Lightweight Multifunctional Lattice Materials with Enhanced Impact Energy and Vibration Dissipation Properties for Space Structures

By engineering their local architecture, lattice materials can be tailored to provide excellent mechanical properties while exhibiting several desirable multifunctional properties of direct relevance to space exploration system design. However, though their high stiffness to weight ratio makes them ideal for mass reduction applications, it also makes them more sensitive to vibrations induced due to orbital debris impact. To dissipate the resulting impact energy, current state-of-the-art lattice materials rely on plastic deformation modes such as the local buckling or crushing of the lattice components. Such deformation modes are not only infeasible for lattice core panels attached internally to outer mold line skins, but also unrealistic for internal and external secondary structures used for supporting sensitive equipment and spacecraft appendages such as solar arrays, radiators, and debris shields. Thus, improving the energy dissipation properties of lattice materials without a significantly increasing their mass remains a key challenge towards their wider adoption for space applications. To address this challenge, we are focused on the development of next-generation lattice materials based on the concept of acoustic metamaterials and phononic structures. Acoustic metamaterials utilize the localized resonance of substructures added to the host structure to restrict the propagation of incident waves within frequency bands known as local resonance (LR) band gaps. Thus, the dynamic behavior of the metamaterial can be controlled by adjusting the behavior of the local resonant subsystem. The cellular architecture of lattice materials provides an excellent framework for the integration of locally resonant trusses for generating LR band gaps. Further, their periodic architecture causes interference effects which result in additional wave attenuation frequency regions classically referred to as phononic or Bragg band gaps. Formation of LR and phononic band gaps offers the possibility of effectively dissipating incident energy due to orbital debris impact without inducing irreversible plastic deformation in the lattice material.

Elastic Wave Attenuation in Hierarchical Structures

The aim of this research is to investigate the dynamic effects of inserting locally resonating elements into sandwich cores. Addition of such resonating elements allows the creation of a wave attenuation which may be tuned for a particular application by choosing the appropriate resonator parameters. A Timoshenko beam model is utilized to model the behavior of such sandwich beams. If modeled as a homogeneous elastic solid, the mass density of such a structure is found to be frequency dependent and it achieves negative values in certain frequency range. Sandwich beams with internal resonators may thus be treated as acoustic metamaterials and may be used to tailor the wave motion and produce anisotropic band gap structures. The presence of such a wave attenuation band gap has been demonstrated experimentally. It was also shown that such structures can be successfully deployed to improve the dynamic behavior of sandwich structures under hull slamming conditions as well as impact loads.

Bandgaps in Meta-Phononic Structures

Typically, in structures containing local resonators, the resonators are embedded with a certain periodicity for manufacturing ease as well as to make analysis easier. Periodicity of the resonators allows for the creation of another wave attenuation band gap which is commonly referred to as a "Bragg" band gap. Thus, in order to completely understand the effect of addition of locally resonating elements to a structure, it is important to understand the effect of their inherent periodicity. This is accomplished by using various analytical methods such as the phased-array method, the transfer matrix method, etc. It is demonstrated that the periodicity of the resonating elements causes a change in the band structure and allows for further tailoring of the wave attenuation zones by tailoring the resonator parameters. The effect of addition of multiple resonators, with the same periodicity or with different periodicities is currently being investigated. A better understanding of the interaction between such band gaps could lead to structures exhibiting extremely wide wave attenuation zones and offering attractive dynamic properties without a significant mass penalty.

Collaborators: Prof. C. T. Sun (Purdue University)

Project Sponsor: Office of Naval Research

Dynamic Behavior of Sandwich Beams with Resonator Embedded Cores

The aim of this research is to investigate the dynamic effects of inserting locally resonating elements into sandwich cores. Addition of such resonating elements allows the creation of a wave attenuation which may be tuned for a particular application by choosing the appropriate resonator parameters. A Timoshenko beam model is utilized to model the behavior of such sandwich beams. If modeled as a homogeneous elastic solid, the mass density of such a structure is found to be frequency dependent and it achieves negative values in certain frequency range. Sandwich beams with internal resonators may thus be treated as acoustic metamaterials and may be used to tailor the wave motion and produce anisotropic band gap structures. The presence of such a wave attenuation band gap has been demonstrated experimentally. It was also shown that such structures can be successfully deployed to improve the dynamic behavior of sandwich structures under hull slamming conditions as well as impact loads.

Collaborators: Prof. C.T. Sun (Purdue University), Dr. J. S. Chen (National Cheng Kung University)

Project Sponsor: Office of Naval Research

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