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  • 1
    Digitale Medien
    Digitale Medien
    A superstable time-discrete scheme for the numerical integration of viscous constitutive equations (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Mechanics of Cohesive-frictional Materials 3 (1998), S. 229-256 
    Details
    ISSN: 1082-5010
    Schlagwort(e): finite element method ; viscous constitutive equations ; time-discrete scheme ; stability ; superstability ; Engineering ; Civil and Mechanical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Maschinenbau
    Notizen: The general framework of the paper deals with the finite element modelling of mechanical problems involving viscous materials such as bitumen or bituminous concrete. Its aim is to present a second-order-accurate discrete scheme which remains unconditionally superstable when used for the time discretization of the linear and non-linear viscoelastic constitutive equations considered. After stating the space- and time-continuous mechanical problem we focus on the time discretization of these equations, considering three different schemes. For both of them sufficiently small values of the time step are required in order to ensure the superstability, whereas the third remains unconditionally superstable. Eventually, some numerical results are presented. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 4 Ill.
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  • 2
    Digitale Medien
    Digitale Medien
    Unusual stabilized finite element methods and residual free bubbles (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 27 (1998), S. 159-168 
    Details
    ISSN: 0271-2091
    Schlagwort(e): finite element method ; Galerkin method ; residual free bubbles ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: An overview of the unusual stabilized finite element method and of the standard Galerkin method enriched with residual free bubble functions is presented. For the first method a concrete model problem illustrates its application in advective-diffusive-reactive equations and for the second method it is shown how static condensation of residual free bubbles gives rise to mass lumping and selective reduced integration, which are viewed as numerical tricks and can now be derived by the standard Galerkin method without tricks. © 1998 John Wiley & Sons, Ltd.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    Linear stability of incompressible fluid flow in a cavity using finite element method (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 27 (1998), S. 139-157 
    Details
    ISSN: 0271-2091
    Schlagwort(e): hydrodynamic stability ; finite element method ; incompressible cavity flow ; Arnold's method ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: Numerical methods have been applied to theoretical studies of instability and transition to turbulence. In this study an analysis of the linear stability of incompressible flow is undertaken. By means of the finite element method the two-dimensional base flow is computed numerically over a range of Reynolds numbers and is perturbed with three-dimensional disturbances. The partial differential equations governing the evolution of perturbation are obtained from the non-linear Navier-Stokes equations with a slight compressibility by using linear stability and normal mode analysis. In terms of the finite element discretization a non-singular generalized eigenproblem is formulated from these equations whose solution gives the dispersion relation between complex growth rate and wave number. This study presents stability curves to identify the critical Reynolds number and critical wavelength of the neutral mode and discusses the mechanism of instability. The stability of lid-driven cavity flow is examined. Taylor-Göertler-like vortices in the cavity are obtained by means of reconstruction of three-dimensional flows. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 14 Ill.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    Finite element analysis of two- and three-dimensional flows around square columns in tandem arrangement (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 95-112 
    Details
    ISSN: 0271-2091
    Schlagwort(e): square columns in tandem ; finite element method ; improved BTD ; 3D computation ; aerodynamic characteristics ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: Two- (2D) and three-dimensional (3D) finite element analyses for flow around two square columns in tandem arrangement were performed with various column spacings and Reynolds numbers. The computed values were compared with the wind-tunnel results in terms of the aerodynamic characteristics of the leeward column. In most 2D computations, strong vortices were formed behind the windward column, irrespective of widely changed Reynolds numbers. This was different from the experimental phenomena of equivalent spacing, so that the computed time-averaged pressure coefficients were not identical to the experimental values except when the distance between the two columns was adequately wide or narrow. On the other hand, in 3D computation, distinct differences in flow structures behind the column were observed between Reynolds numbers of 103 and 104 and the pressure coefficient in the 3D analysis with Re=104 agreed well with the experimental value. Thus, the effectiveness of 3D computations and Reynolds number effects on the flow around two square columns have been confirmed. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 17 Ill.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    An operator splitting algorithm for the three-dimensional advection-diffusion equation (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 461-476 
    Details
    ISSN: 0271-2091
    Schlagwort(e): advection-diffusion equation ; operator splitting algorithm ; Holly and Preissmann scheme ; method of characteristics ; finite element method ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: Operator splitting algorithms are frequently used for solving the advection-diffusion equation, especially to deal with advection dominated transport problems. In this paper an operator splitting algorithm for the three-dimensional advection-diffusion equation is presented. The algorithm represents a second-order-accurate adaptation of the Holly and Preissmann scheme for three-dimensional problems. The governing equation is split into an advection equation and a diffusion equation, and they are solved by a backward method of characteristics and a finite element method, respectively. The Hermite interpolation function is used for interpolation of concentration in the advection step. The spatial gradients of concentration in the Hermite interpolation are obtained by solving equations for concentration gradients in the advection step. To make the composite algorithm efficient, only three equations for first-order concentration derivatives are solved in the diffusion step of computation. The higher-order spatial concentration gradients, necessary to advance the solution in a computational cycle, are obtained by numerical differentiations based on the available information. The simulation characteristics and accuracy of the proposed algorithm are demonstrated by several advection dominated transport problems. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    Simulation of three-dimensional polymer mould filling processes using a pseudo-concentration method (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 1355-1369 
    Details
    ISSN: 0271-2091
    Schlagwort(e): viscous flow ; moving boundary ; fountain flow ; pseudo-concentration method ; finite element method ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: Mould filling processes, in which a material flow front advances through a mould, are typical examples of moving boundary problems. The moving boundary is accompanied by a moving contact line at the mould walls causing, from a macroscopic modelling viewpoint, a stress singularity. In order to be able to simulate such processes, the moving boundary and moving contact line problem must be overcome. A numerical model for both two- and three-dimensional mould filling simulations has been developed. It employs a pseudo-concentration method in order to avoid elaborate three-dimensional remeshing, and has been implemented in a finite element program. The moving contact line problem has been overcome by employing a Robin boundary condition at the mould walls, which can be turned into a Dirichlet (no-slip) or a Neumann (free-slip) boundary condition depending on the local pseudo-concentration. Simulation results for two-dimensional test cases demonstrate the model's ability to deal with flow phenomena such as fountain flow and flow in bifurcations. The method is by no means limited to two-dimensional flows, as is shown by a pilot simulation for a simple three-dimensional mould. The reverse problem of mould filling is the displacement of a viscous fluid in a tube by a less viscous fluid, which has had considerable attention since the 1960's. Simulation results for this problem are in good agreement with results from the literature. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 5 Ill.
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  • 7
    Digitale Medien
    Digitale Medien
    Viscous oscillatory flow around a circular cylinder at low Keulegan-Carpenter numbers and frequency parameters (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 26 (1998), S. 403-442 
    Details
    ISSN: 0271-2091
    Schlagwort(e): oscillating flow ; Keulegan-Carpenter number ; finite element method ; in-line force ; transverse force ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: The results of a numerical study of the viscous oscillating flow around a circular cylinder at low Keulegan-Carpenter numbers (KC) and frequency parameters (β) are presented in this paper. The finite element method was used for the solution of the Navier-Stokes equations in the formulation where the streamfunction and vorticity are the field variables. The computation was conducted at Keulegan-Carpenter numbers extending up to KC=15 and frequency parameters ranging between β=6 and 100. At low values of the Keulegan-Carpenter number the flow remains symmetrical. As the Keulegan-Carpenter number is increased over a certain value which depends also on the frequency parameter, asymmetries appear in the flow which are eventually amplified and lead finally to complex vortex-shedding patterns, some of which are markedly different from those observed at higher frequency parameters. The solution revealed that although for certain values of KC and β the shedding of vortices is periodic, there also exists a complicated flow regime in which the flow is not periodic but switches between different modes in consecutive cycles of flow oscillation. For the various flow cases examined, the traces of the hydrodynamic forces are presented and the hydrodynamic coefficients and RMS values of the in-line force are compared with experimental evidence. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 33 Ill.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    Parallel computation of atmospheric pollutant dispersion under unstably stratified atmosphere (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 26 (1998), S. 677-696 
    Details
    ISSN: 0271-2091
    Schlagwort(e): second-order closure model ; pollutant dispersion ; finite element method ; unstably stratified atmosphere ; parallel computation ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: Pollutant dispersion under unstably stratified atmosphere was investigated numerically using the finite element method. The effects of atmospheric stability on plume trajectory were studied using a three-dimensional second-order closure dispersion model. The numerical model was implemented using domain decomposition method and carried out using a parallel computer. The computation accelerates significantly and the size of computation can be largely increased as a result of the parallelism. A passive contaminant point source was placed at the middle of the convective boundary layer to simulate the atmospheric dispersion. The requirement of the input of dispersion coefficients in k-theory and Gaussian models was replaced with direct input of turbulence flow data. It was found that the present numerical model can predict several non-Gaussian plume behaviours and the computed results agreed well with findings from experimental observations. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 7 Ill.
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  • 9
    Digitale Medien
    Digitale Medien
    Cavitation modelling in saturated geomaterials with application to dynamic strain localization (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 27 (1998), S. 109-125 
    Details
    ISSN: 0271-2091
    Schlagwort(e): multiphase porous material ; cavitation ; water pressure ; vapour pressure ; strain localization ; finite element method ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: A model to simulate cavitation phenomena in the pores of saturated porous media is developed. Such phenomena appear in connection with pore water traction, which may be observed during strain localization in dense sand samples or in dynamic fluid-structure interaction problems where the structure is made of geomaterials. The model makes use of an isothermal two-phase flow approach. Numerical examples relating to strain localization are shown. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    Finite element analysis of transient fluid flow with free surface using VOF (volume-of-fluid) method and adaptive grid (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 26 (1998), S. 1127-1154 
    Details
    ISSN: 0271-2091
    Schlagwort(e): free surface ; transient viscous incompressible fluid ; finite element method ; VOF (volume-of-fluid) method ; adaptive grid ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: The VOF method is adopted for the finite element analysis of transient fluid flow with a free surface. In particular, an adaptation technique for generating an adaptive grid is incorporated to capture a higher resolution of the free surface configuration. An adaptive grid is created through the refinement and mergence of elements. In this domain the elements in the surface region are made finer than those in the remaining regions for more efficient computation. Also, three techniques based on the VOF method are newly developed to increase the accuracy of the analysis, namely the filling pattern, advection treatment and free surface smoothing techniques. Using the proposed numerical techniques, radial flow with a point source and the collapse of a dam are analysed. The numerical results agree well with the theoretical solutions as well as with the experimental results. Through comparisons with the numerical results of several cases using different grids, the efficiency of the proposed technique is verified. © 1998 by John Wiley & Sons, Ltd.
    Zusätzliches Material: 28 Ill.
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  • 11
    Digitale Medien
    Digitale Medien
    A numerical study on flow through the spiral casing of a hydraulic turbine (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 143-156 
    Details
    ISSN: 0271-2091
    Schlagwort(e): turbine ; spiral casing ; finite element method ; Galerkin weighted residual technique ; Gauss-Legendre quadrature ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: Flow through the spiral casing of a hydraulic turbine was analyzed. Reynolds averaged Navier-Stokes equations were solved using a finite element method. The physical domain was divided into a number of hexahedral elements which are isoparametrically mapped onto standard cubic elements. Numerical integration for the unsteady momentum equation is performed over such hexahedral elements to obtain a provisional velocity field. Compliance with the mass conservation equation and determination of the pressure correction are accomplished through an iterative procedure. The velocity distribution inside the spiral casing corroborates the results available in literature. The static pressure at the midplane generally decreases from the outside wall towards the exit of the spiral casing. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 8 Ill.
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  • 12
    Digitale Medien
    Digitale Medien
    Local mesh adaptation technique for front tracking problems (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 719-736 
    Details
    ISSN: 0271-2091
    Schlagwort(e): front tracking ; mesh adaptation ; finite element method ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: A numerical model is developed for the simulation of moving interfaces in viscous incompressible flows. The model is based on the finite element method with a pseudo-concentration technique to track the front. Since a Eulerian approach is chosen, the interface is advected by the flow through a fixed mesh. Therefore, material discontinuity across the interface cannot be described accurately. To remedy this problem, the model has been supplemented with a local mesh adaptation technique. This latter consists in updating the mesh at each time step to the interface position, such that element boundaries lie along the front. It has been implemented for unstructured triangular finite element meshes. The outcome of this technique is that it allows an accurate treatment of material discontinuity across the interface and, if necessary, a modelling of interface phenomena such as surface tension by using specific boundary elements. For illustration, two examples are computed and presented in this paper: the broken dam problem and the Rayleigh-Taylor instability. Good agreement has been obtained in the comparison of the numerical results with theory or available experimental data. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 12 Ill.
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  • 13
    Digitale Medien
    Digitale Medien
    Free convection heat transfer from an isothermal wavy surface in a porous enclosure (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 633-661 
    Details
    ISSN: 0271-2091
    Schlagwort(e): free convection ; porous enclosure ; Darcian model ; wavy surface ; finite element method ; numerical study ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: The coupled streamfuction-temperature equations governing the Darcian flow and convection process in a fluid-saturated porous enclosure with an isothermal sinusoidal bottom sun face, has been numerically analyzed using a finite element method (FEM). No restrictions have been imposed on the geometrical non-linearity arising from the parameters like wave amplitude (a), number of waves per unit length (N), wave phase (Φ), aspect ratio (A) and also on the flow driving parameter Rayleigh number (Ra). The numerical simulations for varying values of Ra bring about interesting flow features, like the transformation of a unicellular flow to a multicellular flow. Both with increasing amplitude and increasing number of waves per unit length, owing to the shift in the separation and reattachment points, a row-column pattern of multicellular flow transforms to a simple row of multicellular flow. A cycle of n celluar and n+1 cellular flows, with the flow in adjacent cells in the opposite direction, periodically manifest with phase varying between 0 and 360°. The global heat transfer into the system has been found to decrease with increasing amplitude and increasing number of waves per unit length. Only marginal changes in the global heat flux are observed, either with increasing Ra or varying Φ. Effectively, sinusoidal bottom surface undulations of the isothermal wall of a porous enclosure reduces the heat transfer into the system. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 21 Ill.
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  • 14
    Digitale Medien
    Digitale Medien
    USE OF EIGENVALUE TECHNIQUE IN FINITE ELEMENT TIDAL COMPUTATIONS (1997)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 24 (1997), S. 953-963 
    Details
    ISSN: 0271-2091
    Schlagwort(e): coastal hydrodynamics ; shallow water equations ; finite element method ; finite difference method ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: This paper presents the results of some studies on the development and application of a finite element method (FEM) with a closed-form solution technique for time discretization. The closed-form solution is based on the eigenvalues/vectors of a coefficient matrix. The method is first applied to the one-dimensional linearized shallow water equations and then extended to the two-dimensional shallow water equations. An attempt is made to improve its efficiency by incorporating time splitting and using the closed-form solution technique only for linear terms. Some case studies of a rectangular channel and harbour are presented to illustrate the satisfactory working of the method. © 1997 by John Wiley & Sons, Ltd. Int. j. numer. methods fluids 24: 953-963, 1997.
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  • 15
    Digitale Medien
    Digitale Medien
    NUMERICAL SIMULATION OF INCOMPRESSIBLE FLOWS WITH MOVING INTERFACES (1997)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 24 (1997), S. 615-638 
    Details
    ISSN: 0271-2091
    Schlagwort(e): finite element method ; front tracking ; incompressible two fluid system ; mold filling ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: A numerical model has been developed for the 2D simulation of free surface flows or, more generally speaking, moving interface ones. The bulk fluids on both sides of the interface are taken into account in simulating the incompressible laminar flow state. In the case of heat transfer the whole system, i.e. walls as well as possible obstacles, is considered. This model is based on finite element analysis with an Eulerian approach and an unstructured fixed mesh. A special technique to localize the interface allows its temporal evolution through this mesh. Several numerical examples are presented to demonstrate the capabilities of the model. © 1997 by John Wiley & Sons, Ltd.
    Zusätzliches Material: 22 Ill.
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  • 16
    Digitale Medien
    Digitale Medien
    Computer-aided analysis of flow past a surface-mounted obstacle (1997)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 25 (1997), S. 495-512 
    Details
    ISSN: 0271-2091
    Schlagwort(e): separated flows ; recirculation length ; finite element method ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: The incompressible, laminar, isothermal flow of a Newtonian fluid at steady state past a surface-mounted obstacle (flow over a step) is studied in a two-dimensional numerical experiment using the Galerkin finite element method. The dimensionless Navier-Stokes equations are solved in the whole range of the laminar flow regime. The numerical predictions are compared with available experimental data. The emphasis in the discussion of the results is on the presentation of the streamlines for various Reynolds numbers, the pressure distribution over and downstream of the step, the shear stress distribution along the surface of the step and the length of the recirculation region as a function of the Reynolds number. This analysis may be used in numerous applications from agricultural to civil, mechanical and chemical engineering. © 1997 John Wiley & Sons, Ltd.
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  • 17
    Digitale Medien
    Digitale Medien
    A three-dimensional fictitious domain method for incompressible fluid flow problems (1997)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 25 (1997), S. 719-736 
    Details
    ISSN: 0271-2091
    Schlagwort(e): finite element method ; fictitious domain method ; three-dimensional ; internal parts ; incompressible fluid flow ; constrained optimization ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: A new Galerkin finite element method for the solution of the Navier-Stokes equations in enclosures containing internal parts which may be moving is presented. Dubbed the virtual finite element method, it is based upon optimization techniques and belongs to the class of fictitious domain methods. Only one volumetric mesh representing the enclosure without its internal parts needs to be generated. These are rather discretized using control points on which kinematic constraints are enforced and introduced into the mathematical formulation by means of Lagrange multipliers. Consequently, the meshing of the computational domain is much easier than with classical finite element approaches.   First, the methodology will be presented in detail. It will then be validated in the case of the two-dimensional Couette cylinder problem for which an analytical solution is available. Finally, the three-dimensional fluid flow inside a mechanically agitated vessel will be investigated. The accuracy of the numerical results will be assessed through a comparison with experimental data and results obtained with a standard finite element method. © 1997 John Wiley & Sons, Ltd.
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  • 18
    Digitale Medien
    Digitale Medien
    Calculation of vertical velocity in three-dimensional, shallow water equation, finite element models (1997)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 25 (1997), S. 779-802 
    Details
    ISSN: 0271-2091
    Schlagwort(e): finite element method ; vertical velocity ; three-dimensional ; Vancouver Island ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: Computation of vertical velocity within the confines of a three-dimensional, finite element model is a difficult but important task. This paper examines four approaches to the solution of the overdetermined system of equations arising when the first-order continuity equation is solved in conjunction with two boundary conditions. The traditional (TRAD) method neglects one boundary condition, solving the continuity equation with the remaining boundary condition. The vertical derivative of continuity (VDC) method involves solution of the second-order equation obtained by differentiation of the continuity equation with respect to the vertical co-ordinate. The least squares (LS) method minimizes the residuals of the continuity equation (in discrete form) and the two boundary conditions. The adjoint (ADJ) method minimizes the residuals of the continuity equation (in continuous form) and the two boundary conditions.Two domains are considered: a quarter-annular harbour and the southwest coast of Vancouver Island. Results indicate that the highest-quality solution is obtained with both LS and ADJ. Furthermore, ADJ requires less CPU and memory than LS. Therefore the optimal method for computation of vertical velocity in a three-dimensional finite element model is the adjoint (ADJ) method. © 1997 John Wiley & Sons, Ltd.
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  • 19
    Digitale Medien
    Digitale Medien
    Numerical modelling of shear-dependent mass transfer in large arteries (1997)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 25 (1997), S. 847-857 
    Details
    ISSN: 0271-2091
    Schlagwort(e): finite element method ; blood flow ; arterial transport processes ; curved tubes ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: A numerical scheme for the simulation of blood flow and transport processes in large arteries is presented. Blood flow is described by the unsteady 3D incompressible Navier-Stokes equations for Newtonian fluids; solute transport is modelled by the advection-diffusion equation. The resistance of the arterial wall to transmural transport is described by a shear-dependent wall permeability model. The finite element formulation of the Navier-Stokes equations is based on an operator-splitting method and implicit time discretization. The streamline upwind/Petrov-Galerkin (SUPG) method is applied for stabilization of the advective terms in the transport equation and in the flow equations. A numerical simulation is carried out for pulsatile mass transport in a 3D arterial bend to demonstrate the influence of arterial flow patterns on wall permeability characteristics and transmural mass transfer. The main result is a substantial wall flux reduction at the inner side of the curved region. © 1997 John Wiley & Sons, Ltd.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 20
    Digitale Medien
    Digitale Medien
    A mixed Lagrangian-Eulerian approach to modelling fluid flow during mould filling (1997)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 25 (1997), S. 931-952 
    Details
    ISSN: 0271-2091
    Schlagwort(e): finite element method ; free surface ; updated Lagrangian-Eulerian ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: An updated free surface Lagrangian-Eulerian finite element kinematic description is used to simulate free surface flow problems associated with mould filling. The method proposed results in an accurate determination of the front, making it ideal for problems in which free surface boundary conditions play an important role. Significant saving in CPU time can be obtained over other fixed mesh approaches by virtue of the air domain being ignored. Assuming a laminar regime for the flow field, a mixed interpolation formulation is used to approximate the discretized governing equations for elimination.   Of particular interest is the method implementation to restrict the number of remeshing operations and track the moving free surface within an arbitrary domain, either with or without internal obstacles. The method used to automatically assign boundary conditions to the changing domain is described. A dam break problem is modelled numerically and compared against experimentally derived data in order to validate the model. A further numerical example demonstrates the capabilities of the algorithm developed to model the filling of an industrial casting. © 1997 John Wiley & Sons, Ltd.
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  • 21
    Digitale Medien
    Digitale Medien
    NUMERICAL SOLUTIONS OF OPTIMAL CONTROL FOR THERMALLY CONVECTIVE FLOWS (1997)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 25 (1997), S. 205-223 
    Details
    ISSN: 0271-2091
    Schlagwort(e): optimal control ; Navier-Stokes equations ; finite element method ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: We study the numerical solution of optimal control problems associated with two-dimensional viscous incompressible thermally convective flows. Although the techniques apply to more general settings, the presentation is confined to the objectives of minimizing the vorticity in the steady state case and tracking the velocity field in the non-stationary case with boundary temperature controls. In the steady state case we develop a systematic way to use the Lagrange multiplier rules to derive an optimality system of equations from which an optimal solution can be computed; finite element methods are used to find approximate solutions for the optimality system of equations. In the time-dependent case a piecewise-in-time optimal control approach is proposed and the fully discrete approximation algorithm for solving the piecewise optimal control problem is defined. Numerical results are presented for both the steady state and time-dependent optimal control problems. © 1997 John Wiley & Sons, Ltd.
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  • 22
    Digitale Medien
    Digitale Medien
    A high-order characteristics/finite element method for the incompressible Navier-Stokes equations (1997)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 25 (1997), S. 1421-1454 
    Details
    ISSN: 0271-2091
    Schlagwort(e): incompressible Navier-Stokes problem ; finite element method ; high-order time scheme ; method of characteristics ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: In this paper we consider a discretization of the incompressible Navier-Stokes equations involving a second-order time scheme based on the characteristics method and a spatial discretization of finite element type. Theoretical and numerical analyses are detailed and we obtain stability results abnd optimal eror estimates on the velocity and pressure under a time step restriction less stringent than the standard Courant-Freidrichs-Levy condition. Finally, some numerical results obtained wiht the code N3S are shown which justify the interest of this scheme and its advantages with respect to an analogous first-order time scheme. © 1997 John Wiley & Sons, Ltd.
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  • 23
    Digitale Medien
    Digitale Medien
    The three-dimensional prolonged adaptive unstructured finite element multigrid method for the Navier-Stokes equations (1997)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 25 (1997), S. 371-392 
    Details
    ISSN: 0271-2091
    Schlagwort(e): adaptive grids ; finite element method ; iterative solvers ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: This paper presents the development of the three- dimensional prolonged adaptive finite element equation solver for the Navier-Stokes equations. The finite element used is the tetrahedron with quadratic approximation of the velocities and linear approximation of the pressure. The equation system is formulated in the basic variables. The grid is adapted to the solution by the element Reynolds number. An element in the grid is refined when the Reynolds number of the element exceeds a preset limit. The global Reynolds number in the investigation is increased by scaling the solution for a lower Reynolds number. The grid is refined according to the scaled solution and the prolonged solution for the lower Reynolds number constitutes the start vector for the higher Reynolds number. Since the Reynolds number is the ratio of convection to diffusion, the grid refinements act as linearization and symmetrization of the equation system. The linear equation system of the Newton formulation is solved by CGSTAB with coupled node fill-in preconditioner. The test problem considered is the three-dimensional driven cavity flow. © 1997 John Wiley & Sons, Ltd.
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  • 24
    Digitale Medien
    Digitale Medien
    SOME VALIDATION OF STANDARD, MODIFIED AND NON-LINEAR k-ε TURBULENCE MODELS (1997)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 24 (1997), S. 965-986 
    Details
    ISSN: 0271-2091
    Schlagwort(e): turbulence models ; k-ε ; non-linear k-ε ; finite element method ; validation ; FEAT ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: Standard, modified and non-linear k-ε: turbulence models are validated against three axisymmetric flow problems - flow through a pipe expansion, flow through a pipe constriction and an impinging jet problem - to underpin knowledge about the solution quality obtained from two-equation turbulence models. The extended models improve the prediction of turbulence as a flow approaches a stagnation point and the non-linear model allows for the prediction of anisotropic turbulence. Significantly different values for the non-linear model coefficients are proposed in comparison with values found in the literature. Nevertheless, current turbulence models are still unable to accurately predict the spreading rate of shear layers. © 1997 by John Wiley & Sons, Ltd. Int. j. numer. methods fluids, 24: 965-986, 1997.
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  • 25
    Digitale Medien
    Digitale Medien
    Oxidation of methanol catalyzed by silica-supported polystannazane-copper complex (1996)
    New York, NY : Wiley-Blackwell
    Polymers for Advanced Technologies 7 (1996), S. 73-75 
    Details
    ISSN: 1042-7147
    Schlagwort(e): oxidation ; methanol ; polymer-copper complex ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau
    Notizen: Silica-supported polystannazane-copper complex has been prepared and used as a catalyst for the oxidation of methanol. The results showed that the catalyst could catalyze the oxidation of methanol to formaldehyde at a high yield and selectivity at 30°C and under 1 atm mild conditions. The N/Cu mole ratio in the complex, temperature and the amount of NaOH additive had much influence on the catalytic activity. The complex was stable during the reaction and could be used repeatedly.
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  • 26
    Digitale Medien
    Digitale Medien
    A multiphase medium model for localisation and postlocalisation simulation in geomaterials (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Mechanics of Cohesive-frictional Materials 1 (1996), S. 95-114 
    Details
    ISSN: 1082-5010
    Schlagwort(e): multiphase material ; strain localisation ; averaging theories ; pore pressure ; cavitation ; finite element method ; Engineering ; Civil and Mechanical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Maschinenbau
    Notizen: It is recalled that negative water pressures are of importance in localisation phenomena of fully saturated, undrained samples of dilatant geomaterials. A model to simulate cavitation phenomena connected with such pore water tractions is developed and implemented in a simplified form in a dynamics code for partially saturated porous media. A case of localisation is studied from the onset of the instability up to the full developed shear band. The weak mesh dependence of the maximum effective plastic strain, due to the employed physical model, is also shown.
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  • 27
    Digitale Medien
    Digitale Medien
    CONVECTIVE HEAT TRANSFER FROM A CIRCULAR CYLINDER UNDER THE EFFECT OF A SOLID PLANE WALL (1996)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 23 (1996), S. 163-176 
    Details
    ISSN: 0271-2091
    Schlagwort(e): convective heat transfer ; finite element method ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: The purpose of this investigation is to study the convective heat transfer from a horizontal circular cylinder under the effect of a solid plane wall. The full Navier-Stokes and energy equations for two-dimensi onal steady flow are solved by a finite element method. The variations in surface shear stress, local pressure and Nusselt number around the surface of the cylinder as well as the predicted values of average Nusselt number, location of separation and some flow and temperature fields are presented. It is found that the average Nusselt number and drag force increase as the gap between the cylinder and the wall is increased.
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  • 28
    Digitale Medien
    Digitale Medien
    A DIRECTIONALLY ADAPTIVE METHODOLOGY USING AN EDGE-BASED ERROR ESTIMATE ON QUADRILATERAL GRIDS (1996)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 23 (1996), S. 673-690 
    Details
    ISSN: 0271-2091
    Schlagwort(e): Euler equations ; directionally adaptive meshes ; edge-based error estimate ; structured grids ; mesh movement ; finite element method ; high-speed flows ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: The present paper describes a directionally adaptive finite element method for high-speed flows, using an edge-based error estimate on quadrilateral grids. The error of the numerical solution is estimated through its second derivatives and the resulting Hessian tensor is used to define a Riemannian metric. An improved mesh movement strategy, based on a spring analogy, but with no orthogonality constraints, is introduced to equidistribute the lengths of the edges of the elements in the defined metric. The grid adaptation procedure is validated on an analytical test case and the efficiency of the overall methodology is investigated on supersonic and hypersonic benchmarks.
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  • 29
    Digitale Medien
    Digitale Medien
    ON BREAKING WAVES AND WAVE-CURRENT INTERACTION IN SHALLOW WATER: A 2DH FINITE ELEMENT MODEL (1996)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 22 (1996), S. 429-444 
    Details
    ISSN: 0271-2091
    Schlagwort(e): modified Boussinesq equations ; finite element method ; wave-current interaction ; breaking waves ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: A two-dimensional (horizontal plane) coastal and estuarine region model, capable of predicting the combined effects of gravity surface shallow- water waves (shoaling, refraction, diffraction, reflection and breaking), and steady currents, is described and numerical results are compared with those obtained experimentally.Two series of observations within a wave flume and a combined wave-current facility were developed. In the first case, the wave was generated via a hinged paddle located within a deepened section at one end of the channel, as, in the second case, the wave propagating with or against the current was generated by a plunger-type wavemaker; the re-circulating current was introduced via one passing tank connected to a centrifugal pump.Several comparisons for a number of 1D situations and one 2D horizontal plane case are presented.
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  • 30
    Digitale Medien
    Digitale Medien
    MODEL VERIFICATION ON 3D TIDAL CURRENT ANALYSIS IN TOKYO BAY (1996)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 22 (1996), S. 43-66 
    Details
    ISSN: 0271-2091
    Schlagwort(e): multiple-level model ; finite element method ; open boundary condition ; tidal current analysis ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: The results of a research project to verify the newly improved multiple- level model for 3D tidal current analysis in Tokyo Bay are presented. The improved multiple-level model includes additional effects due to Coriolis force, river inflows and wind shear stresses. Furthermore, a new numerical treatment of the open boundary condition was applied which effectively eliminated the spurious reflective waves often generated by various numerical methods simulating free surface flows. The mean (time-averaged or residual) and tidal currents in Tokyo Bay were simulated as examples to demonstrate the validity and capability of the newly improved multiple-level model. A series of numerical experiments was conducted to carefully examine the tidal circulations affected by the forcing factors of Coriolis force, river inflows and wind shears, both individually and combined. The numerical results demonstrated that the effects of each forcing term are physically reasonable, with the wind shear effect being the most significant and the case including all forcing terms being in best overall agreement with the field data collected in Tokyo Bay by the Ministry of Transportation. This study has contributed not only to the verification of the newly improved multiple-level model but also to the enhancement of the accuracy of numerical simulations of three-dimensional flow in coastal waters by this model.
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  • 31
    Digitale Medien
    Digitale Medien
    AN EULERIAN FINITE ELEMENT METHOD FOR TIME-DEPENDENT FREE SURFACE PROBLEMS IN HYDRODYNAMICS (1996)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 22 (1996), S. 175-194 
    Details
    ISSN: 0271-2091
    Schlagwort(e): free-surface flow ; viscous incompressible fluid ; finite element method ; marker particle method ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: A numerical method based on the finite element method is presented for simulating the two-dimensional transient motion of a viscous liquid with free surfaces. For ease of numerical treatment of the free surface expressed by a multiple-valued function, the marker particle method is employed. Numerous virtual particles are spread over all regions occupied by liquid. They move about on a fixed finite element mesh with the liquid velocity at their positions. These particles contribute nothing to the dynamics of the liquid and only serve as markers of liquid regions. The velocity field within liquid regions is calculated by solving the Navier- Stokes equations and the equation of continuity by the finite element method based on quadrilateral elements. A detailed discussion is given of the methodological problems arising in the implementation of the marker particle method on an unstructured finite element mesh and of the solutions to these problems. The proposed method is demonstrated on three sample problems: the broken dam problem, the impact of a falling liquid drop on a still liquid and the entry of a rigid block into water. Good agreement has been obtained in the comparison of the present numerical results with available experimental data.
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  • 32
    Digitale Medien
    Digitale Medien
    FINITE ELEMENT SIMULATION OF GUST LOADING (1996)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 23 (1996), S. 1197-1210 
    Details
    ISSN: 0271-2091
    Schlagwort(e): finite element method ; gust ; Engineering ; Engineering General
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: In the structural design of civil aircraft the critical loads are often those encountered in a gust or atmospheric turbulence. The traditional ‘indicial’ solution is restricted to a simple plate. In this paper a finite element formulation is proposed for an aerofoil or arbitrary shape entering a uniform sharp-edged or sinusoidal gust. The thin rotational gust front and wake in an irrotational flow field are successfully modelled by a novel superposition technique. The finite element solutions are compared with the Kussner function and results by other numerical methods. The agreement is good.
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  • 33
    Digitale Medien
    Digitale Medien
    Blockiness of olefin copolymers and possible microphase separation in the melt (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 18-27 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Solid-catalyzed copolymerization reactions of ethylene and α-olefins can produce complex mixtures generally regarded as “polyethylenes” (including linear low-density polyethylene). The selective nature of those catalysts can lead to block-like character in segments of polymer molecules, and these segments are sufficiently dissimilar (from a thermodynamic viewpoint) to allow for the possibility of microphase separation in the melt. Such a molecular-level phase separation would substantially alter the melt rheology, the crystallization process, and hence the mechanical and optical properties of the resulting product. It would, in principle, be identical to those occurring in conventional well-defined block copolymers, allowing the thermodynamic models developed for those systems to be extended to block-like polyolefins.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350104
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  • 34
    Digitale Medien
    Digitale Medien
    Influence of processing history on the properties of a thermotropic copolyester/polycarbonate blend (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 52-63 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Relationships between the rheological, morphological, and tensile properties of an immiscible blend of 25 wt% of a thermotropic liquid crystalline polymer (LCP) with polycarbonate are presented. The shear viscosity of the blend is intermediate between the two constituent materials, and indicates immiscibility in the melt. Extrudate swell behavior is examined and found to be closely related to that of polycarbonate. The morphology of the dispersed LCP phase varies between droplets and oriented fibrils, and is highly correlated with changes in tensile properties. Fibrils are associated with increased tensile modulus, and their development is favored in the elongation flow fields present in the spinline and in the die convergence section. In all cases, blend stiffness is less than that predicted for a continuous fiber-reinforced composite. Enhanced tensile modulus is associated with both extrusion from shorter length dies and increases in spinline draw ratio, with the latter proving the most important in fibril formation.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350108
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  • 35
    Digitale Medien
    Digitale Medien
    Ultrasonic behavior of polymer blends (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 79-91 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: During the last few years, improvements in control strategies became a necessity, with controls being targeted on material properties. The ever-increasing demand for polymer blends spells the need for in-line instrumentation capable of monitoring blend properties such as morphology. Since ultrasonics have proved to be sensitive to properties of multiphase materials, their performance for discriminating blend morphology was explored here. In-line and off-line (static, with no flow) ultrasonic measurements were made on different blends of polystyrene (PS), polyethylene (PE), and polypropylene (PP) for various viscosity ratios, and over the entire range of composition. Blends were compounded on a ZSK-30 Werner & Pfleiderer intermeshing co-rotating twin-screw extruder. In-line ultrasonic measurements were performed on both single-screw and twin-screw extruders. Ultrasonic properties (velocity and attenuation) were found to vary approximately linearly with composition. Mixing rules were evaluated for the description of ultrasonic behavior. For the attenuation measurements, the positive deviations from these rules were found significant. The additional attenuation was attributed to scattering generated by the presence of the minor phase inclusions.
    Zusätzliches Material: 23 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350111
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  • 36
    Digitale Medien
    Digitale Medien
    Rheo-Optical behavior of binary polymer blends: The effect of simple shear flow on phase behavior (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 92-99 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The phase behavior of polymer blends under simple shear flow has been studied using a custom-designed rheo-optical system consisting of a two-dimensional small-angle light scattering (SALS) device incorporated into a conventional rheometer. Two-dimensional SALS images were gathered for model polymer blend systems with different quiescent phase behavior: polystyrene/polyisobutylene (PS/PIB) that exhibits upper critical solution temperature phase behavior and polystyrene/poly(vinyl methyl ether) (PS/PVME) that shows lower critical solution temperature phase behavior. For the PS/PIB blend, shear-induced phase mixing occurred at a critical shear rate. Below that critical shear rate, the dispersed phase was highly elongated parallel to the flow direction. For PS/PVME blends, a streak scattering pattern was observed even though the sample became optically clear after shearing. We observed, apparently for the first time, the development of a bright-streak pattern from a transient dark-streak pattern for a polymer blend system under shear. Rheo-microscopy studies revealed an intriguing wave pattern that developed coincident with the observation of a streak pattern by SALS. The relationship between the two phenomena has not yet been established.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350112
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  • 37
    Digitale Medien
    Digitale Medien
    Milligrams to kilograms: An evaluation of mixers for reactive polymer blendingPresented in part at: ACS Annual Meeting 1993 Chicago. Presented at: Polyblends '93 Conference 1993 Montreal. (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 100-114 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The dispersions of both reactive and nonreactive polymer-polymer blend systems achieved in three different mixers are compared. The dispersions are prepared using an industrial scale twin-screw extruder, a laboratory internal mixer, and a miniature cup and rotor mixer. The morphology development in the three mixers is remarkably similar: The dispersed phase is stretched into sheets and ribbons; these sheets and ribbons then break into cylinders, which subsequently break into droplets via Rayleigh-type instabilities. Drop size distributions can be accurately predicted if we know the size of cylinders formed in the high shear fields of the mixer. There is a significant effect of quenching time on blend morphology - i.e, to properly evaluate mixing, blends must be quenched extremely quickly (well within a minute). Otherwise, we need to consider the morphology development during the quenching time, which may not be relevant to the mixing. There is a uniform shear stress in the miniature mixer, unlike the other mixers, which have varying stress levels. It is shown that a high stress level followed by a lower stress level is required in polymer blending to achieve efficient mixing. In the high stress level, the dispersed phase is stretched into extended shapes, which undergo instabilities and break up upon entering the low stress level. In the miniature mixer, the dispersed phase sees only one stress level, and thus very extended shapes persist at the end of mixing. The final dispersions in the twinscrew extruder and internal mixer at matched maximum shear rates are almost identical. For similar shear rates in the miniature mixer, the final dispersion of reactive blends is comparable to the other mixers. However, the miniature mixer does a poor job in dispersing high viscosity uncompatibilized blends, and the mixing conditions must be altered to obtain efficient mixing.
    Zusätzliches Material: 14 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350113
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  • 38
    Digitale Medien
    Digitale Medien
    Instrumented impact evaluation of a toughened carbon fiber epoxy composite (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 129-136 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Instrumented impact testing and analysis were performed on an interlaminartoughened carbon fiber epoxy composite (Toray 3900-2/T800H) and a conventional (untoughened) epoxy composite (Fiberite 934/T300). Severity of impact was varied by using a wide range of impact energy. The effect of difference in the tup of the impact instrument was discussed. The residual compressive strengths after compact (CAI's) were measured by using a universal mechanical tester. The impact damage and delamination resistance of the toughened and conventional composites were quantitatively compared. At the same impact energy, the extent of damage was much less severe and the CAI was higher for the toughened composite. Relationships between the CAI's, the state of impact damage, and impact energy were investigated. Impact damage mechanisms for these two composites were not exactly the same. The impact damage of the conventional composite exhibited much greater extents of delamination. By contrast, interlaminar delamination in the toughened composite was found to be significantly suppressed, and the impact damage was more dominated by controlled matrix cracking/fiber damage, instead of catastrophic delamination. As a result, the CAI's of the toughened composite exhibited a monotonous decrease with increase in the impact energy and in the linear dimension of extents of damage.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350202
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  • 39
    Digitale Medien
    Digitale Medien
    Melting behavior and thermal properties of high density polythylene (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 151-156 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Thermal diffusivity of high density polyethylene (HDPE) was studied over a wide range of temperatures (25 to 200°C) by melting powdered HDPE in a cylindrical mold at several pressures (101.3 to 5065 KPa gage) and recording the temperature profiles at several radial positions. The energy equation was solved numerically for cylindrical geometry. The thermal diffusivity of HDPE was fit as a function of temperature, porosity, and pressure.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350205
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  • 40
    Digitale Medien
    Digitale Medien
    Re-examination of a proposed model for nonisothermal crystallization kinetics (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 170-172 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: This communication is a theoretical re-examination of the model proposed by Choe and Lee for the nonisothermal crystallization kinetics of semicrystalline polymers.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350208
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  • 41
    Digitale Medien
    Digitale Medien
    Crosslinking in halogen containing novolac electron beam negative resists (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 180-183 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Halogenophenol novolac (HPN)-based negative resists exhibit excellent sensitivity and pattern resolution properties. The HPNs act as synergists for crosslinking with other irradiation labile compounds such as naphthoquinone diazide and bisazide vs. hydrogen halide (HX) elimination reaction, resulting in additional crosslinking, probably by aryl radical recombination and/or addition. We describe a new resist formulation based on HPN binder and melamine crosslinker (Cymel 303). In this case the irradiation induced HX elimination additionally catalyzes the melamine crosslinking.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350210
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  • 42
    Digitale Medien
    Digitale Medien
    Some relationships for the orientational drawing of polymersPart of the experimental data in this article was presented at the 4Th Rolduc Polymer Meeting, April 1989, Kerkrade, The Netherlands. (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 173-179 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The orientational drawing of films from different thermoplastics has been studied. The value of the activation energy of drawing in the regions of forced elasticity (necking), high elasticity, and viscous flow (ΔE1, ΔE2, ΔE3) has been found to vary directly with the activation energy for viscous flow of the melt (ΔEη). Here ΔE1 〈 ΔE2 〈 ΔE3 = ΔEη. Thus Δ Eη characterizes the potential of thermoplastics for orientational drawing under different deformation conditions, since it reflects simultaneously both the intermolecular interaction level and chain flexibility. For maximum chain orientation, the calculated values for the change in the entropy are close to that of the entropy change during crystallization (melting) of the same polymer. The deformation of polymer may be described as a deformation of an entanglement network from the standpoint of classic elasticity theory. Some parameters for an entanglement network were calculated from the results of the drawing experiments. The density of the entanglement network (DEN) depend on the polymer composition: For flexible-chain polymers the DEN is less, for rigid-chain polymers (with coiled chains) it is higher. The DEN affects the maximum (prebreak) drawing ratio: The greater the DEN, the smaller the ratio to which a film can be drawn. At high orientation, the tensile strength of different polymer films tend to be similar, if drawing is not accompanied by crazing.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350209
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  • 43
    Digitale Medien
    Digitale Medien
    Block copolyetherester. Part 3: Preparation of block copolyetheresters by a terephthalic acid process in the presence of salts (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 190-194 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The block copolyetheresters with hard segments of poly(butylene terephthalate) and soft segments of poly(tetramethylene ether) were prepared by a terephthalic acid (TPA) process in the presence of some salts. The preparations of a block copolyetherester under various conditions were first studied in a 1 L stainless steel reactor to find the best method. Then, the preparations of four block copolyetheresters were run in a pilot plant comprising a 200 L polyesterification reactor and a 200 L polymerization reactor under the suitable condition. The presence of some salts reduced the formation of tetrahydrofuran (THF), and also reduced the total reaction time in the pilot plant. The thermal properties and various mechanical properties of the block copolytheresters prepared by the pilot plant were investigated to evaluate the feasibility of this method.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350212
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  • 44
    Digitale Medien
    Digitale Medien
    Microwave processing of two-phase systems: Composites and plymer blends (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 144-150 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The objective of the current paper was to extend the relationships between complex polymer structures and microwave absorptivity that were formulated in the first three papers of this series (1-3). The microwave processing of composite and polymeric blends via a cylindrical resonance wave cavity and a rectangular standing wave applicator is described. These polymeric materials were irradiated in a low power (〈 100W) electric field at 2.45 GHz. Graphite-epoxy laminates were processed in both standing and traveling wave applicators. Rapid heating and curing were achieved in both cases. An observation of significance was that, with proper tuning of the traveling wave device (the precursor of a protable repair tool), it proved to be highly effective in processing. Additionally, a compatible blend of poly(methyl methacrylate) and poly(vinylidene fluoride) was heated in and applicator and the rates of temperature rise were demonstrated to depend upon morphology.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350204
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  • 45
    Digitale Medien
    Digitale Medien
    Stress-strain behavior and dynamic mechanical properties of poly(1,1-dimethyl-1-sila-cis-pent-3-ene), poly(1-methyl-1-phenyl-1-sila-cis-pent-3-ene) and of these polymers after crosslinking with sulfur (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 157-164 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Mechanical properties of polymers can be described by their stress/strain curves and by their behavior under dynamic mechanical thermal analysis (DMTA). The purpose of this paper is to report such mechanical properties for two unsaturated polycarbosilanes: poly(1, 1-dimethyl-1-sila-cis-pent-3-ene) (I) and poly(1-methyl-1-phenyl-1-sila-cis-pent-3-ene) (II). Tensile strength, elongation at break, modulus, bending modulus, Tg, and tan δ for I, II and for sulfur crosslinked I and II have been measured. The influence of polymer molecular weight, quantity of crosslinking agent, cure time, presence of carbon black filler, the effect of crosshead speed, and frequency on these properties was investigated.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350206
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  • 46
    Digitale Medien
    Digitale Medien
    The effects of physical aging on the brittle fracture behavior of polymers (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 165-169 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The effects of physical aging on the failure behavior of a typical brittle polymer, polystyrene, have been studied. Properties examined were creep rupture lifetimes, fatigue lifetimes, and environmental stress cracking in ethanol. Fractured samples were examined both optically and by scanning electron microscopy to determine the degree of crazing. It was found that a longer physical aging time produced shorter lifetimes in all cases. The main reason for this is the reduction in craze strength caused by a reduced toughness due to physical aging. A long aging time was found to delay craze formation, but once formed, these crazes were much less stable than those formed with a short aging time. The effects of aging are important on failure prediction criteria and on testing methodologies, and the implications are discussed.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350207
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  • 47
    Digitale Medien
    Digitale Medien
    Investigation of cure in epoxy acrylate resins using rheological and dielectric measurements (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 184-189 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Dielectric and rheological measurements are reported for the cure in a series of mixtures of an epoxy-acrylate with n-butyl methacrylate. The level of the initiator and properties of the epoxy acrylate and n-butyl methacrylate influence the cure characteristics and morphology of the film formed. Analysis of the rheological data indicates that during the curing process, microphase separation occurs within the mixture. The changes in the dielectric relaxation behavior with composition of the completely cured material is also consistent with microphase separation occurring in these resins while they are cured.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350211
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  • 48
    Digitale Medien
    Digitale Medien
    Monomer chain cross-transfer constants and cross termination factor evaluations on styrene-acrylonitrile copolymerization (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 195-201 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Using low conversion bulk copolymerization experimental data and the apparent rate constant model, the monomer chain cross-transfer rate constants and the cross-termination coefficient were evaluated. It was found that the dependence of the cross-termination coefficient on composition is a function of initiator efficiency and that monomer chain cross-transfer rate constant are relevant for the theoretical estimation of the molecular weights and molecular weight distributions.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350213
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  • 49
    Digitale Medien
    Digitale Medien
    Rheology of thermoplastic starch: Effects of temperature, moisture content, and additives on melt viscosity (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 202-210 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The melt viscosity of thermoplastic starch has been investigated as a function of temperature, moisture content, and processing conditions. The effects of various low molecular weight additives have also been studied. Starch melts exhibit power law behavior over the range of shear rates studied. Melt viscosity decreased with increasing temperature and moisture content (MC). The power law index m increased with increasing temperature. The consistency K decreased with increasing temperature and increasing moisture content. Moisture content during the pelletizing step influenced melt viscosities measured after equilibration to different MCs. All additives studied except glycerol monostearate (GMS) significantly lowered the melt viscosity of starch, some more effectively than water relative to starch with 15% MC. Starch with GMS had viscosities essentially the same as, or slightly higher than, starch/water. This behavior may be due to the presence of unmelted helical inclusion complexes of starch and GMS. Starch formulations at 160°C exhibited melt visocosities similar to an LDPE of melt index 1.8.
    Zusätzliches Material: 16 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350214
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  • 50
    Digitale Medien
    Digitale Medien
    Preface (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 289-290 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350402
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  • 51
    Digitale Medien
    Digitale Medien
    On the phenomenology of yield in bisphenol-a polycarbonate (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 291-303 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The phenomenology of yield in bisphenol-A polycarbonate is explored through tensile tests on thin rectangular specimens and through pressure-induced bulging of thin, clamped circular disks. In a tensile test, while the nominal critical stress at which yield initiates and the nominal draw stress at which a stable neck propagates along a specimen depend on the temperature and the strain rate, the ratio of the draw stress to the critical stress is shown to be approximately 0.75 over a temperature range of 22 to 65°C and strain-rates in the range of 10-4 to 100 s-1. Specimens subjected to constant tensile loads between the draw and critical stresses are shown first to creep till stretches on the order of 1.06 are attained and then are shown to undergo stable necking. Tensile tests on thin, wide rectangular specimens show that yielding initiates through shear bands that broaden and intersect to generate necks, which subsequently propagate along the specimen. In pressure-induced bulging of clamped disks, biaxial stretching progresses monotonically under increasing pressures; strain localization does occur near the outer edges of the specimens, however. Heating of a specimen with a substantial stably necked region shows that the temperature-induced recovery of the specimen from its deformed state begins well below the transition temperature Tg of the material, although most of the recovery occurs at Tg.
    Zusätzliches Material: 19 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350403
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  • 52
    Digitale Medien
    Digitale Medien
    Plastic behavior and deformation textures of poly(etherether ketone) under uniaxial tension and simple shear (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 317-330 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Samples of poly(etherether ketone) (PEEK) were subjected to large plastic deformations under uniaxial tension and simple shear by means of a new video-controlled testing method at constant true strain rate. The “equivalent” stress-strain curves obtained under the two loading modes are close at the yield point, but diverge drastically at large strains, with a rapidly increasing hardening in tension and a moderate hardening under simple shear. X-ray diffraction goniometry shows that these contrasting behaviors are associated with the different textures developed in the crystallite orientations. Under tension, the PEEK lamellae are progressively tilted in such a way that the chain axis becomes oriented parallel to the tensile axis; in the other mode, the final chain orientation is near to the shear axis. DSC analyses of deformed samples in both modes are carried out. The results show that the tension loading induces a fragmentation of the thin lamellae, while the shear mode generates less fragmentation. A quantitative model is presented that involves a composite approach: (i) the viscoplastic deformation of the crystalline lamellae, which is controlled by chain slip and transverse slip systems on planes parallel to the c axis, and (ii) the hyperelastic deformation of the amorphous phase, which depends on the affine unfolding of statistically distributed subchains. A discussion of the influence of the CRSS values on the stress-strain curves and textures is developed by means of this model.
    Zusätzliches Material: 19 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350406
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  • 53
    Digitale Medien
    Digitale Medien
    Mechanical response of beams of a nonlinear viscoelastic material (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 345-350 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: A constitutive equation for nonlinear viscoelasticity is used to model the mechanical response of solid polymers such as polycarbonate. The nonlinearity arises from a reduced time which causes stress relaxation to accelerate with increasing strain. The constitutive equation can account for the occurrence of yield in a homogeneous uniaxial constant strain rate test. The constitutive equation is used in a study of the pure bending of beams. It is assumed that the classical assumption of beam theory is valid, i.e., plane sections remains plane. At each fixed time, the strains vary linearly through the depth of the beam. At a fixed material element the strain varies in time with the curvature. This spatial variation of the strains combined with the nonlinear dependence of the reduced time on strain leads to a significantly different response from that given by traditional beam theory. The implications of this for the bending moment history, stress distributions, and other factors that relate to beam design are discussed.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350408
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  • 54
    Digitale Medien
    Digitale Medien
    Masthead (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995) 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350501
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  • 55
    Digitale Medien
    Digitale Medien
    Preface (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 385-386 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350502
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  • 56
    Digitale Medien
    Digitale Medien
    The evolution of material properties during physical aging (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 403-410 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Aging experiments using the NIST (National Institute of Standards and Technology) torsional dilatometer have been performed in which the temperature of an isothermally equilibrated epoxy glass was abruptly changed to a new temperature T0 and the evolution of the volume and torsional relaxation responses recorded. The results of down-jump and up-jump experiments were found to differ dramatically. Not only is the normal asymmetry of volume approach to equilibrium found, but the mechanical responses are found to evolve differently from the volume response, contrary to simple free volume models of the physical aging process. It is found that the torsional modulus changes with increasing time after the T-jump. In the case of the down-jump the evolution of the modulus ceases prior to that of the volume of the sample. In the up-jump experiment, the contrary is true, viz., the modulus continues to evolve after the volume has attained its equilibrium value. The implications of this for the description of material behavior are discussed.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350505
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  • 57
    Digitale Medien
    Digitale Medien
    An investigation into the three-dimensional stress-birefringence-strain relationship in elastomers (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 395-402 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The statistical theory of the birefringence of an individual non-Gaussian elastomer chain is used together with a chain network description of rubber elasticity to develop a relationship among the strain, birefringence, and stress in elastomers, valid for large deformations under generalized strain states. The result is a fully three-dimensional internal variable based constitutive model of rubber elasticity in which measurement of the elastomeric birefringence during straining in one deformation state characterizes the optically anisotropic response of the elastomer. Simultaneous measurement of the stress vs. strain response provides the rubbery modulus and limiting network extensibility properties needed to completely characterize the mechanical anisotropy of the material. Once characterized using the single, large deformation experiment, the birefringence and stress responses of the elastomer in other deformation states may then be predicted without adjusting any model parameters. The theory is compared to experimental studies from the literature of large strain deformations of elastomers in uniaxial tension and compression for which the exhibited birefringence and stress responses of deforming elastomers have been simultaneously recorded.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350504
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  • 58
    Digitale Medien
    Digitale Medien
    A constitutive theory for rigid polyurethane foam (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 387-394 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Rigid, closed-cell, polyurethane foam consists of interconnected polyurethane plates that form cells. When this foam is compressed, it exhibits an initial elastic regime, which is followed by a plateau regime in which the load required to compress the foam remains nearly constant. In the plateau regime, cell walls are damaged and large permanent volume changes are generated. As additional load is applied, cell walls are compressed against neighboring cell walls, and the stiffness of the foam increases and approaches a value equal to that of solid poyurethane. When the foam is loaded in tension, the cell walls are damaged and the foam fractures. A constitutive theory for rigid polyurethane foam has been developed. This theory is based on a decomposition of the foam in two parts: a skeleton and a nonlinear elastic continuum in parallel. The skeleton accounts for the foam behavior in the elastic and plateau regimes and is described using a coupled plasticity with continuum damage theory. The nonlinear elastic continuum accounts for the lock-up of the foam due to internal gas pressure and cell wall interactions. This new constitutive theory has been implemented in both static and dynamic finite element codes. Numerical simulations performed using the new constitutive theory are presented.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350503
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  • 59
    Digitale Medien
    Digitale Medien
    Measurement of the J integral in polycarbonate using the method of caustics (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 426-431 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The nonlinear fracture behavior of polycarbonate is investigated. The feasibility of measurement of the J integral through the optical method of reflected caustics is demonstrated. Significant increase in the crack growth resistance during small amounts of crack extension is observed.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350508
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  • 60
    Digitale Medien
    Digitale Medien
    Masthead (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995) 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350601
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  • 61
    Digitale Medien
    Digitale Medien
    Effect of the pressure drop rate on cell nucleation in continuous processing of microcellular polymers (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 432-440 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Microllular plastics are cellular polymers characterized by cell densities greater than 109 cells/cm3 and cells smaller than 10 μm. One of the critical steps in the continuous production of microcellular plastics is the promotion of high cell nucleation rates in a flowing polymer matrix. These high nucleation rates can be achieved by first forming a polymer/gas solution followed by rapidly decreasing the solubility of gas in the polymer. Since, in the processing range of interest, the gas solubility in the polymer decreases as the pressure decreases, a rapid pressure drop element, consisting of a nozzle, has been employed as a continuous microcellular nucleation device. In this paper, the effects of the pressure drop rate on the nucleation of cells and the cell density are discussed. The experimental results indicate that both the magnitude and the cell density are discussed. The experimental results indicate that both the magnitude and the rate of pressure drop play a strong role in microcellular processing. The pressure phenomenon affects the thermodynamic instability induced in the polymer/gas solution and the competition between cell nucleation and growth.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350509
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  • 62
    Digitale Medien
    Digitale Medien
    Effects of variable viscosity on the steady melting of thermoplastics during spin welding (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 441-459 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The steady melting of several amorphous and semicrystalline polymers during spin welding is analyzed by solving a simplified set of momentum and energy balance equations, assuming a shear-rate and temperature-dependent viscosity. A numerical model is developed for predicting the flow field and the temperature distribution in the molten film. It is shown that the steady melting rate of the thermoplastic solid is affected by the variable viscosity, by the pressure applied on the parts to be joined, and by a balance between the viscous heat generation in the melt and the convection of colder material into the molten film. The convection of heat in the outflow direction is shown to have a much smaller effect on the melting process.
    Zusätzliches Material: 21 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350510
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  • 63
    Digitale Medien
    Digitale Medien
    Enhanced polycarbonate toughness. II: Mechanisms (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 477-482 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Glassy shell-rubbery core polymer particles, 0.1 to 0.2 μm in diameter, increase the plane strain JIC values of 3.175 mm thick polycarbonate from 3.05 kJ/m2 (no particles) to 9.5 kJ/m2 (7.5 phr particles) at 23°C. Some modest decreases in these values are caused by tests at -20°C in samples 9.525 and 3.175 mm thick. If only the particle concentration is varied, JIC increases monotonically to 7.5 phr (by wt), then levels off or decreases slightly at 10.0 phr. The total volume of 1 to 2 μm diameter cavities formed in the matrix by the apparently unbonded particles behaves similarly; cavity volume and JIC are directly related. With increasing particle concentration the tensile modulus is unchanged, the yield stress and strain decrease modestly, the strain at fracture decreases appreciably, and the heat recoverable orientation in the fractured samples decreases. Few cavities are formed. The particles reduce the extent of shear deformation in the tensile samples.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350604
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  • 64
    Digitale Medien
    Digitale Medien
    A process model for nonisothermal photopolymerization with a laser light source. I: Basic model development (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 483-492 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: A mathematical model for a laser-induced photopolymerization process has been developed. This model simulates important aspects of stereolithography, a rapid prototyping process used for the production of three-dimensional plastic parts. The model consists of a set of coupled partial differential equations and considers irradiation, chemical reaction, and heat transfer in a small zone of material exposed to a stationary UV laser source. Numerical techniques are used for an approximate solution of the model equations, and the output includes spatial and temporal variations in the conversion of monomer to polymer, depletion of photoinitiator, and local variations of temperature in and around the region contacted by the laser light. Maximum conversions of approximately 60% and peak temperature rises of approximately 35° C were calculated for the cylindrical exposed region. Results have provided insights concerning laser dwell time, depth penetration, and the uniformity of polymer formed during the stereolithography process.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350605
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  • 65
    Digitale Medien
    Digitale Medien
    The relationship between structure and deformation behavior of sulfone polymers (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 499-505 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The deformation of three types of sulfone polymers - polysulfone (PSF), poly(ether sulfone) (PESF), and polyarylsulfone (PASF) - was performed with a mechanical testing system (MTS). The result and samples were studied using a transmission electron microscope (TEM), a dynamic mechanical analyzer (DMA), and a dielectric thermal analyzer (DETA). Stripes on TEM micrographs for small deformations increase with the fracture toughness (GIc). The activation energy (Ea) of the α-transition was determined from DETA. The results show that both Ea and TEM micrographs can be used to qualitatively estimate the order of GIc of sulfone polymers. An energy model was proposed to explain this phenomenon.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350607
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  • 66
    Digitale Medien
    Digitale Medien
    Molecular weight dependence of the fracture toughness of glassy polymers arising from crack propagation through a craze (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 419-425 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: We investigate criteria for craze failure at a crack tip and the dependence of craze failure on the molecular weight of the polymer. Our micromechanics model is based on the presence of cross-tie fibrils in the craze microstructure. These cross-tie fibrils give the craze some small lateral load bearing capacity so that they can transfer stress between the main fibrils. This load transfer mechanism allows the normal stress on the fibrils directly ahead of the crack tip in the center of the craze to reach the breaking stress of the polymer chains. We solve for stress field near the crack trip and use it to relate craze failure to the external loading and microstructural quantities such as the craze widening (drawing) stress, the fibril spacing, the molecular weight, and the force to break a single polymer chain. The relationship between energy flow to the crack tip due to external loading and the work of local fracture by fibril breakdown is also obtained. Our analysis shows that the normal stress acting on the fibrils at the crack tip increases linearly as the square root of the craze thickness, assuming that the normal stress distribution is uniform and is equal to the drawing stress acting on the craze-bulk interface. The critical crack opening displacement, and hence the fracture toghness is shown to be proportional to [1-(Me/qMn)]2, where Me is the entanglement molecular weight, Mn is the number average molecular weight of polymer before crazing, and q is the fraction of entangled strands that do not undergo chain scission in forming the craze.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350507
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  • 67
    Digitale Medien
    Digitale Medien
    Enhanced polycarbonate toughness. I: Measurement methodology (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 471-476 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The JIC values for core-shell-particle-toughened polycarbonate were determined at different temperatures and at 0, 2.5, 5.0, 7.5, and 10.0 phr particle content by six similar methods, using compact tensile specimens. At the 2.5 phr toughener level, the JIC values ranged from 2878 to 6100 J/m2, and at 7.5 phr, they ranged from 6125 to 10,760 J/m2, dependent only upon how the same JI-Δ a data were interpreted. This indicates that more work will be required before a reliable method of JIC measurement that can be applied to tough polymers is achieved.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350603
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  • 68
    Digitale Medien
    Digitale Medien
    Kinetics modeling and time-temperature-transformation diagram of microwave and thermal cure of epoxy resins (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 461-470 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Stoichimetric mixtures of a diglycidyl ether of bisphenol A (DGEBA)/ diaminodiphenyl sulfone (DDS) and a DGEBA/meta phenylene diamine (mPDA) were cured using both microwave and thermal energy. Fourier transform infrared (FTIR) was used for the measurement of the extent of cure and thermal mechanical analysis (TMA) was used for the determination of the glass transition temperature (Tg). The cure kinetics of the DGEBA/mPDA and DGEBA/DDS systems were described by an autocatalytic kinetic model up to vitrification in both the microwave and thermal cure. For the DGEBA/mPDA system, the reaction rate constants of the primary amine-epoxy reaction are equal to those of the secondary amine-epoxy reaction, and the etherification reaction is negligible for both microwave and thermal cure. For the DGEBA/DDS system, the reaction rate constants of the primary amine-epoxy reaction are greater than those of the secondary amine-epoxy reaction and the etherification reaction is only negligible at low cure temperatures for both microwave and thermal cure. Microwave radiation decreases the reaction rate constant ratio of the secondary amine-epoxy reaction to the primary amine-epxy reaction and the ratio of the etherification reaction to the primary amine-epoxy reaction. Tg data were fitted to the DiBenedetto model. A master curve and a time-temperature-transformation (TTT) diagram were constructed. The vitrification time is shorter in microwave cure than in thermal cure, especially at higher isothermal cure temperatures. For the DGEBA/mPDA system, the minimum vitrification time is two to five times shorter in the microwave cure than in the thermal cure. For the DGEBA/DDS system, the minimum vitrification time is 44 times shorter in the microwave cure than in the thermal cure.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350602
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  • 69
    Digitale Medien
    Digitale Medien
    A process model for nonisothermal photopolymerization with a laser light source. II: Behavior in the vicinity of a moving exposed region (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 493-498 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: A mathematical process model that stimulates important aspects of stereolithography, a rapid prototyping technique used for the production of three-dimensional plastic parts, has been developed. The model consists of a set of coupled partial differential equations and considers irradiation, chemical reaction, and heat transfer in a vat of photomonomer exposed to a moving UV laser source. Laser motion occurs in a straight line (vector path), and the model thus simulates the production of a single strand of plastic. Numerical techniques are used for approximate solution of the model equations, and output includes spatial and temporal variations in conversion of monomer to polymer, depletion of photoinitiator, and variations of temperature along the line of exposed material. The formation of a temperature wave that moves along the line of plastic is observed, together with the fact that the leading edge of the wave is steeper than the trailing edge, i.e., the material heats considerably faster than it cools. The maximum temperature of the wave reaches a pseudo-steady state after a short time. The results have provided useful information concerning the temperature at which the majority of the polymerization occurs; provided information on overall transient temperature behavior; allowed computer prediction of stereolithography working curves (cure depth and cure width vs. laser scan rate); and afforded a means for evaluating the amount of reaction that occurs in the dark period after light exposure.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350606
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  • 70
    Digitale Medien
    Digitale Medien
    Correlations between relaxation time spectrum and melt spinning behavior of polypropylene. 1: Calculation of the relaxation spectrum as a log-normal distribution and influence of the molecular parameters (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 513-517 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The linear viscoelastic behavior of commercial broad-distribution polypropylenes is studied. The samples underwent different controlled peroxide degradation rates, so they exhibit different molecular distributions. The relaxation spectrum is obtained by assuming that it takes the shape of a Log-Normal distribution. It is in agreement with the linear viscoelasticity theory by providing limiting values, contrary to other models. Moreover, the ratio τw/τn which takes place in this law is very useful to distinguish the synthesis differences of the samples when the Melt Flow Index alone cannot.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350609
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  • 71
    Digitale Medien
    Digitale Medien
    A study of creep and creep rupture of polycarbonate (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 546-554 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The creep characteristics of polycarbonate at elevated temperatures are investigated. The onset of glass transition temperature of polycarbonate is determined. An Arrhenius type relationship is used to describe the creep process and the concept of property retention index as applied to creep is discussed. An attempt is made to construct the master rupture curves for polycarbonate. The onset of glass transition temperature of polycarbonate was placed at around 110°C. It is concluded that the Arrhenius theory and the concept of property retention index are extremely useful in the construction of master rupture curves and that they require further investigation.
    Zusätzliches Material: 21 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350613
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  • 72
    Digitale Medien
    Digitale Medien
    Morphology and mechanical properties of liquid crystalline copolyester and poly(ethylene 2,6-naphthalate) blends (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 538-545 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Blends of poly(ethylene 2,6-naphthalate) (PEN) and a liquid crystalline copolyester (LCP), poly(benzoate-naphthoate), were prepared in a twin-screw extruder. Specimens for mechanical testing were prepared by injection molding. The morphology and mechanical properties were investigated by scanning electron microscopy (SEM) and an Instron tensile tester. SEM studies revealed that finely dispersed spherical domains of the liquid crystalline polymer (LCP) were formed in the PEN matrix, and the inclusions were deformed into fibrils from the spherical droplets with increasing LCP content. The morphology of the blends was found to be affected by their composition and a distinct skin-core morphology was found to develop in the injection molded samples of these blends. Mechanical properties were improved with increasing LCP content, and synergistic effects have been observed at 70 wt% LCP content whereas the elongation at break was found to be reduced drastically above 10 wt% of LCP content. This is a characteristic typical of chopped-fiber-filled composites. The improvement in mechanical properties is likely due to the reinforcement of the PEN matrix by the fibrous LCP phase as observed by scanning electron microscopy. The tensile and modulus mechanical behavior of the LCP/PEN blends was very similar to those of the polymeric composite, and the tensile strength and flexural modulus of the LCP/PEN 70/30 blend were two times the value of PEN homopolymer and exceeded those of pure LCP, suggesting LCP acts as a reinforcing agent in the blends.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350612
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  • 73
    Digitale Medien
    Digitale Medien
    Coefficients of dynamic friction as a function of temperature, pressure, and velocity for several polyethylene resins (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 557-563 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The coefficient of dynamic friction is often the controlling factor for solids conveying, pressure generation, and thermal decomposition of a resin in the feed section of a single-screw plasticating extruder. The coefficients of friction are, however, very poorly understood, and the interpretation of the measurements are complicated by the dissipation of frictional energy at the sliding interface. A new instrument was recently built to help understand dynamic friction, and a numerical technique was developed to estimate the interface temperture. Coefficients of dynamic friction for several polyethylene resins are presented in this paper as a function of the surface temperature, pressure, and velocity. The relationship of the data with respect to the extrusion process is discussed.
    Zusätzliches Material: 19 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350702
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  • 74
    Digitale Medien
    Digitale Medien
    A flow model for non-newtonian liquids inside a slot die (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 577-586 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: A one-dimensional flow model for non-Newtonian liquids inside a dual-cavity slot die is presented. The model is capable of analyzing slot dies of any cavity shape, cavity taper, slot-length variations, and slot-gap variations. The proposed model incorporates a truncated-power-law model for the viscosity of non-Newtonian liquids. According to flow models with power-law approximation for liquid viscosity, the distribution of non-Newtonian liquid through a slot die depends on the slot Reynolds number only. With our model, we find that the zero shear viscosity and the relaxation time of a non-Newtonian liquid have large effects on its distribution. For non-Newtonian liquids which are expected to experience shear-thinning over portion of a slot die, it is concluded that a flow model with a truncated-power-law approximation for liquid viscosity be used to predict the liquid distribution from the die.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350704
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  • 75
    Digitale Medien
    Digitale Medien
    Residence time distribution in non-intermeshing counter-rotating twin-screw extruders (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 598-603 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: This paper deals with the residence time distribution (RTD) in a non-intermeshing counter rotating twin screw extruder.The RTDs were measured in three vent zones of the extruder sparately, and in the adjacent zones combined, using a soluble dye as the tracer. Assuming that the RTDs in the adjacent zones are independent of each other, the overall RTD was also calculated using a previously developed statistical theory. The theory has also confirmed the consistency of the present measurements.A predictive RTD model for the non-intermeshing twin screw extruder, based on the flow analysis of the individual screw zones and their statistical superposition, was also developed. The predictions are in good agreement with experiment.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350706
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  • 76
    Digitale Medien
    Digitale Medien
    The flow-induced phase morphology of fluoroelastomer and polycarbonate blends during extrusion (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 619-636 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The flow-induced phase morphological development under different extrusion conditions was studied in terms of the rheological property and interfacial tension of various elastomers and thermoplstics. The interfacial tension for elastomers and thermoplastics was investigated by using a breaking thread method (1-4). We found that the method is suitable for measuring interfacial tension without degradation. The droplet-fibrillation transition phenomenon was observed in various extrudates of fluoroelastomer/polycarbonate blends. The criteria for the flow-induced morphology, in particular the droplet-fibrillation transition, are critically discussed in this paper.
    Zusätzliches Material: 23 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350708
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  • 77
    Digitale Medien
    Digitale Medien
    The conducting behavior and stability of conducting polymer composites (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 637-641 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Results of measurements of the electrical conductivity of low density polyethylene/polypyrrole and polystyrene/polypyrrole composites are reported. It is observed that the electrical conductivity of the composite vs. concentration follows the power law predicted by the percolation theory. The manufacturing process influences the homogeneity of the composite at microscopic scale and thus the percolation threshold. Annealing studies show that the stability of the electrical conductivity of the composite is related to the thermal expansion of the polymers and the relaxation of the polymer chains. The decrease of the electrical conductivity of the composite is attributed to the interruption of the percolation path.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350802
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  • 78
    Digitale Medien
    Digitale Medien
    The effect of a partly hydrolyzed styrene-tert-butyl acrylate diblock copolymer on the properties of poly(2,6-dimethyl-1,4-phenylene ether) (PPE) and polyamide-6 (PA) blends (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 648-657 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The compatibilizing effect of a polystyrene-hydrolyzed poly(t-butyl acrylate) diblock copolymer (SBAH) on the phase structure, rheological properties, and mechanical properties of immiscible poly(2,6-dimethyl-1,4-phenylene ether) (PPE) and polyamide-6 (PA) blends was investigated. The SBAH was prepared by sequential anionic polymerization of styrene and t-butyl acrylate, followed by acid-catalyzed hydrolysis of t-butyl acrylate block. Scanning electron micrographs show that the blends exhibit a more regular and finer dispersion when the SBAH of 47% hydrolyzed t-butyl acrylate block is added. By addition of small amount of the block copolymer, the blends show non-Newtonian power-law behavior, and the contribution of storage modulus (G′) to the total response increases. Solubility tests support the formation of graft copolymer by chemical reaction between amine groups of the PA and carboxyl groups of the SBAH. Both modulus and strength are improved about 20% with addition of the 3 wt% SBAH, while the elongation at break decreases notably; thus, the blends fail in a brittle manner.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350804
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  • 79
    Digitale Medien
    Digitale Medien
    A study on interfacial adhesion of poly(vinylidene fluoride) with substrates in a multilayer structure (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 666-672 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The peel force of a PVDF/3-APS/Si joint and a PVDF/3-APS/Al joint can reach the same level by treating the Si substrate with ≥ 0.3% 3-aminopropyltriethoxy silane (3-APS) solution and treating the aluminum substrate with NH3 solution (pH 10.5) first and then with ≥ 3% 3-APS solution. Scanning electron micrographs show that the interfacial adhesion mechanisms of PVDF/3-APS/Si joints and PVDF/3-APS/Al joints are different. In the peel test, the PVDF [poly(vinylidene fluoride)] break surfaces from PVDF/3-APS/Si joints reveal striations on the surface and less plastic deformation. The significant plastic deformation of the PVDF at the break surface may result from the deeper interpenetration of 3-APS with PVDF in the PVDF/3-APS/Al joint than in the PVDF/3-APS/Si joint. The peel force of PVDF film/substrate joint depends on many factors: film thickness, peel rate, concentration of coupling agent, the treatment time of the coupling agent on the substrate, and the substrate pretreatment.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350806
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  • 80
    Digitale Medien
    Digitale Medien
    Morphologies of mechanically mixed amorphous blends before and after annealing (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 693-702 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The morphologies of amorphous polymer blends produced by extrusion were investigated by transmission electron microscopy. Polymers with similar viscosities, i.e. poly(methyl methacrylate) (PMMA), polystyrene (PS), and random copolymers P(SxMMA1 - x) were mixed pairwise, in different compositions. Finely dispersed phase structures were produced in the blends, with domains in the submicron range. The structure patterns were considerably perturbed by the stress fields in the extruder. Domain-matrix and co-continuous morphologies were obtained, in a distribution controlled mainly by the viscosity ratio. Annealing after extrusion led to structure coarsening, whereby the patterns were changed until a steady state was established. Sometimes, matrix inversion was observed.
    Zusätzliches Material: 17 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350809
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  • 81
    Digitale Medien
    Digitale Medien
    Morphology and barrier properties of oriented blends of poly(ethylene terephthalate) and poly(ethylene 2,6-naphthalate) with poly(ethylene-co-vinyl alcohol) (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 680-692 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Morphology and oxygen permeability studies were carried out for blends of poly(ethylene terephthalate), PET, and poly(ethylene 2,6-naphthalate), PEN, with poly(ethylene-co-vinyl alcohol), EVOH. PET/EVOH blends are seen as a possible substitute for poly(vinylidene chloride)-coated PET packaging films. The effects of several processing parameters such as draw temperature and draw ratio on blend morphology and barrier properties suggest that the morphology of the EVOH phase dictates to a large extent the oxygen permeabilities of these blends. The relationships between morphology and oxygen permeability and explained are explained by consideration of two-phase conduction models. The model of Fricke is found to be a good predictor of the barrier properties of the PET/EVOH system. The oxygen permeability of PET was reduced by a factor of 4.2 with the addition of 20 wt% EVOH and that of PEN by a factor of 2.7 with the addition of 15 wt% EVOH. Water vapor permeabilities and mechanical properties of PET and PEN were only slightly affected by the addition of 15 wt% EVOH.
    Zusätzliches Material: 18 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350808
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  • 82
    Digitale Medien
    Digitale Medien
    Masthead (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995) 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350901
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  • 83
    Digitale Medien
    Digitale Medien
    Application of statistical experimental strategies to the process optimization of waterborne polyurethane (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 722-730 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: A modified acetone process for the preparation of aqueous polyurethane (PU) dispersion is investigated. PU dispersions were prepared by polyaddition of isophorone diisocyanate (IPDI) to poly(tetramethylene ether glycol) (PTMG) and dimethylolpropionic acid (DMPA), followed by neutralization of pendant COOH groups with triethylamine (TEA). The resulting prepolymer chain was then extended through reaction with an ethylenediamine (EDA) derivative bearing sulfonate groups. The effect of such preparation conditions as catalyst (dibutyltin dilaurate, DBTDL) concentration, the acetone/PU ratio, phase-inversion temperature, agitation rate, and water-addition rate on the average particle size of aqueous PU anionomer dispersions is systematically studied using fractional factorial design and response surface methodology. Fractional factorial analysis indicates that the effects of the acetone/PU ratio, phase-inversion temperature, water-addition rate as well as the two factor interactions of DBTDL concentration and phase-inversion temperature, of the acetone/PU ratio and phase-inversion temperature, and of acetone/PU ratio and agitation rate are the key variables influencing average particle size of PU dispersions. Empirical models for average particle size are fitted and plotted using central composite experimental design as contour diagrams in order to facilitate examination of the average particle size results. The results show that for a 100 g PU anionomer containing 0.311 wt % COOH and 1.51 wt % SO3H groups, a minimum number-average particle size of the dispersion ∼ 25 nm can be obtained under an acetone/PU ratio, water-addition rate, phase-inversion temperature, catalyst concentration, and agitation rate of 3.65, 2 mL/min, 50°C, 150 ppm and 350 rpm, respectively.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350812
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  • 84
    Digitale Medien
    Digitale Medien
    Master curve approach to polymer crystallization kinetics (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 733-740 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Nonisothermal crystallization kinetic data obtained from differential scanning calorimetry (DSC) for a poly(ethylene terephthalate) are corrected for the effects of temperature lag between the DSC sample and furnace using the method of Eder and Janeschitz-Kriegl which is based on experimental data alone without resort to any kinetic model. A method is presented for shifting the corrected nonisothermal crystallization kinetic data with respect to an arbitrarily chosen reference temperature to obtain a master curve. The method is based on experimental data alone without reference to any specific form of kinetic model. When the isothermal crystallization kinetic data for the same material are shifted with respect to the same reference temperature, a master curve is also obtained which overlaps to a large extent the corresponding master curve from nonisothermal data. It follows that nonisothermal DSC measurements provide the same crystallization kinetic information as isothermal DSC Measurements, only over a wider range of temperatures. The shift factors obtained from experimental data alone are compared in turn with the corresponding values calculated from the Avrami equation, the Hoffman-Lauritzen expression, and the Nakamura equation as a means of evaluating these models individually. It is concluded that the Avrami equation is very good at describing isothermal crystallization kinetics, the Hoffman-Lauritzen extrapolation of the limited isothermal data to a wide range of temperatures is quite good, and the Nakamura equation yields reliable crystallization kinetic information over a narrower range of temperatures than nonisothermal data alone without using any specific model.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350902
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  • 85
    Digitale Medien
    Digitale Medien
    The effect of curing of unsaturated polyester resin on the dynamic relaxation time (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 754-758 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The effect of hot curing of unsaturated polyester resin on the dynamic relaxation time was studied using dielectric measurements along with two dynamic mechanical measurement methods. It was found that the dynamic response during cure was a material frequency dependent property and did not depend on the measurement method. All relaxation times, measured during cure, by all three measurement methods used, converged to a single equation: τ(t)av=atb where t= curing time, a, b=constants. The increase of the relaxation time during cure followed the same trend as a friction factor, which was found to increase with conversion. The crosslinking density was found to increase slowly with conversion, while the relaxation time increased exponentially. These two different modes of behavior during cure explain the high resolution of dynamic measurements as a cure monitoring tool, which can easily detect small curing changes. This behavior of the relaxation time was explained by the sharp rise of activation energy due to a parallel decrease of free volume at high conversion.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350904
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  • 86
    Digitale Medien
    Digitale Medien
    Masthead (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995) 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760351001
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  • 87
    Digitale Medien
    Digitale Medien
    Effect of matrix ductility on the fracture behavior of rubber toughened epoxy resins (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 778-785 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: This paper investigates the effect of matrix ductility on toughness in a carboxyl-terminated butadiene-acryionitrile copolymer (CTBN) toughened diglycidyl ether of bisphenol-A (DGEBA)-piperidine system. Two kinds of epoxides were blended separately into this system to change the matrix ductility. One was a rigid and polyfunctional 4,4′-diaminodiphenol methane (MY720), and the other was a flexible diglycidyl ether of propylene glycol (DER732). The matrix Tg was significantly changed, but without alteration of the microstructure of the dispersed rubbery phase. The result of fracture energy tests reveals that the toughness of the neat epoxy resins increases slightly with the increase in the resin ductility. The toughness of the rubber-modified epoxy resins increases strongly with matrix ductility. Studies on the morphology of the toughened systems and their fracture surfaces indicate that the size of the plastic deformation zone under constant rubbery-phase morphology is determined by the multiple but localized plastic shear yielding. Increasing matrix ductility increases the size of the plastic deformation zone by inducing more extensive shear yielding. In addition, fracture surfaces reveal that as the matrix rigidity is increased, an increasing proportion of the fracture energy is dissipated by rubber cavitation during crack initiation.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760350907
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  • 88
    Digitale Medien
    Digitale Medien
    Quiescent nonisothermal crystallization kinetics of isotactic polypropylenes (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 797-804 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Recently, a model was developed for the nonisothermal crystallization of normal alkanes with chain lengths between 30 and 50. The model was derived based on the fundamental equation of Ozawa for nonisothermal crystallization, the surface nucleation theory, and the growth rate theory for extended chain crystals. In this paper, the proposed model is modified and extended to the case of polymer crystallization. Experimental differential scanning calorimetry data for three isotactic polypropylene resins with different molecular weights are presented at five cooling rates from 2 to 40 K/min. Model predictions are in excellent agreement with the experimental data for the three polymers at low and high supercoolings.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760351002
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  • 89
    Digitale Medien
    Digitale Medien
    The effect of particles on failure modes of filled polymers (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 813-822 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The effect of rigid particles on the fracture mode of polymers that yield with necking was analyzed theoretically with a model of regularly arrayed spherical particles. The adhesion between a polymer and particles was assumed to be weak, and particles were assumed to debond from the polymer before necking. A linear decrease in engineering draw stress with an increase in the filler content was derived. An increase in filler content leads to a transition in deformation mechanism. The transition depends on the ability of the polymer to strain-harden. If the ability to strain-harden is insignificant and the engineering fracture stress (strenght) of the polymer is lower than its yield stress, the transition is from ductile to brittle fracture. If the ability to strain-harden is essential and the strength of the unfilled polymer is higher than its yield stress, the transition (ductile-to-ductile) is from neck propagation to uniform ductile yield. The critical filler contents were determined for both transitions from the properties of an unfilled polymer. The ductile-to-ductile transition without embrittlement is possible if the strength of the unfilled polymer is higher than its yield stress. Results for polymers filled by weakly bonded particles were compared with polymers filled by particles that debond after the yield stress.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760351004
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  • 90
    Digitale Medien
    Digitale Medien
    Micro scale flow behavior and void formation mechanism during impregnation through a unidirectional stitched fiberglass mat (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 837-851 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Liquid composite molding (LCM) processes such as resin transfer molding (RTM) and structural reaction injection molding (SRIM) have been perceived as high potential processes for the near-net-shape manufacturing of composite parts. This paper addresses two major issues in LCM technology: fiber wetting and void formation during mold filling. Flow visualization experiments were carried out to develop a better understanding of the flow induced voids. The formation and elimination of voids were studied using several liquids and a unidirectional stitched fiberglass mat. Void formation was correlated to capillary number and liquid-fiber-air contact angle.
    Zusätzliches Material: 16 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760351006
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  • 91
    Digitale Medien
    Digitale Medien
    An overview of the basic aspects of polymer adhesion. Part I: Fundamentals (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 957-967 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Adhesion between two substrates is a complex phenomenon which at present is still not well understood. The important existing adhesion models (electrical, diffusion, thermodynamic adsorption, chemical, etc.) are reviewed in order to try to explain their mechanisms. Thermodynamic adsorption is now believed to be one of the most importnat mechanisms by which adhesion is achieved. Difusion and wetting are kinetic means in attaining good adsorption of a polymer at the interface. In the case of this model (thermodynamic adsorption), the notion of surface energy is developed and the importance of this property in the understanding of adhesion phenomena is emphasized. The methods of determining the surface characteristics of low and high energy solids are presented. The role played by acid-base interactions in adhesion is also mentioned.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760351202
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  • 92
    Digitale Medien
    Digitale Medien
    Copolymerization of t-butoxycarbonyloxystyrene and sulfur dioxidePresented at the 205th National Meeting of the American Chemical Societry, Denver, Colorado, March 28, 1993 (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 989-999 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The reaction kinetics of radical chain copolymerization of t-butoxycarbonyl-oxystyrene (TBS) and sulfur dioxide have been studied using a reaction/sampling apparatus that permits accurate determination of the reaction mixture concentrations during polymerization. The results are compared with the styrene-sulfur dioxide copolymerization kinetics. The influence of temperature and reactant concentrations on the polymerization rate and copolymer composition are reported. With increasing reaction temperature, the amount of SO2 incorporated and the molecular weight fo the copolymer are found to decrease. For a constant TBS concentration in the reaction solutio, raising the SO2 concentration causes an increase of SO2 incorporation in the copolymer, up to a maximum SO2 content corresponding to a TBS:SO2 mole ratio of 2:1. However, for a constant SO2 concentration, the amount of TBS incorporated in the copolymer increases with decreasing TBS concentration in the reaction solution. The polymerization rate and copolymer molecular weight increase proportionally with monomer concentration as expected for a normal radical chain polymerization mechanism. Comparison of these findings with various kinetic models for styrene-SO2 copolymerization indicates good agreement with models proposed by Barb (1-3) and Walling (4); however, the data do not agree with the predictions of Matsuda et al. (5) The understanding of the kinetics and reaction mechanism provided in this study will aid in the manufacture of this lithographically important copolymer.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760351205
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  • 93
    Digitale Medien
    Digitale Medien
    Indentification of plastic waste using spectroscopy and neural networksBased on a Dupont Company Internal Report Issued in February 1992 (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 1011-1015 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: In this paper we investigate a new approach for the automated sorting of post-consumer plastic waste. We show that rapid and relible identification of polymers can eb achieved using a combination of fixed-filter near-infrared spectroscopy and neural network data analysis, and we demonstrate the effectiveness of the proposed method for sorting polyethylene terephthalate, high density polyethylene, and poly(vinyl chloride). Finally, we discuss a proposed compact, rugged instrument based on the new sorting method. Owing to the flexibility gained by incorporating neural networds in our system, thismethod can easily be extended to include additional polymers.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760351208
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  • 94
    Digitale Medien
    Digitale Medien
    Analysis of titanium dioxide agglomerate dispersion in linear low density polyethylene and resulting properties of compounds (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 1037-1045 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The dispersion of titanium dioxide agglomerates within linear low density polyethylene (LLDPE) melts has been investigated by using a cone-and-plate device installed within a temperature controlled oven. Observation of fragment evolution indicates that erosion is the predominant mechanism of dispersion. The erosion rate of titanium dioxide agglomerates in LLDPE was consistenty with the results obtained in previous dispersion studies of titanium dioxide in polydimethyl siloxane (PDMS). The effect of agglomerate dispersion on the optical, tensile, and dynamic mechanical properties of compounds incorporating titanium dioxide was also investigated. Changes in compound properties were correlated with observed morphology changes of agglomerates in order to clarify the effect of dispersion.
    Zusätzliches Material: 15 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760351212
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  • 95
    Digitale Medien
    Digitale Medien
    Dynamic simulation of flow-induced fiber fracture (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 1022-1030 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: A dynamic simulation method has been developed of the fracture process of a fiber in a flow field using the particle simulation method proposed i a previous paper. The fiber is modeled with bonded spheres as a fiber model. The flexibility of the fiber model is altered by changing three parameters of the stretching, bending, and twisting constants between adjacent spheres. The stress induced in each bond of the fiber model as a result of deformation is formulated using displacement of the bodn distanc, bond angle, and torsion angle fr each pair of spheres. After deformation, the fiber model fractures at the bond at which the stress surpasses the strength of the fiber. The motion of the fiber model in a flow field is determined by solving the translational and rotational motion equations for individual spheres under the hydrodynamic force and torque exerted on them. The correctness of the method and formulation was verified by comparing the simulated deflection curve of a cantilever beam (with a concentrated load at the end) with the theoretical curve. Good agreement was found in both the deflection and slope of the beam. The fracture process of a fiber after bending deformation in a two-dimensional siimple shear flow was simulated under assumptions of an infinitely dilute system, no hydrodynamic interaction, and a low Reynolds number of a particle. The calculated critical conditions of the flow field for fiber fracture were compared with Forgacs and Mason's theoretical ones. Simulated values of the fracture condition of the fluid shear stress related to the Young's modulus of a fiber agree with theoretical ones over an aspect ratio of 15.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760351210
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  • 96
    Digitale Medien
    Digitale Medien
    Masthead (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995) 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760351301
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  • 97
    Digitale Medien
    Digitale Medien
    On the structure/properties relationships in photoinitiators of polymerization (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 1061-1065 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The choice of photoinitiators is partly governed by the requirement of a high curing speed. Many reactive monomers and efficient photoinitiators have been synthesized and are commercially available. However, improved photoinitiator systems, exhibiting increasingly faster curing speeds and/or increased photosensitivity, are increasingly required. The intrinsic reactivity in the exicited states determines te interest of a given photoinitiator with reference to its efficiency. However, other factors e.g. high molecular absorption coefficients and a broad spectral absorption range, synergistic effects, yellowing, extractability, and th effect on the long-term stability, must be considered as important. An attractive field of research and development is found in the role played by decisive parameters affecting the reactivity of a given structure, such as chemical substitution in well-chosen positions, the character of water solubility, acid release ability, and copolymerization potential. Laser spectroscopy proved a most convenient tool for the real time investigation of the excited state dynamics and the processes involved.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760351215
    Standort Signatur Erwartet Verfügbarkeit
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  • 98
    Digitale Medien
    Digitale Medien
    Morphology and mechanical properties of epoxy resins containing functionalized perfluoroether oligomers (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 1069-1076 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Chain extended perfluoroether oligomers were found to be miscible with bisphenol epoxy resins at all concentrations. These were evaluated as modifiers for anhydride cured resin systems, taking advantage of the carboxylic acid functionality at the chain ends. By altering the mixing and curing procedure different two-phases morphologies could be obtained varying from fine co-continuous networks, which produced transparent castings, to opaque systems consisting of precipitated heterogeneous particles. While the Tg and flexural modulus were found to be slightly lower than the control cure resin, the addition of the fluoroligomer modifier produced large increases in flexural strength, ductility, and fracture toughness. Samples with an IPN type morphology were found to exhibit an increase in ductility after aging at 200°C for three weeks proportionally to the concentration of fluoroligomer used.
    Zusätzliches Material: 14 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760351302
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  • 99
    Digitale Medien
    Digitale Medien
    The leveling of thermosetting waterborne coatings. Part II: Drying of coated wet films (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 1098-1105 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Evaporation behavior of water/solvent blends was estimated using the universal functional activity coefficient, UNIFAC, method. The evaporation rate from a free surface of a waterborne coating, WBC, containing a co-solvent was experimentally determined. These results were used to estimate the evaporation rate from wet films of a WBC containing a variety of co-solvents with a range of initial thickness. Knowing the composition of the WBC during the drying process, the change in the viscosity and the surface tension was determined. The results strongly support the development of a surface tension gradient in the film. It is also suggested that a surface tension gradient would accelerate the leveling of the ribs if a proper co-solvent were employed.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760351305
    Standort Signatur Erwartet Verfügbarkeit
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  • 100
    Digitale Medien
    Digitale Medien
    Effect of casting solvent on the heterogeneity of films of polymer blends (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 1113-1116 
    Details
    ISSN: 0032-3888
    Schlagwort(e): Chemistry ; Chemical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The miscibility window of the 50/50 w/w poly(styrene-co-4-vinylphenyl)-dimethylsilanol/poly(n-butyl methacrylate) (ST-VPDMS/PBMA) blends prepared from toluene was studied and determined to be in the VPDMS composition range of 4 to 18 mole% in the copolymers. The observed miscibility window was to be compared to the range of 9 to 34 mole% found for the blends prepared from methyl ethyl ketone which was capable of competing for hydrogen bonding. The fact that the observed miscibility windows are influenced by the choice of solvents illustrates that an equilibrium state of polymer mixing is not always attained in solvent casting films and that caution needs to be exercised in studying polymer miscibility when solvent cast films are used.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pen.760351307
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