Design and Analysis of Crack Stopper

Abstract

One of the fail-safe design features is the two-bay crack arrest capability of the airframe. In particular two-bay longitudinal and two-bay circumferential crack arrest feature is the main aspect of design for damage tolerance of the pressurized fuselage cabin. Under fuselage pressurization load cycles fatigue cracks develop at location of maximum tensile stress. There are locations on the airframe which are favorable for the initiation of longitudinal cracks and other locations for circumferential cracks. This investigation identifies one such location from where a longitudinal crack can initiate and studies the fast fracture and crack arrest features under the action of uni-axial hoop stress. The main crack arresting features are the bulkheads and crack stopper straps. A finite element modeling and analysis approach will be used for a realistic consideration of bulkheads and crack stopper straps and their role in the two-bay crack arrest capability of the aircraft. In particular through a stress analysis at a hoop stress corresponding to the design limit load, the load carrying ability of the bulkheads and the crack stopper straps will be assessed. For a realistic representation of two-bay cracking scenario it will be examined under what condition a two-bay crack can be arrested. For the evaluation of crack arrest capability of bulkheads in the stiffened panel with and without the presence of tear strap is studied. The SIF(stress intensity factor) value for different crack length is calculated by analytical (FEM) method.