Introduction.
The polymeric materials are often subjected to complex loadings so that the strain rate can change in a range of
several decades from very slow at the creep to very fast at dynamic loading. For adequate evaluation of the
durability the parts of constructions from polymeric materials it is necessary to take into account the rheonomous
type of mechanical behavior of these materials and in particular the dependence of mechanical characteristics on the
strain rate. As it was noted Word and Sweeney (2013) increasing of the strain rate caused the increasing of strength
and nonmonotonic change of the ultimate deformation. At high strain rates the fast change of many characteristics is
occurred with increasing the loading velocity. Similar behavior is caused by the change of dominance mechanisms
of the resistance of material to mechanical loading. In this work, the effect of the strain rate on mechanical
properties at the tension of filled cellulous (FC) was investigated in range from 7·10-6 to 700 s-1. The transition from
viscous failure to brittle fracture at the increasing of the strain rate was discussed. The criterion of the long-term
strength of polymeric materials was suggested. The experimental verification of suggested criteria for two polymeric
materials at the tension and at the complex stress state was carried out.