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Reologická charakterizace LDPE materiálů pomocí diferenciálních konstitučních rovnic
Pivokonský, Radek ; Zatloukal, M. ; Filip, Petr
For rheological description of branched LDPE melts (Escorene LD165BW1 a Bralen RB0323) the following differential constitutive equations were used: eXtended Pom-Pom, Phan Thien-Tanner-XPP, and modified Leonov models. There was carried out quantitative and qualitative comparison of efficiency of the predictions determined by these models with the experimental data measured at 200oC. For both materials there were measured linear viscoelastic properties, shear and uniaxial extensional viscosities.
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Empirický model zohledňující lokální extrém průběhu viskozity
Filip, Petr ; David, Jiří ; Pivokonský, Radek
Almost all empirical models dealing with the flow curves of non- Newtonian fluids can be applied only in the case of monotonous course of these curves. Exceptionally it is possible to model viscosity behaviour of rheologically more complex materials if there appears, in the course of a flow curve, a global extreme. The 8-parameter model proposed enables a description of viscosity behaviour in dependence on shear rate or shear stress also for the case when an extreme (maximum or minimum) is only local.
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K charakterizaci Vočadlova modelu pomocí postupu zpětného vytlačování
Filip, Petr ; David, Jiří ; Pivokonský, Radek
Back extrusion represents one of the cheapest and time-saving experimental methods how to determine rheological characteristics of the fluids studied. This method is based on plunging of a circular rod into an axisymmetrically located circular cup containing the experimental sample. Formerly this method was successfully applied to power-law, Bingham and Herschel-Bulkley fluids. The aim of this contribution is to present a sufficiently simple user-friendly procedure how to determine the individual rheological parameters appearing in the Vočadlo model (sometimes called Robertson-Stiff one) - yield stress, consistency parameter and flow behaviour index.
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Critical shear values of extruded polymer blends
Filip, Petr ; David, Jiří ; Keyzlarová, L. ; Sáha, P.
The onset of flow instabilities (encountered during extrusion of polymer melts) corresponds to the flow conditions when the critical shear stresses or the critical shear rates are attained. These critical values were experimentally determined for two cases of polymer blends. Consequently there were used the mixture rules of a logarithmic type for desciption of behaviour of critical shear values.
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