Vibration Reduction of Sandwich Composites Via 3-D Manufactured Acoustic Metamaterial Cores

Open Access
Author:
Yu, Tianliang
Graduate Program:
Aerospace Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
None
Committee Members:
  • George A Lesieutre, Thesis Advisor
Keywords:
  • Vibration reduction
  • acoustic metamaterial
  • sandwich panel
  • 3-D manufacture
Abstract:
Sandwich panels are often used as aerospace structures where high stiffness-to-weight is required, such as aircraft fuselage shells. Interior noise reduction in aircraft using such panels is a challenge because acoustic attenuation is reduced for light, stiff composite structures, especially those manufactured to have fewer mechanical joints. Conventional strain-based damping approaches are not effective over a broad range of operating temperatures, and are also reduced in effectiveness by the presence of tensile pressure loads. Acoustic meta-materials offer an approach to reducing the dynamic response of, and noise transmission through, sandwich panels. The key concept underlying this approach is to consider the meta-materials as a highly-distributed system of tuned vibration absorbers that introduces one or more stop bands in which range the response of the global structure is reduced. The resonance frequencies of the absorber system may be tuned to match an excitation frequency (or a range of excitation frequencies) and / or to match one or more global resonance frequencies. Using the assumed-modes method, a meta-material system was designed to be integrated into the honeycomb core of a representative sandwich panel. To determine the dynamic response of the global sandwich panel, the meta-material system was modeled as an effective distributed complex mass. The cores for two sandwich panels were fabricated using 3-D printing technology, using a stiff polymer for the baseline honeycomb core, and a combination of a stiff and soft/lossy polymers for the meta-material-augmented core. The two cores were characterized statically to determine effective elastic properties, and dynamically to determine the natural frequencies and loss factors of the meta-material system. Unidirectional carbon-fiber face sheets were bonded to both cores to construct sandwich panels. The sandwich panels were tested dynamically for two different boundary conditions, cantilevered and free-free. Experimental results confirmed that the vibration absorbers reduced the peak responses near the natural frequencies of the meta-material system; multiple well-separated local modes of the meta-material system turned out to be significant. Future work will address broadband damping by tuning the local natural frequencies of the meta-material system over a range of design frequencies, and distributing the mass of the system optimally over the global sandwich panel for the modes of interest.