IMPACT TOUGHNESS - Fractal Mechanics of Polymers - page 200

The Eq. (5.16), which both qualitatively and quantitatively corresponds to
experimentally obtained dependence A p ( B ) [13, 24], allows to confirm this
postulate. So, at testing temperature T = 293 K the value r p ≈ 0.8 mm for
HDPE [21]. The calculated at this condition according to the Eq. (5.16) cor-
relation d fr1 ( B ) is adduced i n Fig. 10.9 . It is obvious, that at the condition 2 r p
= B , corresponding to the brittle-ductile transition [12], the greatest possible
value d fr = 2 is reached.

d

r -

1

FIGURE 10.8 The dependence of critical strain energy release rate G Ic on parameter

a

for HDPE (1) and PS (2) [21].

In addition the obtained value B = 1.6 mm corresponds well to the liter-
ary data for samples with the greatest plasticity thickness [13]. Then the fast
d fr1 reduction at B growth is observed, that corresponds completely to simi-
lar fracture toughness decrease within the frameworks of polymer fracture
two-component model [25, 26] and also corresponds to the stressed state
transition from plane-stressed to plane-strained one [13]. At B = 20 ÷ 25
mm the values d fr1 reach asymptotic magnitude, that also corresponds to the
experimental B value, obtained for transition to plane-strained state [24].
The plots of Fig. 10.8 are of interest from two points of view. Firstly, they
confirm the intercommunication of G Ic and local plastic deformation zones
fractality. Secondly, such plot allows to determine the value G I0 in the Eq.
(10.14), which is actually material property. From the data of Fig. 10.8 it
follows, that for HDPE G I0 = 2.35 kJ/m 2 and for PS - 1.70 kJ/m 2 , that is very
close to the cited earlier results [22].