Large-Area Fabrication of Ordered Micro-Indentation Arrays via Velocity-Matched 2D Elliptical-Vibration Dynamic Nanoindentation

Large-area ordered micro-indentation arrays are highly desirable for flexible pressure sensors and electronic skins, but their fabrication is often limited by the low throughput and poor scalability of conventional indentation-based methods. In this work, a velocity-matched dynamic nanoindentation approach is proposed for the continuous-feed fabrication of ordered micro-indentation arrays. A non-resonant two-dimensional elliptical vibration tool holder (2D-VTH) is developed to generate controllable elliptical trajectories, in which the horizontal vibration of the indenter is matched with the feed motion of the workpiece to enable continuous-feed texturing. Finite element simulations are performed to clarify the effects of the elliptical trajectory on stress evolution, plastic deformation, and pile-up behavior during indentation formation. The results indicate that more uniform indentation morphology can be achieved when the relative motion between the indenter and the workpiece is minimized in the feed direction. Experiments are conducted to evaluate the influences of feed velocity, phase difference, indentation depth, and spacing on feature morphology and array integrity. Under optimized conditions, a large-area ordered indentation array with a size of 12 mm × 10 mm is successfully fabricated on AL6061 alloy after surface leveling. In addition, a ring-shaped piezoelectric self-sensing unit is integrated into the tool holder for real-time process monitoring, and its signal envelope shows an approximately linear relationship with indentation depth within the stable contact regime. Finally, the fabricated arrays are replicated into PDMS/MWCNTs composite layers for the fabrication of piezoresistive flexible pressure sensors, achieving a sensitivity of 1.03 kPa⁻¹ below 5 kPa, response/recovery times of 28/23 ms, and reliable wrist-motion detection capability.