A NEW APPROACH OF STICK-SLIP BASED ON QUASI-HARMONIC TANGENTIAL OSCILLATIONS

It is generally accepted that stick-slip behaviour is caused by a nega tive slope of the friction force-relative sliding velocity relation. I n this paper, it is shown that the F-v(rel) gradient derived from stea dy-state friction fundamentally differs from the instantaneous F-v(rel ) gradient, which is determined by the instantaneous change of the fri ction force at a sudden infinitesimal change of the relative sliding v elocity. This instantaneous F-v(rel) gradient, not the stationary F-v( rel) gradient, is the real initiator of stick-slip. The occurrence of quasi-harmonic tangential oscillations during friction induced by a ne gative instantaneous F-v(rel) gradient is explained. Moreover, it is s hown that a correlation exists between the amplitude of the quasi-harm onic oscillations occurring during friction and the instantaneous F-v( rel) gradient. In literature, stick-slip is always explained with an i nitial stick-phase. In this paper, it is explained how stick-slip can arise from quasi-harmonic tangential oscillations during pure slip (wi thout stick). It is of great interest to explain the occurrence of sti ck-slip after a decrease of the impressed velocity, starting from abov e the critical (stick-slip free) velocity. For this new approach of st ick-slip, the same qualitative influences of the system parameters (ve locity, damping, stiffness) on intermittent motion are found as for th e classic models with an initial stick-phase. (C) 1998 Elsevier Scienc e S.A.