Asymmetric surface textures decrease friction with Newtonian fluids in full film lubricated sliding contact

• A calibrated experimental setup avoids misinterpretation of friction reduction.
• Depth-profile symmetry must be broken for textures to produce normal force.
• Surface textures reduce shear stress and produce normal forces from viscous effects.
• An optimal asymmetry angle exists for decreasing friction in lubricated sliding.

Surface texturing can decrease friction in lubricated sliding contact. The majority of existing experimental work has focused on symmetric-depth-profile surface textures. This experimental work examines asymmetric-depth-profile surface textures using gap-controlled experiments with Newtonian fluids on a custom tribo-rheometer setup. Measurements of normal force and shear load are reported as a function of texture geometry, gap height, and bi-directional sliding velocity. This work shows that, in the absence of cavitation, surface texture depth symmetry must be broken to produce normal forces (through viscous effects) for gap-based Reynolds Number up to Reh=ρVhη=1.21. Asymmetric surface textures reduce shear stress and generate normal load, and therefore decrease the effective friction coefficient, which we observe to be smallest for the shallowest texture angle tested, β=5.3°.