Analytical evaluation of the Stress Intensity Factor in stiffened sheets with multiple side damage

A closed form solution of the Stress Intensity Factor (SIF) for stiffened flat sheets, typically used in aircraft construction, in Multiple Site Damage (MSD) conditions, has been developed. The well-known theory of complex variable functions has been used, through the application of functions specifically developed for the case of cracks equally spaced and of equal length. Moreover, the superposition principle has been applied to evaluate the compression loads transmitted by the stringers through the rivets, by imposing the equilibrium on the crack free surfaces and the compatibility of displacements between sheet and stringers at the rivets location. The results have been compared with solutions available in the literature, obtained by combination of various analytical techniques and experimental methodologies, showing a good agreement. The proposed method is a reference for the validation of other numerical or analytical methods and effectively can replace the Finite Element Method for simple geometries.