bluuebunny/crossref_metadata_2025_split huggingface dataset:
Some corrosion mechanisms in attack of resin and resin‐glass laminates
Authors: Allen R. C. 
Published: December 2004

AbstractIn contrast to metallic corrosion where electrochemical corrosion mechanisms are dominant, a variety of mechanisms play a role in degradation of fiber reinforced plastic (FRP) structures. Attack may occur by physical or chemical means or by a combination of both. Although some actions of particular attacking species may be quite specific, there are a number of general corrosion mechanisms and broad guidelines that can be established in order to choose a resin suitable for a particular service. Corrosion mechanisms are illustrated by interactions of environments with vinyl ester resins. Attack in non‐aqueous media is often related to chemical similarity between attacking specie and the resin. Among chemically similar resins, the extent of this type of attack is often influenced by the crosslink density of the resin. It is shown that the solubility parameter of the attacking specie is useful in predicting suitability of a resin for service, if the resin has been evaluated by a test sequence in organic media of varying solubility parameters. In aqueous media it is found that physical attack can occur by means of an osmotic permeation of the resin by water. Degradation by pure water is often more severe than that caused by ionic solutions. Such physical attack can cause delamination and blistering of laminates and must be regarded as a potentially serious corrosive mechanism, although not primarily chemical in nature. In addition to physical attack, chemical attack can occur. Saponification by sodium hydroxide and oxidation by sodium hypochlorite are discussed in some detail as examples. It is shown that in both these cases the chemical corrosive process may be inhibited by controlling the physical corrosion process due to water.
The thermal expansion of reinforced nylon‐6 composites through the matrix glass transition temperature
Authors: Segal Leon 
Published: December 2004

AbstractThe coefficient of thermal expansion (CTE) of nylon‐6 reinforced with particulate filler, short glass fibers, and long‐to‐continuous glass fibers was measured between −30 and 170°C. As the reinforcement level, the reinforcement aspect ratio, or degree of orientation increases, the linear CTE decreases. The Tg range for the composite system is equal to the Tg for the pure nylon‐6 matrix. An unexpected result is observed when the nylon‐6 is reinforced with long or continuous glass fibers in random planar orientation and the weight fraction of reinforcement exceeds 10 percent. In this case, the longitudinal linear CTE (parallel to the plane of the fibers) above the Tg is lower than the longitudinal linear CTE below the Tg. Analysis of the mathematical descriptions of composite thermal behavior indicates that an extremely low composite modulus in the transverse direction above the Tg may be a cause for this low CTE. The differences in CTE between short fiber and long fiber reinforced compositions indicate that the critical fiber length for thermal stress transfer may be higher than the critical fiber length for mechanical stress transfer.
An ultrasonic‐acoustic technique for nondestructive evaluation of fiber composite quality
Authors: Vary Alex , Bowles Kenneth J. 
Published: December 2004

AbstractThis report describes an ultrasonic‐acoustic technique used to measure a “stress wave factor” in order to nondestructively assess the quality of composite structures. In a prior study this factor was found effective in evaluating the interlaminar shear strength of fiber‐reinforced composites. Details of the method used to measure the stress wave factor are described. In addition, frequency spectra of the stress waves are analyzed in order to indicate the nature of the wave phenomena involved. The stress wave factor can be measured with simple contact probes requiring only one‐side access to a part. This is beneficial in nondestructive evaluations because the waves can run parallel to fiber directions and thus, in many cases, measure material properties in directions assumed by actual loads. Moreover, the technique can be applied where conventional through transmission techniques are impractical or where more quantitative data are required. The stress wave factor was measured for a series of graphite polyimide composite panels and results obtained are compared with through transmission immersion ultrasonic scans.
Flow of polymers with pressure‐dependent viscosity in injection molding dies
Authors: Lord Herbert A. 
Published: December 2004

AbstractConsiderable effort has been expended recently by a number of researchers to develop methods of simulating the flow of polymers in injection molding dies. The computer models developed by these researchers provide the mold designer with useful quantitative information concerning the predicted effect of design parameters on mold, filling characteristics. This paper will describe some recent work which is aimed at increasing the usefulness of these models by more accurately describing the flow behavior of those polymers, such as polycarbonate resins, which exhibit a strong effect of pressure on viscosity.
Review of forging, stamping, and other solid‐phase forming processes
Authors: Kulkarni K. M. 
Published: December 2004

AbstractIn the last ten years, a considerable amount of work has been conducted on many different processes distinct from common plastics processing methods such as injection molding, extrusion, and compression molding. Perhaps the most common feature of these new techniques is that they resemble more the methods used for fabricating metallic materials in solid phase. However, there is a lack of uniform terminology. More importantly, the commercial acceptance and applicability of these processes have been slow. This review attempts to summarize the important findings of various publications and, whenever possible, to give information about potential or actual industrial applications. The purpose is to provide a brief overview of the state‐of‐the‐art of the whole technology. Advantages, disadvantages, and the need for more work are pointed out as they relate to different processes and to crystalline and amorphous materials. A few instances where material was heated beyond the melting temperature by a small amount are included in the review when the processing method was similar to solid‐phase forming.
Time constants for moisture diffusion through a permeable barrier into an airspace
Authors: Pinnes Edward L. 
Published: December 2004

AbstractThis paper arose from a study of the use of polymeric materials to protect humidity‐sensitive items from damp ambient conditions. A one‐dimensional model for the Fickian diffusion of moisture through a permeable wall into a volume of air is considered. The humidity in the airspace asymptotically approaches equilibrium with the exterior, and the time constant is defined as the time to reach 1–1/e of its ultimate value. Exact and approximate solutions are considered. Depending on the system geometry and properties, the time constant is either permeability‐controlled or diffusivity‐controlled, or somewhere in between. Under certain conditions, there exists an optimum combination of airspace depth and wall thickness that maximizes the time constant.
Physiochemical quality assurance methods for composite matrix resins
Authors: May C. A. , Hadad D. K. , Browning C. E. 
Published: December 2004

AbstractFiber reinforced composite structures have gained a significant position as materials of construction for the aerospace industry. It thus follows that large expenditures of funds and human lives are dependent on the reliability of these products. An important step in gaining confidence in a part is knowing that the starting prepreg has the same chemical formulation in each lot of material and that each lot has been processed in the same manner. This can be accomplished by physiochemical characterization. The techniques described herein were developed for 177°C (350°F) epoxy matrix systems. However, the methods form a basis for developing similar procedures for other types of matrices.
Orientation in injection molded polystyrene
Authors: Kamal Musa R. , Tan Victor 
Published: December 2004

AbstractThe ultimate properties of injection‐molded thermoplastics articles are controlled to a large extent by flow and heat transfer phenomena that take place during the injection‐molding process. In fact, the thermo‐mechanical history of the melt during the molding process leads to a non‐uniform distribution of many of the critical properties of the molding. Birefringence has been employed as an indirect measure of the distribution of frozen stresses or strains in amorphous polymers. The present study employs birefringence to study the development of frozen stresses in injection‐molded polystyrene. In general, orientation in the flow direction is much greater than the orientation in the transverse direction of the moldings. In the vicinity, of the gate, where mold filling is characterized by spreading radial flow of the melt, the hoop stresses (planar deformation) at the melt front give rise to high orientation in the transverse direction. It appears that relaxation phenomena are not very important during the filling stage; however, they become more, important in the packing and pressure holding stages. With the aid of the appropriate rheo‐optical relationship, it is shown that the distribution of frozen‐in orientation in injection‐molded polystyrene may be estimated on the basis of data relating to pressure variations during the filling stage.
Poly(vinyl chloride), Part II: Effect of polymerization temperature and molecular weight on the glass transition and melting point of poly(vinyl chloride)
Authors: Daniels Charles A. , Collins Edward A. 
Published: December 2004

AbstractA detailed study was made of the thermal behavior of poly(vinyl chloride) (PVC) homopolymers, whose chain length and structure were independently manipulated. Normal PVC polymerizations are made at temperatures, the selection of which determines the polymer chain length. In the case of PVC, this choice of temperature also determines its syndiotacticity, and so, its glass transition temperature, and in many ways, its processibility. The ability to understand how to control chain structure and length in PVC is critical in designing polymers for selected specific end use conditions. The thermal spectrum is known to be one measure of how polymers will perform. This study reveals how such controlled chain length/structure PVCs are characterized by thermal methods, and how one can separate individually the effects of syndiotacticity and molecular weight on thermal properties of poly(vinyl chloride).
An experimental study of the influence of carbon black on the rheological properties of a polystyrene melt
Authors: Lobe Vincent M. , White James L. 
Published: December 2004

AbstractA broad range of experiments on carbon black filled polystyrene melts shows the reinforcing effect of the filler. This study represents one of the most extensive investigations of a series of highly filled polymer melts. Stress relaxation and dynamic experiments characterize the small strain behavior while the steady state shear viscosity, normal stresses, and elongational flow experiments describe the large strain deformation rate response. Extrudate swell and unconstrained shrinkage of extrudates are also measured. Highly filled systems exhibit yield values. This is seen in the dynamic experiments and in the shear and elongational viscosities. Viscosity does not level off at finite values with decreasing deformation rate but continues to increase in an approximately inverse manner. This corresponds to yield values of order 5 × 105 dynes/cm2. The storage modulus also does not tend to zero at low frequencies. The small strain dynamic properties and stress relaxation results suggest high memories for small strain experiments. Txtrudate swell values are however small and the systems exhibit minimal delayed recovery. The implications of this are considered. Generally it is argued that at volume loadings between 10 and 20 percent, the system takes on the characteristics of a gel and the response is similar to that of a Schwedoff body.
The torsion pendulum in the investigation of polymer
Authors: Heijboer J. 
Published: December 2004

AbstractThe early history of the use of the torsion pendulum in the investigation of polymers is described together with the development of dynamic mechanical testing at TNO. Examples are listed of studies of structure‐property relationships by means of the torsion pendulum. Techniques using supported. Samples are compared with those using unsupported samples, particular attention being paid to the advantages and restrictions of torsional braid analysis (TBA). The comprehensive application of TBA by Professor Gillham is reviewed; a few TBA results are compared with our torsion pendulum measurements. A rheologist's view on the so‐called liquid‐liquid transition (Tn) in polymer melts, as observed by TBA, is presented.
Effect of cure history on dynamic mechanical properties of an epoxy resin
Authors: Lewis A. F. , Doyle M. J. , Gillham J. K. 
Published: December 2004

AbstractThe effect of cure history on the dynamic thermomechanical properties of a high temperature curing epoxy resin has been studied using torsional braid analysis. In isothermal cures “full cure” is not possible except at temperatures above the maximum glass transition temperature (Tg) of the cured resin, hence the necessity of a “post‐cure” after lower temperature isothermal cures. The highest Tg and maximum cross‐linking in the cured resin was for a linear heating rate of 0.05°C/min from 30 to 200°C; higher heating rates lead to lower glass transition temperatures.
Interaction of water with macromolecules by dynamic mechanical analysis
Authors: Hiltner Anne 
Published: December 2004

AbstractThe dynamic mechanical relaxation of macromolecules is found to be very sensitive to the presence of water which is strongly associated with the macromolecule. Polymers with the amide group exhibit a characteristic loss process (β or β2) in the region of 200K which is associated with the amide‐water complex. Changes in the relaxation parameters with water content permit the stoichiometry of the interaction to be determined. Polymers with ionic groups on the side chain exhibit a higher temperature relaxation (β1) associated with side chain motion. This relaxation is also affected by the presence of water. Analysis of the effect of water on the loss parameters of the β2 and β1 processes has provided insight into the nature of the interaction of water with complex biological macromolecules.
Contributions of torsional braid analysis to Tu
Authors: Boyer Raymond F. 
Published: December 2004

AbstractThe accomplishments of Borden Award Winner John K. Gillham and his colleagues using Torsional Braid Analysis (TBA) and Differential Scanning Calorimetry (DSC) to investigate the Tg and T > Tg or Tu regions of anionic and thermal poly styrenes (PS) are evaluated and related to work on PS and other polymers and to controversies surrounding TBA and the Tu transition. Arguments are presented to refute the contention that Tu by TBA is an artifact produced by the braid and the contention that Tu has a relaxational nature but no thermodynamic basis. Two distinct behavior patterns are found for Tu vs log M̄n plots: quasi‐static methods such as DSC on fused films show Tu to level off above Mc and approach an asymptotic value of ∼435K; dynamic methods involving melt flow show that Tu increases without limit above Mc because of entanglements. A compilation is presented of 25 investigations of Tu on polybutadiene, poly(methyl methacrylate) (PMMA), PS, plasticized PS, and atactic polypropylene, involving twenty experimental techniques. The behavior of zero shear melt viscosity for PS is summarized. Gillham's work has not only led to clarification of many isolated papers in the literature but has also inspired various parallel experimental and literature studies on Tu. We conclude that Tu is a molecular level transition which, like Tg, exhibits both kinetic (relaxational) and thermodynamic aspects. It is shown that heat capacity should be a more sensitive method than dilatometry for studying the Tu transition.
Fourier transform infrared spectroscopic study of transitions above Tg in atactic polystyrene
Authors: Enns John B. , Boyer R. F. , Ishida Hatsuo , Koenig J. L. 
Published: December 2004

AbstractFourier transform infrared spectroscopy (FT‐IR) has been applied to the study of the molecular mechanisms of transitions of atactic polystyrene above Tg. Intensity measurements of vibrational modes as a function of temperature revealed two transitions above Tg, which are designated as Tu and T′u. T′u is independent of molecular weight as opposed to the molecular weight dependent Tu whose behavior is similar to Tg. Infrared measurements are more sensitive to T′u than Tu. Conformationally sensitive bands show that T′u may be related to disruption of local order where there is a negligible barrier to conformational change.
The influence of drawing, twisting, heat setting and untwisting on the structure and mechanical properties of melt spun polypropylene filament
Authors: Kitao Toshio , Spruiell Joseph E. , White James L. 
Published: December 2004

AbstractThe changes in structure and mechanical properties of melt spun polypropylene filaments were determined as the filaments were successively (i) drawn, (ii) twisted, (iii) annealed, and (iv) untwisted. Filaments spun to two different melt draw down levels were studied. The effects of draw temperature and draw ratio, extent of twist, annealing temperature, and the extent of untwisting were examined. Melt spun and twisted filaments (draw ratio of 1) were also considered. Structural characterization techniques used in this study include wide angle (WAXS) and small angle (SAXS) diffraction, scanning electron microscopy (SEM), birefringence and density measurement. Drawing increased crystalline orientation and at low temperatures disrupted the monoclinic unit. cell existing in the melt spun fibers. The drawing produced considerable fibrillation under all conditions even when carried out at 120°C. The fibrillation quid void formation due to low temperature drawing was more pronounced. The variation of WAXS patterns and mechanical properties of twisted drawn filaments was interpreted by presuming that the fibrils act in a manner analogous to that of the filaments in a continuous filament twisted yarn. In the case of incompletely drawn filaments the effect of additional drawing occurring during twistin must be considered. Twisted fibers annealed at 150°C sowed a drastic reduction in tensile properties, while those annealed at 125°C did not set the twist and caused the fibers to tend to untwist. Annealing at 140°C appeared to give satisfactory heat setting. Annealing of cold drawn and cold drawn and twisted fibers increased the density, removed many defects and reformed a well defined monoclinic crystal structure and a lamellar morphology. Untwisting of heat set filaments tended to give back the properties of hot drawn fibers. In some cases, however, the opening of cracks was noted.
Some performance aspects of the extruder as a reactor
Authors: Siadat B. , Malone M. , Middleman S. 
Published: December 2004

AbstractContinuous flow reactors are increasingly utilized for polymerization. Two aspects of reactor performance are considered here, with major emphasis on the screw extruder as a reactor. First, the effect of residence time distribution is discussed, and comparative calculations are made for several flow reactors using a simple model for a polycondensation reaction. We conclude that the extruder behaves nearly as a plug flow reactor. Second, the effect of viscous heating in the extruder is accounted for, in the limiting case of adiabatic operation. A model for the effect of heating on conversion is developed, and some implications for scale‐up are noted.
Simultaneous interpenetrating networks based on castor oil elastorners and polystyrene. IV. Stress‐strain and impact loading behavior
Authors: Devia N. , Manson J. A. , Sperling L. H. , Conde A. 
Published: December 2004

AbstractThe stress‐strain and impact loading behavior of simultaneous interpenetrating networks (SIN's) based on three elastomers derived from polymerized castor oil and polystyrene was studied. The elastomers included the sebacic acid polyester, the 2,4‐tolylene diisocyanate (TDI) polyurethane, and the mixed sebacic acid‐TDI poly(ester‐urethane). Both toughened plastic and reinforced elastomer compositions were prepared. Stress‐strain measurements and Izod impact studies were carried out at room temperature. Both the plastic and the elastomeric SIN's proved tougher than their corrresponding homopolymer networks. Elongations to break of about 8 to 16 percent were found for the plastics, while the elastomers ranged from 55 to 125 percent. The castor oil polyester elastomer toughened plastic yielded the greatest improvement in impact resistance, having a value of 68 J/m.
Sintering behavior of poly(methyl methacrylate) particles
Authors: Narkis M. 
Published: December 2004

AbstractThe sintering behavior of poly(methyl methacrylate) (PMMA) particles was studied by photographic, means and mechanical testing. Interpretation of the data gives the sequence of events taking place during high temperature sintering (without pre‐compaction). Optical observations, show essentially two main sintering regions while mechanical studies also give an intermediate transition zone separating these two regions. It is suggested that the flow mechanisms involved in the sintering process are viscoelastfc flow in the lower temperature range and shorter times and non‐Newtonian viscous flow in the higher temperature range and longer times.
Wall thickness distribution in thermoforming
Authors: Rosenzweig N. , Narkis M. , Tadmor Z. 
Published: December 2004

AbstractThis paper presents an isothermal, one‐dimensional model predicting wall‐thickness profiles of vacuum‐ or pressure‐formed products. After formulating a set of simplifying assumptions theoretical analyses of forming into conical and truncated (deep and shallow) molds are presented and discussed. Fair agreement is found between previously reported experimental results and the proposed theoretical models.
Grüneisen functions of semicrystalline polymers
Authors: Shen Mitchel 
Published: December 2004

AbstractThe current, and rather incomplete, understanding of the role of amorphous contribution to the Grüneisen functions of semicrystalline polymers is reviewed. There are two kinds of Grüneisen functions. The microscopic mode Grüneisenr parameter is a measure of the volume dependence of lattice frequencies in a solid. Their magnitudes vary with the specific mode. The macroscopic Grüneisen constant relates the mechanical and thermal parameters in solids. It is a weighted average of mode Grüneisen parameters. At a given temperature there is only one Grüneisen constant for a material. Because the various experimental techniques often favor certain lattice modes, there is a great variation in the literature values of Grüneisen functions for polymeric solids., For semicrystalline polymers, the degree of crystallinity and thermal history also affect the measured magnitudes. In this work a unified derivation of the existing equations will be given. Current theoretical models for the Grüneisen constants are described. The available literature data on Grüneisen constants of semicrystalline polymers, principally polyethylene, will be discussed.