Fig. 5

Experimental data and the friction parameter modeling results. a Friction as a function of shear displacement with velocity steps between 0.1 and 100 μm/s at normal stresses of 2, 5, 10 and 20 MPa. Curves are offset vertically for clarity. b An example of the friction response to a velocity step from 1 to 10 μm/s (gray) with a best-fitting curve obtained by inversion analysis (red). c Velocity-dependent friction parameter (a – b) and d critical slip distance D_c plotted as a function of normal stress for all velocity steps (blue circle, 0.1 μm/s; red square, 1 μm/s; green triangle, 10 μm/s; orange diamond, 100 μm/s)