Naive model for stick-slip processes

This paper is a tutorial description of stick-slip in soft materials (rubber beads, gels) where inertial effects are negligible. A typical example is a rubber sphere, pressed against a glass surface (JKR contact). The sphere is driven from the top at a prescribed velocity U (similar to 100 mu m/s). At moderate U (and with suitable surface treatment) a periodic stick-slip regime is often observed. We present a simple picture of the stick-slip cycle, describing the growth of a slip zone from the rear end of the sample, and the resulting plot of force vs. time. All our estimates are restricted to scaling laws.