Stick-slip in the scratching of styrene-acrylonitrile copolymer

Stick-slip process occurred during the scratch test of styrene-acrylonitrile copolymer, For the first time, a bamboo-like morphology of the scratch track corresponding to the stick-slip phenomenon was observed. A ''joint'' was formed during the stick stage and during slip a uniform ''stem'' was made, The period and amplitude of the stick-slip both increase with the vertical load and decrease with the driving speed. A theoretical model is constructed based on the stiffness of the system and the plastic deformation of polymer both in the vertical and horizontal directions. The model assumes no distinction between the coefficients of static and kinetic friction and gives quantitatively consistent results with experiments.