Exploration on the Unified Model for Fatigue Properties Prediction of Metallic Materials

The fatigue of metallic materials can be divided into high-cycle fatigue (HCF) and low-cycle fatigue (LCF); the damage of these two types of fatigue is commonly evaluated through stress amplitude and strain amplitude of cyclic loading, respectively. The mismatch of the evaluation standards between HCF and LCF leads to difficulties in the design and selection of anti-fatigue materials. Under this condition, systematic researches on fatigue properties and microscopic damage mechanisms of HCF, LCF and extra-low-cycle fatigue (ELCF) for pure Cu and Cu-Al alloys were summarized in this work. On the bases of the experimental results, a three-dimensional fatigue model is proposed, which is simultaneously applicable to both the HCF and LCF properties. The model is built up in a three-dimensional coordinate system of stress amplitude-strain amplitude-fatigue life; it could be associated with the cyclic stress-strain (CSS) curve, S-N curve and E-N curve through the projection method, or be transformed into the Basquin equation, Coffin-Manson equation and hysteretic energy model under specific conditions. In this way, this generally applicable fatigue model helps provide a new viewpoint for the evaluation and optimization of fatigue properties based on the classical fatigue theories.