Abstract: Fatigue limit prediction is an important basis for anti-fatigue design of engineering structures under complex loads. The stress field strength theory can not give the fatigue limit relation considering mean stress and belongs to the criterion of critical region. The criterion of critical point can not describe the local characteristics of high cycle fatigue damage, which is inconsistent with the characteristics of high cycle fatigue damage. A fatigue limit equivalence relation model for high cycle fatigue, which is based on intrinsic damage dissipation in critical region, is established by means of continuum damage mechanics and its irreversible thermodynamic framework. The equivalence relation includes the tensile fatigue limit under mean stress considering the tension-compression anisotropy and the ratio of the symmetrical rotational bending fatigue limit to the symmetrical torsional fatigue limit. The life predictions of LC4 and LC9 aluminium alloys is carried out using the prediction model for tensile fatigue limit under mean stress. It is shown that the proposed model is superior to the existing models associated with fatigue limit equivalence relations of single linear (GOODMAN and THORDBERG) and GERBER elliptic, and in good agreement with the test results. The anisotropy of tension and compression can not be described using the single linear equivalent model for predicting fatigue limit. The fatigue properties of eleven kinds of common metal materials are predicted using the model for predicting the ratio of symmetrical bending-torsion fatigue limit, and it is shown that the proposal is superior obviously to the ratio prediction induced by stress field intensity approach. That fatigue limit prediction based on uniform intrinsic damage dissipation in critical domain provides a new idea for fatigue strength prediction of metal materials.

Key words: critical region, damage mechanics, fatigue limit, intrinsic damage dissipation, life prediction