Fatigue tolerant multifunctional pentamode materials with simultaneous acoustic invisibility and vibration isolation

Abstract

Multifunctional metamaterials with simultaneous acoustic stealth and vibration attenuation capacities are greatly needed in underwater applications. Pentamode metamaterial is firstly proposed as a novel mechanical metamaterial, whose fluid-like properties make it very promising in broadband acoustic stealth applications and are widely investigated nowadays. But the practical engineering applications of pentamode metamaterials also need to satisfy the requirements of harsh environments such as fatigue durability, environmental adaptability, etc., which are rarely reported. In this study, a novel fatigue tolerant multiphase pentamode metamaterial configuration consists of metallic lattice, additional mass blocks and interconnecting polymer materials is proposed. Taking water as the designing target, both single-phase and multiphase pentamode prototypes are designed, fabricated and experimentally verified. The two prototypes exhibit similar acoustic stealth properties, while the multiphase prototypes demonstrated superior vibration isolation performance. Moreover, the acoustic and vibration isolation performances of two fabricated samples after fatigue loading of 1000 cycles and 2000 cycles are also studied. The single-phase pentamode metamaterial prototype exhibits obvious shear band deformation under fatigue loading of 2000 cycles with a loading amplitude of 1 MPa and lead to deteriorated acoustic stealth performances. While the multiphase pentamode prototype demonstrates no obvious sign of deformation after fatigue loading of 2000 cycles under a loading amplitude of 1.5 MPa, wherein the acoustic and vibration performances are not affected. The multiphase PMs offer a new avenue to tackle the issue of durability and functional limitations of existing underwater acoustic metamaterials.