects of processing parameters (pressure, temperature, and number of layers) on resin flow as measured by the Kozeny constant and the bulk modulus. The Kozeny constant obtained was between 0.0205 and 0.107. It was found to depend on the consolidation pressure, temperature, number of layers, and their interactions at a 99% confidence level. The value of the bulk modulus was found to be between 1.21 MPa (175 psi) and 8.58 MPa (1244 psi). It also was found to depend on the temperature, pressure, number of plies, and their interactions at a 99% confidence level. These results show the critical effects of fiber orientation on resin flow during processing.
Processing of poly(ethersulfone)/graphite fiber composites: Thermooxidation, rheology, and consolidation
Authors: Brauman S. K. , Chow A. W.
Published: May 2005

This study relates the formability of thermoplastic poly(ethersulfone) HTA composites to thermooxidative history and rehological behavior. HTA/IM8 graphite fiber performs were prepared under various temperature, time, and environmental (unbagged and vacuum‐bagged) conditions, then consolidated into finished laminates under identical conditions. X‐ray photoelectron spectroscopy and pyrolysis/gas chromatography/mass spectrometry were used to assess chemical degradation, and dynamic mechanical analysis (DMA) was used to evaluate Tg and rheological behavior in the finished laminates. All performing conditions resulted in some degradation of the HTA matrix, the presence of air being especially detrimental. The nature of this degradation is discussed and related to changes in Tg., melt viscosity of the matrix resin, and the extent of consolidation. A new DMA approach to evaluating degree of consolidation is developed and shown to offer considerable promise for quantitative assessment and ranking of composites.
Development of a thin film technique for an amorphous metallic ribbon/thermoplastic matrix composite system
Authors: Sidhu A. S. , Varin R. A. , Wronski Z.
Published: May 2005

A thin film method is developed for the fabrication of an amorphous metallic ribbon/PP (polypropylene) matrix composite system. The interfacial shear strength of composites fabricated with thin film is 0.52 ± 0.09 MPa (process B), which is comparable to that of the sandwich method of composite fabrication reported recently. The optical micrographs of the interfacial zone appear to be defect free and there are no visible voids, cracks, or air entrapment during fabrication. This qualitative analysis of the ribbon/matrix interface suggests that thin film can provide a better interfacial bond, a result which is supported by the results of pullouts tests. The composite fabrication time using the thin film method is short, and this method therefore has the potential to produce composites at a high volume fraction of ribbon reinforcements as compared to the sandwich method.
The silane/sizing composite interphase
Authors: Al‐Moussawi Hassan , Drown Edward K. , Drzal Lawrence T.
Published: May 2005

Silane coupling agents are but one of many ingredients in commercial sizings that are applied to glass fibers. The chemistry of a silane coupling agent alone allows it to react with both the glass fiber surface and the epoxy matrix to increase the fiber/matrix adhesion. However, the action of a commercial sizing system containing a silane coupling agent along with other components is not well understood. Research has been conducted in which the physical properties have been measured of blends of epoxy‐compatible silane/sizing made with bulk matrix at concentrations representing likely compositions found at the fiber‐matrix interphase as a result of processing and fabrication. It has been shown that the silane/sizing interaction with the epoxy matrix produces a material with vastly different properties than those of the bulk matrix. In this particular system, the model interphase has a lower Tg higher modulus, and greater tensile strength, but lower toughness. The results from the present study show that a themical interaction theory of adhesion alone is not sufficient to explain the role of silane coupling agents in glass fiber‐epoxy matrix adhesion. Consideration must be given to the interphase and its mechanical properties.
Hydrothermal effects on the physico‐chemical properties of pure and glass fiber reinforced polyester and vinylester resins
Authors: Ghorbel I. , Valentin D.
Published: May 2005

The effect of aging by immersion in water at 60°C on polyester and vinylester resins, unreinforced and reinforced with glass fibers, was investigated. Changes in weight, glass transition temperature, secondary relaxations, and storage modulus, as well as loss modulus were measured, and the environmental effects on these parameters were assessed. Moreover, the chemical structure changes of the materials during aging were studied by the use of IR spectra. The evolution of the physico‐chemical and the mechanical properties as a function of the aging time was established. The results indicate the importance of the matrix morphology, the structure regularity, the presence of the fibers on the water diffusion mechanisms, and the thermomechanical properties through gravimetric changes, DSC, DMA and IR experiments.
Prepreg process analysis
Authors: Ahn K. J. , Seferis J. C.
Published: May 2005

A description of the hot‐melt prepreg process was developed by coupling resin matrix flow at the coating and impregnation zones with heat transfer considerations. Both bismaleimide (BMI) and epoxy resin systems were used as matrices. With continuous carbon fiber reinforcement. For the laboratory scale prepregger utilized in this study, the thickness of the resin film produced in a doctor blade was approximately 63% of the blade distance, showing good agreement with experimental data. In addition, the measured heat transfer coefficient between prepreg and atmosphere indicated that surface convective resistance is large compared to the internal conductive resistance and thus the chill plate in the prepregging operation plays on important role in determining prepreg quality. By formulating an analytical methodology in terms of the “Prepreg Flow Number” (PFN) that combined important operating parameter (e.g., temperature, pressure, and production rate), a temperature‐pressure‐velocity superposition was confirmed for the prepregging process. In addition, the model could easily be extended to different scales and types of prepregging processes with the aid of dimension‐less parameters that are quite descriptive of the operating conditions employed in prepreg manufacturing.
Evaluation of polybutene electrofusion joint performance
Authors: Nishimura Hiroyuki , Nakashiba Akio , Kawakami Ryuichiro , Inoue Fumio , Inoue Toshio , Oshimo Shinzaburo
Published: May 2005

This paper describes methods of evaluating polybutene electrofusion joints and results of mechanical strength measurements for an electrofusion joint. Suitable fusion conditions were determined qualitatively through measurement of fusion interface temperatures and observation of the fusion zone. A method of determining standard fusion conditions, based on the relation between heating time and tensile strength, is also indicated. Differences in thermal properties between polybutene and polyethylene resins are discussed. It was found that polybutene required less supplied power per unit fusion area for suitable fusion. It was also confirmed that an electrofusion joint required a cold zone.
Crystallization and chain adsorption of poly(etheretherketone) in discontinuous pitch‐derived carbon fiber composites
Authors: Jonas Alain , Legras Roger
Published: May 2005

The crystallization kinetics of poly(etherether ketone) (PEEK) in chopped mesophase pitch‐derived carbon fiber/PEEK composites have been studied. Various processing techniques are used in order to obtain controlled fiber length in the composites. Scanning electron microscopy performed on properly etched long fiber composite samples reveals that the nucleating sites density is low at the carbon fiber surface: transcrystalline layers are rarely observed. This is confirmed by differential scanning calorimetry. However, samples processed by mixing carbon fibers and molten polymer in a high temperature mixer have a widely different behavior: the nucleation density and the crystallization rate increase, the glass transition of these samples is displaced towards higher temperatures, and the solubility is dramatically lowered. We ascribe these phenomena to the adsorption of the polymer chains on carbon particles created by attrition during the mixting.
Numerical simulation on the permeability variations of a fiber assembly
Authors: Cai Zhong , Berdichevsky Alexander L.
Published: May 2005

Finite element simulations on permeability variations of an aligned fiber assembly have been conducted. Two dimensional viscous flow in longitudinal and transverse directions has been studied respectively, using the steady state Navier‐Stokes equation but with small Reynolds numbers. Two groups of packing structures are investigated, both with introduced disturbances in the fiber assembly. One is the idealized packings, including hexagonal and square packings, but with selected fibers removed randomly, and with fiber center positions disturbed randomly. This gives random effect within the modeled cells, but on the macro‐scale the structure is still periodic. Numerical simulations are performed using available finite element packages. The result shows clearly that different physical mechanisms doninate the flow process in longitudinal and transverse permeabilities in the longitudinal flow case, the disturbance introduces openings within the bundle, and these openings become between fibers. Thus flow resistance increases substantially in the idealized packing cases. Numerical data are then compared with available data from other studies, particularly that from using self‐consistent methods.
Evaluation of test methods in the determination of in‐plane shear modulus of poly(phenylene sulfide) matrix composites
Authors: Shih Gary G. , Tseng Wen W. , Lou Alex Y.
Published: May 2005

An investigation was conducted to evaluate the validity of various test methods in the dtermination of in‐plane shear moduli of semicrystalline, poly(phenylene sulfide) (PPS) thermoplastic composites. Materials studied included composites based on an orginal, non‐optimized composite grade of PPS reinforced with carbon and glass fibers, and another based on the new improved, high‐ductility, rapid crystallizing, composite grade of PPS along with optimally sized glass fiber reinforcement. Specimens were prepared in a matched die mold, either as‐molded or annealed. It was found that shear test methods, such as ±45° in plane, Iosipescu, and 45° pff‐axis tension, are validfor shear modulus measurements of PPS composites if the material has no internal stress cracks. For example, there was no significant difference for in‐plane shear moduli determined from these three shear testsw for the improved, thoughened PPS composites. This was attributed to the thoughness and fast crystallization of the PPS composites. This was attributed to the thoughness and fast crystallization of the PPS matrix resin, and the strong fiber/maxtrix interface, however, the ±45° in‐place shear test should be used with caution for certain thermoplastic composites,. Becuase of the ±45° lay‐up, the annealed[±45]2s original PPS composite la, omates siffered jogj resodia; stresses and were observed to have stress‐related cracks. Consequently, the measured shear moduli are lower than the true values. Since we have demostrated that some shear tests amy not be appropriate for modulus measurements of certain composites, it is important to choose the proper test method for the shear characterization of thermoplastic composites.
Microstructure‐based processing parameters of thermoplastic composite materials. Part II: Experimental results
Authors: Yang Heechun , Colton Jonathan S.
Published: May 2005

The permeability of termoplastic composites and the elastic behavior of their fiber networks were measured during compression molding. As these processing parameters depend on the microstructure of the composite, experiments were performed to determine them for tape prepreg, commingled two repreg, and powder‐coated tow prepreg. The experimental results agree closely when compared to the theoretical predictions.