NORMAL LOAD, SLIP RATE AND ROUGHNESS INFLUENCE ON THE POLYMETHYLMETHACRYLATE DYNAMICS OF SLIDING 1 - STABLE SLIDING TO STICK-SLIP TRANSITION

We present the results from an extensive study on (PMMA)-PMMA polymeth ylmethacrylate dry friction. For a wide range of normal pressures, sli p rates and grades of roughness of sliding surfaces, we analysed the c onditions in which steady and catastrophic sliding appear. For the gra des of roughness and slip rates investigated, we observed a steady-sta te regime at low normal pressures and a stick-slip regime when the nor mal pressures were high. For intermediate normal pressures, the transi tion between the two regimes was controlled by the roughness and slip rates. In this last case, slip motion was steady at high slip rates fo r the range of grades of roughness considered, and at all slip rates f or the roughest surfaces. In other conditions, we observed stick-slip. In the case of steady sliding, the dynamic coefficient of friction de creased linearly with the logarithm of increasing sliding velocity. Fu rthermore, this coefficient of friction and its variations with slip v elocity were lower for smooth surfaces. For stick-slip motion, the sta tic coefficient of friction was mostly influenced by normal pressure. For the three highest normal pressures, the static coefficient of fric tion decreased linearly when normal pressure increased. This coefficie nt was not influenced by slip rate and showed a slight increase when t he roughness of the sliding surfaces increased. (C) 1998 Elsevier Scie nce S.A.