THE RELATION BETWEEN FRICTION FORCE AND RELATIVE SPEED DURING THE SLIP-PHASE OF A STICK-SLIP CYCLE

In order to better understand the stick-slip phenomenon, several attem pts have been performed in the past to measure the friction force-rela tive speed relation during the slip portion of a stick-slip cycle. In literature, two different shapes for this relation are reported: clock wise loops and counter-clockwise loops. In this paper, it is shown tha t both shapes can be obtained by changing the tangential stiffness of the test rig. Likewise, it is shown that the counter-clockwise frictio n-speed loop does not really occur, but that it results from neglectin g the velocity variation (by vibration) of the most rigidly connected sliding specimen. Finally, a sufficiently large difference between the stiffness of both tangential sliding specimen-frame connections is re commended for accurate friction measurements during stick-slip. (C) 19 98 Elsevier Science S.A. All rights reserved.