Abstract: A criterion of fatigue damage for combined bending and torsion based on local stress-strain method is presented and a formula for local equivalent stress eq (i. e. stress strength) at notch root of notched structures is derived. It is pointed out that the structures will contain the same fatigue damage if only their local equivalent stresses are equal. Therefore, the fatigue life of a notched structure under combined bending and torsion can be predicted based on only a simple bending stress-life curve obtained from smooth specimens.

Key words: fatigue .life, bending and torsion, damage criterion