Study of fatigue crack growth in lugs under spectrum loading

Optical fractography and special load sequencing were used to characterize the growth of naturally initiating fatigue cracks under FALSTAFF spectrum loading in lugs with bushes fitted to varying degrees of interference.The same technique was used to obtain a stress intensity calibration under constant amplitude loading. This calibration, combined with crack growth analysis using the hysteretic closure concept and Rainflow cycle count, correlated well with experimental observations of growth rate down to crack depth of 100 microns. Available analytical stress intensity solutions do not appear to explain observed high crack growth rates, particularly as crack size diminishes to part through dimensions