Fatigue Lifetime Events Detected Using Acoustic Emission Technique

Fatigue crack initiation and growth process of model AA7075-T6 subjected to simulated marine environment and varying stress ratio is studied using acoustic emission technique.The results indicate a significant reduction in crack initiation and overall lifetime when specimens were tested in the presence of marine environment, while an increase in fatigue life was observed as a function of increasing stress ratio.SEM fracture surface analysis exhibited intergranular, transgranular and cleavage as modes of failure.In general terms, Cleavage fracture produce lower AE signal amplitude, whereas, transgranular tearing produces an increment of signals amplitude.However, the correlation between those modes of failure with the AE results can be cumbersome since the AE signals are highly dependent upon the loading and environmental testing conditions.