Chepil R. The assessment of the fatigue durability of a notched structural element using the deformation parameters of a local fracture

Сrack growth resistance and fatigue life time of notched specimens. To develop the method of the fatigue macrocrack initiation period Ni assessment near the structural stress concentrators based on strain parameters and the method of the structure element durability Nf determination using of the fatigue fracture unified model. The experimental fatigue fracture mechanics approach, theoretical models of the stress-strain state calculation for bodes with stress concentrators, means of the local displacement (strain) measurement is a methodological foundation of the research. The new methods of the notch and crack tip opening displacement measurement and local elastic and elasto-plastic local strain calculation are proposed. It is shown that the fatigue macrocrack initiation (Ni) and propagation (Np) periods in specimen (structure element) are determined by the local strain range of the process zone in the vicinity of notch or crack tip. The new mode of the process zone size d* assessment and formulae for parameter d* and effective (cyclic) stress concentration factor Kf calculation are proposed. The possibility of the fatigue macrocrack growth diagrams prediction on the basis of the crack initiation resistance diagrams in the air and corrosive environment at the stress and strain approaches is shown. The new method of the total durability Nf = Ni + Np prediction for the specimens with stress concentrators on the basis of fatigue fracture unified model is proposed and experimentally confirmed. The elaborated methods and practical recommendations for the durability estimation of the "Antonov's" airplane structure elements are applied.