Rheological functions standard flows

However, for non-Newtonian fluids, even though continuity equation and the equation of motion written as Equation 11.2 remain valid, the Newtonian constitutive equation is not correct and a different constitutive equation is needed. To find constitutive equations, experiments are performed on materials using standard flows described above. The functions of kinematic parameters that characterize the rheological behavior of fluids are called rheological material functions. Standardized material functions are shown in Table 11.1 [2-4]. 

To conclude, a brief review on the state-of-art of the rheology of structured fluids has been carried out giving special emphasis on the structure-rheology correlation. Two systems have been investigated polymeric liquids and dispersions. After a brief introduction on fluid mechanics, material functions and standard flows are explained. Then, existing theories are summarized and compared with experimental results. Even thongh current researchers continue searching for new constitutive equations, those reported in this chapter serve as a base for future developments. 

The effect of temperature on biaxially squeezed ar-PS is seen more completely in Figure 6 where the apparent true stress at = 2.2 is plotted as a function of temperature for several initial strain rates. As previously discussed (Fig. 5), the values of stress fall sharply in the temperature range up to MO C. However, the stress values do not decrease in a monotonic fashion but appear to show a region of instability around 157-165 C for most of the strain rates used. The temperamre regime over which this effect occurs appears to be relatively insensitive to the rate of deformation but is most noticeable with an initial strain rate of 0.67 sec l. The standard deviation in measured loads was less than 10% for the temperature interval from 120°C to 155 C, but in some cases at 160 C the standard deviation was as great as 20%. Evidence of instability was quite reproducible at temperatures around 160°C. The observed behavior does not seem to be reconcilable within the scope of simple theories of viscoelasticity or with the more recent theories of rheological flow developed by Doi and Edwards, and will be discussed further later. 

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