Two-stage cumulative bending fatigue behavior for the adhesively bonded aluminum honeycomb sandwich panels

This study experimentally investigates two-stage cumulative bending fatigue behavior of adhesively bonded aluminum sandwich panels with local indentation failure mode. Experimental results show that the sums of cycle ratios of both stages are larger and less than unity when their loading sequence is low-to-high and high-to-low, respectively. The Miner’s rule fails to predict the loading sequence effect observed in cumulative fatigue tests. The variations in stiffness and residual strength of the studied specimens with the applied cycles in the constant-amplitude fatigue tests were also observed and recorded. Furthermore, the non-linear damage rule, which is based on the stiffness degradation of the specimens, provides better prediction of the remaining fatigue lives in the second stage than the traditional linear damage rule. However, the residual strength remains almost constant until the final stage of the constant-amplitude fatigue tests, demonstrating that residual strength is not a suitable indicator of non-linear damage in predicting the cumulative fatigue lives.