Stored energy density research on the fatigue crack initiation at twin boundary and life prediction of Inconel718 superalloy

•The back-stress-based stored energy density could serve as a valid indication of crack initiation.•The activation of the slip system parallel to the TB and the absence of γ'' near the TB, were the root cause for fatigue crack initiation of IN718 alloy.•The back-stress-based stored energy density could be used in life prediction in HCF and VHCF regimes.