bluuebunny/crossref_metadata_2025_split huggingface dataset:
Processing conditions for electromagnetic interference shielding effectiveness and mechanical properties of acrylonitrile‐butadiene‐styrene based composites
Authors: Chiang Wen‐Yen , Cheng Kai‐Yuan 
Published: April 2004

AbstractA conductive plastic was compounded in a twin screw extruder by incorporating conductive carbon fiber (CF) into an acrylonitrile‐butadience‐styrene (ABS) copolymer. The effects of various processing parameters prior to injection molding were investigated; then, the electromagnetic interference shielding effectiveness (EMI SE), fiber length, processability, and mechanical properties of the composite were studied. Results showed that the EMI SE of the composite increased as the final fiber length increased. The longer final fiber was produced by feeding fibers into the ABS melt at 240°C and 60 rpm. A more conductive network was formed by adding lubricants to the composite to reduce fiber damage and increase fiber dispersion. The increase of the fiber content affected processability. When the fiber content was higher than 40 phr (parts per hundred resin) in the composite, the average fiber length shortened. This study shows that better shielding can be obtained by adding a fiber at a rate higher than 30 phr. The best shielding obtained is about 30 decibels (dB).
Interfacial properties of glass fiber/brittle‐ductile dual‐matrix composites using micromechanical techniques and acoustic emission
Authors: Lee Sang‐il , Park Joung‐man , Shin Dong‐woo , Yoon Dong‐jin 
Published: April 2004

AbstractThe interfacial adhesion and microfailure modes of glass fiber‐reinforced brittle unsaturated polyester/modified epoxy composites were investigated via micromechanical techniques and acoustic emission (AE). Various silane coupling agents caused different degrees of interfacial adhesion and subsequent microfailure modes. In the brittle matrix layer, the number of matrix fragments was significantly influenced by the type of silance coupling agents. The more cracks, the higher the interfacial adhesion under both dry and wet conditions. This is attributed to the chemical and hydrogen bondings in two interphases. The results obtained from microdroplet and fragmentation tests were correlated by associating with the AE technique. The sequential occurrence of mainly three groups of AE were as follows: the first group originated mainly from brittle matrix cracking. The second and the third groups resulted in fiber breakage and ductile matrix cracking and debonding. For dual‐matrix specimens the micromechanical tests provide reliable information with regard to the interfacial adhesion and characterize the microfailure modes when combined with the AE technique.
Simulation of compression molding for sheet molding compound considering the anisotropic effect
Authors: Lin Chao‐ming , Weng Cheng‐i 
Published: April 2004

AbstractAn improved model of the anisotropic flow characteristics of SMC (sheet molding compound) during compression molding is developed. This study is intended to complement our previous paper, which was conducted to determine the anisotropic parameters for short fiber reinforced thermosets SMC (16). Our prior study measured flow viscosities and material anisotropy by means of axisymmetric and plane strain compression molding tests. The current study, in order to identify the superior flow model from the choices (1) isotropic, (2) constant anisotropic and (3) varying anisotropic, applies the finite element method to obtain numerical results, which are subsequently compared with experimental results to determine the flow model with the best fit. The anisotropic parameters of the shear directions are determined by use of normal and planar parameters because SMC is planar isotropic. Six varying anisotropic parameters and six viscosity values are estimated during molding experiments, which are conducted at room temperature so that the polymer does not cure. Two‐dimensional molding numerical analyses are carried out to explain two experimental classes, axisymmetric and plane strain compression molding. The load‐levels predicted by the isotropic model, anisotropic model (parameter values fixed) and anisotropic model (parameter values varying) are compared with the experimentally derived values, the results showing that the varying anisotropic model best fits SMC compression behavior.
Rheological characterization of commercial glass mat thermoplastics (GMTs) by squeeze flow testing
Authors: Kotsikos G. , Bland J. H. , Gibson A. G. 
Published: April 2004

AbstractThe flow behavior of commercial glass mat thermoplastics (GMTs) has been investigated by isothermal axisymmetric squeeze flow testing between parallel circular plates. Tests have been performed over a range of squeeze rates and the analysis is based on simple power law constitutive equations. A key part of the work is determining the relative contributions of shear and extensional flow to the overall squeezing force response. By developing a variational flow model, based on the upper bound theory, the behavior has been found to be predominantly extensional, with shear effects becoming important at very small plate separations. In addition, a predictive model for the radial pressure distribution during squeezing has been developed, based on fiber suspension rheology. Since fibers are generally long or continuous, treating the material as a statistically homogeneous fluid does not yield accurate results in this respect.
Comparison of spectroscopic and dynamical‐mechanical characteristics of some polymer composites on polypropylene base
Authors: Mamedov Sh. V. , Alekperov V. A. , Lenger Y. , Ören D. , Abasov S. A. , Bayramova R. L. , Subasi M. 
Published: April 2004

AbstractIn this study the mutual investigation of the results obtained from the mechanical stability properties and the IR spectra of polypropylene‐based but differently doped low‐density polyethylene (LDPE) and o‐o‐di‐n‐cresylditio phosphorous (CTPh) acid polymer composites is given. As opposed to the studies of the writers in recent years here, dynamical‐mechanical properties are explained not only by the variations in the oxidation peaks but also by the optical density in the peaks of the variations in the groups in amorphous and crystalline regions. The properties are also explained by the spectra variations in the IR region, which, according to Mamedov (2), is important, and by the extreme variations of the polymer properties. IR spectra analyses show that for both composites, (1) the optical density of the peaks in the crystalline regions for LDPE decreases while for PP those of the peaks in the amorphous regions increase; (2) the optical density of the peaks belonging to the CC groups get higher, whereas those of the peaks 1717, 1748 cm−1 diminish; and (3) the dynamical‐mechanical properties change accordingly, and these changed composites have the maximal characteristics, since the added amount is 0.2–0.3% CTPh by mass and 20–30%LDPE by mass. On the basis of the paper by Abdullayev et al. (3), the mechanism of these processes is given.
Fatigue crack growth model and mechanism of a random fiber SMC composite
Authors: Atodaria D. R. , Putatunda S. K. , Mallick P. K. 
Published: April 2004

AbstractThe primary purpose of this study is to investigate the fatigue crack growth rate and mechanism in a random fiber sheet molding compound (SMC) composite. The fatigue crack growth rate in this study was measured using a compliance approach. The fatigue crack growth rate in the SMC studied here shows a good agreement with a new power law model proposed earlier. This new model takes into account not only the effect of the stress intensity factor range, but also the effect of crack growth at various stages of loading using a weight average stress intensity factor. It was observed that this new model can represent the fatigue crack growth rate of the SMC at three different load ratios in a single unifying curve.
An empirical model for the viscosity buildup of hydroxy terminated polybutadiene based solid propellant slurry
Authors: Lakshmi R. , Athithan S. K. 
Published: April 2004

AbstractThe Polar Satellite Launch Vehicle (PSLV) makes use of hydroxy terminated polybutadiene (HTPB) based solid propellant in the booster stages, strap‐ons, and the third stage. An empirical model that describes the change in viscosity of various formulations of propellant slurry with time and temperature has been developed as an extension of the Andrade equation. The model incorporates constants that account for the viscosity of the slurry caused by the combined effect of the continuous binder phase, dispersed particulate solids, and progress of crosslinking between reactive species of the binder and curators. The correspondence between predicted viscosity buildup and measured values obtained during casting of motors is verified and found satisfactory. A method of tailoring some constants, so as to make them batch‐specific, is explained. Several practical applications are described. The model serves as a predictive tool for evaluating the potlife and rheological behavior of the slurry during production of large solid motors. The experimental method and approach used for data analysis can be used for other slurries that are similar in composition to propellant slurry.
The performance of calcium carbonate filled, random fiber composites
Authors: Steenkamer D. A. , Sullivan J. L. 
Published: April 2004

AbstractThis paper describes an investigation into the performance of calcium carbonate filled, random fiber reinforced composites. A series of composite plaques were fabricated by resin transfer molding (RTM) a calcium carbonate filled, unsaturated polyester resin with either an A‐glass continuous strand mat (CSM) or an E‐glass CSM preform. The influence of fiber type and calcium carbonate filler loading level were then evaluated through a combination of experiments and micro‐mechanics based modeling. The results of these studies indicate that the use of the E‐glass reinforcement led to better mechanical properties relative to their A‐glass counterpart. In addition, the composite moduli increased as the calcium carbonate filler level increased; however, the composite strengths were insensitive to filler loading level. Finally, a previously developed micro‐mechanics based model was extended to consider the presence of the filler within the resin matrix. This model was used to predict the tensile moduli and strength as well as the overall shape of the stress‐strain curves. Good agreement was found between the model predictions and the experimental results which suggests that this model could be used as a preliminary design tool to examine the effect of constituent composition on structural performance.
Separation of a thermotropic liquid crystalline polymer from polypropylene composites
Authors: Collier Monty C. , Baird Donald G. 
Published: April 2004

AbstractThis work is concerned with determining how to effectively recycle wholly thermoplastic composites comprised of a polypropylene (PP) matrix reinforced with a thermotropic liquid crystalline polymer (TLCP). A novel reclamation process was developed in which the TLCP could be recovered from the PP matrix. Reactive extrusion was used to reduce the molecular weight of the PP (Montell 6523) and to facilitate phase separation. The melt was then extruded into a heated mineral oil bath, which separated the TLCP (DuPont HX8000) from the matrix by dissolving the PP. It was found that greater than 70 wt% of the TLCP could be reclaimed from the PP matrix at a purity of greater than 96 wt%. In order to determine the ability to reuse the reclaimed HX8000, injection molded in situ composites were generated and their mechanical properties were determined. When the neat HX8000 component was partially replaced with reclaimed HX8000, the injection molded TLCP/PP composites showed no discernible difference in mechanical properties.
Processing induced residual stress in asymmetric laminate panels
Authors: Theriault R. P. , Osswald T. A. , Castro J. M. 
Published: April 2004

AbstractIn this research, a one‐dimensional finite difference model has been developed to simulate the progression of material properties during the processing of metal‐clad, multi‐layered, fiber mat reinforced, thermoset resins. Using a micro‐mechanical model, the simulation is also capable of predicting the dimensional movement observed during processing and the through‐thickness residual stress distribution within thin laminates that will lead to the development of warpage or curling. The ability to predict the overall movement is quite complex; however, the contributing factors that lead to warpage of epoxy, glass‐fiber mat laminate composites have been experimentally and numerically identified. It has been found that the dominant factor that leads to warpage in asymmetric multi‐layered laminates is the differences in the coefficient of thermal expansion of the individual plies. Thus, by selecting appropriate combinations of the degree of cure and resin content of the thermoset in the individual plies, it is possible to reduce the material property variability of the laminate through thickness. The planar movement of individual plies is a function of the glass‐fiber mat tension during pre‐processing operations. Variability in pre‐processing mat tension can be compensated for after lamination via post‐baking processes.
Use of a simple, inexpensive pressure sensor to measure hydrostatic resin pressure during processing of composite laminates
Authors: Lynch Katherine , Hubert Pascal , Poursartip Anoush 
Published: April 2004

AbstractA simple and cheap method of measuring the resin pressure within a composite laminate during processing is presented. The method consists of using a small diameter, long needle filled with inert fluid and connected to an external pressure sensor, to measure the resin pressure at a point inside a composite laminate. This method can be used to investigate resin flow, laminate compaction, the control of voids, and in several composite material processing methods such as autoclave processing, hot press curing and resin transfer molding. The sensors are suitable for research and development or troubleshooting, but not for production. Sensor assemblies were developed and tested to show that their response is reproducible, linear and stable with temperature and time. Resin pressure profiles for two AS4/3501‐6 laminates were generated and compared. The experimental results were also compared to the resin flow simulation of a general processing model for composites, COMPRO. It is shown that the resin profile in the laminate is influenced by the presence of the bleeder cloth and the vacuum bag pressure. A significant pressure drop corresponded to the point of minimum viscosity of the resin. Finally, the resin pressure was stabilized when the resin reached gelation.
Prediction and experimental verification of damping in 3‐D braided textile structural composites
Authors: Yim Jong Hee , Jang Bor Z. 
Published: April 2004

AbstractThe material damping characteristics of 3‐D braided textile structural composites were investigated in this paper. A model for predicting damping in these materials was developed based upon the classical laminated plate theory. The model modified the existing models for predicting the static moduli of 3‐D textile structural composites by using the elastic‐viscoelastic correspondence principle. The basic engineering constants were replaced with their corresponding complex forms by applying the elastic‐viscoelastic correspondence principle to them. In this study, the basic damping loss factors (i.e. ηL, ηT, ηLT and ηvLT) were obtaiend by a modified Hashin's theory, Rule‐of‐Mixture Laws, and an indirect method on the basis of empirical works. From complex numerical results, we concluded that axial damping, flexural damping, coupling damping, and in‐plane shear damping coefficients were all functions of the yarn orientation angle and fiber volume fraction in 3‐D braided textile structural composites. Experimental data supported theoretically predicted results.
Effect of coupling agent and filler particle size on melt rheology of polymer‐bonded Nd‐Fe‐B magnets
Authors: Otaigbe Joshua U. , Kim Hyun Seog , Xiao Jun 
Published: April 2004

AbstractThe effect of coupling agents and filler particle size on melt rheology of poly(phenylene sulfide)‐bonded neodymium‐iron‐boron (Nd‐Fe‐B) alloy magnets was studied with oscillatory flow experiments to accelerate efforts to optimize their processing. The minimum viscosity of the polymer‐bonded magnets near 290°C was obtained with NdFeB fillers (106–150 particle size range) that were coupled with a silane coupling agent. All the samples tested followed power‐law fluid flow behavior. Morphological and dynamic mechanical analysis of the samples showed that the beneficial function of the coupling agent may be ascribed to enhanced wetting of the magnetic NdFeB powders by the polymer, improving the processability of the polymer bonded magnets.
Analysis of acoustic emission signals resulting from fiber breakage in single fiber composites
Authors: Giordano M. , Calabrò A. , Esposito C. , Salucci C. , Nicolais L. 
Published: April 2004

AbstractAcoustic emission techniques are able to sense micro failures in loaded structures for a wide range of materials. Moreover, a spread application of such techniques to structural health monitoring requires further efforts in the signal analysis in order to assess the relationships between the micromechanics of the failure and the signal features as recorded by a transducer. In the case of polymer matrix composites, the main sources of acoustic emission signals are fiber breakage, matrix cracking, and fiber/matrix debonding. In this work, single fiber composites have been tested to produce fiber breakage acoustic emission events. Three different fiber/matrix systems have been investigated: PCA polyster matrix/carbon fiber (6 μm diameter), ECA epoxy matrix/carbon fiber (6 μm diameter), and ECB epoxy matrix/carbon fiber (12 μm diameter). Acoustic emission signals recorded through a wide band transducer have been analyzed in the frequency domain in order to study the amplitude spectra characteristics. The irregular shape of the amplitude spectra suggested the fractal dimension as a feature. The Richardson fractal dimension resulted in a key parameter in the signal identification among the different fiber/matrix systems: DPCA = 1.28 ± 0.02, DECA = 1.46 ± 0.03, DECB = 1.42 ± 0.02. On the basis of this finding, the shape of the amplitude spectra has been analyzed. An algorithm able to extract shape similarities from a class of spectra has been developed. It permits the definition of the representative spectra together with the identification of the relevant frequencies for the fixed fiber/matrix system.
Measurement and prediction of the glass transition temperature during processing of copper‐clad epoxy resin systems
Authors: Theriault R. P. , Osswald T. A. , Castro J. M. 
Published: April 2004

AbstractThe determination of the glass transition temperature of a cured resin system is necessary for the classification of the temperature region of usable service. For the printed circuit board industry, accurate and consistent properties of the copperclad laminates that are used as the substrate are essential. Variations in material properties of the finished laminates may become a hindrance in subsequent steps in the manufacturing of printed circuit boards and more importantly in the failure rate of the boards during service. In this research, a one‐dimensional finite difference method has been implemented with constitutive models to simulate the progression of the degree of cure and glass transition temperature during the processing of copper‐clad, multi‐layered, fiber mat reinforced, epoxy laminates. The numerical results have been compared to experimental measurements and it has been found that the simulation predicts the experimental observations quite well.
Optimization of filling process in RTM using a genetic algorithm and experimental design method
Authors: Kim Byoung Yoon , Nam Gi Joon , Lee Jae Wook 
Published: April 2004

AbstractIn the resin transfer molding (RTM) process, preplaced fiber mat is set up in a mold and thermoset resin is injected into the mold. An important issue in RTM processing is minimizing the cycle time without sacrificing part quality or increasing the cost. In this study, a numerical simulation and optimization process for the filling stage was conducted in order to determine the optimum gate locations. The control volume finite element method (CVFEM), modeled as a 2‐dimensional flow, was used in this numerical analysis along with the coordinate transformation method to analyze a complex 3‐dimensional structure. Experiments were performed to monitor the flow front to validate the simulation results. The results of the numerical simulation corresponded with that of the experimental quite well for every single, simultaneous, and sequential injection procedure. The optimization analysis of the sequential injection procedure was performed to minimize fill time. The complex geometry of an automobile bumper core was chosen. A genetic algorithm was used to determine the optimum gate locations in the 3‐step sequential injection case. Taguchi's experimental design method was also used for determining the pressure contribution of each gate. These results could provide the information on the optimum gate locations and injection pressure in each injection step and predict the filling time and flow front.
Study of the bending induced gap in fiber preforming of woven fiber mats
Authors: Gao Zheng‐Sen , Young Wen‐Bin 
Published: April 2004

AbstractIn the preforming of an RTM process, the configuration of the fiber mats should deform in order to conform to the mold surface. Several deformation modes may occur during a forming process. It can be characterized by factors such as the local surface curvature of the mold, the loading condition and the type of reinforcement. It has been suggested that fiber deformation modes may include fiber stretching, fiber straightening, shear slip, and buckling. As the fiber is bent at the bending edge in the preforming, a small gap may emerge from the outer side owing to the movement of fiber bundles. Studies on the relation between the channel gap formation and the bending angle together with the effect of the fiber content were investigated in order to establish a useful guide for the design of mold with bending edges. A model with a slip factor was proposed to estimate the bent fiber thickness.
Axial impregnation of a fiber bundle. Part 1: Capillary experiments
Authors: Amico S. C. , Lekakou C. 
Published: April 2004

AbstractThis is an experimental study to investigate the axial capillary impregnation of an E‐glass fiber bundle by using two Newtonian infiltrating fluids: (a) silicone oil and (b) epoxy. First, the wetting properties of the systems were measured, i.e. the surface tension of each fluid and the contact angle between the fluid and a single fiber filament. Liquid height and weight data as a function of time were collected from several capillary impregnation experiments of single fiber bundles. A data analysis is presented following either the integral or the differential approach to determine capillary pressure, permeability and porosity. The so‐determined values of capillary pressure were compared to corresponding theoretical values and were generally found much lower, unless the duration of the capillary experiment was around a month. This long‐term experiment brought substantial improvement in the determined values of capillary pressure. The infiltration plots from the experimental data will be further used for validation of theoretical inpregnation curves, which will result in the theoretical prediction of permeability and capillary pressure in Part 2 of this study (1).