bluuebunny/crossref_metadata_2025_split huggingface dataset:
Development and evaluation of surface teratmetns to enhance the fiber‐matrix adhesion in PAN‐based carbon fiber/liquid crystal polymer composites. Part II: Electrochemical teatments
Authors: King Julia A. , Buttry Daniel A. , Adams Donald F. 
Published: May 2005

AbstractVarious electrochemical surface treatments, designed to improve the fiber‐matrix adhesion, were applied to commingled as‐received continuous AS4 carbon reinforcing fiber/liquid crystal polymer (LCP) matrix fibers. Unidirectional composite plates (norminally 60 vol% carbon fiber) were fabricated and short beam shear (SBS) tests were conducted to provide an indication of the effect of the treatments on AS4 carbon fiber‐LCP matrix adhesion. The mean SBS strength of the as‐received AS4/LCP system was 49 MPa. Three elecrtrochemically polymerized coatings‐poly‐para‐phenylene (PPP), polyphenylene oxide (PPO), and polyaniline (PA)‐were applied. Only the PPO coating, however, had a beneficial effect on the composite shear strength. The coating enhanced the shear strength by 14% relative to the as‐received AS4/LCP system. Scanning electron Microscope (SEM) observations of the PPO treated shear failure surface indicated the presence of a strong fiber‐matrix bond. That is, the failure location was in the LCP matrix material.
An improved self‐consistent method for estimating the permeability of a fiber assembly
Authors: Cai Z. , Berdichevsky A. L. 
Published: May 2005

AbstractThis paper presents an improved self‐consistent method for estimating the permeability of an aligned fiber assembly, in both longitudinal and transverse directions. In this method an insertion is assumed to include open space surrounded by densely packed fibers. This improvement allows us to describe effectively the permeability of dense structures containing distributed voids. As used in self‐consistent methods, the insertion is placed into a homogeneous medium with an unknown permeability. Stokes flow and Darcy flow are then considered, respectively, at different regions. Boundary and interface conditions as well as two consistency conditions, including the total amount of the flow and the dissipation energy, are applied accordingly. The permeability is solved from these considerations. This improved permeability model captures the flow characteristics of a fiber bundle. In the longitudinal flow case, the openings within a bundle due to disturbance dominate the flow path. In the transverse flow case, the gaps between neighboring fibers govern the flow resistance. The derived expression for the transverse permeability contains two variables, the averaged fiber volume fraction and the maximum packing efficiency, which adequately describe the status of a fiber bundle. These two variables can also be measured experimentally. The predictions agree with available data reported. The result for the longitudinal flow shows not only the influence of these two parameters, but also the very strong effect of the openings within the bundle on the permeability. This explains the significant differences between the data of idealized packings, such as square and hexagonal packing, and those measured from real fiber bundles. The comparison also provides an estimation of the average opening sizes within a fiber bundle as a function of fiber volume fraction. Numerical simulation results of previous studies are also used to verify this approach.
Epoxy polymer modification with metals
Authors: Kurnoskin A. V. 
Published: May 2005

AbstractThe modification of epoxy polymers with some metal cations, viz., Zn2+, Fe3+ and Mn4+, has been studied. These cations were introduced into the epoxy matrices by hardening of diglycidyl ether of bisphenon‐A with the chelates of the metal salts with some aliphatic amines. Studies center on the dependence of the mechanical strength and heat resistance of the metal containing epoxy polymers with Zn2+ and Fe3+ increases the strength and heat resistance significantly. These metal‐containing hardeners have excellent processability and can be used to produce high strength and high thermal resistance thermosets.
Preparation and properties of optically transparent, pressure‐cured poly(methacrylate) composites
Authors: Weaver Kevin D. , Stoffer James O. , Day Delbert E. 
Published: May 2005

AbstractThe objective of this work was to develop optically transparent glass fiber reinforced poly(methyl methacrylate) (PMMA) composites by matching the refractive index of the glass fiber reinforcement to that of the PMM, A matrix, thereby minimizing the quantity of light which is normally scattered and reflected at the interface of dissimilar materials. A pressure curing process is described for preparing composites 10 by 15 by 0.6 cm thick and containing up to ∼ 35% glass fiber. By curing at 65°C under 6.9 MPa N2 for 18 H, composites have been produced with optical quality surfaces and flexural strengths more than seven times that of commercial PMMA of the same thickness. A transparent composite containing 10.4 vol% of 13 μm diameter fiber had an 84% optical transmission (92% maximum for PMMA) at 600 nm and 25°C.
Modeling resin transfer molding of polyimide (PMR‐15)/fiber composites
Authors: Chan Albert W. , Hwang Sun‐tak 
Published: May 2005

AbstractPolyimide (PMR‐15)/fiber composites are important structural components in many high temperature applications requiring high performance lightweight materials. Most composites are fabricated from “prepregs,” but resin transfer molding (RTM) is an alternative route to the formation of a resin‐saturated perform, further processing of which yields the final part. A simple model is proposed for the RTM of “thin” composite parts. Numerical solution of the model is accomplished through integration of the equation s formulated using he finite element method. This approach accounts for the changing shape of the flow front during RTM. The resulting computational schemes are numerically stable and efficient.
The development of an epoxy resin system for the injection molding of long‐fiber epoxy composties
Authors: Ishida H. , Zimmerman D. A. 
Published: May 2005

AbstractThe Combination of reaction injection molding and pultrusion has resulted in a new processing technique, RIM‐Pultrusion, Which has been used to produce a thermoplastic epoxy prepreg. This prepreg has been used to produce a long‐fiber injection molded phenoxy/carbon fiber composite with near‐Zero void content. A heat‐activated curing system has been developed, which allows injecton molding of the prepreg to form a thermostet long‐finer epoxy/carbon finber composite. The RIM‐ pultrusion conditions for producing an injection moldable prepreg are described. Capillary rheomety is used to study the epoxy resin to determine the proper molar ratio for RIM‐Pultrusion. The long‐fiber epoxy compostie is analyzed with dynamic mechanical analysis (DMA) and Fourier transform infrared spectroscopy (FTIR). Also., the impact strength and solvent resistance of the long‐fiber composite are examined. The properties of the thermoset long‐fiber epoxy xomposite are compared to those of a thermoplastic injection molded long‐fiber phenoxy composite.
The fracture behavior of rubber‐toughened, short‐fiber composites of nylon 6,6
Authors: Pecorini T. J. , Hertzberg R. W. 
Published: May 2005

AbstractThis study critiques the use of both rubber particles and short‐glass fibers for the improvement of polymer fracture toughness (Kc). Although dry neat nylon is brittle with only a moderateKcvalue (4.2 Mpa√m), additions of either second phase produce risingKR‐curves and associated highKcvalues (8.1 Mpa√m for rubber‐toughened nylon, and 10.0Mpa√m for 17 vol% Glass‐fiber neat nylon). In the rubber ‐modified resin, the highKcvalue is associated with extensive plastic blunting at the crack tip. In the fiber‐reinforced neat resin,Kcis improved due to a combination of fiber‐bridging and increased strength, the latter being associated with additional load carrying capacity of the fibers. When both rubber and fibers are added, however, no further increase inKcis noted (Kc= 9.3 Mpa√m for 17 vol% glass‐fiber rubber‐modified nylon). The extent of ductile blunting in the rubber + fiber resin is not as great as in the rubber‐only resin. Furthermore, the fracure strength of the rubber + fiber resin is not as high as the fiber‐only resin. The net result is a balance of properties for the rubber‐toughened composite.
The devolatilization of polyimide fiber composites: Model and experimental verification
Authors: Yoon In Seon , Yang Yubo , Duduković Milorad P. , Kardos John L. 
Published: May 2005

AbstractA one‐dimensional devolatilization model is developed for autoclave processing of themroplastic polyimide, graphite‐reinforced, composites. The model rests on the assumption that continous gas passages are formed during processing due to partical crystallization of the polymer in the course of polymerization. Both DSC and optica microscopy indicate that crystallinity develops in the Avimid‐III polyimide resin during polymerization, which in turn facilitates formation of cracks. These cracks heal upon removal of volatiles and polymer melting. Model‐Calculated temperature profiles in the laminate during polymerization, and the predicted removal rates of volatile species (water, ethanol, NMP) are compared to experimental miniautoclave data for the DuPont Avimid K‐III/IM6 system. Good agreement is obtained when the volumetric mass transfer coefficient required by the model is assumed to vary proportionally to the inverse of the changing resin viscosity. The model allows the investigation of desired cure cycle parameters for different laminate thicknesses.
Interfacial toughness and its effect on compression strength in polycarbonate/carbon fiber composites
Authors: Stone Paul R. , Nairn John A. 
Published: May 2005

AbstractProcessing Polycarbonate/carbon fiber composites for long times at high temperatures significantly improved adhesion between the matrix and the fibers. The interfacial properties were studied by measuring transverse fracture toughness, observing fracture specimens by scanning electron microscopy, and by monitoring composite cross‐sections using atomic force microscopy. The processing treatment provided an ideal method for varying the properties of the interface without changing any other properties. We used this method to study the effect of interfacial properties on the axial compression properties of unidirectional composites. Both the compression strength and compression modulus increased significantly as the fiber/matrix adhesion improved. We concluded that improving interfacial adhesion increased compression properties by inhibiting fiber microbuckling.
Self‐reinforced thermoplastic‐LCP prepregs and laminates
Authors: Isayev A. I. , Joldengreber Y. , Viswanathan R. , Akhtar S. 
Published: May 2005

AbstractSelf‐reinforced sheets (prepregs) have been prepared by stretching extruded sheets made of thermoplastic (TP) and a thermotropic liquid crystalline polymer (LCP) blend. The sheets are formed by extrusion through a coathanger die, device. Processing at this stage is done at a temperature at which both components in the blend are melt processable. These prepregs are laid up in multi‐layers in a direction parallel to the stretching direction or in the direction of 45° with respect to each previous layer. The lay‐ups are compression molded into unidirectional or isotropic laminates at temperatures below the melt processing temperature of the LCP. Various pairs of TP and LCP have been studied. These include polypropylene and an LCP based on p‐oxybenzoyl, terephthaloyl and hydroquinone moieties, polyphenylene oxide (PPO) and polystyrene/PPO alloy and a LCP based on 6‐oxy‐2‐naphthoyl and p‐oxybenzoyl moieties. Mechanical properties of the prepregs and laminates were measured and compared with those obtained from injection molded samples. Surprisingly, tensile strength and modulus of isotropic laminates are found to be higher than those of injection molded samples in the flow direction. Morphlogical studies of the prepregs and laminates indicate the presence of well‐defined LCP fibers in various thermoplastic matrices.
Coating carbon fibers with a thermoplastic polyimide using aqueous foam
Authors: Chary Rajendran R. , Hirt Douglas E. 
Published: May 2005

AbstractMany techniques have been developed to coat carbon fibers with thermoplastic resins to form a prepreg. These techniques include melt impregnation and solution/slurry coating. The applicability of these techniques, however, may be restricted by high melt viscosities or significant drying times. Recent emphasis has been towards a dry powder coating technique using a fluidized bed. This technique may be limited by difficulties in fluidization of the polymer powders. To overcome these difficulties, a technique has been developed to continuously coat carbon fibers with thermoplastic resins using aqueous foam as a carrier medium. The polymer is slurried in a surfactant solution, into which air is dispersed using a foam‐generating device. A predetermined amount of this foam is then applied to a moving carbon fiber tow using a foam application unit. The tow is then pulled through ovens where the foam is collapsed and the power fused to the fibers. Other aspects that are addressed include the stability of foams in the presence of powders, the mechanical properties of the composites formed using foam prepregging, and the effect of surfactant on composite properties.
Permeability characterization. Part 1: A proposed standard reference fabric for permeability
Authors: Parnas Richard S. , Howard J. Grant , Luce Thomas L. , Advani Suresh G. 
Published: May 2005

AbstractA three‐dimensionally woven fabric is proposed as a standard reference material for permeability characterization. The 3‐D woven fabric requires care in cutting and handling, although it is more robust than 2‐D woven or braided fabrics. If prepared carefully, the permeability of the 3‐D woven fabric can be measured reproducibly within 15% in either radial flow or saturated 1‐D flow geometries. The material was characterized for permeability in radial, unsaturated and saturated 1‐D, and through‐thickness flow geometries. The transient results demonstrated the importance of structural heterogeneity on the unsaturated flow behavior, and agree qualitatively with a simplistic model of flow in heterogeneous unsaturated porous media. The effects of heterogeneity were manifested in the proposed SRM by an increasing trend in the “unsaturated permeability.” Experiments were also conducted with a random mat that displayed transient flows dominated by wicking. The effects of wicking on the macroscopic flow behavior were manifested by transients in the “unsaturated permeability” in which a decreasing trend was observed.
Permeability characterization. Part 2: Flow behavior in multiple‐layer preforms
Authors: Luce Thomas L. , Advani Suresh G. , Howard J. Grant , Parnas Richard S. 
Published: May 2005

AbstractWithin the resin transfer molding (RTM) process, flow is generally characterized by the progression of a distinct, nonuniform flow front into the preform as a function of time. The flow front progression introduces unsaturated characteristics into RTM flow fields. As a result, the definition of an effective in‐plane permeability (Keff) is used to determine the permeability of actual preforms as they fill with fluid. This Keff expression expands upon the original definition of Darcy's law by generalizing its applicability to unsaturated creeping flows. Results of experimentally obtained Keff for flow in single‐layer preforms have been detailed for two common RTM materials, a random mat and a 3‐D weave, in Part 1. In this paper (Part 2), we characterize the unsaturated and saturated permeabilities of multiple‐layer preforms constructed from the random mat and 3‐D weave materials characterized in Part 1. This work identifies the apparent permeability characteristics of a specific unsaturated multiple‐layer flow that demonstrates behavior inherent to this important class of heterogeneous flows. Also, parallels are drawn between the unsaturated permeability behavior of complex 3‐D weave materials and multiple‐layer preforms.
Thermal dispersion in resin transfer molding
Authors: Dessenberger Richard B. , Tucker Charles L. 
Published: May 2005

AbstractThis investigation focuses on the effects of thermal dispersion in resin transfer molding (RTM). A set of volume‐average balance equations suitable for modeling mold filling in RTM is described and implemented in a numerical mold filling simulation. The energy equation is based on the assumption of local thermal equilibrium and includes a dispersion term. Thermal dispersion is an enhanced transport of heat due to local fluctuations in the fluid velocity and temperature away from their average values. Nonisothermal mold filling experiments are performed on a center‐gated disk mold to investigate and quantify dispersion effects. Good agreement is found between the experimentally measured and numerically predicted temperatures, and a function for the transverse dispersion coefficient in a random glass fiber mat is determined. The results indicate that thermal dispersion is important in RTM processes and must be included in simulations to obtain accurate predictions.
The effect of pyrolysis on the properties of stabilized PAN fabric reinforced phenolic resins for 2D carbon/carbon composites
Authors: Ko Tse‐Hao , Jaw Juu‐Jiuh , Chen Ying‐Chie 
Published: May 2005

AbstractTwo‐dimensional (2D) carbon/carbon composites were prepared with phenol‐formaldehyde resin and a commercial stabilized PAN fabric. The effect of pyrolysis on the microstructure and flexural strength of the composites during the carbonization process was studied. The interaction between fabric and matrix inhibited the decomposition and the thermal fragmentation, leading to a higher carbon yield for the final composition. Because of the formation of strong bonding in the fiber/matrix interface, the composites made with stabilized PAN fabric showed catastrophic failure and low flexural strength below carbonization temperatures of 600°C. Above 600°C, the flexural strength of the composites increased with the increase in the carbonization temperatures, even when the fracture behavior showed catastrophic failure.
Electroconductive nylon 6 and copper composites
Authors: Larena Alicia , Pinto Gabriel 
Published: May 2005

AbstractA study is reported on the effect of the filler size and concentration on the electrical resistivity, density, and hardness of composites made of copper powder embedded in nylon 6 matrix by means of compression molding. The electrical resistivity of the composites is > 1011ohm·cm unless the metal content reached the percolation threshold, beyond which the resistivity decreased markedly by as much as 1012. The percolation concentration was found to decrease with a decrease in the average particle diameter. The density of the composites was measured and compared with values calculated assuming different void levels within the samples. However, there is no sharp variation in the density due to the onset of percolation. Furthermore, it is shown that a percolation concentration can be also defined in the hardness/metal concentration curves as the intercept of linear regression curves of thelowandhighmetal content regimes, respectively.
Interfacial shear strength studies of nicalon fibers in epoxy matrix using single fiber composite test
Authors: Ho A. , Netravali A. N. , Phoenix S. L. 
Published: May 2005

AbstractInterfacial properties of Nicalon (SiC) fiber in epoxy matrices of varying stiffnesses were studied using the single fiber composite test, in conjunction with stress birefringence patterns. Extensive debonding was observed with hard epoxies, but transverse matrix cracks were found in the more flexible epoxies, with the interface remaining intact. Micromechanical modeling and Monte Carlo simulation of the single fiber composite fragmentation process provided a basis to compute the interfacial shear stress from the final fragmentation length distribution. The interfacial shear stress appeared to decrease moderately with increasing matrix ductility. The large diameter Nicalon fibers create transverse cracks in the single fiber composite specimens made with flexible epoxies. Consequently, there is a high possibility of premature failure of the specimen before fiber break saturation is reached. This poses some difficulty in interpreting the results for flexible epoxies. It was also found that the interfacial shear stress values from the single fiber composite tests were always considerably higher than the ultimate shear stress values obtained from bulk epoxy (without fiber) tension tests. This effect is similar to what was seen earlier for single fiber composite tests based on graphite fibers and similar epoxy blends, though the difference between the two values was not as great.
Crystallinity in high polymers and copolymers: A determining factor for their practical applications
Authors: Natta Giulio 
Published: May 2005

AbstractThe relationships between crystallinity and physical and technological properties of high polymers are examined. In addition, the relationships between structure and crystallinity are discussed and polymers consisting of asymmetric monomeric units are examined in particular. In correspondence with the different possible configurational successions, different conformational characteristics (chain structures) and different physical properties are observed. Polytactic polymers are taken into consideration for the most part. With regard to copolymers, various types of crystalline polymers, in particular those which due to isomorphism of monomeric units are crystalline for any composition, and new classes of alternating copolymers are described.
Fire‐retardant components of self‐extinguishing polyesters
Authors: Roberts Carleton W. 
Published: May 2005

AbstractAn attempt has been made to categorize the various materials which have been utilized in polyester compositions to impart or enhance the fire‐retardancy of these compositions. Examples of halogen‐containing and phosphorus‐containing compounds are classified according to where they may be thought to occur in the complex chemical structures which are polyesters. The classifications are basically designed to take advantage of the known chemical reactions which lead to polyesters; the fire‐retardant component may be incorporated into the final composition in the diacid, diol, crosslinking agent or may be merely mechanically added as a diluent.
The interpretation of tacticity measurements
Authors: Miller Robert L. 
Published: May 2005

AbstractTo date, quantitative stereochemical data are available for a few polymers only. A convenient and graphic representation of this data has been developed. Analysis of this data yields two parameters characterizing a polymer, one representing the tacticity and the other representing the nature of the tactic sequence distribution. The statistical parameters obtained may be related to the polymerization conditions and, hence, to the mechanism of stereoregulation. Furthermore they may be related to a number of physical properties, such as melting point, equilibrium crystallinity, and melting curve. Thus, the proper analysis of the NMR data supplies a link between polymerization conditions and the properties of the resulting polymer.
Analysis of pressure transducer data from screw extruders
Authors: McKelvey James M. , Wheeler Norton C. 
Published: May 2005

AbstractBased on the simplified, flat‐plate, isothermal, Newtonian flow model of the screw pump, an expression for pressure as a function of time at a fixed point on the extruder barrel has been derived. This expression predicts a periodic saw tooth pressure cycle under most flow conditions. It also establishes the flow conditions under which an inversion of the saw tooth cycle will occur. Pressure transducer data, in conjunction with extrusion rate data, can be used to calculate the average fluid viscosity in a region near the transducer.