Textured surfaces with varied functionalities are generally fabricated by etching, cutting, or printing. In this study, different from the usual generation of grooves along the sliding direction in friction, regular parallel ripples that are perpendicular to the sliding direction were generated on a polymer surface by the stick–slip friction of polymer/metal friction pairs lubricated with water. Ripple height was proportional to the peak friction force in the sticking process. Ripple wavelength decreased as the sliding velocity increased. The generation of ripples was ascribed to the adhesion and plastic deformation during stick–slip motion. The achieved rippled surface effectively improved the lubrication property of the two surfaces. These findings demonstrate a new method of in situ manufacturing ripples on a soft material surface through a controlled traditional sliding friction and also provide a new insight into the stick–slip friction behavior of materials.

The coefficient of friction (COF) between two materials is usually believed to be an intrinsic property of the materials themselves. In this study, metals of stainless steel (304) and brass (H62), and polymers of polypropylene (PP) and polytetrafluoroethylene (PTFE) were tested on a standard ball-on-three-plates test machine. Significantly different tribological behaviors were observed when fixed and moving materials of tribo-pairs (metal/polymer) were switched. As an example, under the same applied load and rotating speed, the COF (0.49) between a rotating PP ball and three fixed H62 plates was approximately 2.3 times higher than that between switched materials of tribo-pairs. Meanwhile, the COF between H62 and PTFE was relatively stable. The unexpected tribological behaviors were ascribed to the thermal and mechanical properties of tribo-pairs. Theoretical analysis revealed that the differences in the maximum local temperature between switching the fixed and moving materials of tribo-pairs were consistent with the differences in the tested COF. This result indicated the precise prediction of the COF of two materials is complexcity, and that thermal and mechanical properties should be properly considered in designing tribo-pairs, because these properties may significantly affect tribological performance.

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