bluuebunny/crossref_metadata_2025_split huggingface dataset:
Determination of the rheological properties of thermoplastic composites for compression flow molding
Authors: Törnqvist Ronnie , Sunderland Paul , Månson Jan‐Anders E. 
Published: April 2004

AbstractThe influence of the fiber mat structure and the matrix rheology on the squeeze flow behavior of thermoplastic composites for compression flow molding has been investigated. An analytical model for isothermal squeeze flow has been developed and experimentally confirmed. The model is based on the role of the matrix at local fiber interaction points. The squeeze flow rheology of the composite can be evaluated from the shear flow of the pure matrix as expressed by a Carreau equation, using two micromechanical‐based shift factors. It was found that the fiber mat structure influences the yield stress of the composite, but has a minor influence on the squeeze flow in comparison to the influence of the matrix.
Phthalonitrile‐glass fabric composites
Authors: Sastri S. B. , Armistead J. P. , Keller T. M. , Sorathia Usman 
Published: April 2004

AbstractPhthalonitrile polymers, under development at the Naval Research Laboratory, offer promise as high temperature, high performance composite matrix materials. A fully cured resin shows outstanding thermal stability with no evidence of a glass transition temperature or Tg up to 450°C, good mechanical properties, and is easily processed into void‐free components. Phthalonitrile/glass fabric composite panels have been successfully fabricated by conventional consolidation of prepregged glass and by a more recently developed simplified process, resin infusion molding. Both processes can be used to produce panels with comparable mechanical properties. More important, flammability performance of these composites, evaluated in terms of specific optical density, combustion gases, heat release, and ignitability, excels over other state‐of‐the‐art polymer/glass composites. This finding is significant given that overcoming flammability obstacles has been the main limiting factor for use of composites in marine applications.
The effect of microwave resin preheating on the quality of laminates produced by resin transfer molding
Authors: Johnson M. S. , Rudd C. D. , Hill D. J. 
Published: April 2004

AbstractCycle times in resin transfer molding (RTM) of an unsaturated polyester have been reduced significantly using an in‐line microwave resin preheating system. Microwave preheating lowers the resin viscosity during injection and modifies the thermal age of the resin, potentially influencing the quality of RTM laminates. The tensile properties of RTM laminates have been measured with regard to improved fiber wet‐out by the lower viscosity resin. Degree of cure measurements have been included to establish the effect of microwave preheating on resin conversion within the laminate. Local pressure that develops within the mold during the cure phase can lead to mold deflections. Variations in the laminate thickness associated with these deflections are presented, and the use of microwave resin preheating to reduce these variations is discussed.
Thermoplastic nanocomposites filled with wheat straw cellulose whiskers. Part II: Effect of processing and modeling
Authors: Dufresne Alain , Cavaillé Jean‐Yves , Helbert William 
Published: April 2004

AbstractThe reinforcing effect of cellulose microcrystals, or whiskers, dispersed in a thermoplastic matrix is analyzed. In Part I [Polym. Compos., 17, 604 (1996)], the preparation and the characterization of cellulose whiskers obtained from wheat straw were detailed. Composite films were processed by freeze‐drying and molding a mixture of aqueous suspension of these microcrystals and a film forming latex of poly(Styrene‐co‐ButylAcrylate). Using the same filler and latex, materials were processed by casting and evaporating the mixture of aqueous suspensions. It was found that the reinforcing effect is greater in the latter case. This behavior is ascribed to the sedimentation of the filler during evaporation, evidenced by scanning electron microscopy, wide angle X‐ray scattering, and dynamic mechanical analysis, and to the formation of a network of whiskers governed by a percolation mechanism. The behavior of the composite is modeled by subdividing the sample into layers with different whisker contents lying parallel to the film surface.
Uniaxial, shear, and poisson relaxation and their conversion to bulk relaxation: Studies on poly(methyl methacrylate)
Authors: Lu H. , Zhang X. , Knauss W. G. 
Published: April 2004

AbstractMultiple viscoelastic properties were determined for poly(methyl methacrylate) in the context of examining experimental limitations on deriving other properties from these measurements, specifically time dependent bulk modulus behavior. By means of master curves for uniaxial extension on plate and cylinder specimens, as well as shear (torsion) and Poisson behavior from measurements in the temperature range from −40°C to 125°C, it is established that excessive precision is needed for reliable interconversion of some properties to others. While normal inverse relations (modulus‐compliance) are readily obtained from one set of measurements, bulk (relaxation or creep) properties cannot be derived reliably from other functions and must be determined directly.
Effects of flange/web on the buckling behavior of fiber‐reinforced composite channel section column under axial compression
Authors: Rhee K. Y. , O J. 
Published: April 2004

AbstractThe flange height (bf) to web length (bw) effect on the buckling behavior of a composite column with a channel section was studied. The channel section collumns of bf /bw values 0.3, 0.5, and 0.7 were employed. A theoretical analysis was conducted to decide the dimensions of the columns so that the columns produce as many buckling modes as possible. The buckling mode and critical buckling load for each column were determined from the experiments. Results showed the columns exhibited local buckling and overall buckling (flexural and torsional‐flexural) modes depending on the bf /bw and column length. That is, the flexural buckling occurred only for columns having a bf/bw value of 0.3, while the torsional‐flexural buckling occurred for columns with bf /bw values of 0.5 and 0.7. The results also showed that the local buckling load decreased as bf /bw increased.
Hydrostatically extruded glass fiber reinforced polyoxymethylene. II: Modeling the elastic properties
Authors: Hine P. J. , Wire S. , Duckett R. A. , Ward I. M. 
Published: April 2004

AbstractThis paper describes an investigation into modeling the elastic properties of hydrostatically extruded short glass fiber reinforced polyoxymethylene (POM). The starting material for the extrusion was randomly arranged short glass fibers (25 wt%, average length 150 μm) in an isotropic POM matrix. Extrusion was carried out through a reducing conical die at 15°C below the melting point of the matrix phase (hence the composite was extruded in the solid state), such that after extrusion, preferential alignment along the extrusion direction was developed for both the fibers and for the crystalline fraction of the polymer matrix. The elastic properties of samples, made over a range of extrusion ratios, were measured using the ultrasonic immersion method, a technique that allows a complete set of elastic constants to be determined for a composite. Theoretical predictions for the elastic properties of the oriented extrudates were generated by combining a modification to the theory of Wilczynski to allow for the fibers' being surrounded by an oriented matrix phase, together with the aggregate model of Ward to model the effects of partial orientation of the fiber oriented matrix units.
Model resin permeation of fiber reinforcements after shear deformation
Authors: Lai Chyi‐Lang , Young Wen‐Bin 
Published: April 2004

AbstractIn liquid composite molding processes such as resin transfer molding and structural reaction injection molding, fiber reinforcements are formed with automated processes to conform to the complex shape of the mold cavity. Deformation of the fiber reinforcement during the forming operation can be characterized by factors such as the local surface curvature of the mold and the type of reinforcement. For bidirectional fiber fabrics, simple shear is the major deformation mode in the forming process. Deformation of the fiber reinforcement after being formed to the mold cavity shape results in variations of local fiber content. In addition, the network structure of the fiber reinforcement is also rearranged. This may cause some significant effects on the fiber permeability and result in a mold filling pattern quite different from that expected. Therefore, a good understanding and measurement of the permeabilities for the deformed fiber reinforcements is of great importance. In the flow simulation of the filling process, the success of the prediction depends greatly on the correct values of in‐plane permeabilities. A change of the in‐plane permeability of the fabric after shear deformation must be well understood before an accurate flow simulation can be obtained. This article investigates the permeability of fiber reinforcements in relation to different shear angles. Several flow experiments were conducted on bidirectional woven roving fabrics at different shear angles. Two relevant factors—the ratio of principal permeabilities and the direction of principal axes with respect to the orientation of the fabric—are studied to investigate their variations with respect to shear deformation of the fiber reinforcements. It is found that the angle shift of the principal axes increases with the shear angle. At the same time, the in‐plane permeability ration may decrease with the shear angle.
Effect of surface coverage of silane treated CaCO3 on the tensile properties of polypropylene composites
Authors: Demjén Zoltán , Pukánszky Béla 
Published: April 2004

AbstractPolypropylene (PP) composites were prepared with a constant volume fraction of a CaCO3 filler, which was treated with eight trialkoxy functional silane coupling agents and the routinely used stearic acid, as comparison, The tensile properties of the composites were determined as a function of surface coverage and the chemical composition of the coupling agent. Significant differences were detected in the effect of the silane coupling agents on the tensile properties of the composites studied. They could be classified into groups of reactive, nonreactive and inactive compounds, in accordance with an earlier study. Moreover, tensile properties proved to be very sensitive to surface treatment. Reactive coupling leads to a maximum in tensile strength, while the use of nonreactive agents decreases strength rapidly with increasing surface coverage. The rate of strength decrease slows down above the concentration necessary for the formation of a monolayer coverage. Treatment influences deformability accordingly, it decreases on reactive coupling, while agents with a surfactant effect increase elongation. Amino functional silanes show a strong reactive coupling effect. A trialkoxy derivative of stearic acid, (3‐stearyloxy‐propyl‐triethoxy‐silane), synthesized the first time in our laboratory, has an outstanding surfactant effect; its use increases both the elongation and the tensile strength of the composites. Both characteristics exceed the corresponding properties of the reference composite containing the filler treated with stearic acid.
In‐plane permeability measurements on fiber reinforcements by the multi‐cavity parallel flow technique
Authors: Lundström T. Staffan , Gebart B. Rikard , Sandlund Erik 
Published: April 2004

AbstractThis report discusses the advantages and drawbacks of the multi‐cavity parallel flow technique for permeability measurements. An experimental series with repeated measurements on material from the same roll shows that the repeatability of the technique is very good considering the manufacturing variability of the fabric. The measured standard deviation in the repeatability study is about 10%. It is, however, shown that the permeability can vary considerably‐ between reinforcements of similar geometry. Furthermore, computer simulations were used to estimate the errors when highly anisotropic materials are oriented at an angle to the material principal direction in the parallel flow technique. The conclusion based on the simulations is that the length to width ratio of the cavity should be larger than the anisotropy of the reinforcement for an acceptable error.
Use of genetic algorithms to optimize gate and vent locations for the resin transfer molding process
Authors: Mathur Roopesh , Advani Suresh G. , Fink Bruce K. 
Published: April 2004

AbstractResin infusion processes are finding increasing applications in the manufacture of composite parts that have geometric and material complexities. In such cases, the placement of gates and vents is non‐intuitive and may require expensive repetitive experimentation. Finite element based resin flow simulation codes have been successfully used for modeling and analysis of the mold filling process. Such filling simulations, when coupled with a search algorithm, can also prove useful for optimal design of the filling process. Genetic algorithms (GAs) mimic natural selection and can efficiently “evolve” near‐global optimal solutions from a large number of alternative solutions. In this paper, GAs are used to optimize gate and vent locations for the resin transfer molding process in order to minimize fill times and dry spot formation. A process performance index or cost function is defined that incorporates the fill time and dry spot formation as primary variables. A part having material and geometric complexities was chosen for a case study. A genetic algorithm and mold filling simulations were used interactively to search for optimal gate and vent locations to locate near optimal solutions. The GA was able to find good solutions using less than 1% of simulations of the possible permutations of gates and vents. The case study was also repeated in the presence of recetracking channels. Again, the optimal locations were found by the GA using less than 1% of all possible combinations. Thus, GAs can be efficiently used for minimization of fill time and dry spot formation through optimal location of gates and vents in RTM processes. However, the optimal location will be a function of the cost function, the choice of which depends on the trade‐offs between different factors and the quality of the part desired.
The effects of preforming induced variable permeabilities on the rtm molding flow
Authors: Lai Chyi‐lang , Young Wen‐bin 
Published: April 2004

AbstractForming bidirectional woven fabric into complex shapes consisting of double curvature surfaces leads to rearrangement of the network structure of fiber mats. In this study, the geometric configuration of the fabrics after deformation is modeled using a modified pin‐jointed net model. Deformation of the fabric can result in the local change of the permeability in the reinforcements. In the flow simulation, the prediction of the filling flow highly depends on the correct values of permeabilities. The primary goal of this study is to investigate the effects on filling flow phenomena caused by the deformation of the fiber mats. A general integrated procedure of computer simulation with variable permeabilities for the filling process of arbitrary mold shape is also presented.
Uniaxial elongational viscosity of various molten polymer composites
Authors: Takahashi Tatsuhiro , Takimoto Jun‐ichi , Koyama Kiyohito 
Published: April 2004

AbstractUniaxial elongational viscosity of low density polyethylene (LDPE) that was filled with glass bead, glass flake, talc, or glass fiber was measured. The effect of various inorganic fillers on the strain‐hardening property in elongational viscosity was investigated. The strain‐hardening property of LDPE became weaker by the addition of fillers in the order of glass bead, glass flake, and talc. Glass fiber filled LDPE showed a strain‐softening property. The smaller the particle and the larger the aspect ratio, the weaker the strain‐hardening property. Their causes were analyzed from the two terms, i.e., the relaxation spectrum and the damping function, by Bernstein‐Kearsley‐Zapas (BKZ) model. By the incorporation of fillers, the relaxation modules became larger, and the damping function became stronger in the order of glass bead, glass flake, talc, and glass fiber. Recoverable strain was also measured to understand weaker strain‐hardening properties. The degree of recovery became smaller by the addition of fillers. It was found that the smaller the particles and the larger the aspect ratio, the smaller the degree of recovery. It was concluded that weaker strain‐hardening properties of LDPE composite than that of LDPE are caused by stronger damping function and smaller degree of recovery.
A model to predict the strength of short fiber composites
Authors: Van Hattum F. W. J. , Bernardo C. A. 
Published: April 2004

AbstractThe material properties of short fiber composites, such as modulus, strength and thermal expansion, are greatly dependent on the fiber orientation state in the composite. Although the orientation pattern is often quite complex, models that allow its prediction have been successfully applied in combination with micromechanical models to calculate moduli and thermal properties. This paper describes the derivation of a model to predict the strength of short fiber composites with arbitrary fiber orientation and fiber length distribution based on classical (micro‐) mechanical theories. The predictions are in good agreement with data measured on short fiber composites with different fiber contents.
Local buckling analysis of composite laminate with large delaminations induced by low velocity impact
Authors: Li Guoqiang , Pang Su‐seng , Zhao Yi , Ibekwe Samuel I. 
Published: April 2004

AbstractLarge delaminations can be induced by a low velocity impact on a laminated composite. The local buckling behavior of a laminated composite containing large delaminations is not as well understood as that with small delaminations. This paper presents analytical modeling of the local buckling behavior of a laminated composite containing a large elliptic delamination embedded near the surface and rested partially on a Winkler foundation. A formula for estimating the elastic modulus of the Winkler foundation is also proposed based on an elastic model. It is shown that the buckled shape predicted by the proposed model is similar to the experimentally observed shape. A small portion of the delaminated sub‐laminate between the delamination tip and the inward portion is found to show slight deflections outward. The first buckling mode takes place at higher mode shapes with a more flexible sub‐laminate, larger delamination, and a stiffer Winkler foundation. Increasing the transverse elastic modulus of the laminate within a certain extent, decreasing the size of the delamination, and enhancing the stiffness of the delaminated sub‐laminate are effective in increasing the local buckling resistance.
Electrically and thermally conductive nylon 6,6
Authors: King Julia A. , Tucker Kenneth W. , Vogt Bryan D. , Weber Erik H. , Quan Congling 
Published: April 2004

AbstractIncreasing the thermal and electrical conductivity of typically insulating polymers, such as nylon 6,6, opens new markets. A thermally conductive resin can be used for heat sink applications. An electrically conductive resin can be used in static dissipative and Electromagnetic Interference/Radio Frequency Interference shielding applications. This research focused on adding various carbon based conductive fillers and a chopped glass fiber to nylon 6,6. These materials were extruded and injection molded into test specimens. Tensile tests as well as in‐plane electrical resistivity, in‐plane thermal conductivity, and through‐plane thermal conductivity tests were conducted. One successful formulation consisted of 10% 3.2 mm chopped E‐glass fiber/15% Thermocarb (high quality synthetic powdered graphite)/5% carbon black/70% nylon 6,6 (all % in wt%). For this formulation, the in‐plane electrical resistivity was reduced from 1015 ohm‐cm (neat nylon 6,6) to 15 ohm‐cm. The through‐plane thermal conductivity increased from 0.25 W/mK (neat nylon 6,6) to 0.7 W/mK. The tensile elongation at failure was 1.4%.
Fracture toughness of fiber‐polymer interfaces estimated from single fiber peel tests
Authors: Alimuddin M. A. , Piggott M. R. 
Published: April 2004

AbstractSingle fibers of carbon, glass, and DuPont Kevlar have been embedded to about half their diameters in an epoxy resin and then peeled off. The work of fracture GI can be estimated from the peel force by a simple formula, so long as the fibers are fully elastic during the peel process. This was true with glass, which had GI = 140 Jm−2 and carbon with GI = 60 Jm−2. With Kevlar, inelastic effects obscured the results. The effect of water on the glass epoxy interface was readily shown. Carbon, however, required high temperature water at the interface to cause significant losses. Strong acids at 25°C had about the same effect as water at 90°C. Organic fluids such as kerosene had very little effect. Similar environmental effects could also be detected with Kevlar, though further work is required here to separate out the inelastic contribution.
Fluid flow reconstruction modeling with application to liquid molding processes
Authors: Walsh Shawn M. , Freese Colin E. 
Published: April 2004

AbstractA unique mathematical reconstruction technique is coupled with discrete experimental flow front detection data to provide continuous fluid flow analysis. A fully finite element based methodology for the construction of surfaces from scattered and sparse data is presented and applied to experimental observations derived from a new class of sensors enlisted as monitors of the resin transfer molding (RTM) process. The basic numerical technique is shown to yield interpolant models capable of flow front position and fluid flow velocity reconstruction. The extrapolative/predictive performance is enhanced through the introduction of a new hybrid procedure. Two‐dimensional and quasi‐three‐dimensional examples are used to demonstrate the effectiveness of the techniques.
A new fabrication technique utilizing a composite material applied to orthopedic bracing
Authors: Morrison Bryan J. , Creasy Terry S. , Polliack Adrian A. , Fite Richard 
Published: April 2004

AbstractAn orthopedic brace fabrication and fitting technique was explored as a rapid and cost‐effective alternative process to polypropylene fabrication. Other potential benefits could also be reduced weight and lower profile with the added advantage of allowing profile and firmness variation where desired. The novel process concept is based on the finding that a partially cured composite remains somewhat malleable. Clinicians conceivably can adjust an ankle‐foot brace to the patient directly before fully curing the brace. Flexure experiments assessed both the partial curing concept and the ability to post‐form. Results indicate that partial curing followed by ambient or heated adjustments and full curing compromises the strength by no more than 7%. However, adjustments resulted in a net displacement change averaging only 50% of that desired when heat was applied. It is also possible to post‐form the fully cured brace. This compromises the material strength significantly in the deformed area, but it may be feasible for minor adjustments where applied loads are not extreme. This research demonstrates the feasibility of the process as an alternative to current techniques, especially for patients needing a strong brace.