Effecting rate-dependent behavior with friction based geometrical design

This work investigates whether the architecture of a unit cell, rather than the properties of its base material, can govern strain rate sensitive behavior. We focus on additively manufactured Ti6Al4V, a lightweight titanium alloy with weak intrinsic rate sensitivity, and employ it to fabricate friction unit cells. The friction cell redirects compressive loads into frictional sliding between internal surfaces produced by the LPBF (Laser Powder Bed Fusion) process. Structural characterization from quasi-static (0.01 /s) to crash-relevant strain rates (500 /s) reveals a factor of 2.5 increase in peak stress, substantially exceeding the rate sensitivity of the base material. To identify the mechanism, the dynamic friction coefficient of the as-built Ti6Al4V tribo-pair is measured across sliding velocities from 0.01 to 8 m/s at 7.5 MPa and up to 6.5 m/s at 40 MPa. The kinetic friction coefficient more than doubles between the quasi-static plateau and the crash-relevant regime. Correlating the structural and tribological data establishes velocity-strengthening interfacial friction as the dominant mechanism behind the pronounced rate sensitivity of the friction cell. These results show that meso-scale friction, embedded through unit cell geometry and surface morphology, can dictate crash-relevant rate sensitivity that the base material alone does not possess.