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°.