Slip and partial slip under conditions of reciprocating motion have been studied on time-scales ranging from microseconds to seconds. The technique employed was the quartz crystal microbalance (QCM), which was employed as a high-frequency tribometer (applying oscillatory displacements in the range of a few nanometers). The QCM surface is brought into contact with spheres (dry and in aqueous environments). As long as linear mechanics holds, the frequency increases in proportion to the stiffness of the sphere-plate contact. As one increases the amplitude, partial sets in at the edges of the contact. The apparent contact stiffness decreases, while the dissipated energy (as extracted from the resonance bandwidth) increases. Also, partial slip (of following the Cattaneo-Mindlin scenario) leads to third harmonic generation (THG), meaning that the stress is no longer a harmonic function of time.<br/>The amplitude of the third-harmonic signal is much lower than what is expected based on the reduced apparent contact stiffness (as extracted from the amplitude-dependence of the resonance frequency and the resonance bandwidth). This disproves the Cattaneo-Mindlin picture. A sliding ring evolves over many periods of oscillation. Experiments undertaken in air and water are compared.

Partial slip takes time

2019 Fall National Meeting

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