Plastic deformation occurs as a result of irreversible displacement of dislocations:
one part of the crystal moves relative to the other; that leads to the strain hardening. As
a result, the curve rises to the value of the certain maximum stress in its parabolic part
due to the increasing resistance of the material to the build-up of plastic deformation.
If discrete fibers are used as fillers, the degree of reinforcement effect for PCM is
determined by their length (tab. 13).
Table 13 The impact of the length of discrete aramide threads Rusar-С
on physicomechanical properties of organoplastics based on PFR
(degree of filling is 60 mass.%)
Thread
length, mm
Fracture toughness,
kJ/m
2
Breaking point, MPa
under
Martens heat
resistance, К
Coefficient of
anisotropy of properties
bending compression
5
57
120
213
444
1,04
10
100
134
211
466
1,13
20
111
143
206
470
1,21
Source: developed by the author
It is established that strength properties and heat resistance of OP increase with
increasing of fiber length. However, with the increase in the length, the anisotropy
coefficient increases. It affects a certain decrease in the values of breaking point under
compression with increasing values of fracture toughness, breaking point under
bending and heat resistance. It is known that further increase of fiber length up to
50 mm slightly increases the toughness and heat resistance, but reduces other strength
properties connected with the decrease of the isotropy of properties of OP, because
fibers are twisted; that leads to the increase of internal stresses in phenolic matrix.
Thus, it was found that OP containing 60 mass.% of fibrous filler with the length
of fiber of 10 mm has the optimal complex of physicomechanical properties [9].
Tribological properties of organoplastics. The results of the study of the
processes of friction and wear of developed organoplastics are presented on Fig. 9, 10.
The analysis of numerical values (Fig. 9) showed that OP containing 60 mass.% of
Rusar-С fiber has the highest friction coefficient; with the content of the Tanlon fiber
(60-70 mass.%) this indicator reduces twice.
During the friction of OP filled with Rusar fiber (Fig. 9, curve 1) deep plough
furrows appear on its surface: harder surface (disk) plows through a softer one
(polymer) forming the friction track. The surface of OP containing Tanlon fiber is
smoother in comparison with OP reinforced by Rusar-С fiber. In both cases the
coefficient of friction decreases with the increase of the length of path, because
boundary layer appears in the process of friction of OP on the steel disk. It significantly
reduces the adhesion of organoplastics to the counterbody.
- 438 -