bluuebunny/crossref_metadata_2025_split huggingface dataset:
Resin transfer molding with powder‐coated preforms
Authors: Shields K. , Colton J. 
Published: May 2005

AbstractIncomplete fiber wetting in a resin transfer molded composite may result in poor surface finish, high void content, and reduced mechanical properties. This work studied the use of tows that are precoated with a powdered version of the liquid molding resin (towpregs). The goal is to see if such preforms improve the final part properties because of better fiber wetting. Hercules 12K AS‐4 fibers and PR500 (liquid) and PS500 (Powder) resins (3M) were used to make fabrics from towpregs containing 50 wt% total resin (liquid and powder combined). The powder fractions were 0, 13, 21, 50 wt%. Samples were resin transfer molded from preforms made from the towpreg fabrics. Results showed that samples molded with powder‐coated preforms had improved surface finishes and reduced void contents (1.4 vs. 5%), but that the mechanical properties were not improved (transverse moduli of ∼ 7.8 Gpa and axial moduli of ∼ 100 Gpa), probably because of defects inherent in the hand‐woven towpreg fabric that was used.
Controlled interactions in cellulose‐polymer composites. 1: Effect on mechanical properties
Authors: Felix Johan M. , Gatenholm Paul , Schreiber H. P. 
Published: May 2005

AbstractThe surface properties of cellulose fibers have been modified by heat treatment, by silane coupling agents, and by maleated polypropylene grafts. The effectiveness of these methods has been evaluated by electron spectroscopy (ESCA), by contact angle measurements, and by inverse gas chromatography. The latter analyses yielded information on the fibers' acid/base interaction potential. Cellulose was found to be amphoteric, with prevalent acidic properties. Heat and chloro‐silane treatments accentuated acidity, while amino‐silane treatment produced net basicity in the fiber surface. Modification with maleated polypropylene reduced specific interactions and converted the fiber to a predominantly dispersion‐force solid. The modified fibers were used in composites with polypropylene (neutral), polystyrene (base), and chlorinated polyethylene (acid) as matrix. Stress/strain and dynamic mechanical parameters were found to vary with acid/base interactions between polymer and fiber, significant improvements being noted in elastic and storage moduli, in tensile strength and elongation. In polypropylene, properties were unaffected by acid/base considerations. Acid/base forces, not necessarily dominant, merit consideration in the design of surface modification strategies intended to optimize composite mechanical properties.
Particulate interlayer toughening of dicyanate matrix composites
Authors: Zeng Shangying , Hoisington Mark , Seferis James C. 
Published: May 2005

AbstractToughening of dicyanate matrix composites with particulate‐modified resin‐rich interlayers was investigated in this study. Specifically, the cure behavior, viscosity, and fracture toughness of the modified dicyanate systems were analyzed. Creation of a layered composite structure showed no improvement in Mode 1 interlaminar fracture toughness (GIc), but greatly increased the Mode II interlaminar fracture toughness (GIIc). Furthermore, the concentration of modifier particles in the interlayer resin was found to directly affect the toughness improvement and fracture path.
Influence from process parameters on void formation in resin transfer molding
Authors: Lundström T. Staffan , Gebart B. Rikard 
Published: May 2005

AbstractThe influence of different process variables on the void content in resin transfer modling (RTM) has been investigated experimentally. The moldings were made in a flat mold filled by a parallel flow from one edge of the laminate to the other. The viods were found concentrated in a narrow region close to the ventilation side of the laminate. The void volume fraction in this region was almost constant and dropped over a short distance to basically no voids in the rest of the laminate. Micrographs from cross sections in different directions revealed that the voids were of two different types, long cylinderical bubbles inside the fiber bundles. An efficient way of reducing the void content was to use vacuum assistance during mold filling. This technique was benefical both for the magnitude of the void content and for the extent of the void region. The void content with the highest level of vacuum assistance (≈︁ 1 kPa absolute pressure), was practically negligible. Strong indications for void generation by mechanical entrapment at the flow front was found. The lowering of the void content with vacuum assistance can be interpreted as aresult of compression of voids when the vacuum is released and a higher mobility of voids created at a lower pressure.
Formation and elimination of voids during the processing of thermoplastic of matrix composites
Authors: Leterrier Y. , G'Sell C. 
Published: May 2005

AbstractThe mechanisms of void formation and elimination during the stamping process of a polypropylene/glass fiber composite have been infestigated as a function of temperature, pressure, and time. Experiments were performed in a temperature and pressure controlled chamber, equipped with a rapid cooling facility. Samples of the composite as well as model polypropylene specimens containing calibrated voids were held at 200°C at different levels of hydrostatic pressure (1,10,100, and 300 bars), for a period of either 1 or 10 min. The speciments were subsequently characterized by denstiy measurements and morphologival observation. It was shown that: i) the expansion of the composite observed during the heating at 200°C under atmospheric pressure is largely induced by the gases previously dissolved in the polymeric matrix, ii) the rapid increase of the pressure during the stamping process leads to the closing of voids and, iii) the final holding under high calculation of void growth and shrinkage is in agreement with the morphological observations.
Interfacial adhesion and failure modes in single filament thermoplastic composites
Authors: Pisanova E. V. , Zhandarov S. F. , Dovgyalo V. A. 
Published: May 2005

AbstractThe single filament composite (SFC) test has been uses to investigate the adhesion of carbon and glass fibers to thermoplastic matrices. A new modification of the test is proposed, consisting of SFC specimens stretched until the neck formation is complete. This makes the measuring of fiber fragment lengths much easier and allows a wider class of matrices to be investigated. The adhesion between fiber and thermoplastic matrix is strongly dependent on the contact forming conditions. With increased time of thermal treatment, interfacial bonding is improved and the failuere mode is changed. In the case of por fiber‐mitrix adhesion, interfacial failure occurs. With an increase in interfacial shear strength, the martix cracks perpendicular to the fiber at the fiber breaks.
Predicting shrinkage and warpage of fiber‐reinforced composite parts
Authors: Tseng Shi‐Chang , Osswald Tim A. 
Published: May 2005

AbstractOne major problem that arises in the design of plastic parts, especially those that are fiber reinforced, is the change of shape and dimension as a result of shrinkage and warpage. These material inhomogeneities are caused by flowinduced fiber orientation, curing, poor thermal mold lay‐out, and other processing conditions. This paper presents a simulation that predicts shirnkage and warpage of 3‐D compression molded fiber reinforced composite parts. The simulation represents the structure with the 3‐noded shell elements used in mold filling simulations. The calculated results indicate that fiber orientation strongly affect the final properties, which vary with different chage locations, have a significant effect on warpage. Unsymmetric curing, caused by uneven mold temperatures, could lead to a thermal moment that could possibly help reduce warpage.
In‐plane permeability measurement and analysis in liquid composite molding
Authors: James Wang T. , Wu C. H. , James Lee L. 
Published: May 2005

AbstractThis work presents methods to measure and analyze in‐plane permeabilities of various fabric reinforcements. The principal flow directions need to be determined first by conducting flow visualization. From the flow front pattern, the ratio of the permeabilities in the two principal directions can be determined. The pressure and the flow rate relationship from both radial and unidirectional flow measurement methods are then used to calculate the values of the permeabilities. By the use of the unidirectional flow measurement method, the edge flow effect can also be estimated.
Trans‐plane fluid permeability measurement and its applications in liquid composite molding
Authors: Wu Cheng‐Hsien , James Wang T. , James Lee L. 
Published: May 2005

AbstractThis work discusses tow independent methods to measure and analyze the trans‐plane fjuid permeability of various fiber reinforcements. In the unidirectional flow method, the measured injection pressure and flow rate, together with a one‐dimensional Darcy's law were used to calculate the trans‐plane permeability of fiber mats was independent of flow rate only at low injection pressure. Flow‐induced fiber mat permeability change occurred when the injection pressure exceeded the clamping pressure. Measured permeability in conjunction with a three‐dimensional mold filling computer program was used to simulate the effect of stacking sequence for a combination of different fiber mats on the mold filling pattern. Finally, a method is proposed to simplify the simulation of a three‐dimensional flow through the fiber perform.
In situ sensor monitoring and intelligent control of the resin transfer molding process
Authors: Kranbuehl D. E. , Kingsley P. , Hart S. , Hasko G. , Dexter B. , Loos A. C. 
Published: May 2005

AbstractAn intelligent closed‐loop expert control system has been developed for automated control of the resin transfer molding process of a graphite fiber preform using an epoxy resin, E905L. The sensor model system has been developed to make intelligent decisions based on the achievement of landmarks in the cure process, such as full preform impregnation, the viscosity, and the degree of cure of the resin rather than time or temperature. In‐situ frequency dependent electromagnetic sensor (FDEMS) and the Loos resin transfer model are used to monitor and control the processing properties of the epoxy resin during RTM impregnation and cure of an advanced fiber architecture stitched preform. Once correlated with viscosity (η) and degree of cure (α), the FDEMS sensor monitors and the RTM processing model predicts the reaction advancement of the resin, viscosity and the impregnation of the fabric. This provides a direct means for monitoring, evaluating, and controlling intelligently the progress of the RTM process in situ in the mold throughout the fabrication process and for verification of the quality of the composites.
An electrostatic powder spray process for manufacturing thermoplastic composites
Authors: Ramani Karthik , Woolard Daniel E. , Duvall Mark S. 
Published: May 2005

AbstractManufacture of thermoplastic composites is expensive because of the difficulty of impregnating the resin into the fibers. Powder processing shows great promise as an impregnation technique for cost‐effective manufacturing. This paper discusses an electrostatic powder spray impregnation technique that uses glass fibers. A geodesic fiber spreader is used to spread the fibers locally in the region of maximum powder deposition. A negative corona electrostatic spray gun is employed to charge and direct the powder for coating both sides of the spread fiber tow. The process has been used to impregnate glass fibers with poly(aryl ether ketone ketone) powder. The effect of the powder mass flow, corona voltage, and fiber tow velocity on powder deposition has been investigated. Particle image velocimetry is utilized to determine particle velocities. Compression molded panels have been produced and tested in three point bending.
Strain recovery of polyester and nylon 66 monofilaments under various temperature histories
Authors: Lunn A. C. , Lee B‐L. , Yannas I. V. 
Published: May 2005

AbstractStrain recovery of polyester and nylon 66 monofilaments, following stress relaxation at constant strain, has been measured under two types of temperature history. In the first (experiments here called type A), the monofilament, extended at an elevated temperature, was held at constant strain at that temperature, and then air‐quenched to room temperature while still under stress. The stress was later removed with the fiber at ambient temperature, and the recovery from strain determined. In the second (experiments of type B), the monofilament was also extended at an elevated temperature, but it was then allowed to recover, under zero load, at the same temperature, prior to quenching. A cylindrical heater is described which surrounded the fiber specimen and which could be removed suddenly to permit rapid air quenching of the specimen. Recovery was characterized by the percent of applied strain which was recovered 100 sec after load removal. The percent recovery, in type A experiments, decreased to low values with increasing stretch temperature. Recovery in type B experiments, however, was markedly different, and showed a minimum value at stretch temperatures in the vicinity of the glass transition. At higher temperatures, recovery was high, but it decreased rapidly as TM was approached due to the onset of viscous flow. There was thus a discontinuity in recovery behavior as the time of quenching increased through the time of unloading (transition between type A and type B conditions). The results were interpreted to show that the achievement of good heat setting (poor recovery) is critically dependent on the temperature of the fiber during both stretching and recovery periods.
Flow analysis network (FAN)—A method for solving flow problems in polymer processing
Authors: Tadmor Z. , Broyer E. , Gutfinger C. 
Published: May 2005

AbstractA finite element method is proposed for solving two dimensional flow problems in complex geometrical configurations commonly encountered in polymer processing. The method is applicable to flow in relatively narrow gaps of variable thickness and any desired shape. It was developed for analyzing flow in injection molding dies and certain extrusion dies. The fluid can be any non‐Newtonian fluid which is incompressible, inelastic, and time independent. The flow field is divided into an Eulerian mesh of cells. Around each node, located at the center of the cell, a local flow analysis is made. The analysis around all nodes results in a set of linear algebraic equations with the pressures at the nodes as unknowns. The simultaneous solution of these equations results in the required pressure distribution, from which the flow rate distribution is obtained. Solution for the isothermal Newtonian flow problem is obtained by a one‐time solution of the equations, whereas solution of a non‐Newtonian problem requires iterative solution of the equations.
High modulus/high strength polyethylene obtained by high‐pressure injection molding
Authors: Kubáut J. , Månson J.‐A. 
Published: May 2005

AbstractIncreasing the nominal injection pressure up to 500 MP a improves the mechanical properties (modulus and strength) of injection‐molded high‐molecular‐weight high‐density polyethylene substantially. By a proper combination of barrel and mold temperature, the modulus of the molded parts (test bars) may be increased at least eight times compared to parts molded at 100 MPa. This improvement is partly due to the formation of high‐strength crystalline modifications of the polyethylene induced by flow and pressure. The extent to which these structure modifications occur in the samples molded at various conditions has been determined by thermal analysis (DTA). When increasing the thickness of the samples, a sharp reduction of the modulus and strength was observed, even though the concentration of the crystalline high‐strength phase was higher. An explanation of this effect in terms of the relaxation of the tie‐molecules connecting the crystallites is suggested.
Effect of morphology on stress relaxation of polypropylene
Authors: Attalla G. , Guanella I. B. , Cohen R. E. 
Published: May 2005

AbstractSamples of isotactic polypropylene having different morphologies and crystallinities were prepared and subjected to stress‐relaxation experiments at different levels of strain. The relaxation moduli were determined in the range of temperature between – 20 and 40°C over a period of time from 1 to 1000 seconds. Using the time‐temperature superposition principle, the activation energy values of the shift factors aT were determined and the master curves were obtained for the various structures. Increasing crystallinity and/or crystalline aggregate size increases the relaxation modulus of the material and changes both shape and location of the spectrum of relaxation times so that no simple method can be found to correlate the various master curves.
Submicron patterns in substituted polystyrene resists by focused‐ion‐beam lithography
Authors: Brault R. G. , Kubena R. L. , Jensen J. E. 
Published: May 2005

AbstractSubmicron lines in negative working, substituted polystyrene resists by focused‐ion‐beam lithography were demonstrated. These features were transferred into an underlying molybdenum layer by plasma etching using the resist as an etch mask, with the minimum continuous line having a width of 0.20 μm.
Poly(methyl α‐trifluoromethylacrylate) as a positive electron beam resist
Authors: Willson C. Grant , Ito Hiroshi , Miller Dolores C. , Tessier T. G. 
Published: May 2005

AbstractA mechanistic hypothesis is presented which explains the radiation chemistry of poly(methyl α‐haloacrylate)s. In order to test the hypothesis poly(methyl α‐trifluoromethylacrylate) PMTFMA was synthesized together with copolymers of methyl methacrylate (MMA), and the α‐trifluoromethyl analog. The mechanistic hypothesis predicts that PMTFMA should have a higher G scission than PMMA and that it should have no crosslinking propensity. This prediction was verified by experiment. Imaging of PMTFMA as a positive e‐beam resist is also presented. The new material is a more sensitive resist than PMMA.
Chemical amplification in the design of dry developing resist materials
Authors: Ito Hiroshi , Willson C. Grant 
Published: May 2005

AbstractA new resist system is described which undergoes spontaneous relief image formation. The resist is formulated from end capped poly(phthaladehyde), PPA, and a cationic photoinitiator such as a diaryliodonium or triarylsulfonium metal halide. The extreme sensitivity of the resist is the result of designing for chemical amplification. The desired amplification results from the fact that photolysis of the sensitizer generates acid which catalyzes main chain cleavage of the polyaldehyde. The uncapped polymer is thermodynamically unstable with respect to reversion to monomer at room temperature so a single acid catalyzed scission results in complete depolymerization to volatile monomer. A single radiochemical event is thereby amplified in the sense that it produces an enormous number of subsequent chemical transformations. PPA/onium salt resist films are so sensitive that exposure to low doses of e‐beam, X‐ray or ultraviolet radiation results in complete self development without post‐exposure processing of any kind. The exposed area simply vaporizes.
Mathematical modeling of melting of polymers in a single‐screw extruder
Authors: Elbirli B. , Lindt J. T. , Gottgetreu S. R. , Baba S. M. 
Published: May 2005

AbstractThis paper addresses the apparent controversy surrounding the role of the solid bed mechanics in the Maddock melting mechanism. It is demonstrated that the inability of the melting models based on the freely deformable solid bed concept to predict accurately the pressure gradients in the melting zone is not exclusively due to the highly simplified isothermal Newtonian treatment of the melt pool as presumed previously. This study has shown that when using a non isothermal non‐Newtonian flow model for the melt pool, the freely deformable solid bed concept still results in unrealistically low pressure gradients while it may give good predictions of the melting rates. To the contrary, when a rigid solid bed is assumed, the pressure predictions tend to represent the experimental data more closely, whereas the theoretical melting rates seems to become less realistic. In view of the fact that both the freely deformable and the rigid solid bed concepts show such inconsistencies, it has been concluded that the mechanics governing the solids and melt transport in the melting zone require some additional examination, most notably, the influence of the constitutive behavior of the solid bed and of the cross‐channel melt circulation around the solid bed, and possibly of the melting kinetics for semicrystalline polymers.
Wood fibers as reinforcing fillers for polyolefins
Authors: Woodhams R. T. , Thomas G. , Rodgers D. K. 
Published: May 2005

AbstractWood pulp fibers possess strength and modulus properties which compare favorably with glass fibers when the differences in fiber densities are considered. Softwood pulp fibers with fiber aspect ratios near 100 are readily dispersed into high‐density polyethylene or isotactic polypropylene with the aid of carboxyic dispersing agents to form mixtures containing 50 weight‐percent wood pulp which can be readily injection molded. The mechanical properties of the molded specimens were similar for all types of pulp including Kraft (bleached and unbleached), mechanical and chemical‐mechanical pulps, waste pulps, and reclaim newspapers. Comparisons of the stiffness/weight efficiencies revealed that pulp composites equal or exceed the stiffness of most traditional materials of construction including steel, aluminum, glass‐fiber composites, and talefilled polyolefins, while retaining a major material cost advantage. The measured strength values of the pulp composites were less than the theoretically predicted values due to the presence of voids created by the formation of volatiles during processing. Mechanical pulps which were available in dry form were preferred because of lower cost and ease of handling. Wood fibers are non‐abrasive so that relatively large concentrations may be incorporated into polyolefins without causing serious machine wear during mixing and fabrication.
Enhancement of melting through corotating disk processors
Authors: Mekkaoui Abdallah M. , Valsamis Lefteris N. 
Published: May 2005

AbstractMelting mechanisms in the corotating disk processor (DISK‐PACK) Farrel Company trademark.
are presented and discussed. This polymer processor consists of disk elements attached to a shaft with the entire assembly fitted into a housing. All polymer processes are induced by the drag action of the jointly moving disks, compared to only one moving surface characteristic of single screw extruders. Experiments carried out in a 150 and 7‐1/2″ diameter corotating disk polymer processors indicate that polymers can be melted by either of two mechanisms: The drag melt removal mechanism and the dissipative mix‐melting mechanism. The former mechanism occurs when a molten film is constantly removed from both sides of the solid bed, while the latter takes place throughout a system of molten and solid particulate mixture occupying the space between the disks. A theoretical model is presented for the drag melt removal (DMR) mechanism in such corotating disk polymer processors. The additional capability to induce a dissipative mix‐melting (DMM) mechanism can increase the melting rate obtained from conventional mechanism by 300 percent and lower the exit melt temperature substantially. Melting rates over a broad range of conditions are presented for a variety of polymers.