The analysis of the durability of structural elements subjected te complex stress is an urgent problem ef modern mechanical engineering. Up to now a unified criterion of long-duration strength, enabling such analyses to be carried out for various temperature and load levels, has not been established. In this paper we give the results of processing experimental data with the use ef the long-duration strength criteria propesed in recent times. Tile relationship is established between the constants entering into the respective expressions and the stress. This necessitates a particular consideration ef the variation of these constants te obtain the required accuracy.