Multifunctional auxetic re-entrant metastructure for low-frequency broadband sound absorption and energy absorption

For sound-absorbing structures, previous studies generally focused only on their sound-absorbing, resulting in limited application in practical engineering. In this work, leveraging the excellent energy absorption properties of auxetic re-entrant metamaterials, a multifunctional auxetic re-entrant metastructure (MARM) with lowfrequency broadband sound absorption and high energy absorption is proposed. The re-entrant cavity with internally extended tubes as a unit cell. Firstly, using the mechanism of Helmholtz weak resonance, the diameter and length of the tube are adjusted to obtain better low-frequency sound absorption. It has been demonstrated systematically through experimental, numerical, and theoretical methods, that the average sound absorption coefficient of MARM is 0.9 at 330-500 Hz and a deep-subwavelength thickness of 40 mm. Secondly, the lowfrequency sound absorption of the MARM was researched by filling the porous materials and adjusting the thickness of the structure. Finally, the MARM was compressed both in-plane and out-of-plane through quasistatic compression and numerical, and the results show that the energy absorption of the MARM, in-plane reaches 8,000 kJ/m3 and out-of-plane reaches 14,000 kJ/m3 when the strain of the structure is 0.6. This research not only provides a method for designing multifunctional metamaterials but also has a good potential for application in the fields of transportation and engineering.