Towards understanding the surface rippling process by periodic reciprocal nanoscratching

The bundle structure formed perpendicular to the scratching direction is a type of wear-induced structure for thermoplastics. In this study, the formation mechanism of bundle structures on polycarbonate (PC) surfaces is investigated by reciprocal scratching experiments. Based on the analysis of the morphologies, friction forces, and height signals, the formation of the bundle structure is reproduced. The influence of scratching parameters, including the feed value and scratching direction, on the formation of the bundle structure is also studied. It is found that the bundle structure is accumulated by the continuous stacking of the sample materials plowed by the tip in stick–slip motion, and that the stick–slip behavior is enhanced with increased scratching times. This work reproduces the formation process of bundle structure in experiments for the first time and demonstrates that the stick–slip enhancement mechanism exists in the reciprocal scratching process, providing further insight into the friction behavior of polymers.