1. Experiment.
Two materials were tasted to investigate the effects of the strain rate on mechanical behavior of the filled
polymers. The first one was a filled cellulous (FC) containing about 15% of technical carbon as a reinforcement.
This material was tested at the tension in wide range of the strain rate. The samples of FC in the form of flat dogbone
were cut from the sheet with the thickness about 2 mm with use of figured knife. The size of working part of
the sample was 40x7.5 mm for static tests and 12x4.5 mm for dynamic tests. The tests at slow strain rate were
carried out by the use of the standard test equipment. The tests at high strain rate were carried out using of the
rotational impact testing machine, Zezin et al. (1985). The series of tests was carried out with notched specimens of
FC. The edge notches were made by the razor blade. The depth of the notch was measured by the optical
microscopy of the fracture surfaces after testing of the specimens. The results of these tests were used to determine
critical size of inherent flow of FC.
The high-filled polymeric material (HFPM) was tested at the complex stress state with different intensity
strain rate. HFPM is the polymeric composite on the base of a synthetic rubber. The dispersed oxides of calcium and
of magnesium were acted as the reinforcements in this material. The fillers content of composite constituted about
70% by the volume of the material. The complex stress state of HFPM was applied during loading of the specimens
in the form of hollow cylinders by the tensile force and the torque. The external diameter of the specimens was 24
mm, the wall thickness was 4 mm the length of the working part was 70 mm. All tests were carried out using the
special equipment for testing of polymeric materials at the complex stress state with proportional loading in wide
range of the strain rate intensity: from 0.02 s-1 to 2 s-1, Zezin et al. (1988). All tests were carried out at the room
temperature of 20oC. The force of tension, the torque, the increment of the specimen length and the angle of torsion
were measured during tests as a function of time.
2. Viscous-brittle transition at fracture of FC.
The stress-strain curves for FC were obtained at different values of the strain rate in investigated range. These
curves were used to determine the mechanical characteristics of FC: strength, ultimate strain and energy of fracture.
The additional tests of the notched specimens enabled us to determine the critical size of inherent flows (lC).
Three stress-strain curves of FC at different values of the strain rate are presented in figure 1 (left). From
these data we can see that ultimate proprties of FC dependent essentially on the loading rate. Moreover, it is
evidence that the ultimate strain changes nonmonotoniously with increasing of the strain rate in investigated range.
It is possible to see more detail the rate dependencies of ultimate properties of FC on fig. 1 (right). We can see that
all three characteristics increase slowly with increasing of the strain rate to the level 10 s-1. The fast changes of the
strength are obtained with further increasing of the strain rate. The ultimate strain and the fracture energy decrease
quickly with increasing of the strain rate in the range from 10 to 700 s-1.
It was suggested that the changes of mechanical behavior of the FC with the variation of the strain rate are
determined by the change of the dominant mechanisms of the material resistance to the deformation and to the
fracture. At slow loading (with value of the strain rate 7·10-6 s-1) the change of conformational state of polymeric
chances and the damage accumulation are the main mechanisms of the material deformation. Rebuilding of