Fatigue characteristics of foam core sandwich composites

In situ AE and post test microscopic analysis of quasi-static and flexural fatigue testing of sandwich composites indicated core damage to be the predominant failure activity while fiber rupture served as a precursor to catastrophic failure. Multiple crack initiation sites were observed under fatigue loading conditions in the vicinity of the notch tip. Both modes I and II cracking was observed in the core and along the interface between the core and the facesheets. Flexural fatigue life was found to be beyond a 500,000 cycle arbitrarily established cutoff below 75% of the ultimate static load. A statistical model based on experimental lifetime and corresponding AE data was developed to quantify the extent of damage; a reasonably good correlation with the experimental results has been obtained.