Abstract: The established nonlinear fatigue life prediction model based on the theory of damage mechanics has been widely applied to multiaxial fatigue life prediction. However, this model does not take into account the location of damage and its physical significance. A new multiaxial nonlinear fatigue life prediction model is put forward based on damage mechanics and critical plane method. The new model can make up the shortage of the existing nonlinear fatigue life prediction model, which did not consider the significance of critical plane. The new model predicts multiaxial fatigue life from the perspective of damage. It not only considers the physical significance of crack formation and propagation and the influence of the phase delay on additional strengthening phenomenon, but also revises the mean strain under asymmetrical loading. The new model can predict the multiaxial fatigue life only using the uniaxial fatigue test data and uniaxial fatigue material constants, which avoids the costly multiaxial fatigue test. The new model is evaluated by the multiaxial fatigue test data of 45 steel, 316 stainless steel and titanium alloy TC4. The multiaxial fatigue life prediction results of these materials under proportional/non-proportional loading and symmetrical /asymmetrical loading are almost within a factor of five scatter band of the test result. The result shows the new multiaxial fatigue life model has high prediction accuracy.

Key words: critical plane method, damage mechanics, multiaxial fatigue, nonlinear fatigue life prediction model