| Polymer melts or solutions are generally visco-elastic fluid materials. Viscosity is a material's physical property that with strain rate increasing, the rapid deformation of fluids will be resisted. The stress response of polymers can be divided into viscous and elastic ones.Typically, study of rheological properties for polymers contains two aspects. One is shear flow and the other is extensional flow. Currently, rheological study of shear flow has been studied more thoroughly than extensional flow. That is because it is easier to establish a pure shear flow than pure extensional flow, which is hardly to set up as the polymer material itself has a yield of strain and extensional flow is always accompanied by shear flow. In view of this, a generalized viscosity definition based on the permittivity of rheology has been proposed for generalized Newtonian fluids in this project. With this new viscosity definition, shear viscosity and extensional viscosity can be measured simultaneously. A rheometer prototype has been designed and manufactured to testify the new viscosity model, which can measure shear viscosity and extensional viscosity simultaneously.Firstly, a generalized viscosityηG which contains shear viscosity and extensional viscosity has been proposed for generalized Newtonian fluids in a complex flow, which mixes simple steady-state shear flow and extensional flow. In the new viscosity, it is believed that viscosity is depended on the intrinsic property of polymeric fluid and the uniqueness of viscosity is also emphasized. That means the viscosity is not only independent of flow type, but also independent of the coordinate system where the observer is. Shear viscosity and extensional viscosity are two different faces of the generalized viscosityηG, but not two independent viscosities of a polymeric fluid. Then, a new viscosity model with the dependence of the generalized viscosity on the second invariantsⅡτ,Ⅱd and the third invariantsⅢd of stress and rate of deformation has been suggested, which is essential to the establishment of a concrete viscosity model. And effect of the third invariantsⅢd has been also analyzed. As the pure shear viscosity in pure shear flow and pure extensional viscosity in pure extensional flow are contained in the new generalized viscosity model and the viscosity in complex flow mixing shear and extensional flow can be also characterized by the new model, so the new viscosity model is more suitable for characterizing the true viscosity of polymer fluid in actual flows.Secondly, a rheometer prototype has been designed which shear viscosity and extensional viscosity can be measured simultaneously with the new viscosity model and a constant extensional rate in a certain flow rate can be obtained by the new rheometer. According to the new viscosity model and micro-element analysis, the dependence of extensional and shear stressσ,τon flow rate Q and pressure drop△p has been calculated. Here, the flow rate is up to servo motor speed and pressure drop is measured by transducers which located between a certain distance along axial direction of the flow channel. The steady-state viscosities at extreme positions of flow channel can be measured, such as pure shear viscosityηSH at channel wall and pure extensional viscosityηEX at core axis. For the Data Acquisition System (DAQ), it contains USB series data acquisition card of NI Company (USA), virtual program LABVIEW and DYNISCO transducers special for polymer melt.Additionally, with the same range flow rate, the shear rate and shear stress at the channel wall, velocity distribution v(r,z) and pressure drop△p along the axial direction are also simulated by POLYFLOW in which power law model is adopted. Therefore, the pure shear viscosityηSH′and pure extensional viscosityηEX′at the same extreme location are calculated by generalized viscosity when four rheological parametersσ,τ,ε,γare obtained by POLYFLOW. On the other hand, shear viscosityηSH″can be also calculated by POLYFLOW directly, but not for extensional viscosity. So the pure shear and extensional viscosities are calculated by the new generalized viscosity model indirectly.Finally, the velocity distribution in the flow channel can not be directly expressed in a concrete equation since the stress and strain rate fields are very complex in a mixed flow. So the pure shear viscosity and pure extensional viscosity calculated by the new model are compared with shear viscosity or extensional viscosity measured by several commercial rheometers, such as shear viscosity measured by INSTRON capillary rheometer, shear and extensional viscosity measured by ROSAND RH 7-D double-barrel capillary rheometer and extensional viscosity measured by TA ARES-G2 rotational rheometer. The results shows that shear viscosity or extensional viscosity are consistent within a certain range of error, or with the same trend, or with a factor of 3, which have indirectly proved the rationality of the new viscosity model. On the other hand, the results also demonstrate that study of extensional viscosity with the continuous contraction channel which can generate a constant extensional rate at core axis is feasible.In a word, it is a novelty project to study generalized viscosity model for generalized Newtonian fluid. Because the new viscosity model contains extensional viscosity and is closer to the true viscosity of polymer materials, so it has certain theoretical and practical significance and also has broad development prospects in polymer dispersion, precision molding, etc. At the same time, a rheometer prototype by which shear viscosity and extensional viscosity can be measured simultaneously has been invented and developed. This prototype has been applied for patent already and has great significance in breaking the monopoly by foreign rheometer suppliers in the domestic market currently.
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