Investigation of the Flatwise Compressive Behavior of Hollow Glass Microsphere‐Filled Nomex Honeycomb <scp>CFRP</scp> Sandwich Structures

ABSTRACT The rapid development of deep‐sea exploration has increased the demand for lightweight materials with high load‐bearing capacity and energy absorption under compressive loading. In this study, the mechanical response of conventional carbon fiber‐reinforced polymer (CFRP)–Nomex honeycomb sandwich structures was enhanced by filling the honeycomb core with hollow glass microspheres (HGM). Three configurations were investigated: an HGM syntactic foam with CFRP skins (HC), a Nomex honeycomb core with CFRP skins (NC), and an HGM‐filled Nomex honeycomb core with CFRP skins (NHC). Flatwise compression experiments and finite element analysis were conducted to quantify compressive strength and energy absorption, and artificial seawater immersion tests (6‐day exposure) were performed to evaluate the retention of stiffness and peak compressive load. The results show that NHC exhibits the highest compressive strength, achieving a 308% increase in compressive strength compared with NC. NHC also demonstrates superior energy absorption (109 J) relative to HC (44.7 J) and NC (5.52 J), corresponding to an approximately 19‐fold increase in specific energy absorption. Following the artificial seawater immersion, NHC retains stiffness and compressive performance more effectively than NC. These findings indicate that HGM‐filled Nomex honeycomb CFRP sandwich structures represent a promising approach for lightweight, energy‐absorbing core design with potential applicability in deep‐sea engineering.