Variation of frictional strength in precut foam rubber, with implications for slip instability

Abstract

Foam rubber is useful for modelling earthquakes and stick-slip, chattering that occurs readily in foam rubber and is controlled by friction weakening and stiffness. This study investigates frictional parameters and variable friction potentially causing stick-slip. The best friction coefficient for foam rubber is: friction over normal load to the two-thirds power. Increasing the system stiffness sufficiently enabled smooth sliding. In these experiments, contact time has no effect on static friction. However, peak friction increases during a second sliding interval from asperities interlocking. Friction also significantly increases inversely with load rate, with effects amplified by dynamic conditions. No negative friction-velocity relation is exhibited. Rather, the curve increases rapidly then remains constant over velocities corresponding to stick-slip events. Displacement weakening (demonstrated when asperities interlock) and load rate may cause stick-slip in foam rubber, but pot velocity or contact time.