High-cycle fatigue fracture of structural materials under elastic-plastic deformation

The developed method of recording current values of crack tip opening displacement made it possible to reliably establish the instant when the “material” contact between the borders of a fatigue crack near its tip in a tension half-cycle ceases and the upper time limit after which the phenomenon of contact does not occur again, as well as to develop experimentally fatigue crack growth criteria. The phenomenon of “material” contact is evidenced by the presence of residual compressive stresses on the fatigue crack borders near the tip during fracture, which impede the crack propagation in the passive part of the stress cycle. Analysis of the revealed regularities in the fatigue crack propagation, changes in its kinetic diagrams and the upper time limits of the contact phenomena due to various factors, and existing formulas for crack growth rate calculations combined with the criteria and approaches developed enabled reliable description of the fatigue crack propagation kinetics and determination of the crack growth rate, life, and fracture types, as well as establishing the relation between time-dependent local parameters of stress- and strain-based fracture criteria, which accounts for the effect of any factors, their values lying in a wide range, which cause elastic-plastic deformation of structural materials, on the fracture process