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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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K výběru odpovídajícího fenomenologického modelu pro vazkoplastické kapaliny
David, Jiří ; Filip, Petr
At present a series of phenomenological models are used for the description of flow curves of viscoplastic materials. Their application for the given materials hitherto subjects to the two following factors: number of entering parameters and agreement with the experimental data. However, for the case of viscoplastic fluids there is still one point playing a crucial role: determination whether a mutual ratio of ciscous and plastic effects generated by the proposed model corresponds to the physical characteristics of the material studied. This contribution aims to analyse partially this topic and to provide a hint for a choice of a corresponding model
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