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Thus, the true shear stress T is given by
where
L = length of the capillary
R = radius of the capillary
p = pressure of the melt (see Figure 1.39).
1.3.4 Apparent Viscosity
The apparent viscosity 7]a is defined as
and is shown in Figure 1.8 as a function of shear rate and temperature for a LDPE.
Viscosity 7\
Pa-s
Figure 1.8 Viscosity functions of a LDPE [8]
1.3.5 True Shear Rate
Shear rate f
(1.21)
(1.22)
The true shear rate yt is obtained from the apparent shear rate by applying the correction
for the non Newtonian behavior of the melt according to Rabinowitsch
The meaning of the power law exponent n is explained in the Section 1.3.7.2.
s" 1
(1.23)