Contact Area Measurements Reveal Loading-History Dependence of Static Friction

S. M. Rubinstein, G. Cohen, and J. Fineberg

The Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem 91904, Israel

(Received 31 January 2006; revised manuscript received 30 March 2006; published 30 June 2006)

We perform quantitative measurements of the actual area of contact, A, formed by two rough solids that

are subjected to different normal loading protocols.We show that microscopic motion, induced by Poisson

contraction or expansion, produces a strong memory dependence of A on the loading history with a large

corresponding influence on the system’s frictional strength. These effects, together with accompanying

transient dynamics, are independent of humidity, loading rates, and material contrast across the interface.