Research on the Scatter of Structural Load-Time History in a Fleet

Scatter of structural fatigue life is mainly caused by the variability in structures and load-time histories. To study the scatter of structural load-time history of aircrafts in a fleet, this research is focused on analysis of operational load spectra at four typical structure details, of which representative coupon fatigue tests have been carried out. First, operational load-time histories at critical locations in question of each aircraft are obtained according to the flight-data based load equation and transfer function relating the monitored load to the critical location stresses. Then, the fatigue notch coefficient in local stress-strain method is calibrated and validated by representative coupon test data and then used to calculate fatigue damage under different structural load-time histories of each aircraft. Finally, statistical analysis of the fatigue damages is conducted on the assumption of log-normal distribution and scatter factor are obtained. It has indicated that there are significant differences in the scatter factor of different structural load-time histories. It may be advisable to fully consider the differences of scatter factor among different structures in structure fatigue life assessment.