bluuebunny/crossref_metadata_2025_split huggingface dataset:
Three‐dimensional models for predicting the modulus and yield strength of polymer blends, foams, and particulate composites
Authors: Kolařík Jan 
Published: April 2004

AbstractTwo models are introduced to predict mechanical properties of two‐component isotropic systems: (i) the cross orthogonal skeleton (COS) with co‐continuous components and (ii) the cubic orthogonal skeleton (three perpendicular plates–3PP) with one component continuous and one discontinuous. Simultaneous prediction of the modulus and yield (or tensile) strength is based on phase continuity parameters (calculated for the two models) which serve as input data in an equivalent box model. At yielding (or breaking), the upper and lower bounds are distinguished which are related, respectively, to interfacial adhesion sufficient and insufficient for the transmission of stress inducing plastic deformation. The moduli and the upper bound of yield (or tensile) strength of the COS model, which is applied to polymer blends, are monotonic functions of composition. If partial or complete debonding occurs before yielding (or breaking), the corresponding strength passes through a minimum as a function of composition. The 3PP model renders an approximate prediction of the modulus and yield strength of closed‐cell foams and particulate composites. Predicted dependences reasonably agree with those of other models and/or with experimental data from literature.
Evaluation by torque‐rheometer of suspensions of semi‐rigid and flexible natural fibers in a matrix of poly(vinyl chloride)
Authors: Ayora Martha , Ríos Rolando , Quijano Jafet , Márquez Alfredo 
Published: April 2004

AbstractThe flow properties of three different PVC‐natural fiber suspensions were evaluated using a torque‐rheometer. The fibers used were extracted from henequen leaves, coconut husk, and bovine leather. They have distinct mechanical properties that produce suspensions with different flow behaviors. Nevertheless, the experimental results show that, at the rates employed, the behavior of the suspensions can be described by a power‐law (\documentclass{article}\pagestyle{empty}\begin{document}$ \sigma = m\dot \gamma ^n $\end{document}). The flow (n) and consistency (m) indexes of each suspension were evaluated using an approximate technique previously developed. The evolution of these indexes as a function of the volume fraction of fibers (Φ) are studied and discussed. It was found that, at diluted concentrations, the value of the flow index unexpectedly increases with the concentration of fibers, especially in those suspensions containing the more flexible fibers. However, at elevated concentrations it substantially diminishes. To model this behavior an empirical function for n(Φ) is proposed. The index of consistency (m) presents a continuous increment with the concentration of fibers. To model the evolution of this parameter with the content of fibers, we have defined a relative consistency index mr(mr = ms/mo, where ms and mo are the suspension and matrix indexes) in a similar form to that established for the relative Newtonian viscosity. The function mr(Φ) is modeled using several equations used to describe the behavior of this last viscosity (Maron and Pierce, Mooney, Thomas, Sudduth and Polynomial models). Among them, the Sudduth and Polynomial equations were those that better fit the behavior of these type of suspensions. Finally, to test the previous methodology, the theoretical torque values obtained were compared with experimental data for each suspension. Excellent agreement among them was found.
Optimal cure cycles for the fabrication of thermosetting‐matrix composites
Authors: Rai Neeraj , Pitchumani Ranga 
Published: April 2004

AbstractPolymer‐matrix composites using thermosetting resins as the matrix are increasingly finding use. However, a major impediment to their widespread commercial use is the high cost associated with their manufacture, arising from the long processing cycle times. This paper addresses the problem of determining cure temperature and pressure variations with time for a time‐optimal manufacture of thermosetting‐matrix composites subject to practical constraints. The optimal cure cycles are determined using the nonlinear programming scheme of sequential quadratic programming combined with a physical model base to simulate the process phenomena. The optimized cycles are shown to improve upon the manufacturer‐recomended cycles as well as the improved cycles reported in the literature. The optimization results are reported for a wide range of resin materials, product specifications, and process constraints to illustrate their effects on the optimal cure cycles. Parametric studies are presented in terms of dimensionless groups to assess the combined effects of the product and process variables on the optimal cycles in a generalized manner.
Manufacturing of composite links by structural reaction injection molding
Authors: Castro Jose , Conover Steve , Wilkes Charles , Han Kerang , Chiu Hung‐Tzu , James Lee L. 
Published: April 2004

AbstractAn innovative approach has been developed to fabricate composite parts with complicated geometry. The part is first divided into several simple substructures and each substructure is produced by an optimal process. These preformed substructures are then assembled on a specially designed tool and transferred into a mold cavity for resin impregnation by structural reaction injection molding (SRIM). A composite link is used as an example in this study. The mold filling pattern is simulated using a 3‐D computer model. The simulated results compared well with the experimental results when race tracking and fiber impingement effects were considered in the model.
Crosslinking characterization of a polyimide: AFR700B
Authors: Russell John D. , Kardos John L. 
Published: April 2004

AbstractCrosslinking in AFR700B polyimide was studied using several techniques. Crosslinking could not be detected using Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). Swelling in n‐methyl pyrrolidone (NMP) showed network formation occurs at cure temperatures ≥325°C (617°F), but the reaction kinetics could not be determined from the data. Dynamic mechanical analysis (DMA) studies have shown that the storage modulus (G′) increased with increasing cure temperature up to 350°C (662°F), and was constant above 350°C (662°F), indicating that crosslinking via the reverse Diels‐Alder reaction was occurring. A broad secondary transition was seen in the loss modulus (G″) curves, centered between 150 and 180°C (302 and 356°F). This secondary transition appeared at a cure temperature of 300°C (572°F) and became more dominant with increasing temperature and time. This secondary transition was not seen for cures <300°C (572°F) when the chains have not crosslinked. Therefore, this is likely due to a crosslink bond rather than one in the backbone. At 1 atm, crosslinking followed second‐order kinetics based on the increase in glass transition temperature (Tg). The Arrhenius plot of the rate constant showed a break in the slope, possibly indicating a change in reaction mechanism. At 1.38 MPa (200 psi), the Tg data was too scattered to determine the kinetics.
Experimental investigation of flow through multi‐layered preforms
Authors: Mogavero Jeffrey , Advani Suresh G. 
Published: April 2004

AbstractThis research investigates resin flow phenomena through preforms composed of multiple layers of reinforcement material. Two complete studies were performed: the first investigates the effect of varying the order of lay‐up of a fixed number of plies, and the second studies the impact of varying the thickness of the individual layers of a thick preform. In each case, a set of compression experiments were first performed to characterize the preforms so that in‐situ layer thicknesses can be calculated. Next, flow experiments were performed upon the preforms to determine the permeability and flow front behavior. In the first study, it was found that the weighted average scheme provides a reasonable estimate for the effective permeabilities of the preforms, with errors ranging from 14.2% to 23.8%. In the second study, however, the weighted average scheme was found to provide only a rudimentary estimate of the permeability, with an error that was seen to increase in magnitude during the course of each experiment. In addition, computer simulations were performed for the second study, which show the possibility of deriving transverse permeability values without direct measurement, although significant errors in inlet pressures were once again evident.
Forced in‐plane flow through complex deformable structures: Influence of an imposed curve
Authors: Friedman Henry L. , Johnson Robert A. , Miller Bernard , Salem David R. , Parnas Richard S. 
Published: April 2004

AbstractForced in‐plane flow of liquids through contiguous flat and curved regions of confined fabrics has been studied both as a general phenomenon and for predicting the flow of polymers during injection molding of monolithic composite structures with complex configurations. A controlled pressure difference is applied to drive the flow, while the mass flow rate is measured gravimetrically by Liquid/Air Displacement Analysis (LADA). Measurements have been carried out along fabric paths that are first vertical, then curved, and finally horizontal. Fluid flow equations have been adapted for analyzing flow in the flat sections, leading to the evaluation of permeability constants and capillary pressures. A saturated flow rate measured at constant hydrodynamic pressure is used to evaluate the overall permeability coefficient of the encapsulated fabric. Data are presented showing that permeability can be reduced as a consequence of flow through the curved region.
Resin flow in a pultrusion process
Authors: Giordano M. , Nicolais L. 
Published: April 2004

AbstractA simple model for the resin flow in a pultrusion die based on the theory of lubrication has been developed. The velocity field in the pultrusion die has been calculated together with the pressure drop. A useful tool to evaluate the energy loss due to the viscosity dissipation along the die has been developed. Model results have been evaluated, by using chemorheological submodels, in terms of the contribution to the pulling force due to the viscous drag.
Injection molding of poly(ethylene terephthalate) reinforced with pregenerated thermotropic liquid crystalline polymer microfibrils
Authors: McLeod M. A. , Baird D. G. 
Published: April 2004

AbstractThis work was concerned with the injection molding of poly(ethylene terephthalate) (PET) reinforced with pregenerated thermotropic liquid crystalline polymer (TLCP) fibrils, where the TLCP had a higher melt processing temperature than PET. These composites, referred to as pregenerated microcomposites, were produced using a two step processing scheme. First, a novel dual extrusion process was used to spin strands of PET reinforced with nearly continuous TLCP fibrils. Second, these strands were subsequently chopped into pellets and injection molded below the melt processing temperature of the TLCP but above that of PET. This allowed the high modulus TLCP fibrils generated in the spinning step to be retained in the injection molded samples. TLCP concentration and strand draw ratio were varied in the composite strands to determine how they affected mechanical properties. It was shown that the best properties were obtained using strands containing 50 weight percent TLCP with draw ratios greater than 50, which were diluted to the desired loading level with a low viscosity injection molding grade of PET. Specifically, these composites had tensile moduli as high as 5.7 GPa when reinforced with 30 weight percent HX1000. Also, it was determined that pregenerated microcomposites had smoother surfaces than glass‐filled PET.
Interfacial properties and initial step of the water sorption in unidirectional unsaturated polyester/vegetable fiber composites
Authors: Riccieri J. E. , Vázquez A. , De Carvalho L. Hecker 
Published: April 2004

AbstractIn this work the interfacial properties of polyester/vegetable fiber composites were analyzed by flexural testing. The compressive/tensile (σ) and shear (τ) stresses were determined for each composite in function of the span‐to‐depth ratio (λ). The general behavior of the composites was similar to that of composites reinforced with DuPont Kevlar fiber, i.e., a maximum σ stress value is obtained. Flexural test validity for determining the Young's and shear moduli, E11 and G12, was ascertained. The Young's modulus agreed with that expected from the rule of mixtures for the composites with lowest fiber content. Short beam tests were performed on the composites. The shear stress value was improved by means of the matrix modification. Moisture sorption experiments and dynamic mechanical analysis were also performed on the natural fiber composites in the first Fickian step. Water sorption at 50% RH and 90% RH can be satisfactorily described by using a diffusional model. Water diffusion on parallelepiped samples shows a positive deviation from the Fickian behavior. Fiber capillary flow occurs through the fiber and the debonded matrix/fiber interphase during the initial Fickian step.
Processing of highly elastomeric toughened cyanate esters through a modified resin transfer molding technique
Authors: Hillermeier Roman W. , Hayes Brian S. , Seferis James C. 
Published: April 2004

AbstractModel cyanate ester resins containing different quantities of epoxy functional butadiene‐acrylonitrile rubber (ETBN) to improve the fracture performance were developed as matrices for composites. With the elastomeric modification, the resin systems exhibited rheological characteristics inappropriate for laminate fabrication by conventional resin transfer molding (RTM). To fabricate the carbon fiber based laminates in one liquid molding operation successfully, a process named bleed resin transfer molding (BRTM) was established. The BRTM process combines features of RTM and resin film infusion processes (RFI) and was therefore appropriate for processing high viscosity matrix resins. A novel catalyst was selected for the cyanate ester resin that provided enough latency for the impregnation steps in the BRTM process. Through the use of thermal analytical tools, a high degree of phase separation and conversion was obtained. The conversion and the glass transition temperature were found not to decrease with increasing elastomer content, which is in contradiction to most toughening modifications. Mode I and Mode II interlaminar fracture toughness were found to increase significantly with increasing elastomer content. In Mode I, an increase of up to 140% was observed. Collectively, this work showed that through the use of the BRTM technique, matrices with toughness improvements usually only achieved by prepreg systems can be processed in an RTM‐like manner.
Compressibility and relaxation of a new sandwich textile preform for liquid composite molding
Authors: Luo Yiwen , Verpoest Ignaas 
Published: April 2004

AbstractIn liquid composite molding, such as RTM or SRIM, the dry reinforcement is first compressed in the mold, and then the resin is injected into the mold cavity and cured. Knowledge of the compressibility of the reinforcement is important in order to estimate the mold closing force and the attainable range of fiber volume fraction. Moreover, in a lay‐up composed of several types of fabrics, the compressibility of each fabric should be known to predict the thickness of each fabric layer, which is a prerequisite for the mold filling simulation. In this work, the relaxation and compressibility of a new sandwich fabric, Multimat®, and its components (a weft knit and a random mat) were studied and compared with a woven fabric. The different fabric relaxation behavior is explained in terms of fabric stiffness and volumetric dissipation energy. Fabric compression tests were performed by taking the fabric relaxation behavior into account. Fabric compression curves are fitted with the power law equation and agree well with the clamping pressure experimentally measured with a pressure transducer in an RTM mold. The influence of the number of layers was also investigated. Finally the compressibility of the Multimat is correlated to its components with a simple model.
An analytical method for prediction of the damping in symmetric balanced laminated composites
Authors: Yim Jong Hee , Jang Bor Z. 
Published: April 2004

AbstractTo obtain the effective damping of a laminated composite beam, two different analytical methods were compared. Also, we modified the basic loss factors on the basis of experimental data. In the first method, Ni and Adams's theory was used. In the second method, new energy approach was developed to determine the damping of laminated composite beams. Five typical laminated composites with [±Θ]s, [0/±Θ]s, [0/Θ]s, [0/±Θ/90]s and [90/±Θ/0]s stacking sequences were employed for this study. The present method was favorably compared with Ni and Adams's method. In this study, we found that damping was highly influenced by fiber volume fraction, fiber orientation and stacking sequence.
Mechanical properties of aligned long glass fiber reinforced polypropylene. I: Tensile strength
Authors: Yang Shean‐Wei , Chin Wei‐kuo 
Published: April 2004

AbstractLong‐fiber reinforced thermoplastic composites were made from 9 mm long glass fiber reinforced PP pellets by alternative procedures of roll‐mill and hot‐press molding. The severe problem of fiber breaking during the process could be avoided by this method. The average fiber length of this composite was ∼7 mm long. More than 80% of fibers in the composite were aligned within the 20° range. In the major fiber‐oriented direction, at 25°C, the tensile strength of this composite was 205 MPa. At elevated temperatures in the range of 25°C to 125°C, the tensile strength was inversely proportional to the temperature. The two‐parameter Weibull distribution function was used to simulate the strength distribution of the composite. Results showed that the strength distribution curve shifted from high to low as the temperature increased.
Mechanical properties of aligned long glass fiber reinforced polypropylene. II: Tensile creep behavior
Authors: Yang Shean‐wei , Chin Wei‐kuo 
Published: April 2004

AbstractThe creep behavior of long glass fiber reinforced thermoplastic composite was investigated under different constant tensile stress and temperature. From the time‐dependent strain curve, the critical creeping time was defined as the transition point from steady to unsteady deformation and measured correspondingly. A statistical Weibull distribution function was adopted to describe the critical creeping time distribution at each stress level. A power law was employed to analyze the behavior of steady deformation stage of strain during loading. The relation between the critical creeping time and the parameter (m) of the power law is analyzed and discussed.
Yield behavior and energy absorbing characteristics of rubber‐modified epoxies subjected to biaxial stress states
Authors: Kody Robert S. , Lesser Alan J. 
Published: April 2004

AbstractHollow cylinders of aromatic‐amine cured epoxies, modified with 0%, 10%, and 20% CTBN rubber by weight were tested in stress states ranging from uniaxial compression to biaxial tension. Our results showed that rubber particles decrease the yield strength uniformly over all stress states and suppress brittle fracture in the more demanding stress states. Particle size has no effect on yield strength. Samples were also biaxially loaded and unloaded to varying stress levels to monitor and study their dissipative characteristics. From these tests, a threshold stress was observed where the stiffness of the rubber‐modified resin decreases and the deformation becomes increasingly irreversible. By comparing the changes in damage morphology with the change in loading path, we determined that a significant amount of energy is absorbed in the rubber‐modified samples prior to macroscopic yield. Additionally, this irreversibility does not appear to be associated with rubber particle cavitation or inelastic void growth.
Modeling of the consolidation of polycarbonate/carbon fiber towpregs
Authors: Nunes J. P. , Bernardo C. A. , Pouzada A. S. , Edie D. D. 
Published: April 2004

AbstractTowpregs are a new class of pre‐impregnated materials that can be used to obtain structural composites by compression molding. Consolidation is an important part of this process. In this work, a mathematical model was developed to predict the evolution of the compression pressure during the isothermal consolidation of thermoplastic matrix towpregs. The model relates the applied pressure to operational variables (speed and temperature) and material variables (viscosity, particle size, and polymer volume fraction). Tests were carried out at different temperatures and platen closing speeds, using carbon fiber‐reinforced polycarbonate towpregs. The data obtained was compared with theoretical calculations, demonstrating the applicability of the model.
Study of the flow behavior of polymer‐natural fiber suspensions in the power law validity range
Authors: Márquez Alfredo , Quijano Jafet , Ríos Rolando , Ayora‐cámara Martha Helena 
Published: April 2004

AbstractThe melt flow properties of PVC suspensions with henequen, coconut and bovine leather, in their raw condition, and after extraction of all their low molecular weight substances were studied. The experimental results show that, at the strain rates employed, the behavior of the suspensions is described by a power law (η = mγn–1). It is important to mention that in the present work we do not restrict our analysis to the evolution of the suspension Newtonian viscosity with the fiber concentration (as commonly is reported in the literature), but a more complete analysis is performed by describing the evolution of the consistency (m) and the power law (n) indices with the fiber concentration. Both indices were evaluated using a technique previously developed. The flow index (n) presents an anomalous behavior, it increases when the fibers are incorporated into the melted matrix at low fiber concentrations. This unexpected behavior is very different from that commonly reported in the literature and is apparently due to the flexibility of fibers. Moreover, the influence of the fiber extractable materials on the behavior of these suspensions was also evaluated. It was found that these latter materials apparently influence the value of the consistency index (m) of suspensions, at fiber concentrations above the critical pigment volume fraction; however, they do not have a significant effect on the power law index (n). Concerning the mechanical behavior of composites molded from the previous suspensions, it was found that when the fiber content augments, their elastic modulus increases, but their tensile strength falls. This behavior, however, could be improved by increasing the adhesion between the fibers and matrix.