Stress Analysis of Fuselage Frame with Wing Attachment Beam and Fatigue Damage Estimation

Abstract

Airframe is a built-up structure. Fatigue cracks are bound to occur at maximum tensile stress locations. Fatigue cracks due to fluctuating loads are common problems experienced during service life of the aircraft. Cracks are allowed in the aircraft, but they should not lead to catastrophic failure of the structure. Fatigue cracking locations are identified through linear static stress analysis of the structure. Wings are the major components of the airframe. Spars in the wing carry most of the bending due to lift load during flight. Wings will almost behave like cantilever structures. Therefore, the maximum bending moment will be at the root. Wings are attached to the fuselage structure through attachment brackets. The bending moment and shear loads from the wing are transferred to the fuselage through the attachment brackets. The current project includes the linear static analysis of the bulkhead frames along with spar beam and fatigue damage estimation at the critical location due to fluctuating loads. Lug-holes and bolt-holes are likely to experience more stress due to high stress concentration. Stress analysis will be carried out finite element method. A local analysis will be carried out to capture high stress magnitude and stress distribution. Airframe experiences variable loading during flight conditions. A typical transport aircraft load spectrum will be used for fatigue damage calculation. In a metallic structure fatigue manifests itself in the form of a crack, which propagates. If the crack in a critical location goes unnoticed it could lead to a catastrophic failure of the airframe. Fatigue damage estimation will be carried out using constant amplitude S-N data for various stress ratios and local stress history at stress concentration.