Characterization of the cyclic hygroscopic aging behavior of balsa wood core bio‐composite sandwich structures with preexisting defects in laminate skins

Abstract Aimed at the decarbonization of marine structures under harsh humid environments, the present study explores the cyclic hygroscopic aging behavior of balsa wood core bio‐composite sandwich structures with manufacturing defects in Glass‐Fiber Reinforced‐Polymer (GFRP) skins. Both experimental investigations and analytical predictions are presented. Two distinct protocols were proposed to realize complete‐cycle and incomplete‐cycle absorption conditions of moisture, to characterize moisture diffusion mechanisms due to non‐Fickian effects. The Dual Fickian model was found to be effective in predicting moisture diffusion kinetics during absorption cycles, while the Fickian model demonstrated superior fit with the moisture desorption processes. Furthermore, the maximum moisture content of 13.80% after 33 days reveals that an 18 mm diameter hole in the skin of the GFRP‐balsa sandwich could result in a considerable water uptake, which cannot be neglected. However, it can be fully dried at 35 °C within 3 days. It indicates that balsa core sandwich structures possess notable repairability. Additionally, the significant impact of the initial desorption cycle on moisture diffusion coefficients in subsequent resorption cycles was highlighted to investigate the long‐term effects of cyclic moisture exposure on the properties of balsa core sandwich structures. Highlights Multiple aging cycles were performed to replicate harsh, humid environments. The Fickian model was employed to characterize moisture desorption behavior. Dual‐Fickian model was proven to predict moisture absorption mechanisms. Balsa wood was found to be a good candidate due to rapid repair capabilities. Effect of the first desorption cycle on resorption rates cannot be ignored.