bluuebunny/crossref_metadata_2025_split huggingface dataset:
Process modelling for manufacture of orthopedic implants from short fiber composites
Authors: Gupte SuniL K. , Advani Suresh G. 
Published: May 2005

AbstractIn 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

AbstractCross‐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

AbstractThe 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

AbstractFour 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

AbstractIn 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

AbstractA 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

AbstractThe 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

AbstractThe 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

AbstractDetermination 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

AbstractProblems 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

AbstractHigh‐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

AbstractThin 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

AbstractThe 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

AbstractA 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

AbstractThis 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

AbstractIn 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

AbstractWhen 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

AbstractThe 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

AbstractTorsional 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

AbstractChange 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

AbstractIt 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.
Confined parison inflation behavior of a high‐density polyethylene
Authors: Dutta A. , Ryan M. E. 
Published: May 2005

AbstractAn analysis of the confined parison inflation step associated with the extrusion blowmolding of a high‐density polyethylene is presented. Based upon simple geometrical considerations and material conservation principles, relationships describing the wall thickness variation have been obtained for various mold configurations. The experimentally measured part thickness distribution is found to be in good qualitative agreement and reasonable quantitative correspondence with the theoretical predictions. Furthermore, the expressions for the thickness variation have been utilized in order to estimate the confined inflation time for the case of a power‐law constitutive equation. In addition, a brief discussion of some practical mold design considerations is given based upon the theoretical analysis.
Analysis of void formation in extruded bars
Authors: Titomanlio G. , Piccarolo S. , Marrucci G. 
Published: May 2005

AbstractIn extruding thick polymeric objects such as bars, voids may form as a consequence of fast cooling. As is well known, this phenomenon is due to volume contraction of the inner zone which takes place when the external “shell” is already solidified. Recent experimental results on this effect show the influence of various parameters such as polymer melt viscosity, bar diameter, and operating pressure upon a critical extrusion velocity above which voids are detected. A detailed analysis of the phenomena which are thought to be relevant is presented and compared with the experimental results.