Analysis of the Critical Threshold Stress of Hybrid Metamaterial for Bulkheads in GFRP Hulls

This study investigates the critical threshold of a hybrid metamaterial designed to optimize bulkhead reinforcements in GFRP hulls. A quantitative experimental approach was employed, analyzing five specimens without the metamaterial and five modified with a corrugated brass core. The specimens underwent Mode II interlaminar shear tests to analyze delamination. Data from these tests were interpreted using the Cohesive Zone Model (CZM) to characterize fracture energy and interfacial tensile strength. The results demonstrate that the hybrid specimens exhibit superior effective tangential stiffness and steeper load-displacement slopes compared to the GFRP-only specimens. Notably, the modified specimens reached a critical load up to 1.5 times higher than the typical specimens. Although initially showing lower energy dissipation due to their stiffness, they surpassed the fracture energy of the control specimens at larger local separations, activating dissipation mechanisms through metal-polymer interaction. Microscopic analysis confirmed more tortuous and irregular damage pathways in the metamaterial, validating a less brittle behavior. It is concluded that this hybrid configuration represents a viable alternative for naval engineering, improving structural strength without compromising the system's lightness.