Effect of water immersion types on residual strength of impact-damaged CFRP honeycomb sandwich structures under hygrothermal aging conditions

This study experimentally investigates the long-term effects of marine (5% NaCl solution) and lacustrine (distilled water) hygrothermal environments on the mechanical properties of T300 carbon fiber/epoxy resin-based honeycomb sandwich structures. Edgewise compression (EC) and compression-after-impact (CAI) tests were conducted after various aging durations. The results show that the EC strength decreased by 37.23% and 42.46% for distilled water and the 5% NaCl solution, respectively, after 30-day immersion. The CAI strength demonstrated a two-stage decay, with an initial 38.54%–41.46% reduction after 30 days and progressing to 58.63%–61.32% after cyclic aging. In addition, the saline environment caused 3%–9% greater strength reduction than distilled water, although it resulted in a marginally higher retained compressive modulus. Furthermore, this study shows the nonlinear damage evolution characteristics of CFRP sandwich structures under coupled hygrothermal-mechanical loading, providing critical data support for the durability design and environmental adaptability assessment of amphibious aircraft structures.