bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synergistic effect of carbon fillers in electrically conductive nylon 6,6 and polycarbonate based resins
Authors: Clingerman Matthew L. , Weber Erik H. , King Julia A. , Schulz Kirk H. 
Published: April 2004

AbstractThe electrical conductivity of polymeric materials can be increased by the addition of carbon fillers, such as carbon fibers, carbon black, and synthetic graphite. The resulting composites could be used in applications such as electromagnetic and radio frequency interference shielding and electrostatic dissipation. A significant amount of work has been conducted varying the amount of single conductive fillers in a composite material. In contrast, very limited work has been conducted concerning the effect of combinations of various types of conductive fillers. In this study, three different carbon fillers were used: carbon black, synthetic graphite pareticles, and pitch based carbon fiber. Two different polymers were used: nylon 6,6 and polycarbonate. The goal of this project was to determine the effect of each filler and combinations of different fillers on the electrical conductivity of conductive resins. A 23 factorial design was analyzed to determine the effects of the three different carbon fillers in nylon 6,6 and polycarbonate. The results showed that carbon black caused the largest increase in composite electrical conductivity. The factorial design analysis also showed that combinations of different carbon fillers do have a positive synergistic effect, thereby increasing the composite electrical conductivity.
Thermal diffusivity of lead titanate/polyvinylidene fluoride‐trifluoroethylene nanocomposites by the mirage method
Authors: Aravind M. , Ong C. W. , Chan H. L. W. 
Published: April 2004

AbstractThermal diffusivity D of lead titanate/polyvinylidene fluoride‐trifluoroethylene {PT/P(VDF‐TrFE)} nanocomposites has been measured by the skimming configuration of the mirage method. Diffusivity values are calculated by measuring the phase variation of the probe beam deflection signal upon changing both the vertical and horizontal probe beam offset values at different modulation frequencies of the pump beam. The thermal diffusivity of the nanocomposites is found to depend on the volume fraction of the ceramic in the composites. The composites with higher volume fraction of ceramic have higher thermal diffusivity and conductivity. Different models were used to predict the thermal conductivity (k) of composites and the measured values agree quite well with the Looyenga model.
Electrical properties of composites of hard metal carbides in a polymer matrix
Authors: Vilčáková Jarmila , Sáha Petr , Hausneroná Berenika , Quadrat Otakar 
Published: April 2004

AbstractThe electrical conductivity of composites containing hard metal carbide powder in a nonconducting polymer matrix has been studied. In composites with low and medium filler contents, the expansion of the nonconducting matrix with increasing temperature caused interruption of conducting paths and a rapid drop in conductivity (switching effect). In contrast, at high filler loadings (ΦP > 50 vol%), a continuous and slight decrease in conductivity with temperaute inducates a specific composite structure with a dense particle arrangement and a great number of conducting contants, which change only little during heating.
Mechanical properties of Al2O3/polymethylmethacrylate nanocomposites
Authors: Ash Benjamin J. , Rogers Diana F. , Wiegand Christopher J. , Schadler Linda S. , Siegel Richard W. , Benicewicz Brian C. , Apple Tom 
Published: April 2004

AbstractAlumina/polymethylmethacrylate (PMMA) nanocomposites were produced by incorporating alumina nanoparticles, synthesized using the forced gas condensation method, into methylmethacrylate. The particles were dispersed using sonication and the composites were polymerized using free radical polymerization. At an optimum weight percent, the resulting nanocomposites showed, on average, a 600% increase in the strain‐to‐failure and the appearance of a well‐defined yield point when tested in uniaxial tension. Concurrently, the glass transition temperature (Tg) of the nanocomposites dropped by as much as 25°C, while the ultimate strength and the Young's modulus decreased by 20% and 15%, respectively. For comparison, composites containing micron size alumina particles were synthesized and displayed neither phenomenon. Solid‐state deuterium NMR results showed enhanced chain mobility at room temperature in the nanocomposites and corroborate the observed Tg depression indicating considerable main chain motion at temperatures well below those observed in the neat polymer. A hypothesis is presented to relate the thermal and mechanical behavior observed in the composites to the higher chain mobility and Tg depression seen in recent ultrathin polymer film research.
Key factors affecting permeability measurement in the vacuum infusion molding process
Authors: Hammami Adel 
Published: April 2004

AbstractThe composites industry, under increased environmental constraints, is seeking to shift from existing open mold manufacturing processes for composite parts. A promising manufacturing technology known as the vacuum infusion molding process is gaining acceptance among composite‐parts manufacturers since it involves low tooling cost and allows complete elimination of volatile organic compounds (VOC). The process is similar to the resin transfer molding process; however, in the vacuum infusion technique, a polymeric film, often referred to as vacuum bag, replaces the stiff mold cover. The film is sealed against the lower half of the mold, at the periphery. Air expelled from the mold cavity results in the compaction of the reinforcement by the atmospheric pressure present on the outer side of the polymeric film. Finally, resin impregnates the mold cavity, usually through a resin distribution channel. The process is mainly developed for large‐scale structures, where material cost is an important parameter and users cannot afford any production pitfalls. Among process parameters that affect resin flow in the vacuum infusion molding process is the permeability of the reinforcement stack, which has to be measured and evaluated taking into consideration the requirements of the process. A possible approach is the definition of a parameter that defines the maximum infused length, and this parameter will take into account the structure of the reinforcement, the resin viscosity, the fiber volume fraction and inlet geometry.
Study of electrophysical characteristics of lead‐natural rubber composites as radiation shields
Authors: Gwaily S. E. , Hassan H. H. , Badawy M. M. , Madani M. 
Published: April 2004

AbstractThe dependence of the attenuation of both gamma rays and neutrons on lead concentration in leaded‐natural rubber composites incorporated with paraffin wax and boron carbide as radiation shields was investigated. Moreover, the dc conductivity and swelling characteristics of the rubber vulcanizates and the effect of aging on them were studied. It was found that samples of 18 mm thickness incorporated with 20 phr of B4C and 60 phr of paraffin wax can reduce the fast neutron beams by about 50%. For slow neutrons, the reduction was about 46%. The attenuated γ‐dose increased exponentially with increasing lead content.
Control of flow in resin transfer molding with real‐time preform permeability estimation
Authors: Nielsen D. R. , Pitchumani R. 
Published: April 2004

AbstractVariabilities in the preform structure in situ in the mold are an acknowledged challenge to achieving reliable preform saturation in liquid molding processes. Physical models offer an effective means of deriving real‐time process control decisions so as to steer the resin flow in a desired manner, which ensures complete preform saturation. An important parameter influencing the fidelity of the simulations is the preform permeability, which is a strong function of the preform microstructure. A model‐based control strategy that incorporates the ability to determine and utilize local permeability information in real‐time is of much value, and forms the focus of the paper. An intelligent model‐based controller is developed that uses virtual sensing of permeability to derive optimal decisions on controlling the injection pressures at the mold inlet ports in a resin transfer molding (RTM) process. The controller employs an artificial neural network, trained using process simulation data, as an on‐line flow simulator, and a simulated annealing algorithm to optimize the injection pressures on‐the‐fly during the process. Preform permeability is virtually sensed during the process, based on the flow front velocities and the local pressure gradient along the flow front, estimated using a fuzzy logic model. The controller, implemented on an RTM process, is shown to be able to accurately steer the flow fronts through various preform configurations.
Compressive damage in two‐step braided thermoplastic composites
Authors: Kuo Wen‐Shyong , Ko Tse‐Hao , Fang Jiunn 
Published: April 2004

AbstractThis work examines compression‐induced damage in a 3D, braided carbon/nylon 6 composite. The two‐step braiding was used to form the fabric, and the yarn used was a carbon tow commingled with nylon 6 powder. About 82% of overall fibers were arranged along the axial direction, and the rest were the braiding fibers. A matched mold was designed for melting the resin and pressing the fabric into a predetermined thickness for the resulting composite. The molding temperature was varied to examine its influence on the compressive properties. The compressive tests were carried out by using an end‐supported, end‐loaded fixture designed for thicker specimens. The results showed that the molding temperature greatly affected the composite modulus and strength. Microscopic observations revealed that the induced damage modes differ from those in 3D thermosetting composites. Miniscopic failure of the yarns appears to be the dominant mode. Two types of damage were observed. One is miniscopic kink‐band caused by the through‐thickness shear stress; the other is the folding of the axial yarns into a corrugation form. These modes are related to the 3D structure and the interfacial bonding condition. Some key features of the capability of energy absorption of this material are also discussed.
A unified approach to determine principal permeability of fibrous porous media
Authors: Weitzenböck J. R. , Shenoi R. A. , Wilson P. A. 
Published: April 2004

AbstractThis paper presents a unified approach (UA) to determining permeability in liquid composite molding. The UA applies both to the channel flow and the radial flow experiment and it unifies the data processing of almost all known permeability measurement methods. It permits principal permeability to be calculated from experimental measurements which are carried out in an arbitrary co‐ordinate system. This paper describes the UA and its main features. Further, the UA is applied to a number of experimental results for radial flow and channel flow measurements to demonstrate its validity. In addition, the algorithms of current permeability measurement methods are classified according to the UA, and, where necessary, differences are discussed. Some data processing algorithms were found to contain weaknesses or shortcomings.
Surface treatment of CFRP composites by Ar+ irradiation to improve bonding strength between aluminum and CFRP composites
Authors: Rhee Kyong Y. , Choi Nak‐Sam , Park Soo‐Jin 
Published: April 2004

AbstractThe effect of surface treatment of carbon fiber reinforced plastic (CFRP) composites on the T‐peel strength and the shear strength between CFRP and aluminum panels was studied. The surface of the composite panel was treated with Ar+ irradiation under oxygen environment. The optimal Ar+ ion dose was determined by measuring the changes of contact angle and surface energy as a function of ion dose. T‐peel tests and SLS tests were performed using irradiated CFRP/aluminum specimens and unirradiated CFRP/aluminum specimens to determine the treatment effect by Ar+ irradiation under oxygen environment on the T‐peel strength and shear strength of CFRP/aluminum composites. The results showed that contact angle on the surface of the composite panel was reduced from ∼80° to ∼8° and the surface energy increased from 31 ergs/cm2 to 72.4 ergs/cm2 with an ion dose of 1017 ions/cm2. T‐peel strength and shear strength are significantly affected by the surface treatment of composite panel. T‐peel strength and shear strength improved 650% and 56%, respectively, when the treatment was made with an ion dose of 1016 ions/cm2. SEM examination showed that the improvement of bonding strength was attributed to the uniform spread and fracture of epoxy adhesive.
A structure and property based process window for void free thermoset composites
Authors: Eom Yongsung , Boogh Louis , Michaud Véronique , Månson Jan‐anders 
Published: April 2004

AbstractA process window providing guidelines to minimize internal stress levels and to prevent void formation during cure of thermoset composite materials is presented. A model taking into account the applied pressure and the level of stress borne by the fiber assembly was introduced to calculate the hydrostatic internal stress state in the resin during cure. Based on the fundamental mechanisms of matrix shrinkage and evolution of viscoelastic properties under the given processing conditions, the internal stress in the resin was calculated as a function of fiber volume fraction, fiber stacking sequence, applied pressure and resin conversion. This level of stress is compared to a criterion for void initiation in the resin. A process window was hence constructed for preventing void formation during cure. Composite laminates with different stacking sequences and fiber volume fractions were cured with different applied pressures within and out of the process window boundaries. The composite void contents were measured and correlated perfectly with the process boundaries. This process window construction taking into account the material vis‐coelastic properties and the composite architecture is a unique tool for determining optimum process condition of composite laminates.
A gas flow method for determination of in‐plane permeability of fiber preforms
Authors: Um Moon‐Kwang , Daniel Isaac M. , Childs Brian W. 
Published: April 2004

AbstractResin flow plays a crucial role in many composite manufacturing processes. The most important parameters used in modeling and designing mold filling are the permeability of the fibrous preform, which is a kind of flow conductance and a property of the reinforcement, and the viscosity of the resin. The extent reaction, or degree of cure, is also important and causes change of chemical during mold filling. To determine the permeability of fiber preform searchers have been using liquid flow analysis. In this study, a new scheme for determining permeability using gas flow is proposed. In conventional liquid flow methods, radial propagation of the polymer into a porous medium is measured and used to determine permeability, whereas in the gas flow method, the several different preform geometries is measured and used. The effectiveness of the gas flow method was verified by comparing it with conventional methods.
Tearing mode interlaminar fracture toughness of composite materials
Authors: Hwang Shun‐Fa , Hu Chiao‐Lin 
Published: April 2004

AbstractThe Simplified Split Cantilever Beam (SSCB) is proposed in this work and compared with the Split Cantilever Beam (SCB) to obtain the tearing mode interlaminar fracture toughness. The materials considered are single‐fiber system composites and interply hybrid composites. For interply hybrid composites, three different types of stacking sequence for SSCB specimens, which are [0/0//0],[0/0//0]. and [0/0//0], are tested to compare their suitability. Finite element analysis combined with a modified crack closure integral has been applied to separate the different components of the strain‐energy release rate. In addition, the method of compliance calibration was used to calculate Gc values. The effects of crack growth, initial crack length, specimen width, and number of glass fiber plies were also studied. The results show that SSCB testing has a more dominant Mode III component and more stable Gc values than SCB testing. For SSCB testing, the crack growth and the specimen width for the range considered have no clear effects on the interlaminar fracture toughness, but the initial crack length should be carefully selected to obtain corrected values. The tearing mode interlaminar fracture toughness of interply hybrid composites is higher than that of carbon/epoxy composites, and the three different types of stacking sequence considered are all suitable to approximate the Mode III interlaminar fracture toughness for interply hybrid composites.
Conducting aluminum‐filled nylon 6 composites
Authors: Pinto Gabriel , Jiménez‐Martín Ana 
Published: April 2004

AbstractThis work is concerned with the preparation and characterization of composite materials prepared by compression molding of a mixture of aluminum flakes and nylon 6 powder. The electrical conductivity, density, hardness and morphology of composites were investigated. The electrical conductivity of the composites is < 10−11 S/cm unless the metal content reached the percolation threshold, beyond which the conductivity increased markedly by as much as 1011. The volume fraction of conductive filler at the percolation threshold was calculated from experimental data, by fits to functions predicted by the percolation theory. Decreasing the average particle diameter of filler leads to increased percolation threshold (it varies from 23 to 34 vol% for the three different fillers studied) and decreased maximal conductivity of composites. The density of the composites was measured and compared with values calculated assuming different void levels within the samples. Furthermore, it is shown that for certain sizes of particle filler, the hardness decreases initially with the increase of metal concentration, possibly because of poor surface contact with the nylon matrix, but, starting from a certain value, there is a hardness increase. For the smallest particle filler, the hardness of samples is not influenced by the presence of the filler.
Isothermal and non‐isothermal consolidation of carbon fiber towpregs
Authors: Nunes J. P. , Brito A. M. , Pouzada A. S. , Bernardo C. A. 
Published: April 2004

AbstractThe purpose of this work is to establish and validate a model to predict the isothermal and non‐isothermal consolidation behavior of unidirectional towpregs, made of carbon fibers and a thermoplastic polymer. A Finite Difference Method program was devised based on a set of analytical expressions developed in a previous work. The program allows the determination of pressure‐displacement curves at constant press closing speed and fixed or variable molding temperature, allowing comparison with experimental data obtained in the same conditions. There was good agreement between theoretical predictions and experimental results for both the isothermal and non‐isothermal consolidation. However, in the former case, the agreement was limited to low closing speeds and long pre‐heating times. In the latter case these limitations did not exist, showing that the non‐isothermal model is a good tool for the optimization of the consolidation process.
Impact behavior of aramid fiber/glass fiber hybrid composites: The effect of stacking sequence
Authors: Park Rohchoon , Jang Jyongsik 
Published: April 2004

AbstractAramid fiber/glass fiber hybrid composites were prepared to examine the effect of stacking sequence on the impact behavior of thin laminates. The effect of position of the aramid layer on the impact properties of hybrid composites was investigated using driven dart impact tester. The delamination area and fracture surface of hybrid composites were analyzed for correlation with impact energy. The addition of glass layer to aramid layer reduced the impact resistance of hybrid composite due to the restriction in the deformation of aramid layer. The position of aramid layer resulted in variations in the impact behavior of hybrid composites. When the aramid layer was at the impacted surface, the composite exhibited a higher impact energy. This was attributed to the fact that the flexible layer at the impacted surface in thin laminates can experience larger deformation. In three‐layer composites, the aramid fiber‐reinforced composite (AAA) exhibited the highest total impact energy due to high impact energy per delamination area (1EDA) in spite of low delamination area. Aramid fiber and glass fiber‐reinforced composites showed a different impact behavior according to the change of thickness. This was attributed to the difference in the energy absorption at interface between laminae.
Modeling and simulation of the hole pressure problem
Authors: Wu G. H. , Ju S. H. , Wu C. C. 
Published: April 2004

AbstractWhenever a polymeric or viscoelastic liquid flows over a depression in a channel, the phenomenon of hole pressure occurs. Modeling and simulation for the flow of an Oldroyd‐B type fluid passing over a transverse slot is considered here. This type of fluid is a good model for some polymeric liquids. In the model, it is assumed that the extra stress of the solution is the sum of the contribution from the solvent and the contribution from the polymer molecules. The results obtained in the study are computed by using the elastic‐viscous split‐stress finite element method incorporating the non‐consistent streamline‐upwind scheme (EVSS/SU finite element method). As a verification of the numerical scheme, the algorithm is first applied to compute the corresponding flow of the upper‐convected Maxwell fluid model, a special case of the Oldroyd‐B model. Hole‐pressure is evaluated for various Deborah numbers (De), and compared with that derived from the Higashitani‐Pritchard (HP) theory. The agreement between the two is found to be satisfactory for creeping flow in the De range for which the Higashitani‐Pritchard theory is valid. Subsequently, hole‐pressure and characteristics of this flow problem are predicted. Futhermore, the effects of fluid elasticity, inertia, and slot geometry on hole‐pressure are investigated.
Dynamic mechanical behavior of LCP fiber/glass fiber–reinforced LLDPE composites
Authors: Hashmi S. A. R. , Kitano Takeshi , Chand Navin 
Published: April 2004

AbstractLiquid crystalline polymer (LCP) fibers and glass fibers have been used to rein force linear low density polyethylene (LLDPE) by using an elastic melt extruder and the compression molding technique. The impact behavior of hybrid composites of different composition is compared and is explained on the basis of the volume frac tion of the fibers. Addition of glass fibers decreases the Izod impact strength LLDPE. The impact strength of the composites increases when glass fibers are placed by LCP fibers. Dynamic mechanical α and β relaxations are studied and effect of variation of fiber composition on these relaxations is reported in the tem perature range from −50 to 150°C at 1 Hz frequency, a relaxation shifts toward higher temperatures with addition of fibers in LLDPE. Addition of fibers increases the storage modulus of LLDPE.
Structure and properties of PP/SBS/glass fiber hybrid composites. Past II: Property measurement
Authors: Saujanya C. , Radhakrishnan S. 
Published: April 2004

AbstractThe mechanical properties viz. impact and tensile modulus of hybrid composites of PP/SBS/glass in the composition range 0‐40 wt% of glass fibers (GF) were studied. Both impact and tensile modulus increased with respect to glass content at a certain composition of the blend. Synergistic effects were seen in the value of elongation and toughness at a certain composition of the glass content. The above findings could be associated with the high aspect ratio and nucleation ability of GF together with good interfacial adhesion between the GF and SBS, rather than the PP matrix. These have been supported by the investigations on structures and morphologies of the hybrid composites.