Fatigue damage accumulation of sandwich panels with glass/polypropylene faces and aluminum foam core under two-stage cyclic flexural loading

The two-stage cumulative flexural fatigue behavior of sandwich beams with glass/polypropylene (PP) faces and aluminum (Al) foam core was experimentally analyzed to study the loading sequence effect of the studied innovative sandwich composites subjected to variable-amplitude cyclic loading. The constant amplitude load-life curve was established first for reference. Subsequently, the two-stage cumulative fatigue tests were performed, and the high/low loading sequence and cycle ratio of the first stage were used as experimental variables in the cumulative fatigue tests. Experimental results showed that the sum of the cycle ratios of the two stages for all cases was approximately 1.3. Furthermore, the loading sequence effect was slight. Because the interaction of damage evolution for the two stages was nonsignificant, the different failure modes for the high- and low-loading levels contributed to the high sums of cycle ratios.