A Two-point Method for Multiaxial Fatigue Life Prediction

Fatigue fracture is one of the most common failure modes of engineering components, and the combined action of geometric discontinuity and multiaxial loading is more likely to cause severe fatigue damage of components. This work focuses on the fatigue behavior of U-notched Q345 steel specimens with different notch sizes under proportional cyclic tension–torsion. Firstly, based on the concept of strain energy, the calculation method of critical plane is given and the equivalent stress of the specified path on the critical plane is extracted to characterize the equivalent stress distribution state and the stress gradient effect. Then, based on the high stress volume method and theory of critical distance, a simple method for determining the critical distance is given considering the contribution of stress at the dangerous point and the critical point. In addition, based on the idea of stress–distance normalization, a new stress gradient impact factor is defined and a new method for predicting the multiaxial fatigue life of notched specimens is given. The prediction results of the proposed model, the local stress–strain method and the point method of theory of critical distance are compared with the experimental results. The comparisons show that the prediction results of the proposed model are closer to experimental life, and the calculation accuracy is higher.