Influence of bending patterns on soft tribology

Soft tribology is of increasing importance given the usage of deformable materials in robotics, haptics, and biomechanics studies. The introduction of microscale patterns to soft surfaces in fully flooded conditions changes the elastohydrodynamic lubrication (EHL) friction. We previously showed that soft patterns introduce local friction peaks at the micro- to macro-EHL transition, μ_c. Despite these advances, the effect of pattern bending on frictional behavior is not well understood. To investigate the influence of bending on EHL friction, we fabricate elastomer patterns consisting of stripes of varying height-to-width aspect ratios c/a. The space between the stripes is held constant. We find that when c/a < 0.75, the aspect ratio has no influence on μ_c while c/a > 0.75 results in a power-law decrease in μ_c. To explain this phenomenon, we employ cantilever beam theory and empirical statistical regression. Both models show that the reduction in μ_c is a result of larger bending angles of the stripes as their aspect ratios increase. These results suggest that significant bending of tall and slender patterns leads to a reduction in the effective load-bearing surface area of the stripes in the micro-EHL regime.