Integrity of aircraft structural elements with multi-site fatigue damage

Abstract

Integrity evaluation of aging structures is extremely important to ensure economic and safe operation of the flight vehicle. A two step analytical approach has been developed to estimate the residual strength of pressurized fuselage stiffened shell panels with multi-bay fatigue cracking. A Global Finite Element Analysis is first carried out to obtain the load flow pattern through the damaged panel. This is followed by the Schwartz-Neumann Alternating Method for local analysis to obtain crack tip stresses and the relevant crack tip parameters that govern the onset of fracture. Static residual strength is evaluated using fracture mechanics based, as well as net section yield based, criteria. The presence of holes, with or without Multi-Site Damage (MSD), ahead of a dominant crack is found to significantly degrade the capacity of the fuselage structure to sustain static internal pressure. An Elastic-Plastic Alternating Method has been developed and applied, to evaluate the residual strength of flat panels with multiple cracks. The computational methodologies presented herein are marked improvements to the present state-of-the-art, and are extremely efficient, both from engineering man-power, as well as computational costs, points of view.