bluuebunny/crossref_metadata_2025 huggingface dataset:
A review of recent progress in the studies of molecular and microstructure of coupling agents and their functions in composites, coatings and adhesive joints
Authors: Ishida Hatsuo
Published: May 2005

Recent progress in the studies of molecular and microstructure of interfaces and interphases in composites, coatings, and adhesive joints is reviewed. Remarkable progress has been made in elucidating the structure of silane coupling agents and their function with respect to dry and wet strengths of multiphase systems. Aminosilanes attracted major effort in the past. It is now understood that the structure of partially cured hydrolyzate is complicated. When adsorbed from a natural pH solution and dried in air at room temperature, approximately half of the amine groups form amine bicarbonate salt with the CO2 in air. The rest of the amine groups are either intra‐ and intermolecularly hydrogen bonded to neighboring silanol groups or free from hydrogen bonding. There exists chemical bonding at the glass/silane or metal/silane interfaces. The surface characteristics, including acidity, topology and homogeneity, influence the structure of the coupling agent. The coupling agent interphase shows a gradient in various properties. Silanes tend to be ordered in the interphase and the degree of organization depends largely on the organofunctionality. The orientation and organization of the silane affects the reinforcement mechanism. There are chemisorbed and physisorbed silanes in the interphase. The coupling agent/matrix interface is a diffuse boundary where intermixing takes place due to penetration of the matrix resin into the chemisorbed silane layers and the migration of the physisorbed silane molecules into the matrix phase. With proper selection of the organofunctionality and the curing conditions, silanes can chemically react with the matrix to form copolymers. The existence of the matrix interphase is now well accepted and the effect of the interphase on the mechanical properties has been studied. It has been recognized that modification of the matrix interphase, such as a coating applied on the fiber using a similar resin as the matrix, has a complex effect on the mechanical performance. It is noteworthy that attempts to synthesize new coupling agents and to utilize the existing coupling agents more effectively still continue. Based on the molecular understanding, new concepts in the reinforcement mechanism have appeared which recognize the importance of interpenetrating networks, the structure of silane in the treating solution, and the microheterogeneity of the glass surfaces. The knowledge obtained through the studies of composites can be applied to organic coatings and adhesive joints provided that the geometrical factors are taken into consideration.
Dynamic mechanical experiments for probing process‐structure‐property relations in amine‐cured epoxies
Authors: Chu Helen S. , Seferis James C.
Published: May 2005

Dynamic mechanical experiments were performed on an amine‐cured high performance epoxy system containing two types of epoxies and one amine. The system approximates a commercial resin system used widely as matrix material for graphite composites and whose main ingredients and composition are 88.5 percent of tetraglycidyl 4,4′‐diamino diphenyl methane (TGDDM) and 11.5 percent of polyglycidyl ether of Bisphenol A Novalac epoxy with varying compositions of 4,4′‐diaminodiphenyl sulfone (DDS), ranging from 19 to 40 PHR. Specifically, the effects of DDS and Novalac content as well as processing conditions including the particle size of solid components, the mixing speed, mixing temperature, and the mixing duration of the components on the dynamic mechanical properties of the epoxy polymer were investigated. A viscoelastic transition in the dynamic spectrum which was observed to be quite sensitive to the sample's Tg in conjunction with incomplete crosslinking reactions allowed for interrelating the composition and processing variables to the structure and bulk properties of this epoxy system.
Electric breakdown of a poly(ethylene terephthalate)/glass composite
Authors: Schultz J. M. , Lhymn Chang
Published: May 2005

The voltage lifetime of a poly(ethylene terephthalate)/glass composite is measured for two different orientations of short fiber with respect to the applied electric field (perpendicular and parallel). The difference in the voltage lifetime between two configurations is attributed to the microstructural features at the (fiber/matrix) interface, particularly microvoids. The morphological observations by scanning and transmission electron microscopy (SEM, TEM), and optical microscopy reveal the presence of microvoids as well as the crazed matrix and consequent erosion channel. The tree initiation site is identified and the nature of tree propagation is explained. A theoretical model based on such microstructural features is constructed, which explains the voltage lifetimevsfiber orientation in a relative framework. It is concluded that the graseous discharge at microvoids is the main mechanism for electrical breakdown and the site of such gaseous discharge is the (fiber/matrix) interface. Therefore, the orientation dependence of the electrical breakdown is the geometrical effect of the interface voiding with respect to the direction of the applied electric field.
Polyfunctional epoxies: Part II. Nonrubber versus rubber‐toughened brominated formulations for graphite composites
Authors: Nir Z. , Gilwee W. J. , Kourtides D. A. , Parker J. A.
Published: May 2005

Initial screening of carboxy‐terminated butadiene acrylonitrile (CTBN) rubber‐toughened brominated formulations for graphite composites has been reported previously. This study is a further investigation, focusing on the performance of the brominated polymeric additives as a potential flexibilizing agent for graphite composites, using different molecular weights of the Br source. Increasing segment lengths of the polymeric backbone chain of brominated polymeric additives (BPA) are examined in a new development, trifunctional epoxy resin and is compared with a 10 percent rubber‐toughened formulation of the same epoxy resin. Results show that when the Br content in the graphite composite was increased without the use of rubber, the mechanical properties improved. Mechanical and other properties of the graphite composites are discussed.
Induced orientational behavior of liquid crystal polymer by carbon fibers
Authors: Chung T. S. , Gurion Z. , Stamatoff J. B.
Published: May 2005

Experimental results are presented that show that the structure of carbon fibers induces molecular orientation of liquid crystal polymers. X‐ray diffraction data are used to demonstrate final collinearity of the polymer molecular axis and carbon fiber axis independent of fabrication approaches or prefabrication orientation of the polymer relative to the carbon fiber direction. The final degree of polymer molecular orientation approximately equals the degree of carbon basal plane orientation within the carbon fiber.
The interface between glass and carbon fibers and thermosetting polymers
Authors: Piggott M. R. , Chua P. S. , Andison D.
Published: May 2005

The interface between the fibers and the polymer matrix controls the properties of fiber composites and has been the subject of much study. Recently, special techniques have been developed for single fiber pull‐out experiments on production fibers, which make it possible to obtain data on the frictional forces which govern sliding after the interface has fractured, as well as the adhesion strength of the interface. Tests on glass in polyester and epoxy resins show that the work of fracture of the interface is much smaller than that of the resin, and that the shrinkage pressures of these matrices, when fully postcured, are approximately the same (about 20 MPa). Coefficients of friction at the interface are 0.6 for the polyester and 1.0 to 1.6 for the epoxy. The carbon‐epoxy interface yields at shear stresses as high as 60 MPa, instead of fracturing, and the coefficient of friction during sliding is about 0.4.
Fracture of mica‐reinforced polypropylene: Mica concentration effect
Authors: Vu‐Khanh T. , Sanschagrin B. , Fisa B.
Published: May 2005

Concepts of post‐yield fracture mechanics were used to characterize the crack initiation and propagation resistances of mica‐reinforced polypropylene containing different mica concentrations. Although mica addition leads to an apparently brittle composite, the crack initiation resistance is slightly increased with mica concentration up to 10 percent by weight; and significant improvement in crack propagation performance was found for polypropylene reinforced by up to 20 percent of mica in comparison to that of virgin polypropylene. The debonding of the interface between mica flakes and the matrix leads to a micro‐ductility ahead of the crack tip in which the matrix is able to pull‐out from mica particles and to stretch. This micro‐ductility also prevents the brittle, unstable crack propagation, which is due to the coalescence of voids in pure polypropylene. Above 20 percent of mica, the reduction of the effective amount of the matrix material results in a substantial drop in the resistance to crack growth of mica‐reinforced polypropylene.
Use of wood fibers in thermoplastic composites II: Polyethylene
Authors: Beshay Alphons D. , Kokta Bohuslav V. , Daneault Claude
Published: May 2005

Wood fibers of aspen in the form of chemithermomechanical pulp (CTMP) has been used as reinforcement in polyethylene (PE). The secant modulus, tensile strength, energy, and elongation at yield were measured. It was found that the mechanical properties of the composite were higher than those of PE by a factor of 2.6 for modulus, 2.3 for stress, and 2.1 for energy at yield. Compared to glass fiber composites, the CTMP composites showed higher elongation, about 100 percent higher energy, 106 percent higher stress, and 75 percent higher modulus. Note that the cost of treated wood fibers is several times lower than that of treated glass fibers.
Fiber matrix interactions in jute reinforced polyester resin
Authors: Semsarzadeh Mohammad A.
Published: May 2005

The effect on packing resulting from the filling of unsaturated polyester resin with fillers and jute fibers has been investigated. The influence of absorbed water on the interfacial interactions involved in the fiber matrix system of the jute reinforced polyester resin also are discussed. An approach to reduce water absorption and soluble matter lost from the jute reinforced polyester resin is proposed.
Fatigue of glass‐fiber‐reinforced polyester laminates
Authors: Ouellette Paul , Hoa S. V.
Published: May 2005

Materials used in making glass‐fiber‐reinforced plastic pressure vessels are tested in uniaxial tensile fatigue. Specimens of mat/woven roving/mat are tested with the warp direction parallel to the load axis and ±45 degrees to the load axis. Filament‐would specimens are tested at ±54.7 and ±35.3 degrees to the load. A stress ratio of R = 0.1 is used with load control. The residual properties of surviving specimens after 400,000 cycles indicate they have sustained no damage. The S′‐N curves show a strength loss of about 10 percent per decade of cycling. The failure mode of the filament‐would specimens is similar to that of angle‐ply laminates. Stress levels of one‐third the strength appear safe for the range of cycles investigated.
Void content of a viscoelastic composite melt: Reduction during mixing
Authors: Watson Robert J. , Chaffey Charles E.
Published: May 2005

Mica and polystyrene in four ratios were sheared for three different times, each at three speeds, and at two temperatures in the viscoelastic region, in a screw mixer. From precise density measurements on the resulting composites, void volume fractions were calculated and found to be proportional to mica concentration and independent of total screw rotations. Experimental void/mica ratios were represented by a kinetic model; they decreased from a single value common to all conditions to a steady‐state value proportional to the square root of the screw speed. Void formation and elimination occur simultaneously. The goodness of the fit to the data is insensitive to the details of the kinetic model. The characteristic rate constant depends only on temperature, increasing at the same rate as the reciprocal of the low‐frequency dynamic viscosity. Cavitation in regions of diverging flow of the mixer may inhibit void elimination.
Ultrasonic evaluation of filled polymers II. Elastic moduli of a resin filled with iron inclusions of different aspect ratios
Authors: Piché L. , Hamel A.
Published: May 2005

An ultrasonic technique is used for the nondestructive evaluation of elastic moduli of polymer composites. Samples with varying amounts of randomly oriented iron inclusions, having aspect ratios p = 0.20 (flakes) and p = 20.0 (short fibers), were fabricated and fully characterized. The results for the moduli are discussed in terms of available theoretical models. It is demonstrated that models which account for the microscopic details of the material offer a good description of the bulk properties. Also, experimental evidence is obtained for the effect of particle contiguity and allows not to evaluate the influence of particle/particle interaction.
An apparatus for measurements of thermal conductivity of neat epoxies and their composites
Authors: Mijović Jovan , Mei Henry L.
Published: May 2005

In the modeling studies of processing of composites one must determine the changes in thermal conductivity during cure as a function of both temperature and the extent of reaction. An apparatus for measurements of thermal conductivity of neat thermosets and their composites was designed and built in our laboratory. A detailed description of the apparatus is given in this paper. Also included are some initial results obtained with an epoxy resin formulation of the type used in filament‐wound structures.
Controlled energy dissipation in fibrous composites I. Controlled delamination
Authors: Jang B. Z. , Lieu Y. K. , Chung W. C. , Hwang L. R.
Published: May 2005

Delamination mechanisms in continuous fiber reinforced composites were investigated. The concept of controlled interlaminar bonding (CIB) is proposed as a guideline for preparing fiber‐epoxy composite laminates with enhanced fracture toughness without significant degradation in strength properties. The interlaminar bonding was manipulated by several specialized techniques including insertion of delamination promotors and surface modification of laminae. Results indicated that the plane‐strain fracture toughness of E‐glass‐epoxy laminates could be improved by inserting perforated interlaminar films of aluminum, paper, polyester and polyimide, and fabrics. Such interlayers were used to promote delamination which dissipate strain energy by blunting and diverting a propagating crack. The fracture resistance of a laminate was found to be dependent on the degree of delamination. The competition between the growth of delamination cracks and the propagation of a main crack is controlled by the relative magnitude of the interlaminar bonding strength and the lamina cohesive strength. The interlaminar bonding is controlled by the degree of interlayer perforation and the adhesion between interlayer and lamina. The loading direction was found to be very important in dictating the failure processes. Experimental results from several composite systems are presented and discussed along with post‐failure analysis data.
Acoustic emission during fracture of short glass fiber reinforced poly(vinyl chloride)
Authors: Koenczoel L. , Hiltner A. , Baer E.
Published: May 2005

The fracture mechanics approach and acoustic emission (AE) analysis have been coupled in an investigation of slow crack growth of short fiber reinforced poly(vinyl chloride). It was found that AE occurs during less than one percent of the time of crack growth suggesting that so‐called continuous crack propagation is based on discontinuous microscopic damage. The time dependence of various AE parameters exhibits a good linear relationship with crack speed. For a unit of newly created fracture surface, a constant amount of acoustic energy is released independent of crack speed. At very low speeds, below 3·10−3mm/s, a change in mechanism from pure matrix related to fiber related crack growth is observed, which is also reflected by a change in the amplitude distribution of the AE events.
Nylon fiber reinforcement for polyurethane composites
Authors: Córdova C. W. , Young J. A. , Rowan H. H.
Published: May 2005

The potential of a nylon 6 fiber was evaluated for composite applications involving rigid polyurethane systems. A study showed that the use of COMPET N, a nylon 6 based fiber surface treated to enhance wetout and adhesion, in an ISP polyurethane system results in composites with higher impact values and lower weight than those reinforced with glass fiber. A 2 percent loading of COMPET N matt increased impact values by more than 300 percent over an unreinforced control while a 3 percent loading of glass matt resulted in increases of less than 100 percent. A drop impact test showed COMPET N fabric reinforced composites to absorb twice as much energy as an unreinforced and glass reinforced composite without major damage. These advantages have also been observed in COMPET N/Glass hybrids, in which layer orientation can be used to produce composites with specific properties. Cut fiber reinforced composites were found to exhibit similar properties as fabric reinforced ones resulting in the commercialization of a canoe end cap containing cut nylon fiber. Additional property benefits such as improved impact fatigue and decreased stress cracking have also been observed in nylon 6 reinforced composites resulting in the consideration of these materials for a wide range of applications.
Thermal and rheological properties of poly(phenylene sulfide) and poly(ether etherketone) resins and composites
Authors: Ma Chen‐chi M. , Hsia Hung‐chung , Liu Wen‐liang , Hu Jiann‐tsun
Published: May 2005

Poly(phenylene sulfide) (PPS) and poly(ether etherketone) (PEEK) are high performance engineering thermoplastics with a unique combination of excellent environmental, mechanical, and thermal properties. Research on the thermal and rheological properties of PPS and PEEK resins and carbon fiber reinforced prepregs are described. Experimental studies of the dynamic viscoelasticity and thermal properties of these materials are summarized. The effects of processing cycles and environment on the thermal and rheological properties are discussed. The effects of the processing environment and the addition of carbon fiber on the thermal stability are reported. Crosslinking of poly(phenylene sulfide) in air, enhancing thermal stability, is also investigated.
A composite characterization of high speed spun semicrystalline fibers
Authors: Pournoor Kaveh , Seferis James C. , Vassilatos George
Published: May 2005

A systematic study of thermo‐mechanical properties of high speed spun poly(ethylene terephthalate) fibers was undertaken as part of a broad quantitative process—structure—property examination of semicrystalline polymers through appropriate composite models. Calorimetric experiments on a series of fibers spun at different speeds show that crystallinity increases with takeup speed rapidly below 4500 m/min but at a slower rate above that speed. The glass transition, cold crystallization, and melting temperatures were also found to increase with speed. A similar increase is exhibited by both the refractive index of these fibers along the fiber axis and the fiber birefringence. Comparison of birefringence measurements with those predicted from a composite two‐phase optical model led to the conclusion that form birefringence may be a significant contributor to the overall birefringence and that it may not be ignored in calculations of orientation functions with this experimental technique.
The effect of fiber‐matrix adhesion on the fatigue fracture of glass‐fiber‐reinforced poly(vinyl chloride)
Authors: Nguyen P. X. , Moet A.
Published: May 2005

Fatigue crack propagation (FCP) of injection‐molded glass‐fiber‐reinforced poly(vinyl chloride) was examined as a function of fiber‐matrix adhesion (coupling) and fiber content at different load levels. Considering the entire FCP history, from crack initiation to critical propagation, it is shown that fatigue lifetime and fracture toughness of coupled composites increase with fiber weight fraction. Uncoupled material exhibits the highest fracture toughness at 10 wt% fiber, yet its fatigue life is considerably shorter. Damage analysis indicates that fiber debonding, pullout, and particularly fiber fracture seem to contribute to the higher fatigue lifetime noted in coupled composites. The Crack Layer Theory is employed to describe the observed FCP behavior. The effective enthalpy of damage parameterizes the resistance of the composite to FCP in terms of the observed mechanisms.
Crack‐arrest study in mode II Delamination in composites
Authors: Vu‐Khanh T.
Published: May 2005

Procedures for measuring the crack initiation and arrest toughnesses in Mode II interlaminar fracture in composite materials were analyzed. Different techniques using flexural specimens were studied. The strain energy release rate,G, which is the energy available for crack propagation was calculated using simple beam theory. The calculation takes into account the transverse shear effect. Stable and unstable fractures are analyzed, and conditions required to measure the arrest toughness of interlaminar fracture are discussed. The methodology was applied to the measurement of fracture energy at the onset and arrest of delamination in glass/epoxy laminate.
Survey of current status and future trends in reinforced plastics composites
Authors: Vu‐Khanh T.
Published: May 2005

The production of reinforced plastics has constantly increased since the Second World War. With a forecast growth rate of 8 to 12 percent annually over the next decade, composites are one of the fastest growing sectors of the plastics industry. Advanced composites will show the largest expansion, due to a strong increase in demands in aerospace and military markets. Penetration of advanced composites into big‐volume markets has not occurred, but it is believed that advances in both materials and machinery will accelerate the mass‐production of these materials. High‐volume composites will see a less rapid growth rate but demands for these materials will continue to increase. Land transportation will remain the largest and will be also the fastest growing market for high‐volume composites. Current status and future trends in the uses of various reinforcing fibers and matrix resins are presented. Hurdles to the expansion of reinforced plastics are also discussed.
Weldline integrity of reinforced plastics: Effect of filler shape
Authors: Fisa B. , Dufour J. , Vu‐Khanh T.
Published: May 2005

The paper is a preliminary report on glass fiber and glass flake orientation in the weldline zone of injection molded reinforced polypropylene. Two types of weldlines were studied using simple shape molds: one where two melt streams meet head‐on and become immobilized, the other where the weldline formation is followed by additional flow. In the weldlines of the first type, which are characteristic of current standard molds used to test weldline strength, the anisometric particles are almost perfectly oriented perpendicular to flow. As a result, the weldlines of this type tend to be weak and brittle. In the second case when the weldline is formed by merging of melt streams separated by an insert, particle orientation in the weldline area remains different from other areas of the sample for long distances from the insert. It is shown that in molds where the weldline formation is followed by laterally expanding flow the change of particle orientation is faster than for unidirectional flow.
The characterization of thermoset cure behavior by differential scanning calorimetry. Part I: Isothermal and Dynamic Study
Authors: Lam Patrick W. K.
Published: May 2005

A study of the isothermal cure kinetics of an unsaturated polyester resin by differential scanning calorimetry is described. An autocatalyzed second order kinetic model is adopted to elucidate the cure reaction and also assess the kinetic parameters. The rate constant, the maximum cure rate, the extent of cure, and the degree of conversion at the maximum cure rate, all increase with increasing cure temperature, while the half‐life and the time required to reach the maximum cure rate both decrease. Discrepancies between the experimental results and the predicted values of some of the kinetic parameters, especially at high degrees of conversion, are attributed to the highly different‐controlled cure reaction following the gel point. The activation energy (E) and the pre‐exponential factor (1n A) of the polyester cure reaction were estimated, using differential graphical techniques, to be 131 ± 4 kJ/mol and 39 ± 1 respectively. An ASTM method (E698) produces erroneously low values of the Arrhenius parameters, suggesting that the assumptions of the method may be overly simplified.
Effects of fiber length and orientation distribution on the elastic modulus of short fiber reinforced thermoplastics
Authors: Chin Wei‐Kuo , Liu Hsin‐Tzu , Lee Yu‐Der
Published: May 2005

A method including the effects of fiber length and orientation distribution to predict elastic moduli of short fiber reinforced thermplastics (FRTP) is presented. The fiber length distribution in FRTP has an asymmetric character with a tail at the long fiber end. Statistical distribution functions such as Weibull or log‐normal can be used to represent this kind of distribution. Orientation distribution of fibers in FRTP can be characterized by a single parameter exponential function, \documentclass{article}\pagestyle{empty}\begin{document}$F(\theta) = \frac{{1 - \lambda \theta }}{{1 - e^{ - \frac{\P}{2}\lambda } }}$\end{document}. A large λ indicates a highly oriented material whereas small λ represents a quasi‐isotropic material. As fiber length and orientation distribution functions have been characterized, the elastic moduli of FRTP can be predicted. First, the mean elastic moduli of unidirectional plies are predicted through the fiber length distribution. Then the stacking sequence of laminate is assumed to be as the fiber orientation distribution of FRTP, and the overall elastic moduli of FRTP are estimated based on the laminate‐plate method.
Mechanical properties and morphology of polypropylene composites II. Effect of polar components in talc‐filled polypropylene
Authors: Stamhuis J. E.
Published: May 2005

Using the concept of filler coating, a study has been made of the morphology and mechanical properties of polypropylene/talc/elastomer composites with a series of polar components as added elastomers. Both impact strength and stiffness of the blends were better than those of polypropylene homopolymer. Most of the polar components showed a considerable amount of filler coating, as evidenced by morphological studies. However, the impact strength of the composites was generally lower than that of similar blends with non‐polar elastomers, probably owing to (a) the high glass transition temperatures of the polar components, (b) the poor dispersion of some of the elastomeric phases, and (c) a reduced affinity of the elastomers for polypropylene.
Interlaminar stresses in tapered laminates
Authors: Hoa S. V. , Daoust J. , Du B. L. , Vu‐Khanh T.
Published: May 2005

Tapered laminates of unidirectional layers of glass/epoxy and graphite/epoxy are investigated. These laminates have a thickness variation along their length. This was accomplished by having layers dropped off near the midlength of the laminate. Stress and strain variations were obtained using three‐dimensional finite element models. Calculated values using the finite element method compare well with experimental results for the point of first delamination. This agreement allows the determination of a suitable finite element mesh for subsequent models of other tapered laminates with fiber orientations other than unidirectional.
Simulation of flow in compounding machinery: Internal mixers and modular corotating intermeshing twin‐screw extruders
Authors: White James L. , Kim Jin‐Kuk , Szydlowski Witold , Min Kyonsuka
Published: May 2005

Hydrodynamic lubrication theory has been applied to analyze flow in internal mixers and twin‐screw extruders. Fluid motions in mixing regions are interpreted as being due to coupling of drag flow and pressure gradients. Pressure fields and mean flow patterns have been computed. Distributive and dispersive mixing are interpreted in terms of computed fluid fluxes in the processing machinery.
Short fiber reinforced thermoplastics. II. Interrelation between fiber orientation and rheological properties of glass fiber‐reinforced Noryl
Authors: Vaxman A. , Narkis M. , Siegmann A. , Kenig S.
Published: May 2005

Mechanical properties of short fiber reinforced thermoplastics depend on the fiber orientation distribution produced during the melt flow processing step. An experimental investigation of fiber orientation during shear flow through a circular die is presented. A quantitative determination of the glass fiber orientation distribution was done by analyzing photomicrographs of polished extrudate sections. Planar and axial fiber orientation distributions as affected by shear rate and total shear are discussed. The reliability of a classical metallographic technique for fiber orientation determination was evaluated. Orientation effects are expressed by a single orientation parameter which is used to account for the average fiber orientation contribution to the relative viscosity. The influence of shear rate, total shear, fiber concentration, and temperature on fiber orientation has been investigated. It is concluded that an orientation parameter should be used to account for fiber concentration effects on the relative viscosity. Calculated values, considering the orientation parameter, show good agreement with the experimental relative viscosity results.
Effects of sorbed caprolactam on the crystallinity, morphology, and deformation behavior of polyetheretherketone and poly(phenylene sulfide)
Authors: Wilfong Debra L.
Published: May 2005

Studies on the high temperature sorption of caprolactam by polymer resins and their composites have been conducted. The systems investigated were glass fiber reinforced (GFR) poly(phenylene sulfide) (PPS), polyetheretherketone (PEEK) neat resin, GFR PEEK and carbon fiber reinforced (CFR) PEEK. To measure changes of caprolactam sorption, melting behavior, mechanical properties, and fracture surface morphology were determined. Absorption of caprolactam by the PEEK composites was 30 to 40 percent less than by the neat resin. This is attributed to the fibers, which acted to constrain the matrix and thus limit its swellability. Reductions in melt temperature, percent crystallinity, ultimate tensile strength, and modulus were observed following exposure to the chemical environment. The loss of strength and stiffness was a consequence of the degradation of the matrix/fiber interface by the sorbed caprolactam.
Graphite/polyimide composites with improved toughness
Authors: Delvigs Peter
Published: May 2005

Studies were performed to determine the toughness characteristics of composites prepared from modified addition‐type polyimides, using Celion 6000 graphite fiber as the reinforcement. The polyimides were prepared from aromatic diamines containing flexibilizing ether connecting groups. The composite flexural and short beam shear strengths were determined at room temperature and elevated temperatures. Composite toughness was evaluated using 10° off axis tensile tests and double cantilever beam fracture tests at room temperature. The effects of the flexibilized resin structure on composite mechanical properties, toughness characteristics, and thermo‐oxidative stability are discussed.
A study of glass fiber–epoxy composite interfaces
Authors: Liao Y.‐T.
Published: May 2005

Fourier transform infrared spectroscopy was utilized to characterize the interfacial bonding in glass‐fiber‐reinforced composites. The pH of the treating solution significantly affects the interfacial chemical bonding. The natural pH of the solution gives the maximum interfacial bonding. The decrease of the interfacial bonding is due to the side reactions that occur when NaOH or HCl is added to the solution. The temperature of the curing process has little effect on the amount of the interfacial chemical bonding. We attribute this to the reaction rate constant of the interfacial reaction being much larger than that of the epoxy polymerization. From the hygrothermal behavior, we have found the amount of silane needed for hygrothermal condition is different from that for dry condition.
The response of fibrous composites to impact loading
Authors: Jang B. Z. , Chen L. C. , Hwang L. R. , Hawkes J. E. , Zee R. H.
Published: May 2005

The response of advanced composites to low‐velocity projectile loading was investigated. The impact failure mechanisms of composites containing various fibers with different strength and ductility were studied by a combination of static indentation testing, instrumented falling dart impact testing, acoustic emission monitoring, and scanning electron microscopy (SEM). The composites containing fibers with both high strength and high ductility (eg., polyethylene (PE) fibers) demonstrate a superior impact resistance as compared to those containing fibers with high strength (eg., graphite fibers) or high ductility (eg., nylon fibers) but not both. Upon impact loading, the composites containing PE fibers usually exhibited a great degree of plastic deformation and some level of delamination. These mechanisms acted to dissipate a significant amount of strain energy prior to the penetration phase of the impact process. No through penetration was observed in all the samples containing more than three layers of PE fabric except when loaded at relatively high rates and low temperatures. Although certain levels of delamination also took place in other composite systems, very little plastic deformation occurred, allowing ready penetration of the projectile. The stacking sequences in the hybrid laminates studied were found to play a critical role in triggering or inhibiting the processes of plastic deformation and delamination and, therefore, controlling their energy absorption capability. The penetration resistance of composites appeared to be dictated by the fiber toughness. The later property must be measured in a simulated high‐rate condition.
The resin‐fiber interface in polyurethane and polyurethane‐unsaturated polyester hybrid
Authors: Damani S. G. , Lee L. James
Published: May 2005

A polyurethane (PU) is compared with the polyurethane‐unsaturated polyester (PU‐UPE) hybrid to examine the changes of the resin‐fiber interphase in the presence of a sizing compatible component, UPE, in the matrix resin. The formation of resin‐fiber interphase is critical in structural reaction injection molding (SRIM) and resin transfer molding (RTM) because resin solidification (i.e., gelation and vitrification) occurs in seconds (SRIM) or minutes (RTM). Kinetic (DSC, FTIR spectroscopy), mechanical (single fiber test, fracture surface analysis), and microscopic (birefringence, SEM) studies were used to analyze the interface. Kinetic results indicate poor chemical compatibility of the sizing with PU and increased chemical interactions of the sizing with the PU‐UPE resin. Mechanical and microscopic analyses also point in favor of improved interphasial behavior with the PU‐UPE resin.
Review of cure of polymers and composites by microwave energy
Authors: Mijović Jovan , Wijaya Jony
Published: May 2005

The fundamental concepts of microwaves and their application as an alternative energy source for cure of polymers and composites are discussed. The mechanisms of interaction between electromagnetic waves and organic materials are described, and studies reported in the literature on microwave cure of polymers and their composites are discussed. Information is presented about materials, microwave applicators, modes of microwave energy application, and means of monitoring reactions. It is concluded that microwaves as the source of energy offer advantages over thermal cure but that a fundamental study of cure in the microwave field is necessary to fully assess their effect on the physical/mechanical properties of cured polymers.
Multi‐Nuclear NMR spectroscopic and proton NMR imaging studies on the effect of water on the silane coupling agent/matrix resin interface in glass fiber‐reinforced composites
Authors: Hoh Ka‐Pi , Ishida Hatsuo , Koenig Jack L.
Published: May 2005

Multi‐nuclear NMR spectroscopy and proton NMR imaging are used to investigate the absorption of water as well as the effect of water on the relaxation of the silane coupling agent/epoxy resin interface. For samples in which leaching occurred, proton NMR imaging is used to complement weight measurements by showing the amount and location of the water in the sample.13C and29Si solidstate NMR spectroscopy show that the water can interact with the silane coupling agent and affect the relaxation of the sample. Water can leach out the low molecular weight oligomers and/or further hydrolyze the silane coupling agent.
Effects of environmental exposure on fiber/epoxy interfacial shear strength
Authors: Gaur Umesh , Miller Bernard
Published: May 2005

The TRI microbond technique for direct determination of fiber/resin interfacial shear strength in composites has been used for investigation the influence of environmental conditions on adhesive bonding in certain systems. The small dimensions involved in the method facilitate uniform exposure and short exposure times. We have observed significant changes in both average shear strength and in shear strength distributions on exposing aramid/epoxy and glass/epoxy microbond assemblies to steam or hot water. Shear strength dropped to a plateau value in both cases, the reduction being more drastic with the glass fiber. Vacuum drying restored shear strength completely in aramid/epoxy microassemblies, even when the surface of the aramid fiber had been chemically modified, but there was only partial regeneration of bond strength with the glass/epoxy system.
Solvent stress cracking and failure mechanisms in polyetherimide composites
Authors: Hsieh Alex J. , Schneider Nathaniel S. , Mandell John F.
Published: May 2005

Solvent stress cracking studies have been carried out in o‐xylene and other solvents on polyetherimide (PEI) based materials including neat resin, woven fabric composites, and adhesively bonded systems. The results show crack growth in solvents at very lowGIlevels as compared with tests in air. The composite and adhesively bonded systems have sufficiently high residual thermal stresses to drive an array of intersecting matrix/adhesive cracks even without mechanical loading. The matrix/adhesive residual stress driven crack patterns in these systems are shown to retard main delamination crack growth relative to that in the neat resin, and to raise the applied thresholdG1level for main crack growth by about a factor of ten, as predicted by an approximate model.
Interfacial phenomena in cellulose/polyethylene composites
Authors: Bataille P. , Allard P. , Cousin P. , Sapieha S.
Published: May 2005

A systematic study of the mechanical properties of linear low density polyethylene (LLDPE) and high density polyethylene (HDPE) filled with cellulose was conducted. When benzoyl peroxide (BPO) was used and when the components were mixed at 160°, the yield strength of the LLDPE/cellulose composite increased by 70% whereas that of HDPE increased by only 15%. If BPO is replaced by dicumyl peroxide (DCP) the yield strength attains a plateau value at a lower concetration. Yield strength for the cellulose/LLDPE system, where the cellulose had been pretreated with silane, showed a relatively small improvement as compared to the effect of the peroxides addition. The presence of gel in the compound is also discussed.
A model for composite laminate bend‐forming under arbitrary curvature distribution and extensive interlaminar sliding
Authors: Talbott Margaret F. , Miller Alan K.
Published: May 2005

While thermoplastic matrix composites are of increasing interest for a variety of applications, methods of forming these materials are still under development. One way of hastening their development and utilization is to develop models which predict the material response to processing. One such model is under development and will predict the response of a consolidated laminate which is being formed to a singly‐curved shape. The model accounts for the unique features of thermoplastic composites, namely the continuous inextensible fibers and the need for extensive relative ply sliding. At this stage in model development, it treats a laminate as a series of alternating layers of elastically hard and elastically soft material. The hard layers can slide over each other because of the soft shearable layers between them. In its present stage, the model predicts, for any arbitrarily complex singly‐curved shape, the extent of relative ply sliding, the stresses generated, and the array of point forces that are required to produce the specified shape. The behavior of a beam with extensive ply sliding is very different from that described by classical beam theory. First, the ply normal stresses depend not only on the local curvature and distance from the neutral axis, but also on the position along the laminate. Second, the relative ply sliding and the bending stresses occur not only in bent sections of the laminate, but also in nearby straight sections. Thus, the response of a given element of material depends not only on local conditions, but also on the curvature distribution throughout the laminate.
Solidification in anisotropic thermoplastic composites
Authors: Gilmore Scott D. , Güçeri Selçuk İ.
Published: May 2005

Heat transfer analysis in thermoplastic composites manufacturing offers several challenges. The melting/solidification process results in the appearance of a molving solid‐fluid interface or two‐phase zone. The presence of reinforcing fibers with thermal conductivities substantially different than those of matrix meterials causes the composite material to behave anisotropically. Furthermore, an analysis should be adaptable to complex geometries if it is to be useful for practical applications. In this paper, a numerical approach is presented to develop an analysis tool for the processing of thermoplastic‐matrix composites. A numerical grid generation technique is employed to determine the temperature distribution within the part while accounting for the heat absorption and liberation during the solidification stage. The influence of anisotropy in the domain is accounted for by considering thermal conductivity as a second‐order tensor which varies continuously throughout the domain. Sample part configurations are used to demonstrate the applicability of this technique to thermoplastic composites processing.
Design of particulate composites for optical applications
Authors: Dunlap P. N. , Howe S. E.
Published: May 2005

This paper reviews the basic theoretical approach to describing light scattering in filled materials with nearly matching refractive indices (Rayleigh‐Gans‐Debye Theory). The modifications necessary to handle high filler concentrations (interparticle interference and multiple scattering) are included empirically. The primary result of this analysis is an expression for the optical transmission of a polymer composite as a function of particle size, volume fraction, composite thickness, and refractive index difference between the components. The angular dependence of the scattering is included so that scattered light which falls within the aperture of the transmission detector can be accounted for, Particular attention is given to including the temperature dependence of the refractive index and the effect of fillers on the thermal expansion properties of the polymer matrix in order to predict the temperature range over which the composite will be optically useful. Similarity to analyses of the Christiansen filter is discussed.
Modified fibers for polymer composites with improved mechanical properties
Authors: Wang Q. , Ait‐Kadi A. , Kaliaguine S.
Published: May 2005

In this paper, a new composite material, AEG, which was developed in our laboratory by catalytic grafting polymerization of ethylene on asbestos fibers, was used to improve the properties of asbestos/HDPE composites. Tensile testing shows that the AEG modified asbestos/HDPE composites exhibit significantly higher tensile strength and elongation at break than the unmodified ones. Instrumented impact testing permits a detailed understanding of the modifying effect of AEG on impact properties. The records acquired during impact for the unmodified composites were truncated at the onset of initial fracture, showing a typical brittle cleavage fracture. In contrast, the records for the AEG modified composites showed an effective post‐initial fracture behavior. The load at peak, the energy required to initiate and propagate the fracture, and the deformation during impact increase dramatically for the AEG modified composites. SEM micrographs of the fractured surfaces also demonstrate the difference in the morphology of the two composites.
The properties of wet‐formed thermoplastic sheet composites
Authors: Bigg D. M. , Hiscock D. F. , Preston J. R. , Bradbury E. J.
Published: May 2005

Glass fiber reinforced thermoplastic matrix sheet composites of polypropylene and poly(ethylene terephalate) were produced in a two‐stage pilot scale impregnation and consolidation process. The first stage consisted of preparing wet‐formed mats of long, discontinuous fibers and polymer powder on an inclined wire paper‐making machine. The second stage consisted of consolidating approximately 15 wet‐formed mats into a solid composite laminate by the application of heat and pressure in a compression press. The resulting composites had a nominal glass content of 26 wt% (∼12 vol %). Flexural strengths as high as 108 MPa for polyproplene composites and 132 MPa for poly(ethylene terephthalate) composites were measured on specimens cut from stamped parts. The flexural modulus of the polypropylene compsites reached 5.4 Gpa, while the modulus of the stiffest poly(ethylene terephthalate) composite was 8.1 Gpa. The impact properties of the composites were equally good. Polyproplene compsites absorbed up to 62 J/cm during an instrumented falling dart impact test, while poly(ethylene terephthalate) composites absorbed as much as 32 J/cm during the same test.
Mold filling and curing analysis in liquid composite molding
Authors: Lin R. J. , Lee L. James , Liou Ming J.
Published: May 2005

Non‐isothermal mold filing and curing experiments of liquid composite molding were carried out in this work. To compare the experimental results with a previously developed numerical simulation model, measurements of volumetric heat transfer coefficient between the resin and the fiber, and characterization of resin kinetics and rheological changes were also conducted. Combined with the previously measured fiber perform permeability, the numerical model provided a good prediction of temperature profiles during molding for a polyurethane/glass fiber composite.