FUNDAMENTALS OF STICK SLIP

Simultaneous measurements of momentary friction and electrical resistance using the hoop apparatus have resulted in new insights into the behavior of the ubiquitous thin interfacial films at contact spots. The experimental focus of the present paper is the amplitude of the stick-slip motion of a multifiber slider as a function of the humidity, speed and applied load. The stick-slip amplitude is found to increase with increasing relative humidity and contact spot size, respectively, and to decrease with increasing substrate speed. Furthermore, the interfacial electrical resistance spikes at the beginnings of slip episodes and shows an unexpected hysteresis during stick-slip cycling. The data suggest a two-component model, including (i) an approximate double molecular layer of adsorbed water between the contact spots and (ii) menisci at the periphery of the contact spots at high humidities. Together with the general analysis presented in appendix A, this model presents a framework for the understanding and control of stick-slip in sliding systems.