Fatigue damage detection for advanced military aircraft structures

Abstract

Modern military aircraft are evolving into more sophisticated structures, with exotic new materials and stealthy designs. But in all of the advances, what is the implication for overhaul procedures and tooling? Looking at implementation of new technologies employed by the Air Force for the repair of aging F-16's, A-10's, KC-135's and C-130's, we can see how the new fleet of F-35's, F-22's and KC-46's will face certain unexpected challenges that deserve proper review and analysis. One primary concern is the widespread use of composite skins on the wings of fighter planes. There are several key advantages but few manufacturers have understood the complications from repairing these materials. For instance, on the F-16, the horizontal tail is made of carbon fiber riveted to aluminum subsurface. Besides the difficulties in finding the fractures, there are relatively few repair procedures for mitigating these problems like there are in classic sheet metal work. In this presentation, we analyze the most recent advances to address the overhaul concerns arising from composite skins in military aircraft. A cost analysis is presented to show the various reasons why composite skins may cause a headache for the military as the technology of detection and repair tries to catch up to these advanced new materials. Some computations will also be performed to show the reduction in strength over time for carbon fiber composites as compared to 7475 series aluminum. Simulations that focus on the growth of expected cracks that may escape NDI will be presented to show the difference in damage and fatigue life between the two materials and how current inspections will need to be improved to solve this difficult problem.