bluuebunny/crossref_metadata_2025_split huggingface dataset:
Crazing in glassy polymers: Studies on polymer‐glass bead composites
Authors: Narkis M. 
Published: December 2004

AbstractStress‐strain curves of glass bead‐filled glassy polymers show a slope discontinuity related to crazing in the matrix. This discontinuity serves as basis for a simple method for determining εp′ the critical strain in the polymer to initiate crazing. The stress at the discontinuity (σD) is governed by the nature of the dispersed particles acting as stress concentrators. The two parameters, εp′ and σD, (neither of which is a function of the filler content) have the following values in ascending order σ = 1540, 1750, 1880, 2390 and 3300 psi for polystyrene, ABS, poly(vinyl chloride), SAN and poly(phenylene oxide) respectively; εp = 0.63, 0.72, 0.81, 1.10 and 1.67 percent for poly(vinyl chloride), polystyrene, SAN, ABS and poly(phenylene oxide) respectively. In coupled particulate systems, (σD) is increased and apparently vaies with the efficiency of the coupling agent. The modulus of a particulate system can be predicted by a one‐parameter equation.
An analysis of caprolactam polymerization
Authors: Tirrell M. V. , Pearson G. H. , Weiss R. A. , Laurence R. L. 
Published: December 2004

AbstractA versatile model for ε‐caprolactam polymerization is presented. A deterministic, mathematical basis for obtaining the most probable distribution of molecular weights in batch polymerization is developed. Continuous polycaproamide production has been modeled and shown to give othe than most probable distribution in many cases. The effect of adding monofunctional agents has been investigated. Results of some preliminary studies toward determining the optimal reactor configuration are presented.
Characterization of the time‐temperature‐viscosity behavior of curing B‐staged epoxy resin
Authors: Roller M. B. 
Published: December 2004

AbstractThe work described herein was initiated in order to generate resin characterization data that could describe a B‐staged epoxy material via the viscosity‐time‐temperature interactions that are inherently related to the nature of thermoset processing. The technique of chemorheology is explored as a means of characterizing the viscosity‐time‐temperature behavior of the B‐staged epoxy resins. The resins studied are typical of those available as glass‐impregnated prepreg bonding sheets used to manufacture multilayer printed wiring boards. The B‐staged resins were characterized isothermally at various curing temperatures. Their isothermal behavior was correlated via an empirical viscosity expression in the form of a dual Arrhenius model. Experiments were then conducted in a nonisothermal temperature mode, measuring viscosity as a function of both time and temperature. The viscosity model was taken into the nonisothermal temperature mode by introducing a time‐temperature integral. Good correlations between measured and predicted dynamic viscosity profiles are presented. Deviations are explained in terms of resin chemistry. The generalizations of behavior are discused. Calculations are presented which allow the comparison of the various B‐staged resins in terms of their viscosity behavior under the influence of an actual lamination thermal profile.
Reproducibility of stress‐cracking test results
Authors: Roe R. J. , Gieniewski C. 
Published: December 2004

AbstractThe environmental stress crack resistance of polyethylene is measured most conveniently by the bent‐strip method described in ASTM D‐1693‐70. The method has, however, suffered from poor reproducibility of test results. In this work we have carefully studied the effect of individual experimental variables that enter the test method. The effects considered are: the thermal history of test specimens; uncontrolled variations in the test procedures such as the sample holder width, the specimen thickness, and the stress relaxation occurring during the test; and the variability in the test results arising from the statistical nature of fracture process. It is concluded that each of the following four factors, when not properly controlled, could contribute an apparently random variation of a factor of two or more in the test results. These are (1) the aging of polyethylene specimens at room temperature, (2) the width of the specimen holder, (3) the dimensions of the tools employed for bending and transferring specimens, and (4) statistical fluctuations of the final results arising from the limited number of specimens tested and also from the stress relaxation occurring in the specimen during the test. By carefully controlling these and other variables, it should be possible to design a test procedure which is expected to yield results of a known precision and can serve even as a research tool.
Mechanical properties of discontinuous fiber reinforced thermoplastics. II. Random‐in‐plane fiber orientation
Authors: Blumentritt Bruce F. , Vu Ban T. , Cooper Stuart L. 
Published: December 2004

AbstractThe mechanical properties are presented for a series of discontinuous fiber‐reinforced thermoplastic composites made with random‐in‐plane fiber orientation. The matrix and fiber materials were chosen to provide a wide range of strength, modulus, ductility and adhesive properties. In many cases strong, rigid, yet tough composites were fabricated. Strength levels of over 20,000 psi and modulus values over 1,000,000 psi were reached in several systems reinforced with short Kevlar‐49 and graphite fibers. A strong dependence of composite strength and modulus on fiber strength and modulus was noted indicating good transfer of load from matrix to reinforcement. Fiber efficiency factors for modulus and strength were calculated for the experimental composite systems and averaged 0.19 and 0.11 respectively. Data were analyzed using basic composite theory. Properties of the experimental composites could not be predicted from constituent properties.
Residence time distribution in twin‐screw extruders
Authors: Todd David B. 
Published: December 2004

AbstractTwin screw extruders are finding increased usage in reacting and devolatilizing applications. Using self‐wiping profiles, the twin screws fulfill the requirement that there be no “dead” or “unmixed” zones. Agitator design must be chosen with care so that a reasonable balance can be obtained between forwarding rate, surface‐generation rate, vapor passageway, power, and axial mixing. Techniques have been developed for measuring residence time distributions and characterizing axial flow behavior. The method also permits direct determination of the holdup in starved barrel applications. Data on residence time distribution are presented for 4‐in. diameter twin screw equipment with a variety of rotor configurations.
An experimental study of sandwich injection molding of two polymer melts using simultaneous injection
Authors: White James L. , Lee Biing‐Lin 
Published: December 2004

AbstractAn experimental study of two phase flow of polymer melts relating to injection molding has been carried out. The experiments specifically concern rheological phenomena which may occur when two melts are simultaneously injected through a runner system leading to a mold cavity. Injection in the form of annulus‐core configurations and simple stratified flow are investigated. A new injection molding method is proposed which is based upon the latter technique. Encapsulation of one melt by the other occurs in the runner system and formation of a sandwich structure in the cavity results. Annulus‐core injected configurations were only found to be stable when the lower‐viscosity melt is in the annular region.
Environmental effects on deformation, strength, and degradation of unidirectional glass‐fiber reinforced plastics. I. Survey
Authors: Ishai Ori 
Published: December 2004

AbstractThis survey covers the topic of environmental effects on the mechanical behavior of fiber‐reinforced plastics. It deals also with the separate and combined effects of temperature, hygrometry and loading on mechanical characteristics. The response of the phases of the composite‐fiber, the matrix and the interfacial region to the environmental loading history, is discussed. Conflicting hypotheses regarding the causes and mechanism of the degradation process and of the long‐range durability of the composites are examined.
Predicting toughness of impact thermoplastics from high‐speed tensile data
Authors: Fenelon Paul J. 
Published: December 2004

AbstractA photographic procedure is presented for evaluating uniaxial true stress‐true strain tensile behavior of thermoplastics at strain rates typical of impact situations. The advantage of combining this information with observed macroscopic material changes which occur during tensile deformation is discussed in terms of establishing parameters which define end use abuse resistance of impact thermoplastics. In particular, test parameters are evaluated which provide a direct correlation with measured bottle drop failure resistance for selected materials. These test parameters are obtained by measuring the area under true stress‐true strain curves obtained at impact strain rates. Area is measured up to the point of ultimate uniaxile tensile strain. Ultimate uniaxial tensile strain corresponds to either (a) strain at onset of necking in materials which produce necking during deformation, or (b) strain at fracture in materials which deform without necking. Measured test parameters are discussed in terms of modern theories of strength of materials. Pitfalls associated with quantitatively defining the abuse resistance of thermoplastics based on total energy for breaking, i.e., conventional numeric criterion of impact strength, it also discussed.
Mold‐filling studies for the injection molding of thermoplastic materials. Part II: The transient flow of plastic materials in the cavities of injection‐molding dies
Authors: Lord H. A. , Williams G. 
Published: December 2004

AbstractA practically‐oriented computer model which computes the temperature, pressure, and velocity fields in a cavity during the mold filling portion of the injection molding process is described. The model is structured so that it can be used for cavities having non‐simple shapes and for commonly used molding compounds with complicated viscosity, shear rate, temperature relationships. Predictions from the model are found to be in good agreement with results obtained from exact solutions to special cases. Model predictions in molding problems have been found to correctly describe trends such as an increase in the pressure required to fill molds as injection rate, shot temperature, and mold temperature decrease, and to be reasonably accurate when compared to data for plaque, disc, and telephone housing molds over a wide range of molding conditions. Some illustrative examples of the use of the model in solving real molding problems are provided.
Asymmetric loading of bonded rubber cylinders
Authors: Sims D. F. 
Published: December 2004

AbstractElastomeric bearings which consist of cylindrical rubber layers bonded on their inner and outer curved surfaces to metal cylinders are investigated theoretically and experimentally. Emphasis is placed on two asymmetic loading modes, radial loading and bending or tilting moments. An approximate theoretical treatment based on linear elastic behavior is proposed. Experimental spring constants are compared to the theoretical predictions for thin elastomer layers of various lengths. It was found that for highly confined layers, the theoretical spring constants must be modified to obtain agreement with experimental results. The importance of elastomer bulk deformation, shrinkage stresses from elastomer cure, and tension‐compression stress‐strain behavior is also evaluated.
The effect of interlayers on the transverse stresses in fiber composites
Authors: Arridge R. G. C. 
Published: December 2004

AbstractNumerical results are given of calculations of the radial, transverse, and shear stresses in the matrix surrounding a cylindrical inclusion in plane strain perpendicular to the cylinder axis, this being taken as a model of a fiber composite under transverse loading. It is shown that the presence of an interlayer on the fiber at a thickness which is a small fraction of the fiber diameter can significantly affect the stress concentrations in the matrix. The interlayer‐fiber ‘composite’ can be ‘matched’ to the matrix by suitable choice of interlayer elastic moduli. In particular, if the shear modulus of the interlayer is smaller than that of the matrix and its Poisson's ratio is very small, the stress concentrations in the matrix are considerably reduced and the composite should be less subject to failure by delamination.
Thermal expansion transients of a cis‐1,4 polybutadiene elastomer at various levels of strain
Authors: Caruthers J. M. , Cohen R. E. 
Published: December 2004

AbstractThe length‐temperature behavior of elongated elastomeric networks of cis‐1,4 polybutadiene was observed following abrupt, nearly step‐function changes in the temperature of the specimen environment. The thermal expansion behavior is reversible, and the transient length changes are in the direction anticipated from rubber elasticity theory, i.e., dL(t)/dT is negative. The observed long‐time values of the thermal expansion coefficient are in good agreement with equilibrium length‐temperature coefficients reported for other elastomers. Results indicate that both thermal diffusion and retarded creep deformation contribute to the transient phenomenon, with the latter mechanism dominating.
Silicone‐polyethylene blends
Authors: Falender James R. , Lindsey Sarah E. , Saam John C. 
Published: December 2004

AbstractPolyethylene and reactive, high molecular weight polydimethylsiloxanes have been blended under conditions of shear and elevated temperature in order to form uniform, thermoplastic blends. The materials can be extruded, coated on wire, injection molded, or compression molded. Despite the thermoplastic nature, a high gel fraction is present. A structure is proposed consisting of microgelled and grafted particles of silicone dispersed in polyethylene. When compared to pure polyethylene, the blends show lowered modulus over a temperature range of −150 to +65°C increased gas permeability, and lowered mixing energies. Electrical properties include corona resistance superior to polyethylene and a resistance to degradation under conditions simulating those experienced by buried cables superior to typical silicone rubber. Other electrical properties are intermediate between the values observed in the component polymers.
Experimental studies on the biaxial extensional viscosity of polypropylene
Authors: Hoover Kenneth C. , Tock Richard W. 
Published: December 2004

AbstractFor fabrication processes such as blow molding, vacuum forming, film blowing and fiber spinning, extensional flow is the dominate mode of melt deformation. Under these conditions, extensional viscosity is a significant rheological property. Thus, the biaxial extensional viscosity was measured for several samples of polypropylene. A technique based on the bubble inflation method of Denson and Gallo was used. Experimental values of biaxial extensional viscosities ranging from 1014 to 1010 poise as a function of strain rate, 10−5 to 10−2 reciprocal seconds, were obtained at 25°C. The technique used was critiqued and found to be useful in characterizing unoriented and biaxially oriented films, Uniaxially oriented films gave unsatisfactory results. It may be possible to use this testing method to assist in materials selection decisions.
The morphology of fibrous polymeric crystals formed isothermally in stationary shear fields
Authors: George Waller , Tucker Paul 
Published: December 2004

AbstractA discussion is presented of the morphology of the fibrous crystals, shish kebabs, produced in an initially simple shear flow. When the crystallizable Component of the fluid is sufficiently dilute one usually finds along the stream line at the end of the large scale fibrous crystal, a continuation of that structure which consists of an extremely fine sequence of morphological entities. This fine row structure appears to have transverse dimensions comparable to and slightly greater than the resolution power of the transmission electron microscopical methods used in its observation.Certain tentative suggestions were made regarding the nature of the shish kebab morphology. These are based upon a loose application of general results in the field of irreversible thermodynamics. This leads to the suggestion that the morphological nature of the row structure which has been generally observed in fibrous crystallizations may find its explanation in the nature of the local manner in which the associated entropy production is balanced while preserving a global state of stationary deformation with its associated lack of global entropy production.
Bubble growth in thermoplastic structural foams
Authors: Hobbs S. Y. 
Published: December 2004

AbstractThe inflation and growth kinetics of bubbles in thermoplastic structural foams are discussed in some detail using a model which assumes the initial existence of very small voids in the pressurized polymer melt. The effects of a drop in external pressure, the presence of a distribution of bubble sizes, and the diffusion of gas between neighboring bubbles are considered. It is shown that at a given pressure the number of growing bubbles present in the melt at any onetime depends on the ratio of the critical radius to the average radius of the microvoids assumed to be present in the melt It is also demonstrated that gas diffusion between neighboring bubbles reduces the growth rate appreciably only when the interbubble distance is reduced to a micron or less.
Some new aspects of the crystallization of bisphenol‐A polycarbonate
Authors: Gallez F. , Legras R. , Mercier J. P. 
Published: December 2004

AbstractThis paper concerns the action of plasticizers and nucleating agents on the crystallization of bisphenol‐A polycarbonate. The influence of plasticizers is to increase the rate of crystallization to a great extent using 10 percent of a plasticizer such as trimellitic acid, tridecyloctyl ester. The influence of nucleating substances on plasticized and undiluted polycarbonate is investigated. A large number of substances have been found capable of nucleating polycarbonate crystallization. The un‐plasticized semi‐crystalline polycarbonate is characterized by a much higher melting point (300°C) than the plasticized semi‐crystalline systems (210–245°C). The stability of bisphenol‐A polycarbonate in the presence of nucleating salts is also examined. We observe a substantial decrease in the molecular weight in the presence of a great number of nucleating substances. The modulus‐temperature curves of two semi‐crystalline polymers are reported in the last series of experiments.
Structure‐property relationships of isomeric addition polyimides containing nadimide end groups
Authors: St. Clair Anne K. , St. Clair Terry L. 
Published: December 2004

AbstractAddition polyirnide oligomers with nadimide end groups (I) have been synthesized from 4,4′‐oxydiphthalic anhydride and 3,3′,4,4′‐benzophenone tetracarboxylic acid dianhydride with several isomeric diamines and, nadic anhydride. The low molecular weight amic acid? and corresponding imides were isolated and characterized. Solubility and melt‐flow properties of the imide prepolymers were studied to determine the applicability of the resins as adhesives and composite matrices. Thermomechanical transitions of the polymers were obtained by torsional braid analysis. Properties were compared with a similar addition polymer, P13N. magnified image
The Halpin‐Tsai equations: A review
Authors: Affdl J. C. Halpin , Kardos J. L. 
Published: December 2004

AbstractThe Halpin‐Tsai equations are based upon the “self‐consistent micromechanics method” developed by Hill. Hermans employed this model to obtain a solution in terms of Hill's “reduced moduli”. Halpin and Tsai have reduced Hermans' solution to a simpler analytical form and extended its use for a variety of filament geometries. The development of these micromechanic's relationships, which form the operational bases for the coniposite analogy of Halpin and Kardos for semi‐crystalline polymers, are reviewed herein.
The elastic constants of a particulate‐filled glassy polymer: Comparison of experimental values with theoretical predictions
Authors: Smith Jack C. 
Published: December 2004

AbstractCalculation of the elastic constants of a participate composite material in terms of the elastic constants of the filler and the matrix is discussed. The theories of Kerner or Hashin and Shtrikman, the equivalent theories of Budiansky and Hill, and a generalized van der Poel type theory are presented and discussed. Data from several sources are compared with the predictions of these theories. The van der Poel theory provides the best agreement and gives good values for volume fractions of filler up to 0.35.
Hot‐melt adhesive bonding of polyethylene with ethylene copolymers
Authors: Yamakawa S. 
Published: December 2004

AbstractThe melt bon debility of ethyl en e copolymers to a high, pressure polyethylene has been investigated by a T‐peel test consisting of polyethylene–copolymer–polyethylene. The three ethylene copolymers involved separately vinyl acetate, ethyl acrylate, and acrylic acid. The ethyl acrylate copolymers produce the highest peel strength over the test temperature range of −20 to 50°C, and also yield a high peel strength even at the bonding temperatures of 105–110°C, at which the welding of polyethylene to polyethylene does not occur. The observations of cross sections of the joints with an interference microscope show the presence of an interfacial boundary layer and a mixed layer (of the polyethylene and the copolymer). The relationship between the peel strength and these two layers is discussed. Further, the peel strength‐temperature curves are compared with the tensile properties of the copolymers.
Computer‐aided optimal melt screw design
Authors: Helmy H. A. A. , Parnaby J. 
Published: December 2004

AbstractThe paper describes a computer software package applying a steady‐state hill‐climbing optimization routine to the plastics melt‐extruder screw constrained‐design problem. The purpose primarily is to introduce the optimal screw‐design technique, to show how it is applied to this particular type of problem, to indicate its potential and to encourage its wider use. Screw performance criteria are defined by a theoretical model consisting of the non‐Newtonian isothermal polymer flow equations in terms of the screw‐geometric variables for particular process conditions. The design method is quite general however and a non‐isothermal model may be substituted. Use of the method offers considerable scope and potential for the design engineer to make design processes faster, more positive and logical while reducing the effort required. Interactive use is possible and empirical adjustments can be incorporated with experience. In using the method, the design engineer first specifies the required process conditions of pressure and flow rate at the die and the computer then searches for the set of screw design variables which optimizes the screw power utilization efficiency or any other specified criterion of performance. Such optimal designs are obtained within the set limits of practical constraints on machine dimensions, screw strength and product quality requirements. Some experimental evidence is given relating to the accuracy of the isothermal non‐Newtonian polymer flow model and to its use in the design of small diameter extruder screws. The optimal search technique offers considerable potential as a computer‐based design tool.