Stress intensity factor calibration for a longitudinal crack in a fuselage barrel and the bulging effect influence

摘要

Aircraft structures require minimum weight configurations with high strength in order to support all operational stresses with high reliability. Framework construction is the base of these airframes where cross sectional shapes are connected into a rigid assembly. The vertical and horizontal cross-members are arranged to withstand all structural loads and the skin to support the pressure gradient. This type of fuselage has been in use for about 80 years; it is very strong and relatively lightweight when used with materials of high specific strength. Due to the difficulty of producing defect free structures and to avoid damage during the life of a structure, damage tolerance is an important requirement. Damage tolerance is a design philosophy predominantly applied in the primary structural parts of civil airframes in order to tolerate a defect that can be detected and repaired during the next maintenance check. In this article, the stress intensity factor (SIF) for a longitudinal crack under the pressurization load was studied. For this purpose, a barrel composed of two frames with the longitudinal stiffeners and with the geometry usually found in civil airframes was chosen. A central crack, between the two frames, was simulated in a geometrically nonlinear finite element model composed by solid elements. The stress intensity factor for different crack lengths, until the crack tips reach the frame, was calculated using linear elastic fracture mechanics assumptions and the modified virtual crack closure technique. In addition, stress intensity factors along the skin thickness were determined. The variation of the SIF values along the thickness due to the bulging effect is modeled, and comparisons were made with the behavior of an equivalent reinforced flat panel.