Chemistry Reference
In-Depth Information
[46]. The authors of Ref. [47] considered this problem on concrete example
of HDPE samples with sharp notch fracture process.
d
d
FIGURE 5.11
The relation between fractal dimensions of fracture surface
,
(1) and
fr
fr
f
d
(2), calculated according to the Eqs. (5.16), (4.50) and (5.17), respectively, for HDPE.
In insertion overhead-diagram
P
−
t
for HDPE sample with sharp notch. In insertion below -
schematic cross-section of sample with “shear lips” [47].
1
2
3
In the insertion of Fig. 5.11, the typical diagram load − time (P - t) for
HDPE with a sharp notch is adduced, illustrating quasibrittle fracture pro-
cess. Such diagram
P
−
t
allows to give the following treatment of the in-
dicated samples deformation and fracture processes [4]. At sample bend-
ing elastic energy accumulation occurs, local deformation zone is formed
at notch tip (stationary crack), which retards main crack propagation. At the
greatest load
P
max
achievement accumulated elastic energy becomes large
enough for sample fracture and this process is realized by instable crack
propagation, occurring almost momentarily. This postulate is confirmed by
vertical line of load decay immediately beyond
P
max
. Thus, all mechanical
properties of sample are defined on its deformation stage, but not fracture.
So, impact toughness
A
p
is a linear function of shear local plastic deforma-
tion zones (“shear lips”) size
r
p
, visually observed on samples surface [33].
The same can be said about other parameters of fracture process [47]. The
