Fatigue life prediction under random amplitude loading spectra with shock

The Remaining Useful Life (RUL) estimation of physical systems is of paramount importance to structural prognostics and system health management, which is based on the current health state and the following loading conditions. Fatigue damage is one of the most significant failure mechanisms in engineering structural components. Typically, the excited structures are generally subjected to shock and random amplitude loading spectra in the fatigue weakness area during their service lives. The nonlinearity of fatigue damage evolution makes the calculation of fatigue crack propagation under variable amplitude loading complicated. In this paper, a cycle-by-cycle model is proposed to predict remaining useful life of metallic material structures with a fatigue crack under random amplitude loading spectra with shocks. Right after the shock, if the specimen does not fracture, the shock can be treated as the spike loading which dramatically influences the following fatigue crack growth behavior. The proposed formulation is developed based on physical mechanisms, in which the interaction effect is taken into account. The crack closure and plastic zone concept are employed to account for the crack growth retardation phenomenon due to shock loading. The proposed methodology is validated by experimental data of Al D16 and Al2024-T3 specimens under different typical loading conditions. In addition, a simulation example of fatigue life assessment under random amplitude loading spectra with shocks is performed to verify the proposed approach.