Library

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Two-dimensional planar flow of a viscoelastic plastic medium (1993)
    Springer
    Rheologica acta 32 (1993), S. 181-191 
    Details
    ISSN: 1435-1528
    Keywords: Two-dimensional flow ; viscoelastic plastic medium ; yield surface ; contraction and expansion flow ; pressure drop
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The present study is concerned with finite element simulation of the planar entry flow of a viscoelastic plastic medium exhibiting yield stress. The numerical scheme is based on the Galerkin formulation. Flow experiments are carried out on a carbon black filled rubber compound. Steady-state pressure drops are measured on two sets of contraction or expansion dies having different lengths and a constant contraction or expansion ratio of 4:1 with entrance angles of 90, 45 and 15 degrees. The predicted and measured pressure drops are compared. The predicted results indicate that expansion flow has always a higher pressure drop than contraction flow. This prediction is in agreement with experimental data only at low flow rates, but not at high flow rates. The latter disagreement is possibly an indication that the assumption of fully-developed flow in the upstream and downstream regions is not realistic at high flow rates, even for the large length-to-thickness ratio channels employed. The evolution of the velocity, shear stress, and normal stress fields in the contraction or expansion flow and the location of pseudo-yield surfaces are also calculated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00366681
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Volumetric effects in the injection molding of polymers (1985)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 25 (1985), S. 271-278 
    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: Density and shrinkage measurements have been performed in quenched and molded slabs from polystyrene (PS) and poly (methylmethacrylate) (PMMA). Various processing conditions have been employed and their effect on density and shrinkage variation in the final parts, as well as volumetric aging vs. Elapsed time at room temperature, have been elucidated. A numerical simulation of the density variation in quenched parts and their aging has been performed by using first-order rate theory for volumetric changes in conjunction with solving the transient one-dimensional heat-conduction equation with a convective heat-transfer boundary condition at surface. A numerical simulation of the shrinkage in molded parts has been carried out by using the equation of state with a simultaneous solving of the governing equations for one-dimensional mold filling during the cavity filling stage followed by transient one-dimensional conduction during packing and cooling stages. Predicted results for density and shrinkage are compared with experimental data.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760250504
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Filling thin cavities of variable gap thickness: A numerical and experimental investigation (1983)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 23 (1983), S. 20-26 
    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 theoretical and experimental investigation is presented for filling thin cavities of variable gap thickness. The modeling is based upon a finite-element/finite-difference formulation for an inelastic power-law fluid and includes the effects of viscous heating and conduction upon the flow dynamics. Extensive results are presented for polypropylene and polystyrene melts injected into two variable-gap-thickness cavities, of which one has an insert. Good agreement is found between the predictions and measurements concerning the shape of the advancing melt front, the location of weld lines, and the temporal pressure trace at various positions in the cavity.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760230106
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Flow of polymeric melts in short tubes (1985)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 25 (1985), S. 264-270 
    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 an attempt to further understand the flow of polymeric melts through gates in injection molding, the present investigation deals with measurement of pressure drops during isothermal extrusion of fiber-filled and unfilled polystyrene, polypropylene, and polycarbonate melts in short tubes with sudden contraction at high shear rates typical of injection molding. Flow curves for these materials have been determined over a wide range of shear rates at various temperatures by using a capillary rheometer and extruder. Measurements indicate that rheological properties of fiber-filled melts after injection molding differ from those of fresh samples. Moreover, it has been found that decreasing the tube length increases the slope of the curve for pressure drop vs. Volumetric flow rate. Extra pressure losses due to end effects have been determined which show that at high shear rates these losses can reach levels as high as 100 bar, with the effect being higher for the fiber-filled melts. By using a viscoelastic consitutive equation, the extra pressure losses have been separated into entrance and exit losses. Model parameters required for this calculation have been determined from viscosity-shear rate curves for the melts. For various polymers, master curves useful for industrial applications have been constructed for the extra pressure losses.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760250503
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    Master curve approach to polymer crystallization kinetics (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 733-740 
    Details
    ISSN: 0032-3888
    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: Nonisothermal crystallization kinetic data obtained from differential scanning calorimetry (DSC) for a poly(ethylene terephthalate) are corrected for the effects of temperature lag between the DSC sample and furnace using the method of Eder and Janeschitz-Kriegl which is based on experimental data alone without resort to any kinetic model. A method is presented for shifting the corrected nonisothermal crystallization kinetic data with respect to an arbitrarily chosen reference temperature to obtain a master curve. The method is based on experimental data alone without reference to any specific form of kinetic model. When the isothermal crystallization kinetic data for the same material are shifted with respect to the same reference temperature, a master curve is also obtained which overlaps to a large extent the corresponding master curve from nonisothermal data. It follows that nonisothermal DSC measurements provide the same crystallization kinetic information as isothermal DSC Measurements, only over a wider range of temperatures. The shift factors obtained from experimental data alone are compared in turn with the corresponding values calculated from the Avrami equation, the Hoffman-Lauritzen expression, and the Nakamura equation as a means of evaluating these models individually. It is concluded that the Avrami equation is very good at describing isothermal crystallization kinetics, the Hoffman-Lauritzen extrapolation of the limited isothermal data to a wide range of temperatures is quite good, and the Nakamura equation yields reliable crystallization kinetic information over a narrower range of temperatures than nonisothermal data alone without using any specific model.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760350902
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    Quiescent polymer crystallization: Modelling and measurements (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 461-471 
    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 problem of predicting nonisothermal crystallization kinetics based on isothermal data is considered, with reference to the difficulties involved, both experimental and theoretical. The kinetic model used is the differential form of the Nakamura equation which is an extension of the Avrami equation so as to apply to nonisothermal crystallization. Nonisothermal induction times are obtained from isothermal induction times according to the concept of induction time index. The theory of Hoffman Lauritzen is used to extrapolate the limited isothermal crystallization rate data. Good agreement between DSC (differential scanning calorimetry) nonisothermal crystallinity results and model predictions is obtained for our own data on poly(ethylene terephthalate) (PET) and some literature data on nylon-6, if the temperature lag between the sample and the DSC furnace is taken into account. The advantages of the present approach in process modeling are pointed out. Quenching experiments have also been performed in which PET slabs are allowed to cool and crystallize from the melt under quiescent conditions. The resulting crystallinity distributions in the thickness direction are measured and predicted by using kinetic parameter values obtained from isothermal DSC measurements alone.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340602
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 7
    Electronic Resource
    Electronic Resource
    Effect of ultrasonic waves on foam extrusion (1991)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 31 (1991), S. 1051-1056 
    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 ultrasonic waves upon foam extrusion has been investigated by using a special die attached to an extruder. The die consists of a special ultrasonic horn, having a circular channel, that vibrates at 20 KHz. Various ultrasonic amplitudes and flow rates were employed during extrusion of a foamed polystyrene. Ultrasonic waves were found to affect both die pressure as well as physical and mechanical properties of the foam. Increases in the amplitude of the ultrasonic waves resulted in a decrease of the pressure at the die entrance. The density of the foam was found to increase with an increase of the amplitude and a decrease of the flow rate. Extrudate swell was found to decrease with an increase in the amplitude. Ultrasonic waves also influenced cell size and distribution in extruded samples: increases in amplitude resulted in reduced cell size and in narrowing their distribution. These effects are likely caused by break up of large cells or by disruption of coalescence of small cells. The tensile strength and Young's modulus of samples of extruded foam were found to increase with ultrasonic treatment. A unique correlation of these mechanical properties with the density of the foam was established.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760311409
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 8
    Electronic Resource
    Electronic Resource
    Self-Reinforced composites of two thermotropic liquid crystalline polymers (1993)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 33 (1993), S. 32-42 
    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 two thermotropic liquid crystalline polymers (LCP) based on 6-oxy-2-naphthoyl and p-oxybenzoyl moieties and p-oxybenzoyl, terephthaloyl and hydroquinone moieties have been studied. The blends were prepared by melt mixing using a twin screw extruder. Thermal, rheological, mechanical, and morphological studies were carried out. Based on the dynamic mechanical thermal analysis and the morphological observations, the blends are found to be immiscible. The viscosity ratios of pure LCP melts exceed values of 10 over a wide range of shear rates, with the viscosity of the blends lying between those of the pure components. The prepared blends are shown to be self-reinforced composites in which one LCP enhances the molecular orientation of the other. Studies of the injection molded bars by scanning electron microscopy indicate a complicated hierarchical morphology with microfibrils of submicron level in diameter, bundled, and intertwined into fibrils of a substantially larger diameter. Due to self reinforcement, impact and tensile properties of the blends show significant synergism when compared to those of the pure LCP components. The properties obtained are remarkably higher than those known for any high performance engineering thermoplastics.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760330105
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 9
    Electronic Resource
    Electronic Resource
    Dynamic properties of crosslinked epoxy resin at large cyclic and static deformation (1981)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 21 (1981), S. 566-570 
    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: Measurement of dynamic properties of crosslinked epoxy resin have been performed under torsional cyclic deformation with different amplitudes and frequencies and with extensional creep under different loads. It is found in both cases that the dynamic modulus decreases above a certain critical value of deformation. Truncation of the glassy state region and shifting of the transition zone to lower temperatures and higher frequencies have been observed as effects of large amplitude deformation. The maximum reduction in the modulus value and the minimum in the critical amplitude both occur in the region of Tg Shear fatigue of the material has been observed in the glassy state with a frequency- and temperature-dependent fatigue life. It is found that the loss modulus under extensional creep depends upon the values of the deformation and stress whereas the storage modulus depends solely upon the deformation. The ratio of energy expended during static and cyclic deformations is shown to depend only upon the extensional deformation.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760210909
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 10
    Electronic Resource
    Electronic Resource
    Orientation development in the injection molding of amorphous polymers (1983)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 23 (1983), S. 271-284 
    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: Frozen-in orientation in the injection-molding of amorphous polymers has been considered in terms of flow- and cooling-induced birefringence. In particular, measurements of the frozen-in orientation distribution in polystyrene (PS) molded strips and circular runners have been performed. Three birefringence components, Δn, n22 - n33, and n11 - n33, have been measured for strips, and two components, Δn and nrr - nθθ, for runners. The effects of various processing conditions, of strip thickness, and of runner diameter on orientation development have been analyzed and compared with those predicted by our previously developed viscoelastic theory. In addition to injection-molding experiments, free and constrained quenching experiments for PS and poly(methyl methacrylate) (PMMA) strips have been carried out and the gapwise distribution of cooling-induced (thermal) birefringence has been measured. Relaxation of thermal birefringence following quenching has been observed for PMMA. The effects of flow- and cooling-induced orientation on various components of birefringence in molded parts have been elucidated and limitations on the applicability of the stress-optical law to the injection-molding of amorphous polymers have been discussed.
    Additional Material: 19 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760230507
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...