bluuebunny/crossref_metadata_2025 huggingface dataset:
Weathering of glass‐fiber‐reinforced polystyrene and poly(ethersulfone)
Authors: Qayyum M. M. , White J. R.
Published: May 2005

Glass‐fiber‐reinforced polystyrene (GFPS1) and polyethersulfone (GFPES) injection‐moldings containing 20 wt% glass have been weathered in Jeddah, Saudi Arabia, for up to one year. The retained strength and ductility were, generally, better than in the corresponding unreinforced polymers. The tensile strength fell to ca 73% of the initial, unexposed value, (GFPS1) and ca 77% (GFPES), whereas the extension to break values fell to ca 50% and 76%, respectively, after one year of weathering. The inclusion of carbon black in reinforced polystyrene (GFPS(B)) resulted in a barely perceptible drop in strength (to ca 98%) and a greatly improved reduction in extension to break, dropping only to ca 81% after one year. Residual stress levels were measured and were found to be insufficient to have a significant influence on fracture behavior. In GFPES they were generally less than 2MN/m2except at a location ≃0.3 mm from the surface, where compressive stresses of up to 4 MN/m2were present. No significant change in residual stress occurred with exposure in GFPES. With GFPS1 the stress levels were insignificant ( <1 MN/m2) through most of the bar both before and after exposure. With unexposed GFPS(B) the stresses were <1 MN/m2except within 0.2 mm of the surface, where they rose steeply, though probably not above 5 MN/m2. After weathering the stresses were everywhere <1 MN/m2, but the sense of the residual stresses had reversed near to the exposed surface. This is attributed to radiant heating, and is undesirable because it may lead to distortion.
Random glass mat reinforced thermoplastic composites. Part II: Analysis of model materials
Authors: Stokes Vijay K.
Published: May 2005

The mechanical properties of random continuous glass mat reinforced composites, as determined by standard tensile tests, are known to have a very large scatter. New test procedures have shown that the tensile modulus in these materials can vary by a factor of two over a 12.7‐mm (½‐in) distance. The elastic modulus in a 150 × 305‐mm (6 × 12‐in) plaque can vary by a factor of three. In order to understand the effects of the gauge length on the properties of such materials measured in tensile and flexural tests, a simple model, in which the tensile elastic modulus is modulated by a spacewise sinusoidal variation, has been analyzed. The effect of the functional form of the modulus variation has been assessed by analyzing a square‐wave variation.
Acoustic emission in single filament carbon/polycarbonate and Kevlar®/olycarbonate composites under tensile deformation
Authors: Ma B. T. , Schadler L. S. , Laird C. , Figueroa J. C.
Published: May 2005

An analysis of envelope signals of acoustic emission (AE) produced from carbon/polycarbonate and Kevlar®/polycarbonate composites undergoing tensile deformation has been carried out to identify the sources of emission. The Kaiser effect was reproduced to validate the AE technique. Two different fiber failure mechanisms, i.e., fiber fracture and fiber degradation in Kevlar®/polycarbonate composite have been identified. A one‐to‐one correspondence between acoustic emission signals and fiber fracture and degradation has been established. It is shown that the critical length of the fiber, evaluated by using acoustic emission signals, is helpful in understanding the fracture behavior of the composites, as affected by surface treatments of the fibers.
Stiffness and thermal expansion predictions for hybrid short fiber composites
Authors: Camacho Carolyn W. , Tucker Charles L. , Yalvaç Selim , McGee Robert L.
Published: May 2005

A model is developed to predict thermal expansion coefficients and elastic moduli of multi‐component (hybrid) composites. The model includes the influences of fiber aspect ratio; isotropic and anisotropic fiber materials; planar, three‐dimensional or arbitrary fiber orientation; hollow and solid spherical reinforcements; and voids. The first step in the procedure is to predict the properties of an aligned‐fiber single‐reinforcement composite for each reinforcement type. Various micro‐mechanics approaches are used, depending on the type of reinforcement. A simplified version of Lee and Westmann's theory is found to work well for hollow spherical reinforcements. Performing an orientation average accounts for the spatial orientation of each reinforcement, then an aggregate averaging procedure combines the single‐reinforcement properties to model the hybrid. Predictions of the model compare favorably to experimental elastic and thermal properties of short fiber/hollow sphere composites designed for very high speed integrated circuit (VHSIC) board applications.
Stamping rheology of glass mat reinforced thermoplastic composites
Authors: Davis S. M. , McAlea K. P.
Published: May 2005

Glass mat reinforced thermoplastics (GMTs) offer a useful combination of mechanical properties and formability. In principle, these composites may be based on any thermoplastic matrix. In practice, matrix selection is limited because of its impact on the manufacturing and compression molding processes. In this work an isothermal squeezing flow technique is used to determine the apparent biaxial extensional viscosities of polycarbonate, polybutylene terephthalate, and polypropylene‐based GMTs. Experimental load‐deformation data are interpreted by treating the GMTs as viscous, incompressible Newtonian fluids. Two primary effects are observed: (1) the composites appear to strain harden as they are deformed, and (2) GMT apparent biaxial extensional viscosities correlate with the high rate of deformation shear viscosities of the matrices. A mechanism that explains the second result is proposed.
A finite element/control volume approach to mold filling in anisotropic porous media
Authors: Bruschke M. V. , Advani S. G.
Published: May 2005

Mold filling in anisotropic porous media is the governing phenomena in a number of composite manufacturing processes, such as resin transfer molding (RTM) and structural reaction injection molding (SRIM). In this paper we present a numerical simulation to predict the flow of a viscous fluid through a fiber network. The simulation is based on the finite element/control volume method. It can predict the movement of a free surface flow front in a thin shell mold geometry of arbitrary shape and with varying thickness. The flow through the fiber network is modeled using Darcy's law. Different permeabilities may be specified in the principal directions of the preform. The simulation permits the permeabilities to vary in magnitude and direction throughout the medium. Experiments were carried out to measure the characteristic permeabilities of fiber preforms. The results of the simulation are compared with experiments performed in a flat rectangular mold using a Newtonian fluid. A variety of preforms and processing conditions were used to verify the numerical model.
Compressibility and relaxation of fiber reinforcements during composite processing
Authors: Kim Young Roak , McCarthy Stephen P. , Fanucci Jerome P.
Published: May 2005

In many reinforced composite manufacturing processes it is necessary to compact the fiber materials to obtain the desired fiber/resin ratio in the finished part. Detailed knowledge of applied surface force versus material fiber volume is particularly important in processes such as pultrusion, resin transfer molding, and compression molding. The force required to compact a stack of reinforcing material is strongly dependent on the type of fiber used and its material form. Complicated interactions are possible, particularly when mixtures of unidirectional, oriented cloth and random fiber mats are used. This paper will present results of an experimental and analytical investigation of the response of various dry reinforcing materials subjected to compressive forces applied normal to their principle plane. Experiments were conducted by applying up to 8.6 MPa normal force to thick stacks of E‐glass, graphite cloth, mat and unidirectional material and combinations of two different fiber orientation. Pressure versus fiber volume data were generated for both individual materials and various combinations. Experimental results were compared to analytical predictions. Data showed that the force versus deformation is very strongly dependent on the details of the fiber form or forms being used. There is structural relaxation during fiber compression. Relaxation is very related to fiber orientation, span length, and fiber breakage during compaction. Relaxation behavior decreases with fiber alignment. Random mats and 0/90 cloth show much more relaxation than unidirectional fibers. Data of relaxation is very well fitted with a Maxwell‐Wiechert viscoelastic model.
Real time cure monitoring of composite structures using the techniques of mechanical impedence analysis
Authors: Jang B. Z. , Hsieh H. B. , Shelby M. D.
Published: May 2005

A dynamic mechanical apparatus, based on the concept of mechanical impedance analysis (MIA), was constructed for real‐time cure monitoring of composites. The frequency response function (FRF), in terms of the inertance, impedance or admittance value, can be obtained from the ratio of the Fourier Transforms of excitation and response signals. Spectra during curing of several different kinds of composite materials were obtained with the Fast Fourier Transform spectrum analyzer while the material was continually excited with a random input generated by an electro‐magnetic shaker. The dynamic properties, such as storage modulus (E′) and loss tangent (tan δ), of the composite can be obtained from the FRF spectra as a function of cure time and temperature. Variations of the inertance spectra with cure time, reflecting the changes in the dynamic mechanical properties, for the composite materials under various isothermal cure conditions are discussed. Optimal cure cycles of a new resin can be determined by characterizing the phase transformation of the material, which can be identified from the MIA measurement results. The MIA technique is found to be a sensitive and direct means for monitoring the overall cure state of composites. The signals obtained can be integrated in real‐time in a closed‐loop feedback control system for composite fabrication.
Dynamic mechanical analysis of thermoplastic composites and resins
Authors: Scobbo J. J. , Nakajima N.
Published: May 2005

The anisotropy of continuous fiber thermoplastic composites limits the number of geometries that can be employed effectively in dynamic mechanical analysis (DMA). Therefore, a Mechanical Energy Resolver, developed for use with elastomers, was modified with a bending fixture using a cantilever beam sample geometry and a high temperature oven. The bending fixture allows determination of composite transition temperatures. Based upon the simple geometry, one can also determine elastic moduli. This test scheme can be coupled with simple shear DMA on melts to determine neat resin properties, including solidification temperature. Results are presented for several semicrystalline and armorphous thermoplastic/graphite fiber laminates and neat resins.
Low temperature impact properties of long fiber thermoplastic composite molding materials
Authors: Voelker Marvin J.
Published: May 2005

Four long fiber thermoplastic resin matrices, nylon 6, polypropylene, polyethylene terephthalate, and styrene maleic anhydride, containing differing amounts of long fiber glass reinforcement, were tested for notched Izod impact strength over the temperature range of 22 to −32°C. The notched impact properties of the long fiber thermoplastic composite molding materials are substantially greater than literature values for short fiber analogues. The fiber dominant performance of the long fiber materials is evidenced by increasing impact values with corresponding increases in weight percent fiber content. No apparent ductile/brittle transition in the fracture mode was observed for the long fiber materials that were tested.
Effects of graphite fiber and epoxy matrix physical properties on the temperature profile in a composite during cure
Authors: Mijović Jovan
Published: May 2005

An investigation was carried out into the effects of graphite fiber and epoxy matrix physical properties on the temperature profile in their laminates during cure. An accurate prediction of the temperature profile within a composite is of paramount importance in determining the processing conditions. In this study, a model for the temperature profile was established first. Then, three physical parameters of composites that change during cure, namely, density, heat capacity, and thermal conductivity, were varied in magnitude, and the ensuing effect on the temperature profile was examined. The range of their variation was based upon the values measured in our laboratory as well as those reported in the literature. Changes in the neat resin thermal conductivity were found to significantly influence the temperature profile.
Crosslinking‐property relationships in PMR polyimide composites. Part I
Authors: Pater R. H. , Whitley K. , Morgan C. , Chang A.
Published: May 2005

This study examines for the first time how matrix crosslinking affects the composite physical and mechanical properties of a graphite fiber reinforced PMR polyimide composite during long‐term isothermal aging. Unidirectional composite specimens of Celion 6000/PMR‐P1 were isothermally exposed at 288°C in air for various time periods up to 5000 h. The matrix crosslink densities were estimated from the kinetic theory of rubber elasticity and shifts in the glass transition temperatures (Tgs). TheTg, coefficient of thermal expansion, density, weight loss, moisture absorption, and elevated temperature flexural and interlaminar shear properties were also determined. Several linear relationships were found between the matrix crosslink density and composite physical and mechanical properties. TheTg, initial weight loss and density, and elevated temperature interlaminar shear strength increase with an increase in crosslink density. Conversely, the initial moisture absorption and coefficient of thermal expansion decrease with increasing crosslink density. As expected, the elevated temperature flexural strength and modulus show no direct correlations with crosslink density. Further, after achieving the highest matrix crosslink density, several of the composite properties begin to decrease rapidly. These findings suggest that time‐temperature dependent nature of attaining the maximum matrix crosslinking is closely linked to the onset of the composite property degradation. Though much more work is needed, a fundamental understanding of the relationships between matrix crosslinking and composite physical and mechanical property can provide a scientific basis for the prediction of the extent of composite service life not only for PMR polyimides but also for other thermosetting matrix resins, such as epoxies and bismaleimides.
Chemical resistance of carbon fiber‐reinforced poly(ether ether ketone) and poly(phenylene sulfide) composites
Authors: Ma Chen‐Chi M. , Lee Chang‐Lun , Tai Nyan‐Hwa
Published: May 2005

Studies have been conducted to investigate the aircraft fluid and chemical solvent resistance of the carbon fiber‐reinforced poly(phenylene sulfide) (PPS) and poly(ether ether ketone) (PEEK) composites. The solvents and aircraft fluids utilized in this work include hydraulic fluid, paint stripper, JP‐4 jet fuel, methyl ethyl ketone, and methylene chloride. The weight gain of the composites as a function of time is measured. Tensile and flexural strength, thermal behavior, and dynamic mechanical properties of the composites are examined. The alteration of crystallinity change of the composites is investigated by X‐ray diffraction. It is found that paint stripper degraded the mechanical properties of the composites significantly. Furthermore, crystallization enhancement of the low crystallinity composites in the presence of solvents and aircraft fluids is also observed.
A model for determining fiber reinforcement efficiencies and fiber orientation in polymer composites
Authors: Rosenthal Jay
Published: May 2005

Fiber length contributions to the reinforcement potential in composites have been decoupled from fiber orientation effects with the use of a fiber orientation model. Fiber length efficiency factors and fiber orientation factors are calculated based upon a procedure that requires measuring the composite properties in specified directions relative to a reference direction. The procedure is straightforward and relatively quick compared to the tedious task of actually measuring the fiber length distribution. An example illustrating the utility of the procedure is given and then followed by a discussion qualifying the significance of the factors and the results.
Modification of E‐glass fiber surfaces with polyacrylic acid polymers from an aqueous solution
Authors: Lassas Ann‐Cathrine , Fagerholm Lars E. , Stelound Bengt G. , Näasman Jan H.
Published: May 2005

The research reported in the article focuses on modifying glass fiber surfaces with polyacrylic acid (PAA) compounds. E‐glass fibers were treated with aqueous polyacrylic acid solution. Polyacrylic acid exchanges its protons with the ions present in the glass surface. Hydrolyzed metal cations may form salt complexes with the dissociated polyacrylic acid. Angular dependent electron spectroscopy for chemical analysis (ESCA) demonstrated that the atomic concentrations of aluminum and calcium in the glass fiber surface were constant throughout the analyzed interval. The cation exchange property of glass fiber was studied using direct current plasma (DCP), which showed that both calcium and aluminum ions were extracted by low concentration polycrylic acid solutions. ESCA studies of were extracted by low concentrationb polyacrylic acid solutions. ESCA studies of the PAA‐treated glass fiber showed that the amount of PAA of the glass surface increases with increased acid concentration. A broadened and shifted ESCA peak of the carbon (0CO) indicates the formation of salt complexes between the polyacrylic acid and metal ions on the glass surface. Polyacrylie acid was modified by an esterification reaction with glycidyl acrylate (GA) in aqueous solution in order to insert organofuctional groups into the PAA chain.
The effect of microstructure on the elastic modulus and strength of performed and commercial GMTs
Authors: Ericson Mats L. , Berglund Lars A.
Published: May 2005

A new technique was used to fabricate performed glass fiber/polypropylene GMTs. The method utilizes thermoplastic powder and fiber roving in a spray‐up procedure in which a porous perform in fabricated, heated and molded. The objective was to compare the properties of various preformed GMT composition with two commercial GMTs and to relate the mechanical properties to the microstructure of the materials. Preformed GMTs were fabricated with various fiber lengths and with or without a fiber/matrix adhesion promotor. Processing observation, microstructure, tensile creep modulus, and tensile strength of these preformed GMTs are reported. Fiber length and the addition of a fiber/matrix adhesion promotor had generally little effect on the modulus and strength of the preformed GMT. Comparisons with two structurally different commercial GMTs also showed negligible effects on modulus and strength. The major reason for this is suggested to be the inhomogeneities of the materials. The mechanical properties are controlled by local inhomogeneities rather than by the general microstructure of the material. These inhomogeneities arise from the fiber arrangement in the semi‐finished sheet or perform. Since the microstructure of preformed GMT can be controlled, this material is well suited for future studies on the effect of better fiber dispersion.
Effects of PVA concentration and ribbon immersion time on the interfacial shear strength of amorphous metallic ribbon/polypropylene composites
Authors: Sidhu A. S. , Varin R. A.
Published: May 2005

The effect of PVA (polyvinyl alcohol) concentration and the immersion time of the Fe40Ni40B20 ribbon was studied in terms of interfacial shear strength. First, the PVA concentration was constant at 9 wt% while the immersion time of the ribbon is the solution was changed form 20 to 200 h. Second., the immersion time was constant at 144 h while the concentration of the PVA was changed form 1 to 12 wt%. The interfacial shear strength improved only slightly by increasing the immersion time from 20 h (0.55 ± 0.09 MPa) to 100 h (0.86 ± 0.12 MPa). The interfacial shear strength increased sharply form 0.86 ± 0.12 MPa at 100 h of immersion time to 3.02 ± 0.66 MPa at 144 h of immersion time. After 144 h of immersion, the interfacial shear strength almost leveled off (2.97 ± 0.26 MPa) at 200 h of immersion. The surface of the polypropylene (PP) after pullout and just before the ribbon fracture was studied with a scanning electron microscope (SEM). The low interfacial shear strength of composites immersed for less than 100 h is related ot the insufficient coating on the ribbon and a lack of the well developed interfacial zone. This is manifested by the presence of circumferential bands and impression from rough marking of the ribbon contact side left on the PP surface. The presence of parabolic markings and growth of spherulites on the PP surface may explain the higher interfacial shear strength observed at longer immersion times in the PVA, which suggests the existence of the well developed interfacial zone between ribbon and the PP matrix. The effect of PVA concentration on interfacial shear strength is almost similar to the effect of immersion time.
Wilhelmy plate studies of carbon fiber/viscous fluid systems
Authors: Giannotta G. , Morra M. , Occhiello E. , Garbassi F. , Nicolais L. , D'amore A.
Published: May 2005

The use of Wilhelmy plate techniques for studying the interactions of fibers with fluids of variable viscosity is discussed. The influence of hydrodynamic effects of force (F) VS. DEPTH (z) plots is interpreted on the basis of surface tension‐independent added terms of the constitutive equation of the Wilhelmy experiment. Wetting experiments using pseudoplastic fluids (polyethyleneglycol/water solution) show that viscoelasticity is indeed important in the interpretation of Wilhelmy plate experiments. The comparison of wetting experiments performed on untreated and plasma‐treated carbon fibers showed that at low stage speed and fluid viscosity, surface chemistry and morphology determines contact angles. At higher stage speeds and viscosities and advancing and receding angles are affected by surface chemistry‐independent and hydrodynamics‐dependent added contributions.
Empirical relations of the mechanical properties of polyamide 6 reinforced with short glass fibers
Authors: Ularych F. , Sova M. , Vokrouhlecḱy J. , Turčić B.
Published: May 2005

The dependence of the mechanical properties on the length of reinforcing fibers in hydrolytic polyamide 6 (PA 6) Matrix was studied. The fibers create a polydisperse system and the fiber distribution can be expressed by the Tung distribution function. Modulus, tensile strength, and also impact strength measured on test pieces seem to be a linear function of the part of fiber length population (percentile) representing the reinforcing fibers longer than 200 μm (value P2). These were determined not only on test pieces but also in starting pellets. The mutual relations between the individual mechanical properties seem to be linear as well. Consequently, the mechanical properties of these PA 6 composites can be estimated from the known distribution of fiber lengths in pellets and from the P200values, without preparing and testing the test pieces. The fiber length distribution in pellets of the composite can be estimated from the values of mechanical data (modulus, strength, impact strength) measured on test pieces.
Energy loss partitioning during ballistic impact of polymer composites
Authors: Zee Ralph H. , Hsieh Chung Y.
Published: May 2005

The objective of this study is to determine the energy dissipation processes in polymer‐matrix composites during impact of ballistic projectiles. These processes include heat, fiber deformation and breakage, matrix deformation and fracture, and interfacial delamination. In this study, experimental measurements were made, using specialized specimen designs and test methods, to isolate the energy consumed by each of these processes during impact in the ballistic range. Using these experiments, relationships between material parameters and energy dissipation were examined. Composites with the same matrix but reinforced with Kevlar, PE, and graphite fabric were included in this study. These fibers were selected based on the differences in their intrinsic properties. Matrix cracking was found to be one of the most important energy absorption mechanisms during impact, especially in ductile samples such as Spectra‐900 PE and Kevlar‐49 reinforced polymer. On the contrary, delamination dominated the energy dissipation in brittle composites such as graphite reinforced materials. The contribution from frictional forces also investigated and the energy partitioning among the different processes evaluated.
Effect of viscosity on the electrical properties of conducting thermoplastic composites made by compression molding of a powder mixture
Authors: Li Lin , Chung D. D. L.
Published: May 2005

The viscosity of thermoplastics above Tg was found to greatly affect the room temperature electrical properties of conducting thermoplastic composites made by compression molding of a powder mixture, while the mechanical properties are essentially not affected. The electrical resistivity decreased and the electromagnetic interference shielding effectiveness increased with increasing viscosity, as shown by using (i) the same filler, namely nickel particles, in polyimidesiloxane and polyether sulfone, and (ii) the same filler and matrix at different composite molding temperatures. This effect is attributed to the flow of the low viscosity thermoplastic particles during composite fabrication tending to disturb the connectivity of the filler particles achieved prior to heating.
Process modelling for manufacture of orthopedic implants from short fiber composites
Authors: Gupte SuniL K. , Advani Suresh G.
Published: May 2005

In the case of total hip joint replacement, it has been shown that matching of femur and implant stiffness would positively decrease the chances of resorption of bone and clinical failure of the procedure. Short fiber composites (SFC) which are biocompatible can offer high strength with stiffness comparable to that of natural bone and hence are an excellent candidate to replace metal alloys used in orthopedic implants. In this work a computational process simulation is presented to investigate the possibility of making an artifical hip implant which is most biocompatible. This simulation computes three dimensional flow induced fiber orientation in manufacturing of an SFC hip implant, estimates its mechanical properties, and predicts its “in vivo” response. This is done using a model 3‐D geometry representing implanted femur. The potential use of such an approach is demostrated by comparing principal stresses at the interface of the bone and the implant for metallic and SFC implant which is manufactured using a variety of by proper selection of material and process variables one can potentially create implants which are most biocompatible.
Flexural behavior of stepped graphite/epoxy laminates
Authors: Gopal P. , Yen S. ‐C. , Dharani L. R.
Published: May 2005

Cross‐ply tapered/stepped laminates with taper angles of 1 and 2° between the top and bottom surfaces were fabricated using T300/943 graphite/epoxy by compression molding. Ply terminations were done internally within the laminate and externally on the surface of the laminate at various cross‐sections in order to obtain the taper. Equivalent cross‐ply specimens with internal and external ply terminations, respectively, were tested in three point bending. The bending stiffness of the equivalent corss‐ply are nearly equal, while the failure modes are significantly different. The tapered laminates with internal ply terminations failed due to a series of delaminations originating at the step corners of the 0° plies. Macroscopically, the specimens with internal ply term nations failed by tensile fracture of the outer plies at relatively higher loads.
On‐line consolidation mechanisms in thermoplastic filament winding
Authors: Carpenter C. E. , Colton J. S.
Published: May 2005

The on‐line consolidation process, using a single roller, in thermoplastic filament winding (tape laying) has been investigated. A one‐dimensional, semi‐empirical, on‐line consolidation process model is proposed that describes the deformation and flow phenomena. The model is used to predict the applied load necessary to achieve a desired fiber volume content of filament wound thermoplastic composite rings consolidated at various process conditions. Composite rings are fabricated from 50 layers of 12K carbon fiber tow APC‐2 tape (6 mm wide) on a 178 mm diameter mandrel. It was found that the winding speed had statistically significant effects on the void content, the fiber volume fraction, and the final thickness; whereas the applied load had a statistically significant effect on the final thickness. These results show the effect of shear thinning on the viscoelastic response of the material, facilitating faster processing speeds. The results of the experiments compared well to the consolidation model's predictions.
The elastic properties of random‐in‐plane short fiber reinforced polymer composites
Authors: Gong X. , Hine P. J. , Duckett R. A. , Ward I. M.
Published: May 2005

Four types of random‐in‐plane short fiber reinforced polymer composites were manufactured by the prepreg route using carbon or glass fiber tissue and 913 or 924 epoxy resin. The in‐plane Young's modules and in‐plane shear modulus of the composites were measured over the temperature range − 100 to + 200°C by dynamic mechanical analysis using three point bend and rectangular torsion testing geometries. Theoretical predictions of the elastic properties of the composites were determined over the same temperature range and compared with the experiment. Of particular interest was the use of the “S mixing rule” of McGee and McCullough to determine a single theoretical estimate for the composite elastic properties. Excellent agreement between experiment and theory was found for the four composites over the majority of the measured temperature range.
Elastic modulus of in‐situ composites of a liquid crystalline polymer and polycarbonate
Authors: Lin Qinghuang , Yee Albert F.
Published: May 2005

In this paper, we model the elastic modulus of in‐situ composite fibers from polymer blends where a fibrous liquid crystalline polymer (LCP) phase is induced by drawing. We propose a composite model to account for the change of the elastic moduli of the reinforcing LCP phase with the draw ratio of the composite fibers. We envisage the LCP phase as a composite of a perfectly oriented chain aggregate and a randomly oriented chain aggregate which are connected in series. We then derive equations for the longitudinal and the transverse elastic moduli of the composite fibers based on the well‐known Halpin‐Tsai equation and the composite model of the reinforcing LCP phase. Using this approach, we are able to make a number of predictions including the transverse elastic modulus and mechanical anisotropy. Our results show that theoretical predictions of the longitudinal elastic modulus agree fairly well with experimental results for polycarbonate/Vectra composites. The proposed modulus equations will be useful in providing guidelines for fabrication and applications of this new class of polymeric materials.
Effect of moisture absorption on the dynamic mechanical properties of short carbon fiber reinforced nylon 6, 6
Authors: Mohd Ishak Z. A. , Berry J. P.
Published: May 2005

A study of hygrothermal aging in terms of the kinetics of moisture absorption by nylon 6,6 and its carbon fiber reinforced composites has been carried out. The single free phase model of absorption has been applied to the kinetic data and thereafter the values of diffusivity have been evaluted. The diffusivity was found to be dependent on the conditioning temperatures and the volume fraction of fibers. Dynamic mechanical properties of unaged and aged samples were studied using a free resonance torsion pendulum which covers a temperature range of 350°C. Incorporation of carbon fibers has led to an increase in structural rigidity of the nylon 6,6 matrix especially at higher temperatures. This was reflected by the sharp increase in the relative shear modulus as the glass transition temperature of nylon 6,6 is appoached. Absorbed moisture was observed to plasticize the polymer matrix and decreased the temperatures of all the transitions. For instance, the α‐transition was shifted by almost 95°C. The intensities of the transition peaks of both unaged and aged samples were found to decrease with fiber volume fraction. Increasing the conditioning temperatures has resulted in a reduction of the shear storage modulus and this effect was found to be more pronounced in the reinforced nylon 6,6. This has been attributed to the increase in the extent of degradation at the fiber‐matrix interface.
A computational analysis of the heating of glass mat thermoplastic (GMT) sheets by dual beam microwave sources
Authors: O'Brien Keith T. , Kasturi Shrenik , Mekkaoui Abdallah M.
Published: May 2005

The use of dual beam microwaves to heat glass mat thermoplastic has been investigated numerically using a finite difference technique, known as the alternating difference implicit (ADI) method. The variation in thermophysical properties throughout the GMT has been accounted for using a table look‐up procedure, which provides the appropriate thermophysical properties for the thermal conditions at each mesh point. The use of dual beam microwaves has been shown to significantly reduce the heating times under all geometric conditions, material variations, and glass loadings. Sheet thicknesses were varied from 1 to 12 mm, glass loadings from zero to 40 wt% polypropylene, polycarbonate and nylon were all simulated. The computations indicate a clear advantage in heating times when dual beam microwave heating sources are emplyed.
Adhesion improvement of high modulus polyethylene fibers by surface plasma treatment: Evaluation by pull‐out testing
Authors: Masse P. , Cavrot J. P. , François P. , Lefebvre J. M. , Escaig B.
Published: May 2005

The effect of plasma treatment duration on adhesion promotion of high modulus polyethylene fiber to a polyesterresin matrix has been studied. The adhesion level was evaluated using pull‐out tests. The relevant parameters are the average interface shear strength and the critical embedded length. Particular attention was paid to the sample preparation and testing procedure to minimize data scatter inherent to this method due in part to structural and surface defects of the fiber. The results demonstrate that adhesion is enhanced for plasma treatment times as short as 2 s, mostly because of chemical bonding. Interfacial shear resistance gradually increases for the longer times considered, up to 10 min. In the latter case, improvement may be due to fiber surface etching and roughening, rather than chemical bonding.
Tab adhesive in a composite compression specimen
Authors: Xie Ming , Adams Donald F.
Published: May 2005

Determination of the compressive strength of a composite depends on many experimental parameters. One of them is the adhesive used to bond the tabs to the compression specimen. Experimental results show that the compressive strength has no significant change when different adhesives with different moduli are used. The compressive strength was also shown to be independent of adhesive thickness in a composite compression specimen. A finite element analysis was utilized in this study to investigate the effect of tab adhesive properties, i.e., the modulus and thickness of the adhesive layer, on the compressive strength. The stress distributions along the adhesive layer and stress concentrations at the tab tip of a composite compression specimen are presented. The analytical prediction coincides with the limited experimental data.
Characterization and control of a structural epoxy adhesive
Authors: Fountain Roger
Published: May 2005

Problems associated with single‐lap shear testing of a structural epoxy adhesive are discussed relative to analyses of the epoxy by infrared spectroscopy, gel permeation chromatography, scanning electron microscopy and other instrumental methods. The value of analytical techniques for assessing the adhesive's cure are shown, including a peculiar correlation of lap shear bond strength with the adhesive's initial uncured state as defined by infrared spectroscopy and gel permeation chromatography. This resulted in the development of definitive batch‐to‐batch adhesive quality control methods and specifications involving the water content, curing agent, and oxirane concentrations of the uncured system.
Influence of mold design on the mechanical properties of high‐pressure injection—molded polyethylene
Authors: Kubáut J. , Månson J.‐A. , Rigdahl M.
Published: May 2005

High‐pressure injection molding (nominal pressure 500 MPa) is known to substantially improve the mechanical properties of high‐density polyethylene of a high molecular weight (HMWPE). This work shows that if the mold is equipped with an exit cavity, the tensile modulus and strength of HMWPE‐bars molded is further improved at high pressure levels. The maximum values of the stiffness and strength (thin bars, 1 mm) obtained with the exit chamber is about 12 GPa and 260 MPa, respectively. The improvement due to the exit cavity is of the order of 30 percent for the tensile strength for thicknesses lower than 4mm, while the modulus increases about 1 to 1.5 GPa for bars with thicknesses between 1 and 6 mm. The orientation of the melt during the filling of the mold was also found to have an influence on the mechanical properties of the HMWPE bars.
Dynamics of ion beam modification of polymer films
Authors: Venkatesan T. , Brown W. L. , Murray C. A. , Marcantonio K. J. , Wilkens B. J.
Published: May 2005

Thin polymer films were irradiated in a high vacuum environment with energetic (∼2MeV) ions. The emitted molecular species were studied with a quadrupole mass spectrometer during bombardment. The emitted species are predominantly small molecules. The efficiency of emission depends strongly upon the electronic energy loss of the incident ions in the film and, hence, upon the velocity and atomic number of the incident ion. The emission efficiency of all species decreases with increasing damage in the film. By pulsing the ion beam, the time dependence of irradiation induced emission of molecular species from the films has been studied. Emission delays of hundreds of milliseconds are observed in some cases. These delays are found to depend upon the emitted species as well as the host film and seem to be associated with diffusion of the species in the films.
Possibilities for photoimaging using onium salts
Authors: Crivello James V.
Published: May 2005

The recent discovery that the photolysis of certain onium salts produces strong Brønsted acids presents a unique opportunity to design novel photoimaging systems based on these materials. For example, when used as photoinitiators, they can induce the negative image wise cationic polymerization of multifunctional epoxides, vinyl ethers, and lactones. Alternatively, they may be used to catalyze the degradation of hydrolytically sensitive polymers to give positive photoresists. The ability of still other onium salts to generate radical species as well as strong acids has been exploited to develop photoimaging processes which have no parallel in present photoresist technology. The processes consist of simultaneous radical polymerization and acid‐induced cationic polymerization. Finally, the recent observation that the onium salts can be dye‐sensitized allows them to be responsive to both the ultraviolet and visible regions of the spectrum and to be used with many commercial optical imaging systems.
Electron beam lithography of copolymeric resists containing styrenes and allyl acrylates
Authors: Shu Jing , Lee Wei , Venable Larry , Varnell Gil
Published: May 2005

A series of electron beam sensitive negative resists based on styrene allyl methacrylate copolymers and substitutional modifications thereof were prepared and their resist characteristics were investigated. Depending on the molecular parameters, such as monomeric ratios, molecular weights and molecular weight distributions, the sensitivity to electron beam irradiation of the copolymer resist can vary from 10−7 μC/cm2 to 10−6 μC/cm2. A styrene allyl methacrylate copolymer having a 57/43 mol‐percent and a molecular weight of 3.3 × 105 shows a sensitivity of 1.4 μC/cm2 (Dg0.5) and a resolution of 1.10 μm line/space at 6000A remaining thickness.
A metallurgical approach to the pre‐yield and yield behavior of glassy polymers
Authors: Escaig B.
Published: May 2005

This paper discusses some new mechanical and small angle neutron scattering (SANS) data on glassy polymers, both thermoplastics and thermoset resins, from the point of view of dislocation‐like defects introduced in the molecular chain arrangement by deformation. In the pre‐yield stage, a new parameter, the work‐hardening rate K is introduced and its measurement is defined. Experiments are reported which show that K can be used as a very sensitive probe for microstructural changes during physical aging or curing. In one hand, the theory of yielding is revisited to make clear how dislocations and their propagation in polymers depend on specific features like entanglements and chain stiffness. On this basis, experimental internal stresses and activation volumes at yield (i.e., the temperature slope of yield stress) are accounted for. On the other hand, SANS data provide us with experimental evidence at the scale of 10 to 20 Å of the dislocation nature of the molecular “shear defects” introduced in the polymer by deformation. Finally, temperature is known to have a pronounced influence on yield processes. It is shown that two distinct deformation modes exist below and above a critical temperature Tc. Above Tc, a dislocation climb, which probably involves β‐processes, gives rise to a “diffusional” deformation mode where chains within a (diffuse) shear band are no longer oriented. A tentative formalization of this behavior, and its relation to the small strain creep of polymers, are then presented.
Craze development in poly(methyl methacrylate) during stable fatigue crack propagation
Authors: Lang R. W. , Manson J. A. , Hertzberg R. W. , Schirrer R.
Published: May 2005

In order to obtain a more complete understanding of failure mechanisms in glassy polymers subjected to fatigue loading conditions, craze zone dimensions (i.e., length and thickness at the crack tip) were measured simultaneously with fatigue crack propagation data in poly(methyl methacrylate) (PMMA) by optical interferometry. Since the craze shape was observed to assume a wedge‐shaped configuration similar to the one described by the Dugdale plastic strip model, crazing stresses were inferred on the basis of this model. When varying the stress ratio (R = minimum load/maximum load) of the applied cyclic load in the range from 0.1 to 0.7, it was found that both craze length and craze thickness are essentially independent of theR‐ratio and can be correlated in terms of the maximum stress intensity factor only. On the other hand, significant variations in craze dimensions with test frequency occurred over the range from 0.1 to 250 Hz. The results are discussed in terms of the viscoelastic nature of the material and a competition between the effects of strain rate and hysteretic heating.
Mechano‐chemical degradation and stabilization of polymers
Authors: Scott Gerald
Published: May 2005

When polymers are subjected to sheer, macroalkyl radicals are formed which lead to accelerated oxidation. This may occur in the polymer melt during processing or under conditions of mechanical fatigue at lower temperatures (e.g., in cross‐linked rubbers). Under these conditions, chain‐breaking electron acceptor (CB‐A) antioxidants are found to be relatively more effective than under conditions of thermal oxidation and the evidence suggests that the reduced and oxidized couples of some antioxidants, for example, phenol/phenoxyl or hydroxylamine/nitroxyl, can deactivate radicals catalytically.
Kinetic analysis of the data on the effect of humidity on the stability of poly(butylene terephthalate)
Authors: Kishore K. , Sankaralingam S.
Published: May 2005

The effect of temperature and humidity on polymer aging is well recognized. Gardner and Martin and Kelleher, et al., have collected extensive data on the effect of temperature and humidity during the course of aging of poly(butylene terephthalate) (PBT). They proposed an empirical equation to predict the half‐life of aging. In the present work the data of Gardner and Martin have been reanalyzed to evolve an empirical equation which is applicable to the entire range of changes during aging.
An application of a unified relaxation model to the aging of polystyrene below its glass temperature
Authors: Plazek D. J. , Ngai K. L. , Rendell R. W.
Published: May 2005

Torsional creep measurements of physical aging in high‐molecular‐weight glassy polystyrene are presented. The data are analyzed using a relaxation model which has been successful in quantitatively describing a wide range of relaxation phenomena. The model predicts the time‐functional dependences of the creep compliance and, upon physical aging, a possible systematic change of the functional dependence as creep is shifted to longer time scales. These features are established by experimental measurements. Good quantitative fits are found using a restricted application of the model in which all but one of the model parameters are held constant with annealing. Relations of the present study to other polymer relaxation phenomena are discussed.
Changes in yield and deformation of polycarbonates caused by physical aging
Authors: Bubeck R. A. , Bales S. E. , Lee H.‐D.
Published: May 2005

Change in yield and deformation associated with physical aging was studied on a series of polycarbonates (bisphenol‐A polycarbonate, polyestercarbonates, and phenolphthalein‐bisphenol‐A copolycarbonates) and a polysulfone. A combination of tensile and biaxial yield measurements, dynamical mechanical analysis, and high‐resolution density measurements were performed. These data indicate that both free volume arguments and molecular entanglement arguments are inadequate for explaining the differences in large‐scale deformation associated with physical aging for the polymers and the superiority of polyestercarbonates over the other resins. The local intramolecular and intermolecular conformation in the glassy state, as predicated by molecular structure, is apparently an important key to understanding physical aging in polycarbonate‐type polymers.
Effect of the cooling rate in the formation of glass on the α and β relaxations of some amorphous polymers
Authors: Ribelles J. L. Gómez , Calleja R. Díaz
Published: May 2005

It has been observed in dynamic mechanical measures that the range of temperatures in which relaxation properties are affected by the diminishing of the free volume has, as a lower limit the temperature at which the maximum of G″ or tgδ, corresponding to the β relaxation, occurs. In dielectric measures on polymers in which the β relaxation is not predominant over the α relaxation, this temperature range is scarcely affected by changes in frequency, whereas the peak shifts according to its activation energy. This fact leads to the conclusion that the decrease in free volume due to a slow cooling from a temperature above Tg mainly affects mobility of the main chains under Tg, without disturbing the groups that give rise to the secondary relaxations.