bluuebunny/crossref_metadata_2025_split huggingface dataset:
Three‐dimensionally woven and braided composites. I: A model for anisotropic stiffness prediction
Authors: Pochiraju Kishore , Chou Tsu‐Wei 
Published: April 2004

AbstractA model for the prediction of anisotropic elastic stiffness of 3‐D textile structural composites based on the preform architecture and the preforming process parameters is presented. The methodology presented in this paper uses a preform model to represent the fiber microstructure and employs a micro‐mechanical analysis to determine the macroscopic anisotropic stiffness. Representative volume elements (macro‐cells) are identified for three‐dimensionally woven and braided preforms and geometric descriptions of the path and interactions between the tows within the cells are generated. This geometric modeling enables the estimation of the fiber volume fraction and the directional distribution of the fiber in the composite. The macro‐cell is further decomposed into simpler elements whose stiffness is determined from tow geometry and the stiffness of the fiber/matrix constituents. The macroscopic stiffness of the textile composite is obtained from the macro‐cell definition using an Effective Response Comparison (ERC) technique. Numerical examples are presented illustrating the developed methodology. Experimental characterization of several textile composites and the correlation of the experimental data with model predictions are considered in a companion paper.
Modeling fiber slippage during the preforming process
Authors: Lai Chyi‐lang , Young Wen‐bin 
Published: April 2004

AbstractUntil now, the pin‐jointed net model has been a widely used method for the prediction of preforming shape for woven fabrics. However, it deals only with pure trellising (or shear) and neglects other possible deformation modes. In some cases, there is evidence showing that other deformation modes have relevance to, and effectiveness in forming the final shape. A model considering only the shear mode will not result in an adequate prediction. In this study, a slippage model is developed to modify the pin‐jointed net model. Macrostructure of the fabrics is included in the slippage model in order to capture more deformation modes. Comparisons of experimental and simulation results are presented. It is shown that the numerical prediction using the slippage model has better agreement with experimental measurements.
Effect of cyclic moisture absorption desorption on the mechanical properties of silanized jute‐epoxy composites
Authors: Gassan Jochen , Bledzki Andrzej K. 
Published: April 2004

AbstractThe goal of this paper is to discuss the influence of water absorption‐desorption cycles on the mechanical properties of natural fiber reinforced plastics. Therefore, epoxy resins with jute wovens as reinforcement with untreated and silane treated fibers were investigated. Silane treatment of fibers led to increased tensile, flexural strength, and Young's modulus of composites with up to 30%. Absorption‐desorption cycles of fibers changed the fracture mechanisms of fibers without having significant effects on the tensile strength of the fibers. Light microscopic investigations showed that absorption‐desorption cycles of composites led to the debonding of resin from fibers as well as to cracks in the adjacent resin. Because of these mechanisms, tensile strength and Young's modulus decrease, independent of the quality of fiber resin adhesion. For dynamic loadings, storage cycle induces damages, further bringing about a decreased dynamic modulus and an increased progress in damage with increasing load cycles during the first two environmental cycles, being constant afterwards.
Visualization and quantification of forced in‐plane flow through deformed porous media
Authors: Friedman Henry L. , Johnson Robert A. , Gusev Vladimir , Neimark Alexander V. , Buvel Dianne , Salem David R. , Parnas Richard S. 
Published: April 2004

AbstractFluid flow in liquid molding processes and in other applications involving porous media is often characterized with a permeability tensor and modeled by d'Arcy's law. The permeability is a sensitive function of pore structure, which, in deformable materials, is influenced by compression and extension. The majority of previous permeability measurements on composite reinforcement fabrics did not account for deformations imposed on them by corners and curves in the mold. In the present study, transparent molds were designed with a single 90° bend in which the gap between plates was held constant throughout the flow path. Thus, the effects of fabric curvature on permeability were investigated independently of the effects of fabric compression in the thickness direction. A new experimental system was developed to visualize and quantify fluid flow in fabrics mounted in transparent molds. The reported measurements were conducted with fluid flowing through a (vertical) flat region of fabric, around the 90° curve, and then along a second (horizontal) flat region. Permeability was found to be reduced by the imposed curvature for a nonwoven polyester and three‐dimensional woven glass fabric. We were able to quantify the effect of curvature on permeability for the former, but not for the latter because of an enduring, dominant nonlinear entrance resistance. For the glass, comparison of two flow rates indicates that the faster flow is characterized by a two stage filling process, whereas, at the slower rate, the liquid front fills all pores at the same time.
Processing and properties of resol and epoxy blends for resin transfer molding
Authors: Manfredi L. B. , Claro J. A. , Kenny J. M. , Mondragón Egaña I. , Vázquez A. 
Published: April 2004

AbstractBlends of epoxy and resol matrices for resin transfer molding (RTM) have been prepared and characterized with the double aim of improving the processability of resols and the fire resistance of epoxies. The reaction rate of the overall system is enhanced by the exothermic reaction between the epoxy and an aliphatic amine, which also promotes the resol reaction. In addition, the mechanical behavior of the resol is improved as the shear stress increases with the addition of epoxy resins. However, blending also produces a reduction of the intrinsic fire resistance of phenolic resins. The study demonstrated the feasibility of producing blends for matrices of composites processed by resin transfer molding. The recommended range for the epoxy content was determined through a balance of processability, fire resistance, and mechanical properties of the composites obtained. Moreover, the effects of fiber surface modifications were studied as a way to promote higher shear stresses in the epoxy‐resol matrix composite without jeopardizing the fire resistance properties.
Use of acoustic emission to characterize corrosion fatigue damage accumulation in glass fiber reinforced polyester laminates
Authors: Kotsikos G. , Evans J. T. , Gibson A. G. , Hale J. 
Published: April 2004

AbstractThe acoustic emission technique has been used to characterize fatigue damage accumulation in glass fiber woven roving (0/90°) polyester laminates after prolonged exposure in sea water. Comparisons were made with fatigue tests of “as‐received” laminate under similar loading conditions. Pre‐exposure has been found to substantially reduce the fatigue strength of the composite. Acoustic emission monitoring during fatigue testing has shown that the amplitude distribution of the acoustic events shifts from predominantly low amplitude (40–55 dB), associated with matrix cracking, in as‐received specimens, to intermediate amplitude (55–75 dB) associated with delamination and debonding after pre‐exposure. Optical microscopy of fatigued samples has verified these failure mode changes. The number of recorded high amplitude events (≥ 80 dB) associated with fiber fracture is the same in both cases, which indicates that the glass reinforcement is unaffected by pre‐exposure.
Toughening mechanisms in rubber‐modified glass fiber/unsaturated polyester composites
Authors: Sjögren B. A. , Berglund L. A. 
Published: April 2004

AbstractAn important case of composite failure is the leakage of pipes and pressure vessels subjected to internal pressure. The primary damage mechanism leading to leakage is transverse cracking parallel to the fibers. Effects of matrix toughening on transverse cracking strains were therefore investigated for GF/UP cross‐ply laminates with matrices of different liquid rubber content. The strain to the first transverse crack was increased from 0.2 to 0.6% with 10 wt% rubber. Debonding occurred at similar strains in GF/UP and GF/UP‐rubber. However, whereas debonding was almost simultaneous with transverse cracking in GF/UP, gradual growth of debonds to short cracks took place initially in GF/UP‐rubber. This was followed by slow extension of short cracks to a critical flaw size corresponding to unstable growth.
Hydrolytic aging of polysiloxane networks modeling the glass fiber epoxy‐amine interphase
Authors: Salmon L. , Thominette F. , Pays M. F. , Verdu J. 
Published: April 2004

AbstractIt has previously been shown that polycondensates of trialkoxysilanes (AlkO)3SiR could chemically simulate coupling agent layers located at the interphase of amine‐crosslinked epoxy/glass fiber composites (1) and that a humid environment modifies the degree of condensation of the network. Although it is generally believed that water will inevitably hydrolyze the polysiloxane structure and destroy the interphase (2), the authors have demonstrated that the siloxane links of the network evolve toward an equilibrium state. This state depends on the chemical structure of the organic chain that can react with the matrix. For example, in the case of aminopropyltriethoxysilane, the siloxane equilibrium concentration is low enough to allow total hydrolysis of the polymer. Conversely, propylsilane network stability could be explained by a very high siloxane equilibrium concentration. In this article, one of the previously studied systems has been selected: GPS (glycidylpropylsilane), in which the coupling function is an epoxide group (glycidyl). In an epoxy/glass fiber composite, this group is expected to react with an amine group belonging to the epoxy network. Aniline has been used here to model the GPS‐epoxy network bonding. This reaction modifies the chemical nature of the organic chain branched on the silicon and then potentially displaces the siloxane equilibrium. A gravimetric method, size exclusion chromatography (SEC), Fourier transform infrared spectroscopy (FTIR), 29Si nuclear magnetic resonance (NMR), and 13C NMR have been used. The results are that, when exposed to hot water, the GPS and the GPS‐aniline networks evolve contradictorily. Although GPS tends to hydrolysis, GPS‐aniline tends to condensation. This article analyzes the compatibility of the different behaviors with the simple kinetic model reported in a previous paper (1) and the importance of this phenomenon concerning the aging of the glass/matrix interphase of composite materials.
Numerical simulation of resin transfer molding using linear boundary element method
Authors: Schmidt F. M. , Lafleur P. , Berthet F. , Devos P. 
Published: April 2004

AbstractUsing mass conservation and Darcy's law to describe flow through isotropic porous media leads to a Laplace equation, which may be solved numerically at each time step using the boundary element method. For anisotropic porous media in which the permeability matrix is symmetric, the problem can be solved in the same way by rotating and stretching the coordinates. The numerical model has been compared with analytical solutions and experimental data in the case of radial front flows and with finite element for a frontal injection.
Three‐dimensionally woven and braided composites. II: An experimental characterization
Authors: Pochiraju Kishore , Chou Tsu‐wei 
Published: April 2004

AbstractThe results of an experimental characterization of the elastic and failure behavior of several 3‐D textile composites under tension, compression, shear, and bending loads are reported in this paper. Composites reinforced with several textile preforms comprising of layer‐to‐layer weaves, through‐the‐thickness weaves, and four‐step circular braids were characterized. The preform architectures examined included variations in tow size, pitch for the woven composites, and braid angle in the braided composites. The experimental methods, stress‐strain relationships and descriptions of the failure modes of the test specimens are described. Correlations of the predictions from a model described in the companion paper with the experimental results are also presented.
Mechanical and thermal behavior of poly(acrylonitrile‐butadiene‐styrene)/polycarbonate blends reinforced with potassium titanate whiskers
Authors: Tjong S. C. , Jiang Wei 
Published: April 2004

AbstractPoly(acrylonitrile‐butadiene‐styrene) (ABS)/polycarbonate (PC) blends reinforced with potassium titanate (K2Ti6O13) whiskers were prepared in a twin screw extruder followed by injection molding. The whiskers were pretreated with tetrabutyl orthotitanate prior to compounding. The tensile, dynamic mechanical, impact, morphology and thermal properties of the blends were studied. Tensile tests showed that the modulus of ABS/PC/K2Ti6O13 blend increased markedly with increasing whisker content. However, the variation of the modulus of ABS/PC/K2Ti6O13 blend with PC content followed a sigmoidal relation. In addition, the tensile strength of the blends containing 20 wt% PC tended to increase markedly with increasing whisker content. But the impact strength of the blends containing 20 wt% PC decreased rapidly with increasing whisker content. Dynamic mechanical analyses (DMA) results indicated that the storage modulus of the blends increased markedly with increasing K2Ti6O13 whisker content. Differential thermal analysis and thermogravimetric measurements showed that potassium titanate whiskers tend to induce chemical decomposition of PC during blending of the PC/whisker blends. However, the incorporation of ABS into PC was beneficial to reduce the PC decomposition during compounding with the whiskers.
Processing and properties of co‐injected resin transfer molded vinyl ester and phenolic composites
Authors: Gillio Emanuele F. , McKnight Geoffrey P. , Gillespie John W. , Advani Suresh G. , Bernetich Karl R. , Fink Bruce K. 
Published: April 2004

AbstractVacuum Assisted Resin Transfer Molding type processes have been proven to be cost effective manufacturing techniques for large composite structures. However, their use has been limited to a single resin system. A large variety of composite structures require multiple resins to serve different purposes while being integrated into a single structure. Co‐Injection Resin Transfer Molding (CIRTM) is a new manufacturing process, developed at the University of Delaware's Center for Composite Materials in collaboration with the U.S. Army Research Laboratory, that enables the user to manufacture multi‐layer hybrid composite parts in a single processing step (1). In this paper, CIRTM is used to manufacture a dual layered structure consisting of a vinyl ester layer for structural integrity and a phenolic layer for fire, smoke, and toxicity protection. The two resins are simultaneously injected into a mold filled with a stationary fiber bed and are co‐cured. Resin separation is maintained by a 0.0254 mm (0.001 in) thick polysulfone film sandwiched between two layers of 0.165 mm (0.0065 in) thick adhesive. A Differential Scanning Calorimeter (DSC) is used to select the optimum cure cycle for all of the materials. Mechanical testing is used to evaluate the performance of the interphase formed between dissimilar materials. Short beam shear (SBS) is used to evaluate the overall quality of the part produced. Double cantilever beam (DCB) is used to quantify the fracture toughness of the interphase, and the wedge test is used to evaluate the durability of the interphase. Experimental results show that co‐injected, co‐cured materials offer properties equivalent, or in some cases, superior, to those provided by single injection resin composites. This case is used to develop and present a methodology that can be followed to co‐inject different resins.
Effects of interlaminar stresses on damping of 0‐degree unidirectional laminated composites
Authors: Yim Jong Hee , Jang B. Z. , Suhling J. C. , Gillespie J. W. 
Published: April 2004

AbstractThe principal aim of this paper is to formulate a general model for predicting damping in composites on the basis of the concept of strain energy‐weighted dissipation. In this model, the effects of interlaminar stresses on damping have been included in addition to the effects of in‐plane extension/compression and in‐plane shear. Validation of the model was confirmed by performing damping measurements on 0° unidirectional composite beams with varying length and thickness. The results of theoretical predictions of damping in laminated composites were found to compare favorably with experimental data. The transverse shear (σxz) reveals to have a considerable effect on the damping mechanisms in 0° unidirectional polymer composites. However, the other interlaminar stresses (σyz, σz) were shown to have little influence on damping in composite beam.
Polymer composites prepared by compression molding of a mixture of carbon black and nylon 6 powder
Authors: Pinto Gabriel , López‐gonzález Cipriano , Jiménez‐martín Ana 
Published: April 2004

AbstractThe results of an experimental study on the effect of processing variables and filler concentration on the electrical resistivity of conductive composites based on nylon 6 filled with carbon black are reported. A typical percolation behavior in the effect of electroconductive filler content on the resistivity was found. The electrical resistivity of the composites is > 1012 ohm°Cm unless the carbon black content reaches the percolation threshold at ∼9 wt%, beyond which the resistivity decreases markedly by as much as twelve orders of magnitude. Two parameters of molding process—temperature and time—were shown to have a notable effect on the resistivity of composites, whereas pressure has no influence on this property in the pressure range considered. There is no sharp variation in the density due to the onset of percolation, and the hardness of samples is not influenced by the presence of the filler.
Development of an isothermal lubricating layer model for injection pultrusion of electronic prepregs
Authors: Hogade Ranjeet , Lee Ming , Castro Jose M. , Lee L. James 
Published: April 2004

AbstractThe current process for manufacturing electronic prepregs uses solvent‐based resin systems. Solvents are environmentally unfriendly and contribute to voids in the pre‐preg, which are a source of product variability. Prepreg inconsistencies are one of the major sources of scrap on the board shops. To overcome these drawbacks, a solvent‐less process is currently being developed in our laboratory. The process is based on the concept of injection pultrusion or continuous resin transfer molding (RTM). The centerpiece of the process is an impregnation die. Glass fabric and resin are fed into the die where fiber impregnation and partial resin cure occurs depending on the material chemo‐rheology. The B‐staging is finished in an oven located immediately after the die. A key to the success of the process is being able to predict the pulling force. Fabrics used in electronic prepreg manufacturing are relatively fragile; they could be damaged if the pulling force is too high. A model to predict the pulling force, based on the formation of a continuous lubricating layer between the die surface and the moving fabric, has been developed and experimentally tested using model fluids.
AC conductivity of carbon fiber–polymer matrix composites at the percolation threshold
Authors: R̈ímská Zden̈ka , Křuesálek Vojtěuch , S̈pac̈ek Josef 
Published: April 2004

AbstractThis paper reports results on experimental investigation of the conductivity behavior of carbon fiber filled polymer composites at the percolation threshold. Two types of carbon fiber‐epoxy matrix composites have been studied and comparison of the measured data has been made. These two types of composites differ in the surface modification of carbon fibers (in one case the surface of carbon fibers is covered with polymer beads using the microencapsulation technology, in the other their surface stayed unmodified). Experimental data reveal that surface modification of carbon fibers influences greatly the DC conductivity (percolation threshold moves to higher concentrations) but does not influence the AC electrical properties. From the frequency dependence of conductivity upon fiber concentration it becomes clear that it is not possible to predict the high frequency conductivity (electromagnetic interference shielding properties) based on the DC conductivity. Percolation behavior of conductivity as a function of conductive filler concentration is typical only for DC or low frequency AC conductivity. The percolation threshold gradually vanishes for high frequencies of electromagnetic field. The temperature dependence of electrical properties has also been studied. Composites with concentration near the percolation threshold show the switch‐off effect (at the specific temperature the DC conductivity drops by several orders of magnitude). This switch‐off effect does not occur for high frequency AC conductivity.
Composite machining damage quantification using thermoelastic stress analysis
Authors: Horn Gavin P. , Mackin Thomas J. , Kurath Peter 
Published: April 2004

AbstractA new experimental method is presented for quantifying machining damage in polymer matrix composites. The method consists of capturing infrared images of machined samples and using thermoelastic stress analysis to quantify damage from the machining event. A modified stress concentration factor is presented as an easily measured and useful damage parameter. Circular holes were drilled into the center of plate specimens fabricated from a commercially available glass fiber reinforced composite. A standard drill bit, brad point drill bit, and abrasive water jet machining were the three machine tools investigated. Infrared images were used to quantify the machining damage by assigning a thermoelastic stress analysis based stress concentration factor (mSCF) to each machined hole. The mSCF was then used to rank the damage inherent to each machining method. Optical and electron microscopy were utilized to identify the types of damage associated with the three machining methods. Finally, each sample was fatigued to failure to substantiate the IR results. The ranking of damage based upon the mSCF was in good agreement with the fatigue lifetime rankings: higher mSCF is associated with shorter fatigue lifetimes.