bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of hot compaction pressure on the interfacial properties in the amorphous metallic ribbon/thermoplastic matrix composite system
Authors: Varin R. A. , Ruutopold A. , Wronski Z.
Published: December 2004

The application of rapidly solidified amorphous metal ribbons as continuous reinforcements for thermoplastic composites is examined. The metallic glass alloy Fe40Ni40B20 (at. percent), with good stiffness, strength, and magnetic properties, was selected as the ribbon alloy. The mechanical properties of the ribbons (elastic modulus and fracture strength) were determined by tensile testing under plane‐stress conditions. The continuous FE40Ni40B20 amorphous ribbons were incorporated as reinforcements into a polypropylene (thermoplastic) matrix. To evaluate the quality of the composites formed, ribbon pullout tests were performed to measure the interfacial ribbon/matrix bond strength. It was noted that increasing the hot compaction pressure during fabrication and the surface texture of the ribbons by etching significantly improved the interfacial shear strength between the ribbon and thermoplastic matrix.
Evaluation of carbon‐fiber‐reinforced thermoplastic matrices in a flat braid process
Authors: Hasselbrack Sally A. , Pederson Christopher L. , Seferis James C.
Published: December 2004

An investigation was conducted to evaluate the effect of blending thermoplastic filament fibers with carbon filament fibers in varying yarn forms to study the efficiency of matrix wetting and infiltration into a laminate. Poly(etheretherketone) (PEEK) and poly(phenylene sulfide) (PPS) were studied in commingled, DREF, and powder form, as a flat triaxial braid. The as‐braided and laminated specimens were both subjected to tensile testing and optical microscopy to establish the efficiency of the impregnation process. It was observed that both thermoplastic matrices commingled with carbon yarn maximized the tensile properties and produced the best quality laminate. To impart the best translational properties of the thermoplastic matrix to the carbon/thermoplastic composite, improvements are necessary in the commingling and powder infiltration processes.
A method to determine resin flow during curing of composite laminates
Authors: Poursartip Anoush , Riahi Golnar , Frederick Laurie , Lin Xie
Published: December 2004

An experimental method is presented to determine the amount of resin flow within a composite laminate during cure. The method is analogous to the use of radioactive tracers in other applications. Heavier elements such as chlorine and bromine, which may be naturally present in small amounts in epoxy resins are used to follow resin flow and mixing. The presence and the quantity of these “tags” is determined using wavelength dispersive X‐ray analysis in a scanning electron microscope. With the resins in this study, it is shown that it is possible to measure volume fractions of resin with accuracies ranging from ±0.5 to ±3 volume %. By using brominated resin in only one layer of a laminate, the degree of flow and mixing can be followed accurately. The results suggest that there is considerable resin mixing as well as flow.
A strain‐based parametric biaxial failure criterion for fiber‐reinforced composites
Authors: Makinde A. , Neale K. W. , Sacharuk Z.
Published: December 2004

Orthotropic, fiber‐reinforced composite laminae under biaxial plane stress loading conditions are considered. A new strain‐based strength criterion for such laminae is proposed. This failure criterion, which is cast in parametric form, is completely general. A parametric equation that is expressed as a Fourier series is proposed for describing the failure surface for the laminae. This equation is shown to be valid for most fiber‐reinforced composite laminae through comparisons with experimental data taken from the literature. The advantages of the failure theory are discussed in comparison with the quadratic form of the tensor polynomial theory. Also presented is a biaxial apparatus for testing cruciform specimens under biaxial loading conditions. Efforts under way to characterize composite laminae and laminates under complex stress states are discussed.
Modified Tsai‐Wu failure criterion for fiber‐reinforced composite laminates
Authors: Pang Su‐Seng , Pandian Annamalai , Bradshaw Roger D.
Published: December 2004

The Tsai‐Wu Quadratic Failure Criterion provides satisfactory strength predictions for fiber‐reinforced composite materials but requires five experimental tests to determine the strength parameters. This paper presents two modifications of this criterion, which employ micromechanics to determine these parameters. Experiments on uniaxial and multiaxial vinyl ester/fiberglass composite laminates show that the first modified failure criterion, which is based solely on fiber and resin properties, predicts strength within an average absolute error of 25.4% in comparison to the experimentally determined strength. The addition of a single longitudinal tensile test to the modified expression (second modified failure criterion) reduces the average absolute error to 15.9%. This compares well with the Tsai‐Wu Failure Criterion, which gives an average absolute error of 9.4%. The proposed modified criteria are shown to provide satisfactory failure predictions, while greatly reducing the amount of testing required.
Fiber orientation in simple injection moldings. Part I: Theory and numerical methods
Authors: Bay Randy S. , Tucker Charles L.
Published: December 2004

This paper sets out the theory and numerical methods used to simulate filling and fiber orientation is simple injection moldings (a film‐gated strip and a center‐gated disk). Our simulation applies to these simple geometry problems for the flow of a generalized Newtonian fluid where the velocities can be solved independently of fiber orientation. This simplification is valid when the orientation is so flat that the fibers do not contribute to the gapwise shear stresses. A finite difference solution calculates the temperature and velocity fields along the flow direction and through the thickness of the part, and fiber orientation is then integrated numerically along pathlines. Fiber orientation is three‐dimensional, using a second‐rank tensor representation of the orientation distribution function. The assumptions used to develop the simulation are not valid near the flow front, where the recirculating fountain flow complicates the problem. We present a numerrical scheme that includes the effect of the fountain flow on temperature and fiber orientation near the flow front. The simulation predicts that the orientation will vary through the thickness of the part, causing the molding to appear layered. The outer “skin” layer is predicted only if the effects of the fountain flow and heat transfer are included in the simulation.
Fiber orientation in simple injection moldings. Part II: Experimental results
Authors: Bay Randy S. , Tucker Charles L.
Published: December 2004

Experimental measurements of fiber orientation are reported for two parts injection molded from nylon 6/6 reinforced with 43 wt% of glass fibers. The parts are a center‐gated disk and a film‐gated strip. Orientation is measured from polished cross sections and reported as a function of position, both across the thickness and in the flow direction. Both parts have a layered structure, with outer shell layers of flow‐aligned fibers surrounding a central core of either random‐in‐plane (strip) or transversely aligned fibers (disk). The disk also has surface skins with less alignment. The experiments are compared with predictions of the simulation presented in Part I. The simulation predicts the presence, nature, and location of the layers very well. However, it overpredicts the small out‐of‐plane fiber orientation and places the core‐shell transition too close to the midplane. A comparison with selected experimental results suggests that the major source of error is the closure approximation used by the fiber orientation equation. The simulation is exercised for a variety of cases to show the importance of material and process parameters. A polymer matrix with a small power‐law index or a large heat of fusion gives a thicker core and is less likely to have a skin. Injection time is an important parameter, but injection temperature and mold temperature have little effect on fiber orientation.
The meaning of the critical length concept in composites: Study of matrix viscosity and strain rate on the average fiber fragmentation length in short‐fiber polymer composites
Authors: Monette L. , Anderson M. P. , Grest G. S.
Published: December 2004

Computer modeling is used in order to provide a theoretical understanding of the concept of critical length in composites, and of the factors influencing the critical aspect ratio. The effects of interphase and matrix properties have been investigated. We have identified the interphase parameters which minimize the critical length. Contrary to the assumption that the critical aspect ratio is related to interfacial shear strength and fiber strength only, we find a significant dependence on matrix viscosity and strain rate, for fixed interphase properties. We therefore conclude that the fragmentation test, which relates the measured critical aspect ratio to a value for the interfacial shear strength, has to be reinterpreted in terms of more parameters than those simply present in the Kelly‐Tyson formalism. Moreover, the significance of the concept of critical length for tailoring mechanical properties of composites needs to be reassessed.
Microstructure of long‐ and short‐fiber reinforced injection molded polyamide
Authors: Toll S. , Andersson P.‐O.
Published: December 2004

The variation of fiber orientation and content within injection molded rectangular plates is investigated. Fiber orientation and volume fraction are measured using metallographic polishing and a newly developed image‐analysis system; fiber weight‐fractions are measured using an ashing method. Three different moldings are studied; two of the long‐fiber compound Verton, Molded at different injection speeds, and one of the short‐fiber compound Maranyl. Microstructural regions are identified and characterized, and the flow mechanisms by which they are formed are discussed. The results show that the long fibers segregate extensively, whereas the short ones do not. The major differences between the two compounds are found in the core: the core of the long‐fiber compound has a higher content and orientation of fibers than that of the short‐fiber compound.
Preform permeability predictions by self‐consistent method and finite element simulation
Authors: Berdichevsky Alexander L. , Cai Zhong
Published: December 2004

The self‐consistent method and finite element simulations have been used to estimate the permeability of an aligned fiber bundle. The self‐consistent method gives out formulas for both longitudinal and transverse permeabilities as functions of the fiber volume fraction. The finite element simulation presents the solutions of various periodic fiber packings. The results for square and hexagonal fiber packings are found coincident with the literature results. It is shown that the permeability is not only related to the fiber volume fraction of porosity, but is also greatly influenced by the packing structure or micro‐level disturbance. A unified empirical model is proposed, which uses as variables ultimate fiber volume fraction in addition to fiber volume fraction. The model predications agree with numerical simulation results in different cases.
Influence of processing and material variables on resin‐fiber interface in liquid composite molding
Authors: Patel N. , Rohatgi V. , Lee L. James
Published: December 2004

In this study, systematic investigation of influence of processing variables on the tensile strength and resin‐fiber interface of composites prepared by liquid composite molding process was carried out. The variables studied included injection pressure and mold/fiber mat temperature. Fibers were better wetted and bonded at lower injection pressure and higher molding temperature, which resulted in a higher tensile strength of molded composites. Single filament composite tests were also used in conjunction with birefringence studies to characterize interface bonding. Improved interfacial behavior was observed in the case of compatible systems.
Rheological behavior of two‐ and three‐phase fiber suspensions
Authors: Shuler Stephen F. , Binding David M. , Byron Pipes R.
Published: December 2004

The rheology of two polyamide 6.6 systems filled with long glass fibers, as well as at of a three‐phase polyamide 6.6‐glass fiber‐gas bubble system, was studied using capillary rheometry, To investigate the influence of fiber concentration, the shear and extensional viscosities were determined for both 30 and 40 vol% fiber filled suspensions as well as for the base polymer. Comparison revealed a modest increase in both the shear and extensional viscosities with increased fiber fraction. The shear viscosities, ηs, of both suspensions are shown to be close to one order of magnitude greater than the base matrix fluid viscosity, η. However, the extensional viscosities, ηE, of the suspensions are determined to be approximately four orders of magnitude greater than the shear viscosity of the matrix fluid for strain rates from 100 s−1 to 102 s−1. The addition of a gas bubble phase to the neat polymer and polymer‐fiber suspensions was accomplished through the decomposition of various percentages of an azodicarbonamide blowing agent. The presence gas bubbles resulted in reduced shear and extensional viscosities for both the neat and fiber‐filled polyamide with greater reductions observed for the neat polyamide. Greater viscosity reductions were observed as the blowing agent centration was increased.
Simultaneous interpenetrating networks for tough matrix composites
Authors: Prakash N. A. , Liu Y. M. , Jang B. Z. , Wang J. B.
Published: December 2004

Graphite fiber reinforced epoxy composites normally exhibit low impact strength, poor delamination resistance, and low damage tolerance. Because delamination is a matrix‐dominated failure mode, tougher matrix resins may be utilized to reduce or eliminate the adverse effects of delamination on the structural integrity of fiber composites. The effects of modifying epoxy network morphology by introducing polyurethane in the form of an interpentrating network were studied. The compatibility, toughness, and tensile properties of the matrix as well as the properties of the resultant laminates were evaluated. One of the conclusions arising was that the interpenetrating network morphology results in superior resin and composites toughness with increasing polyurethane content. However, the benefits of increased resin toughness did not necessarily translate into proportionally increased composite owing to the geomertical limitations placed on the plastic deformation zones in laminates.
Mechanical properties of carbon fiber reinforced polyester/urethane hybrid network composites
Authors: Yu J. L. , Liu Y. M. , Jang B. Z.
Published: December 2004

Hybrid resins of unsaturated polyester/urethane were synthesized and characterized. Both the toughness and stiffness of the polyester were improved significantly by incorporating 20 wt% urethane. Unsaturated polyester, styrene, and ethane showed good compatibility during blending and probably formed a simultaneous interpenetrating network (IPN) during polymerization. The resultant IPN morphology possessed a unique glass transition temperature. This IPN morphology not only imparted great fracture resistance to the otherwise brittle polyester, but also changed the fracture mode of new resin composites. The molecular weight of unsaturated polyesters did not have significant effect on the mechanical properties, but did exert an apparent influence on the fracture mode. During the cure process the side reaction, an amine reaction, could be suppressed addition of suitable promoter and catalyst.
Prediction of fiber orientation in the thickness plane during flow molding of short fiber composites
Authors: Ko Jin , Youn Jae Ryoun
Published: December 2004

Fiber orientations caused by the flow in the thickness plane during injection molding of short fiber reinforced polymer composites has been simulated. The Lagrangian scheme was employed for the finite element analysis. Flow fields were solved by using a penalty method with Uzawa's scheme and orientation fields were also solved by using the second order orientation tensor. A generalized Newtonian fluid whose rheological behavior is independent of fiber orientation was assumed. Automatic mesh generation using an elliptic grid generator was developed for quadrilateral elements. Mold filling and orientation analyses were performed for a cavity of rectangular cross section. To determine the orientation state in other cross‐sectional geometries, numerical analyses were also performed for two different typical cross sections. As the result, orientation of short fibers in the flow field was analyzed qualitatively and quantitatively. According to the state of short fiber orientation in the thickness plane, the orientation field can be classified into three regions in the flow direction and three layers in the thickness direction. Orientation of short fibers was mainly influenced by elongational and shear flows. It was observed that critical values are present for upper limits of orientation. Effects of initial orientation at the inlet on the orientation field were examined.
The effects of a nucleating agent and of fibers on the crystallization of nylon 66 matrices
Authors: Klein N. , Selivansky D. , Marom G.
Published: December 2004

Crystallization from the melt of nylon 66 in the presence of carbon fiber, aramid fiber, or nucleating agent was studied using differential scanning calorimetry (DSC) and hot stage microscopy. The use of the nucleating agent resulted in an increase in crystallization rate and a decrease of induction time under both isothermal and nonisothermal conditions. The fibers were found to behave like a giant nucleating site producing a uniform transcrystalline layer having morphology and crystallization kinetics different from those of the bulk matrix. The influence of the cooling rate on the process of nonisothermal crystallization was analyzed, and the values of activation energy, calculated from the cooling rate—crystallization temperature relationship, appeared to be higher for the nucleated and for the reinforced nylon compared with that of the neat nylon 66. This implied that the presence of fibers or nucleating agent led to the development of a more ordered structure, which required a larger amount of energy for crystallization.
Thermoplastic composites from maleic anhydride modified post‐consumer plastics
Authors: Xanthos M. , Grenci J. , Patel S. H. , Patel A. , Jacob C. , Dey S. , Dagli S. S.
Published: December 2004

In attempts to identify potential applications for refined commingled postconsumer plastics, a feedstock containing about 80% polyethylene (PE) and lesser amounts of poly(ethylene terephthalate) (PET), polystyrene (PS), polypropylene (PP), and poly(vinyl chloride) (PVC) was modified through functionalization with maleic anhydride in a co‐rotating intermeshing twin‐screw extruder. The modified and unmodified blends were compounded with various fillers and reinforcements such as glass fibers, mica flakes, talc, and calcium carbonate. Injection molded composites based on the modified matrix had, in general, superior mechanical and thermal properties. These findings are discussed in view of the improved adhesion resulting from reactions and/or enhanced polar interactions at phase boundaries. Several compounds prepared in this work had overall property data comparable to, or approaching those, of equivalent commercial HDPE molding compounds that are commonly used in “durable” applications.
Dielectric studies of mineral‐filled epoxy
Authors: Wu Shiann‐Long , Tung I‐Chung
Published: December 2004

Dielectric studies in epoxy and epoxy composites, containing different volume fractions of three different dielectric fillers, have been performed using the impedance bridge method for the high frequency region, 102 to 105 Hz, and the d.c. transient current method for the low frequency region, 10−4 to 10−1 Hz. It has been observed that, in the high frequency region, the dielectric constants of the epoxy composites increased with the addition of the dielectric filler and with the increase of the dielectric constant of the filler. The intensity of the β‐relaxation was reduced for the composites compared to an equal volume of epoxy, owing to the decrease in the concentration of the diester segments in the composites. From the low frequency data, the epoxy and epoxy composites behaved more debye‐like with increasing temperature. Also, the dielectric loss factor increased, but the thermal activation energy value to relaxation decreased two to four times in going from the unfilled to filled materials, which was thought to be attributed to Maxwell‐Wagner buildup of interfacial charges at the epoxy/fillers interfaces.
Effects of treatment on the surface composition and energy of carbon fibers
Authors: Wu G. M. , Schultz J. M. , Hodge D. J. , Cogswell F. N.
Published: December 2004

The surface composition and energy of carbon fiber has been carefully analyzed and quantified. Untreated, AU, surface‐treated, AS, and heat‐treated AHT fibers were all studied. AS fiber was surface‐treated by an electrolytic oxidation process. AHT fiber was heat‐treated at elevated high temperatures under vacuum. X‐ray photoelectron spectroscopy (XPS or ESCA) was used to investigate the surface elemental concentration of carbon fibers. The corresponding surface free energies of these fibers were calculated from the contact angles measured by a dynamic contact angle analyzer. Results showed a strong correlation between the surface treatment and heat‐treatment history and the surface chemistry of carbon fibers. After oxidation treatment, the surface free energy was increased by adding functional group elements (oxygen and nitrogen). However, these added elements could be removed by high temperature treatment under vacuum. The diffusion of O, N, and Na was discussed. The correlation between oxygen and nitrogen concentration and carbon fiber surface free energy has been plotted. These fibers would be used to quantify the relationship between carbon fiber surface free energy and the interfacial shear strength of the fiber‐polymer interface.
Dynamic mechanical analysis of epoxy composites plasticized by water: Artifact and reality
Authors: Chateauminois A. , Chabert B. , Soulier J. P. , Vincent L.
Published: December 2004

The plasticization of a glass/epoxy unidirectional composite by water has been investigated by Dynamic Mechanical Thermal Analysis (DMTA). The analysis of the thermomechanical spectra of the water aged material revealed the apperance of a splitting of the tan δ peak associated with the α transition. This splitting was found to be dependent on the experimental conditions, i.e., the temperature scan rate, the straining frequency, and the initial water content on the composite. A thermogravimetric analysis (T.G.A) of the wet specimens has shown that this effect could be attributed to an enhanced drying of the specimens above the glass transition, during the DMTA temperature scan. A differential plasticization of the epoxy network at the aging temperature can therefore not be invoked from the appearance of a splitting of the DMTA spectra. In conditions where the sample drying was minimized, plasticization effects on the thermomechanical properties of the composite were found to be temperature independent and reversible after re‐drying of the aged material. Owing to the filling of hygrothermally induced cracks with water, the composite sensitivity to plasticization can be underestimated significantly at elevated aging temperature.
The adhesion of elastomer‐coated glass fibers to an epoxy matrix. Part I: The effect of the surface treatments on the tensile strength of the glass fibers
Authors: Ahlstrom C. , Gerard J. F.
Published: December 2004

E‐glass fibers were subjected to various surface treatments to study the interfacial adhesion with an epoxy matrix by means of the fragmentation test. The glass fibers considered were both untreated and treated with γ‐aminopropyltriethoxysilane (γ‐APS). In addition, glass fibers were coated with a thin layer of a crosslinkable elastomer including (or not) a silane coupling agent. To evaluate the effect of the coating process, the glass fibers were also passed through the pure solvent (washed fibers). The tensile strength of glass fibers at short length (near the critical length, lc, for the fragmentation test) cannot be measured directly, thus, extrapolation techniques were used. The Weibull statistics technique was applied and accurately described the tensile strength data of the tensile strength at various fiber gauge lengths for the different surface treatments. Nevertheless, the Weibull parameter, m, changes with the gauge length, and therefore, the extrapolation value at lc depends on the method. The tensile strength of the silane‐treated glass fibers is higher than for the untreated fibers, in agreement with reported data. This effect could be attributed to the protection against water provided by the silane sizing. The coating process does not induce any damage of the glass fibers since the washed fibers display mechanical properties close to those obtained for the untreated fibers. An additional effect is observed for the elastomer‐coated fibers which present the highest tensile strength. This effect could be attributed to an improved protection and/or elimination of the weakest filaments in the glass strand during the treatment.
Polyamide 6—long glass fiber injection moldings
Authors: Bijsterbosch H. , Gaymans R. J.
Published: December 2004

The injection molding ability of long glass fiber reinforced polyamide pellets was studied. The injection moldable materials were produced by a melt impregnation process of continuous fiber rovings. The rovings were chopped to pellets of 9 mm length. Chopped pellets with a variation in the degree of impregnation and fiber concentration were studied. The injection molded samples were analyzed for fiber concentration, fiber length, and fiber orientation. Dumbbell‐shaped tensile bars were made to evaluate the mechanical properties. The fibers in the tensile bars had a high orientation in the flow direction and minor fiber concentration gradients were observed. The fiber lengths decreased with fiber concentration from 1.6 mm for a 2 vol% to 0.6 mm for a 25 vol% system. The tensile and impact properties increased considerably with fiber concentration. A low degree of impregnation in the pellets of the fibers resulted in somewhat lower tensile and impact properties.
Effects of fiber mat architecture on void formation and removal in liquid composite molding
Authors: Patel N. , Lee L. James
Published: December 2004

Liquid composite molding (LCM) processes such as resin transfer molding and structural reaction injection molding are considered to be high potential processes for the mass production of composite parts. The resin injection step in LCM consists of two simultaneous flows: bulk mold filling and tow wetting. This complexity often results in the entrapment of air in the composite part, which is known to result in degradation of part performance, In this work, systematic investigation of the resin flow behavior through various types of glass fiber reinforcements is carried out by flow visualization. The objective is to relate the fiber mat architecture to the micro scale flow pattern and void formation, movement, and removal. An optical image analysis and processing technique is developed to help quantify void formation. Void formation is related to liquid properties and fiber‐liquid contact angle. Although the focus of the study is LCM, the results can be directly applied to other composite manufacturing processes that involve advancement of resin in a dry fiber reinforcement.
Polymer applications in three dimensional linear fracture mechanics analysis
Authors: Smith F. W.
Published: December 2004

A discussion is given of three types of experimental techniques which make use of polymers for the verification of theoretical solutions to three‐dimensional linear fracture mechanics problems. The three techniques discussed are designated as the fatigue method, the photoelastic stress‐freezing method and the static fracture method. These techniques employ poly(methyl methacrylate) sheets which are cut into appropriate fracture mechanics specimen geometries or castable epoxies which may be cast into flat plates or other appropriate shapes for investigation. The suitability of these materials for linear fracture mechanics testing is discussed and the quality of results obtained is described.
Rapid crack propagation and arrest in polymers
Authors: Kobayashi A. S. , Mall S.
Published: December 2004

Published results on dynamic fracture toughness vs crack velocity relations of polyester resin (Homalite‐100), epoxy resin Araldite‐B, modified epoxy resins and polycarbonate are reviewed. Commonality between the seemingly diversified experimental results as well as the existences of minimum dynamic fracture toughness,KIm, and crack arrest stress intensity factor,KIa, as inherent material properties are discussed.
Calculation of molecular parameters for stepwise polyfunctional polymerization
Authors: Miller Douglas R. , Valles Enrique M. , Macosko Christopher W.
Published: December 2004

Our recursive method is extended to calculate several new parameters for stepwise polyfunctional polymerization. In the pregel region we calculate weight average molecular weight, Mw, for polydisperse reactants and effective average functionality, fe, of a reacting mixture. These quantities are useful for systems employing reactive oligomers. We also calculate weight average number of branches per molecule, Bw, and the weight average of a longest chain. These should be useful for viscosity relations. In the postgel region we give relations for the extent of reaction in the soluble fraction. This result can be used to calculate sol properties directly from existing pregel relations. We also calculate the weight fraction of pendant chains on the gel, wp, and the average molecular weight of the elastically effective network chains, Mc,w.
Moisture effects upon the dimensional stability of an S‐glass/epoxy composite
Authors: McCormick Fred C.
Published: December 2004

An experimental investigation is described of the effects of moisture and a polar solvent upon the changes in the axial dimensions of composite tubes fabricated with S‐glass and an epoxy resin. Test parameters included different axial stress levels, sorption variations, and changes in the short‐beam shear strength with moisture variations. Several wetting and drying cycles were used to establish the reproducibility and reversible characteristics of the observed dimensional changes. Test results are compared and discussed with findings reported by other investigators.
High modulus through lamellar structures nucleated by flow induced fibrous substrates
Authors: Odell J. A. , Grubb D. T. , Keller A.
Published: December 2004

Extremely high modulus (up to 1011Nm−2) strands of poly ethylene have been prepared by the controlled crystallization of lamellar overgrowths onto a small quantity of preformed flow‐induced microfibrils. The requirements for achieving a high modulus from a lamellar system are considered, and indicate that high chain extensions may not be needed. The lamellae satisfying these requirements possess a unique taper, the outer edges having a fold length of less than 40Å. This raises new issues relating to crystallization in confined spaces, and space filling by lamellae in bulk samples in general.
Fatigue crack propagation in, graphite fiber reinforced nylon 66
Authors: Dibenedetto A. T. , Salee Gideon
Published: December 2004

The rate of fatigue crack propagation in graphite fiber reinforced nylon 66 was measured. A model of the form å = β [Kmax1‐γΔKγ]rwas used to correlate the rate of crack propagation å with the maximum stress intensityKmaxand the amplitude of the stress intensity ΔKexperienced by the notched specimen during the fatigue test. The quantities β, γ andrwere constant at fixed temperature and frequency of the test. It was also found that there exists both an upper and a lower threshold of stress intensity for the slow ropagation of damage during fatigue. The mechanism of crack propagation in the short graphite fiber reinforced nylon was found to be similar to the growth and fracture of crazes in thermoplastics. The propagation of damage at the crack tip is controlled by matrix deformation, cavitation, fiber breakage and fiber pullout. Damage can propagate in the absence of crack growth until a critical point is reached at which time the material fractures catastrophically.
Sorption and transport in glassy polymers–a review
Authors: Frisch H. L.
Published: December 2004

After defining Fickian diffusion in rubbery polymers an overview of transport behavior in polymers is presented. Diffusion and sorption below the glass transition are discussed, followed by a review and classification of the various theoretical models which have been proposed to account for these phenomena. A short list of recommendations for future work is included.
Microhardness of extruded high density polyethylene fibers
Authors: Baltá‐Calleja F. J. , Mead William T. , Porter Roger S.
Published: December 2004

High‐density polyethylene of high tensile modulus has been produced by solid state extrusion using an Instron capillary rheometer. Microhardness measurements on these ultraoriented fibers have been made to assess their perfection from values of the tensile elastic modulus and shear strength. The microhardness tests were measured using a Vickers square diamond. The microhardness increased with the common temperature for crystallization and extrusion, likely due to improvement in the lateral packing of microfibrils. The variation of microhardness with draw ratio is also illustrated.
Injection molding into a rectangular cavity with inserts
Authors: Krueger W. L. , Tadmor Zehev
Published: December 2004

Advancing melt front profiles, pressures, and temperatures were measured during the filling stage of an injection molding process into a rectangular cavity with variously shaped inserts. These experimentally measured data, together with weldline location, were compared to predictions of the previously developed theoretical model.
Melt elasticity of low density polyethylene
Authors: Nguyen My N. , Maxwell Bryce
Published: December 2004

The stress vs strain and strain recovery characteristics of a series of low density polyethylenes of various molecular size and molecular size distributions have been studied in the melt state. The results show that the high molecular size portion of the molecular size distribution dominates the stress vs strain behavior. The high molecular size component causes a large increase in the stress overshoot and steady state stress. The high molecular size component also has a strong influence on the magnitude of recoverable strain, The strain recovery characteristics are dependent on the amount of strain applied. For large strains (above the yield point) the strain recovers slowly to a large extent (Type I). For applied strains below the yield point the strain recovery is rapid and finished in a short period of time (Type II).
Oxygen plasma removal of thin polymer films
Authors: Taylor G. N. , Wolf T. M.
Published: December 2004

Relative rates of polymer removal in an oxygen plasma have been measured for 40 polymer samples. The rates of removal are correlated, with structural factors which enhance or retard removal. Strong backbone bonds, aromatic and polar functional groups, and metallic atoms decrease the removal rates. Weak bonds not attached to the‐ polymer backbone have little affect while weak bonds attached directly to the chain or in the chain greatly accelerate removal. Chlorine present in the polymer catalyzes removal. This can be mimicked by mixtures of CF4, and O2 for which much enhanced removal rates are observed.
Qualitative prediction of the effects of changes in spinning conditions on spun fiber orientation
Authors: Hagler Gerald E.
Published: December 2004

A simple model, based on an average elongational rate, correctly predicts qualitatively the effects of changes in all spinning parameters on the orientation of fibers spun from viscoelastic melts. The model may be extended to any extrusion process with an elongational character.
Model reference optimal steady‐state adaptive computer control of plastics extrusion processes
Authors: Hassan G. A. , Parnaby J.
Published: December 2004

The first true hierarchical automatic optimal control scheme for plastics extrusion has operated satisfactorily in the laboratory. The process operator is only required to specify desired output rate and die inlet melt temperature set‐points. The control variable set‐points are continually set by computer in line with an optimal policy pre‐programmed from off‐line solutions using models for extruder and die behavior. Feedback and feedforward control strategies are used to hold the melt temperature and pressure at die inlet within close tolerances using control actions calculated via process models and applied by a hierarchical cascade controller. The methodology is described by reference to a specific 40 mm diameter screw extruder fitted with a variable geometry annular blow molding die head, processing specific polymers. However, the control procedures are completely general and can be applied to any extruder‐die combination.
Monohole flow test with high‐frequency preheating for evaluating flowability of thermosetting compounds
Authors: Tonogai Saburo , Seto Shoji
Published: December 2004

The flow behavior of molding compounds such as phenolics, melamines, and ureas was examined by a monohole flow test in which the compounds were high frequency‐preheated up to the test temperature just prior to being put into the monohole mold. The effect of temperature, pressure, and water content on the flowability has been clarified as follows: (1) The relation between log flow rate and reciprocal absolute temperature consists of two straight lines with different slopes, showing dual activation energies for flow above and below an inflection point. The phenomenon suggests the existence of a phase transition in a resin flow. (2) The inflection point shifts to the lower temperature side with an increase of pressure and water content. (3) The influence of water content on the flowability varies largely according to compatibility between resins and water. (4) The temperature dependence of flow rate in a urea compound decreases during storage due to the advancement of condensation.
Heat transfer in polymer composites containing thermally active fillers: Mathematical modeling
Authors: Joshi Shriram , Astarita Gianni
Published: December 2004

The heat transfer data recently presented by Migliaresi, et al. are used as the basis for developing two models of the coupled heat transfer‐phase transition phenomena in polymeric composites containing thermally active fillers. Both models represent an extension to heat transfer of ideas which have originated in the analysis of mass transfer phenomena in polymeric materials. The second model is able to correlate all the available data within 0.5°C.
Characterization of the interlaminar shear fatigue properties of SMC R‐50
Authors: Wilson Dale W. , Byron Pipes R.
Published: December 2004

The interlaminar shear fatigue behavior of the sheet molding compound SMC‐R50 has been studied. A thick‐laminate, short beam shear test was employed to characterize S‐N behavior for the material at 21 and 90°C. The shear modulus (Gxy) was determined at 21 and 90°C and the effect of fatigue on modulus at both test temperatures is discussed. Scanning electron microscope (SEM) and optical photomicrographs of pristine and post test specimens were studied to assess the relationship between material microstructure and the observed fatigue results for strength and modulus. The experimental evidence suggests that the fatigue life for this material is determined by a single flaw growth mechanism, rather than a global “wear out” process.
Polymer/concrete composites—A review
Authors: Kirlikovali Ergun
Published: December 2004

The development of polymer/concrete composites is directed at both improved and new construction materials by combining the ancient technology of hydraulic‐cement‐concrete with the modern technology of polymers. The need for such materials has always existed since the traditional construction material portland‐cement‐concrete (PCC) suffers the drawbacks 4 little or no resistance to chemical attack; rapid deterioration under freeze/thaw conditions due to cyclic temperature changes; low tensile, shear and bond strengths; and inherent micro‐structural menaces (voids, shrinkage‐cracks, capillaries) which, individually or in combination with each other, shorten the service life of the structures.
Glass transition temperature (Tg) determination of partially cured thermosetting systems
Authors: Lee C. Y‐C. , Goldfarb I. J.
Published: December 2004

Previous experiments have shown that Tg of a partially cured thermosetting system can be measured with conventional thermal scan methods only if no appreciable additional cure occurred during the scan. For high temperature performance systems, the partially cured Tg is often at a temperature where kinetics rate is very rapid, causing either an observation of a more advanced cured Tg, or only the completely cured system's Tg [Tg (∞)]. Two methods to interpolate the Tg information in spite of additional cure are presented and illustrated with an epoxy resin as a testing material. The Isocure State Curve method is demonstrated with a two‐step curing experiment with the Torsion Impregnated Cloth Analysis (TICA) technique, which is a forced torsion measurement on the Rheometrics mechanical spectrometer, with the resin impregnated on a glass cloth specimen. The calibration method is demonstrated by the post cure experiments of TICA, using the time to loss modulus maximum, and the softening parameter R as the calibration parameters.
Properties of polyether‐polyurethane zwitterionomers
Authors: Hwang Kirk K. S. , Yang Chang‐Zheng , Cooper Stuart L.
Published: December 2004

Polyether polyurethanes based on 4,4′‐diphenylmethane diisocyanate (MDI), N‐methyl diethanolamine (MDEA), and polytetraniethylene oxide (PTMO) were synthesized with varying levels of hard segment content. The tertiary amine of MDEA was sulfonated with γ‐propane sultone thereby converting the polyether polyurethane to a polymeric zwitterion. The effect of the chemical composition and the degree of ammonium sulfonation on the extent of phase segregation, and physical properties were studied by differential scanning calorimetry (DSC), dynamic mechanical analysis and tensile testing. It was found that the MDEA chain extender inhibits microphase separation of the polymer in the solid state. As the degree of ammonium sulfonation increases in the zwitterionomers, an improvement of phase separation and domain structure was observed. In addition the tensile properties change dramatically with increasing sulfonate content going from properties characteristic of soft, weak gum rubbers to those of hard, strong thermoplastic elastomers.
The transesterification of bisphenol‐a polycarbonate (PC) and polybutylene terephthalate (PBTP): A new route to block copolycondensates
Authors: Devaux J. , Godard P. , Mercier J. P.
Published: December 2004

In this work, the exchange reaction taking place in molten blends of bisphenol‐A polycarbonate and polybutylene terephthalate was studied. A direct transesterification mechanism catalyzed by titanium residues, present in commercial PBTP, was deduced. The transesterification reaction can be ‐stopped at various levels by additives capable of complexing the titanium catalyst.

This work enhances the possibility of a new approach in macromolecular engineering by directly combining polycondensates in a processing machine such as an extruder.
Some rheological aspects of fracture in thermoforming
Authors: Tsai James T.
Published: December 2004

This paper focuses on several aspects of drawability, including the interactions between material parameters, operating temperatures, and frictional properties of the material. The deep draw process for a molten plastic sheet can be described by a simplified model using the characteristics of the normal stress as a lumped parameter. A rapid evaluation of the draw ratio and mold closing speed can be obtained by systematically drawing a series of three draw ratios. The fracture mode should then be examined to determine the appropriateness of molding temperatures. Therefore the maximum attainable draw ratio can be calculated from the elongational viscosity data. To support the analysis, data is provided on the formation of a cup with polystyrene sheets and using Maxwell extensional model as an example.
Solid‐phase backward extrusion of thermoplastics
Authors: Okine Richard Kafue , Suh Nam P.
Published: December 2004

The backward extrusion process was studied as a means of forming projections and ribs on flat sections of thermoplastic parts. The simplified, open‐die axisymmetric and plane‐strain extrusion cases were mainly considered. The results were applied to the development of a continuous solid‐phase‐forming process. Commercial‐grade polycarbonate (PC), polypropylene (PP), and polystyrene (PS) were used in the investigation. The projection height and extrusion loads in the unconstrained extrusion were measured as a function of the initial temperature of the material, the load hold time, and geometric variables. Cold dies were used in the experiments, and the samples were kept below their melt temperatures. The dimensional recovery of the flange section of the formed samples was also measured as a function of the hold time for given initial temperature and geometric variables. The slab and the upper‐bound methods‐in plasticity analysis were used to theoretically derive the projection heights and forming loads. The degree of correlation between the predictions and the experimental results depended on the estimates used for the frictional factors at the interfaces between the deforming material and the dies.
Molecular weight distribution of polyethylene terephthalate in homogeneous, continuous‐flow‐stirred tank reactors
Authors: Kumar Anil , Gupta Santosh K. , Somu N.
Published: December 2004

Poly(ethylene terephthalate) (PET) formation in homogeneous, continuous‐flow‐stirred tank reactors (HCSTRs) operating at steady state has been simulated. The feed to the reactor is assumed to consist of the monomer bis‐(hydroxyethyl) terephthalate and monofunctional compound (MF1) cetyl alcohol. The overall polymerization is assumed to consist of the polycondensation, reaction with monofunctional compounds, redistribution, and cyclization reactions. At a given time, the reaction mass consists of polyester molecules (Pn), polyester molecules with an ending of molecules of monofunctional compound (MFn), and cyclic polymers (Cn). A mass balance for each of these species in the reactor gives rise to a set of algebraic equations to be solved simultaneously. The MWD calculations show that the redistribution reaction plays a major role and cannot be ignored, This result is in contrast lo the observation for semi‐batch reactors, for which redistribution becomes important when the cyclization reaction is included. For the same residence times of semi‐batch and HCSTRs, the latter gives considerably lower‐number average molecular weight, Nav, and polydispersity index, ρ. However, for the same conversions, the ρ for CSTR is higher. The concentration of the monofurctional compound, [MF1]0, in the feed and the reactor temperature both influence ρ, but the effect is small within the range studied.