Analytical methodology for predicting widespread fatigue damage onset in fuselage structure

A comprehensive analytical methodology has been developed for predicting the onset of widespread fatigue damage (WFD) in fuselage structure, The determination of the number of flights and operational hours of aircraft service life that are related to the onset of WFD includes analyses for crack initiation, fatigue crack growth, and residual strength. Therefore, the computational capability required to predict analytically the onset of WFD must be able to represent a wide range of crack sizes, from the material (microscale) level to the global (structural-scale) level. The results of carefully conducted teardown examinations of aircraft components indicate that fatigue crack behavior can be represented conveniently by the following three analysis scales: 1) small three-dimensional cracks at the microscale level, 2) through-the-thickness two-dimensional cracks at the local structural level, and 3) long cracks at the global structural level. The computational requirements for each of these three analysis scales are described in this paper.