Abstract: A series of controlled strain fatigue tests are conducted. The tests are carried out with thin walled cylindrical specimens 30CrMnSiNi2A under the combination of tension and torsion Loadings. The cycle of the loading is symmetric. The purpose of the test is to find the optimum criterion of estimation of strain fatigue life under the condition of plane stress. Using the parameters of equivalent strain, a new method of estimation of fatigue life is also suggested. The new method is suitable for strain fatigue under the combination of tension and torsion loadings. The optimum criterion is approved by the results of the tests sufficiently.

Key words: strain fatigue, estimation of fatigue life, combined load of tension and torsion