Design and analysis of a re-entrant honeycomb resonator structure for mechanical and acoustic protection in rocket fairings

In this study, a novel re-entrant honeycomb resonator structure (RHRS) based on the Helmholtz resonator theory and negative-Poisson's-ratio structures was developed by integrating an enhanced bending modulus and energy absorption with sound absorption capabilities to satisfy the multifunctional protection requirements of rocket fairings. Mechanical and acoustic test specimens were fabricated using three-dimensional printing, and three-point bending and impedance tube experiments were conducted. The bending and sound absorption performances of the RHRS were assessed by performing a combination of theoretical analyses, experimental tests, and numerical simulations to validate the effectiveness of the theoretical design and finite element model. The results revealed that compared with the two conventional honeycomb structures, the RHRS exhibited enhanced bending performance, with a specific energy absorption increase of 10.79–14.42 % when the resonator cells were positioned on the non-load-bearing side. In terms of sound absorption, the resonance frequencies observed in the theoretical, experimental, and simulation results showed excellent consistency, confirming the efficacy of the RHRS in noise reduction. Although variations in the resonator dimensions had minimal impact on the mechanical performance, the acoustic resonance frequency increased with the neck tube diameter and decreased with the neck tube length. The coupling effect of multi-RHRSs expanded the sound absorption bandwidth to 632–771 Hz, and the sound absorption mechanism of the RHRS was analyzed using relative impedance. The RHRS demonstrated promising mechanical properties and can be further optimized for noise reduction within specific frequency ranges; thus, it offers valuable insights into the design and application of multifunctional structures.