CYCLE-BY-CYCLE ACCUMULATION ALGORITHM FOR PREDICTING FATIGUE LIVES OF BOX-CORNER BOLT AND STRINGER JOINT UNDER SPECTRUM LOADING

Fatigue tests are respectively carried out on box-corner bolts and stringer joints under spectrum loading, failure modes and mechanisms are investigated through SEM analysis, and fatigue crack growth lifetimes are determined from fractographic-quantitatively-interpreted data by using the reverse inference method. From the nominal stress method, a fatigue S-N-K_TE (stress-life-stress concentration factor) surface model is developed to characterize the fatigue characteristic of complex jointed structures, and the cycle-by-cycle accumulation algorithm is developed for predicting the fatigue lifetimes and crack growth lifetimes of jointed structures subjected to random spectrum loading. Finally, a new model and an algorithm are used to predict the fatigue lives of box-corner bolts and stringer joints under spectrum loading, demonstrating good agreements between the predictions and experiments.