The effect of long-term operation on fatigue and corrosion fatigue crack growth in structural steels
Olha Zvirko, О. І. Venhryniuk, H. М. Nykyforchyn
Abstract
Operational degradation of steels under a combined action of mechanical loading and aggressive hydrogenating environments is a crucial problem for structural integrity. Among the mechanical properties, the characteristics of brittle fracture resistance, namely, impact strength and fracture toughness, as well as the plasticity characteristics, are highly sensitive to the operational degradation of structural steels. However, in the case of exposing of structures beside environmental influences to cyclic mechanical loading scenarios, their reliability depends on the degradation degree due to fatigue and corrosion fatigue. Tendency of in-service changes in the fatigue characteristics (fatigue crack growth rate and fatigue strength) can be unambiguous. In-service lifetime of structure due to the non-monotonic character of operational degradation of certain mechanical characteristics is divided into two stages: deformation strengthening (stage I) and in-bulk dissipated damaging (stage II). The operational degradation of steels is accelerated under influence of corrosive hydrogenating environments as a result of intensification of dissipated damaging. The effect of environments on acceleration of fatigue crack growth rate is mainly revealed in the mid-region of stress intensities, more significantly for in-service degraded metal, indicating its susceptibility to stress corrosion fatigue.