Fatigue crack growth analysis of 2024 T3 aluminium specimens under aircraft service spectra

The fatigue crack growth behaviour of 2024 T3 aluminium was investigated ex perimentally. The fatigue experiments were performed under constant stress amplitude, constant amplitude with single and multiple overloads and aircra ft service spectra. The fatigue spectra used correspond to the air-to-air, air-to-ground and instrumentation and navigation flight phases. They were a pplied for different stress levels. In total 11 different random flight ser vice spectra were examined. The retardation effects caused by the overloads on the fatigue crack growth behaviour and the fatigue crack growth under a ircraft service spectra were predicted using an in-house-developed code. Th e code makes use of the strip plastic zone approximation to account for mat erial hardening effects along the path of prospective crack growth. Crack g rowth is treated incrementally and corresponds to failure of material eleme nts ahead of an existing crack after a certain critical number of fatigue c ycles. For the simulation of irregular service spectra by equivalent sequen ces of distinguished stress cycles a modified rainflow counting method is u tilized. Spectrum simulation accounts also for non-linearity in fatigue dam age accumulation and load sequence effects. The computed fatigue curves fit well with the experimental results.