bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of ambient aging of 5245C/graphite prepreg on composition and mechanical properties of fabricated composites
Authors: Scola Daniel A. , Vontell John , Felsen Marvin
Published: May 2005

A bismaleimide modified epoxy 5245C/graphite prepreg was subjected to ambient conditions for periods up to 140 days. The effect of this ambient aging on the prepreg composition and mechanical properties of composites fabricated from aged prepreg was investigated. The results show that small but definite composition changes occur as a result of ambient aging. These compositional changes are also reflected in small decreases in shear and flexural properties at room and elevated temperatures, dry and wet.
Slow crack propagation in a heavily‐filled particle reinforced epoxide resin
Authors: Montes‐g G. M. , Draughn R. A. , Simpson T. H.
Published: May 2005

The fracture properties of two proprietary composite dental restorative materials and a model composite system were studied to determine the effects of filler concentration, exposure to water, and particle/polymer adhesion on subcritical crack propagation. Particle content ranged from 36 to 60 volume percent. The double torsion (DT) test was used to measure relationships between the stress intensity factor (K1) and the speed of decelerating cracks or the rate of loading in dry and wet materials in air at laboratory conditions. Materials with weak particle/polymer interfaces fractured by continuous crack growth in both dry and wet conditions. In dry and wet materials with strong interfaces, continuous cracking also occurred at the low end of the range of speeds observed (10−7 to 10−3 m/s), but under test conditions of high crack speeds unstable (stick‐slip) crack propagation was found in dry specimens and in wet model composites with 41 percent vol, filler. Water had a corrosive effect lowering K1c for continuous crack propagation. The exponential dependence of K1c on crack velocity, representing the viscoelastic response of the materials, was positively correlated to the filler concentration and the plasticizing effect of water. Observations on fracture surfaces indicate that low velocity cracks (<10−5 m/s) propagate through regions of high stress concentrations (interfaces, corners, pores) while at higher crack velocities failure occurs by a combination of interparticle and transparticle fracture.
The effect of the interface/interphase on fiber composite properties
Authors: Piggott M. R.
Published: May 2005

The interfacial region between fibers and matrix in fiber composites governs the transfer of forces between the relatively weak and compliant matrix and the reinforcing fibers. An effective interphase can ensure that the mechanical properties of the composite reflect the high strength and modulus of the fibers. Although composites can be made with the expected strengths and moduli, it is not entirely clear why this is achieved: Tests with critical composites, i.e., those containing very short aligned fibers, do not show the expected stress‐strain behavior. This paper examines the effect of an interphase having a shear modulus that is less than that of the matrix. It is found that to explain the Young's moduli of the short fiber composites, the interphase must have a very low modulus indeed; i.e., a few kPa at most. In addition, the strength results can be accounted for only if we assume that the short lengths of fiber used in the experiments had higher strengths than anticipated. Although agreement between experiments and theory is thus not very good, the small amount of experimental evidence available indicates a need for further systematic experiments on critical (i.e. short aligned fiber) composites before firm conclusions are drawn.
Dynamic mechanical analysis studies of the interphase
Authors: Chua Ping Seng
Published: May 2005

The dynamic mechanical properties of unidirectional glass‐fiber‐reinforced polyester measured along the fiber direction were recently investigated. In the same polyester, the type of organosilane coated on the glass fiber, the amount of organosilane, the fiber volume fraction, and the fiber diameter affect the value of the loss tangent, tan δ, at the glass‐transition temperature of the glass‐fiber‐reinforced polyester. The interfacial shear strength and the tan δ at the glass‐transition temperature of the glass‐fiber‐reinforced polyester show good correlation suggesting that the latter can be used to characterize the quality of the interphase. Factors affecting the glass‐transition temperature and the application of Zorowski and Murayama's equation in the characterization of the interfacial adhesion are also discussed.
Parameters determining the strength and toughness of particulate‐filled epoxy resins
Authors: Roulin‐Moloney A. C. , Cantwell W. J. , Kausch H. H.
Published: May 2005

The effects of such parameters as the filler volume fraction, particle size, aspect ratio, modulus and strength of filler, resin‐filler adhesion, and toughness of the matrix on the stiffness, strength, and toughness of particulate‐filled epoxy resins were evaluated. The mechanisms of crack initiation and subsequent crack propagation in these multiphase materials are discussed and illustrated by scanning electron microscopy of fracture surfaces.
Optothermal analysis of polymer composites
Authors: Krapez J. C. , Cielo P. , Maldague X. , Utracki L. A.
Published: May 2005

A number of thermographic techniques under optical‐radiation heating are described for the nondestructive evaluation of different kinds of fiber‐filled polymer‐based composites. Shallow delaminations within carbon‐fiber reinforced laminates can be detected by this method under wide‐area surface heating to 5 or 10° above ambient. A number of image‐processing algorithms are described for improving the visibility of subsurface defects. Spot‐heating techniques are presented for the characterization of fiber concentration, distribution, and orientation in carbon or steel fiber‐filled composites. Particular emphasis is given to the possibility of mapping fiber‐orientation properties at gradually deeper layers below the surface. These optothermal techniques appear to be a convenient tool for the inspection of opaque composites in terms of rapidity, lack of sample preparation requirement, and simplicity both in its implementation and in the interpretation of results.
Characterizing high performance composite processability with dynamic fiber wettability measurements
Authors: Lee Walter J. , Seferis James C. , Berg John C.
Published: May 2005

Dynamic fiber wettability measurements are performed on T‐300 carbon and Teflon fibers immersed in hexa methyl disiloxane (HMDS) silicone oil and a difunctional liquid epoxy resin, neopentyl diglycidyl ether (NPDGE). Specifically, four types of these carbon fibers, which are used to reinforce high performance composites, are studied. Decreases in the wetting force are observed for progressive immersions of all carbon fibers in the silicone oil but not observed with Teflon fibers, indicating adsorption may be occurring on the carbon surface. Perimeters determined from these wetting measurements on carbon fibers are larger than those calculated, assuming the fibers to be smooth cylinders. Scanning electron micrographs suggest this difference is attributable to surface crenulations. All carbon fibers immersed in the epoxy resin show non‐zero contact angles.
The influence of the interphase on composite properties: Poly(ethylene‐co‐acrylic acid) and poly(methyl vinyl ether‐co‐maleic anhydride) electrodeposited on graphite fibers
Authors: Crasto A. S. , Own S. H. , Subramanian R. V.
Published: May 2005

The electrodeposition of saturated copolymers onto carbon fibers is investigated, focusing particular attention on improvement of shear and impact properties of the corresponding composites. Carbon fibers are electrocoated with poly(ethylene‐co‐acrylic acid) and poly(methyl vinyl ether‐co‐maleic anhydride) from aqueous media, and fabricated into epoxy composites. The results of interlaminar shear strength (ILSS) tests, initially employed to assess fibermatrix adhesion, are vitiated by the occurrence of mixed‐mode failure. Interfacial shear strength (IFSS) is hence evaluated by stressing single‐fiber composite specimens to obtain ultimate aspect ratios of the fiber fragments. The data are combined with fiber strengths by a recently developed statistical theory (1) to yield a distribution for IFSS. Both copolymer interphases improve fiber‐matrix bonding to an extent greater even than that obtained with commercial fiber surface treatment. Good fiber‐matrix adhesion is further apparent from SEM studies of fractured ILSS test specimens. A key to this improved adhesion is the interpenetration of matrix resin and interphase polymer, revealed by electron microprobe analysis (2). Notched Izod impact strength is also increased over uncoated‐fiber composites. These copolymer interphases behave as deformable interlayers, absorbing impact energy and blunting the growing crack tip. Further energy is absorbed in deflecting the crack through a more tortuous path. Simultaneous improvements in impact and shear strengths are thus obtained, which may be further enhanced by optimizing the electrodeposition parameters and the coating thickness. The influence of the interphase on composite properties is better understood from this study, paving the way for refinement in interphase design.
Review of manufacturing of fiber composite components by filament winding
Authors: Munro M.
Published: May 2005

A summary of the simple to very complex fiber composite components that have been fabricated by automated filament winding is presented. The process of filament winding, where resin‐impregnated, high strength, high modulus fibers are placed on a rotating mandrel (under controlled tension) in a specified geometric pattern, is then described in detail. A qualitative comparison of the filament winding of fiber composite components by conventional and robotic winding systems is presented next. The results indicate that a robotic winding system can be a viable alternative to conventional filament winding for certain applications. Finally, the concepts of lightweight winding systems, hybrid filament winding processes, and advanced filament winding techniques are presented.
Short fiber reinforced thermoplastics. I. Rheological properties of glass fiber reinforced Noryl
Authors: Vaxman A. , Narkis M. , Siegmann A. , Kenig S.
Published: May 2005

An experimental study on the flow behavior of glass fiber reinforced Noryl (a commercial poly(phenyleneoxide)/polystyrene blend) using a capillary rheometer is described. The effect of fiber concentration on shear viscosity and die swell was studied at various temperatures. Breakage of glass fibers during flow through the rheometer is discussed; it was found that the average fiber length (about 230 μm) was not significiantly altered, except at the highest shear rate (575 s−1) studied. The incorporation of short fibers into thermoplastic polymer melts increases their viscosity without changing the basic rheological character‐shear rate dependency. No discernible viscosity changes were measured by incorporating 10 weight percent fibers, and upon further increase of fiber concentration from 20 to 30 weight percent no appreciable increase in viscosity was noted. It is shown that short glass fibers cause a large reduction in extrudate swell. The presence of voids and fiber orientation contribute to the decrease of the die swell, an effect greater than expected from volumetric considerations alone.
Void formation in short‐fiber thermoplastic composites
Authors: Vaxman A. , Narkis M. , Siegmann A. , Kenig S.
Published: May 2005

Voids, or bubbles, are formed in short‐fiber thermoplastic composites because of entrapment of air in the compounding and melt flow processing steps and as a result of uneven shrinkage due to temperature gradients involved in the solidification step by cooling. The experimental results suggest that bubble nucleation takes place at fiber ends and their volume content depends on processing conditions. The shape and distribution of the voids were studied by optical examination of longitudinal sections of extrudates, using standard metallographic polishing technique and reflected light microscopy. The void volume fraction of extrudates was found to increase with increasing extrusion rate, temperature, fiber concentration, and fiber length, and with a decreasing draw ratio. The void content in fiber‐glass‐reinforced injection moldings is low, ≈︁1% by volume; however, by heating these moldings, the contained pressurized bubbles expand and significant void volume fractions are observed.
A method of forming composite structures using in situ‐formed liquid crystal polymer fibers in a thermoplastic matrix
Authors: Bassett B. R. , Yee A. F.
Published: May 2005

A new high speed and potentially economical method of creating a composite material and structures therefrom is tested. The method consists of spinning composite fibers from a melt blend of a thermoplastic with a liquid crystal polymer (LCP). Discontinuous fibrils of the LCP are formed in situ during the spinning process. These composite fibers are aligned and placed in a mold and heated to melt the thermoplastic matrix, but not the fibrils. A finished composite structure reinforced by the LCP fibrils is obtained when the thermoplastic phase is consequently consolidated. Our experiments show the proposed process is reasonable for an easily processed polystyrene matrix. High modulus fibrils with essentially infinite L/D ratios are readily produced in the extrusion process using 40 wt% of a wholly aromatic poly(ester‐co‐amide) LCP from Celanese. The integrity and alignment of the LCP fibrils is retained in the molding step. Mechanical tests show that the fibers produced by high shear rate processing have a stiffness approaching 23 GPa and match an axial rule‐of‐mixtures theory. The use of polystyrene resulted in brittleness. Molded composite plates exhibit slightly lower stiffness and significantly lower strength than individual fibers.
Modeling fracture of resin matrix composites
Authors: Herakovich Carl T.
Published: May 2005

Characteristics of the fracture of resin matrix fibrous composites are discussed with emphasis on the physical parameters influencing fracture and the requirements of a suitable model for predicting crack growth. The influences of notch geometry, fiber orientation, specimen geometry, and far field loading on crack growth in unidirectional resin matrix composites are discussed. The normal stress ratio theory is reviewed and its applicability for crack initiation in unidirectional resin matrix composites is considered. Experimental results from a variety of tests on resin matrix composites are reviewed and compared with theoretical predictions. It is shown that the normal stress ratio theory correctly predicts the initiation site and direction of crack growth from an existing notch. Predictions of critical stress are less consistent being quite accurate in some cases, but less accurate in others.
Random glass mat reinforced thermoplastic composites. Part IV: Characterization of the tensile strength
Authors: Stokes Vijay K.
Published: May 2005

Random glass mat thermoplastic composites, which can be thermostamped to form complex deep‐drawn parts with ribs and bosses, are excellent materials for making low‐cost stiff parts with relatively high impact strength. However, the mechanical properties of these materials, as determined by standard tensile tests, are known to exhibit large scatter. And the tensile modulus in these materials can vary by a factor of two over a 12.7‐mm distance. In an earlier effort, measurements of the local tensile moduli of long, thin, 12.7‐mm‐wide strips along both thin edges (left and right) of the specimen and across the face were used to show that the local tensile modulus is well approximated by the arithmetic mean of the local left‐ and right‐edge tensile moduli. To establish the tensile strength of these materials, the local tensile moduli of long dog‐bone specimens are first characterized along the length, after which the specimens are pulled to failure. The tensile strength is shown to correlate well with the arithmetic mean of the local left‐ and right‐edge tensile moduli.
Analysis of resin injection molding in molds with preplaced fiber mats. I: Permeability and compressibility measurements
Authors: Trevino L. , Rupel K. , Young W. B. , Liou Ming J. , Lee L. James
Published: May 2005

This work presents the characterization of fibrous reinforcement mats in resin injection molding. The fiber mat characterization involved determining the mat permeability and compressibility. Mold filling experiments were conducted using two or more different fiber types in the mat stack, which created transverse porosity, permeability, and compressibility variations. The effect of these variations was studied by taking flow pressure measurements and observing the progress of the flow front of a non‐reactive fluid filling a clear acrylic mold that contained the reinforcement mat stack.
Effect of physical aging on the toughness of carbon fiber‐reinforced poly(ether ether ketone) and poly(phenylene sulfide) composites. I
Authors: Ma Chen‐Chi M. , Lee Chang‐Lun , Chang Min‐Jong , Tai Nyan‐Hwa
Published: May 2005

The effect of physical aging on the penetration impact toughness and Mode I interlaminar fracture toughness of continuous carbon fiber (C.F.) reinforced poly(ether ether ketone) (PEEK) and poly(phenylene sulfide) (PPS) composites has been investigated by using an instrumented falling weight impact (IFWI) technique and a double cantilever beam (DCB) test. Composite materials studied are aged below their glass transition temperature (Tg) at various periods. Initiation force and energy of damage, failure propagation energy, impact energy and ductility index (D.I.) are reported. The Mode I critical value of strain energy release rate (GIC) of the unidirectional carbon fiber‐reinforced PEEK (APC‐2) composites is obtained. Results show that aging has a significant effect on the toughness of both composite materials. Energy absorbed during impact decreases with the increase of aging temperature and period. The PEEK/C.F. composites exhibit a higher retention of impact toughness than that of the PPS/C.F. composites after aging; however, the PPS/C.F. composites show a much higher ductility index. The Mode I fracture mechanism of the APC‐2 composite is a combination of stable and unstable failure and shows a “stick‐slip” behavior. Owing to the formation of a relative rigid structure, the fracture toughness (GIC) of APC‐2 decreased with the increase of aging temperature and period.
Hygrothermal behavior of carbon fiber‐reinforced poly(ether ether ketone) and poly(phenylene sulfide) composites. I
Authors: Ma Chen‐Chi M. , Lee Chang‐Lun , Chang Min‐Jong , Tai Nyan‐Hwa
Published: May 2005

The hygrothermal behavior of carbon fiber‐reinforced poly(ether ether ketone) (PEEK) and poly(phenylene sulfide) (PPS) composites subjected to moisture and temperature is investigated in this study. The properties of both composites exposed to temperature/humidity and immersed in water for extended periods are studied. Properties studied include moisture sorption, crystallinity, dynamic mechanical response, tensile strength, and flexural strength. Both the PEEK/C.F. and the PPS/C.F. composites exhibit good moisture/temperature resistance and property retention after hygrothermal exposure. The diffusivities and the equilibrium moisture absorption are measured at 60, 70, 80°C with 85% R.H. (relative humidity). A Fickian type diffusion is observed at all exposures. Crystallinity increase of the composites is found for the PPS/C.F. composites exposed to 80°C with 85% R.H. environment and is correlated with the damping properties in the dynamic mechanical study. However, the hygrothermal effect on the crystallinity and the glass transition temperature of the PEEK/C.F. composites is negligible. Mechanical properties of the PEEK/C.F. composites decrease slightly with the increase of temperature/moisture and exposure period. Mechanical property reductions of the PPS/C.F. composites decrease with the increase in exposure temperature when subjected to a similar environment; this is due to the relatively complete molecular relaxation and additional crystallization at higher temperatures.
Bioabsorbable composites. II: Nontoxic, L‐lysine‐based poly(ester‐urethane) matrix composites
Authors: Storey Robson F. , Wiggins Jeffrey S. , Mauritz Kenneth A. , Puckett Aaron D.
Published: May 2005

Bioabsorbable composites were fabricated from poly(D, L‐lactide‐urethane) matrix reinforced with poly(glycolic acid) (DEXON) surgical mesh. The crosslinked polyurethane matrix was formed from the reaction of ethy1–2, 6‐diisocyanatohexanoate and poly (D, L‐lactide) triol, initiated from glycerol; the ultimate degradation products of this matrix, L‐lysine, lactic acid, glycerol, and CO2, are all nontoxic, naturally occurring metabolites. The composites were fabricated by two processing methods, with the final composite structures displaying very different physical properties. Composites fabricated by vacuum bag molding displayed tensile strength and modulus of 66 MPa and 468 MPa, respectively, with total elongation of 39%. Composites fabricated by the same method, but whose final cure included 24 h at 5000 psi, displayed tensile strength and modulus of 86 MPa and 3.4 Gpa, respectively, with total elongation of 18%, suggesting a more fully developed matrix/fiber interphase and a reduction in microvoids, which lead to lower force failures. As poly(D, L‐lactide) prepolymer molecular weights decreased, tensile strengths and glass transition temperatures of the polyurethane networks increased. These trends were attributed to increased hydrogen bonding with an increased crosslink density. The composites were sensitive to cyclic loading, regardless of the processing technique, suggesting an inefficient transfer of energy from the matrix into the load‐bearing fibers. This weakness was confirmed by SEM microscopy, which revelaed a gap at the fiber/matridx interface of an unfatigued composite sample, poly(D, L‐lactide‐urethane) matrix composites were found to be unique since they can be custom shaped when heated above the glass transition of the matrix. DSC revelaed the glass transitions for the matrices of around 60°C. The composites were easily shaped above this temperature, yet remained rigid at biological temperature.
A modeling approach to thermoplastic pultrusion. I: Formulation of models
Authors: Åström B. Tomas , Pipes R. Byron
Published: May 2005

A fundamental understanding of the effects of processing parameters and die geometry in a pultrusion process requires a mathematical model in order to minimize the number of necessary experiments. Previous investigators have suggested a variety of models for thermoset pultrusion, while comparatively little effort has been spent modeling its less well understood thermoplastic counterpart. Herein, models to describe temperature and pressure distributions within a thermoplastic composite as it travels through the pultrusion line are presented. The temperature model considers heat transfer in an infinite slab with either prescribed boundary temperature, or prescribed heat flux from the surfaces. The pressure model is based upon matrix flow relative to the fibers and incorporates a non‐Newtonian matrix viscous, compaction, and friction resistance, is also presented. The models are evaluated studying and ideal pultrusion process for manufacturing of unidirectional carbon‐fiber‐reinforced polyether ehterketone composites.
The effects of thermal history on the structure/property relationship in polyphenylenesulfide/carbon fiber composites
Authors: Deporter Joellen , Baird Donald G.
Published: May 2005

The purpose of this investigation was to examine the effects of thermal history during cooling from the melt on the degree of crystallinity, morphology, and mechanical properties of polyphenylenesulfide (PPS)/carbon fiber composites. Three thermal treatments were employed in this tudy: isothermal crystallization from the melt at 140, 160, 180, 200, and 22O°C; quenching from 315°C and then annealing at 160 and 200°C; and nonisothermal crystallization from the melt at rates varying from 0.4°C/min to 38°C/s. The effect of varying the thermal history of the sample on the degree of crystallinity developed in the matrix polymer was determined using differential scanning calorimetry (DSC). The effect of thermal history on and the resulting matrix morphology was examined by scanning electron microscopy (SEM). The subsequent effects of the degree of crystallinity and the morphology on the mechanical behavior of the samples were monitored by transverse tensile tests and flexural tests. In all cases, the transverse tensile and flexural moduli increased as the amount of crystallinity in the samples increased. However, samples with greater amounts of crystallinity did not always yield higher transverse tensile or flexural strengths. Upon examination of the composite samples by electron miscroscopy, it was observed that large increases in the values of the transverse tensile and flexural strengths could be correlated with structural changes in the matrix.
Mechanical properties of in situ composites based on partially miscible blends of polyetherimide and liquid crystalline polymers
Authors: Baird D. G. , Bafna S. S. , De Souza J. P. , Sun T.
Published: May 2005

Results related to the mechanical properties of in situ composites based on partially miscible blends of polyetherimide (Ultem) and liquid crystalline polymers (HX1000 and HX4000) are discussed. It is observed that, at least in terms of the tensile and flexural modulus, there is a positive deviation from the law of mixtures. These results are analyzed and an attempt is made to explain the origin of this synergistic behavior based upon morphological data. The behavior of these partially miscible systems is compared to that of an immiscible system (Ultem/Vectra) and also that of glass‐reinforced Ultem. Using blends subjected to two passes through a single screw extruder, and thereby increasing the mixing history of the Ultem/HX4000 blend, led to improved dispersion but did not lead to any measurable improvement, within experimental error, in the tensile modulus or ultimate strength (though the toughness was enhanced). The dynamic creep compliance was measured and the creep behavior with composition and temperature is discussed. The data seem to suggest that a number of factors (including partial miscibility, the properties of the specific LCP chosen as the reinforcement and the final blend morphology) all interact in a complex and as yet undetermined manner to produce the enhanced mechanical properties.
Thermo‐stimulated creep study of the α retardation mode in epoxy‐glass beads composites
Authors: Dufresne A. , Lacabanne C.
Published: May 2005

Thermo‐stimulated creep (TSCr) analysis was performed to characterize the anelastic properties around the glass transition of the model system: expoxy resin‐glass beads. Different interphase regions have been deliberately formed by means of a silane coupling agent and an elastomeric adduct coating. In all samples the primary retardation mode, labeled α, has been found around 140°C. this retardation mode has been associated with the anelastic manifestation of the mode in filled epoxy has been used to estimate the interphase thickness. By applying “fractional stresses” the complex α peak has been experimentally resolved and local changes of morphology in the interphase zone are evidenced in terms of mobility and kinetic of motion. This last technique has also allowed us to compare the length of the mobile units liberated at the glass transition as a function of the filler‐matrix interphase.
Tow impregnation during resin transfer molding of bi‐directional nonwoven fabrics
Authors: Chan Albert W. , Morgan Roger J.
Published: May 2005

A model has been developed for analyzing resin impregnation of fiber tows during resin transfer molding of bi‐directional nonwoven fiber performs. The model is based on the existence of two main regions of resin flow: the macropore space formed among fiber tows and the micropore space formed among individual fiber filaments within a tow. The large difference in permeability between these two regions of flow leads to the potential for void formation during resin transfer molding. The model was formulated for both constant flow rate and constant pressure mold filling. For ambient pressure mold filling, the model predicts a difference in the size of the voids and distribution between axial tows (oriented along the flow direction) and transverse tows (oriented in the transverse direction). When vacuum is imposed on the mold, the model predicts the same resin impregnation behavior for both axial and transverse tows. Furthermore, given sufficient time, voids generated under vacuum mold filling will eventually collapse because of the absence of an opposing internal void pressure. In addition to insights on void formation, the model also provides a basis for the study of the relationship between resin transfer molding parameters and the resin impregnation process.
Numerical simulation of non‐isothermal SMC (sheet molding compound) molding
Authors: Twu J.‐T. , Hill R. R. , Wang T. J. , Lee L. James
Published: May 2005

Design of molding tools and molding cycles for sheet molding compounds (SMC) is often expensive and time consuming. Computer simulation of the compression molding process is a desirable approach for reducing actual experimental runs. The focus of this work is to develop a computer model that can simulate the most important features of SMC compression molding, including material flow, heat transfer, and curing. A control volume/finite element approach was used to obtain the pressure and velocity fields and to compute the flow progression during compression mold filling. The energy equation and a kinetic model were solved simultaneously for the temperature and conversion profiles differential scanning calorimetry (DSC) was used to experimentally measure the polymer zation kinetics. A rheometrics dynamic analyzer (RDA) was used to measure the rheological changes of the compound. A series of molding experiments was conducted to record the flow front location and material temperature. The results were compared to simulated flow front and temperature profiles.
Quantitative image processing analysis of composite materials
Authors: Yang Heechun , Colton Jonathan S.
Published: May 2005

Quantitative digital image processing has been used to analyze unidirectional thermoplastic composites. The fiber volume fraction is determined by the template matching method and compared with the conventional thresholding method. A combination of skeleton and edge cutting is used to obtain the centers of the fibred in the image. The Voronoi distances are calculated from the result. The Hough transform is applied to the fiber orientation in conjunction with thresholding by the line length in the image. To describe the fiber orientation, characteristic function are defined in the width and thickness directions, which allow a much more accurate and effective description of the fiber distribution and orientation than other methods. Advantages of the template method are that similar results to the threshold method can be obtained as thresholding with a lower magnifications, resulting in an improved statistical sample with a reduced number of photomicro‐graphs.
A T1 lattice relaxation study of the molecular motions of a semicrystalline polyimide matrix
Authors: Russell Vernon M. , Koenig Jack L.
Published: May 2005

The molecualr dynamics of a semicrystalline polyimide were studied by 13C nuclear magnetic resonance (NMR) spectroscopy. The T1 spin lattice relaxation times were observed over a temperature range of 24°C to 94°C.
Performing analysis of thermoformable glass fiber mats—deformation modes and reinforcement characterization
Authors: Fong Lihwa , Xu Jingyi , James Lee L.
Published: May 2005

This work is and anyalysis of the performing process of a thermoformable glass fiber mat. Important processing variables associated with the preforming operations were extracted from stamping experiments. From the study of deformation modes, we may conclude that the defects found in fiber mat preforming are closely related to these deformation modes. Stretching causes finer thinning and re‐orientation. Bending results in mat springback and thickness reduction, while in‐plane compression induces wrinkles through buckling. Each defect may be reduced by specific adjustments. These adjustments, however, tend to interact with each other, and make the preforming control a challenging task.
X‐ray diffraction analysis technique for determining the polymer crystallinity in a polyphenylene sulfide composite
Authors: Lee T. H. , Boey F. Y. C. , Khor K. A.
Published: May 2005

The degree of crystallinity in polymers is commonly known to significantly affect their mechanical properties. To that extent, it also affects the mechanical properties—such as compression, buckling, and creep—of thermoplastic composites that are matrix dominant. For this reason, it is important that the degree of crystallinity in a thermoplastic composite be precisely determined, which is the focus of this paper. In particular, the crystallinity for a thermoplastic poly(phenylene sulfide) composite reinforced with glass fibers is determined using an X‐ray diffraction technique (XRD). While conventional methods have been adopted for homogeneous phases, a modified method has been adopted to account for the heterogeneous nature of the composite. The results have also been compared with results obtained using DSC and DMA techniques, indicating that the XRD method yielded lower values, which are considered to be more accurate. This was attributed to the absence of a recrystallization effect in the XRD method, which was unavoidable in the other two methods.
Assessment of the dispersibility of surfactant‐treated titanium dioxide powders for compounding with polyethylene
Authors: Arellano Martin , Manas‐Zloczower Ica , Feke Donald L.
Published: May 2005

A strategy involving the use of anionic surfactants to compatibilize titanium dioxide powders with nonpolar polymers has been applied to facilitate the dispersion of these powders into polymer composites. The methodology first involves the adsorption of surfactant onto the powder within aqueous dispersions. Surfactantcoated powders are then removed from the dispersion and dried. The cohesivity and some surface properties of the surfactant‐coated powders were measured and compared to that of the uncoated powders. Dispersion experiments of titania agglomerates in polyethylene were performed in a rotating cone‐and‐plate device set within a temperature controlled oven. The titania agglomerates dispersed by an erosion mechanism in which small fragments detached from the surface of the parent agglomerate. The erosion rate was higher for the surfactant treated powders in comparison to uncoated powders. The links between the enhanced erosion rates and the surfactant coating were investigated in terms of the cohesivity of the powders, the penetration of the polymer into the agglomerates, and the interactions between the powders and the polymer media that govern wetting and the transmission of hydrodynamic stress.
Swelling behavior in extrusion
Authors: Miller John C.
Published: May 2005

The diameter increase of a molten thermoplastic extrudate is discussed in terms of the viscoelasticity of the resin. A swelling index, the ratio of the extrudate diameter to the orifice diameter, is defined. It was observed that swelling data taken at different temperatures can be correlated with stress in the die. An unexpected influence on the swelling for polyethylenes is the length of the die where short dies show larger swelling than long dies. Some suggestions for reducing swelling tendencies are made based on a simple model for flow in a capillary.
Short‐ and long‐term strength characteristics of particulate‐filled cast epoxy resin
Authors: Hojo Hidemitsu , Toyoshima Wataru , Tamura Masayasu , Kawamura Noriyuki
Published: May 2005

Particulate‐filled thermosetting composites are widely used, yet little systematic work has been done on their long‐term strength characteristics. In this study short‐term tensile, flexural, and impact tests as well as tensile creep‐rupture tests were made for unfilled and filled epoxy to clarify the effects of filler size, filler content, and temperature. Fillers used were silica, alumina particles, and glass beads. Test temperatures were varied from 25 to 110°C. As a result of short‐term testing, it was found that the Petch relation held between strength and filler size if brittle fracture occurred, while a strength and filler size if brittle fracture occurred, while a strengthening effect existed when ductile fracture occurred. On creeprupture testing, a strengthening is observed with filler size and content for silica and glass beads. The Arrhenius plot of rupture time for various filler sizes and contents converges to a characteristic point corresponding to the glass transition temperature of the material. Using this relation, a modified Larson‐Miller master rupture curve is proposed which can predict the long‐term strength of particulate‐filled thermosetting composites as functions of rupture time, temperature, filler size, and content.
Thermal, mechanical, and rheological behavior of blends of ultrahigh and normal‐molecular‐weight linear polyethylenes
Authors: Bhateja S. K. , Andrews E. H.
Published: May 2005

Physical Blends of ultrahigh‐molecular‐weight linear polyethylene (UHMW LPE) and normal‐molecular‐weight linear polyethylene (NMW LPE) have been evaluated in terms of melt flow rate, tensile stress‐strain behavior, heat of fusion, melting temperature, and crystallinity. The behavior of the blends is intermediate between that of the parent polymers; no synergistic effects are observed. The addition of small quantities of NMW LPE does not improve the flow behavior of UHMW LPE sufficiently to render it amenable to conventional melt processing.
X‐ray photochemistry: ω‐Chloro olefin sulfones
Authors: Kaplan Michael
Published: May 2005

To be efficacious as an x‐ray resist, a material must efficiently undergo a desirable chemical change upon being irradiated with x‐rays. The probability of such a change taking place is given by the product of the fractional x‐ray absorption and the “inherent sensitivity,” which we define as the yield per unit energy absorbed. Increasing the absorption of the polymer, as, for example, by chlorinating an olefin sulfone thereby increasing the absorption at wavelengths just below the chlorine absorption edge will result in improved usefulness if, and only if, this increased energy absorbed can be used by the polymer to enhance the desired chemical reaction. The “usefulness” of chlorinating is thus dependent on the efficiency of intramolecular energy transfer. We have studied the efficiency of this transfer by monitoring the loss of SO2 from the main‐chain backbone as a function of absorbed x‐ray energy, using x‐ray wavelengths both abov and below the chlorine absorption edge. The polymers studied were 1‐olefin sulfones, with and without the chlorine atom in the ω‐position. Through the use of this series of polymers it was hoped to observe an effect due to the changing separation of the chlorine atom from the backbone. The experiments indicate that (a) the inherent sensitivity is independent of irradiating wavelength, for both the chlorine‐containing and the non‐chlorine‐containing polymers; (b) the hexene polymers are considerably more sensitive than the lower members of the series (which exhibit a sensitivity which is approximately independent of the side chain length); and (c) the chlorine‐containing polymers are less sensitive than the non‐chlorine‐containing species. At this time the explanation for these observations is speculative.
Evaluation of poly(allyl methacrylate)‐co‐(hydroxyethyl methacrylate) as negative electron‐beam resist
Authors: Tan Zoilo C. H. , Georgia Sharon S.
Published: May 2005

Poly(allyl methacrylate)‐co‐(hydroxyethyl methacrylate) has been evaluated as a high‐sensitivity, high‐resolution, high temperature‐resistant negative electron resist. The effects of molecular weight and polydispersity of the copolymer on its lithographic performance as an E‐beam resist were studied. The sensitivity of the copolymer is nearly constant in the weight‐average‐molecular‐weight range of 50,000 to 75,000, and it gradually decreases with a decrease in molecular weight. As expected for a negative resist, the resist contrast increases as the polydispersity is decreased. The sensitivity curve shape of the polymer was independent of the prebake temperature, which varied from 70 to 110°C, and of the various developers used. The exposed coating requires vacuum curing for image optimization. Resolution of 0.5 μm line/space pairs was obtained from a 0.6 μm thick resist by exposing the resist to 10 keV electrons with either a raster‐scan‐type or vector‐scan‐type electron‐beam exposure machine. After postbaking at 170°C, the resist had good resistance to both chemical etching and dry etching. The plasma‐etch resistance was about twice that of PMMA.
Recent resist developments in Japan—a review
Authors: Nonogaki Saburo
Published: May 2005

Several kinds of resist materials for microlithography have been developed in Japan. Poly(4‐vinyl phenol) sensitized with 3,3′‐diazidodiphenyl sulfone has been proved to be a high resolution negative deep UV resist with high sensitivity and good resistance to dry etching. The use of this resist enables a 1:1 projection printer to replicate fine patterns with 1 micrometer (μm) minimum feature size at the rate of 90 wafers per hour. Poly(methyl isopropenyl ketone) (PMIPK) has been investigated as a positive deep UV resist. Several resists composed of PMIPK with or without sensitizers are commercially available. Dry‐developable photo‐ and deep UV resists comprising PMIPK and aromatic bisazides have been developed. Poly(glycidyl methacrylate) having the sensitivity of 0.4 micro Coulomb (μC)/per square centimeter (cm2) is now being routinely used as a negative electron beam resist in the fabrication of chromium masks. Recently, aromatic polymers such as chloromethylated polystyrene, iodinated polystyrene, chloromethylated poly(α‐methylstyrene), poly(vinylnaphthalene) and its copolymers have been investigated as dry‐etching resistant electron beam resists.
Ketocoumarins as photosensitizers and photoinitiators
Authors: Williams J. L. R. , Specht D. P. , Farid S.
Published: May 2005

Several 3‐ketocoumarins with alkoxy or dialkylamino substituents in the 7 position, which are efficient sensitizers for crosslinkable polymers, were evaluated as photoinitiators. Proper combinations of certain derivatives of these ketocoumarins with activators such as amines, acetic acid derivatives, and alkoxypyridinium salts gave quantum yields for initiated radical polymerization much higher than that obtained from the Michler's ketone/benzophenone combinations. For each class of activators the dependence of the efficiency of polymerization on the redox properties of the ketocoumarins is explained in terms of charge transfer or electron transfer from the activator to the excited ketocoumarin (acetic acid and amine activators, respectively) or electron transfer in the opposite direction (pyridinium salt activators).
Deep UV photolithographic systems and processes
Authors: Wilkins C. W. , Reichmanis E. , Chandross E. A. , Hartless R. L.
Published: May 2005

Deep UV[200 to 300 nanometers (nm)] photolithography has received much recent attention because it promises higher resolution than conventional exposure technology. Except for the change in wavelength from the 400 nm region, the exposure technology would remain virtually unchanged. We will discuss resist materials and processes explored in the last few years for optimization of deep UV lithography. Particular emphasis is placed upon the chemistry of resist design, multilevel processing schemes, and new sources for deep UV exposure.
Evaluation of the influence of process factors on plasma developed X‐ray resist properties
Authors: Taylor G. N. , Hellman M. Y. , Feather M. D. , Willenbrock W. E.
Published: May 2005

UV spectroscopy, gel permeation chromatography (GPC) and liquid chromatography (LC) have been used to analyze process factors that influence the properties of PDXR‐2 plasma developed X‐ray resist comprised of 92.5 wt percent poly(2,3‐dichloro‐1‐propyl acrylate) and 7.5 wt percent bis‐acryloxybutyltetramethyldisiloxane (BABTDS). The GPC‐LC method is particularly useful in optimizing fixing conditions, determining monomer concentration in the film, and studying molecular processes caused by absorbed X‐rays and thermal effects during fixing. Evidence for a synergistic sensitivity enhancement resulting from fixing and exposure is presented. Optimally processed O2 reactive‐ion etch developed patterns exhibit a microgranular texture in both exposed and unexposed regions of <500 Å size. Unexposed region texture consists of SiO2 resulting from the BABTDS monomer. It is completely removed by reactive ion etching with CHF3 for short times at low power. The exposed area texture is not removed and affords an edge roughness per line edge of <500 Å. Resolution appears mask limited while granular size is dependent on exposure time. A 20 sec exposure optimizes resolution, pattern uniformity, and granularity. 0.5 μm line and space resolution can be obtained with the X‐ray machine and masks currently in use.
Materials for multilevel resist schemes
Authors: Reichmanis E. , Wilkins C. W. , Ong E.
Published: May 2005

Bilevel resist processing techniques, offering the advantage of forming images on a planar substrate, and thus improving the resolution capability of optical projection printers are discussed. After careful consideration of such materials characteristics as UV absorption, solubility, compatibility, and Tg, practical schemes can be developed, the simplest of which is one that uses conventional novolak‐quinone diazide positive resists as the top masking layer and short wavelength sensitive methacrylate based resists to planarize the substrate. Sub‐micron resolution and excellent line‐width control are achieved in these systems.
Organosilicon polymers for lithographic applications
Authors: Shaw J. M. , Hatzakis M. , Paraszczak J. , Liutkus J. , Babich E.
Published: May 2005

Linear polymers of silicone gums (polysiloxanes) have many attributes that make them attractive for lithographic applications, such as oxidative and thermal stability, good adhesion properties, solubility in common solvents, and resistance to etching in an oxygen plasma. When polysiloxanes are used as the top imaging layer (∼2000Å) in a two‐layer resist system, the developed negative siloxane images act as a high resolution etch mask for the oxygen plasma etching of the bottom planarizing polymer layer. Commercially available polysiloxanes have been evaluated for their deep UV sensitivity at 2537Å, and have been found to have very high resolution capabilities (∼0.5μ) and high contrast (γ = 4). The negative images do not swell in the developer, and the line width is therefore independent of development time. The combination of high resolution, sensitivity, and ease of processing make this a simple multilayer system for deep UV and e‐beam applications.
The disentanglement time of the craze fibrils under cyclic loading
Authors: Schirrer R. , Masson J. Le , Tomatis B. , Lang R.
Published: May 2005

In a previous publication a breaking or disentanglement‐time was defined for the fibrils in the craze at the tip of a steady‐state moving crack. In this paper the case of a cyclic sinus loading is investigated, whereas in the previous one the case of a static loading was studied. In both cases the craze fibrils break due to a thermally activated process. The apparent activation energy corresponds to that of the secondary relaxation peak (b̃) in poly(methyl methacrylate). Under cyclic loading conditions the breaking time may be expressed as a time or as a number of cycles carried by the fibrils before breakage. It seems that the relevant parameter is the time rather than the number of cycles. At high frequencies and temperatures an hysteretic heating effect has been detected by means of the breaking‐time of the fibrils.