The fatigue limit of metals as a characteristic of the multimodal fatigue life distribution for structural materials

摘要

Based on the concept of physical mesomechanics, the sequence of damage accumulation mechanisms was considered in accordance with stress level increasing. It was shown that metals behavior evolution takes place in the direction from micro- to meso- and then macroscale level in accordance with introduced bifurcation diagram. It was explained why metals mechanical characteristic named "fatigue limit" cannot be used for simulation of structure durability and in-service lifetime. The problem of bimodal fatigue life distribution for different types of metals was discussed when bifurcation transition from one to another scale level of metals evolution takes place. Test data for "fatigue limit" determination in accordance with the standard technique of more than 250 aviation structural materials were reviewed. Influence of mechanical characteristics on the "fatigue limit" value was analyzed. It was demonstrated that the major part of materials realized all three scale level during stress level increasing. Realization of low-cycle-fatigue is not designed case for operating complex structures when the mesoscale level of metal fatigue does not exist.