Crack bridging effect in hybrid reinforced fuselage structure

icaf2023 Tracking Number 113

The A400M fuselage main frames at the wing-to-fuselage interface have the function of introducing the wing loads into the fuselage. The loads that are introduced by the wing are pre-dominantly tension, which results in an in-plane bending moment in the frame due to their curved shape, especially on the rear wing attachment. These fuselage frames are primarily sized by fatigue and damage tolerance requirements. In order to avoid heavy weight impact these frames had been reinforced by adhesively bonded GLARE straps. The development of the design principles, using bonded reinforcements have been presented in the ICAF conference in 2009. This paper now continues and closes this circle by presenting the outcome of the detailed analysis and test campaign that was done in frame of the development, comprising of component testing and full-scale fatigue testing. It outlines the different aspects of assessing a full-scale fatigue test result. A correlation is provided of this design with main focus on the crack bridging effect of the bonded GLARE strap. Finally the initial assumptions are compared to the latest outcome confirming the crack bridging ability of the GLARE reinforced frame.