Adaptive planning in-service inspections of fatigued structures in damage tolerance situations via observations of crack growth process

From an engineering standpoint the fatigue life of a fatigued structure consists of two periods: (i) crack initiation period, which starts with the first load cycle and ends when a technically detectable crack is presented, and (ii) crack propagation period, which starts with a technically detectable crack and ends when the remaining cross section can no longer withstand the loads applied and fails statically. The main aim of this paper is to present more accurate innovative stochastic fatigue model for adaptive planning inspections of fatigued structures in damage tolerance situations via observations of crack growth process during a crack propagation period. A new crack growth equation is based on this model. It is attractively simple and easy to apply in practice for effective in-service inspection planning (with decreasing intervals between sequential inspections as alternative to constant intervals often used in practice for convenience in operation). During the period of crack propagation (when the damage tolerance situation is used), the proposed crack growth equation, based on the innovative model, allows one to construct more accurate and effective reliability-based inspection strategy in this case. For illustration, a numerical example is given.