Blast protection of underwater tunnels with 3D auxetic materials

In recent years, the risk of blast attacks on underwater tunnels, important transportation routes, has increased due to the growing prevalence of vicious regional conflicts and global terrorist activities. In this work, we investigate the blast impact behavior of underwater tunnels filled with honeycomb core and covered by solid panels. The core is composed of 3D auxetic materials with high energy absorption compared to conventional honeycombs. In order to improve the stiffness of the auxetic structures, a pair of crossed rods is introduce to each cell. The relative densities of 3D auxetic structures are derived theoretically. The coupling effects of the geometrical parameters on the relative density are investigated. Then the deformation patterns of the underwater tunnels at different blast heights are analyzed. The kinetic energy and absorbed energy are discussed for tunnels with 3D auxetic materials and solid materials. Results show that tunnels composed with 3D reinforced auxetic structures can absorb much more energy than solid ones. Moreover, localized damage is observed which means greater chance of survival and smaller repairs after extreme impact. Finally, a stiffness-improved 3D reinforced auxetic structure is presented to enhance the tunnel’s strength and stability further.