bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental study on the accuracy of advanced composite tools for slanted shapes
Authors: Huang C. K. , Yang S. Y. 
Published: April 2004

AbstractHigh quality advanced composite tools (ACTs) have been introduced to the growing tooling market. Since ACTs are used for high precision composite parts, even minor warpage in a tool might render the parts useless. Trial and error in making or remaking an accurate ACT are time‐consuming and expensive. This paper is devoted to investigating the effects of processing on the accuracy of ACTs for slanted shapes. An experimental design based on the Taguchi Method is employed. The experimental parameters investigated are postcure, mold material, laminate thickness, cure temperature, preheat, bleeder, pressure, and caul sheet. Warpage is used to verify the accuracy of ACTs. Optimum processing conditions and critical parameters have been found. The warpage that results under optimum processing conditions decreased significantly. Based on the findings in fiber volume fraction gradients, the observed convex and concave angle differences in warpage can be explained. To overcome the tendency to warpage, by means of an asymmetric doubler or insert in angle corners, a proper amount of asymmetry is implemented, which successfully improves the accuracy of the ACT shape.
Simulation of the injection process in resin transfer molding
Authors: Phelan Frederick R. 
Published: April 2004

AbstractA simulation based on Darcy's law for modeling mold filling in resin transfer molding has been developed. The simulation uses a new Flow Analysis Network (FAN) technique to predict and track the movement of the free‐surface, and a finite element method to solve the governing equation set for each successive flow front location. A variety of element types have been incorporated into the simulation, enabling modeling of flow for a variety of conditions of industrial interest including runner distribution systems, “2.5‐D” shell geometries, and fully 3‐D flows. The FAN technique developed here has two main benefits: it enables conservation of mass, even for highly distorted element shapes, and also, allows elements of different dimension to be simultaneously used in a single simulation. At present, the simulation predicts flow front position as a function of time, and the pressure distribution during the filling process for a number of inlet gating conditions. A number of examples are presented and discussed to highlight the simulation's capabilities, including the filling of a complex automotive part.
Effect of crosslinking and field strength on the electrical properties of carbon/polyolefin composites with a large positive temperature coefficient of resistivity
Authors: Yang Gengcheng 
Published: April 2004

AbstractCrosslinking is a promising method for stabilizing the electrical properties of polyolefin composites with a positive temperature coefficient of resistivity (PTCR) for application as self‐controlled heaters. An interesting phenomenon is that the measured room temperature resistivity of such materials is independent of applied voltage at low DC fields, but crosses over to display an apparent decrease with the accretion of voltage above a critical value. Measured current vs. time of voltage application has been recorded that shows an equilibrium varying with temperature and voltage. Theoretical approaches to these results are discussed.
Creep behavior of nylon‐6 thermoplastic composites
Authors: Liou W. J. , Tseng C. I. 
Published: April 2004

AbstractA systematic investigation of the creep behavior of nylon‐6 thermoplastic composites reinforced with continuous carbon fibers was conducted by a strain gauge method. The creep strains of carbon fiber/nylon‐6 composites were measured at various stress conditions and temperatures. The relationship between the creep strain, strain rate, creep compliance and stress condition, time, and temperature were established. The experimental creep strain data were shifted to a reference temperature to form a master curve by using the time‐temperature superposition principle. The master curve can be used to predict the creep behavior of the carbon fiber/nylon‐6 composites over long times. The effect of fiber orientation on the creep behavior was also measured and reported.
Thermal stability of PEEK/carbon fiber in air and its influence on consolidation
Authors: Phillips Richard , Glauser Thierry , Månson Jan‐Anders E. 
Published: April 2004

AbstractThe thermal stability of carbon fiber‐reinforced polyetheretherketone (PEEK/CF) in air and its influence on consolidation are characterized under simulated processing conditions. The changes in dynamic shear modulus, melting temperature, heat of fusion and glass transition temperature due to chemical reactions and morphology changes were monitored by dynamic rheological analysis and differential scanning calorimetry. Thermal decomposition in air and simultaneous thermooxidative reaction of PEEK resin exposed to temperatures slightly higher than normal processing temperatures were observed by thermogravimetric and dynamic rheological analysis. The initial stage of this thermo‐oxidative reaction, under isothermal and non‐isothermal conditions, was modeled by a exponential‐based Arrhenius expression. The consolidation of PEEK/CF is affected by the thermal oxidation of the resin, which delays time to intimate contact between the plies. A consolidation model, predicting the degree of intimate contact, is extended to also take into account the rheological changes of the system. Finally, a processing limit regarding the thermal stability is defined based on the model and the experimental results.
Synthesis, cure analysis, and composite properties of allylated cyclopentadiene resins
Authors: Mathias Lon J. , Tregre Gregory J. 
Published: April 2004

AbstractAllylated cyclopentadiene was synthesized through the phase transfer reaction of cyclopentadiene and allyl chloride in the presence of a strong base. The reaction yielded a mixture of isomers with 2 to 6 allyl groups per cyclopentadiene ring. Variations in reactant ratios changed product ratios only slightly; however, lower ratios of allyl chloride to cyclopentadiene (4:1 and 2:1) produced lower substituted products. DSC analysis of the ACP showed thermal cure without added catalyst. The total enthalpy of cure was ∼750 J/g with a peak energy at 310°C. FTIR analysis of the thermal cure showed the predominate cure mechanisms to be ene reactions and polyadditions of allyl groups with a small amount of oxidation. Partial curing (B‐staging) of ACP was conducted thermally at 180 and 200°C. An increase in viscosity with time was found in each case with gelation occurring at ∼15 h and 3 h, respectively. ACP resin was also cured using various concentrations of peroxide and BF30 dibutyl etherate catalysts. In all cases gelled materials were formed. ACP/carbon fiber and ACP/glass fiber composites gave flexural moduli of 165 and 42 GPa, respectively. Flexural strength values were found to be 956 MPa for ACP/carbon and 681 MPa for ACP/glass. Treatment of ACP/carbon fiber composites in boiling water or refluxing toluene had no significant effect on their mechanical properties.
Use of a charged coupled device (CCD) camera for evanescent wave optical fiber cure monitoring of liquid composite molding resins
Authors: Neff Raymond A. , Woerdeman Dara L. , Parnas Richard S. 
Published: April 2004

AbstractAn optical fiber evanescent wave fluorescence cure sensor described in a previous paper (1) has been interfaced with a fast detector and computer software to provide real‐time monitoring of fast‐reacting systems. Advantages to the new system include a reduction in data acquisition time (to 200 ms from 3 min), improved time resolution (to 5 sec from 10 min), and improved signal quality. Isothermal cure monitoring measurements were conducted in both distal and evanescent wave sampling modes for an epoxy‐amine system. Following a second order background correction, the results for the two sampling modes were identical. Thus the evanescent wave measurement was unable to detect differences between the chemistry in the bulk and at the fiber‐resin interface (if there were any differences to observe). The sensor system was also demonstrated for a fast curing (<3 min gel time) polyurethane‐isocyanurate system designed for high volume (short cycle time) automotive applications. The system is currently being modified for implementation in a “real world” manufacturing environment.
The effect of laminating factors on the thermal properties of unfired multilayer glass‐ceramic and alumina substrates
Authors: Yang Thomas C. K. , Viswanath Dabir S. , Natarajan Govindarajan 
Published: April 2004

AbstractThis paper presents experimental data on heat capacities and thermal conductivities of two ceramic tapes measured using standard ASTM methods. The two ceramic tapes were prepared using alumina and a glass ceramic of aluminum‐magnesium silicate with poly(vinyl butyral) binder, and laminated at pressures of 208E5 to 620E5 Pa at two laminating temperatures and times. The measured properties showed that laminating pressures have a greater effect, and that thermal conductivities are affected more than heat capacities. Empirical models have been developed to fit the experimental data. A correlation is developed to express the density of laminated green sheets in terms of the laminating variables—time, temperature, and pressure.
Anisotropy in sheet molding compounds during compression molding
Authors: Lin Chao‐Ming , Weng Cheng‐I , Ho Cheng‐Ter 
Published: April 2004

AbstractThis paper deals with an improved mathematical description of the anisotropic behavior of chopped fiber reinforced polymer composites, SMC (sheet molding compound). The material possesses isotropy in its planar direction and anisotropy normal to its plane. Axisymmetric compression and plane strain compression moldings are simulated via uniaxial compression testing and biaxial compression testing, respectively. Flow stresses and anisotropic parameters are obtained by solving nonlinear algebraic equations which are derived from a modified anisotropic flow rule and the constrained condition of the anisotropic parameters, together with two sets of experimental data curves. The solutions were obtained via nonlinear iteration. The results show that the SMC possesses anisotropic behavior, and the anisotropic parameters vary during compression processing. It is also shown that the effective strain‐rate plays an important role in the flow stress. Numerical simulation of short‐fiber composite compression molding is easily implemented by use of our derived relationships of flow stress and anisotropic parameters as functions of strain‐rate and strain.
A permeability database for composites manufacturing
Authors: Parnas Richard S. , Flynn Kathleen M. , Dal‐Favero Mary E. 
Published: April 2004

AbstractThe National Institute of Standards and Technology (NIST) has developed a database containing a set of permeability results from carefully controlled measurements for both saturated and unsaturated flows in glass fabrics. The materials studied are fully documented in the database, and in some cases the material compressibility is also included. The experimental techniques used to generate the permeability data are briefly described and the included permeability data summarized. A sample search is illustrated to demonstrate the database user interface and the extent of the data documentation.
Continuous glass‐fiber reinforced nylon 6 by using a new impregnation die
Authors: Yoon Byung Seon , Lee Suck Hyun , Suh Moon Ho 
Published: April 2004

AbstractThis paper describes a process for the manufacture of thermoplastic composites reinforced with continuous fibers and the equipment for producing such a product. The process makes it possible to expand and reconsolidate the fibers of rovings by passing them into the impregnation die filled with molten thermoplastic. The die consists of three rollers and numerous pins fixed on the roller surfaces over which the roving is drawn under tension. The material chosen to illustrate the die process is a glass‐fiber reinforced nylon‐6, PA6. The void content and mechanical properties were measured to investigate the influence of processing variables on properties. These process experiences indicated that poor fiber resin impregnation and fiber damage, due to harsh prepreg fabrication, result in low values for longitudinal tensile strength and impact properties. However, the composites manufactured by this technique show a significant improvement in mechanical properties over conventionally prepared thermoplastic composites.
Modeling and simulation of the vacuum forming of wood fiber–filled thermoplastic composites
Authors: Liu Shih‐Jung 
Published: April 2004

AbstractVacuum forming of wood fiber–filled thermoplastic composite sheets has become an important process in the industry because of their low cost, good formability, and high strength to weight. Nonuniform thickness distribution of a vacuum formed part caused by inappropriate mold design and processing condition is one of the problems that confound the overall success of this technique. A novel viscoelastic model of two‐dimensional finite element scheme, with eight noded overlay isoparametric elements was developed to numerically simulate the vacuum forming of wood fiber filled isotactic polypropylene. Computed results are in agreement with literature experimental data. Numerical simulation of a vacuum forming process can be used to optimize the molds and the forming parameters to achieve a product with ideal thickness distribution.
Fiber stability analysis for in‐situ liquid crystalline polymer composites
Authors: Rey Alejandro D. 
Published: April 2004

AbstractWe present a simple mathematical model based on classical theories of macroscopic elasticity that provides a fundamental description of the liquid crystal polymer (LCP) fiber break‐up instability that is observed during the annealing ofin‐situliquid crystal‐thermoplastic polymer composites. The thermodynamic model is solved using a number of consistent simplifying assumptions, and is restricted to thin liquid crystal polymer fibers. A significant feature of the liquid crystal surface energy incorporated in the model is the elastic storage due to deviations of the macroscopic orientation and of the orientational order from the preferred equilibrium values. The model predicts that thin LCP fibers are unstable to periodic surface perturbations that eventually would produce fiber break‐up and lead to an array of LCP droplets, as in the case of Rayleigh's fiber instability. The additional liquid crystalline elastic storage modes incorporated in the model, but not present in isotropic melts, tend to increase the magnitude of the critical wave‐length for fiber break‐up over that given by the Rayleigh criteria (i.e., fiber circumference) by a relatively small factor that depends on the ratio of the interfacial tension and the nematic anchoring energy.
Sensing delamination in a carbon fiber polymer‐matrix composite during fatigue by electrical resistance measurement
Authors: Wang Xiaojun , Chung D. D. L. 
Published: April 2004

AbstractDelamination in a crossply [0/90] continuous carbon fiber polymer‐matrix composite was sensed in real time during fatigue by measuring the electrical resistance of the composite in the through‐thickness direction. Upon 0° tension‐tension fatigue at a maximum stress of 57% of the fracture stress, the resistance irreversibly increased both in spurts and continuously, because of delamination, which started at 33% of the fatigue life. The resistance increased upon loading and decreased upon subsequent unloading in every cycle, thereby allowing strain sensing. The minimum resistance at the end of a cycle irreversibly increased during the first 0.1% of the fatigue life. The resistance became noisy starting at 62% of the fatigue life, at which delamination occurred rapidly and the fraction of laminate area delaminated reached 4.3%.
Some issues on impregnation in manufacturing of thermoplastic composites by using a double belt press
Authors: Wang Xiaoming , Mayer Christoph , Neitzel Manfred 
Published: April 2004

AbstractThe manufacturing of thermoplastic composite intermediates by a continuously running double belt press (System of Held Comp., Germany) has become one of the most effective techniques for high quantity production. The process of combining thermoplastic materials and reinforcing fabrics during the manufacturing results in impregnation phenomena of the reinforcing layers distinct from one in resin transfer molding (RTM). Here, the work is focused on the clarification of the impregnation process that occurred in such a continuous manufacturing process. A composite intermediate of 50 wt% fibers consisting of E‐glass fabrics and nylon 66 films (Zytel, DuPont) was produced at different processing conditions to exhibit the influence of the degree of impregnation on mechanical properties and damage patterns of thermoplastic composites. It can be proved that because of strong inhomogeneity in the fabric concerning the permeability of the yarns and the weaving structure, respectively, the time required to impregnate the fabrics is governed by transversal micro‐flow into the fiber bundles rather than macro‐infiltration of the polymer into the fabric structure. Imperfect impregnation resulted in specific damage pattern in the center of the compressed yarns after flexural loading. The results are to be applied to guide the optimization of the manufacturing process with respect to material selection and preselection of processing conditions.
Estimation of the volume resistivity of electrically conductive composites
Authors: Weber Mark , Kamal Musa R. 
Published: April 2004

AbstractThe modeling of the electrical conductivity of polymer composites reinforced with conductive fibers is investigated. Existing models generally can be divided into percolation theories and non‐percolation theories. The basis of the percolation theory is the fact that the conductivity of the composite increases dramatically at a certain fiber concentration called the percolation threshold. This theory can be used to model the behavior of the composite or to predict the percolation threshold itself. Non‐percolation theories include terms, which account for microstructural data such as fiber orientation, length, and packing arrangement. A comparison of experimental data with predictions from the various models reveals that only the percolation theory is able to accurately model the conductive behavior of an actual composite. Two alternative new models, which predict the volume resistivity of a composite using microstructural data, are evaluated. The first model relates resistivity to the concentration and orientation of the fibers, while assuming perfect fiber‐fiber contact. The relationship between resistivity and fiber concentration predicted by the model is in qualitative agreement with actual data, and predictions of the anisotropy in volume resistivity compare well with experimental results. The second model accounts for the effect of fiber‐fiber contact and fiber length on composite resistivity. Predictions are in excellent agreement with experimental data for polypropylene composites reinforced with nickel‐coated graphite fibers.
Microstructure and volume resistivity of composites of isotactic polypropylene reinforced with electrically conductive fibers
Authors: Weber Mark , Kamal Musa R. 
Published: April 2004

AbstractThe effect of processing method on the microstructure and volume resistivity of polypropylene reinforced with nickel‐coated graphite (NCG) fibers or stainless steel (SS) fibers is presented. Samples were produced by compression molding, extrusion, and injection molding. The volume resistivity of the composites was measured in three perpendicular test directions to determine anisotropy. The stress and thermal fields experienced during processing determine the ultimate microstructure. The measured resistivity is dependent on this processing‐induced microstructure as reflected by the distribution of fiber orientation, length, and concentration. Composites in which the fiber orientation is anisotropic also exhibit anisotropic resistivity. Volume resistivity is lowest in the principal direction of fiber orientation. Samples with the greatest fiber length become conductive at the lowest fiber loadings. Resistivity decreases with an increase in fiber loading, but concentration gradients are often produced, especially in the injection molded samples. High fiber concentrations generally resulted in poor dispersion and wetting. The intertwining and bending of the SS fibers make processing difficult. A comparison between the two types of fibers reveals that, for the systems considered in this study, the SS fibers impart conductivity at lower loadings, but that the NCG fiber composites are ultimately more conductive.
Mechanical properties of polypropylene/polyamide 6 blends: Effect of manufacturing processes and compatibilization
Authors: Yoon Byung Seon , Joang Joon Young , Suh Moon Ho , Lee Yong Mu , Lee Suck Hyun 
Published: April 2004

AbstractThe properties of polypropylene (PP)/polyamide 6 (PA) blends, obtained by the following two different blending methods, were investigated. Blends of PP/PA and PP/PA/maleic anhydride have been prepared using a twin screw extruder and a fiber cutting, flying and mixing apparatus that directly commingles PP fiber and PA fiber. The properties measured include rheological properties by means of a capillary rheometer, morphologies by scanning electron microscopy, and mechanical properties by a universal testing machine and a high rate impact tester. In the presence of compatibilizer, a marked dispersibility of the polymer blends of PP and PA was observed, and mechanical properties were found to increase as a result of improvement of the interfacial adhesion and the dispersibility. The properties of PP/PA blends manufactured by two different pieces of equipment were shown to be similar in the case of melting both resins. But in particular, superior impact properties were obtained in blends not melting PA fibers as a dispersed phase rather than blends using maleic anhydride grafted polypropylene (PP‐g‐MA) as a compatibilizer.
Interfacial behavior of epoxy/E‐glass fiber composites under wet‐dry cycles by fourier transform infrared microspectroscopy
Authors: Noobut W. , Koenig J. L. 
Published: April 2004

AbstractThe interfacial behavior of epoxy/glass fiber micro‐composites under cycles of wet and dry environment change was investigated by Fourier Transform Infrared (FTIR) microspectroscopy. The adsorbed water content in the epoxy/fiber interphase under moist conditions is reduced by treating the glass fibers with a silane coupling agent, γ‐aminopropyltriethoxysilane. This results in a significant decrease in the ring‐opening polymerization of epoxy in the epoxy/fiber interphase. It is also found that the wet‐dry cycles cause the significant variation of the residual adsorbed water in the interphase regions. There is an indication that the debonding in the epoxy/silane‐treated fiber interphase is slower than the epoxy/heat‐cleaned fiber interphase.