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  • Articles  (2,132)
  • Chemical Engineering  (2,075)
  • Navier-Stokes equations  (57)
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  • 1995-1999  (428)
  • 1985-1989  (1,704)
  • 1930-1934
  • Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics  (2,132)
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  • Articles  (2,132)
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  • 1
    Electronic Resource
    Electronic Resource
    Some weight-type high-resolution difference schemes and their applications (1999)
    Springer
    Acta mechanica Sinica 15 (1999), S. 313-324 
    Details
    ISSN: 1614-3116
    Keywords: TVD schemes ; ENO schemes ; WENO schemes ; Euler equations ; Navier-Stokes equations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract By the aid of an idea of the weighted ENO schemes, some weight-type high-resolution difference schemes with different orders of accuracy are presented in this paper by using suitable weights instead of the minmod functions appearing in various TVD schemes. Numerical comparisons between the weighted schemes and the non-weighted schemes have been done for scalar equation, one-dimensional Euler equations, two-dimensional Navier-Stokes equations and parabolized Navier-Stokes equations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02487929
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  • 2
    Electronic Resource
    Electronic Resource
    A mixture differential quadrature method for solving two-dimensional incompressible Navier-Stokes equations (1999)
    Springer
    Applied mathematics and mechanics 20 (1999), S. 1358-1366 
    Details
    ISSN: 1573-2754
    Keywords: numerical method ; differential quadrature method ; Navier-Stokes equations ; O357.1
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract Differential quadrature method (DQM) is able to obtain highly accurate numerical solutions of differential equations just using a few grid points. But using purely differential quadrature method, good numerical solutions of two-dimensional incompressible Navier-Stokes equations can be obtained only for low Reynolds number flow and numerical solutions will not be convergent for high Reynolds number flow. For this reason, in this paper a combinative predicting-correcting numerical scheme for solving two-dimensional incompressible Navier-Stokes equations is presented by mixing upwind difference method into differential quadrature one. Using this scheme and pseudo-time-dependent algorithm, numerical solutions of high Reynolds number flow are obtained with only a few grid points. For example, 1∶1 and 1∶2 driven cavity flows are calculated and good numerical solutions are obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02459169
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  • 3
    Electronic Resource
    Electronic Resource
    The fundamental solution method for incompressible Navier-Stokes equations (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 565-568 
    Details
    ISSN: 0271-2091
    Keywords: fundamental solution method ; integral equation method ; Navier-Stokes equations ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A complete boundary integral formulation for incompressible Navier-Stokes equations with time discretization by operator splitting is developed using the fundamental solutions of the Helmholtz operator equation with different order. The numerical results for the lift and the drag hysteresis associated with a NACA0012 aerofoil oscillating in pitch show good agreement with available experimental data. © 1998 John Wiley & Sons, Ltd.
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  • 4
    Electronic Resource
    Electronic Resource
    Algebraic multigrid methods for the solution of the Navier-Stokes equations in complicated geometries (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 26 (1998), S. 281-301 
    Details
    ISSN: 0271-2091
    Keywords: Navier-Stokes equations ; SIMPLE algorithm ; algebraic multigrid methods ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The application of standard multigrid methods for the solution of the Navier-Stokes equations in complicated domains causes problems in two ways. First, coarsening is not possible to full extent since the geometry must be resolved by the coarsest grid used. Second, for semi-implicit time-stepping schemes, robustness of the convergence rates is usually not obtained for convection-diffusion problems, especially for higher Reynolds numbers. We show that both problems can be overcome by the use of algebraic multigrid (AMG), which we apply for the solution of the pressure and momentum equations in explicit and semi-implicit time-stepping schemes. We consider the convergence rates of AMG for several model problems and demonstrate the robustiness of the proposed scheme. © 1998 John Wiley & Sons, Ltd.
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  • 5
    Electronic Resource
    Electronic Resource
    A spectral-finite difference solution of the Navier-Stokes equations in three dimensions (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 129-142 
    Details
    ISSN: 0271-2091
    Keywords: Navier-Stokes equations ; unsteady flow ; three-dimensional channel ; finite differences ; spectral techniques ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A new computational code for the numerical integration of the three-dimensional Navier-Stokes equations in their non-dimensional velocity-pressure formulation is presented. The system of non-linear partial differential equations governing the time-dependent flow of a viscous incompressible fluid in a channel is managed by means of a mixed spectral-finite difference method, in which different numerical techniques are applied: Fourier decomposition is used along the homogeneous directions, second-order Crank-Nicolson algorithms are employed for the spatial derivatives in the direction orthogonal to the solid walls and a fourth-order Runge-Kutta procedure is implemented for both the calculation of the convective term and the time advancement. The pressure problem, cast in the Helmholtz form, is solved with the use of a cyclic reduction procedure. No-slip boundary conditions are used at the walls of the channel and cyclic conditions are imposed at the other boundaries of the computing domain.Results are provided for different values of the Reynolds number at several time steps of integration and are compared with results obtained by other authors. © 1998 John Wiley & Sons, Ltd.
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  • 6
    Electronic Resource
    Electronic Resource
    An improved projection scheme applied to pseudospectral methods for the incompressible Navier-Stokes equations (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 501-521 
    Details
    ISSN: 0271-2091
    Keywords: projection scheme ; Navier-Stokes equations ; pseudospectral Chebyshev methods ; unsteady flows ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: An improved projection scheme is proposed and applied to pseudospectral collocation-Chebyshev approximation for the incompressible Navier-Stokes equations. It consists of introducing a correct predictor for the pressure, one which is consistent with a divergence-free velocity field at each time step. The main objective is to allow a time variation of the pressure gradient at boundaries. From different test problems, it is shown that this method, associated with a multistep second-order time scheme, provides a time accuracy of the same order as the temporal scheme used for the pressure, and also improves the prediction of the velocity slip. Moreover, it does not exhibit any numerical boundary layer mentioned as a drawback of fractional steps algorithm, and does not require the use of staggered grids for the velocity and the pressure. Its effectiveness is validated by comparison with a previous time-splitting algorithm proposed by Goda (K. Goda, J. Comput. Phys., 30, 76-95 (1979)) and implemented by Gresho (P. Gresho, Int. j. numer. methods fluids, 11, 587-620 (1990)) to finite element approximations. Steady and unsteady solutions for the regularized driven cavity and the rotating cavity submitted to throughflow are also used to assess the efficiency of this algorithm. © 1998 John Wiley & Sons, Ltd.
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  • 7
    Electronic Resource
    Electronic Resource
    Method of finite difference solutions to the transient bubbly air-water flows (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 26 (1998), S. 1155-1180 
    Details
    ISSN: 0271-2091
    Keywords: Navier-Stokes equations ; averaged volume transport equations ; void wave propagation speed ; interfacial effects ; two-phase flow ; finite difference method ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A one-dimensional, time-dependent, isothermal, incompressible, Newtonian fluid, two-phase volume averaging model was developed to study momentum interaction effects in vertical ducts with bubble flow regime. For the evaluation of averaged description, potential inviscid flow around bubbles was considered in order to get closure relationships. The linear dynamic analysis is based on the eigenvalue technique, determining the domain of the hyperbolic behavior and the void fraction wave velocity, which are compared with previous models and experimental data. The solution to the partial differential equations is based on the finite difference technique implicit scheme. These schemes serve to demonstrate the numerical solution procedure. The numerical results are compared with analytical solution and experimental data for void fraction wave propagation. The importance of the surface tension effect in the behavior of the phases in transient conditions is shown. © 1998 John Wiley & Sons, Ltd.
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  • 8
    Electronic Resource
    Electronic Resource
    Orthogonal grid generation for Navier-Stokes computations (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 215-224 
    Details
    ISSN: 0271-2091
    Keywords: orthogonal grids ; hyperbolic grid generation ; Navier-Stokes equations ; higher-order methods ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Body conforming orthogonal grids were generated using a fast hyperbolic method for aerofoils, and were used to solve the Navier-Stokes equation in the generalized orthogonal system for the first time for time accurate simulation of incompressible flow. For grid generation, the Beltrami equation and the definition equation for the orthogonality are solved using a finite difference method. The grids generated around aerofoils by this method have better orthogonality than the results published by earlier investigators. The Navier-Stokes equation at Reynolds numbers of 3000 and 35 000 for NACA 0012 and NACA 0015 respectively, have been solved as an application. The obtained results match quite well with the corresponding experimental results. © 1998 John Wiley & Sons, Ltd.
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  • 9
    Electronic Resource
    Electronic Resource
    Modelling of Non-coalescing Liquid Drops in the Presence of Thermocapillary Convection (1997)
    Springer
    Meccanica 32 (1997), S. 115-133 
    Details
    ISSN: 1572-9648
    Keywords: Free boundary problems ; Navier-Stokes equations ; Numerical simulation ; Two-phase convection ; Fluid dynamics.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract A fluid-dynamic model of two non-coalescing liquid drops of the same liquid, pressed against one another in the presence of thermocapillary convection, is proposed to correlate experimental results on the deformation of the drop surfaces, on the pressure distribution and on the thickness of the air film between the drops. The two-point boundary value problem for the Gauss–Laplace hydrostaticequation, subjected to the constant volume constraint, is solved by a fourth order Runge Kutta method to evaluatethe shapes of the drops for different values of the applied pressure jump across the surface exposed to a constant ambient pressure. The flow fields in the liquid drops and in the air layer are obtained by numerical solutions of the dynamic problem. Thenumerical results qualitatively agree with the experimental ones, explain why an air film could be created between the two drops and show that film thicknesses of some microns exist with excess pressures of the same order of magnitude of the pressure needed to deform the drops.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004287930384
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  • 10
    Electronic Resource
    Electronic Resource
    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
    Keywords: optimal control ; Navier-Stokes equations ; finite element method ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: 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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  • 11
    Electronic Resource
    Electronic Resource
    A FINITE ELEMENT MODEL FOR THE SIMULATION OF DENSE GAS DISPERSION IN THE ATMOSPHERE (1997)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 24 (1997), S. 291-317 
    Details
    ISSN: 0271-2091
    Keywords: Navier-Stokes equations ; dense gas dispersion ; density stratification ; anisotropic turbulent viscosity ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A state-of-the-art model is developed for the simulation of the dispersion of hazardous toxic or flammable gases heavier than air in the atmosphere. The model depends on solving the Reynolds-averaged Navier-Stokes equations in addition to the energy equation and a species concentration equation for the contaminant gas. Turbulence closure is achieved by using a buoyancy-extended version of the standard k- ∊ two-equation model. The buoyancy extension is introduced to account for the anisotropic turbulent viscosity resulting from the strong stratification introduced by the dense gas clouds. The spatial discretization is achieved via the Galerkin finite element method, while the solution is advanced in time using the forward Euler method. A special element layer is introduced in the near-ground region to bridge the gap between the solid wall and the main solution domain where the turbulence model can be applied. This special element layer eliminates the need to apply the wall function in the standard way where any oscillations in the pressure field could contaminate the velocity solution. The model was tested against the Burro-8 field trial and could predict the experiment satisfactorily to within the experimental uncertainties of the reported results. © by 1997 John Wiley & Sons, Ltd.
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  • 12
    Electronic Resource
    Electronic Resource
    Localization of Hopf bifurcations in fluid flow problems (1997)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 24 (1997), S. 1185-1210 
    Details
    ISSN: 0271-2091
    Keywords: Hopf bifurcation ; hydrodynamic stability ; Navier-Stokes equations ; eigenproblem ; direct simulation ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: This paper is concerned with the precise localization of Hopf bifurcations in various fluid flow problems. This is when a stationary solution loses stability and often becomes periodic in time. The difficulty is to determine the critical Reynolds number where a pair of eigenvalues of the Jacobian matrix crosses the imaginary axis. This requires the computation of the eigenvalues (or at least some of them) of a large matrix resulting from the discretization of the incompressible Navier-Stokes equations. We thus present a method allowing the computation of the smallest eigenvalues, from which we can extract the one with the smallest real part. From the imaginary part of the critical eigenvalue we can deduce the fundamental frequency of the time-periodic solution. These computations are then confirmed by direct simulation of the time-dependent Navier-Stokes equations. © 1997 John Wiley & Sons, Ltd.
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  • 13
    Electronic Resource
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    A boundary element method for steady viscous fluid flow using penalty function formulation (1997)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 25 (1997), S. 907-929 
    Details
    ISSN: 0271-2091
    Keywords: Navier-Stokes equations ; penalty function formulation ; boundary element method ; driven cavity flow ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A new boundary element method is presented for steady incompressible flow at moderate and high Reynolds numbers. The whole domain is discretized into a number of eight-noded cells, for each of which the governing boundary integral equation is formulated exclusively in terms of velocities and tractions. The kernels used in this paper are the fundamental solutions of the linearized Navier-Stokes equations with artificial compressibility. Significant attention is given to the numerical evaluation of the integrals over quadratic boundary elements as well as over quadratic quadrilateral volume cells in order to ensure a high accuracy level at high Reynolds numbers. As an illustration, square driven cavity flows are considered for Reynolds numbers up to 1000. Numerical results demonstrate both the high convergence rate, even when using simple (direct) iterations, and the appropriate level of accuracy of the proposed method. Although the method yields a high level of accuracy in the primary vortex region, the secondary vortices are not properly resolved. © 1997 John Wiley & Sons, Ltd.
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  • 14
    Electronic Resource
    Electronic Resource
    Fourth-order method for solving the Navier-Stokes equations in a constricting channel (1997)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 25 (1997), S. 1119-1135 
    Details
    ISSN: 0271-2091
    Keywords: fourth-order methods ; Navier-Stokes equations ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A fourth-order numerical method for solving the Navier-Stokes equations in streamfunction/vorticity formulation on a two-dimensional non-uniform orthogonal grid has been tested on the fluid flow in a constricted symmetric channel. The family of grids is generated algebraically using a conformal transformation followed by a non-uniform stretching of the mesh cells in which the shape of the channel boundary can vary from a smooth constriction to one which one possesses a very sharp but smooth corner. The generality of the grids allows the use of long channels upstream and downstream as well as having a refined grid near the sharp corner. Derivatives in the governing equations are replaced by fourth-order central differences and the vorticity is eliminated, either before or after the discretization, to form a wide difference molecule for the streamfunction. Extra boundary conditions, necessary for wide-molecule methods, are supplied by a procedure proposed by Henshaw et al. The ensuing set of non-linear equations is solved using Newton iteration. Results have been obtained for Reynolds numbers up to 250 for three constrictions, the first being smooth, the second having a moderately sharp corner and the third with a very sharp corner. Estimates of the error incurred show that the results are very accurate and substantially better than those of the corresponding second-order method. The observed order of the method has been shown to be close to four, demonstrating that the method is genuinely fourth-order. © 1997 John Wiley & Sons, Ltd.
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  • 15
    Electronic Resource
    Electronic Resource
    Fourier nonlinear Galerkin approximation for the two dimensional Navier-Stokes equations (1996)
    Springer
    Applied mathematics and mechanics 17 (1996), S. 879-887 
    Details
    ISSN: 1573-2754
    Keywords: Navier-Stokes equations ; nonlinear Galerkin methods ; Fourier methods
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract In this paper, for viscous incompressible Navier-Stokes equations with periodic boundary conditions, we prove the existence and uniqueness of the solution corresponding to its Fourier nonlinear Galerkin approximation. At the same time, we give its error estimates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00127187
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  • 16
    Electronic Resource
    Electronic Resource
    VALIDATION OF A NAVIER-STOKES SOLUTION ALGORITHM WITH EXPERIMENTAL VALUES IN A SUPERSONIC WAKE (1996)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 22 (1996), S. 137-148 
    Details
    ISSN: 0271-2091
    Keywords: validation ; Navier-Stokes equations ; Taylor-Galerkin approach ; finite elements ; laser Doppler anemometry ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: This paper describes the validation of a finite element solver for an axisymmetric compressible flow with experimental values, especially velocities measured with a laser Doppler anemometer in the near wake of a circular cylinder. The equations under consideration are the Navier-Stokes equations with turbulent terms. A time-stepping scheme for the solution of these equations can be produced by applying a forward-time Taylor series expansion including time derivatives of second order. These time derivatives are evaluated in terms of space derivatives in the Lax-Wendroff fashion. The method is based on unstructured triangular grids with a high resolution in the radial direction. In order to predict the measured turbulent intensites more exactly, a modification of the Baldwin-Lomax model is necessary.
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  • 17
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    A COMPARISON OF COUPLED AND SEGREGATED ITERATIVE SOLUTION TECHNIQUE FOR INCOMPRESSIBLE SWIRLING FLOW (1996)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 22 (1996), S. 353-373 
    Details
    ISSN: 0271-2091
    Keywords: Navier-Stokes equations ; finite differences ; unsymmetric linear systems ; Krylov subspace methods ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: In many popular solution algorithms for the incompressible Navier-Stoke equations the coupling between the momentum equations is neglected when the linearized momentum equations are solved to update the velocities. This is known to lead to poor convergence in highly swirling flows where coupling between the radial and tangential momentum equations is strong. Here we propose a coupled solution algorithm in which the linearized momentum and continuity equations are solved simultaneously. Comparisons between the new method and the well-known SIMPLEC method are presented.
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  • 18
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    ARTIFICIAL BOUNDARIES AND FLUX AND PRESSURE CONDITIONS FOR THE INCOMPRESSIBLE NAVIER-STOKES EQUATIONS (1996)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 22 (1996), S. 325-352 
    Details
    ISSN: 0271-2091
    Keywords: Navier-Stokes equations ; artificial boundary conditions ; flux and pressure conditions ; finite elements ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Fluid dynamical problems are often conceptualized in unbounded domains. However, most methods of numerical simulation then require a truncation of the conceptual domain to a bounded one, thereby introducing artificial boundaries. Here we analyse our experience in choosing artificial boundary conditions implicitly through the choice of variational formulations. We deal particularly with a class of problems that involve the prescription of pressure drops and/or net flux conditions.
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  • 19
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    A NON-LINEAR ADAPTED TRI-TREE MULTIGRID SOLVER FOR FINITE ELEMENT FORMULATION OF THE NAVIER-STOKES EQUATIONS (1996)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 22 (1996), S. 1041-1059 
    Details
    ISSN: 0271-2091
    Keywords: grid generation ; tri-tree ; unstructured grid ; multigrid ; finite element ; mixed formulation ; analytic integration ; adaptive solver ; Navier-Stokes equations ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: An iterative adaptive equation multigrid solver for solving the implicit Navier-Stokes equations simultaneously with tri-tree grid generation is developed. The tri-tree grid generator builds a hierarchical grid structur e which is mapped to a finite element grid at each hierarchical level. For each hierarchical finite element multigrid the Navier-Stokes equations are solved approximately. The solution at each level is projected onto the next finer grid and used as a start vector for the iterative equation solver at the finer level. When the finest grid is reached, the equation solver is iterated until a tolerated solution is reached. The iterative multigrid equation solver is preconditioned by incomplete LU factorization with coupled node fill-in.The non-linear Navier-Stokes equations are linearized by both the Newton method and grid adaption. The efficiency and behaviour of the present adaptive method are compared with those of the previously developed iterative equation solver which is preconditioned by incomplete LU factorization with coupled node fill-in.
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  • 20
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    NUMERICAL SIMULATION OF UNSTEADY VISCOUS FLOWS USING AN IMPLICIT PROJECTION METHOD (1996)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 23 (1996), S. 897-921 
    Details
    ISSN: 0271-2091
    Keywords: Navier-Stokes equations ; unsteady flow ; laminar flow ; turbulent flow ; projection method ; approximate factorization technique ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: In this paper an implicit projection method for the solution of the two-dimensional, time-dependent, incompressible Navier- Stokes equations is presented. The basic principle of this method is that the evaluation of the time evolution is split into intermediate steps. The computational method is based on the approximate factorization technique. The coupled approach is used to link the equations of motion and the turbulence model equations. The standard k-∊ turbulence model is used. The current methodology, which has been tested extensively for steady problems, is now applied for the numerical simulation of unsteady flows. Several cases were tested, such as plane or axisymmetric channels, a backward-facing step, a square cavity and an axisymmetric stenosis.
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  • 21
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    ONSET OF ASYMMETRY: FLOW PAST CIRCULAR AND ELLIPTIC CYLINDERS (1996)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 23 (1996), S. 1327-1345 
    Details
    ISSN: 0271-2091
    Keywords: unsteady flows ; incompressible viscous flows ; onset of asymmetry ; Navier-Stokes equations ; finite difference method ; bluff bodies ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A computational study of the development of two- dimensional unsteady viscous incompressible flow around a circular cylinder and elliptic cylinders is undertaken at a Reynolds number of 10,000. A higher- order upwind scheme is used to solve the Navier-Stokes equations by the finite difference method in order to study the onset of computed asymmetry around bluff bodies. For the computed cases the ellipses develop asymmetry much earlier than the circular cylinder. The receptivity of the computed flows in the presence of discrete roughness and surface vibration is studied. Finally, the role of discrete roughness in triggering asymmetry for flow past a circular cylinder is studied and compared with flow visualization experiments at Re=10,000
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    ADAPTIVE SOLUTIONS FOR UNSTEADY LAMINAR FLOWS ON UNSTRUCTURED GRIDS (1996)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 22 (1996), S. 85-101 
    Details
    ISSN: 0271-2091
    Keywords: Navier-Stokes equations ; time-dependent, separated flow ; unstructured, adaptive, dynamic grids ; local time-stepping scheme ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: An adaptive finite volume method for the simulation of time-dependent, viscous flow is presented. The Navier-Stokes equations are discretized by central schemes on unstructured grids and solved by an explicit Runge-Kutta method. The essential topics of the present study are a new concept for a local Runge-Kutta time-stepping scheme, called multisequence Runge-Kutta, which reduces the severe stability restriction in unsteady problems, a common grid generation and adaptation procedure and the application of dynamic grids for capturing moving flow structures. Results are presented for laminar, separated flow around an aerofoil with a flap.
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    THE NO-SLIP BOUNDARY CONDITION IN FINITE DIFFERENCE APPROXIMATIONS (1996)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 22 (1996), S. 713-729 
    Details
    ISSN: 0271-2091
    Keywords: finite difference ; boundary conditions ; Navier-Stokes equations ; convergence analysis ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A finite difference method for the Navier-Stokes equations in vorticity -streamfunction formulation is proposed to resolve the difficulty of the lack of a vorticity boundary condition at a no-slip boundary. It is particularly suitable for flows in regions with complicated geometries. Convergence with second-order accuracy in vorticity and velocity is established. In numerical experiments the convergence rates agree with theoretical predictions. Test results for the two-dimensional driven cavity problem and for the flow in expansion and contraction channels are given.
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    NUMERICAL SIMULATION OF THE MECHANISMS GOVERNING THE ONSET OF THE BÉNARD-VON KÁRMÁN INSTABILITY (1996)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 23 (1996), S. 753-785 
    Details
    ISSN: 0271-2091
    Keywords: numerical simulation ; spectral time discretization ; Navier-Stokes equations ; laminar flow ; shear flow ; unsteady flow ; periodic flow ; instability ; Hopf bifurcation ; non-linearity ; non-linear theory ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The onset of the Bénard-von Kármán instability consisting of the selective amplification of the linear unstable mode and yielding finally the well-known saturated state has been described many times on the basis of both numerical and experimental results in various configurations. However, neither the role of the harmonics and their coupling has been examined quantitatively, nor has the spatial structure of the instability been studied in detail. A recently developed numerical method of simulation of quasi-periodic flows makes it possible to integrate the investigation of linear and non-linear characteristics within a single numerical method. The simulation of the 2D afterbody wake presented in this paper allows us to follow the amplification of the instability over many orders of magnitude. It is shown that at all stages of its development the instability is characterized by a series of harmonics, each of them amplified with a multiple of the fundamental amplification rate during the linear regime. The amplification of harmonics results from an energy transfer from the mean flow to harmonics of increasingly higher order. Ultimately the energy losses compensate this transfer and an equilibrium, commonly called saturation of the instability, is reached. It is shown that the coupling between the fundamental harmonic and the mean flow is mainly responsible for the saturation. The convergence rate of the development of the instability into harmonics is investigated. A full description of the spatial structure of all significant harmonics both in the linear regime and at saturation is obtained. The results show that time and space characteristics of the instability can be investigated simultaneously in an efficient way. Such an approach might be particularly important in 3D wakes where the geometry has a strong influence on the behaviour of unstable flows.
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    A NUMERICAL PROCEDURE FOR PREDICTING MULTIPLE SOLUTIONS OF A SPHERICAL TAYLOR-COUETTE FLOW (1996)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 22 (1996), S. 1135-1147 
    Details
    ISSN: 0271-2091
    Keywords: Navier-Stokes equations ; Taylor-Couette flow ; multiple solutions ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A new numerical procedure for predicting multiple solutions of Taylor vortices in a spherical gap is presented. The steady incompressible Navier-Stokes equations in primitive variables are solved by a finite- difference method using a matrix preconditioning technique. Routes leading to multiple flow states are designed heuristically by imposing symmetric properties. Both symmetric and asymmetric solutions can be predicted in a deterministic way. The current procedure gives very fast convergence rate to the desired flow modes. This procedure provides an alternative way of finding all possible stable steady axisymmetric flow modes.
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    AN APPROXIMATE PROJECTION SCHEME FOR INCOMPRESSIBLE FLOW USING SPECTRAL ELEMENTS (1996)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 22 (1996), S. 673-688 
    Details
    ISSN: 0271-2091
    Keywords: Navier-Stokes equations ; projection methods ; operator splitting ; spectral element methods ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: An approximate projection scheme based on the pressure correction method is proposed to solve the Navier-Stokes equations for incompressible flow. The algorithm is applied to the continuous equations; however, there are no problems concerning the choice of boundary conditions of the pressure step. The resulting velocity and pressure are consistent with the original system. For the spatial discretization a high-order spectral element method is chosen. The high-order accuracy allows the use of a diagonal mass matrix, resulting in a very efficient algorithm. The properties of the scheme are extensively tested by means of an analytical test example. The scheme is further validated by simulating the laminar flow over a backward-facing step.
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    AN ARTIFICIAL BOUNDARY CONDITION FOR TWO-DIMENSIONAL INCOMPRESSIBLE VISCOUS FLOWS USING THE METHOD OF LINES (1996)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 22 (1996), S. 483-493 
    Details
    ISSN: 0271-2091
    Keywords: Navier-Stokes equations ; Oseen equations ; method of lines ; artificial boundary condition ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: We design an artificial boundary condition for the steady incompressible Navier-Stokes equations in streamfunction-vorticity formulation in a flat channel with slip boundary conditions on the wall. The new boundary condition is derived from the Oseen equations and the method of lines. A numerical experiment for the non-linear Navier-Stokes equations is presented. The artificial boundary condition is compared with Dirichlet and Neumann boundary conditions for the flow past a rectangular cylinder in a flat channel. The numerical results show that our boundary condition is more accurate.
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    Interactions of three-dimensional vicous axisymmetric vortex rings with a free surface (1995)
    Springer
    Acta mechanica Sinica 11 (1995), S. 229-238 
    Details
    ISSN: 1614-3116
    Keywords: vortex ring ; free surface ; Navier-Stokes equations ; the method of VOF
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The unsteady nonlinear interaction of three-dimensional vortices with a free surface is a great challenge in fluid mechanics, which has deep theoretical significance and important practical background. Applying the three-dimensional VOF method, the interactions of three-dimensional axisymmetric vortex rings with a free surface in an incompressible viscous fluid are numerically simulated. The influence of the Froude number and the surface tension are studied and the evolution of the vorticity, the trajectories of the vortex rings and the baroclinic vorticity on the surface are obtained. The results agreed well with the experiments reported in the literature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02487726
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    Navier-Stokes analysis of a circulation control airfoil (1995)
    Springer
    Acta mechanica Sinica 11 (1995), S. 137-143 
    Details
    ISSN: 1614-3116
    Keywords: circulation control airfoil ; Navier-Stokes equations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The two-dimensional, compressible, mass-averaged Navier-Stokes equations are used to investigate flows about a typical circulation control airfoil. The governing equations are solved using the implicit approximate-factorization algorithm of Beam-Warming with a modified algebraic eddy viscosity model. Results are compared with experimental data, and excellent agreement is obtained. The effects of different jet momentum coefficients and angles of attack on the flow are studied. The mechanism of genenating large lift by circulation control is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02487621
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    The eccentric effect of a coaxial viscometer (1995)
    Springer
    Applied mathematics and mechanics 16 (1995), S. 359-367 
    Details
    ISSN: 1573-2754
    Keywords: coaxial viscometer ; the measurements of the viscosity ; the eccentric effect ; Navier-Stokes equations ; the perturbation technique
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract This paper studies the effect of the eccentricity between the inner bob and the outer cup in a coaxial viscometer on the measurements of the viscosity, by using a perturbation scheme. Our numerical examples demonstrate that the error incurred by the eccentricity would become larger as the characteristic Reynolds number decreases or as the gap width between the bob and the cup gets narrower. However, such errors may not be significant if the eccentric distance is not larger than 1/10 of the gap width for the usual working range of a coaxial viscometer.
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    URL: http://dx.doi.org/10.1007/BF02456949
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    Compatibility of poly(ethylene 2,6-naphthalate) and poly(butylene 2,6-naphthalate) blends (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 1807-1810 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Blends prepared from poly(ethylene 2,6-naphthalate) (PEN) and poly(butylene 2,6-naphthalate) (PBN) show only partial miscibility judged from their glass transition temperatures. Two distinct mechanical behaviors are observed: brittle for the blends 〈 20 wt% of PBN, while ductile 〉 20 wt% of PBN. The experimental modulus and strength values of the blends are within the predicted values according to Kleiner and Paul models, respectively. This means that PEN/PBN blends are somewhat compatible based on their tensile properties. Especially for 20 wt% of PBN blend, the high modulus and strength are observed. The viscosity of the blend is high, which may imply a somewhat entangled morphology in the amorphous state.
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    Masthead (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995) 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760352301
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    Effects of mixing porcedures on properties of compatibilized polypropylene/nylon 6 blends (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 1821-1833 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The paper consides the effects of compatibilization with maleic anhydride grafted polypropylene (PP-g-MAH) on the propertie of immiscible blends of polypropylene (PP) and nylon 6 (N6). We prepared the blends by three different mixing processes; single-step blending, two-step blending with reactive premixing, and two-step blending with nonreactive premixing, to determine the effective mixiing process for fine morphological structure thermal stability, and mechanical properties. Dynamic melt reheological properties were measured to examine the modification of elastic properties by the compatibilizer. In addtion, thermal analysis was also carried out to detect the change in crystallization and thereby to probe the degree of compatibilizaton. The results show that compatibilized blends prepared by teh single-step process exhibit improved phase morphology, thermal stability, and mechanical properties for dried conditions, compared with other blend types. Finally, the water absorption test indicates that the added compatibilizer yields enhanced water resistance in spite of the strong intrinsic hydrophilicity of N6. In particular, two-step blending with reactive premixing is most effective in improving water resistance and reducing degradation of mechanical properties after moisture absorption.
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    A hybrid numerical technique to model 3-D flow fields in resin transfer molding processes (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 1834-1851 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A hybrid two-/three-dimensional solution technique is presentedto model 3-D flow fields in resin transfer moeling using Darcy's low. The 3-D flow field is only solved for regions where all three velocity components are significant, thus largely reducing the number of unknowns. Elsewhere, the commonly used 2-D approximation for flow in thin gaps between plates is employe.d The method is applied to regions where the flow splits, such as T-joints. Because of the uncertainties associated with an accurate determination of the permeability in these regions, a simplified decompled procedure is procesed, which reduces the computational complexity. In this procedure, the flow front is advanced using the 2-D formulation. The 2-D formulation also provides the boundary conditions for the subsequent computation of the 3-D flow field without feedback of flow field information to the 2-d model. The governing equations are solved using boundary fitted coordinate systems (BFCS) together with the finite difference method (FDM). Numerical as well as algebraic grid generation and domain decomposition are employe dto generate grids that always concide with the continuously deforming and enlarging flow domain. Results that include the trackingof numerical tracer particles to visualize the three-dimensionality of the flow field are presented for isothermal flow of a Newtonian fluid through a T-joint. This detailed flow field description is expected to form the basis for a rather accurate simulation of quantitities that largely depend on the fluid particle pathlines, such as the degree of cure. The method is also extendable to shear-thinning fluids as well as to 3-D flow in the vicinity of the flow front.
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    Theory of competition between breakup and coalescence of droplets in flowing polymer blends (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 1872-1877 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The Smoluchowski equation for the breakup and coalescence of dispersed droplets has been solved for flowing polymer blends. A scaling form for the distribution of droplet sized derived and published for a system of clusters with fragmentation and coagualation was used in our dervation. Equations are developed here for the average droplet size and for the characteristic time of transition to steady state flow of blends with a high content of the dispersed phase. Expressions reasonably describing the average size of droplets for all concentrations were obtained by a theory modification. Measured dependences of droplet size on the blend composition can be matched only if simultaneous collisions of three and more droplets are considered. The results of the theory indicate that the mechanism of droplet breakup (formation of pieces with the same or different volumes) has only a small effect on their average size in concentrated systems. The dependence of droplet size on the shear rate in flow is determined by properties of the blend components, and is generally nonmonotonic.
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    Performance of reprocessed multilayer LDPE/nylon-6 film (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 1878-1883 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Multilayer LDPE/nylon-6 films with an overall content of 71 wt% LDPE, 24 wt% nylon-6, and 5 wt% PE-based tie-layer adhesive were reprocessed under both minimal and extensive mixing conditions. Thermal and mechanical properties, oxygen and water vapor permeability, and morphology of the reprocessed samples were determined. The modulus and yield stress of the reprocessed films fell between those of the pure homopolymers, whereas percent elongation at break and energy-to-break for all reprocessed films were less than those of the homopolymers. In minimally reprocessed film, layering of LDPE (low-density polyethylene) and nylon-6 was retained, whereas in extensively mixed samples, nylon-6 domains were spherical and ranged from 0.2 to 7 μm. Minimally reprocessed film exhibited good O2 and H2O vapor barrier properties, whereas extensively-mixed samples had poor barrier properties. Properties of well-mixed blends prepared both with and without adhesive showed that 5 wt% adhesive did not compatibilize the LDPE and nylon-6 components.
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    Assessment of residual stresses during cure and cooling of epoxy resins (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 1895-1898 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A new stress monitoring technique, a stress-tracking device, is described here. It has been used to study some important properties of epoxy resin. Residual stresses, including a curing shrinkage stress and a cooling shrinkage stress, were measured automatically and continuously during curing and cooling. Simultaneously, information such as an apparent gelation time and glass transition temperature were obtained directly during the experiment. These epoxy resin properties were related to the extent of cure. Varying cure temperature produced changes of cure behavior, which resulted in different residual stresses.
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    Study of reaction injection molding of polyurethane microcellular foam (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 1899-1906 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Processing of microcellular foam was investigated for the feasibility of production of tough and lightweight polyurethanes. To increase the nucleation rate in a gas-supersaturated resin, ultrasonic excitation was applied to the mixture of polyol(polyether-based polyol) and isocyanate(diphenyl methane diisocyanate). A microcellular structure was produced by two sequential steps, i.e., supersaturationof the polyol resin with nitrogen gas at elevated pressure and ultrasonic bubble nucleation right after the impingement mixing of two components of the polyurethane system. Theoretical analyses based on nucleation theories were employed to predict the rate of nucleation in the gas-supersaturated polyurethane. The rate of nucleatio in the resin was predicted by classical nucleation and cluster theories. In the experimental investigation, ultrasonic excitation was applied to increase the nucleation rate in the resin that had been saturated by nitrogen at a saturation pressure 〈 2.0 MPa.
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    Modeling the mechanical properties in polypropylene/polyamide-6 blends with core shell morphology (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 1917-1922 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Polypropylene/Polyamide-6 (PP.PA) blends containing maleic anhydride grafted elastomers were prepared by reactive blending. Three different types of core shell morphologies were obtained and characterized by transmission electron microscopy (TEM). The midulus of these elastomer midified PP/PA (70/30) blends with core shell type morphology is compared to predictions derived from the Kerner model. The multiphase morphology of these blends could be modeled by sequential application of the Kerner equation to two-phase subinclusions. Using morphological data ontained by TEM, good agreement between experimental and calculated values was ontained. The results are used to tailor PP/Pa-6 blends combining stiffness and toughness.
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    URL: http://dx.doi.org/10.1002/pen.760352402
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    Creep analysis of thermiplastics using stress relaxation data (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 1931-1937 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: One of the major factors limiting the use of thermoplastics in engineeing applications is the inadequacy of existing design data. Much of the data do not span appropriate ranges of stress, strain, time, or temperature. This study addresses the need to develop an accelerated method for generating long-time design data to support the innovative use of engineering thermoplastics. In particular, stress relaxation tests (SRT) were performed on polycarbonate (PC) and midified poly(phenylene oxide)(PPO), and used to generate time-dependent design data through the short-time measurement of the material's current state without dependence on elastic modulus. The test results and analyses reported here indicate the SRT method to be an efficeint means of generating accurate and repeatable creep and secant modulus data which may be directly used in design. Therefore, SRT shows great potential both as a design parameter development tool, and as a quality control instrumetn for assessing batch-to-batch variability.
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    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
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: 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.
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    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
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: 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.
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    Masthead (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995) 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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    URL: http://dx.doi.org/10.1002/pen.760350101
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    Preamble (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 1-1 
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    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760350102
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    History of commercial polymer alloys and blends (from a perspective of the patent literature)Based on: encyclopaedic dictionary of commercial polymer blends, L. A. Utracki, ed., ChemTech Pub., Toronto, Canada (1994). (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 2-17 
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    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Polymer blends are defined as mixtures of at least two polymeric species. Thus, the first patent polymer blend was a mixture of natural rubber, NR, with gutta percha patented by Alexander Parkes, an artist of Birmingham, in 1846. The first man-made polymer, nitrocellulose, NC was prepared by Braconnot in 1833. The resin was commercialized in 1868, but its first blends (with NR) were patented three years earlier. The first patent on blends of two synthetic polymers was granted in 1928 for poly(vinylchloride)/poly(vinylacetate), PVC/PVAc (latex blending). During the intervening 65 years, the polymer blend patent literature grew at an exponential rate; since 1983 the annual output has doubled, to exceed 3000 patents/year in 1993.
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    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 
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    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: 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.
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    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 
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    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: 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.
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    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 
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    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: This communication is a theoretical re-examination of the model proposed by Choe and Lee for the nonisothermal crystallization kinetics of semicrystalline polymers.
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    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 
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    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: 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.
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    Morphology and mechanical properties of virgin and recycled polyethylene/polyvinyl chloride blends (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 64-71 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: In this study, blends of virgin and recycled polyethylene (PE) and poly(vinyl chloride) (PVC), with a methylmethacrylate-ethylacrylate copolymer as a processing aid, were prepared in the molten state. Different additives such as ethylenevinylacetate copolymers, ethylene-methacrylic acid ionomer, and two peroxides (dibenzoyl and dicumyl), in the presence of a coupling agent, were used to compatibilize the blend or possibly induce graft structures. The blends' morphologies, tensile properties, and impact properties were studied. For blends with low copolymer concentration (below 3 wt%) the mechanical test data indicated a good performance. In the case of blends with ethylene methacrylic acid ionomer, improvements in the mechanical properties were obtained also at higher additive concentrations. Of the two peroxides, better results were obtained using the dibenzoyl one. The morphological studies indicated that the blends that showed good mechanical properties were better dispersed and had improved interphase adhesion.
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    Performance blends based on recycled polymers (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 72-78 
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    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The recent growth in the post-consumer recycling of plastics presents an opportunity for developing new, value-added blend products from the recycled polymers. However, in order to develop blends with useful performance characteristics, suitable techniques of compatibilization and impact modification must be employed. In this study, reactive toughening and compatibilization techniques have been found to be particularly useful in achieving high thermal embrittlement resistance in the blends of recycled poly(ethylene terephthalate) containing functionalized ethylene copolymers and polycarbonate. Reactive compatibilization of recycled polyolefin blends with poly(ethylene terephthalate) and polyamide has also been investigated.
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    Masthead (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995) 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760350201
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    Development of polymer blend morphology during compounding in a twin-screw extruder. Part IV: A new computational model with coalescence (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 115-127 
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    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: In Part II of this series of publications, the first generation model of morphology evolution during polymer blending in a twin-screw extruder was presented. The model was based on a simplified flow analysis, and an assumption that dispersion occurs via drop fibrillation followed by disintegration. In the present Part IV, several modifications of the model are discussed. (i) The flow analysis was refined by computing the pressure profiles. (ii) The flow paths and strain history of the dispersed droplets within the screw elements are computed directly, which makes it possible to determine the drop susceptibility to deformation and break. (iii) Besides the fibrillation mechanism, a drop-splitting mechanism for low supercritical capillary numbers is incorporated. (iv) The choice of breakup mechanism is based on micro-rheological criteria. (v) The coalescence effects are taken into account. (vi) The theoretical model is self-consistent, without adjustable parameters. The validity of theoretical assumptions was evaluated by comparing the model predictions with the experimental droplet diameters at different positions in the twin-screw extruder.
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    Water sorption in a novel liquid crystalline epoxy resin (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 137-143 
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    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Water sorption tests have been carried out for a novel epoxy resin having liquid crystalline character. The sorption isotherm. Relative to the expoxy resin cured in the nematic phase, does not indicate any substantial difference from the resin cured in the isotropic state. This is an indication that, as far as this class of thermosets is considered, the liquid crystalline order does not affect mechanism and equilibrium values of water uptake.
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    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 
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    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: 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.
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    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
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: 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.
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    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 
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    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: 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.
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    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 
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    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: 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.
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    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 
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    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: 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.
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    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 
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    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: 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.
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    Review of stabilization of polyolefin insulated conductors. Part II: Characteristics of good stabilizers and methods of evaluation (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 218-221 
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    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: In a previous paper, the theory of polylefin stabilization and the major factors contributing to degradation were discussed. This paper reviews the methods of test employed to date, the characteristics of a good stabilization system, and the experimental work we propose to use to study the problem. The characteristics of a stabilizer which are reviewed are: color, melt temperature, solubility, resistance to extraction, migration, phase state, structural arrangement, energy considerations, and thermodynamic potential. The methods of test reviewed include: pedestal testing, oven aging, oxygen uptake, testing under stress, melt flow testing, thermal analysis by DSC, thermal analysis by TGA, color change, torque rheometry, and aged elongation. Our approach will be to quantify the effects of antioxidant, metal deactivator, and blowing agent on stability by doing differential scanning calorimetry (DSC); to study fracture surfaces with scanning electron microscopy (SEM) to study diffusion rate of the stabilizer and reaction rate of the degradation process; and to use dynamic mechanical analysis (DMA) to measure the change in loss modulus with aging.
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    Comparison of microwave and thermal cure of an epoxy/amine matrix (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 233-239 
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    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: An investigation was carried out into the effect ofa microwave cure on an epoxy prepolymer with a cycloaliphatic diamine mixture, as compared to a standard thermal cure. The microwave waveguide and process (propagation mode TE01) were adjusted to obtain large homogeneous samples. The extent of reaction, x, was measured during the microwave processing by size exclusion chromatography and differential scanning calorimetry. A good estimate of x was found using a modified DiBenedetto equation correlating x and the glass transition temperature Tg. The homogeneity of the samples was checked during the last steps of cure, showing the efficiency of the microwave processing and waveguide. The influence of the nature of the mold (metallic or dielectric) on the reaction kinetic was also investigated. Samples cured by both thermal and microwave processing were characterized by dynamic and static mechanical properties and then compared with those of fully crosslinked networks, i.e., postcured at a high temperature.
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    Effects of inserts on the injection molding process (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 247-251 
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    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Injection molds often contain blocks of dissimilar material for improved cooling; they may also contain blocks of movable metal as a means of ejecting large parts from the mold. In this case, the blocks of metal are made of the same material, but the resistance at the interface between them has a marked influence on the cooling in the local area near the interface. In many other cases, inserts may be required because of wear in a particular mold section, or because efficient mold design is needed to produce similar parts. Hence, any mathematical model for analysis of heat transfer in injection molds must be general enough to apply to interfaces with and without gaps (i.e., with and without resistance to the flow of heat at the interface) for similar, as well as dissimilar, materials. A new and accurate model for prediction of heat transfer in heterogeneous (zoned) molds is presented in this paper. Through the solution of real problems with this model, the effects of differing material properties and interfacial thermal resistance are studied and the results are reported. It is observed that inserts have both local and global effects on the injection molding process; the overall ejection time for a part may be shortened, and the surface appearance of a part may be improved by correct placement of inserts.
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    A simple approach to determining three-dimensional screw characteristics in the metering zone of extrusion processes using a total shape factor (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 274-283 
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    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: It is of great importance in designing extruders to predict the screw characteristics, that is, the throughput in terms of the screw speed and the pressure gradient along the down-channel direction. The screw characteristics depend on the extruder geometry, the operating conditions, and material properties of non-Newtonian fluids. This paper suggests a simple approach to determining the screw characteristics for a three-dimensional flow in a channel with a finite aspect ratio (ratio of a width to a depth, W/H) by introducing a Total Shape Factor (Ft) to correct a two-dimensional flow analysis for a channel with an infinite aspect ratio. In the present study, the Total Shape Factor (Ft) was defined as a ratio of a net flow rate obtained by the three-dimensional analysis to that by the two-dimensional analysis. In the proposed approach, the quantity, ∂Ft/∂(H/W), which turns out to be almost constant, offers important information for understanding the effects of the flights. Threfore, ∂Ft/∂(H/W) is extensively reported in this paper in terms of several dimensionless parameters. This simple approach with such a database will be very useful for extruder designers to predict screw characteristics.
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/pen.760350308
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    Masthead (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995) 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760350401
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    Modeling the dielectric response of unsaturated polyester resin during cure (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 284-288 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The dielectric relaxation of unsaturated polyester resin during cure was modeled using a modified Williams-Watts decay function. The dielectric response was studied using dielectric measurements coupled with two dynamic mechanical measurement methods. It was found that the variation of the relaxation time during cure is a WLF process using Tg (α) (α-conversion) as the varied temperature. It was shown that this process fits the Williams-Watts decay function Φ(t)=exp(-(t/τ)β) where τ-relaxation time and β-empirical parameter are time dependent. It was found that τ obeys a time dependent power law rule and β depends linearly on log(time). Using this modified decay function, it was shown that the experimental dielectric response measured during cure agrees well with the computed response. Relaxation times above and below the dielectric measurement system capability were computed thus, demonstrating the capability of yielding the entire relaxation times spectrum during cure, out of a single limited frequency dielectric measurement.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/pen.760350309
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    Cold-drawing (necking) behavior of polycarbonate as a double glass transition (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 304-309 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The thermomechanical behavior of poly(bisphenol A carbonate) (PC) undergoing cold-drawing (necking) over a large range of temperature and strain rate has been studied. The cold-drawing of PC has been described from a material particle perspective in terms of true stress and strain relationships. The isothermal draw stress is shown to be a material parameter, and the true stress-strain behavior of necked material above the true drawing stress follows conventional treatment by rubber elasticity. Cold-drawing is described as a double glass transition: first, a transition from an isotropic glass to an isotropic rubber at the yield point, then, on unloading after stretching of a rubbery mesophase, a transition from an oriented rubber to an oriented glass.
    Additional Material: 12 Ill.
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    URL: http://dx.doi.org/10.1002/pen.760350404
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    A state variable model for high strength polymers (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 310-316 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Displacement controlled experiments on nylon 66, poly(etherether ketone), and poly(ether imide) at room temperature suggest that nonlinear elastcity is not a good model for these polymers. Rather, qualitative evidence is presented that a state variable model shows promise. In this model, the rate of deformation is the sum of the elastic and the inelastic rates of deformation. The elastic rate of deformation is given by an objective formulation of Hooke's law, and the inelastic deformation is an increasing function of the overstress, the difference between the Cauchy stress and the equilibrium stress. The equilibrium stress is a state variable, and represents the stress that can be sustained at rest following deformation. Load controlled tests, intended to verify or falsify the model, show that the creep rate at the same stress level can be different on loading and unloading, and that the creep rate need not increase with an increase in creep stress level. These anomalous results can easily be explained by the introduction of the overstress concept, and by proper evolution of the equilibrium stress. They confirm the usefulness of the overstress concept for the modeling of these polymers.
    Additional Material: 11 Ill.
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    URL: http://dx.doi.org/10.1002/pen.760350405
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    A constitutive model for the nonlinear viscoelastic viscoplastic behavior of glassy polymers (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 331-344 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Two features of the glassy state of an amorphous polymer, which play a key role in determining its mechanical properties, are the distributed nature of the microstructural state and the thermally activated (temporal) evolution of this state. In this work, we have sought to capture these features in a mechanistically motivated constitutive model by considering a distribution in the activation energy barrier to deformation in a thermally activated model of the deformation process. We thus model what is traditionally termed the nonlinear viscoelastic behavior as an elastic-inelastic transition, where the energetically distributed nature of inelastic events and their evolution with straining is taken into account. The thermoreversible nature of inelastic deformation is modeled by invoking the notion of strain energy stored by localized inelastic shear transformations. The model results are compared to experimental data for constant true strain rate uniaxial compression tests (nonmonotonic) at different rates and temperatures; its predictive capabilities are further tested by comparison with compressive creep tests at different stress levels and temperatures.
    Additional Material: 19 Ill.
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    URL: http://dx.doi.org/10.1002/pen.760350407
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    Solidification of thermoviscoelastic melts. Part I: Formulation of model problem (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 351-364 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The solidification of a molten layer of amorphous thermoplastic between cooled parallel plates is used to model the mechanics of part shrinkage and warpage and the buildup of residual stresses in the injection molding process. Flow effects are neglected, and a thermorheologically simple thermoviscoelastic material model is assumed. The equilibrium thermomechanical properties of the material and the shift function can be temperature- and pressure-dependent. The model allows material to be added to fill the space created by the packing pressure applied during solidification; therefore, this model can be used to assess packing-pressure effects in injection molding. The model also accounts for freeze-off effects in which the cavity pressure is controlled by the solidification process and must therefore be determined as a part of the solution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760350409
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    Solidification of thermoviscoelastic melts. Part II: Effects of processing conditions on shrinkage and residual stresses (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 365-383 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The solidification of a molten layer of thermoplastic between cooled parallel plates is used to model the mechanics of part shrinkage and the buildup of residual stresses in the injection-molding process. Flow effects are neglected, and a thermorheologically simple thermoviscoelastic material model is assumed. The model allows material to be added to fill the space created by the pressure applied during solidification, so that this model can be used to assess packing-pressure effects in injection molding. Parametric results are presented on the effects of the mold and melt temperatures, the part thickness, and the packing pressure - the pressure applied during solidification to counteract the effects of volumetric shrinkage of the thermoplastic - on the in-plane and through-thickness shrinkages, and on residual stresses in plaque-like geometries. The packing pressure is shown to have a significant effect on part shrinkage, but a smaller effect on residual stresses. Packing pressure applied later in the solidification cycle has a larger effect. Mold and melt temperatures are shown to have a much smaller effect. The processing parameters appear to affect the through-thickness shrinkage more than the in-plane shrinkage. While the results are presented in terms of normalized variables based on the properties of bisphenol-A polycarbonate, they can be interpreted for other amorphous thermoplastics such as modified polyphenylene oxide, polyetherimide, and acrylonitrile-butadiene-styrene.
    Additional Material: 35 Ill.
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    URL: http://dx.doi.org/10.1002/pen.760350410
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    Effect of NOx environments and stress on degradation of mechanical properties of Kevlar 49 and nylon 6 (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 411-418 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Mechanical and chemical mechanisms may act synergistically to degrade the mechanical properties of polymers. This synergism should be considered during design of components for sustained loads in hostile environments. If these polymers are to be used as load-bearing structural elements in automobile and industrial environments, they are likely to be simultaneously exposed to such environments and stress. These studies explore the deleterious effects of gaseous pollutants (e.g. NOx in air) and mechanical stress on polymers. This research included studies on nylon-6 and composites of nylon-6 yarns embedded in a bis-A-phenolic resin with an amine curing agent, as well as single fibers and yarns of poly(p-phenylene terephthalamide) (DuPont Kevlar 49) as bare fibers and also embedded in an epoxy matrix. The protective effect of embedding fibers in the epoxy matrix was demonstrated. NOx concentrations were varied between 0 and 1.5%. The sustained loads during exposure were in the range of 50 to 80 percent of the ultimate stress short term load carrying capability of the fibers. Exposure times varied from several minutes to months. Electron spin resonance spectroscopy (ESR) is used in these studies to explore the kinetics of bond rupture and how they relate to the environmental and stress loading histories in nylon. Kevlar 49 degradation studies were conducted by measuring times required for sample failure in NOx concentrations at various stress levels. Preliminary studies on the single fibers indicate a stress-NOx synergism over the range of stresses (48 and 77% of ultimate) and 0.1 and 1.5% gas concentrations. Yarn samples exhibited this synergism over a wide range of stresses (40 to 80% of ultimate). Bare yarn degradation was accelerated by NOx concentrations in air as low as 0.1%. We view these effects as having practical technological significance since these lower NOx concentrations approach the level of emissions from exhaust from older model automobiles.
    Additional Material: 11 Ill.
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    URL: http://dx.doi.org/10.1002/pen.760350506
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    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
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: 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.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/pen.760350507
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    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
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: 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.
    Additional Material: 11 Ill.
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    URL: http://dx.doi.org/10.1002/pen.760350603
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    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
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: 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.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/pen.760350602
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    Morphology and mechanical properties of liquid crystalline copolyester and polyester elastomer blends (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 528-537 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Blends of a polyester elastomer (PEL) having a hard segment of polyester (PBT) and soft segment of polyether (PTMG) 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 of the LCP/PEL blends was characterized under different processing conditions. To determine what conditions were necessary for the development of a fibrillar morphology of LCP, we have studied the effect of processing method (extrusion and injection molding), injection molding temperature (below and above the melting point of LCP), and gate position in the mold (direct gate and side gate). SEM studies revealed that some extensional flow was required for the fibrillar formation of LCP and the fibrillar structure of LCP was controlled by the processing method. The morphology of the blends was found to be affected by their compositions and processing conditions. SEM studies revealed that finely dispersed spherical domains of LCP were formed in the PEL matrix and the inclusions were deformed in fibrils from the spherical droplets with increasing LCP content and injection temperature. The mechanical properties of the LCP/PEL blends were also found to be affected by their compositions and processing conditions. The mechanical properties of LCP/PEL blends were very similar to those of polymeric composite. An attempt was made to correlate the structure of the blends from the scanning electron microscope with the measured mechanical properties. All of the aspects of the morphology were possible to explain in terms of the mechanical properties of the blends. A DSC study revealed that the crystallization of PEL was accelerated by the addition of LCP in the matrix and a partial compatibility between LCP and PEL was predicted. The rheological behavior of the LCP/PEL blends was found to be very different from that of the parent polymers, and significant viscosity reductions were observed in the blend consisting of only 5 wt% of LCP.
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    URL: http://dx.doi.org/10.1002/pen.760350611
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    Masthead (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995) 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760350701
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    Rubber modified epoxy resin. III: Reaction injection molding process (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 564-576 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Reaction injection molding of amine terminated butadiene acrylonitrile copolymer (ATBN) modified epoxy resin was investigated through computer simulation and experiment. The epoxy system composed of diglycidyl ether of bisphenol A (DGEBA) and triethylene tetramine (TETA) was employed since this system indicated a relatively high reaction rate. The coupled balance equations of momentum, chemical species, and energy within the disc-type mold cavity were solved using finite difference techniques. The predicted temperature and conversion profiles within the mold were compared to experimental results. The domain correlation length data calculated from the simulation model were compared with the results of SEM micrographs. A moldability analysis was performed to find the optimum molding conditions. The moldability window decreased as the mold thickness was increased.
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    The copolymerization of methacrylates in a counter-rotating twin-screw extruder (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 587-597 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The copolymerization of n-butylmethacrylate with 2-hydroxypropylmethacrylate was studied in a closely intermeshing counterrotating twin-screw extruder. The average molecular weight of the product can be increased by increasing the screw rotation rate or the die resistance or by decreasing the throughput or the barrel temperature. The conversion can be improved by decreasing the throughput, increasing the die resistance, and (within limits) increasing the barrel temperature, as well as through post-initiation. Compared with various classical polymerization processes, this situation requires that particular attention be paid to the occurrence of a gel effect, the existence of a thermodynamic ceiling temperature, and the reactivity ratio of the monomers used.
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    URL: http://dx.doi.org/10.1002/pen.760350705
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    Masthead (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995) 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760350801
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    Numerical simulation of fiber orientation in injection molding of short-fiber-reinforced thermoplastics (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 604-618 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The present study develops a numerical simulation program to predict the transient behavior of fiber orientations together with a mold filling simulation for short-fiber-reinforced thermoplastics in arbitrary three-dimensional injection mold cavities. The Dinh-Armstrong model including an additional stress due to the existence of fibers is incorporated into the Hele-Shaw equation to result in a new pressure equation governing the filling process. The mold filling simulation is performed by solving the new pressure equation and energy equation via a finite element/finite difference method as well as evolution equations for the second-order orientation tensor via the fourth-order Runge-Kutta method. The fiber orientation tensor is determined at every layer of each element across the thickness of molded parts with appropriate tensor transformations for arbitrary three-dimensional cavity space.
    Additional Material: 19 Ill.
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    URL: http://dx.doi.org/10.1002/pen.760350707
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    Chemically oxidized polypyrrole: Influence of the experimental conditions on its electrical conductivity and morphology (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 642-647 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The effect of synthesis conditions on the electrical conductivity and the morphology of a chemically oxidized polypyrrole was investigated. It was found that the electrical conductivity of polypyrrole was strongly dependent on the pyrrole/FeCl3 ratio, which controls the redox potential of the reaction medium. The reaction temperature and the reaction duration also influence the electrical conductivity of the polypyrrole. A considerable influence of the nature of the solvent used on the aggregation state of polypyrrole particles was demonstrated. Optimal experimental conditions are proposed.
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    URL: http://dx.doi.org/10.1002/pen.760350803
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    In situ composite: Phenolphthalein polyethersulfone - thermotropic liquid crystalline polymer blends (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 658-665 
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    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Phase behavior, thermal, rheological and mechanical properties plus morphology have been studied for a binary polymer blend. The blend is phenolphthalein polyethersulfone (PES-C) with a thermotropic liquid crystalline polymer (LCP), a condensation copolymer of p-hydroxybenzoic acid with ethylene terephthalate (PHB-PET). It was found that these two polymers from optically isotropic and homogeneous blends by means of a solvent casting method. The homogeneous blends undergo phase separation during heat treatment. However, melt mixed PES-C/PHB-PET blends were heterogeneous based upon DSC and DMA analysis and SEM examination. Addition of LCP in PES-C resulted in a marked reduction of melt viscosity and thus improved processability. Compared to pure PES-C, the charpy impact strength of the blend containing 2.5% LCP increased 2.5 times. Synergistic effects were also observed for the mechanical properties of blends containing 〈 10% LCP. Particulates, ribbons, and fibrils were found to be the typical morphological units of PHB-PET in the PES-C matrix, which depended upon the concentration of LCP and the processing conditions.
    Additional Material: 13 Ill.
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    URL: http://dx.doi.org/10.1002/pen.760350805
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    Time dependent response of polycarbonate and microcellular polycarbonate (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 673-679 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Microcellular polycarbonate is a novel cellular material with cells on the order of 10 μm in diameter and a cell density on the order of 109 cells per cm3. In this study the room temperature creep response of microcellular polycarbonate is experimentally determined and compared with the creep behavior of polycarbonate. The viscoelastic response of polycarbonate and microcellular polycarbonate is characterized using Schapery's theory of nonlinear viscoelasticity. Polycarbonate exhibited a nonlinear creep response at stress levels above 24.13 MPa, while the nonlinear behavior in microcellular polycarbonate was initiated at lower stress levels. Creep strains of microcellular polycarbonate contain a significantly higher viscoplastic component compared with the unfoamed material.
    Additional Material: 8 Ill.
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    URL: http://dx.doi.org/10.1002/pen.760350807
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    Diffusion of butanediol in poly(butylene terephthalate) (PBT) melt and analysis of pbt polymerization reactor with surface renewal (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 703-708 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A reactor with surface renewal, originally designed for poly(ethylene terephthalate) (PET) polymerization, was applied for poly(butylene terephthalate) (PBT) polymerization. A comprehensive model including side reactions was developed and compared with the experimental results. The diffusivity of butanediol (BD) in PBT melt was measured separately by desorption experiments (Db - 1.08 × 106 exp(-32600 / RT) (m2/min)). Optimum operating temperature for PBT polymerization was found to be around 250°C in order to avoid degradation.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/pen.760350810
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    Diffusion of low molecular weight substances into a laminar film. I: Rigorous solution of the diffusion equation in a composite film of multiple layers (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 709-721 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A rigorous solution of the diffusion of penetrant into a laminar film comprised of multilayers of m components is presented by an orthogonal-expansion method. As the simplest practical cases of m - 2 and m - 3, with stepwise distribution of both diffusion coefficients and solubility coefficients at the boundary between respective layers, the diffusion properties in the transient state are analyzed in detail. That is, changes in the penetrant concentration distribution within the laminar film and the total amount of penetrant sorbed within the film both with time after exposing the film to an atmosphere of fixed penetrant concentration are calculated for A-B as well as A-B-A type layer arrangements. The calculation is performed while keeping (L2/L1) at a constant value of 2.0 but varying the diffusion coefficient ratio of (D1/D2) from 102 to 10-2, and/or varying the solubility coefficient ratio of (S1/S2) from 1 to 10, where L1 and (L2 - L1) are the thickness D1 and D2 are the diffusion coefficients of penetrant, and S1 and S2 are the solubility coefficients in the A-component and B-component, respectively. The sorption curves deviate considerably from those of Fickian curves of homogeneous film with (D1/D2) - 1 in their respective ways. The results obtained here can be applied to the diffusion in a single component polymer film having a surface layer with different diffusion properties from that of the inner side of the film caused by differing distributions in molecular orientation or degrees of crystallinity.
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/pen.760350811
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    Finite element analysis modeling of powder injection molding filling process including yield stress and slip phenomena (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 741-753 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: For a science-based design of the Powder Injection Molding (PIM) process, it would be desirable for designers to have a numerical analysis tool capable of predicting the PIM filling process as a design aid. In this regard, the present study is aimed at developing a numerical analysis system to simulate the PIM filling process based on a new physical modeling taking into account rheological characteristics of powder/binder mixtures, namely the yield stress and the apparent slip phenomena. In particular, two different slip models were employed to represent the apparent slip phenomena. In accordance with the new physical modeling, the numerical simulation of the PIM filling process was accomplished by combining a finite element method and a finite difference method. It was found that the slip layer plays a role of not only a lubricating layer but also a thermal insulation layer. In this aspect, the slip layer model seems to represent the apparent slip phenemena better than the slip velocity model with regard to both the momentum and the thermal transport phenomena. The present paper presents the physical modeling, numerical scheme, and some numerical analysis results showing the effect of the yield stress and slip phenomena.
    Additional Material: 18 Ill.
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    URL: http://dx.doi.org/10.1002/pen.760350903
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    Extrusion die design for multiple stripes (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 759-767 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Two numerical approaches have been applied to examine the possibility of adding shims to conventional extrusion dies such as T-dies and coat-hanger dies to produce multiple stripes. The first numerical approach is based on a one or two-dimensional lubrication approximation and the second one is the three-dimensional finite element simulation. Both approaches are applicable, but the lubrication approximation is accurate and much simpler to use. The extruded stripes are assumed to obey a non-Newtonian power-law model. It has been found that the T-die with a shim can produce multiple stripes of acceptable uniformity, irrespective of the strip numbers and widths and the power-law index. The coat-hanger die with a shim did not deliver multiple stripes with good uniformity. Adding an outer manifold to the coat-hanger die can serve as an effective means to reduce flow nonuniformities.
    Additional Material: 12 Ill.
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    URL: http://dx.doi.org/10.1002/pen.760350905
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    A constitutive theory for polyolefins in large amplitude oscillatory shear (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 768-777 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A versatile transient network theory has been used as a framework for the interpretation of large amplitude oscillatory behavior of polyolefin melts in terms of their entanglement kinetics. The model reasonably describes all previously published measurements of the large amplitude oscillatory shear behavior on melts. Seven polyolefins are examined, three new materials and four previously studied. A qualitative difference in the nonlinear behavior in large amplitude oscillatory shear has been identified between the polyethylenes examined and the two other polyolefins, polystyrene and polyisobutylene.
    Additional Material: 18 Ill.
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    URL: http://dx.doi.org/10.1002/pen.760350906
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    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
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: 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.
    Additional Material: 18 Ill.
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    URL: http://dx.doi.org/10.1002/pen.760350808
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    Masthead (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995) 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760350901
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    Numerical simulation of the fountain flow problem for viscoelastic fluidsThe contents of this article were presented orally at the Polymer Processing Society 9th Annual Meeting, Manchester, U.K., 5-8 April 1993. (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 805-812 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Fountain flow for isothermal viscoelastic fluids is simulated by a numerical method based on a combination of a finite element method and a finite volume method. For the treatment of moving free surfaces, a fringe element generation method is used. Circulating flow and elongation in the transverse direction at the melt front are simulated well. Numerical results also suggest that circulation in fountain flow and viscoelastic retardation may give rise to symmetric V-shaped patterns of birefringence between the center-plane and wall. Such information on molecular orientation in fountain flow is important for physical properties of thick molded products.
    Additional Material: 13 Ill.
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    URL: http://dx.doi.org/10.1002/pen.760351003
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    Dilatometric study of low profile unsaturated polyester resins (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 823-836 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: An in-house-built and designed dilatometer was applied to the study of low profile unsaturated polyester resins. This article first describes the dilatometer used including its calibration then its application to low profile unsaturated polyester resins. Several series of dilatometry experiments were performed, to study the effect of low profile additive concentration and cure temperature on shrinkage control. Scanning electron micro-graphs of the samples were also prepared to show the correlation between shrinkage control and polymer morphology.
    Additional Material: 17 Ill.
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    URL: http://dx.doi.org/10.1002/pen.760351005
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    Analysis of volumetric changes of unsaturated polyester resins during curing (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 852-859 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Two models were proposed to predict the volume changes that occur during the cure of unsaturated polyester resin/styrene systems. These models are able to account for both thermal expansions/contractions and polymerization shrinkage during processing. One model, which is based on coversion, was developed by combining experimental results from differential scanning calorimetry and dilatometry. The second model is based on radical concentration, and was developed using results from electron spin resonance spectroscopy and dilatometry. Predictions obtained from both models were compared with experimental results and reasonable agreement was obtained.
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    Characterization of poly(3-octylthiophene). I: Molecular characterization in dilute solutionWe note with sorrow the passing of Dale S. Pearson in October 1993-The Editors. (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 860-867 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The poly(3-alkylthiophenes) are a class of electrically conducting polymers which are of particular scientific and commercial interest due to their solubility and meltability. A series of poly(3-octylthiophene) (P3OT) fractions having molecular weights in the range Mw=30,000 to 400,000 were generated by preparative gel permeation chromatography (GPC). Although the polymer remained weakly aggregated when dissolved in pure THF, the addition of an organic salt (1 wt.% tetrabutylammonium p-toluenesulfonate) resulted in complete molecular dissolution. We were thus able to completely and consistently describe the polymer's single-chain properties using three dilute solution characterization methods: viscometry, GPC, and integrated light scattering. The molecular weight dependence of the intrinsic viscosity and the radius-of-gyration were established, and were characteristic of solutions near the theta condition, indicating poor solvent quality. Calculation of the persistence length from our data revealed that the polymer backbone is only 2 to 3 times more rigid than common flexible polymers, despite its conjugated ring structure.
    Additional Material: 6 Ill.
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    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
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: 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.
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    URL: http://dx.doi.org/10.1002/pen.760350907
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    Structure and mechanical anisotropy of cold-rolled ultrahigh molecular weight polypropylene (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 902-910 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Wide angle X-ray diffraction pole figure, small angle X-ray scattering (SAXS), and refractive index techniques have been employed to investigate structure and deformation mechanisms in unidirectionally cold-rolled ultrahigh molecular weight polypropylene (UHMWPP) films. All reciprocal lattice vectors (plane normals) of (110), (040), and (130) were found to populate in the film normal (thickness) direction, suggesting that more than one orientation process must be involved in the deformation. SAXS studies on the cold-rolled UHMWPP reveal an oriented lamellar structure with its long axis perpendicular to the rolled direction, however, the lamellae are somewhat tilted. Refractive index and tensile measurements were undertaken to determine the optical and mechanical anisotropy of the cold-rolled UHMWPP films. A similar study was undertaken of unidirectionally rolled conventional polypropylene (PP) for comparison.
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    URL: http://dx.doi.org/10.1002/pen.760351104
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    Wall thickness uniformity in plastic pipes: Computer simulations of the effectiveness of die mandrel offsetting and pipe rotation in combatting sag (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 921-928 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A computer simulation, based on a thermoviscous model of cooling and gravity induced flow (sag) in plastic pipe manufacture, which has previously been described in detail and validated against experimental results, is here used to investigate the effectiveness of die mandrel offsetting and pipe rotation in combatting sag. SDR11 MDPE pipes of 315, 560, 800, and 1000 mm diameter are considered. Results are examined in terms of a waste percentage, representing polymer used in excess of that corresponding to the minimum wall thickness. With a concentric mandrel, waste is predicted to be 4.3, 14.0, 17.9, and 18.7% for the four sizes, respectively. Optimum offsets and minimum waste percentages are found to be: 2 mm, 0.8%; 15 mm, 4.6%; 42 m, 9.8%; 63 mm, 12.7%, respectively. For the largest pipe this corresponds to a wall thickness variation of 19.6 mm. Simulations of rotation of the 800 mm pipe show waste falling rapidly to 5% at 1 revolution/4800s, then a slower decrease, reaching 1.6% at 1 revolution/600s. The simulation is equally applicable to all grades and sizes of pipe, and provides a valuable computer aid for the design and operation of pipe cooling lines.
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    URL: http://dx.doi.org/10.1002/pen.760351106
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    Fiber structure development in high-speed melt spinning of copolyesters: Poly(ethylene terephthalate-co- 1,4-cyclohexylene dimethylene terephthalate) (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 942-949 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: High-speed melt spinning of poly(ethylene terephthalate) (PET), poly(1,4-cyclohexylene dimethylene terephthalate) (PCT) and ET/CT copolysters were performed and the structure and properties of as-spun fibers were investigated. Molecular orientation increased with an increase in the take-up velocity, and orientation-induced crystallization of PET and PCT started at ∼4.5 and 3.5 km/min. With the addition of CT component to PET, and ET to PCT, the onset of crystallization shifted to higher velocities. In as-spun fibers of the copolymer of ET/CT = 66/34 mol%, which is known as an amorphous copolyester, the crystallization was not observed even at the attained highest take-up velocity, 6 km/min. On the other hand, crystallization of these fibers occured on annealing suggesting that although the incorporation of copolymer component suppresses the crystallization, the molecular orientation enhances the crystallization of copolymer systems as in the cases of homopolymers.
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    URL: http://dx.doi.org/10.1002/pen.760351108
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    Masthead (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995) 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760351201
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