bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the characterization of nonlinear viscoelastic materials
Authors: Schapery R. A. 
Published: December 2004

AbstractStarting with specific constitutive equations, methods of evaluating material properties from experimental data are outlined and then illustrated for some polymeric materials; these equations have been derived from thermodynamic principles, and are very similar to the Boltzmann superposition integral form of linear theory. The experimental basis for two equations under uniaxial loading and the influence of environmental factors on the properties are first examined. It is then shown that creep and recovery data can be conveiently used to evaluate properties in one equation, while two‐step relaxation data serve the same purpose for the second equation. Methods of reducing data to accomplish this characterization and to determine the accuracy of the theory are illustrated using existing data on nitrocellulose film, fiber‐reinforced phenolic resin, and polyisobutylene. Finally, a set of three‐dimensional constitutive equations is proposed which is consistent with nonlinear behavior of some metals and plastics, and which enables all properties to be evaluated from uniaxial creep and recovery data.
Flow properties of plasticized PVC: Reduction to composition and interaction variables
Authors: Schreiber H. P. 
Published: December 2004

AbstractExisting theory of polymer flow has been applied to a definition of shift factors which reduce the widely different melt viscosity/shear rate diagrams of plasticized PVC compounds to well‐defined master curves. The master curves are temperature dependent and also define the flow properties of the unplasticized polymer on which a group of plasticized compounds is based. For given plasticizers, the value of the shift factor was found to depend on melt temperature and plasticizer volume fraction. Explicit relationships have been generated for three plasticizer systems; for these, melt viscosity/shear rate data can be precalculated over several decades of shear, and in the temperature range of 150–200°C. Absolute values of the shift factors depend on the type of plasticizer, and a correlation with polymer/diluent interaction parameters has been attempted. Initial results, valid only at high plasticizer volumes and near the reduced melt temperature of a polymer/plasticizer mixture, support the existence of such a correlation.
Flow properties of polyethylene melts
Authors: Mendelson R. A. 
Published: December 2004

AbstractThis discussion will illustrate some of the factors which go into the design of experiments required to solve problems in the field of plastics. Two quite diverse problems were considered. In the first case a series of experiments was described which provided a very general technique for predicting polyethylene flow behavior as a function of shear rate over a wide range of temperatures from a minimum of new data. In this case the experimentation concerned only the viscous aspect of flow and was not limited by the availability of special samples. In the second case it was desired to learn what the effect of a specific molecular structural variable was on the general melt rheological properties of polyethylene. This required the polymerization of special samples followed by detailed characterization by both solution property and melt rheological techniques.
Shear modification of polythene
Authors: Hanson D. E. 
Published: December 2004

AbstractThe changes occurring when polythene melts are subjected to shear, have been investigated using a rotating bob fitted into a ram extruder. In addition to chain scission, low density polythene exhibits reversible changes in mechanical and viscoelastic properties. The magnitude of the changes is controlled by total shear strain, and is related to molecular weight and long chain branching. The mechanism appears to be one of reversible disentanglement operating mainly on the large highly branched molecules. The work is relevant to various extrusion processes and to other long‐branched polymers.
Fatigue behavior of glass‐fiber fortified thermoplastics
Authors: Dally J. W. , Carrillo D. H. 
Published: December 2004

AbstractThis investigation deals with the fatigue behavior of a group of thermoplastics fortified with discontinuous glass fibers dispersed by an injection molding process. The thermoplastics included nylon, polystyrene and polyethylene reinforced with short (1/8 in.) and long (1/2 in.) glass fibers.Several aspects of the fatigue behavior are included in the study. First, classical S–N curves were generated under fluctuating tension with R = 0.05 to show the loss of strength due to cyclic load application. Next, the extent of progressive fatigue damage was established by measuring the residual strength after cyclic loading. Finally, hypotheses pertaining to the fatigue mechanisms operative in all four materials were made based on microscopic examinations of sections removed from fatiguedamaged specimens.
Meaning and measurement of crystallinity in polymers: A Review
Authors: Kavesh S. , Schultz J. M. 
Published: December 2004

AbstractA useful concept in polymer science is the degree of crystallinity—the fraction of the polymer that exists in a relatively ordered state. Methods of determination of the degree of crystallinity using density, infrared, thermal, N.M.R. and X ‐ray measurements are examined in light of modern notions of the structure of semi ‐crystalline polymers.
Studies on the stress relaxation of polystyrenes in the rubbery‐flow region
Authors: Narkis M. , Hopkins I. L. , Tobolsky A. V. 
Published: December 2004

AbstractRelaxation modulus curves for narrow distribution and broad distribution polystyrenes are compared and the significant effect of molecular weight distribution on these curves is shown. An empirical three‐parameter equation is shown to describe the stress relaxation behavior of narrow distribution polystyrenes. New data for high molecular weight, narrow distribution polystyrenes are presented and used to extend the applicability of previous quantitative relations for higher molecular weights. The stress relaxation technique is shown to be sensitive to the type of plasticizer used at low concentrations.
The rheology of polypropylene—the influence of molecular weight distribution on melt elasticity
Authors: Petraglia G. , Coen A. 
Published: December 2004

AbstractThe structure of isotactic polypropylene, obtained by means of Ziegler‐Natta catalysis, can be characterized only by molecular weight distribution. The mechanism of stereospecific catalysis eliminates other variables, i.e., short and long branching. In this case it is possible to develop a rheological study dependent only by polydispersity. The spectrum of relaxation times of five samples of polypropylene have been calculated from swelling measurement in the molten state and from flow master curves. The molecular weight distribution of the samples has been calculated by means of the relaxation spectrum, as suggested by Ferry. This information has been compared with that obtained by a fractionation method. There is a good agreement between the calculated and measured polydispersity curves.
Description of tensile failure of viscoelastic materials under multiaxial loading
Authors: Dong R. G. 
Published: December 2004

AbstractA description of tensile failure of polymeric materials under multiaxial loading has been formulated, based on a combination of ideas and implications derived from Smith's work on uniaxial tensile failure envelopes and the author's earlier theoretical work. Some simplification of the formal expressions was achieved by imposing restrictions that would assure that the uniaxial failure envelope is recovered under uniaxial tensile stress conditions and that the progression toward failure is monotonically increasing under monotonically increasing loads. The final result emerges as an extension of the uniaxial failure envelope applied to failure under multiaxial loads. Subsequently, the result is capable of describing rate effects to the same extent as can be described by the uniaxial failure envelope. This is an added capability over many of the existing multiaxial failure descriptions. Unfortunately, the result applied at best, only to those materials for which the uniaxial failure envelope applies; thus the generality is restricted. Some preliminary verification is presented for LX‐04‐1, a high‐explosive material composed of 85% HMX and 15% Viton by weight, using Peterman's results from 68°F biaxial tests. Further experimental work is underway.
On the solvent stress‐cracking of polycarbonate
Authors: Miller G. W. , Visser S. A. D. , Morecroft A. S. 
Published: December 2004

AbstractThe stress‐cracking of polycarbonate by a gaseous or liquid agent results from the diffusion of this agent into the polymer. The low molecular weight polymer fractions and the chain ends within the bulk of the polymer become more ordered during the diffusion and swelling process by their partial solubility in the crazing agent, causing crystallization. The creation of interfaces at areas of order‐disorder causes high shearing forces at this boundary and voids within the bulk of the polymer. These voids are then propagated as crazes or cracks at stresses much lower than the tensile strength of the polymer. Therefore, a stress‐cracking agent need not diffuse rapidly, but must be an effective environment for swelling and/or crystallization. Data from diffusion, density, thermal and molecular analyses are presented to support this mechanism.
Plasticating single‐screw extrusion theory
Authors: Chung Chan I. 
Published: December 2004

AbstractVarious solid conveying, melting, and metering theories developed for plasticating screw extrusions are reviewed. Some recommendations for improving the present melting theories are presented. It is pointed out that the overall performance of a screw extruder can be predicted only by combining the solid‐conveying, melting and metering theories into a complete mathematical package because the three functions of a screw extruder depend on each other and cannot be separated. A suggestion is made on how to combine these three theories.
Modulus of short carbon and glass fiber reinforced composites
Authors: Brody H. , Ward I. M. 
Published: December 2004

AbstractA theoretical model for a short fiber reinforced composite is proposed. The composite is assumed to consist of an aggregate of sub‐units, each sub‐unit possessing the elastic properties of a reinforced composite in which the fibers are continuous and fully aligned. The elastic constants of a partially oriented composite are then calculated by the Voigt and Reuss averaging procedures, giving upper and lower bounds respectively for the composite modulus. Comparison is made with experimental data for such composites. The measured modulus of glass and carbon fiber composites is found to be given by the Reuss or lower bound, to a good approximation compared with the difference between the bounds, for fiber orientations ranging from almost isotropic to highly aligned.
Unstable flow of amorphous polymers through capillaries I. Velocity profiles of polymer having discontinuous flow curve
Authors: Bartǒs Otakar , Holomek Josef 
Published: December 2004

AbstractCiné film was employed for recording the movement of tracer particles, thus directly determining the velocity profile in the capillary flow of model materials of polybutadiene over a range of shear stresses relating to (1.) flow conditions in which there is no distortion of the regular stream of melt emerging from a capillary, (2.) severe surface fracture, (3.) elastic turbulence, (4.) oscillatory flow of melts with discontinuous flow curves. No qualitative difference was found between the velocity profiles in conditions (1) and (2); surface fracture is not related to laminar flow disturbances and originates at the capillary exit. Surface fracture must be distinguished from elastic turbulence. The streamline velocities undergo both local and time variations within the capillary under conditions of developed elastic turbulence; the wall velocity is non‐zero. A periodic pulsation of velocities occurs in the flow curve discontinuity region; it takes place throughout the capillary and is caused by stick‐slipping of polymer on the capillary wall. The frequency of velocity pulsations coincides with the frequency of extrudate variations.
Influence of reservoir diameter on the melt elasticity in capillary flow
Authors: Han Chang Dae , Kim Kwang Ung 
Published: December 2004

AbstractAn experimental study has been carried out to investigate the influence of the reservoir‐to‐capillary diameter (DR/D) ratio on the elastic properties of polymer melts flowing through capillary tubes. For the study, a capillary rheometer, described in an earlier paper by Han, was used with DR/D ratios of 3, 6, 9 and 12. Measurements were taken of wall normal stresses in high density polyethylene along the axis of the capillary, and the axial pressure profile was used to obtain the “exist pressure,” which is believed to be an elastic phenomenon. The analysis of the experimental data indicates that, for a given capillary length‐to‐diameter (L/D) ratio, the exit pressures first increase and then level off, as the DR/D ratio is increased. This behavior of the exit pressure is in accord with that of extrudate expansion which has also been determined in the experiment. This dependence of the exist pressure and extrudate expansion ratio on DR/D ratio is explained with the concept that the amount of recoverable elastic energy stored in the melt flowing through the capillary depends on the strain history, which the melt experiences on entering the capillary.
Thermally stable photoresist polymer
Authors: Kerwin Robert E. , Goldrick Michael R. 
Published: December 2004

AbstractA new photoresist stable to 500°C has been developed. The addition of potassium dichromate to a polyamic acid, believed to be the condensation product of pyromellitic dianhydride and 4,4′‐diaminodiphenylether, results in a photosensitive polymer which can be cast or spun. The resultant film after exposure, development and post‐bake is a crosslinked aromatic polyimide. An efficient developing solution consisting of a 5:1 mixture of hexamethylphosphoramide and dimethylsulfoxide has been discovered. The system has been fully characterized in terms of composition, film formation, exposure, development, hardening and removal. This material has already proven useful as an area‐controlled, thermally stable dielectric and as a sputter‐etch resist. It has been demonstrated that under the conditions of sputter‐etching (bombardment of substrate with Ar, Ar+ species with energies from 1–300 eV) commercial photoresists, of the polyisoprene variety, char to the extent of being ineffective as a masking material. Under these same conditions, the thermally stable resist retains its film integrity and uniform sputter‐etch rate. An exemplary processing sequence is included as an appendix.
Some melt flow and mechanical design aspects of large extruders
Authors: Fenner R. T. , Williams J. G. 
Published: December 2004

AbstractThis paper examines two aspects in the design of large extruders. An analysis of the thermal problems in the flowing melt is given in terms of dimensionless groups and the results are applied to the scale‐up problem in extruder design. An analysis of the mechanical stability of extruder screws is also given including the effect of axial buckling and whirling. The results are examined as a possible limitation on extruder dimensions.
Properties of poly(vinylidene fluoride)
Authors: Stallings J. P. , Howell S. G. 
Published: December 2004

AbstractThe properties of fluorocarbon plastics have made them desirable for numerous new applications. Poly(vinylidene fluoride) (PVF2) can be easily extruded into films or fibers or injection molded into a variety of shapes. It was found that crystallinity, molecular weight distribution and polymer structure are important in establishing resin properties. Highly crystalline PVF2 with a narrow Gaussian molecular weight distribution gives specimens with optimum physical and chemical properties.
Fracture mechanics of polymers
Authors: Williams J. G. 
Published: December 2004

AbstractA review of fracture mechanics and its relevance to designing with plastics is given. The basic philosophy of assuming the presence of flaws is developed, and the relevant equations are given. Data is presented for several polymers illustrating thickness and viscoelastic effects. A method of analysis for impact testing is then described together with some data. The unity of the data from a wide range of tests is emphasized.
Physical aging in plastics and other glassy materials
Authors: Struik L. C. E. 
Published: December 2004

AbstractThis paper surveys the basic aspects of physical aging. It shows that aging i s a general and important phenomenon found in all organic and inorganic glasses and in some metals as well. Moreover, the behavior of all these materials is very similar. It further shows that aging cannot be ignored in the testing of plastics, particularly in the prediction of their long‐term behavior.
Fatigue crack propagation in poly(methyl methacrylate): Effect of molecular weight and internal plasticization
Authors: Kim S. L. , Skibo M. , Manson J. A. , Hertzberg R. W. 
Published: December 2004

AbstractIn spite of the importance of fatigue behavior in engineering plastics, relatively few fundamental studies have been made of the effects of polymer structure, molecular weight, composition, and morphology on fatigue crack propagation (FCP). As, part of a broad program for the study of such effects, the role of molecular weight and internal plasticization has been studied in poly(methyl methacrylate) (PMMA) which had been specially prepared and characterized with respect to molecular weight, dynamic mechanical behavior, and, in some cases, stress‐strain response. As expected, values of fracture toughness,Kc, varied considerably as the molecular weight was rai ed, from 0.7 MPa, √matMv= 1.0 × 105to 1.1 atMv, = 4.8 × 106. However, a specific effect of fatigue was noted: over the same range ofKc, values of FCP rate decreased by two orders of magnitude as molecular weight was; increased. It is proposed that this high sensitivity is due to differences in the degree of chain disentanglement effected by the cyclic loading, with consequent differences in the strength of the craze preceding the crack. With PMMA plasticized internally with a low level (10 percent) of n‐butyl acrylate (nBA), the FCP rate andKc, were similar to those of controls, with very high rates shown. At higher nBA levels (up to 30 percent), the sensitivity of FCP rate to stress intensity factor range decreased considerably,Kc, increased by 30 percent and the pre‐exponential constant in the growth rate law increased. Plasticization weakens the polymer but at high degrees leads to enough hysteretic heating to induce local creep and crack blunting.
Oriented short glass fiber composites. III. Structure and mechanical properties of molded sheets
Authors: Kacir L. , Narkis M. , Ishai O. 
Published: December 2004

AbstractOriented short fiberglass mats prepared by the ERDE converging flow technique of fiber/glycerine dispersions were studied. Fiber orientation distribution in mats, prepregs and molded sheets were investigated by optical and X‐ray techniques. Longitudinal and transverse fracture surfaces of short fiberglass/epoxy molded sheets were analyzed. The effect of fiber length on tensile properties was also studied. The experimental results obtained on longitudinal, transverse, and off‐axis tensile modulus and ultimate strength were compared with classical elastic equations for continuous reinforcement.
Flexural fatigue of unidirectional fiberglass‐reinforced polyeste
Authors: Fesko Donald G. 
Published: December 2004

AbstractFlexural fatigue data about a non‐zero mean stress are presented for unidirectional fiberglass‐reinforced polyester composites. The data are useful for the design of structural components and extend our knowledge regarding the mechanical performance of composite materials. In particular, the dependence of modulus, strength, and fatigue strength on glass content, both dry and wet, is described. Also, the extent to which design allowable stresses are influenced by minor impacts and by machining is discussed.
Wall slip and its implications in the design of single screw melt‐fed extruders
Authors: Worth R. A. , Parnaby J. , Helmy H. A. A. 
Published: December 2004

AbstractThe phenomenon of wall slip during the capillary flow of polymer melt is investigated for low and high density polyethylene. It is found that wall slip occurs in both cases, and that the effect is related to melt fracture. In addition, it is shown that a silicone fluid exhibits wall slip. The performance of the metering zone of a 38 mm diameter single‐screw extruder is discussed in relation to wall slip. It is suggested that the power consumption of the extruder is reduced as a result of slip at the polymer/metal interface. Results based on experiments with the silicone fluid tend to support this hypothesis. A theoretical analysis of the effects of wall slip upon throughput rate and power consumption for a one‐dimensional isothermal Newtonian case is included.
Crosslinking systems in the graft polymerization of chromium‐tanned collagen
Authors: Harris E. H. , Feairheller S. H. 
Published: December 2004

AbstractTen polyfunctional vinyl‐type monomers were graft polymerized with butyl acrylate or methyl methacrylate onto chromium‐tanned collagen in a redox initiated, emulsion‐type system. The thickness of the grafted leathers showed an increase ranging from 9 to 159 percent. The regression of total polymer on thickness gave a better fit than did bound polymer, the correlation coefficient being 0.774. The tensile load at break increased in all but one case, with a maximum increase of 70 percent over the control. Since the thickness increase was usually greater than the load increase, the tensile strength usually decreased. The changes, in tensile elongation were not always in agreement with those anticipated from crosslinked bulk polymers. In addition to these physical effects, inclusion of the polyfunctional comonomers generally reduced the amount of extractable polymer. A hypothesis is proposed to explain some of the observed effects.
Effect of rheological parameters on phase morphology of poly blends: A route to computer aided design and development of industrial polyblends
Authors: Plochocki A. P. 
Published: December 2004

AbstractSet of procedures employing melt viscoelasticity functions for selecting components and composition of the binary polyblends and estimating minor phase domain size is introduced and illustrated with examples. The procedures intended for Computer Aided Manufacture of the polyblends (CAMOBLE) are based on shear stress dependent viscoelasticity ratios, and the selection of the composition exploits stress dependent synergism of the viscoelasticity functions. Also used is auxilary procedure for composition selection is based on verified blending laws accounting for interaction and shear effects. Evaluation of the performance characteristics (“mechanical properties”) is illustrated with a modified Kerner model.
The effect of initial morphology on the mechanical properties of ultra‐high molecular weight polyethylene
Authors: Zachariades Anagnostis E. , Kanamoto Tetsuo 
Published: December 2004

AbstractStudies of the physical and mechanical properties of melt crystallized ultra‐high molecular weight polyethylene morphologies from melts with different thermal histories indicate that their properties depend on the degree of fusion of the powder particles during their processing and can be enhanced by heating the polymer above 220°C. The degree of cohesion of the powder particles and their initial morphology also have a significant effect on the deformability of the polymer in the solid state forming methods used to prepare high modulus and strength products.