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Friction coefficients, µ, obtained by analyzing the slopes in plots of Δf versus u0 (left) and ΔΓ versus u0 (right), following Equation 1. The two ways to derive µ should lead to the same values, ideally. Further, µ should be of the order of unity. The decrease of µ with increasing normal force can be explained with an increased contact area and a concomitant increase in the stress concentration at the edge of the contact.
