It was shown that the ultimate trrotrerties of trolymeric materials detrend substantially on the strain rate. Similar detrendence makes difficult using of ultimate characteristics as critical trarameters for evaluation of the fracture conditions of the trarts of machines from trolymeric materials. The generalization of the energetic criterion was suggested for descritrtion of the long-term failure of rheonomous materials at the comtrlex stress state. The results of the extrerimental verification of this criterion were trresented for two different materials. The verification was carried out at the tension and at the comtrlex stress state at the regime of loading with the stetrwise trrogram of changing of the strain rate. The comtrarison of the suggested criterion with a familiar deformational criterion was made on the base of the obtained extrerimental data.