bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis and properties of a low hygrothermal stress epoxy molding compound for electronic encapsulation
Authors: Tai Horng‐Jer , Wang J. B. , Chou Hui‐Lung
Published: April 2004

A vinyl siloxane‐modified cresol novolac epoxy (CNE)/cresol novolac hardener (CNH) molding compound with both siloxane and epoxy components capable of further crosslinking is synthesized. Through careful adjustment of TPP dosage, the Tg of CNE/CNH resins can be effectively controlled. The VS‐modified CNE/CNH compound possesses a lower Young's modulus, a lower linear coefficient of thermal expansion (LCTE), and a higher break strain than those of its unmodified counterpart. The combination of lower mechanical moduli and lower LCTE results in a 33% reduction in thermal stress caused by thermal mismatch. In addition to thermal mismatch, chemical shrinkage in a molding process is also an important factor that affects the interfacial strain between a compound and a substrate. The incorporation of vinyl siloxane (VS) incurs a 25% reduction in the equilibrium moisture uptake and a 16% reduction in the coefficient of diffusion for the VS‐modified compound. This modified compound can help alleviate the popcorning problems in IC packages resulting from hygrothermal stresses.
Rheological behavior of (short) carbon fiber/thermoplastic composites. Part II: The influence of matrix type
Authors: Carneiro O. S. , Maia J. M.
Published: April 2004

This study is the second of a series of two papers on the rheological properties of VGCF/thermoplastic composites, its aim being to compare the performance of different thermoplastic matrices when reinforced with sub‐micron Vapor Grown Carbon Fibers (VGCF). For this purpose, two polymers (polypropylene, PP, and polycarbonate, PC) were used to produce composites with different levels of fiber incorporation. The highest content VGCF composites were produced, in pellet form, using a co‐rotating twin‐screw extruder. These were subsequently diluted during the injection molding stage to obtain composites with different levels of fiber content. The rheological characterization was performed, using the latter materials, by means of both capillary and rotational rheometries, results being presented and discussed in terms of reinforcing capability and its susceptibility to temperature, for the relevant functions in both shear (steady and oscillatory) and extensional flows. The results show that VGCF have a higher reinforcing capability, both rheological and mechanical, when incorporated in the PP matrix. This better performance can be due either to better adhesion between the fibers and PP in comparison to PC, or to a higher degree of melt penetration of non‐wetted fiber rich areas and lower fiber length degradation, owing to the lower viscosity of PP in the extrusion shear rate range.
Morphological development during injection molding of self‐reinforcing composites. II: Numerical simulations and analytical predictions
Authors: Li Zhigang , Narh Kwabena A.
Published: April 2004

In this study, combined numerical simulation of injection molding and analytical calculations have been used to determine the velocity and elongational strain in the advancing melt front (AMF) region, during the molding of PET/LCP blends, at various injection molding conditions. A model is proposed that establishes the relationship between the aspect ratio of LCP fibers and elongational strain, based on the assumption of an affine deformation of the LCP domains. This model enables us to predict the processing dependent morphology of injection molded PET/LCP blends. The effect of processing parameters on the morphology development during injection molding were investigated. The studies show that injection speed and mold temperature have significant effects on the morphological development of the blends, compared with the effect of the melt temperature. A good correlation between calculated and scanning electron microscopy results was obtained.
Statistical characterization of fiber permeability for composite manufacturing
Authors: Pan Rong , Liang Zhiyong , Zhang Chuck , Wang Ben
Published: April 2004

Resin transfer molding (RTM) is considered one of the most promising composite fabrication techniques because of its relatively low equipment and tooling costs, short cycle times, and excellent design flexibility. Yet several technical issues impede wider application for this process. One of those issues is the measurement and characterization of fiber preform permeability, which plays a key role in process design and control. In this study, an automatic permeability measurement apparatus with automatic data acquisition and processing capabilities has been developed to improve measurement accuracy and reliability. Four major factors and their effects on permeability for a knitted and a woven fabric performs are investigated. Design of experiments, ANOVA analysis, and distribution characterization techniques are used to analyze the permeability‐influencing factors and statistical properties of fiber preform permeability. It is found that the fiber preform permeability values vary significantly for different mold shapes and fiber handling conditions. It is also revealed that permeability values for both fabrics follow normal distributions, even though their means and variances are different. These results can be used to better understand the behavior of the RTM process and to improve process design and control.
Effect of impregnation conditions on prepreg properties and honeycomb core crush
Authors: Martin C. J. , Putnam J. W. , Hayes B. S. , Seferis J. C. , Turner M. J. , Green G. E.
Published: April 2004

The effects of fiber tension, line speed, and impregnation temperature and pressure in the prepregging process used to manufacture a commercial high temperature toughened epoxy prepreg were investigated in a Design of Experiments (DOE) to understand core crush in honeycomb composite structures. The prepregs developed in this DOE were characterized by tack, permeation, optical microscopy, and frictional resistance. Of these methods, frictional resistance was found to correlate with core crush. Tack, permeation, and optical microscopy provided a basis for understanding this relationship through impregnation and morphology. Prepregs manufactured with high fiber tension showed greater crush and less frictional resistance than prepregs with manufactured low fiber tension. These low tension prepregs were found to have more fibers at the prepreg surface, allowing them to grip the adjacent surface and resist slippage. By identifying the key factors influencing honeycomb core crush, the prepregging process was modified, producing a crush‐resistant prepreg for end use manufacture.
A review of methods for improving the interfacial adhesion between carbon fiber and polymer matrix
Authors: Tang Long‐Gui , Kardos John L.
Published: April 2004

The interfacial properties between carbon fibers and surrounding matrix of a composite are drastically affected by interfacial structure. This structure mainly relates to the surface physico‐chemistry of the fiber, which includes its surface chemical groups and microstructure, morphology, surface area, and surface free energy. These properties can be changed by various surface treatments, including various dry and wet oxidation steps, plasma treatment, electrodischarge, and fiber sizing or coating. These methods improve the interfacial properties significantly and synergistically, although each treatment has its specific application area.
Improvement of carbon fiber/PEEK hybrid fabric composites using plasma treatment
Authors: Jang Jyongsik , Kim Hyuncheol
Published: April 2004

A carbon fiber (CF)/polyetheretherketone (PEEK) composite was manufactured using hybrid fabrics composed of CF and PEEK fiber. The fiber/matrix interface was modified by low temperature oxygen plasma treatment. Scanning electron microscopy (SEM), X‐ray photoelectron spectroscopy (XPS) and Fourier transform attenuated total reflection infrared spectroscopy (FTIR‐ATR) were used to relate the roughness and the functionality of the CF surface with the interfacial adhesion strength of the CF/PEEK composite. Scanning electron micrographs showed that plasma treatment increased the roughness of the CF surface up to 3 min of plasma treatment time; and prolonged treatment resulted in overall smoothing. XPS results confirmed that increasing treatment time marginally increased surface functionality: treatment for more than 5 min decreased the surface functionality by removing the active site of the CF surface. In addition, flexural strength and interlaminarshear strength (ILSS) of the CF/PEEK composite were measured. Their maximum values were observed at 3 min of plasma treatment time as a result of surface roughening by plasma etching. The SEM results were correlated with mechanical properties of the CF/PEEK composite.
Kinetic studies of thermoset cure reactions: A review
Authors: Yousefi A. , Lafleur P. G. , Gauvin R.
Published: April 2004

This article presents a review of the kinetic studies on the cure reactions of thermosetting resins. The emphasis is placed on those conducted using the thermal analysis by differential scanning calorimetry. Two important categories of kinetic models are discussed and some existing parameter estimation techniques are presented. A variety of factors affecting the cure reactions, including the formulation of cure and process variables, are discussed. At the end, two different approaches in modeling the chemoviscosity of polymeric reactive systems are presented and some existing chemorheological models developed based on these approaches are briefly reviewed.
Fatigue delamination growth under cyclic compression in glass/epoxy composite beam/plates
Authors: Kardomateas G. A. , Malik B.
Published: April 2004

Results are reported on the fatigue growth of internal delaminations in glass/epoxy composite beam/plates subjected to constant amplitude cyclic compression. Because of compressive loading, these structures undergo repeated buckling/unloading of the delaminated layer with a resulting reduction of the interlayer resistance. A noteworthy feature of the problem is that the state of stress near the delamination tip is of mixed mode (I and II). The present combined experimental/analytical investigation for the glass/epoxy composites complements our earlier studies on delamination growth under cyclic compression in unidirectional graphite/epoxy specimens. Several configurations are studied with the delamination located at different depths (through the thickness) and with different applied maximum compressive displacements. The experimental data are correlated with the predictions from a combined delamination buckling/postbuckling and fracture mechanics model. A mode‐dependent fatigue delamination growth law is used together with an initial postbuckling solution for the deformation pattern of the delaminated layer and the substrate, which does not impose any restrictive assumptions on the delamination thickness and plate length. The experimental data seem to be adequately correlated with the theory and the fatigue delamination growth is found again to be strongly affected by the relative location of the delamination through the plate thickness. Finally, a comparison of the cyclic growth rate in glass/epoxy specimens with the corresponding one in graphite/epoxy specimens of the same geometry and applied loading shows that the delamination would grow much faster in the graphite/epoxy specimens.
Effect of moisture content on the properties of silanized jute‐epoxy composites
Authors: Gassan Jochen , Bledzki Andrzej K.
Published: April 2004

The composites investigated in this article were epoxy resins reinforced with jute‐fibers. The jute‐fibers were modified with an epoxyfunctional‐γ‐glycidoxypropyltrimethoxy‐silane (A‐187 from Osi‐Specialtis GmbH, Germany), which works as a coupling agent between fiber and matrix. The introduction of the coupling agent distinctly influences the mechanical properties of the composite: Dynamic modulus was doubled, damping was reduced by about 50%, and the Wöhler curves showed fatigue limits increased by about 20%. The investigations pointed out further that the moisture uptake of composites with silanized fibers was reduced by about 10–20%. Moisture at equilibrium and kinetics of absorption increase with increasing fiber content. Finally, the application of the coupling agent caused a reduction of moisture effects on mechanical properties. Tensile strength, tensile modulus, and fatigue strength under repeated tensile stress were reduced up to 30%. This tendency was not duplicated in the results for flexural strength and flexural modulus.
Aqueous powder slurry manufacture of continuous fiber reinforced polyethylene composite
Authors: Tang Longgui , Li Lin , Yi Xiaosu , Pan Zuren
Published: April 2004

A model and experiment of an aqueous slurry process are reported. According to an ideal structure of a fiber‐reinforced composite, we present a square geometrical model to build up the relationships among some important parameters in the process such as power particle diameter, wet slurry concentration, flow distance of melting power particle, and fiber volume fraction of the composite. Practical experiments based on these relationships provide the optimum parameters for manufacturing the continuous fiber reinforced polyethylene matrix composite.
Synthesis and characterization of two novel maleimides containing an epoxy backbone
Authors: Liang Guozheng , Gu Aijiuan
Published: April 2004

Two novel maleimides containing an epoxy backbone, diglycidyl ether of bisphenol A and TDE‐85 epoxy, were synthesized and characterized. The maleimides, coded EMs were prepared by reacting the corresponding epoxy resin with N‐(p‐carboxy phenyl) maleimide. EMs have lower softening and curing temperature and a wider processing window than the common bismaleimide. Properties of cured resins show that EMs have improved toughness and good thermal properties. Composites based on EMs and woven glass cloth were also prepared and their properties determined.
Mechanical behavior of textile composite materials using a hybrid finite element approach
Authors: Gowayed Yasser , Yi Li
Published: April 2004

A novel analytical solution is presented to describe the mechanical behavior and failure of textile reinforced composites. This solution is constructed from two parts. First a geometrical model, based on a processing science approach coupled with graphical rendering, is utilized to quantify the spatial characteristics of the fabric preform inside the composite. A 3‐D iterative hybrid finite element analysis is then used, utilizing data acquired from the geometrical model, to predict the stressstrain behavior of the composite. Inelastic behavior is modeled using an expanded Hahn and Tsai model and maximum stress criterion is used to predict initial failure. Damage progression is predicted based on a stiffness reduction approach. AS4 carbon/epoxy plain weave composite laminates, with a range of fiber volume fractions, have been tested. A 3‐D woven E‐glass/poly‐vinyl‐ester (PVE) angle interlock composite was also tested. Analytical results are compared with results from this experiment as well as other analytical models and experimental data in the literature. Theoretical model predictions are in agreement with most experimental data.
Accurate permeability characterization of preforms used in polymer matrix composite fabrication processes
Authors: Lai Yen‐Huang , Khomami Bamin , Kardos John L.
Published: April 2004

The permeabilities of fabrics composed of carbon and glass fibers have been determined by utilizing both simple 1‐dimensional and 2‐dimensional radial flow measurements using silicone oil and motor oil as permeants. The carbon fabric is typical of that used in fabrication of aerospace grade polymer matrix composites, while the glass fabric is a 3‐dimensional woven fabric that has been proposed as a standard reference material for permeability characterization. Our results indicate that reliable permeability data for fiber preforms with varying architectural complexity can be obtained provided that the experiments are performed with utmost care and that appropriate equations are used to analyze the data. In‐plane permeabilities for the carbon fiber preforms from transient unidirectional constant flow rate and constant pressure experiments agreed within 5%, regardless of the preform orientation to the flow direction. Steady‐state results on the same preforms showed agreement within 2% between constant flow rate and constant pressure experiments. The capillary pressure effect was shown to be negligible for the transient experiments. The maximum difference between the transient and steady state permeability values was 3%. The maximum difference between a permeability measured with unidirectional flow and the same permeability measured with radial flow is less than 10%.
Composites as friction materials: Recent developments in non‐asbestos fiber reinforced friction materials—a review
Authors: Bijwe Jayashree
Published: April 2004

Replacement of conventional asbestos based friction materials has been called for because of bans on the use of asbestos. Research in this direction in the last decade has led to the development of more efficient asbestos‐free friction materials for automobiles. Fiber reinforced polymers show great promise for applications in modern vehicles. This review article focuses on the recent developments in the application of composites as friction materials. The first part of the article contains brief information about brakes, their action, brake materials, their desired properties, etc. The second part deals with the recent developments in non‐asbestos fiber reinforced friction materials.
A nonlinear control method for resin transfer molding
Authors: Mogavero J. , Sun J. Q. , Advani S. G.
Published: April 2004

In performing permeability measurements on the fiber reinforced preforms typically used in the resin transfer molding (RTM) process, two types of fluid injection are commonly utilized: constant fluid pressure and constant fluid flow rate. The constant pressure condition is often enforced by placing the test fluid within a pressure pot and supplying a constant gas pressure, thereby forcing the fluid into the mold under a constant pressure. In the case of constant fluid flow rate, the fluid is often supplied by forcing a piston through a fluid‐filled cylinder at a constant rate of displacement through the use of a press or Instron machine. This paper presents a nonlinear control method for providing constant flow rate RTM processes with a pressure pot solely through the use of a regulator. Computer simulations of the control examined the effect of various parameters on the ability to maintain constant flow rate. Rectilinear flow experiments were carried out to evaluate the theoretical development. Experimental results are in good agreement with the computer simulations. Both computer simulations and experiments show significant promise for the proposed control methodology.
Measurement of the electromagnetic shielding properties of mechanically loaded composites
Authors: Laight A. , Court R. , Treen A. , Buijs J.
Published: April 2004

The use of fiber reinforced plastic (FRP) composites for large structures is becoming more widespread. With composites increasingly called upon to replace structures traditionally fabricated from metals the requirement to find suitable methods of providing adequate electromagnetic shielding (EMS) is often of prime importance. This paper describes a measurement technique employing induced magnetic eddy currents for assessing electromagnetic shielding. The technique does not require costly screened rooms or large test panels and is portable and easy to use. The effectiveness of the technique for comparing the electromagnetic shielding of material samples after mechanical loading is demonstrated, and it is concluded that the method offers a cheap and reliable means of comparing screening solutions for composite materials in high loading or fatigue applications. The potential for development of the method into a through‐life shielding monitoring tool is also highlighted.
A comparison of compounding processes for wood‐fiber/thermoplastic composites
Authors: Park Byung‐Dae , Balatinecz John J.
Published: April 2004

This study was carried out to investigate the feasibility of developing a continuous compounding process for wood‐fiber/thermoplastic composites using the Szego mill, a unique, high speed planetary ring‐roller grinding mill. Prior to compounding, air‐dried sawdust was ground to evaluate the grinding effect in the mill. As the feed rate and the mill speed increased, the particle size increased and decreased, respectively. Sawdust particles were successfully compounded in linear low‐density polyethylene using the Szego mill without any major heat application. A Gelimat mixer, used for the compounding of wood fiber through a high‐shear thermokinetic mixing process, was also employed for comparison. Composites with 30 wt% wood fiber were prepared by both compounding processes, and their mechanical properties were evaluated. The use of a compatibilizer in compounding improved the mechanical properties of the composites regardless of the compounding process. The composites prepared by Szego mill compounding showed comparable strength properties with their counterparts from the Gelimat mixer. Power consumption during mill compounding was in the range of twin‐screw extruder processing.
Experimental study on the accuracy of advanced composite tools for slanted shapes
Authors: Huang C. K. , Yang S. Y.
Published: April 2004

High 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

A 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

Crosslinking 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

A 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

The 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

Allylated 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

An 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

This 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

This 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

The 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

This 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

Vacuum 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

We 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

Delamination 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

The 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

The 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

The 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

The 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

The 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.
Compaction of textile reinforcements for composites manufacturing. III: Reorganization of the fiber network
Authors: Robitaille François , Gauvin Raymond
Published: April 2004

The objectives of this series of papers are to describe the mechanical behavior of textile reinforcements under normal load and to quantify the effects of diverse processing parameters on that behavior. In the first and second papers of the series, experimental compaction and relaxation results were reported; general trends were identified and the effects of changes in the processing parameters were analyzed. In this paper, the results of sequences of successive compaction cycles applied to dry textiles and to textiles saturated in distilled H2O and silicone oil are presented. The reinforcements investigated are produced by assembling tows or rovings following different patterns; it is shown that the resulting heterogeneity, or regular variation of the local fiber volume fraction, can be associated to some particular elements of the mechanical behavior of the reinforcements. The reorganization of the fiber network and the effect of friction at the fiber contacts are demonstrated. Different stages in the reorganization process are identified; each stage is controlled by different parameters and corresponds to a precise behavior. Successive compaction cycles applied to a preform can reduce the void content of the final part.
Novel, low‐cost jute‐polyester composites. Part 1: Processing, mechanical properties, and SEM analysis
Authors: Dash B. N. , Rana A. K. , Mishra H. K. , Nayak S. K. , Mishra S. C. , Tripathy S. S.
Published: April 2004

The development of high performance composites from a cheap natural fiber, jute, as reinforcement is particularly significant from an economic point of view. In this work, jute fiber‐unsaturated polyester(GP) composites having appreciable mechanical properties were prepared by using solution impregnation and hot curing methods. Both unbleached (control) and bleached jute slivers with various percentages of fiber loadings were used to prepare the composites and were named JPH (C) i.e., Jute Polyester Hot Curing (control), and JPH (B) i.e., Jute Polyester Hot Curing (bleached), respectively. Mechanical properties such as tensile and flexural strain, toughness, and moduli of both the grades have been compared. Composites having 60 wt% of jute fiber yielded the best results. JPH (B) showed much better flexural properties than JPH (C), although the tensile properties of the latter were better. The inter‐laminar shear strength (ILSS) of the JPH (B) was found to be higher than JPH (C). The nature of fiber‐resin bonding was studied from scanning electron micrographs of the specimens subjected to tensile and flexural fracture. Dynamic mechanical properties were found to be very high, superior even to those of glass fiber reinforced composites. The flexural storage modulus was found to be 12.3 GPa at 30°C and to decrease slowly with temperature. The major finding in this work is the attainment of high mechanical properties of composite specimens with 60 wt %fiber loading. On a weight and cost basis, bleached jute fibres were found to be better reinforcements than other fibers with usual surface modification by coating or grafting processes.