Slip process of stick–slip motion in the scratching of a polymer

The slip process of the stick–slip phenomena during scratching of a styrene–acrylonitrile copolymer was studied. It was found that during slip the indenter velocity starts from zero, increases to a maximum and then decreases to zero again. The scratch groove made during slip showed a non-uniform depth which increased with the decrease of scratch velocity. Although the scratch velocity and groove depth changed markedly during slip, the scratch force remained almost constant for most of the scratch distance. The effects of the normal load and driving speed on the slip behavior showed that the normal load mainly determined scratch force. The results are discussed in terms of a micromechanical model proposed to describe the slip process.