# A Tunable Metamaterial Joint for Mechanical Shock Applications Inspired by Carbon Nanotubes
## 1 Introduction
For example, using appropriate microstructural patterns and architectures, special metamaterial-based components may be created, which, for example, are capable of transforming an axial deformation response to a twisting one [19], or a brittle behavior to a ductile one [20]. As there is a great demand for new protective solutions under vibration or shock types of loadings, special attention is paid to the development of metamaterials that are capable of absorbing energy and present excellent damping properties [21]. In an interesting study, [PERSON] et al. [22] synthetically investigated a series of 3D double-arrow-head auxetic structures made from a carbon fiber-reinforced polymer. The damping performance of the specimens was characterized by compressive loading-unloading tests and sine sweep frequency experiments. In the theoretical framework, [PERSON] and [PERSON] [23] performed systematical simulations of uniform functionally graded double arrowhead honeycombs subject to different impact velocities to reveal their improved energy absorption capacity under high-velocity impacts. [PERSON] et al. [24] focused on both the experimental and numerical investigation of carbon fiber composite auvetic double-arrow corrugated sandwich panels with enhanced vibration damping. Regarding the macro-scale, [PERSON] et al. [25] studied large-scale mechanical metamaterials offering protection against seismic waves of specific frequency ranges. Furthermore, they proposed optimal designs via the exploration of various metamaterial formations by combining phononic crystals and locally resonant structures. Similarly, [PERSON] et al. [26] used a unit cell method including damping to investigate the complex dispersion curves of a locally resonant metamaterial design. The outcome was validated through corresponding experimental measurements, while it was illustrated that locally resonant metamaterials show great potential for use in noise and vibration applications. Several research efforts were made in the field of impact-resistant metamaterials as well. Characteristically, [PERSON] et al. [27] investigated the nonlinear response of 3D-printed polylactic acid (PLA) honeycomb structures to analyze their energy absorption capabilities when utilized as the core component of sacrificial claddings. Similarly, [PERSON] et al. [28] studied the low-velocity impact response of 3D-printed layered structures made of thermoplastic materials such as PLA and polyethylene terephthalate glycol (PETg). They showed that the use of honeycomb and auxetic structures as a core may lead to the development of advanced sacrificial shells for impact protection. Finally, after conducting comprehensive research based on both experimental and FE predictions, [PERSON] et al. [29] provided new designs of a new class of shell lattice, stretching-dominated, mechanical metamaterial that can absorb high-energy shocks by simultaneously retaining a low density. Despite the fact that there have been numerous attempts to characterize metamaterials of various configurations and base materials, their capabilities when used as machine elements or components have not been tested to the same extent. In the present study, a new design of a metamaterial-based mechanical joint is proposed, which is capable of absorbing energy under impact or vibration loadings. In an effort to create a metamaterial component that is ultra-stiff, ultra-strong, and possesses high specific energy absorption at low relative density, the proposed architecture of the joint is inspired by the hexagonal lattice of CNTs, while the used material is a polyurethane-based ultraviolet (UV) sensitive resin of a high inherent material damping. The cylindrical and periodical hexagonal lattices of the load-carrying components of the joint are formed in such a way as to enable the partial conversion of compressive deformations to rotational motion of a cylindrical mass. This inertia disk is inserted and attached between two opposing triple-wall CNT-like tubular wireframes.