Ultra-high mechanical damping in nanopillar arrays of Cu–Al–Ni shape memory alloys: Experimental and computational approaches

• Nanopillar arrays exhibit ultra-high mechanical damping at the nanoscale. • Finite element modeling captures ideal and misaligned damping behavior. • Ultra-high damping is scalable by increasing the surface of nanopillar arrays. • High-density nanopillar arrays enable designing metasurfaces for energy dissipation. Nanostructured mechanical dampers are increasingly required in micro- and nano-electromechanical systems due to the stringent vibration constraints imposed by emerging sensing and communication technologies. This work investigates the mechanical damping performance of nanopillar arrays fabricated from a Cu–Al–Ni shape memory alloy (SMA), focusing on their collective superelastic response under in-situ nanocompression tests at the scanning electron microscope. Nanopillars are arranged in 4 × 4 and 7 × 7 arrays milled by focused ion beam. Nanopillar arrays retain an ultra-high collective damping capacity of approximately ψ=0.40, even after extensive cycling. Finite element simulations, using the Souza–Auricchio model, were used to analyze the damping behavior of the arrays. Under ideal alignment, the simulations predict simultaneous transformation of all pillars, consistent with the expected collective behavior. The same simulation method allows associate the stepped hysteresis loop, experimentally observed in the 4 × 4 array, with a geometric misalignment of the loading punch. Scaling to a denser 7 × 7 configuration preserves the ultra-high damping capacity while enabling substantially higher load-bearing capability. These findings demonstrate that SMA nanopillar arrays function as mechanically dissipative metasurfaces whose performance can be engineered through geometric design, providing a robust platform for developing ultrahigh-damping metasurfaces and mechanically active metamaterials for next-generation vibration-control technologies.