A study of transitional friction behavior at scaled micro contacts

Abstract

Two-dimensional photoelastic experiments were conducted to study the transitional behavior of friction at multipoint contacts. The study was performed using a photoelastic plate to sense both normal and frictional forces at each contact. The fringe patterns, which varied continuously under the contact points of the scaled-up asperities and the photoelastic plate, were recorded by a camcorder. The spatial data from the fringe patterns was sufficient to calculate the normal and frictional forces at each contact point during the transition between static and kinetic friction. The generally accepted fact is that the difference between the coefficients of static and kinetic friction is small and that the coefficient of friction at each micro contact is the same. However, the photoelastic results show that the difference between the coefficients of static and kinetic friction is quite large and that the coefficient of friction at each contact point varies from one point to another and changes during sliding. A local coefficient of friction also is different significantly from the global coefficient of friction.