Damage Tolerance Improvement of Laser Beam Welded Fuselage Structures via Crenellations

Abstract

In this work the concept of the crenellation for improving the fatigue resistance of the fuselage skin by systematic thickness variations was examined under the service-related biaxial loading condition. Fatigue tests imitating the long-term cyclic load due to the repetitive fuselage pressurizations were carried out on both crenellated and flat panels with straight and kinked cracks. An unexpected high propagation rate of the kinked crack in the crenellated specimen was found, which reduced the fatigue life even compared to the uncrenellated specimens. FEM models validated by experiments were applied to understand the corresponding fatigue behavior. The observed high crack propagation rate was found correlated with the mode III load and a possible change in mode I crack closure behavior. The source of the mode III load was analyzed based on FEM simulation, which was found to be coupled with the biaxial loading condition.