Chemistry Reference
In-Depth Information
In Fig. 4.26, the comparison of the experimental s
Y
and calculated theo-
retically
T
s
) dependences of yield stress on
e
for HDPE
and PP are adduced. As one can see, a good correspondence of theory and
experiment is obtained, confirming the offered above model of yielding pro-
cess for semicrystalline polymers.
s
as sum (
s
+
cr
nc
FIGURE 4.26
Comparison of the experimental (1, 2) and theoretical (3, 4) dependences of
yield stress s
Y
on strain rate
e
in logarithmic coordinates for HDPE (1, 3) and PP (2, 4) [93].
Let us note in conclusion the following. As it follows from the compari-
and
G
constancy, that contradicts to the assumed earlier s
Y
and
E
proportion-
ality [101]. Such proportionality absence is assumed even by the Eq. (2.20),
since the value n is a function of several structural factors (see, e.g., the Eq.
(1.10)). Therefore, the postulated in Ref. [101] is
Y
and
E
proportionality is
only an individual case, which is valid either at invariable structural state or
at the indicated state, changing by definite monotonous mode [77].
Hence, the stated above results demonstrate nonzero contribution of non-
crystalline regions in yield stress even for such semicrystalline polymers,
which have devitrificated amorphous phase in testing conditions. At definite
conditions noncrystalline regions contribution can be prevailed. Polymers
yield stress and elastic constants proportionality is not a general rule and is
fulfilled only at definite conditions.
