bluuebunny/crossref_metadata_2025_split huggingface dataset:
A kinetic model for free‐radical crosslinking co‐polymerization of styrene/vinylester resin
Authors: Yang Huan , Lee L. James 
Published: April 2004

AbstractVinylester resin is a major thermoset polymer used In low temperature composite manufacturing processes, such as the Seemann Composite Resin Infusion Molding Process (SCRIMP). In this study, the effect of temperature on the cure kinetics of vinylester resin in the range of 35 to 90°C was investigated using a differential scanning calorimeter (DSC) and a Fourier transform infrared spectrometer (FTIR). A mechanistic kinetic model was developed to simulate the reaction rate and conversion profiles of vinylester vinylene and styrene vinyl groups, as well as the total reaction action rate and conversion. Experimental results from DSC and FUR at different temperatures were compared with model predictions. The glass transition temperature of the vinylester resin cured at different temperatures was identified and used to monitor the final conversion change. A series of SCRIMP molding experiments were conducted. The developed kinetic model in conjunction with a heat transfer model was used to simulate the temperature and conversion changes inside the SCRIMP‐molded composites.
Vacuum‐assisted resin transfer molding using tackified fiber preforms
Authors: Shih Chih‐Hsin , Liu Qingfang , Lee L. James 
Published: April 2004

AbstractA low cost composite fabrication process—tackified SCRIMP—is described for fabricating aerospace‐grade composites based on tackification and vacuum‐assisted resin transfer molding (VARTM). Tackification based on a commercial tackifier (FT 500 from 3M) was used to make the net‐shape fiber preform. It was found that tackifier concentration and application conditions play important roles in governing the moldability of tackified fiber preforms. An epoxy resin (PR 500 from 3M) was used in the VARTM process‐SCRIMP at high temperatures. Experimental results show that composites with high fiber content (> 60% by volume) can be manufactured at low cost using tackification. Effects of tackification methods on composite dimension control, void content and mechanical properties were investigated and compared in both RTM and SCRIMP.
Novel eco‐friendly biodegradable coir‐polyester amide biocomposites: Fabrication and properties evaluation
Authors: Rout J. , Misra M. , Tripathy S. S. , Nayak S. K. , Mohanty A. K. 
Published: April 2004

AbstractBiocomposites are prepared from a cheap, renewable natural fiber, coir (coconut fiber) as reinforcement with a biodegradable polyester amide (BAK 1095) matrix. In order to have better fiber‐matrix interaction the fibers are surface modified through alkali treatment, cyanoethylation, bleaching and vinyl grafting. The effects of different fiber surface treatments and fiber amounts on the performance of resulting bio‐composites are investigated. Among all modifications, cyanoethylated coir‐BAK composites show better tensile strength (35.50 MPa) whereas 7% methyl methacrylate grafted coir‐BAK composites show significant improvement in flexural strength (87.36 MPa). The remarkable achievement of the present investigation is that a low strength coir fiber, through optimal surface modifications, on reinforcement with BAK show an encouraging level of mechanical properties. Moreover, the elongation at break of BAK polymer is considerably reduced by the incorporation of coir fibers from nearly 400% (percent elongation of pure BAK) to 16‐24% (coir‐BAK biocomposites). SEM investigations show that surface modifications improve the fiber‐matrix adhesion. From biodegradation studies we find that after 52 days of soil burial, alkali treated and bleached coir‐BAK composites show significant weight loss. More than 70% decrease in flexural strength is observed for alkali treated coir‐BAK composites after 35 days of soil burial. The loss of weight and the decrease of flexural strength of degraded composites are more or less directly related.
Measurement of in‐plane permeability of anisotropic fiber reinforcements
Authors: Gebart B. Rikard , Lidström Peder 
Published: April 2004

AbstractThree of the most common methods (two with parallel flow and one with radial flow) for determination of the in‐plane permeability tensor are studied both theoretically and experimentally. An error analysis shows that the difference between the methods is negligible if the error levels are equal. However, the radial flow method is found to be susceptible to large errors from mold deflection in an experimental comparison between the methods. Additional experiments with the radial flow method in a stiffer mold show that the method gives the same values for the permeability tensor as the other two methods. A new method with multiple cavities in parallel is proposed that combines the simplicity of the radial flow method with the stiff mold of the parallel flow method. Only mass and time need to be measured in one experiment and it eliminates the need to measure fluid viscosity, temperature, and injection pressure. The method depends on the availability of a reference material with known permeability.
Polymer encapsulation of glass filler in ternary PP/PA‐6/glass blends
Authors: Benderly D. , Siegmann A. , Narkis M. 
Published: April 2004

AbstractThe morphology and rheology of ternary isotactic polypropylene (PP)/polyamide‐6 (PA‐6)/glass blends is investigated and contrasted with the behavior of two‐component (binary) PP/PA‐6 blends. Injection molded samples of binary blends exhibit an interlayer slip morphology for both PP and PA‐6 as the matrix and the blend shear viscosity is lower than expected from a rule of mixtures. The morphology of ternary blends is dependent on the choice of the matrix phase. In ternary blends with a PA‐6 matrix, the PP domains and glass fibers are separately dispersed within the matrix. In ternary blends with a PP matrix, the PA‐6 is mainly found surrounding (encapsulating) the glass fibers, and the extent of the interlayer slip morphology is reduced. Variations in glass surface treatment, blending time, and order of addition did not affect the rapid encapsulation of glass by the PA‐6. A reduction in blending temperature, below the peak PA‐6 melting temperature, hinders encapsulation.
Improvement of adhesion between polyethylene and regenerated cellulose fibers by surface fibrillation
Authors: Karlsson J. O. , Gatenholm P. , Blachot J.‐F. , Peguy A. 
Published: April 2004

AbstractRegenerated cellulose fibers spun from straw pulp using the N‐methylmorpholine N‐oxide (NMMO) process were evaluated as a reinforcement for low‐density polyethylene (LDPE). Surface fibrillation was carried out by a mechanical treatment to improve interfacial adhesion. Surface fibrillation resulted in a gradual change in surface topography, as detected by SEM. Long and numerous twisted fibrils were observed on the surface of the treated fibers. The fiber perimeters, determined by the Wilhelmy plate method, increased with an extended degree of fibrillation, while the strength of the fiber was not affected by the surface treatment. Model composites were prepared by embedding untreated and surface‐fibrillated single fibers into an LDPE matrix, and the single fiber fragmentation (SEF) test was carried out to determine the critical fiber length. The interfacial shear strength (τ) was then calculated by applying a modified form of the Kelly‐Tyson equation. It was found that the interfacial shear strength increased significantly as a result of surface fibrillation. The proposed mechanism for the improvement of interfacial adhesion is a mechanical anchoring between the matrix and the fiber.
On the effects of modifiers on the viscoelastic behavior of composites
Authors: Tsotsis Thomas K. 
Published: April 2004

AbstractSome of the details concerning the reasons for the difference in behavior between untoughened and toughened composites are presented. This work demonstrates the influence of localized plastic deformation on the viscoelastic behavior of polymer composites. As an example, the presence of a thermoplastic modifier and its potential influence on the microscale deformation is presented by using two micromechanical models to determine the conditions under which the observed behavior may occur. Results suggest that the effect of thermoplastic tougheners is to increase the amount of time‐dependent plastic deformation in loadings that produce sufficiently large local stress concentrations. The tougheners, however, do not seem to change the functional form of the time‐dependent response, rather they change the magnitude of this response. The two models discussed are used to qualitatively characterize these phenomena by relating model parameters to constituent properties. Differences in observed behavior with respect to plastic deformation in creep tests vs. tests such as dynamic mechanical analysis are attributed to the small deformations in the latter test types, which do create insufficient localized zones of plastic deformation.
Effects of hygrothermal exposure on the mechanical properties of injection molded glass‐fiber reinforced poly(phenylene sulfide)
Authors: Munson‐McGee Stuart H. 
Published: April 2004

AbstractAn experimental program was used as the foundation for long‐term property prediction for a glass‐fiber reinforced poly(phenylene sulfide). Samples were aged up to 226 days at 95% RH at both 104°F (40°C) and 158°F (70°C) (based on MIL‐STD‐810E and MIL‐STD‐210C), and their mechanical properties measured. Data analysis indicated that property changes were more pronounced at the higher temperature with statistically significant changes, at the 99% confidence level, occurring after 100 days. At the lower temperature, property changes were observed, but their significance was not established. Further analysis of the data indicated that the moisture content did not affect the property changes. Analysis of the data using a viscoelastic description of the property changes resulted in property maps that permit estimation of the mechanical properties for up to a 20‐year exposure as a function of exposure temperature.
Short term isothermal aging of epoxy resin and epoxy‐carbon fiber composites
Authors: Chifu A. F. , Iroh J. O. 
Published: April 2004

AbstractShort term isothermal aging of a neat epoxy resin and one ply epoxy‐carbon fiber composite has been performed. The glass transition temperature, Tg of the neat epoxy resin aged at 204°C increased with aging time. The weight loss of the neat epoxy resin due to aging increased with aging temperature and aging time. The weight loss of the epoxy–carbon fiber composite during aging was slightly less than that of the neat resin. SEM microscopy showed the presence of voids and pores on the surface of the composite due to loss of low molecular weight volatiles. The amount and the size of the voids formed during aging increased with aging temperature and time.
Anisotropic degradation of polymeric composites: From neat resin to composite
Authors: Salin Irene , Seferis James C. 
Published: April 2004

AbstractThe degradation of polymer matrix composites was investigated through weight loss measurements. A methodology originally developed based on the shrinking core model was extended to account for matrix orientation, lay‐up sequence, and differences in neat resin and composite degradation. This methodology was derived based on mass transfer and kinetic considerations taking into account the inherent anisotropy and heterogeneity of polymer composites. The model systems used were a bismaleimide (X5260) and a condensation polyimide (Avimid N). Bismaleimide composites were aged at 250, 260, and 270°C in air, whereas both neat resin and composite Avimid N samples were aged at 371°C. Based on the experimentally observed time exponents, the degradation was modeled as diffusion and reaction controlled. The weight losses of both unidirectional and quasi‐isotropic samples were successfully predicted. In addition, correlation between the degradation of neat resin and composite samples was established for the Avimid N system. Finally, this methodology can be used in scaling up weight loss data, providing an important tool in evaluating materials for long‐term use at elevated temperatures.
Braided thermoplastic composites from powder‐coated towpregs. Part III: Consolidation and mechanical properties
Authors: Ramasamy A. , Wang Youjiang , Muzzy John 
Published: April 2004

AbstractCarbon fiber/nylon 6 powder coated and commingled tows were braided into biaxial braids with a ±45° braid angle. Consolidation experiments were carried out to study the influence of consolidation conditions on the properties of the laminates using a 23 full factorial experimental design. The consolidation studies reveal that commingled tows require more severe consolidation conditions than powder coated tows to obtain comparable properties. The dependence of powder‐coated laminate qualities like void content and fiber volume fraction on the consolidation conditions is reported. The ±45° braided laminates are tested for tensile properties. Although the dominant mode of failure of the laminates is shear failure between the fibers and the resin, the failure is non‐brittle because of fiber interlacement in the braided preforms.
Recyclability of a continuous e‐glass fiber reinforced polycarbonate composite
Authors: Chu J. , Sullivan J. L. 
Published: April 2004

AbstractFiber reinforced plastics are multi‐component materials for which physical properties are strongly dependent on fiber and resin structure. Despite the disruptive nature of recycling methods on such structures, these materials nevertheless can be recycled. In this report, the recyclability of a fiber‐reinforced cyclic BPA polycarbonate has been studied. It is found that ground up composite is recyclable and possesses properties as good as or better than a comparable commercial composite. The processing techniques investigated herein are injection, extrusion compression, and compression molding. As expected, processing technique and parameters are important in determining the mechanical properties of the molded regrind. Our results show that injection and extrusion compression molding yield recycled composites with good tensile properties, though the impact strengths are relatively low. This is due to high fiber orientation and fiber bundle dispersion. On the other hand, compression molded samples, which show random fiber orientation and low fiber bundles dispersion have relatively low tensile properties, but excellent impact strength. Results are discussed in terms of microstructural details, which include resin molecular weight and fiber length and orientation.
Stress distribution in and around a spherically ended fiber embedded in a polymer matrix
Authors: Shuster M. , Sherman D. , Siegmann A. , Narkis M. , Jennewein C.‐M. , Eyerer Peter 
Published: April 2004

AbstractThe effect of fiber end geometry, especially one with an enlarged spherical end, on the stress distribution in a polycarbonate/short glass‐fiber reinforced model composite was studied using photoelasticity and finite element analysis (FEA). The role played by the fiber/matrix interfacial strength was also investigated. The photoelastic method was applied to examine the stress distribution in the vicinity of a single fiber embedded in a thermoplastic polycarbonate matrix. Linear elastic, axisymmetric FEA was carried out to investigate the fibers effectiveness as a load bearing constituent, the effect of interfacial debonding, and stress concentration near the fiber ends. Both photoelastic analysis and FEA demonstrated the efficiency of the spherical enlarged fiber end in load transfer ability and in delayed debonding, which may be important in enhancing strength and modulus of thermoplastic matrices.
In situ composites based on blends of a polyetherimide and thermotropic liquid crystalline polymers subjected to shearfree deformations
Authors: De Souza J. P. , Baird D. G. 
Published: April 2004

AbstractThe effects of shearfree elongational flows on the morphology and mechanical properties of blends of a polyetherimide (PEI) with thermotropic liquid crystalline polymers (TLCP) have been investigated. Extruded sheets and injection molded plaques of PEI/Vectra A and PEI/HX1000 blends, with a TLCP concentration of ≤30 wt%, were subjected to uniaxial elongation, planar and biaxial deformations at 240°C, above the glass transition temperature of the PEI, and at 265°C, which is below the melting point of the TLCPs. Experimental results revealed that each particular mode of shearfree deformation had a distinct effect on the morphology and properties of the blends. For instance, TLCP droplets were deformed into elongated fibrils by application of uniaxial elongation, deformed into elongated ribbon‐like structures after planar deformation, and deformed into a disc‐like shape by application of equibiaxial flow. Regarding mechanical properties, it was observed that the tensile modulus and strength of molded plaques of PEI/HX1000 80/20 wt% increased to about twice their initial values (from 5.13 to 10.40 GPa and from 105 to 198 MPa, respectively) after a strain of 0.75 was applied in a direction parallel to the initial direction of the TLCP fibers. In addition, samples exhibiting equal values of flow and transverse direction tensile modulus of ∼5.0 GPa were obtained when molded plaques of PEI/HX1000 80/20 wt% were subjected to planar stretching in a direction transverse to the initial direction of the fibers. Thus, by subjecting injection molded plaques to planar stretching, it was possible to obtain a sample exhibiting balanced flow and transverse direction mechanical properties and, consequently, reduced anisotropy.
Deep drawing of fabric‐reinforced thermoplastics: Wrinkle formation and their reduction
Authors: Breuer U. , Neitzel M. , Ketzer V. , Reinicke R. 
Published: April 2004

AbstractProducing highly stiff and strong thin‐walled fabric‐reinforced parts for mass application can be economic using a double‐belt press to consolidate thermoplastic sheet and a hydraulic press for non‐isothermal stamp forming in a second step. During stamp forming, undesired wrinkle formation can occur at sites of three dimensional forming. To understand the mechanisms of wrinkle formation, shear tests were performed with different types of reinforcing glass and carbon fabric, both dry and impregnated with a polyamide (PA12) matrix. Evidence has been found that wrinkle formation during fabric shear is strongly dependent on membrane stresses within the fabric. High membrane stresses of ∼20 MPa can prevent wrinkling even at high shear angles of ∼60°. These stresses can be generated during stamp forming by means of blank holders. A new flexible roller tracking device has successfully been installed on a stamp forming pilot plant. It was possible to form chests sized 450 mm. 300 mm. 40 mm (w. l. d) free of wrinkles with a 4‐ply glass plain weave fabric preimpregnated with polyamide matrix (PA12) and a fiber content of 45 vol%.
Reactions of unconverted isocyanate in molded RIM parts and their implications to outgassing
Authors: Mielewski Deborah F. , Anturkar Nitin R. , Bauer David R. 
Published: April 2004

AbstractA convenient, cheap, and reliable method was developed and evaluated to measure the extent of conversion and subsequent water/diisocyanate reaction kinetics for injection molded (RIM) parts using cryogenic grinding and conventional Fourier Transform Infra‐Red (FTIR) spectroscopy. The reliability of the method was independently confirmed by using in‐mold fiber‐optic FTIR and attenuated total reflectance spectroscopy (Priester, private communication, The Dow Chemical Company 1994). The reaction of isocyanate with water produces carbamic acid, which is believed to immediately decompose to carbon dioxide (CO2) and amine, leading to outgassing during the paint cure. Given previous measurements of effective diffusion coefficients of water and CO2, if the molded RIM parts are stored under typical humid conditions for hours, most of the CO2 should form as a product of isocyanate/water reaction and diffuse out of the part. However, our results indicate that relatively little CO2 evolution occurs during ambient storage for up to 6 h, and significant evolution occurs for long times during subsequent high temperature post cure. Therefore, in contrast to the earlier expectations, the outgassing phenomenon seems to be due to carbamic acids that decompose slowly at ambient conditions and become unstable at higher temperatures. Therefore, to assure minimum outgassing in this RIM system one must (1) operate the post cure oven at higher temperatures than the paint baking oven, or (2) keep parts in ambient storage at least for 24 h to allow slow decomposition of carbamic acids, or (3) transfer them to the post cure oven immediately after removal from the mold, thereby preventing possible water/diisocyanate reactions.
Moisture effects on the behavior of graphite/polyimide composites
Authors: Burcham Loyd J. , Vanlandingham Mark R. , Eduljee Rushad F. , Gillespie John W. 
Published: April 2004

AbstractThe effect of moisture on the material behavior of Magnamite® IM7 Graphite/Avimid® K3B thermoplastic polyimide composite laminates has been investigated. Laminates consisting of a 62 vol% fiber were laid up with several different stacking sequences: [90]10or unidirectional, [02/90]Sor thin cross‐ply, [02/902/02]Sor thick cross‐ply, [45/0/‐45/90]Sor quasi‐isotropic, and [0/90] laminates. In this study, the glass‐transition temperature,Tg, and the intralaminar fracture toughness,GIC, were measured for dry and moisture‐saturated unidirectional samples. When laminates were saturated with moisture, the value ofTgwas found to decrease from its baseline (dry) value, but recovered upon redrying the samples. This observation is consistent with the effects of moisture on theTgof other polymer composites. Permanent toughness losses have not been observed in samples conditioned in room‐temperature 75% and 100% relative humidity environments. However, during long‐term conditioning of cross‐ply and quasi‐isotropic samples in liquid water, transverse cracks initiated in the absence of an applied mechanical load. Moisture uptake curves for conditioning in room‐temperature liquid water, 80°C (176°F) liquid water, and at room temperature and 75% relative humidity were used to calculate Henry's Law constants and diffusion coefficients. Non‐Fickian behavior, consisting of a postsaturation increase in moisture uptake, was observed in crossply and quasi‐isotropic laminates and might be due to the observed transverse cracking.
Optimal design of the cure cycle for consolidation of thick composite laminates
Authors: Chang Ming‐hui , Chen Chieh‐li , Young Wen‐Bin 
Published: April 2004

AbstractAutoclave cure of the prepreg lay‐up has been an importance method for fabrication of advanced fiber reinforced composites in the aerospace industry. Quality of the autoclave cured composite is largely affected by the cure cycle. In this study, the genetic algorithm is applied to design a cure cycle for the consolidation of thick laminated composites. The objective of the design is to select a cure cycle that results in a shorter cycle time for the process while avoiding the thermal runaway inside the composites. The results show that the genetic algorithm is a feasible and robust search algorithm to determine the cure cycle for the consolidation process.