Chemistry Reference
In-Depth Information
At present it is known [1-3] that microhardness
H
v
is the property, susceptible
to morphological and structural changes in polymeric materials. For composite
materials the availability of the filler, microhardness of which much exceeds corre-
sponding characteristic for polymer matrix, is an additional powerful factor [4]. At
pressing into polymer indentors sharpened in the shape of a cone or a pyramid the
stressed state is localized in a small enough microvolume and it is supposed, that
in such tests polymeric materials real structure is found [5]. In connection with the
fact, that polymers structure (including cross-linked ones) is complex enough [6],
the question arises, what structure component reacts on the indentor pressing.
The connection of microhardness, determined according to the results of
the tests in a very localized microvolume, with such macroscopic character-
istics of polymeric materials as elasticity modulus
E
and yield stress is
Y
, is
another aspect of the problem. At present a large enough number of derived
theoretically and received empirically relationships between
H
v
,
E
and s
Y
exists [7, 8].
The authors of Ref. [9] conducted cross-linked polymers microhardness
description within the frameworks of the fractal (structural) models and
the indicated parameter intercommunication with structure and mechanical
characteristics clarification. The epoxy polymers structure description is giv-
en within the frameworks of the cluster model of polymers amorphous state
structure [10], which allows to consider polymer as natural nanocomposites,
in which nanoclusters play nanofiller role (this question will be considered
in detail in chapter fifteen).
The authors of Ref. [9] used the cross-linked epoxy polymers based on
diglycidyl ether of bisphenol A (ED-22) of anhydride curing (EP-2) [11].
Two series of EP-2 are used - one of them was cured at atmospheric pres-
sure (EP-2-200) and another at hydrostatic pressure that allowed to obtain
10 samples of EP-2, differing by cross-linked networks topology [11].
Let us consider the intercommunication between microhardness
H
v
and
other mechanical characteristics, in particular yield stress s
Y
, for the studied
epoxy polymers. Tabor [12] found for metals, which were considered as
perfectly plastic solid bodies, the following relationship between
H
v
and s
Y
:
H
s
ยป
,
v
c
(12.1)
Y
where
c
is the constant, which is approximately equal to 3.
The Eq. (12.1) assumes that the applied in microhardness tests pressure
under the indentor is higher than the yield stress in quasistatic tests owing
