Multifunctional cylindrical shell structure comprising metamaterial with mechanical load-bearing and ultra-low frequency broadband characteristics

The deep-sea submersible is an important part of oceanic equipment, where special operating environment must require the outer material to have multi-functional physical properties such as pressure-resistant, buckling, and sound and vibration suppression. A new type of Positive or Negative Poisson’s ratio metamaterial with excellent mechanical load-bearing properties and ultra-low frequency broadband characteristics is proposed in this paper. Compared with the conventional Poisson’s ratio structure, the proposed metamaterial is based on the designability of the local resonance theory, and the subwavelength structure is periodically embedded in the porous Poisson’s ratio structure, so that it has excellent static and dynamic properties. The buckling and underwater bearing characteristics of the designed model and its microscopic deformation mechanism are systematically discussed，and the propagation characteristics of P-wave and S-wave in the designed models are investigated in detail. The results show that compared to the conventional models, the metamaterials based on PMMA can safely withstand the hydrostatic pressure of nearly 7 MPa, where structural strength is increased by nearly 2 times. In addition, the proposed metamaterials can open a lower (the normalized frequency Ω as low as 0.013) and wider (the bandwidth ratio can be as high as 83.50%) bandgap, which is due to the coupling of traveling waves and subwavelength units. It is worth noting that within the studied hydrostatic pressure range of 0.1 MPa-5 MPa, the change of bandgap characteristics in the proposed metamaterial is weak, which directly characterizes the bandgap robustness and hydrostatic pressure insensitivity in the sea-water environment. This work verifies the feasibility of the coupling design of local resonance theory and porous structures and provides theoretical support and technical guidance for the design of external plates and shells with multi-functional marine such as hydrostatic pressure-resistant and underwater acoustic-vibration suppression.