High-cycle and very-high-cycle fatigue properties of CFRP-aramid honeycomb sandwich structure in three-point bending

Abstract In this study, the high-cycle and very-high-cycle fatigue properties of carbon fiber reinforced plastic (CFRP)-aramid honeycomb sandwich structure, which is a commonly used structure in aviation industry, are examined under two different core directions using the ultrasonic three-point bending fatigue test. Further, the fatigue failure modes and damage mechanism of the structure are revealed. The results show that the fatigue stiffness degradation curve of the honeycomb sandwich structure exhibits three different trends: continuous decline, two horizontal regions and two reduction regions, and two horizontal regions and one reduction region. The shape of the stiffness degradation curve is affected by the direction of core. The S-N curve presents a double-linear decline feature, and there is no traditional fatigue limit. The fatigue life of the specimen is related to the type of stiffness degradation. The optical microscopy images show that the main failure modes of specimens are core wrinkles, core cracks, and face delamination. Overall, based on the stiffness degradation curve, failure modes, and real-time images of the test specimens, the damage evolution process and the corresponding mechanism of the honeycomb sandwich structure are analyzed to conclude that the core has multi-point failure damage characteristics.