bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermal expansivity and bulk modulus of polymer composites: Experiment versus theory
Authors: Simha R. , Papazoglou E. , Maurer F. H. J. 
Published: May 2005

AbstractCorrelations between the thermal expansivity, αc, and the compressibility, Kc, of particulate‐filled polymer melts are explored in terms of two different theories and in connection with experiments. Both theories employed [an interlayer approach based on micromechanics (IM), and a molecular one starting from the statistical thermodynamics of mixtures (MM)] account for the effect of filler‐matrix interactions, viewed as a system‐dependent parameter. The concentration dependences of αc and Kc calculated using either IM or MM agree well with experiments on polyurethane and epoxy composites, and it is possible to predict αc based on Kc experimentation. In MM this is always true, but in IM it depends on a knowledge of relations between α and K of the constituents. This point remains to be explored further.
Liquid flow in molds with prelocated fiber mats
Authors: Molnar J. A. , Trevino L. , Lee L. J. 
Published: May 2005

AbstractThe mechanism associated with mold filling in the manufacture of structural RIM (SRIM) and resin transfer molding (RTM) composites is studied by means of flow visualization and pressure drop measurements. To facilitate this study, an acrylic mold with a variable cavity was constructed and the flow patterns of nonreactive fluid flowing through various layers, types, and combinations of preplaced glass fiber reinforcement mats were photographed for both evacuated and nonevacuated molds. The pressure drops in the flow through a single type of reinforcement (e.g., a continuous strand random fiber mat) and also a combination of reinforcement types (e.g., a stitched bidirectional mat in combination with a random fiber mat) were recorded at various flow rates to simulate high‐speed feeding processes (e.g., SRIM) and low‐speed feeding processes (e.g., RTM). By changing the amount of reinforcement placed into the mold, the permeabilities of the different types and combinations of glass fiber mats were obtained as a function of porosity. It is shown that partially evacuating the mold cavity decreases the size of bubbles or voids in the liquid, but ultimately increases the maximum pressure during filling. The results also show that glass fiber mats exhibit anisotropic permeabilities with the thickness permeability, Kz, being extremely important and often the determining factor in the pressure generated in the mold during filling.
Rheological and mechanical characteristics of poly‐p‐phenylene terephthalamide/nylon molecular and particulate composites
Authors: Park H.‐S. , Kyu T. 
Published: May 2005

AbstractPoly‐p‐phenylene terephthalamide (PPTA) and nylons (nylon 6, 66, 11, and 12) molecular and particulate composites were examined with emphasis on rheological, mechanical, and morphological characteristics. These molecular composites were prepared by coagulation in water from isotropic ternary sulfuric acid solutions. Upon heating above the crystal melting temperatures of nylons, the molecular composites undergo phase separation and become two‐phase particulate composites. Shear viscosity measurements indicate that the viscosity of nylon 6 and 66 systems has increased for an order of magnitude because of the presence of PPTA, but decreased in the case of nylon 11 and 12 systems. PPTA/nylon 6 and 66 systems exhibit yield behavior, particularly with high PPTA contents. Measurements show an extrudate swell of around 1 in all composition ranges and shear rates. Scanning electron microscopic investigations of low PPTA content particulate composites reveal spherical or long fibrillar morphology of PPTA phase dispersed in nylon matrices. Wide angle X‐ray diffraction investigations show no preferred orientation in the extrudates, but biaxial orientation in the case of compressed films. The study on mechanical properties of extrudates of 5 to 10 wt.% PPTA compositions exhibits significant improvement in tensile modulus and tensile strength. The heat‐treated extrudates show further increase in tensile modulus and tensile strength, as compared with the unannealed samples, but the elongation at break decreases.
Interlaminar shear test by hybrid sandwich specimen under distributed load
Authors: Rosensaft M. , Marom G. 
Published: May 2005

AbstractA new method is proposed for the determination of the interlaminar shear strength of composites. The method is particularly pertinent to composites of high interlaminar shear strengths, where the ratio of tensile (compressive) strength to shear strength is relatively low. In such materials, including unidirectional composites with improved fiber/matrix bond strength and angle‐ply laminates, an analysis based on a short beam interlaminar shear test is highly problematic and may, in fact, be erroneous. The test method is based on the use of a sandwich composite structure with a core made of layers of the tested composite and skins made of an elastic, strong unidirectional composite. A proper design procedure determines the choice of the skin material and of the relative thicknesses, so that flexural testing under distributed load leads to the intended core failure in shear. Calculations of the stress profile in a hybrid sandwich beam in bending and of the stress ratios under distributed load are presented. Also presented are experimental results recorded with sandwich hybrids made of unidirectional carbon‐fiber‐reinforced epoxy skins and a ±θ aramid‐fiber‐reinforced epoxy angle‐ply core.
Processing and structural optimization of PEEK composites
Authors: Lustiger A. , Uralil F. S. , Newaz G. M. 
Published: May 2005

AbstractThe objective of this experimental program was to understand how changes in processing conditions affect the morphology and ultimately, the performance of polyetheretherketone (PEEK)‐based carbon fiber composites. Based on some initial differential scanning calorimetry (DSC) work, various molding and aging conditions were implemented on compression molded plaques made from PEEK APC‐2 prepreg. These conditions included samples that were physically aged, annealed just below the melting point, slow cooled, prepared under low pressure, and under fast cooling. Using DSC, the crystallinity of plaques prepared according to the ICI procedure, low pressure, and physical aging conditions were found to be 31–33 percent, while the slow cooling and annealing conditions resulted in crystallinity of 42 percent, with slow cooling displaying a „shoulder”︁ on the primary melting endotherm. Optical and plasma etching/scanning electron microscopy on faster cooled plaques generally revealed a mixture of isolated and graphite fiber nucleated spherulites, while the slow‐cooled condition revealed larger fiber nucleated spherulites exclusively. Fracture toughness and impact delamination as measured by ultrasonic C‐scan indicates that slow cooling resulted in the lowest properties, while simultaneously resulting in the highest compression strength, all of which suggests reduced matrix toughness. The annealing condition, which allowed high crystallinity but in a matrix of smaller spherulites, resulted in properties intermediate between slow and fast cooling, suggesting that both spherulite size and degree of crystallinity are important in characterizing these materials. In contrast, physical aging resulted in no degradation in mechanical properties.
Application of digital image processing to the analysis of two‐phase materials with spherical inclusions
Authors: Parsi F. , Husband D. M. , Lisk J. S. , Gadala‐Maria F. , McNeill S. , Sutton M. 
Published: May 2005

AbstractDigital image processing was used to experimentally determine the two‐dimensional pair distribution function of suspensions of solid spheres (cross‐linked polystyrene spheres in silicone oil) and of composite materials with spherical inclusions (surface‐treated glass spheres in unsaturated polyester resin). An assembly of optical devices and computers was used to obtain and store images of two‐phase materials. Software was developed to analyze the information in the images in order to determine the pair distribution function. The technique developed is simple yet powerful, and with some modification could easily be adapted for the analysis of other multiphase systems.
A numerical simulation of short fiber orientation in compression molding
Authors: Advani Suresh G. , Tucker Charles L. 
Published: May 2005

AbstractA computer simulation has been developed to predict the orientation of fibers in a thin, flat part that is compression molded from sheet molding compound. The simulation combines a finite element/control volume simulation of the mold filling flow, a second order tensor representation of the fiber orientation state and a finite element calculation for the transient orientation problem. Sample results and comparison with experiments are presented. Predictions compare favorably with experiments on SMC (sheet molding compound) plaques and a model suspension of nylon fibers and silicon oil.
A study of the impact behavior of chopped fiber reinforced composite
Authors: Kau H. T. 
Published: May 2005

AbstractThe impact behavior of sheet molding compound (SMC) plaques was determined by using an instrumented Instron puncture test machine and the failure mechanism was qualitatively assessed by examining the damage. The impact response of SMC in terms of the load‐deflection curve is fairly consistent and shows the characteristics of a composite, intermediate between a brittle and a ductile material. At the speed of 2 m/s (about 5 miles per hour) the fracture energy, i.e., energy to break, was determined to be about 10 J for a regular 3 mm thick R‐25 SMC panel. This value decreases exponentially with a decrease in the thickness of the panel (power of 2.7). The failure process could also be affected by the material factors (resin and fibers used in the composite). For instance, an examination of the length distribution of the fibers in the damage region indicates that a combination of fiber pull‐out and severe fiber breakage have contributed to the impact resistance. Also, the fiber length in the composite could alter the failure modes. With the 25 mm fibers, the damage consists of an even mixture of fiber breakage and fiber pull‐out, but with a mixture of equal numbers of longer (38 mm) and shorter (13 mm) fibers in the composite, the damage is shifted to predominantly breakage of the longer fibers.
Fracture behavior of hybrid composites containing both short and continuous fibers
Authors: Lin T. L. , Jang B. Z. 
Published: May 2005

AbstractA method for improving the fracture resistance of brittle polymer composites was explored. This method involved the incorporation of short fibers in a thermosetting resin before being used for impregnating the continuous fibers or fabrics. The impact fracture energy and the maximum load experienced by the hybrid can be associated with the parameters of short fibers (e.g., volume fraction and mechanical properties). Electron micrographs of the fracture surfaces of the specimen loaded under mode I and mode II conditions indicate that the short fiber modified composites have a significantly greater fracture surface area and higher level of plastic deformation than the unmodified composites. The data from all the tests demonstrate that adding a small amount of short fibers can significantly improve the interlaminar fracture toughness and impact resistance of graphite/epoxy composites. However, a high volume fraction of added short fibers could make it difficult to out‐gas during compression‐molding, leading to a high void content and reduced mechanical properties of composites.
A micro/macro approach to fracture in composites
Authors: Kollé J. J. , Lin K. Y. , Mueller A. C. 
Published: May 2005

AbstractThe results of an integrated microscopic/macroscopic finite element analysis of fracture in fiber‐reinforced composites are presented. A macroscopic analysis of a composite double‐cantilever‐beam (DCB) fracture toughness test specimen was carried out using a singular finite element method. The effects of fiber layup angle on strain energy release rate are discussed. Results from this analysis were input as boundary conditions to a microscopic model used to calculate J‐integral values in the crack tip region. Nonhomogeneity in this region causes the elastic strain energy release rate to vary with crack tip location and geometry. Elastic‐plastic calculations showed that significant matrix plasticity occurs near fibers away from the crack tip region. The constitutive equation chosen for the matrix plasticity was shown to have an important effect on the J‐integral value. The results show how the microscopic J‐integral is related to the macroscopic strain energy release rate.
Random glass mat reinforced thermoplastic composites. Part III: Characterization of the tensile moudulus
Authors: Stokes Vijay K. 
Published: May 2005

AbstractRandom glass mat thermoplastic composites, which can be thermostamped to form complex deep‐drawn parts with ribs and bosses, are excellent materials for making low‐cost stiff parts with relatively high impact strength. An earlier efforts, aimed at understanding the scatter in the mechanical properties of these materials showed that the tensile modulus in these materials can vary by a factor of two over a 12.7‐mm distance. To better characterize the local tensile modulus for such materials, measurements of the local tensile moduli of long, thin, 12.7‐mm wide strips along both thin edges (left and right) of the specimen and across the face are used to show that the tensile modulus is well approximated by the arithmetic mean of the local left‐ and right‐edge tensile moduli. This arithmetic mean modulus, which is shown to correlate with the local density, is a better practical measure of the response to tensile loads.
Effect of processing parameters on compression molded PMR‐15/C3K composites
Authors: Farouk Alamgir , Kwon Tai Hun 
Published: May 2005

AbstractThe consolidation and curing history during the processing of composite materials affects the final properties of a part in various inter‐related ways. In order to improve the quality of composites, these process‐property relations must be understood in detail. Using a computer‐controlled compression molding and data acquisition system, the processing of PMR‐15/C3k composites has been investigated. The process parameters considered were the pressure, the time at which it was applied and the crosslinking temperature. Parts were tested for inter‐laminar shear strength and flexural modulus, and measurements were made for void content and thickness. Full compaction strength, optimum compaction strength and void sensitivity factor have been defined.
Controlled energy dissipation in fibrous composites. II: Microscopic failure mechanisms
Authors: Lieu Y. K. , Shih W. K. , Jang B. Z. 
Published: May 2005

AbstractMechanical properties and microscopic fracture mechanisms of continuous fiber reinforced polymer composites were investigated. Perforated polyimide films (e.g. Kapton®) were added between composite prepreg layers to modify the interlaminar bonding strength. Addition of highly perforated films can increase the toughness of unidirectional glass/epoxy composites without an appreciable reduction in strength. The fibrous composites studied exhibit two fracture modes (compressive and tensile) when failed by three‐point bending. In general, the compressive failure mode preceded the tensile failure mode. Real‐time acoustic emission (AE) analysis was found to provide more fracture information which is otherwise not discernible from mechanical testing alone. The crack initiation stress level and the subsequent crack propagation mode were identified by real‐time AE during deformation and by post‐failure scanning electron microscopy fracture surface analysis.
Instrumented puncture impact characterization of composite laminates for printed circuit board applications
Authors: Rodriguez Ernesto L. 
Published: May 2005

AbstractOne sided copper glass/epoxy laminates for printed circuit board (PCB) applications were examined using an instrumented puncture impact technique. The effect of the diameter of the support ring, the initial impact velocity, and the preence of a stress concentrator on the impact parameters were evaluated. The orientation of the copper film with respect to the impacter was also varied. The PCB laminate showed brittle failure under the different conditions examined. Results showed that a higher degree of toughness was found for the condition where the copper layer was directly impacted by the dart. The maximum force and the total impact energy were found to be independent of the strain rate. The effect of a stress concentrator on the impact parameters was also found to be minimial. Total impact energies were found to be in the range of 8.8 to 12.6 J for the different testing conditions.
Radiation‐curable prepreg composites
Authors: Saunders Chris B. , Carmichael Alistair A. , Kremers Walter , Lopata Vince J. , Singh Ajit 
Published: May 2005

AbstractAdvanced composites, specifically carbon‐fiber‐reinforced epoxies, are used extensively for a variety of demanding structural applications, primarily because of their high strength‐to‐weight and stiffness‐to‐weight ratios, corrosion resistance, and damage tolerance characteristics. Electron beam (EB) treatment can be used to produce useful physical and/or chemical changes in plastics and composites by initiating various polymerization and crosslinking reactions. The advantages of using EB rather than thermal curing for carbon‐fiber‐reinforced epoxy composites include curing at ambient temperature, reduced curing times, and fewer volatiles. An EB‐curable carbon fiber‐acrylated epoxy composite is being developed for various applications. The tensile properties of the 14‐ply EB‐cured epoxy laminate were comparable with the properties of the thermally cured laminates used in the aircraft industry. Research is continuing to develop resin formulations and select coupling agents to improve the compression properties of EB‐cured laminates.
Dynamic mechanical properties of N‐phenylnadimide modified PMR polyimide composites
Authors: Pater Ruth H. 
Published: May 2005

AbstractTemperature‐frequency dependence of α, β, and γ transitions was determined using a Rheometrics dynamic spectrometer on a series of unidirectional Celion 6000/N‐phenylnadimide (PN) modified PMR polyimide composites. The objective was to see if any correlations exist between crosslinked network structure and dynamic mechanical properties. Variation in crosslinked network structures was achieved by altering the polyimide formulation through addition of various quantities of PN into the standard PMR‐15 composition. As a control, PMR‐15 composite system exhibited well‐defined α, β, and γ transitions in the regions of 360, 100, and −120°C, respectively. Their activation energies were estimated to be 232, 60, and 14 kcal/mole, respectively. Increasing the amount of PN concentration caused (a) lowering of the activation energies of the three relaxations, (b) a decrease of the glass transition temperature, and (c) increasing intensities of the three damping peaks, compared to the control PMR‐15 counterpart. These dynamic mechanical responses were in agreement with formation of a more flexible co‐polymer from PN and PMR‐15 prepolymer.
Processing parameters for filament winding thick‐section PEEK/carbon fiber composites
Authors: Colton J. , Leach D. 
Published: May 2005

AbstractThe consolidation pressure and winding speed for thermoplastic filament winding were studied. Thermoplastic composite parts were manufactured from tape prepreg (APC‐2); powder‐coated, semi‐consolidated towpreg; and commingled fiber towpreg. The material used was carbon fiber (AS‐4) (60 vol%) in a PEEK matrix. The parts made were open‐ended cylinders of the three materials, 177.8‐mm ID, 228.6 mm long, 17 plies thick with a 0° lay‐up angle; and rings, 50 plies of APC‐2 thick, 6.35 mm wide (one strip wide), 177.8‐mm ID, and a lay‐up of 0°. Their quality was determined by surface finish and void percentage. The tubes made from APC‐2 appeared to have the best quality of the three prepregs. For the rings, the speed of lay‐down had a significant effect (at a 99% confidence level) on both the final width of the parts and on the percentage of voids. The pressure of the roller had a significant effect on the final widths at a 99% confidence level, but a significant effect on the percentage of voids at only a 95% confidence level.
Compression molding of sheet molding compounds in plate‐rib type geometry
Authors: Xu Jingyi , Kim Junil , Ho Ted , Lee L. James 
Published: May 2005

AbstractThe flow of fiber‐reinforced composite materials in a plate‐rib type mold geometry during compression molding was investigated using a series of sheet molding compounds (SMC). Material anisotropy in relation to the amount and the length of reinforcing fibers was analyzed. The influence of the interfacial friction between SMC charge and the mold surface on the flow and sink mark formation was also examined. The results were explained qualitatively by computer simulation.
A modeling approach to thermoplastic pultrusion. II: Verification of models
Authors: Åstroöm B. Tomas , Pipes R. Byron 
Published: May 2005

AbstractA set of mathematical models as a thermoplastic pultrusion process is evaluated. The predictions of the models are compared to experimentally obtained data in terms of composite temperature and pressure and process pulling force. The comparisons between predictions and experiments are made for two different material systems, two different die configurations, and a range of processing temperatures and speeds. The correlations between predictions and data are found to be favorable, indicating the soundness of the models.
The effect of pyrolysis on the mechanical properties and microstructure of carbon fiber‐reinforced and stabilized fiber‐reinforced phenolic resins for carbon/carbon composites
Authors: Ko Tse‐Hao 
Published: May 2005

AbstractCarbon/carbon composites were prepared with phenol‐formaldehyde resin, one kind of commercial carbon fiber, and a stabilized fiber that was developed in our laboratory. The effect of pyrolysis on the microstructure, fracture behavior, and flexural strength of the composites during the carbonization process was studied. During the pyrolysis of the composites a chemical reaction at the fiber/resin interface apparently took place. A thermogravimetry (TG) study indicated that the use of stabilized fiber reinforced composites inhibited decomposition reactions and thermal fragmentation in the matrix resin, and reduced the weight loss of the final composites. The X‐ray reflection of the resin and the two composites showed a reflection appearing at 2θ ≈ 12° when the samples were carbonized above 600°C. The intensity of this reflection in the composites made with stabilized fiber was higher than that of the composite made with carbon fiber. Because of the formation of strong bonding in the fiber‐matrix interface, the composites made with stabilized fiber showed catastrophic failure and low flexural strength below carbonization temperatures of 600°C. Above 600°C, the flexural strength of the composites increased with an increase in the carbonization temperatures, even if the fracture behaviors showed catastrophic failure. The flexural strength of the composites made with carbon fiber showed pseudo‐plastic patterns and debonding with very little fiber pullout. Above 800°C, these composites showed a catastrophic failure and smooth failure surfaces. During pyrolysis the flexural strength decreased with an increase in the carbonization temperature.