bluuebunny/crossref_metadata_2025_split huggingface dataset:
The gel‐phase modulus of high‐impact polystyrene from dynamic mechanical spectroscopy
Authors: Kefalas V. , Theocaris P. S. , Kontou E. 
Published: December 2004

AbstractHigh‐impact polystyrene (HIPS) constitutes a mechanically attractive composite, consisting of a glassy matrix and a rubberlike particle phase (gel phase). Dynamic mechanical spectroscopy was performed for the polystyrene matrix for three different types of HIPS as well as for the concentrated gel‐phase material, at the vicinity of the respective glass‐transition temperatures (Tg). An approximate estimation of the gel‐phase modulus was attempted by using known mechanical models. A comparison with experiments was also made. The modulus of the composite was found to be lower than the theoretical lower bound for particulate composites. This was attributed to a separate phase between gel particles and the matrix. A diffusion‐type variation of the modulus of this mesophase layer was estimated, and a correlation between calculated fitting parametric exponents and impact behavior of HIPS was found. Moreover, the Tgs of the materials under investigation were also measured with two independent methods. It was found that all types of HIPS presented higher Tgs than the pure matrix by 5 to 10°C with the highest Tg found being that of the gel‐enriched material. The shift of Tgs to higher temperatures was attributed to an eventual increase of the effective cross‐link density of the matrix because of grafting.
Non‐isothermal crystallization of poly(etheretherketone) aromatic polymer composite
Authors: Cebe Peggy 
Published: December 2004

AbstractNon‐isothermal crystallization kinetics of poly(ether‐etherketone), PEEK, in the presence of carbon fibers has been studied for APC‐2 composites. Samples of APC‐2 PEEK composite were cooled from the melt at rates ranging from −1 to −20°C/min. A differential scanning calorimeter was used to monitor heat flow during the non‐isothermal crystallization. Effects of cooling rate on crystallization temperature, degree of crystallinity, and conversion rate were studied. We show that the Ozawa analysis fails to provide an adequate description of the non‐isothermal crystallization process in composite PEEK. A modified Avrami analysis was used to describe crystallization kinetics. For the composite material, the change from the primary kinetics of free crystal growth to slower secondary kinetics occurred at about 50 percent relative conversion for all cooling rates. Non‐isothermal crystallization in APC‐2 composite PEEK can be characterized by higher initiation temperature, higher heat flow maximum temperature, and greater relative conversion by primary processes when compared to 450G neat resin PEEK crystallization.
Experimental determination of thermal and adhesion stress in particle filled thermoplasts
Authors: Vollenberg Peter , Heikens D. , Ladan H. C. B. 
Published: December 2004

AbstractThe phenomena of dewetting in filled thermoplastics were studied by light microscopy and were correlated with variations in the slope of stress‐strain diagrams in constant strain rate tests. In such diagrams, kinks in the plots were found to correspond to the dewetting stress. The corresponding local stress at a filler particle is then equal to the sum of the thermal compressive stress and the adhesion stress. It was shown that the adhesion stress was proportional to the reciprocal root of the particle radius. Also, values of dewetting stress predicted for inorganic particles with radii smaller than 2–4 micrometers are higher than the stresses at which crazes and shear‐bands are formed near such particles, indicating that dewetting will not occur in those cases, and adhesion aids may be superfluous.
Processing sequence and the properties of vinyl compounds
Authors: Trujillo Eleana , Richard C. , Schreiber H. P. 
Published: December 2004

AbstractAcid‐base interaction parameters were measured by inverse gas chromatography over broad temperature ranges for Poly(vinyl chloride), plasticizer, and CaCO3 fillers. Mixing was performed by three routes. In one, all components were added simultaneously, while in others two of the components were premixed, the third ingredient being added subsequently. Mixing was carried on to equilibrium torque readings. The energy requirement for mixing was found to depend on the interaction balance among the components, and to vary with the procedure selected. Minimum requirement was associated with the simultaneous introduction of all ingredients. Higher energies were needed in sequential mixing schemes, presumably because equilibrium partitioning of components was hindered in these instances. Initial mechanical properties of the compounds did not vary greatly with preparation procedure, but upon aging, mechanical property variations became quite evident. Component repartitioning, driven by shifting interaction balances at aging and at test (room) temperatures are cited as responsible. The kinetics of attaining equilibrium mechanical properties also were found to vary with mixing procedure and to respond to the interaction balance concept.
Fatigue crack propagation in mica‐filled polyolefins
Authors: Allard R. C. , Vu‐Khanh T. , Chalifoux J.‐P. 
Published: December 2004

AbstractEdge notched samples of polypropylene (PP) and high‐density polyethylene (HDPE) containing different mica concentrations were tested in mode I tensile loading. Crack growth was approximated by a non‐linear regression of exponential form using statistical software (SAS). Characterization of fatigue crack propagation (FCP) was made using the Paris‐Erdogan law. The crack front in PP was preceded by a wide plastic zone in which craze developed, leading to a discontinuous crack growth. Using spline functions, a margin between maximum and minimum FCP rates, recorded during the crack progression, is presented along with the average FCP rates. It is shown that mica‐reinforced PP samples exhibit higher FCP rates than unfilled PP. In HDPE, mica reduces FCP rates resulting in a higher resistance to fatigue crack propagation. Effect of test frequency is presented for unfilled polymers and 10 percent mica concentration by weight in both matrices. An increase in the test frequency has no significant effect on FCP rates for both raw and mica‐reinforced PP. Unfilled and mica‐filled HDPE show noticeable decrease in FCP rates with increasing frequency.
Long‐fiber‐reinforced thermoplastic matrix composites by slurry deposition
Authors: Hiscock D. F. , Bigg D. M. 
Published: December 2004

AbstractA process for producing long‐fiber‐reinforced thermoplastic matrix composites is described. This process, based on papermaking technology, consists of depositing a mixture of a polymeric powder and reinforcing fibers from an aqueous slurry. The degree of homogeneity of the mixture and the subsequent ability to handle the dried sheet have been significantly improved by the addition of less than 5% pulp fibers, based on solids concentration, to the slurry. The dried sheet is then consolidated into a composite sheet with a continuous matrix phase by the application of heat and then pressure. Tensile properties and the degree of reinforcement efficiency of composites produced by this process have been shown to be comparable to those produced by melt impregnation techniques.
Expression of activity of the filler surface of composites in inverse gas chromatography
Authors: Cigánek M. , Dressler M. 
Published: December 2004

AbstractA new way is introduced to express the interaction coefficient characterizing the surface activity of fillers. The interaction coefficient is a parameter showing how many times greater a specific interaction of a testing solute with a filler surface is than a nonspecific interaction of a hypothetical alkane with the same vapor pressure. A selectin of testing solutes for the determination of the interaction coefficient is discussed. Due to a high surface activity of the studied fillers for polyolefine composites, less polar solutes (furan, dichloromethane, trichloromethane, and benzene) have been selected to study these fillers. New evaluation coefficients of acidity, basicity, and acidobasicity are proposed for a rapid activity determination of a filler surface. These coefficients can be determined from a single chromatogram of the testing solutes. The surface activity of various fillers (calcium carbonate, talc, magnesium hydroxide), as expressed by the interaction coefficient, differs so much that even the differences of surface activities in one filler type (calcium carbonate), dependent on the origin or arrangement, are conclusive.
Interfacial interactions and properties of filled polymers. II: Dispersion of filler particles
Authors: Boluk M. Y. , Schreiber H. P. 
Published: December 2004

AbstractThe specific interaction characteristics and the inherent agglomeration of variously surface coated rutile pigments have been assessed, respectively, by inverse gas chromatographic and powder rheological methods. Standardized methods were used to disperse the pigments in polyethylene and chlorinated polyethylene. Measurements were made of energy requirements for dispersion and of the quality of dispersion attained. It was found that in the non‐polar polyethylene matrix, dispersion processes depended on the strength of pigment agglomerates, but not on the specific interaction potential of the solids. Conversely, in the acidic chlorinated polyethylene, acid/base interactions influenced dispersion but the process was independent of inherent pigment agglomeration.
Weld‐line characteristics in short fiber reinforced thermoplastics
Authors: Vaxman A. , Narkis M. , Siegmann A. , Kenig S. 
Published: December 2004

AbstractFibers can greatly improve the mechanical properties of polymers but may also severely weaken molded parts at their weld‐line compared to their bulk strength. The tensile properties and fiber orientation of injection and compression molded fiber reinforced Noryl and polypropylene samples with and without a weld‐zone were studied. Distinct differences in structure and mechanical properties of weld‐containing and weld‐free samples were identified. In unfilled Noryl and unfilled polypropylene, the presence of a weld‐line was found to only have a small effect on the tensile strength and modulus, while in the corresponding fiber reinforced systems, orientation of the fibrous reinforcement parallel to the weld‐line caused a significant reduction of the tensile strength compared to the weld‐free products. The strength ratio of welded and unwelded specimens was found to decrease with increasing fiber concentration. Quantitative determination of the glass fiber orientation distribution within the weld‐line region and in the bulk was carried out by analyzing photomicrographs of polished sections at desired locations.
The effects of molding conditions on the surface composition of sheet molding compound
Authors: McEwen D. J. , Newbould J. 
Published: December 2004

AbstractAn improved internal reflection infrared spectroscopy (ATR) technique (1) has been found to be effective for measuring the relative concentrations of polyester and polystyrene (resin) and calcium carbonate filler on sheet molding compound (SMC) surfaces. The technique has been used to determine the effect of molding conditions on the surface compositions of three commercial SMC materials. The surface compositions of two of the materials, of the same formulation but obtained from different sources, were the same and were unaffected by molding conditions. The surface of the third material (or a different formulation) was found to have substantially less resin than the first two materials. The surface composition of the third material varied with molding conditions, the greatest uniformity being obtained with high molding temperatures and pressures. This study has shown that the ATR technique is suitable for determining the relative surface compositions of SMC formulations. This method will be used to correlate the SMC surface composition to SMC properties, such as surface appearance, paintability, and adhesive bond durability.
Instrumented thermoforming of advanced thermoplastic composites. III: Relative performance of various prepregs in forming double curvature parts
Authors: Dutta A. , Cakmak M. 
Published: December 2004

AbstractThermoforming of a double curvature hemispherical cap‐shaped part from different continuous carbon fiber‐reinforced thermoplastic composite prepregs has been investigated. A novel three‐piece matched die mold was used for shaping the prepregs directly from 16‐ply unconsolidated lay‐ups. For poly(ether ether ketone) (PEEK)‐based prepregs, PEEK/graphite fiber unidirectional tapes and commingled knitted three‐dimensional fabric yielded parts that possessed good shape conformity and were free of any major delamination. Encouraging results were also obtained for modified polysulfone (PXM‐8505) based unidirectional fabric as well as PEEK/graphite knitted bidirectional fabrics. Several other prepregs performed rather poorly in forming acceptable quality parts. Fiber alignment was found to be better for fabric prepregs than unidirectional tapes. Both stretching and “draw in” of the material occur during deformation, even though the relative contribution depends strongly on the prepreg form. Our thermoforming studies suggest a cycle time of 10 min or less to form good quality parts, which is an attractive feature, considering that cycle times are typically several hours for conventional thermosetting resins.
Mechanical properties and fracture of an amorphous metallic ribbon/thermoplastic matrix composite with low volume fraction of reinforcement
Authors: Varin R. A. , Ruutopold A. 
Published: December 2004

AbstractComposite specimens with polypropylene matrix containing up to 1.8 percent volume fraction of amorphous metallic ribbons with the interfacial shear strength ∼0.7 MPa were fabricated by hot compaction under 10 MPa pressure. Their tensile properties and fracture behavior were investigated. It is found that within the investigated range of the volume fraction of reinforecement the composite fracture strength is close to the rule of mixtures predictions. Two types of fracture, matrix and ribbon controlled, are observed. The experimental values of the composite elastic modulus are also close to the rule of mixtures predictions.
Studies on the distribution of reinforcement in composites by energy dispersive analysis of X‐rays
Authors: Rao K. V. , Pandey G. C. , Xavier S. F. , Sharma Y. N. 
Published: December 2004

AbstractA method has been developed for studying the distribution of fillers and reinforcement in polymer composites by energy dispersive analysis of X‐rays (EDAX). Conventional methods for such studies are based on the morphological examination of the contrast in the micrographs, which indicates the presence and distribution of reinforcement in a matrix. However, in case of hybrid composites, where two or more fillers of similar morphology are present, the conventional methods fail. The approach described here overcomes this limitation and provides a new semiquantitative method of identification of fillers in composites, especially those containing two or more fillers of similar morphology.
In‐situ composites: Evaluation of the adhesion between the thermoplastic matrix and the fibers of liquid crystalline polymer
Authors: Carfagna C. , Netti P. A. , Nicolais L. , Dibenedetto A. T. 
Published: December 2004

AbstractMechanical properties of fiber reinforced composites depend on the formation of stable adhesive bonds between the constituents. In order to evaluate quantitatively the adhesion between liquid crystal polymer (LCP) fibers and a thermoplastic matrix of polycarbonate, the single fiber composite test (SFC), utilized for testing glass or carbon fiber composites, has been used. Neither chemical nor physical interaction has been found: the PC and LCP phases are completely incompatible. However, a mechanical friction between PC and LCP was observed during the drawing of the sample when the neck of the matrix started.
Thermoplastics composites with ductile fiber coatings based on UHMWPE: A study on short fiber GR nylon 6
Authors: Mascia L. , Kinsella M. 
Published: December 2004

AbstractGlass microscope slides were initially used to develop a technique for bonding UHMWPE films on to glass and polyamides respectively, as well as to provide a simple physical model for interlayered fiber composites. Further experiments were carried out on glass fibers coated with UHMWPE from a xylene solution, in order to evaluate the applicability of the above technique and of the physical model in actual composite systems. Although great difficulties were encountered in achieving a well boned uniform coating on the glass fibers the results have confirmed the viability of the approach: the impact strength of compression molded glass reinforced Nylon plaques, measured with an instrumented falling weight apparatus, was increased considerably with only a corresponding small loss in flexural modulus. Dynamic mechanical analysis results indicate that a UHMWPE interlayer substantially increases the tan δ of the short fiber composite over a wide temperature range, albeit with some reduction in modulus.
A comparison of the unidirectional and radial in‐plane flow of fluids through woven composite reinforcements
Authors: Parnas Richard S. , Salem Andrew J. 
Published: December 2004

AbstractThe in‐plane flow of fluids through dense fibrous woven reinforcements was studied to aid the development of constitutive models for use in simulations of composite fabrication by resin transfer molding. As a first part of this effort, both one‐dimensional and radial flow experiments were conducted with Newtonian fluids in several woven glass fabrics. Analysis of the one‐dimensional flow experiments shows that the two experimental techniques are often, but not always, consistent, and both techniques suggest a relationship between the physical structure of the reinforcement and the mathematical structure of the permeability tensor. Preform features at the laminar and interlaminar scales were hypothesized to influence the experimental results.
Thermal analysis of thermoplastic composites during processing
Authors: Yang Heechun , Colton Jonathan S. 
Published: December 2004

AbstractUnsteady two‐dimensional thermal analysis has been performed on PEEK/AS‐4 fiber thermoplastic composites. To calculate the crystallinity of the composite, a spherulite growth model was applied. A numerical analysis was carried out with variations in mold cooling rate, the prepreg lay‐up, and the composite geometry. The effect of geometry and the cooling rate is significant in the temperature profiles. The degree of crystallinity varies with the cooling rate, but the gradient of crystallinity is small, with the exception of complex geometries at fast cooling rates. The results of numerical calculations are in excellent agreement with the experiments and offer validation of the numerical formulation.
Residual thermal stresses in bismaleimide/carbon fiber composite laminates
Authors: Di Landro Luca , Palonca Alberto , Sala Giuseppe 
Published: December 2004

AbstractThis is a study of residual thermal stresses in composite laminates, due to curing cycles. An extended formulation of Classical Lamination Theory (CLT) is adopted, which is able to take into account geometrical nonlinear effects owed to finite displacements. The approach is applied to square asymmetric laminates that have different dimensions and thicknesses. Final laminate shapes are evaluated after complete curing cycles; they can be cylindrical or saddle‐like, and their equilibrium configuration stable or unstable depending on thickness vs. side length ratio. The same laminates are stacked, press‐cured and the radii of curvature experimentally measured. In addition, they are modeled by means of finite element method (FEM) codes, using both linear and nonlinear techniques. Except for the thick laminates, the results obtained using nonlinear theoretical and numerical approaches show good agreement with experiment. Thermal residual strains are computed from non‐mechanical strains by subtracting laminae free thermal deformations; the corresponding stresses are evaluated through layer stiffnesses. Residual stresses are evaluated both theoretically and experimentally. For thicker laminates the disagreement is mainly due to a mixed viscous phenomenon which takes place in resin interlaminar layers and matrix intralaminae. The share of relaxed stresses is evaluated and methods that include optimal cooling path techniques are suggested.
Effects of water absorption and osmotic degradation on long‐term behavior of glass fiber reinforced polyester
Authors: Castaing Ph. , Lemoine L. 
Published: December 2004

AbstractGlass fiber reinforced polyester composites, with gelcoat, are widely used as structural materials for hulls, pools, pipes, and tanks in aggressive environments, despite the lack of knowledge concerning their resistance to water in the long term. In addition, these materials may be damaged through an osmotic process, especially when immersed in water, as are boat hulls, and this phenomenon can lead to a delamination of the gelcoat and of the laminate plies. The aim of this experimental study is to evaluate the mechanical characteristics with time of orthotropic laminates subjected to accelerated tests of humid aging. The evolution of the properties with water absorption is followed by a nondestructive test procedure based on vibrational mode analysis. The results are additionally confirmed by quasi‐static bending and shear tests. It is shown that the main effects of water on the composite mechanical properties are the plasticization of the matrix an the osmotic delamination of the plies; on the other hand, gelcoat blistering had no influence on the durability. This paper highlights the need for and the complementarity of both nondestructive and destructive mechanical tests for studying the long‐term behavior of composites in marine environments.
Finite element analysis of polymer melt flow in cable‐covering crossheads
Authors: Fenner R. T. , Nadiri F. 
Published: December 2004

AbstractA finite element method is presented for the analysis of isothermal non‐Newtonian polymer melt flow in narrow channels of complex shape. The particular application considered is flow in cable‐covering crossheads. The geometric flexibility of the finite element method allows a mesh of triangular elements to be constructed to suit the shape of the flow channel. Computed results obtainable from the analysis include the distribution of polymer layer thickness on the finished cable, together with the extrusion pressure required to maintain a given flow rate of melt. Some typical thickness distribution results are presented as an introduction to experimental verification of the method and its application to crosshead design.
Problems of structural characterization of polymer networks
Authors: Dušek Karel , Ilavský Michal 
Published: December 2004

AbstractProblems of the characterization of network structure by investigating the network formation and its response to mechanical stress have been analyzed. Attention has been devoted to the effect of reactivity of functional groups and cyclization on the formation of network structure and to problems of obtaining the equilibrium modulus and its relation to the concentration of elastically active network chains (EANCs). It has been demonstrated that a theoretical description of network formation must be based on reliable information on the rules of joining of functional groups and on their relative reactivity; the tree‐like approximation offers a number of structural parameters of the sol and gel including, e.g, chemical clustering of units of a certain type. The main obstacles to reaching the equilibrium modulus are long relaxation, times of lightly crosslinked networks and the occurrence of secondary relaxations. In correlating the equilibrium modulus and the concentration of EANCs, it is necessary to find conditions under which the Mooney‐Rivlin constant C2 can be neglected and to carry out the required corrections of the modulus, if experimental conditions differ from those of network formation.