bluuebunny/crossref_metadata_2025 huggingface dataset:
Spectroscopic determination of the in‐situ composition of epoxy matrices in glass fiber‐reinforced composites
Authors: Antoon M. K. , Zehner B. E. , Koenig J. L.
Published: May 2005

Computerized infrared analysis is applied to the characterization of a glass‐reinforced crosslinked polyester. The method of factor analysis determines the number of independent components which constitute the polymeric matrix. Subsequently, the spectra of those components are fitted by a least‐squares criterion to spectra of the multicomponent matrix, or, if the glass spectrum is included as an additional component, to the spectra of composites. The least‐squares coefficients yield the matrix composition in terms of the initial reactant composition and the extent of crosslinking.
Some theoretical considerations on the long‐term stability of polymer concrete composites in reactive environments
Authors: Zeldin Arkady N.
Published: May 2005

In this report, a theoretical examination is made of the life span of polymer concrete (PC) composites in aggressive environments. Using well known physical chemistry laws, in can be shown that the durability of PC is dependent only on the temperature and concentration of the aggressive environment. This dependence can be extremely useful to potential users of PC materials in aggressive environments since the life span of such materials may be predicted with minimum experimental data.
A model of passive thermal nondestructive evaluation of composite laminates
Authors: Charles John A. , Wilson Dale W.
Published: May 2005

A numerical model of passive thermal nondestructive evaluation (NDE) of composite laminates was developed. This model, based on a transient, three‐dimensional, finite difference solution to the heat conduction equations, can be used to characterize in‐plane defects in the laminates and to predict the laminate response to the thermal test. The model was experimentally verified using two material systems. A parametric study was then conducted to ascertain which variables were critical to the success of passive thermal NDE, and how flaw resolution might be improved.
Tensile failure of notched fiber‐reinforced composite materials
Authors: Wetherhold Robert C. , Whitney James M.
Published: May 2005

The weibull brittle failure model is used to described the tensile strength degradation of a fiber‐reinforced composite material in the presence of a notch. This model uses the description of the state of stress near the notch and the Weibull shape parameter from a series of unnotched tensile tests. The Weibull‐model strengtyh degradation is evaluated using numerical integration of a reduced, one‐dimensional tensile volume. The numberical Weibull integral results are compared with the point stress failure theory. The comparison suggests that the two parameters of the point stress theory stem form the single Weibull shape parameter. The integral results are shown to be conservative when compared with data for two graphite. epoxy systems.
Moisture penetration into composites under external stress
Authors: Marom Gad , Broutman L. J.
Published: May 2005

Moisture penetration at 95°C into glass fiber and graphite fiber‐reinforced epoxies is examined in stressed and unstressed materials. The study focuses on the effect of the angle between the stress and the fiber directions on the diffusivities. It is found that the consequence of applying external stresses to composites is an increase in their rate of moisture absorption, their maximum moisture content, and in the diffusion coefficients. As the angle between the loading and fiber directions in increased the rate and the maximum value of moisture absorption also increase. Their ratio, however, remains constant resulting in loading angle independence of the exposure of the composites to water produces a typical damage mechanism which enhances moisture take‐up.
Combining rules for predicting the thermoelastic properties of particulate filled polymers, polymers, polyblends, and foams
Authors: McGee Stuart , McGullough R. L.
Published: May 2005

Various models that have been proposed to predict the properties of particulate filled systems are reviewed and compared with experimental data. At filler volume fractions less than ∼0.2‐∼0.3, these models give essentially equivalent predictions that are within the scatter of experimental measurements. At higher volume fraction of inclusions, significantly different results are obtained from the various models. These predictions either overestimate or underestimate observed properties. New, theoretical combining rules are presented to predict the Young's modulus, Poisson's ratio shear modulus, bulk modulus, and coefficient of thermal expansion in terms of the properties of the matrix and inclusion and the volume fraction concentration of the inclusion. The predictions of these combining rules are in good agreement with experimental data that cover the feasible concentration range of inclusions for a variety of composite materials, ranging from particulate filled thermosetting resins to thermoplastic foams.
Fatigue crack propagation of sheet molding compounds in various evironments
Authors: Hoa S. V. , Ngo A. D. , Sankar T. S.
Published: May 2005

The effect of the absorption of water and isooctane on the rate of fatigue crack propagation of sheet molding compounds (SMC‐R30 and SMC‐R65) was investigated. A crack extension gage was used to measure the crack length. Results show that the absorption of water decreases the rate of fatigue crack propagation in the initial cycles but increases the rate of propagation in the final cycle. The absorption of isooctane into SMC‐R65 tends to decrease the rate of fatigue crack propagation. Microscopic observation shows considerable swelling of the polyester matrix due to the absorption of water and no significant apparent effect due to the absorption of isooctane.
Liquid absorption of a sheet molding compound
Authors: Hoa S. V. , Ouellette P.
Published: May 2005

The absorption of water, isooctane, methanol and ethanol into a sheet molding compound (SMC‐R30) at room temperature is studied. The absorption behaviors are shown to be Fickian, with constant diffusion coefficients. Desorption of methanol and ethanol soaked specimens causes considerable surface cracking.
Studies on polmer impreganted composites
Authors: Aminabhavi Tejraj M. , Patel Ramesh C. , Biradar Ningond S.
Published: May 2005

Eleven light weight polymeriozed composite materials derived from waste products were investigated. These waste materials after impregnation with a polymer were found to lhave better physico‐mechanical properties than ordinary cement concrete. Such impregnation, combined with fine sand and epoxy hardener, takes advantage of the optimum properties of the composites. The use of such polymerized composites for building constriction on a large scale can be undertaken, economizing on cement.
Analysis of the thickening reaction of a sheet molding compound resin through the use of dynamic mechanical testing
Authors: Gruskiewicz M. , Collister J.
Published: May 2005

The change in viscoelastic response of an unsaturated polyester during the course of thickening with magnesium oxide was evaluated, Rheological measurements were obtained to describe the effects of thickening as functions of time and magnesium oxide concentration. Previous researchers have made similar evaluations utilizing Brookfield viscosities. However, the test geometry asociated with a Brookfield T‐bar spindle is not well defined and data interpretation is consequently obscured. A Rheometrics Thermal Mechanical Spectrometer was used to obtain dynamic mechanical measurements ranging across three decades of frequency. Values of the elastic shear modulus, G′, the viscous shear modulus, G″, and the complex viscosity, η*, were calculated.
Fatigue behavior of thermosetting‐polyester‐matrix sheet‐molding compounds
Authors: Jeffery Mildred R. , Sourour Janine A. , Schultz J. M.
Published: May 2005

Two sheet molding compounds, one containing 65 weight percent E‐glass fiber and no filler (SMC‐65) and the other containing 50 weight percent glass and 15 weight percent CaCO3 filler were subjected to sinusoidal, load‐control, tension‐tension fatigue. The macroscopic behavior showed some notch sensitivity for both materials, but particularly for SMC‐65. The extent of failure damage over the specimen length decreased with decreasing load amplitude. Different failure mechanisms appear to operate under high‐ and low‐cycle fatigue conditions. Microscopic surface damage studies at stresses near the endurance limit showed several stages in the fatigue failure. For SMC‐65, these stages are, sequentially, matrix crack initiation and growth, matrix pulverization, fiber fracture, and fiber pullout. A similar, but less distinct pattern was observed for SMC‐50. Acoustic emission was also followed during fatigue cycling near the endurance limit. Distinct amplitude distribution peaks for each failure process were seen. It is suggested that matrix fracture, permanent deformation and Euler buckling are all important in high cycle fatigue failure.
The effect of water on the fracture surface energy of fiber‐reinforced composite materials
Authors: Thomson K. W. , Broutman L. J.
Published: May 2005

The effect of absorbed water on the fracture surface energy of both glass and graphite fiber unidirectional epoxy composites has been studied. The fracture energy parallel to the fiber direction was measured by the double torsion technique. Water was absorbed at 70°C while the sample was subject to an external tensile stress both parallel and perpendicular to the fiber direction. No degradation of fracture surface energy was measured for specimens stressed and immersed in water at 70°C for up to 1000 h. The fracture surface energy for the glass composite was greater than for the graphite composite, which was attributed to fiber pull‐out in the case of the glass composite.
Modulus development in oriented short‐glass‐fiber‐reinforced polymer composites
Authors: Curtis A. C. , Hope P. S. , Ward I. M.
Published: May 2005

The increase in modulus obtained in a short‐glass‐fiber‐reinforced polymer composite as a result of uniaxial deformation may be related to the observed increase in both fiber and matrix orientation. Quantitative measurements of both fiber and matrix orientation are presented for a series of samples of short‐glass‐fiber‐reinforced polyoxymethylene copolymer, processed to various substantial deformation ratios by solid‐phase hydrostatic extrusion. The polymer matrix becomes highly oriented at modest deformations, but the glass fibers orient in a slower pseudo‐affine manner and dominate the development of modulus in the composite. A simple “law‐of‐mixtures” model is used to demonstrate that perfect uniaxial orientation of the fibers is not achieved, but a better fit to measured modulus data is obtained by using an “aggregate” model applied to oriented fibers in an oriented matrix. The development of modulus with deformation ratio may be predicted very well if it is assumed that:

the composite consists of a series‐coupled array of sub‐units, each containing continuous and fully oriented fibers in a fully oriented matrix; and

orientation of the sub‐units develops with deformation in a pseudo‐affine manner.
Application of differential scanning calorimetry to cure optimization and quality control of a vinyl ester resin
Authors: Cummings L. C.
Published: May 2005

To optimize cure time for a given resin, the relationship between time, temperature, and degree of cure must be established. Using an epoxy‐based vinyl ester as an example, these relationships were determined with the use of differential scanning calorimetry (DSC). DSC curves can indicate the glass transition temperation (Tg) and the residual cure exotyherm (RCE) peak of a plastic of composite smaple. With increasing degree of cure, (Tg) increases, and the RCE peak area decreases. The data confirms a model showing that various timetemperature combinations can lead to the same degree of cure. Graphic representations of the relationships between time, temperature, and degree pf cure presented, which include degration regions (here, both Tg and shear strength are lowered). Graphs may be used for optimizing production cure conditions and for setting quality control criteria. This method should be applicable to most thermoset resins.
Effects of variation in composition and temperature on the amine cure of an epoxy resin model system
Authors: Byrne C. A. , Hagnauer G. L. , Schneider N. S.
Published: May 2005

Prior liquid chromatographic studies have shown that the reactions in epoxy resin model system phenyl glycidyl ether,p‐chloroaniline, and Monuron include amine addition to epoxy, homopolymerization of the epoxy, and a chain‐transfer reaction involving the hydroxy groups of the addition products. The present work examines the effect of variation in concentration of the accelerator Monuron, the amine‐to‐epoxy ratio, and the temperature on the competitive reaction mechanisms. The fraction of phenyl glycidyl ether reacting by homopolymerization increases with accelerator concentration and decreases with increasing amine‐to‐epoxy ratio and increasing temperature. The estimated contribution from chain transfer is much smaller and appears to parallel the homopolymerization reaction, as might be expected.
Measurement of the thermal conductivity of polymer composites to high temperatures using the line source technique
Authors: Henderson J. B. , Verma Y. P. , Tant M. R. , Moore G. R.
Published: May 2005

The line source technique for determination of thermal conductivity has been modified to allow measurement to higher temperatures than previously attained. This required the addition of a high‐temperature tube furnace to the standard experimental equipment. The modified device was used to measure the temperature‐dependent thermal conductivities of a glass‐ and talc‐filled phenol‐formaldehyde(phenolic) resin and a glass‐ and fiberglass‐filled acrylonitrile‐butadiene (AB) copolymer. Thermal conductivities of the virgin material were measured from room temperature to the onset of thermal decomposition. The char material thermal conductivities were measured from room temperature to approximately 900°C. A least‐squares fit of the data yielded a linear‐curve fit for the virgin material and a third‐order fit for the char material.
A study of the kinetics of high‐temperature carbon‐silica reactions in an ablative polymer composite
Authors: Henderson J. B. , Tant M. R.
Published: May 2005

The kinetics of high‐temperature carbon‐silica reactions for a widely used glass‐filled phenolic resin have been studied. Weight‐loss and rate‐of‐weight‐loss data were obtained at four heating rates ranging from 5 to 50°C per minute using standard thermogravimetric techniques. Experimental data were obtained at temperatures between 30 and approximately 1700°C. The kinetic parameters were calculated from these data using a multiple heating rate technique. Close agreement was obtained between the fractional weight loss calculated using the kinetic parameters and the measured values.
Co‐injection molding of reinforced polymers
Authors: Akay G.
Published: May 2005

Co‐injection molding of calcium carbonate filled polypropylene, short glass‐fiber‐filled polypropylene, or unfilled high‐density polythylene melts is studied using a mediumsize injection‐molding machine and a center‐gated disc mold. Injection molding is carried out under non‐isothermal conditions. Order of injection of the melts, injection speed, and mold temperature is changed in order to understand the mold filling in general and to investigate the type of skin/core structure and mechanical interlocking of the phases in the moldings. It is found that the order of injection is not significant in obtaining a skin/core structure but it is important in obtaining extensive phase interlocking, which is reduced if the flow rafe and the mold temperature are low. Presence of fillers appears to result in more mechanical interlocking of the phases.
The formation of coupling agent monolayers on the surface of mica
Authors: Favis B. D. , Blanchard L. P. , Leonard J. , Prudapos;homme R. E.
Published: May 2005

The interaction of very dilute solutions of a cationic vinylbenzyl silane (CVBS), a methacrylate functional silane (γ‐MPS), and an isopropyl‐tri‐(dioctylpyrophosphato) titanate (IDT) with a mica surface has been studied by carbon analysis. For all three coupling agents the dependence of adsorption with time of treatment follows a step‐like curve, where each step corresponds to a monolayer coverage on the mica. Under the operating conditions used it was noted that a particular monolayer is always completed before the next is started. The adsorption of γ‐MPS was found to be very sensitive to the time allowed for hydrolysis of the silane, while the adsorption of CVBS was relatively independent of the hydrolysis time when it is varied from 0 to 5400 s. The results indicate that γ‐MPS and CVBS near the mica surface form a dense structurally regular multilayer phase with the silane molecules oriented normal to the surface. IDT molecules occupy a surface area on mica which is characteristic of their branched nature.
Prediction of thermal and mechanical properties of glass‐epoxy composite laminates
Authors: Raghava R. S.
Published: May 2005

This paper provides an experimental test of the validity of laminate theory used for calculating thermoelastic properties of a unidirectional composite laminate. Theoretically calculated values of elastic moduli and coefficients of thermal expansion for unidirectional glass/epoxy laminates were compared with the measured values. Laminates (8″ × 8″ × 1/4″) as a function of ply orientation were made and their elastic moduli, thermal expansion coefficients, fiber volume, and void contents were measured.
Off‐axis tensile properties and fracture in a unidirectional graphite/polyimide composite (celion 6000/PMR 15)
Authors: Harper Jeffrey , Whittenberger J. Daniel , Hurwitz Frances I.
Published: May 2005

Tensile properties of unidirectional Celion 6000 graphite/PMR 15 polyimide composites prepared by hot molding and cold molding processes were measured at room temperature and 316°C, the upper use temperature of the polyimide resin, at both 45 and 90° to the fiber axis. The resulting fractures were characterized by scanning electron microscopy and materialographic techniques. Variation in tensile properties with processing history occurred in the elastic modulus and strain to failure for specimens loaded at 90° at 316°C, and in the fracture stress, and hence the in‐plane shear stress, for those loaded at 45° at room temperature. Significant plastic deformation was observed in the 45° orientation at 316°C for material produced by both processing methods. In general, fracture occurred by both failure within the matrix and at the fiber‐matrix interface; the degree of interfacial failure increased with temperature. Secondary cracking below the primary fracture surface also was observed.
Design concepts for the tallest free‐standing fiberglass stack
Authors: Plecnik Joseph M. , Whitman Warren E. , Baker Treven E. , Pham Mai
Published: May 2005

This paper presents design and materials considerations involved in the production of large, free standing glass reinforced plastic (GRP) industrial stacks. Because of large wind loads, such stacks must be designed with sophisticated structural analysis techniques, especially at load transfer points. This paper details such considerations for the world's tallest GRP stack.
Modification of epoxy‐reinforced glass‐cloth composites with a perfluorinated alkyl ether elastomer
Authors: Rosser Robert W. , Chen Timothy S. , Taylor Mark
Published: May 2005

A perfluorinated alkyl ether diacyl fluoride prepolymer (molecular weight about 1500) was coreacted with Epon 828 epoxy resin and diamino diphenyl sulfone to obtain an elastomertoughened, glass‐cloth composite. Improvements in flexural toughness, impact resistance, and water resistance, without loss of strength, modulus of elasticity or a lowering of the glasstransition temperature, were realized over those of the unmodified composite. Factors concerning optimization of the process are discussed. Results suggest that a simultaneously interpenetrating polymer network may be formed which gives rise to a measured improvement in composite mechanical properties.
Kinematics of flow in sheet molding compounds
Authors: Barone M. R. , Caulk D. A.
Published: May 2005

Experiments utilizing charges constructed of black and white sheet molding compound (SMC) reveal the basic kinematic mechanisms controlling the flow of the fiber‐filled compound in compression molding. The experimental results show that SMC deforms in uniform extension within individual charge layers, with slip occurring at the mold surface and, for slower closing speeds, also between the layers of SMC. When the mold closes rapidly, the charge extends uniformly through its thickness, with all slip concentrated at the mold surface.
Thermoelastic analysis of residual stresses in unidirectional, high‐performance composites
Authors: Nairn John A.
Published: May 2005

We present a thermoelastic analysis of the composite cylinder model for a undirectional composite including anisotropic fibers and an interphase region. We have found the magnitude of the residual thermal stresses on the micromechanics level induced by differential shrinkage between the anisotropic fibers and the matrix. For typical composites the largest residual stress is tension along the fiber direction, and a simple lower bound expression for this stress is given. Prediction of the magnitude of the thermal stresses requires knowledge of the thermal and physical properties of the matrix. The relevant properties for epoxy and thermoplastic matrices are discussed. The magnitude of the residual stresses can be reduced by tailoring the interphase region, but only if the interphase region serves to reduce the temperature for the onset of stress buildup. The volume fraction dependence of the longitudinal and transverse thermal expansion coefficients of the composite is compared to analogous expressions in the literature which do not include anisotropy of the fibers.
Tensile fatigue of glass fibers and composites with conventional and surface compressed fibers
Authors: Mandell J. F. , Mcgarry F. J. , Hsieh A. J.‐Y. , Li C. G.
Published: May 2005

The mechanism of tensile cyclic fatigue failure in conventional glass fiber dominated composites has been investigated using single fibers, strands, and composites. Surface damage to the fibers resulting from a fretting type of contact is identified as the dominant mechanism. Macrofibers of glass or glassceramic with residual surface compression have been developed to overcome the sensitivity both to cyclic and static fatigue. The macrofibers and their composites with several different matrices show greatly improved tensile fatigue resistance.
Processing of microcellular polyester composites
Authors: Youn Jae R. , Suh Nam P.
Published: May 2005

A new method of producing microcellular polyester composites is developed. The microcellular foam which is produced by supersaturating the polyester resin with nitrogen is cured by dielectric heating. The lightweight composite contains about 10 μm size bubbles. By substituting the microcells for the particulate fillers of the conventional composites, the weight of the composite is reduced by 30 to 40 percent. A theoretical analysis based on classical nucleation theory is applied to predict the rate of nucleation. The diffusion controlled bubble growth is modeled and the theoretical prediction is in good agreement with experiment. The mechanical behavior of the microcellular composite has also been examined. Toughness is improved significantly whereas the flexural strength remains the same as that of a conventional sheet molding compound.
Crack length estimation procedure for short fiber composites: An experimental evaluation
Authors: Agarwal B. D. , Patro B. S. , Kumar Prashant
Published: May 2005

Validity of the compliance matching procedure has been examined for short fiber composites experimentally by studying the behavior of damaged specimens. Comparison between the behavior of damaged and fresh specimens shows that the load—COD (crack mouth opening displacement) curve and fracture load of a damaged specimen are different from that of a fresh specimen having a machined crack of length equal to the estimated crack length in the damaged specimen. However, it has been clearly established that the secondary compliance of the damaged specimen can be used to accurately estimate the extent of damage to the specimen by earlier loading. Therefore, the use of the compliance matching procedure is justified for estimating instantaneous crack length in short fiber composites.
Interaction balances and properties of filled polymers
Authors: Richard C. , Hing Kuntharet , Schreiber H. P.
Published: May 2005

The dispersion behavior of calcium carbonate (CaCO3), of mica and of sized sand fractions in poly(vinyl chloride) (PVC) and polypropylene (PP) has been evaluated using fillers with various surface treatments. Mechanical properties of the compounds were also studied in order to question the role of interfacial forces in the context of dispersion and property parameters. Surface characteristics of polymers and fillers were obtained from inverse gas chromatography data. It has been shown that in the acidic PVC matrix, rapid dispersion of fillers is favored when strong acid‐base interactions exist at polymer filler contacts. Similarly, mechanical properties at large extension are improved by acid‐base interactions. In contrast, for polypropylene (PP), a van der Waals force material, fillers without pronounced acid or base surface characteristics tend to disperse more rapidly and produce mechanically stronger compounds. The importance of filler surface properties and thus, apparently, of acid‐base interfacial forces varies directly with increasing particle size of the dispersed phase.
Flow patterns in calcium carbonate and titanium dioxide filled polyethylene in the entrance region of a capillary die
Authors: Ma Chin‐Yuan , White James L. , Weissert Frederick C. , Min Kyonsuku
Published: May 2005

Experiments to determine the influence of calcium carbonate and titanium dioxide on flow patterns in die entrance regions are reported. The addition of loadings of calcium carbonate and tatanium dioxide of 5 volume percent and more is found to suppress the development of vortices in low density polyethylene at the entrance of a 180° entrance angle die. Vortex suppression was found in more complex entrance regions as well. Similar behavior has been found for carbon black compounds.
Some properties of polypropylene filled with metal fibers
Authors: Katsura T. , Kamal M. R. , Utracki L. A.
Published: May 2005

Polypropylene/steel fiber composites were prepared and tested for mechanical, electrical, and permeability performance. To enhance adhesion of polypropylene to steel fibers, two kinds of coupling agents, maleated polypropylene wax and maleated polypropylene, were used. It was found that maleated polypropylene wax was more effective. However, as indicated by permeability measurements and scanning electron microscopy (SEM), adhesion was rather poor. Oxygen and water vapor permeabilities of the polypropylene/steel fiber composites increased with the steel fiber concentration. The lack of adhesion at the fiber‐polymer interface created diffusive paths for the gas to penetrate the composite. Addition of polyamide to polypropylene caused a decrease in the permeability of the system, due to a reduction of the permeability of the matrix. The polypropylene/steel fiber composites become conductive at a volume loading of about 10 percent. At this concentration the volume resistivity of the composite is 10.8 ohm cm.
Electromagnetic interference shielding with nickel‐coated mica composites
Authors: Kortschot M. T. , Woodhams R. T.
Published: May 2005

The topic of electromagnetic interference (EMI) has been reviewed briefly to outline the need for conductive composite materials. The characteristics of a conductive filler which lead to high efficiency at small filler concentrations were examined qualitatively. One of these characteristics, aspect ratio, was examined in detail by using nickel‐coated micas as a means of molding composites containing ultra‐thin layers of nickel. Using this technique, as little as 1.5 volume percent nickel can provide adequate shielding for 90 percent of current commercial applications.
Tetraglycidyl epoxy resins and graphite fiber composites cured with flexibilized aromatic diamines
Authors: Delvigs Peter
Published: May 2005

Studies were performed to synthesize new ether modified, flexibilized aromatic diamine hardeners for curing epoxy resins. The effect of moisture absorption on the glass transition temperatures of a tetraglycidyl epoxy, MY 720, cured with flexibilized hardeners and a conventional aromatic diamine was studied. Unidirectional composites, using epoxy‐sized Celion 6000 graphite fiber as the reinforcement, were fabricated. The room temperature and 300°F mechanical properties of the composites, before and after moisture exposure, were determined. The Mode I interlaminar fracture toughness of the composites was characterized, using a double cantilever beam technique to calculate the critical strain energy release rate,GIC.
Evaluation of fiber‐matrix interphasial toughness in unidirectional composites
Authors: Newaz Golam M.
Published: May 2005

Interphasial toughness was evaluated for polyester and epoxy unidirectional glass fiber reinforced composites using single edge‐notched specimens. This was accomplished via a calculation of an energy term based onJ‐integral which accounted for the energy required to form a longitudinal split crack ahead of the original notch. It was found that the fiber‐matrix interphasial fracture resistance of the epoxy composite is substantially greater than that of the polyester composite. This technique may be an excellent way of evaluating the interphasial quality in unidirectional composite laminates.
Effect of the filler/polymer interface on the mechanical and morphological properties of a composite based on polyethylene blend matrices
Authors: Arroyo M. , Perez F. , Vigo J. P.
Published: May 2005

A series of composites based on low and high density polyethylene blend matrices with unmodified and previously organophylized sepiolite as filler have been prepared. In the latter case, isopropyl‐methacryl‐diisostearoyl titanate (KR‐6) was used as coupling agent. The Box‐Hunter Statistical Method was used to obtain the maximum information through a wide matrix composition and filler content range from a small number of experiments. The organophylization of the filler has hardly shown any improvement on the tensile, flexural, and impact properties of the composite. A morphological study carried out by means of scanning electron microscopy has shown that the organophylization tends to modify the surface textural characteristics of the sepiolite, compensating the effect of the coupling agent on the properties.
Dynamic mechanical behavior of binary blends polyethylene/EPDM rubber and polypropylene/EPDM rubber
Authors: Kolařík J. , Agrawal G. L. , Kruliš Z. , Kovář J.
Published: May 2005

The dynamic mechanical behavior of the binary blends high‐density polyethylene/EPDM rubber (ethylene‐propylene‐diene terpolymer) and isotactic polypropylene/EPDM rubber was investigated by means of a free‐oscillating torsional pendulum. Comparison of the moduli of the systems studied and predictions drawn from several models show that phase inversion in the polyethylene/EPDM blends takes place at the volume fraction vPE = 0.5, while polypropylene preserves a certain phase continuity also as the minor component (0.5 > vPP > 0.2) in blends with EPDM. Because of faster shrinkage in the course of cooling, inclusions are exposed to negative hydrostatic pressure, which accounts for a drop in the glass‐transition temperature of the rubber. The strength of the relaxation associated with the glass transition of inclusions and tensile impact strength increase proportionately to the rubber content in polypropylene (0 < vEPDM < 0.4). Dynamic mechanical response spectra of commercial EPDM/polyethylene impact modifiers are compared with the results for model systems.
Application of ductile polymeric coatings onto graphite fibers
Authors: Bell J. P. , Chang J. , Rhee H. W. , Joseph R.
Published: May 2005

Thin, high molecular weight copolymers have been applied to the surfaces of commercial, 8 micron diameter, graphite fibers by electropolymerization. Random copolymers were obtained, and the process appears to be consistent with the rules of standard free radical copolymerization. Coating thickness, Tg, and modulus can be systematically controlled. Very preliminary mechanical property measurements indicate a substantially improved impact strength and reduction in the interlaminar shear strength. These effects may be related to poor adhesion between the interlayer and the epoxy resin, however, which may be corrected by use of a “top layer” of appropriate composition.
Poly(aryl‐ether‐ether‐ketone) and its advanced composites: A review
Authors: Nguyen Huy X. , Ishida Hatsuo
Published: May 2005

Poly(aryl‐ether‐ether‐ketone) or PEEK is a highly aromatic semi‐crystalline thermoplastic. Its good mechanical properties and solvent resistances rank it as one of the most promising matrix polymers for high performance composites. This article attempts to provide an in‐depth review of work on PEEK and fiber‐reinforced PEEK composites. Discussions on various areas including synthesis, molecular weight determination, solution properties, structural hierarchy, morphology and mechanical properties of both neat polymer and composites, will be provided. In addition, environmental effects such as physical aging, thermal aging, moisture, solvents, and radiation will be summarized.
A nondestructive method to determine material properties in orthotropic plates
Authors: Fällström K‐e , Molin N‐e
Published: May 2005

An electronic speckle pattern interferometer (ESPI) is used to determine modes of vibration in rectangular, orthotropic, free‐free plates; that is using a noncontact, nondestructive, optical method. It is shown, using the finite element method (FEM), that each of the first three modes of vibration in rectangular orthotropic plates has a strong dependence upon only one of the main material parameters, namely the in‐plane shear modulus and the two Young's moduli, respectively. With this one‐variable dependence it is a simple task to determine the effective material parameters. This method has several obvious advantages compared to the use of test bars and it can be extended to give a measure of the damping parameters and probably also be used for production control. Preliminary results are presented and discussed.
Mechanical properties of particulate filled polymers
Authors: Bigg D. M.
Published: May 2005

The mechanical properties of several types of inorganic fillers were investigated in a number of different thermoplastic polymers. The fillers included minerals, such as talc and silicon carbide, and metals, such as aluminum flake and stainless steel fibers. The polymers included General Electric's Noryl, acrylonitrile‐butadiene‐styrene terpolymer, polypropylene, and modified polypropylene. The talc and some of the aluminum flake were treated with coupling agents to improve interfacial adhesion to the polymers. The results showed that the modulus of the filled polymers was a function only of the concentration of filler used up to 40 volume percent filler. The tensile strength of the filled compositions depended very strongly on the degree of interfacial bond developed between the polymer and the filler. The interfacial bond strength depended on the effectiveness of the coupling agents and the inherent wetting ability of the polymer. Of the polymers investigated in this study, Noryl showed the greatest degree of inherent wetting to inorganic fillers. Chemical modification of polypropylene also resulted in greater adhesion to fillers. The impact strength of filled compounds had an even more complex response, because, in addition to the concentration of the filler, and strength of the polymerfiller interface, it depends on the mechanism of crack propagation.
Cellulose fiber‐polyester composites with reduced water sensitivity (1)—chemical treatment and mechanical properties
Authors: Hua Li , Zadorecki Pawel , Flodin Per
Published: May 2005

Formaldehyde and di‐methylomelamine were used to modify the surfaces of cellulose fibers. Composites were prepared with unsaturated polyester and treated cellulose as the reinforcing material. The tensile strength and the elongation of the cellulose fibers were determined in dry and wet conditions as well as the tensile strength and the tensile modulus of the cellulose‐polyester composites. The water uptake of the composites was reduced by 46 to 52 percent. The wet strength of the composites was improved by more than 50 percent.
Micromechanisms of interlaminar fracture and fatigue
Authors: Russell Alan J.
Published: May 2005

The interlaminar fracture and fatigue properties of AS/3501‐;6 graphite/epoxy are discussed from a mechanistic point of view. Particular emphasis is placed on the interaction between the loading mode and the local geometry of the interlaminar zone and on how this affects the stresses close to the crack tip and the resulting failure path. Delamination growth under Mode I loading is shown to depend on the likelihood of fiber bridging occurring and on how effective these bridged fibers are at diverting strain energy away from the crack tip. The Mode II behavior is controlled by both the work required to shear the fibers from the matrix and the ease with which tensile failure of the matrix between the fibers can occur.
Controlling and monitoring interfacial reactions in composites of azidosilane modified glass filled polyethylene
Authors: Miller James D. , Ishida Hatsuo , Maurer Frans H. J.
Published: May 2005

Model composites of spherical glass particles dispersed in a matrix of high density polyethylene were prepared with controlled variations in the interfacial structure. Dynamic‐mechanical measurements of the composites in the melt state were recorded. The physical properties are found to relate to the morphology, bonding, reactivity, and other characteristics of the interfacial region which can be controlled by the applied chemistry. The interfacial reactions can be monitored in‐sity by dynamic‐mechanical analysis and differential scanning calorimetry.
Computer simulation of the electrical conductivity of polymer composites containing metallic fillers
Authors: Kortschot M. T. , Woodhams R. T.
Published: May 2005

In this study, a theoretical basis for the use of conductive composites was established. A percolation simulation program was used to determine critical area fractions for dispersions of rectangles in two dimensions. Both the aspect ratio and orientations of the rectangles were varied independently, and the simulation results were used to predict the effect of these parameters on the critical concentration of conductive flakes in a filled polymer. Above a certain aspect ratio defined as the “scaling limit,” the critical area fraction for rectangles was inversely proportional to aspect ratio. The scaling limit was smallest for a set of randomly oriented rectangles, and its value became larger as greater degrees of alignment were imposed. The smallest critical area fractions belonged to high aspect ratio, randomly oriented rectangles. The predictions of percolation theory were compared with results for dispersions of nickel‐coated mica in fine glass powder and in compression molded polyethylene. The critical volume fraction of mica was inversely proportional to flake aspect ratio over the range of aspect ratios tested. Electromagnetic interference (EMI) shielding effectiveness was examined for composites containing both aligned and randomly oriented flakes. For a given filler loading, the shielding effectiveness of the aligned flake composites was substantially lower than that of the composites containing randomly oriented flakes.
Testing of new‐generation carbon fiber/toughened resin epoxy systems
Authors: Poon C. , Scott R. F. , Lee S.
Published: May 2005

Four commercially available carbon fiber/prepreg systems were processed and subjected to NASA's proposed standard tests for toughened resins. Narmco Materials Inc. Rigidite T300/5208 was included as a baseline, while the other three systems employed Hercules' IM6 fiber in newgeneration resin systems. Descriptions of the tests, including open‐hole tension and compression, compression after impact, double cantilever beam, and edge delamination tension, as well as results are presented.
Polypropylene/low density polyethylene blend matrices and short glass fibers based composites. I. Mechanical degradation of fibers as a function of processing method
Authors: Arroyo M. , Avalos F.
Published: May 2005

The fiber length degradation during compounding (two‐roll milling and twin‐screw extrusion) of glass fiber and polypropylene (PP)/low density polyethylene (LDPE) blend matrices based composites was investigated. The effect of LDPE percentage and fiber content on fiber length were studied using a semiautomatic image analysis system. Two‐roll milling causes a more severe attrition of the fibers than twin‐screw extrusion. In the first case, the higher the LDPE percentage in the polymer matrix, the larger the final fiber length. Both methods lead to a broader fiber length distribution as LDPE percentage increases. The effect of fiber content is opposite to that of the LDPE percentage, but in the case of twin‐screw extrusion it is less noticeable, During the injection molding of the composites a slight decrease of the final fiber length takes place. This decrease depends on the initial fiber length, the effect being more pronounced for longer fibers.
Study of interfaces of high‐performance glass fibers and DGEBA‐based epoxy resins using single‐fiber‐composite test
Authors: Netravali A. N. , Schwartz P. , Phoenix S. L.
Published: May 2005

The single‐fiber‐composite (SFC) technique was used to study the interfacial behavior between two flexible blends of diglycidylether of bisphenol A (DGEBA)‐based epoxy and polyglycol epoxide and three glass fibers. Dog‐bone‐shaped SFC specimens were made and strained to obtain a distribution of fragment lengths. The fibers were tension‐tested at two different gauge lengths. The fragment length distributions, the fiber strength data, and a Monte Carlo simulation of a Poisson/Weibull model for fiber strength and flaws were used to obtain the effective interfacial shear strength values. The results show that the interface does not fail. Instead, penny‐shaped transverse cracks appear at every fiber break and grow as the specimen is strained. The interfacial shear strength values are many times higher than the yield shear strength values of bulk epoxy obtained from the tension test.
Interfacial shear strength studies using the single‐filament‐composite test. Part II: A probability model and Monte Carlo simulation
Authors: Henstenburg R. B. , Phoenix S. L.
Published: May 2005

A Monte Carlo simulation is developed to provide a foundation for interpreting experimental data from the single‐filament‐composite test. The main focus is on developing an improved procedure for arriving at a realistic value for the shear strength of the fiber‐matrix interface, but it is also shown how the test may be used to characterize the strength distribution of fibers at a length scale much shorter than is achievable in standard tension tests. The simulation is based on the widely used Poisson/Weibull probability model for fiber failure that characterizes the strength in terms of the random flaws distributed along the fiber. The primary mechanical model for stress buildup at the fiber end is the same as that assumed by most authors and assumes a constant interfacial shear stress in this shear transfer zone reminiscent of a yielding plastic matrix. We also, however, consider a bilinear model that allows for a zone of debonding with a constant shear stress lower than in the primary “plastic” zone. Simulation results are cast in terms of nondimensional variables and tabulated to allow for wide applicability. Sample size and confidence interval issues are also discussed.
Short‐fiber‐reinforced thermoplastics. Part III: Effect of fiber length on rheological properties and fiber orientation
Authors: Vaxman A. , Narkis M. , Siegmann A. , Kenig S.
Published: May 2005

The effect of fiber length on fiber‐filled melt viscosity and on shear‐induced fiber breakage and orientation development in polystyrene was studied. The incorporation of fibers, increasing their length, results in an increasing viscosity over the entire shear rate range. Significant fiber length reduction was observed even at low shear rates. Determined fiber orientation distributions, as affected by shear rate and fiber length, are discussed. Orientation effects are expressed by a single orientation parameter which is used to account for the average fiber orientation contribution to the relative viscosity. Calculated orientation parameters indicate higher fiber orientation for shorter fibers. Fiber orientation in the flow direction increases with increasing shear rate and results in the expected viscosity decrease.
Prediction of internal stresses in a circular bilayered laminate glass‐resin
Authors: Aboulfaraj M. , Schirrer R. , Wippler C.
Published: May 2005

A previous paper has shown how it is possible to determine the stress induced in a bilayered circular laminate glass‐resin under various conditions with a nondestructive method. In this paper a more precise mathematical analysis which allows prediction of the stress with time is given. In order to determine numerical values from the theoretical calculations, the relaxation function of the resin, g(t, T), and the shift factor, aT, of the time‐temperature superposition principle have to be known. The relaxation function measured with the experimental setup, under biaxial stress conditions appears to be identical with the one determined by another laboratory under uniaxial compression stress. A systematic exploration of the influence of the different parameters, g(t, T), aT and the thermal expansion coefficient, α(T), shows that the most difficult parameter to determine with sufficient precision is aT. Working under different cooling conditions the experimental results have been compared with the theoretical predictions. The agreement is generally good and even very good for the fast cooling cycle for the final stress if one takes into account the thermomechanical properties of the resin during and after its curing.