bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanical fastening of polymer composites
Authors: Vinson Jack R. 
Published: December 2004

AbstractIn structures composed of polymer materials and polymer matrix composite materials, components must be joined such that the overall structure retains its structural integrity while it is performing its intended function which can include both mechanical loads (static and dynamic) and environmental loads (temperature and humidity). The use of composite materials in complex structures almost always reduces the number of components in the structures compared to the use of metallic alloys for the same structure. Thus, using composite materials not only results in great savings in weight, but also through a reduced number of joining operations, results in significant savings In assembly, inspection, parts storage, and movement, resulting in increased reliability and lower cost. Yet joining is still required. Joining metallic structures is a mature technology involving riveting, bolting, welding, glueing, brazing, soldering, and other methods. However, for most polymer matrix composites only adhesive bonding and mechanical fastening can be utilized. Attention has been given recently, however, to localized welding of thermoplastic polymer matrix composites. Inherently, adhesive bonding is preferable to mechanical fastening because of the continuous connection, whereas in drilling holes for bolts or rivets, fiber or other reinforcements are cut, and large stress concentrations occur at each discrete fastener hole. However, in many structures, it is necessary to employ mechanical fasteners in order to remove components or to have access to the interior of the structure. Hence, both adhesive bonding and mechanical fastening are important in joining structural components of polymer or polymer matrix materials. The following is a review of much of the literature dealing with mechanical fastening of polymer matrix composite structures. Hopefully, it provides an overall introduction for detailed study of the referenced documents as well as others, and a catalyst for further research.
Welding of polymer interfaces
Authors: Wool R. P. , Yuan B.‐L. , McGarel O. J. 
Published: December 2004

AbstractStudies of strength development at polymer‐polymer interfaces are examined and applications to welding of similar and dissimilar polymers are considered. The fracture properties of the weld, namely, fracture stress, σ, fracture energy, GIc, fatigue crack propagation rate da/dN, and microscopic aspects of the deformation process are determined using compact tension, wedge cleavage, and double cantilever beam healing experiments. The mechanical properties are related to the structure of the interface via microscopic deformation mechanisms involving disentanglement and bond rupture. The time dependent structure of the welding interface is determined in terms of the molecular dynamics of the polymer chains, the chemical compatibility, and the fractal nature of diffuse interfaces. Several experimental methods are used to probe the weld structure and compare with theoretical scaling laws, Results are given for symmetric amorphous welds, incompatible and compatible asymmetric amorphous welds, incompatible semicrystalline and polymer‐metal welds. The relevance of interface healing studies to thermal, friction, solvent and ultrasonic welds is discussed.
Fatigue crack propagation of rubber‐toughened epoxies
Authors: Hwang J.‐F. , Manson J. A. , Hertzberg R. W. , Miller G. A. , Sperling L. H. 
Published: December 2004

AbstractEpoxies containing epoxy‐terminated butadiene acrylonitrile rubber (ETBN) or amino‐terminated butadiene acrylonitrile rubber (ATBN) were prepared and studied in terms of fatigue crack propagation (FCP) resistance and toughening mechanisms. Rubber incorporation improves both impact and FCP resistance, but results in slightly lower Young's modulus andTgAsTgincreases, the degree of toughening decreases. Rubber‐induced shear yielding of the epoxy matrix is believed to be the dominant toughening mechanism. Decreasing fatigue resistance with increasing cyclic frequency is observed for both neat and rubber‐toughened epoxies. This result may be explained by the inability of these materials to undergo possible beneficial effects of hysteretic heating. FCP resistance is linearly proportional toMc1/2, whereMcis the apparent molecular weight between crosslinks determined on the rubber‐toughened material. FCP resistance also increases with increasing static fracture toughnessKIC. ATBN‐toughened epoxies demonstrated better fatigue resistance than ETBN‐toughened systems.
Phenolic triazine (PT) resins. I. Gelation phenomenon studied by calorimetric, mechanical, and dielectric techniques
Authors: Khanna Y. P. , Kumar R. , Das S. 
Published: December 2004

AbstractGelation phenomenon in thermoset polymers is an area of extreme importance from the processing point of view. Gel point (GP) has traditionally been detected using rheological and mechanical techniques. We wish to report the use of dielectric and especially calorimetric techniques for detecting GP. Using a particular thermoset system, we have compared the calorimetric, dielectric, and mechanical techniques and shown how to define GP in terms of time and temperature. As a matter of convenience, we have briefly defined the gelation phenomenon in thermosets, its significance and measurement, and a critical evaluation of the techniques for detecting GP.
Structure development in biaxially stretched polystyrene film: Part I. Property‐orientation correlation
Authors: Choi Kyung‐Ju , Spruiell Joseph E. , White James L. 
Published: December 2004

AbstractA study of orientation development in polystyrene film by biaxial stretching is described. Stretch ratios up to 7.2 × 7.2 were used. Mechanical properties of polystyrene films were correlated with the level of molecular orientation developed by uniaxial or biaxial stretching. Sensitivity of the mechanical properties to change due to development of orientation varied as follows: Yield strength < Young's modulus < Tensile strength < Elongation to break. Brittle to ductile transition phenomena were observed at certain orientation values in the orientation triangle diagram. The transition occurs whenf×f∼ 0.0025 for biaxially oriented andf∼ 0.015 in the machine direction for uniaxially oriented films. SEM photomicrographs show that the fracture surfaces of ductile failures exhibit many fibrils while brittle failures exhibit no fibrils.
Optical properties of simultaneous biaxially stretched poly(ethylene terephthalate) films
Authors: Cakmak Mukerrem , White James L. , Spruiell Joseph E. 
Published: December 2004

AbstractWe offer a detailed study on the anisotropic optical properties in uni and simultaneous biaxially stretched Poly(ethylene terephthalate) (PET) films. Cast amorphous sheets of PET were stretched to a series of extension ratios in two mutually perpendicular directions at 80, 90, and 100°C. Additionally, 0selected films were subsequently “heat‐set” by annealing with their width and lengths constrained. The principal refractive indices at sodium D wavelength of these, asstretched and heat‐set films were obtained using a modified Abbe refractometer. The changes in the principal refractive indices with the processing history were correlated with the orientation of PET chains and phenyl plane normals, which were determined independently by wide angle X‐ray (WAXS) pole figure technique.
The joining of biaxially oriented polyethylene pipes
Authors: Atkinson J. R. , Ward I. M. 
Published: December 2004

AbstractDie‐drawing techniques recently developed at Leeds University make it possible to produce oriented polymer tubes with both axial draw and hoopwise expansion. These products have increased axial stiffness, improved barrier properties, and excellent resistance to chemical reagents. Normally mechanical methods are used to join such tubes in order to preserve their orientation: however we show that electrofusion techniques produce joints of strengths such that in tensile tests, failure always occurs in the fittings, not at the joint interfaces. Optical and electron microscopy reveal different zones in the welds and indicate that only 20 percent of the wall thickness is affected by the electrofusion process. The pipe studied was biaxially drawn medium density polyethylene of outside diameter 63 mm with draw ratios of 4 in the axial direction and 2, inner hoop. Optimum welding conditions were determined using socket and saddle electrofusion fittings. The joints did not fail in a standard crush test. Careful control of welding parameters is essential in butt fusion welding when the maximum weld strength exceeds that of the undrawn polymer.
Two‐Dimensional thermal analysis of resistance welded thermoplastic composites
Authors: Jakobsen Tom B. , Don Roderic C. , Gillespie John W. 
Published: December 2004

AbstractA transient two‐dimensional thermal model for resistance welding of thermoplastic composites is presented. A parametric study is conducted that yields insight into the welding process enabling some critical process and material parameters to be identified. Time to melt is predicted by the model and is successfully compared to experimental observations. Local heating and meltthrough can also be explained by the transient thermal model in agreement with experimental observations. Mode I fracture toughness of unidirectional graphite reinforced poly(etheretherketone) resistance welded double cantilever beam specimens are conducted under various process conditions. Experimental results indicate that under optimum process conditions, the interlaminar fracture toughness of the bulk compression‐molded thermoplastic composite material can be achieved using resistance heating as a joining technique.
Thermal behavior of transparent poly(etheretherketone)(PEEK) film
Authors: Gupta Hemant , Salovey R. 
Published: December 2004

AbstractThe thermal behavior of poly(etheretherketone)(PEEK) film heated in an open differential scanning calorimetry (DSC) pan at 20°C/min is distorted by relaxation of the strained film. PEEK film in a closed pan or quenched PEEK in open or closed pans shows a glass‐transition temperature (Tg) around 144°C, cold crystallization (∼22 J/g) at 177°C, melt‐temperature (Tm) peaking at 335–340°C, with an enthalpy of fusion of 32–34 J/g, and recrystallization on cooling at 285°C, with a crystallization exotherm of about 40 J/g. The enthalpy of fusion decreases with increasing heating rate from 2–100°C/min and approaches the enthalpy of cold crystallization. With increasing heating rate, further crystallization of PEEK during the DSC scan is suppressed. With increasing cooling rate, PEEK melt crystallizes at larger supercoolings to a lesser extent. Crystallization on cooling the melt was more complete than cold crystallization and annealing on heating.
Dielectric and magnetic properties of random and segregated ferrite polystyrene composites
Authors: Yacubowicz J. , Narkis M. , Kenig S. 
Published: December 2004

AbstractThe dielectric and magnetic properties of polystyrene composites containing barium or nickel‐zinc ferrites were studied as function of the ferrite concentration and field frequency. The composites were prepared by methods yielding a random distribution of the ferrite particles or segregated structures. Barium ferrite‐poly‐styrene composites exhibited a typical insulator behavior, and only above 60% ferrite were high values of the dielectric properties noted at the lower frequencies, decreasing gradually with frequency to the low values typical of the higher frequencies. The mode of barium ferrite particle distribution did not affect the dielectric properties. The nickel‐zinc ferrite systems demonstrated a conductor type behavior. An apparent insulator‐conductor transition was observed, having lower values for segregated than for random distributions. The magnetic permability of barium ferrite‐polystyrene composites above 10% ferrite increases with the ferrite concentration, whereas the magnetic dissipation factor steeply increases with concentration above 40% ferrite.
Studies on the effect of electrode type and substrate temperature on plasma polymerization of two model compounds: Acrylonitrile and hexamethyldisiloxane
Authors: Akovali G. , Dilsiz N. 
Published: December 2004

AbstractPolymers were prepared from saturated (HMDS) and unsaturated (AN) monomers in a radio frequency discharge (plasma). The effect of selected parameters such as electrode type (such as Cu, Zn, Ni, Al), reactor type, and substrate temperature (other parameters constant) on chemical structure and the rate of polymer deposition was examined by Fourier transform infrared (FTIR) spectroscopy. Differences in the nature of electrodes and reactor types were found to yield similar plasma products with similar rates of deposition for two monomers. In the tubular reactor used, deposition rates were observed to decrease with increasing substrate temperatures showing different dependencies on temperature for the monomers tested.
Viscoelastic material characterization and modeling for polyethylene
Authors: Popelar C. F. , Popelar C. H. , Kenner V. H. 
Published: December 2004

AbstractAn extensive set of stress relaxation and constant strain rate tests for characterizing the mechanical responses of a medium density polyethylene and a high density polyethylene that are commonly used in natural gas distribution piping is described and analyzed. The development of coherent master curves for the relaxation modulus, maximum stress, and the time‐to‐failure for pressurized pipes through a combination of both horizontal and vertical shifting is presented. The relaxation data are used to develop a nonlinear Viscoelastic material model. The model is assessed by making comparisons of the predicted stress‐strain response with the measured response in the constant strain rate tests.
Thermomechanical properties of 1C molding compounds
Authors: Bair H. E. , Boyle D. J. , Ryan J. T. , Taylor C. R. , Tighe S. C. , Crouthamel D. L. 
Published: December 2004

AbstractEight commercial semiconductor grade epoxy compounds that are used to encapsulate 1C (integrated circuit) devices have been evaluated for their ability to minimize the development of thermal stresses which can cause failure during device temperature cycling. Thermal expansion, dynamic modulus and adhesion studies are used to describe the mechanical interaction between the plastic package and the silicon device it surrounds. A “figure of merit” is defined for the development of stress on the 1C device as it is cooled after the packaging process. The stress is shown to be proportional to the product of three terms: (αp‐αs)Ep(Tanch‐T) where αpand αsare the expansion coefficients for the plastic and silicon, respectively,Epis the modulus of the epoxy andTanchis the temperature at which the epoxy becomes anchored to the silicon device during transfer molding. In addition, the importance of good adhesion between the epoxy encapsulant and the silicon device to prevent package cracking has been demonstrated by finite element analysis and a novel adhesion test.
Twin screw extrusion devolatilization: From foam to bubble free mass transfer
Authors: Foster R. W. , Lindt J. T. 
Published: December 2004

AbstractThe present research program, based upon the experimental performance of a 20 mm counter‐rotating, non‐intermeshing twin screw devolatilizer with several polymer/solvent systems has developed theoretical approaches to modeling both the bubble growth dominated mass transfer regime as well as the essentially bubble free regime (1, 2). This work encompasses the area of transition from the bubbling to the non‐bubbling areas. This transition to some degree, probably exists in nearly all real devolatilization processes. The work combines a foam simulation model, which integrates elementary bubble processes, with the mass transfer from single phase liquid films through a penetration theory based model. The modeling is successful at correlating the experimental data and shows realistic effects with regard to residence time, surface area, and average mass transfer coefficient as functions of vent loading.
Influence of solvent and molecular weight on thickness and surface topography of spin‐coated polymer films
Authors: Spangler Lora L. , Torkelson John M. , Royal J. Scot 
Published: December 2004

AbstractThe influence of polymer molecular weight, molecular weight distribution, and polymer‐solvent interactions on the thickness and topography of spin‐coated polymer films was examined. For films prepared from dilute solutions, highly volatile solvents or fair or “poor” solvents for the polymer adversely affect film surfaces causing nonuniformities (waves) to appear. However, if the concentration of these solutions is increased to approximately the concentration at which entanglements are formed, nearly uniform films are produced even if the solvent employed is highly volatile, such as dichloromethane. When toluene is employed as the solvent, which has a relatively low volatility and therefore forms nearly flat film surfaces, films prepared from dilute solution were found to have thicknesses, h, proportional to η Ω−0.49 for polystyrene and η Ω−0.49 for poly(methylmethacrylate) where ηo is the zero‐shear rate solution viscosity and Ω is the rotational speed at which the films were prepared. These results suggest that the exponents associated with ηo and Ω may be nearly independent of the type of polymer used as long as flat films are produced. Finally, the molecular weight parameter most important in controlling final film thickness for films made from dilute solutions is Mv, the viscosity‐average molecular weight.
Composites from compounding wood fibers with recycled high density polyethylene
Authors: Yam Kit L. , Gogoi Binoy K. , Lai Christopher C. , Selke Susan E. 
Published: December 2004

AbstractThe development of composites consisting of wood fibers and recycled plastics offers not only an opportunity to utilize an abundant natural resource but also a means to alleviate the serious plastics disposal problem. In this work, aspen fibers are incorporated into recycled high density polyethylene with a co‐rotating inter‐meshing twin‐screw extruder to study processing‐property relationships. Tensile, impact, and flexural strengths are measured as functions of fiber concentration. The effects of fiber pretreatment, screw configuration, and compounding temperature on the properties of composites are discussed.
Miscibility studies in blends of polybenzimidazoles and poly(4‐vinyl pyridine)
Authors: Makhija S. , Pearce E. M. , Kwei T. K. , Liu F. 
Published: December 2004

AbstractPoly[2,2'‐(m‐phenylene)‐5,5'‐bibenzimidazole] (PBI) is shown to be miscible with poly(4‐vinyl pyridine) over the entire composition range. Experiments were performed with commercial PBI as well as a lower molecular weight material synthesized by us. Blend miscibility is evidenced by single glass transition temperature intermediate between the pure polymers. Hydrogen bonding between the components was detected by infrared spectroscopy.
The V‐notch at weld lines in polystyrene injection moldings
Authors: Tomari K. , Tonogai S. , Harada T. , Hamada H. , Lee K. , Morii T. , Maekawa Z. 
Published: December 2004

AbstractA major factor that weakens the weld line in injection moldings is the V‐notch structure. Though the existence of a V‐notch is well known, its depth variation with molding conditions has not been detailed. The aim of this paper is to clarify the V‐notch structure and its effect on the strength of general purpose polystyrene injection moldings. A dog bone type tensile specimen with a weld line was molded under several molding conditions. The surface of the weld line was partially eliminated by cutting with a milling machine to seven levels of cut depth (Dc). As a result, the weld strength increased with Dc to about 50%. The relationship between the weld strength and Dc made it possible to determine the V‐notch depth, which vas defined as the “depth of the weld line.” From these results, a hypothesis is proposed that the V‐notch has a structure with a fine groove on the surface and a poorly bonded inner layer. This study considered the relationships among the weld strength, the depth of the weld line, and molding conditions.
Numerical and experimental studies of bubble growth during the microcellular foaming process
Authors: Ramesh N. S. , Rasmussen Don H. , Campbell Gregory A. 
Published: December 2004

AbstractA new experimental technique for studying the dynamics of bubble growth in thermoplastics using scanning electron microscopy is developed. The influence of temperature, saturation pressure, molecular weight, and the nature of physical blowing agent are investigated. The experimental results show that, the above, process variables control the growth of foams during processing. The existing Newtonian model for the growth of a single bubble in an infinite amount of polymer has been modified to account for the non‐Newtonian effects by modeling the polymer as a power law fluid. The experimental data has been compared with the appropriate viscoelastic cell model which considers the growth of closely spaced spherical bubbles during the foaming process. The simulation results indicate that the predictions of the cell model are in qualitative agreement with the trends of the experimental data and the quantitative agreement is reasonable. The cell model also gives an equilibrium radius which agrees with the experimental data. Other viscous models do not predict the equilibrium radius of the bubble and underpredict the experimental data.
A non‐isothermal healing model for strength and toughness of fusion bonded joints of amorphous thermoplastics
Authors: Bastien L. J. , Gillespie J. W. 
Published: December 2004

AbstractA study to investigate the influence of processing on the fusion bonding of graphite (AS4) poly(etheretherketone) (PEEK) thermoplastic composites (BASF commingled PEEK/graphite NCS woven fabric) using a polyetherimide (PEI) film at the interface is presented. Fundamental to all fusion bonding processes is the intermolecular diffusion between surfaces in intimate contact. A model based on the healing theory of amorphous polymers has been proposed to predict strength and toughness as a function of non‐isothermal process history. This model considers two different microscopic failure mechanisms of a healed interface. For the first time, using non‐isothermal data and proper data reduction procedures, it is possible to differentiate between these two mechanisms, which are otherwise indistinguishable from isothermal data. Temperature dependent reptation times representative of the kinetics of chain diffusion in the polymer have been evaluated for both mechanisms over a large range of process temperatures using fracture tests conducted on lap shear specimens manufactured using a hot press. Three alternate and independent techniques to estimate the reptation time in PEI indicate that the model based on the average interpenetration distance is most representative of the physical system. Lap shear strength predictions based on this formulation have been generated for various non‐isothermal conditions measured in the hot press and are within 20% of the experimental data. The model was used to show that in isothermal processes, maximum strength and toughness can be achieved in less than 1 s for temperatures exceeding 290°C. Application of the model to a highly non‐isothermal technique such as resistance welding using amorphous film technology is also presented. Model predictions show that asymptotic strength may be achieved in relatively short process times with appropriate welding conditions.