Main step in the data processing procedure include calculating the shear stress as a function of radial position in the pipe, processing the velocity profile image to obtain a velocity profile, calculating the shear rate as a function of radial position from the velocity profile, and generating the rheogram
by plotting the shear stress against the shear rate (Arola et al., 1997, Callaghan 1999 and Tozzi et al., 2012).
observed with an increase in shear rate differed from that observed with a decrease in shear rate, and a hysteresis loop was observed for all ointment formulations.
Marked points represent the average values of the rheogram
experimental data and continuous lines are the fit results calculated using the Herschel-Bulkley model.
Nadkarni, "From melt flow index to rheogram
," Rheologica Acta, vol.22, no.1, pp.
In Newtonian fluids, shear stress and shear rate are directly proportional (N = 1), so the rheogram
will be a straight line, while, in non-Newtonian fluids, there is not a direct relationship between them (N > 1) 17].
For the Brookfield rheometer, the viscosity of the same samples has been obtained, directly from the rheogram
of the oils and independent of the velocity.
of Thixotropy obtained by plotting shear stress versus shear rate shows the down curve (obtained by decreasing shear rate) is displaced to the left of the up curve (obtained by increasing shear rate).
For drawing the rheogram
, shear rate was increased for the samples till maximum.
All the data were used to form rheogram
and are shown in Figure 2.
For a plastic material, the rheogram
does not pass through the origin, and no strain rate occurs until the shear stress exceeds some yield value.
The minimal elastic torque time of the MDR rheogram
for each compound was collected and is hereafter designated as [t.sub.MIN].
were plotted on the shear rate range from 6.46 to 129 s-1.