摘要:

AbstractThe stress‐strain response of crystalline high density polyethylene and of amorphous polycarbonate has been determined in tension and in compression at superimposed pressures up to 1104 MPa(160 ksi). Strain softening occurred in the polycarbonate at low pressures but was inhibited by pressure. Tensile necking occurred in both materials, but was promoted by pressure in polyethylene and inhibited in polycarbonate. The initial modulus,E, and the flow stress, σ, at a given offset strain varied linearly with the mean pressure,P, with essentially the same pressure coefficient, α. Thus,E= (1+αP)E0and σ = (1+αP)σ0, whereE0and σ0are values at zero mean pressure. In polyethylene, the coefficient, σ0, was the same in tension and compression, indicating that the strength differential between tension and compression was a simple manifestation of pressure‐dependent yielding. In polycarbonate the coefficient, σ0, was different in tension and in compression, implying an effect due to the third stress invariant or to anisotropy. The results suggest a constitutive model for polymers in which the flow stress is linearly dependent on mean pressure, but in which inelastic volume change is negligible. The results also suggest that the pressure dependence of flow stress in polymers is the same as that of the ini

ISSN:0032-3888    

DOI:10.1002/pen.760191602

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractA method and apparatus for measuring the elastic and other properties of polymers in the melt state is presented. The recoverable strain magnitude and the rate of strain recovery have been measured as a function of: applied shear rate, applied shear magnitude, temperature and molecular weight. The elastic properties indicate that there is an abrupt change or “transition” in the response of polystyrene melts at temperatures well above the glass transition. This abrupt change is found to be molecular weight dependent. The results are interpreted qualitatively in terms of molecular structure and practical processing operations. The possible relationship of this “transition” toTu, is briefly di

ISSN:0032-3888    

DOI:10.1002/pen.760191603

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractAn improved macroscopic model for predicting the strength of a composite laminate containing a circular notch is developed. Two constants are introduced which uniquely determine the notch sensitivity of a given material. A superposition method for the notched strength of composite laminates is developed which allows data for arbitrary materials and laminate configurations to be superimposed upon a single master curve. The influence of material orthotropy upon notched strength is discussed. A relative notch sensitivity parameter is introduced which allows quantification of the notch sensitivity of a given composite material system, stacking sequence, or laminate configuration.

ISSN:0032-3888    

DOI:10.1002/pen.760191604

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractIn previous publications we have reported our experimental observations that, when the less viscous component flows outside the more viscous component in sheath‐core coextrusion through a cylindrical die, or in sandwich three layer film coextrusion through a slit die, the pressure gradients in a two‐phase system can be lower than those in the two components flowing individually. The experimental observations suggest that the energy requirement for extrusion can be decreased, and the throughput increased, when one judiciously chooses proper combinations of materials and/or optimal processing conditions. In this paper, we present a theoretical analysis, which shows that the seemingly anomalous behavior of the experimentally observed pressure gradient reduction is indeed possible, depending on the rheological properties of the individual components involved in coextrus

ISSN:0032-3888    

DOI:10.1002/pen.760191605

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractPolyethylene (PE) continuous filaments having high tensile strength as well as high Young's modulus have been obtained from several linear polyethylene materials by stretching a partially oriented spun yarn to a draw ratio of ≃30. The high draw ratio was readily attained for linear PE fiber extruded at a temperature of at least 250°C and quenched in air while under some intermediate tension. The number average molecular weight of the polymer was found to have the predominant effect on the ultimate tensile strength of the drawn fiber. Yarn with a tensile strength of 19 gpd (167 kg/mm2) and a Young's modulus of 854 gpd (7380 kg/mm2) was produced. Yarn with a Young's modulus of 1145 gpd (9890 kg/mm2) was made by sacrificing some tensile streng

ISSN:0032-3888    

DOI:10.1002/pen.760191606

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractA method has been developed on the Rheometrics mechanical spectrometer using the eccentric rotating disks mode to study the crystallization kinetics of different semi‐crystalline polymers (polyethylene, polypropylene, poly(butylene terephthalate) and Nylon 11) under oscillatory shear. Dynamic shear moduli (storageG′ and lossG″), loss tangent (tan δ), and dynamic viscosity (η′) were simultaneously, monitored during the crystallization process. The onset and completion of crystallization were characterized by the initial rise and final levelling off ofG′, while the peak time, of crystallization (tp) is calculated from the time elapsed between the onset and peak of crystallization which is indicated by theG″ or η′ maximum. In the case of polypropylene, going from a low frequency of ≃0.1 rad/s, to higher frequencies of up to 10 rad/s, there is a monotonic decrease in peak time of crystallization (tp) together with a progressive decrease in spherulitic morphology. The observed acceleration in crystallization is due predominantly to the increase in nucleation rate and orientation of chains in melt crystalline aggregate. The progressive disappearance of the spherulitic morphology is attributed to the disruption of the spherulite superstructure at higher fr

ISSN:0032-3888    

DOI:10.1002/pen.760191607

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractGas‐liquid chromatography has been used to estimate thermodynamic parameters of a variety of aromatic and aliphatic solvents at infinite dilution in poly(ethyl methacrylate). Heats of solution, Flory‐Huggins interaction parameters, and specific interaction parameters were calculated from specific retention volumes. Comparative interpretation of these thermodynamic quantities has led to the establishment of a solvent selectivity scale for poly(ethyl methacrylate). Limitations of the threedimensional solubility parameter theory on the systems tested here are demonstrated. A significantly improved concept is developed and tes

ISSN:0032-3888    

DOI:10.1002/pen.760191608

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractWe have constructed a rigorous numerical solution of the equations of flow and energy within a general wire‐coating die that provides a far more accurate and detailed description of the flow than any previously available. The program* can accommodate uni‐ or multi‐sectional dies, in which the sections have conical or cylindrical shapes. Melt rheology was satisfactorily represented over the full range of shear rate at processing temperatures by a model with three regions for each isotherm, requiring six constants evaluated from rheometric data. Thirty‐three cases have been run, all of them in the domain of moderate‐to‐high wire speeds, with the two most important wire‐coating resins, low‐density polyethylene (LDPE) and plasticized polyvinyl chloride (PVC). Although the radialconvection term was omitted from the energy equation to overcome calculational instability, we believe the accuracy of our calculated results is chiefly limited by knowledge of melt properties. Temperature profiles typically exhibit two maxima, the more pronounced one being found close to the die wall. In coating a No. 22 AWG wire with LDPE at 2000 ft/min in one cylindrical die, the maximum rise, occurring at the die exit, was 100 K. Profiles of axial velocity across the stream exhibited maxima in some cases, not in others. Shear rates ranged from zero to about 106s−1and viscosity profiles were highly variable. Because the melt passes through the die so quickly, the calculated results for isothermal and adiabatic walls were not very different, even though the melt streams were only about 0.3 mm thick. While the investigation was focused on high‐speed wire coating, in which viscous dissipation is extreme, the program can also be used for analysis and design of dies for making

ISSN:0032-3888    

DOI:10.1002/pen.760191609

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractThe critical concentration at which a metal‐filled composite becomes electrically conductive can be dramatically reduced by adding the metal as randomly dispersed fibers. The higher the aspect ratio of the fibers, the lower the concentration needed to induce electrical conductance. Composites exhibiting resistivities below 20 ohm‐cm have been produced with less than 8 volume percent aluminum fibers, having an aspect ratio of 24:1. At low fiber loadings the tensile strength of the composites is similar to that of the unfilled polymer. The thermal properties of these composites are shown to increase monotonically in accordance with the theoretical development of Niel

ISSN:0032-3888    

DOI:10.1002/pen.760191610

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760191601

出版商:Society of Plastics Engineers, Inc.    

年代:1979

数据来源: WILEY