Growth of Multiple Cracks and Their Linkup in a Fuselage Lap Joint

An issue of concern in aging aircraft is the growth of multiple cracks emanating from a row of fastener holes, typically in a pressurized aircraft fuselage lap splice. This multisite damage (MSB), or widespread fatigue damage, if allowed to progress, can suddenly become catastrophic. The understanding of the failure behavior dictates the level of compromise between safety and economy. The complexity of the structure due to various stiffening elements makes it unamenable to a simple direct analysis. A two-step elastic finite element fatigue analysis combining a conventional finite element method and the Schwartz-Neumann alternating method with analytical solutions is developed to understand fatigue growth of multiple cracks and to obtain a first estimate of the residual life of a stiffened fuselage shell structure with MSD in the riveted lap joint. The analysis procedure is validated by simulating a laboratory fatigue test on a lap joint in a flat coupon. Both the coupon and the shell panel are found to have fatigue lives only up to the first linkup of neighboring crack tips.