A STUDY OF TRANSITIONAL FRICTION BEHAVIOR AT SCALED MICROCONTACTS

Two-dimensional photoelastic experiments were conducted to study the t ransitional behavior of friction at multipoint contacts. The study was performed using a photoelastic plate to sense both normal and frictio nal forces at each contact. The fringe patterns, which varied continuo usly under the contact points of the scaled-up asperities and the phot oelastic plate, were recorded by a camcorder. The spatial data from th e fringe patterns was sufficient to calculate the normal and frictiona l forces at each contact point during the transition between static an d 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. Ho wever, the photoelastic results show that the difference between the c oefficients of static and kinetic friction is quite large and that the coefficient of friction at each contact point varies from one point t o another and changes during sliding. A local coefficient of friction also is different significantly from the global coefficient of frictio n.