Effect of crack plane orientations on damage tolerant fatigue life of critical aerospace structures

Damage tolerance analysis is the latest technique to ensure structural integrity and estimate service life of aerospace structures. The basic parameters which affect the fatigue life of load bearing members are the material properties, dynamic loading spectrum and geometry of the initial cracks. In this research work, the initial cracks on different geometrical orientations of metallic materials have been investigated from fatigue point of view. Experimental and computational analyses were performed on aerospace grade aluminum alloys 7075-T6 and 2219-T6 with different crack plane orientations to compare the fatigue behavior. Crack plane orientation of the actual fractured part of an aircraft store was accurately identified using scanning electron microscopy. The material properties related to static and fatigue strength, were also determined on different standard plane orientations through extensive laboratory testing. Finally, the crack growth simulations were performed using linear elastic fracture mechanics laws to declare the fatigue life of each test case. Six possible orientation combinations have been investigated. On the basis of NASGRO fatigue model, the worst case scenarios of fatigue cracks at critical structural locations of an airborne store have been identified for periodic inspections and safety. This work provides the new dimensions to conventional aircraft structural integrity programs.