bluuebunny/crossref_metadata_2025_split huggingface dataset:
The characterization of uniaxial graphite fiber/epoxy composites by mechanical testing and scanning electron microscopy
Authors: Cha Cheol Y. , Fellers John F. , Mathews Archie 
Published: April 2003

AbstractThe effect of the constituent material on the mechanical properties and on the overall crack propagation behavior of uniaxial graphite/epoxy composites was studied using two different types of graphite fibers, i.e., PAN precursor and pitch precursor fibers in combination with an epoxy known for its toughness. The tensile properties and interlaminar shear strength (ILSS) of composites with various fiber volume fraction were studied using an Instron Universal Testing Machine. The fracture surface of composites was studied using scanning electron microscopy (SEM). The surprising result from the tensile tests is that the percent elongation of AS4/epoxy composites was much higher than that of individual components, i.e., the epoxy and the fiber. The stress–strain curves of AS4 fiber/epoxy composites show yielding. The yielding is interpreted to result from shear stress concentration due to the fiber breakage. Two causes of failure mode were observed in this study: (1) ductile plastic deformation by the PAN‐based AS4/epoxy composites; (ii) brittle catastrophic failure shown by the pitch‐based VSB‐16/epoxy composites. The tensile strengths and moduli of the composites increased as the volume fraction of fibers increased. The principal fracture features of AS4/epoxy composites under tension were fiber pullout (bundles and single fibers) and very rough fracture surface due to the pullout of fiber bundles with epoxy, whereas VSB‐16/epoxy composites under tensile and bending loads showed only tensile (or compressive) failure. The composites of epoxy/PAN (polyacrylonitrile)‐based fibers (AS4) showed greater ILSS than those of the pitch‐based fiber (VSB‐16)/epoxy. The most characteristic features of the interlaminar shear failure surface of AS4/epoxy composites are delamination and formation of hackles.
Effect of pressure on the impregnation of thermoplastic resin into a unidirectional fiber bundle
Authors: Kim T. W. , Jun E. J. , Um M. K. , Lee W. I. 
Published: April 2003

AbstractImpregnation of molten thermoplastic resin into continuous unidirectional fiber tows was investigated. The degree of impregnation is defined as the ratio between the number of impregnated fibers and the total number of fibers of a tow. The degree of impregnation was modeled as a function of time, impregnation pressure, impregnation temperature, and tow size, assuming that the radial inward flow of resin through the fiber tow is governed by Darcy's law. The effect of the impregnation pressure on the permeability was studied. Experiments were performed to evaluate the validity of the model. Toray T300 graphite fiber bundles and Polyetheretherketone (PEEK) resin were used. Pressure and temperature were applied to fiber tows surrounded with resin powder in a mold. After a predetermined time, the sample was taken out and the degree of impregnation was measured from the microphotographs of the cross sections of samples. Experiments were performed for different impregnation conditions such as impregnation time, pressure, temperature, and tow size. Good agreement was found between the model and the experimental data.
An improved analytical melting theory
Authors: Rauwendaal Chris 
Published: April 2003

AbstractThe first quantitative description of melting in single screw extruders was given by Z. Tadmor around 1965. A simple analytical theory was developed for Newtonian fluids, assuming the fluid viscosity to be unaffected by changes in temperature. Also, an approximate analytical theory was developed for a power‐law fluid, assuming the power‐law constants to be independent of temperature and viscous dissipation to be negligible. Later workers extended the theory, however, most of these extensions did not allow closed‐form analytical solutions, thus requiring numerical techniques to obtain solutions. One of the most crucial assumptions in the analytical melting theory is the assumption that the viscosity of the polymer melt in the melt film is not affected by temperature differences in the melt film. This assumption has been eliminated in the improved melting theory by deriving an exact solution of the temperature and velocity profile in pure drag flow of a temperature dependent power‐law fluid between two parallel plates. It will be shown that the inclusion of the temperature dependence of the viscosity dramatically affects the predictions of the melting rate. It will further be shown how the new theory can be used to predict the optimum barrel temperature for melting.
Sheet molding compound—basic considerations
Authors: Stillhard Bruno 
Published: April 2003

AbstractThe SMC process has reached a new level of quality with the recent generation of compression presses. SMC ply preheating has allowed shorter cycle times and improved flow properties. Cycle times of less than 1 min are now possible. Surface quality is improved with accurate press‐velocity control and accurate parallelism control of the movable platen. When mold vacuum is used, the surface quality can approach the auto‐maker's Class A finish standards without the use of time‐consuming in‐mold coating. The parallelism control allows tighter tolerances on the shear edge of the mold. If this is combined with accurately controlled press‐force profile, a substantial reduction in flash can be achieved. The never presses are equipped with microprocessor controls. On‐line quality control is possible, since all relevant parameters can be stored or closed‐loop controlled. Statistical process control (SPC) can therefore be achieved without the need for additional hardware.
Biodegradable plastics: A review
Authors: Huang Jan‐Chan , Shetty Aditya S. , Wang Ming‐Song 
Published: April 2003

AbstractIn this paper, the approach of biodegradation to reduce the environmental impact of plastic wastes is reviewed. The mechanism of biodegradation and the processing and applications of these materials are also discussed in relation to the structural characters of their molecules. The synthetic biodegradable materials such as starch based biodegradable materials are compared with naturally occurring biodegradable materials such as poly(hydroxy butyrate) (PHB) in terms of their applications, processing difficulty, and degradation mechanism. The future trends of these materials are anticipated.
Effect of oscillations during extrusion on rheology and mechanical properties of polymers
Authors: Isayev A. I. , Wong C. M. , Zeng X. 
Published: April 2003

AbstractAn experimental study associated with the applications of sound and ultrasonic waves to extrusion is conducted. Two laboratory setups are developed for these purposes incorporating orthogonal and parallel superposition of oscillations on pressure flow during extrusion. The orthogonal superposition of sound oscillations is imposed in an annular die. The parallel superposition of ultrasound oscillations is imposed in a circular die. Several materials including unfilled and filled thermoplastics, thermoplastic elastomer, and elastomer are tested. Die characteristics, power consumption, and die swell are determined during extrusion. The rheological properties, molecular weight, tensile properties, and impact strength of materials with and without sound and ultrasound treatment are investigated, indicating permanent changes in these properties. The observed effects are found to depend on melt temperature, flow rate, nature of polymer system, and oscillating parameters such as frequency and deformation amplitude.
An investigation of the shrinkage behavior of oriented PVC in a hot air tunnel
Authors: Bigg D. M. 
Published: April 2003

AbstractThe behavior of PVC shrink films in a hot‐air tunnel oven was analyzed. The films were found to undergo two modes of shrinkage. Primary shrinkage, which corresponded to macroscopic dimensional changes to conform to the container surface, occurred rapidly once the film was heated above its relaxation temperature. Secondary shrinkage, which corresponded to the elimination of wrinkles and bubbles in the shrunk film, was a much slower process that occurred only when the film was heated above 70°C. The film temperature could be reasonably estimated from a Nusselt analysis of heat transfer between turbulent air and a cylinder.
Blends of polyolefins: Characteristic melting and crystallization data
Authors: Haghighat Siavash , Birley Arthur W. 
Published: April 2003

AbstractA range of polyolefins have been studied by differential scanning calorimetry (DSC). In addition to the pure polymers, many binary blends and one ternary system have been investigated. Data are reported for HDPE, LDPE, LLDPE, PP, and PB and for many of these binary blends and for the HDPE–LDPE–LLDPE system.
Thermomechanical load and property changes in processing of polymeric materials
Authors: Meissner Konrad , Poltersdorf Bernd 
Published: April 2003

AbstractWe introduce a quantification method for mechanical and thermal loads during processing. In the case of polymers, mechanochemical reactions as well as thermal and thermo‐oxidizing processes are relevant, and rheokinetic analysis is used to understand the property changes in polymeric materials. A formal kinetic equation is established which takes into consideration structurization and destruction phenomena and the nonisothermal of the process. Parameter identification shows that the kinetic equation provides a good description of the change in viscosity over time as a function of mechanical and thermal loads using the example of HDPE in the kneading chamber of a laboratory kneader. Applications in process modeling and optimization are noted, and a so‐called damage diagram is set up.
Application of an enhanced flash‐tank devolatilization system to a degassing extruder
Authors: Craig T. O. 
Published: April 2003

AbstractThe design and operation of a foam‐enhanced flash‐tank devolatilization system applied to a conventional degassing extruder are described. The extruder degenerates to a melt feed device and devolatilization takes place in a static mixer in which foaming is induced. The flash‐tank provides vapor disengagement space. Improved residual volatile levels and throughput rates are achieved, as well as the elimination of downgraded polymer that is caused by vent port flooding in degassing extruders.
Controlling crosslink density of coreactive polymers in an extruder reactor
Authors: Curry John , Andersen Paul 
Published: April 2003

AbstractA common technique for the manufacture of polymer alloys is melt blending of polymers with specific chemical interactions. For instance, an amido ester crosslink forms when oxazoline‐grafted PS is mixed with acid‐grafted PE. The crosslink builds melt viscosity and stabilizes product morphology. Reaction control is critical since overreacted alloys from gels and underreacted alloys have gross composition gradients and/or tend to phase coalesce so that product properties are variable. Polymer reactions in plasticating compounders are particularly difficult control problems since several unit operations involving plastication, heat exchange, mixing, and separating of by‐products must be sequenced properly to control a reaction. Reactive polystyrene (OPS) and reactive polyethylene (APE) with oxazoline and carboxylic acid functionality, respectively, were melt blended in a ZSK compounding extruder under a variety of conditions. The extent of crosslink was monitored by the strong shear viscosity increase of the reacted product, the infrared absorption by the crosslink, and reactant depletion in the melt. The phase morphology was characterized by optical phase contrast microscopy. A response surface of product shear viscosity vs. the primary operational parameters of extrusion rate and extruder RPM is interpreted in terms of characteristic reaction time and development of reactive interfaces during the mixing process. Response surfaces result from storing coordinates and responses while exercising a new feedback loop control system.
Distributive mixing in the nonintermeshing twin‐screw extruder with a newtonian fluid
Authors: Bigio David , Baim William 
Published: April 2003

AbstractVisual studies have been performed on the partially filled, nonintermeshing twin‐screw extruder (NITSE) to determine its distributive mixing abilities. Four parameters were studied: percent screw stagger, percent channel fill, screw speed, and fluid viscosity. It was found that screw speed and viscosity had no statistically significant effect on mixing, while percent channel fill and percent screw stagger were factors affecting mixing that were intimately related by the type of screw‐to‐screw fluid transfer. The two types of transfer were fluid‐to‐fluid, which occurred when the percent fill was greater than the percent stagger, and deposition, which occurred when the percent fill was less than the percent stagger.
Tensor failure criteria for composites: Properties and comparison of the ellipsoid failure surfaces with experiments
Authors: Theocaris Pericles S. 
Published: April 2003

AbstractA realistic criterion was introduced in the 3D principal stress space for describing failure of transversely isotropic bodies taking also into account the strength differential effect. This criterion is represented by an elliptic paraboloid failure surface (EPFS). The criterion stipulates that in the compression–compression–compression octant these materials may sustain very high loadings. To remedy this ambiguous definition of failure in this zone, an improved version of the EPFS was also introduced as a complement of the EPFS criterion. Based on the same principles as the EPFS, a symmetric ellipsoid failure surface is defined whose symmetry axis is parallel to the hydrostatic axis, which is also passing though the three pairs of failure strengths in tension and compression along each of the principal stress axes. Both criteria are completely defined by stipulating that their symmetry axes are parallel to the hydrostatic axis and that the fourth rank tensors H defining failure should have a zero eigenvalue associated with the spherical tensor 1. Extensive experimental evidence with different orthotropic materials has shown that their failure results corroborate both criteria, depending on the form of their structure.
Compression molding using a generalized eulerian–lagrangian formulation with automatic remeshing
Authors: Ahmed Alauddin , Alexandrou Andreas N. 
Published: April 2003

AbstractA generalized Eulerian‐Lagrangian approach is used to study the compression molding of viscoelastic polymers. The complete, unsteady, two‐dimensional equations of motion are used in the analysis. The White–Metzner model is used to describe the constitutive behavior of the material. The solution is obtained using a mixed Galerkin finite element method. An automatic remeshing scheme is introduced to reduce the mesh distortion during the solution procedure. Results for the pressure and force required in mold closing are presented for the isothermal filling of a rectangular cavity. © 1992 John Wiley & Sons, Inc.
An overview of additives and modifiers for polymer blends: Facts, deductions, and uncertainties
Authors: Mascia L. , Xanthos M. 
Published: April 2003

AbstractPolymer blends with enhanced properties and processability for specific applications are modified through the incorporation of a variety of additives. The performance of these additives is often difficult to predict from considerations of their known behavior in the separate blend constituents. This overview article discusses additives and modifiers in terms of types and specific functions (e.g., impact modifiers, compatibilizers, flame retardants, stabilizers) and provides an analysis of the possible effects of their repartition in the constituent phases and at the interface. © 1992 John Wiley & Sons, Inc.
Free‐radical retrograde‐precipitation polymerization process
Authors: Caneba Gerard T. 
Published: April 2003

AbstractIn this article, we present a newly discovered polymerization process, called the freeradical retrograde‐precipitation polymerization (FRRPP) process, that is shown to have certain desirable features not normally found in free‐radical polymerization processes. Here, free radical polymerization occurs with an unusual but widely applicable polymer precipitation phenomenon. Local heating is observed in the vicinity of the radical sites, which results in the controlled rate of propagation with a decrease in the rate of radical–radical termination reactions. In the case experiments, the existence of hot spots in the reactor fluid is shown to occur. There is also evidence of slowdown of the growth of polymer radicals after initiator decomposition. The polymer radicals, shown to have a relatively narrow molecular weight distribution, continue to grow at a controlled rate long after all the initiator molecules have decomposed. The addition of a second monomer results in the formation of a thermoplastic elastomer triblock copolymer. © 1992 John Wiley & Sons, Inc.
Practical aspects of reactive compounding in a continuous kneader
Authors: Jakopin Stan 
Published: April 2003

AbstractReactive compounding is continuously emerging as a novel processing technique to modify existing polymer systems and improve performance/properties. The essential elements of control over the internal pressure and temperature combined with understanding of the chemistry and process equipment brings optimal results. Today's role of contract manufacturer is not only to provide the facilities and hardware but also the understanding of process technology to help develop new products in the most economic and timely fashion. © 1992 John Wiley & Sons, Inc.
Alternative procedures for the recycling of sheet molding compounds
Authors: Patel S. H. , Gonsalves K. E. , Stivala S. S. , Reich L. , Trivedi D. H. 
Published: April 2003

AbstractTo establish the parameters for converting sheet molding compounds (SMCs) to useful products, various technical approaches, viz., solvent extraction, hydrolysis, and pyrolysis, have been explored. Thermogravimetric analysis of an SMC sample indicated that it contains about 25% by weight organics and 75% inorganics, mainly glass fibers and CaCO3 as filler. Solvent extraction of ground SMC with acetone, methylene chloride, chloroform, or chloroform : benzene (1 : 1 vol) yielded low quantities of a gummy, viscous extract. Hydrolysis of the extracted SMC sample under strong alkaline conditions was also studied. A unit structure was postulated for the hydrolysate based upon elemental and molecular weight analysis. Pyrolysis of both extracted and unextracted SMCs in nitrogen at 500°C and in air at 400°C yielded organic oils. These oils were characterized for their calorific values. The products of pyrolysis consisted of mainly aromatics along with some oligomers. The extract and the oil from pyrolysis appear to be compatible with epoxy systems. Their use as an extender for epoxy systems, while that of the inorganic residue (glass fibers and CaCO3) as a filler for epoxy system, have been explored. © 1993 John Wiley & Sons, Inc.
Encapsulation process for electronic devices using injection molding method
Authors: Sakai Tadamoto 
Published: April 2003

AbstractIn this article, a new encapsulation injection molding method for electronic devices such as integrated circuits (ICs) is described as a superior technology to the conventional transfer molding process widely used in the electronics industries. The quantitative analysis has been carried out utilizing a computer simulation program covering cavity‐filling behavior to analyze the relationship between the deformation of gold wires that are bonded with mounted IC chips and mold geometries, operational conditions, and physical properties of a thermoplastic encapsulant, i.e., polyphenylene sulfide. As a result, a new technology to encapsulate ICs has been established, preventing no practical gold wire deformation or break‐up damage. © 1993 John Wiley & Sons, Inc.
Assessing polymer crystallizability from nonisothermal crystallization behavior
Authors: Nadkarni V. M. , Bulakh N. N. , Jog J. P. 
Published: April 2003

AbstractCrystallization of polymers plays an important role in polymer processing because the structure developed during crystallization influences the mechanical and physical properties of the polymer product. The crystallization of polymers takes place under nonisothermal crystallization is essential for optimizing the processing conditions to obtain a product with desired properties. A simple approach based upon analysis of the nonisothermal crystallization behavior of a polymer to characterize the inherent crystallizability of the polymer and its sensitivity to processing conditions is reported. The polymers used in the present investigation include various grades of polyethylenes and polypropylenes. It is shown that a simple graphical analysis of the nonisothermal crystallization parameters can be used to quantify the inherent crystallizability of polymers and sensitivity of its structure development to changes in the cooling rates. © 1993 John Wiley & Sons, Inc.
Viscoelastic simulations of extrudate swell for an HDPE melt through slit and capillary dies
Authors: Kiriakidis D. G. , Mitsoulis E. 
Published: April 2003

AbstractExtrudate swell studies of a high‐density polyethylene (HDPE) melt have been undertaken in flows through slit and capillary dies with the purpose of finding out the effect of die‐length/diameter (gap) (L/D or L/2H) ratio on the viscoelastic behavior. Numerical solutions have been obtained by using the finite element method (FEM) and an integral constitutive equation of the K‐BKZ type with a spectrum of relaxation times. The material parameters have been obtained by fitting experimental viscosity and normal stress data for the melt as measured in shear, and elongational viscosity data available in the literature. Different L/D (L/2H) ratios have been considered ranging from very short to infinitely long dies. The numerical simulations reveal that as the flow rate increases, viscoelastic effects exhibited by the HDPE melt become important and manifest themselves in an enhanced swelling behavior after the die exit, while small, Newtonian‐like vortices exist in the contraction before entry to the die. Elastic recovery is also captured in an enhanced extrudate swell, which is always higher at the same apparent shear rate for the capillary than the slit dies and decreases drastically as the L/D (L/2H) ratio increases, reaching asymptotic values for very long dies. Such behavior is in agreement with experimental findings from flows through slit and capillary dies and in sharp contrast with purely viscous simulations which cannot predict such strong viscoelastic phenomena associated with the memory of the polymer melt. © 1993 John Wiley & Sons, Inc.