Volume 4, Issue 2 (February 2007)
Fatigue Crack Growth Analyses of Aerospace Threaded Fasteners—Part I: State-of-Practice Bolt Crack Growth Analyses Methods
To perform accurate crack growth analyses on roll-threaded fasteners, aerospace designers are required to estimate fatigue crack growth in the threads of a nut-loaded, roll-threaded bolt under tensile fatigue conditions. Threaded fasteners are difficult to analyze due to their asymmetrical geometry and fastener fatigue crack growth data are scant, especially for nondimensionalized crack depths of (a/d)<0.1. Thus, aerospace designers must make simplifying assumptions and perform analyses with presumably conservative methods. History has shown that improper design assumptions/methods on other critical aircraft components has led to catastrophic failures. Because many fasteners are flight safety critical, their analyses must be accurate. Five leading methods to determine the stress intensity multiplication factor, Y(a/d), for threaded fasteners, based on experimental data, analytic equations, or FE methods, or a combination there of, are compared. By comparing and considering these five methods together, critical observations are made to guide future research based on these state-of-practice Y(a/d) solution methods.