New paradigms in metals fatigue description

Present processes of damages accumulation in metals under regular cyclic loads were analyzed. Based on the concept of physical mechanics, a sequence of damage accumulation mechanisms was considered in accordance with the stress level increasing. It was shown that the evolution of metals behavior takes place in the direction from micro-, to meso-, and then macroscale levels in accordance with the bifurcation diagram under consideration. It was explained why metals mechanical characteristic called fatigue limit cannot be used for simulation of structures durability and in-service life-time. The problem of the bimodal durability distribution for different kinds of metals was discussed when the bifurcation transition takes place from one scale level to another one. It was shown that in the bifurcation region metals can experience a constant stress level but its reaction appeared in two ways with a different probability because the difference in damage accumulation belonged to the scale above and below the bifurcation region. Mechanisms of the subsurface fatigue cracking in a very-high-cycle-fatigue regime were reviewed. It was demonstrated that the dominant process in damages accumulation under the metal surface and appearance of the subsurface cracking origin is related to sliding deformation and material torsion during material uploading. Test data for fatigue limit determination of aviation structural materials in accordance with the standard were reviewed. The influence of mechanical characteristics of the fatigue limit value was analyzed. It was demonstrated that the major part of the material realized all three scale levels during the stress level increasing from one unit to another. The realization of the low-cycle-fatigue is not the computationally recommended case for the operated complex structures when the mesoscale of metal fatigue does not exist.