It was shown that the ultimate properties of polymeric materials depend substantially on the strain rate. Similar dependence makes difficult using of ultimate characteristics as critical parameters for evaluation of the fracture conditions of the parts of machines from polymeric materials. The generalization of the energetic criterion was suggested for description of the long-term failure of rheonomous materials at the complex stress state. The results of the experimental verification of this criterion were presented for two different materials. The verification was carried out at the tension and at the complex stress state at the regime of loading with the stepwise program of changing of the strain rate. The comparison of the suggested criterion with a familiar deformational criterion was made on the base of the obtained experimental data