Experimental observations of stick-slip instability: discussion and comparison with numerical results on contact wave and rupture propagation.

In recent years the local dynamics of frictional contacts and its interaction with the global behavior of the system has been the subject of many studies of major interest several in several disciplines as tribology, geophysics, vibration mechanics and fracture mechanics. Recent numerical works, focus the attention on understanding how local interface dynamics (rupture and wave propagation) affects the macroscopic frictional behavior of the system, determining, for example, the transition from stick-slip to continuous sliding. On the other hand experimental studies infer the effect of interface local dynamics, observing the evolution of precursors (interface rupture fronts) which propagate at different velocity during the onset of sliding. In this context the purpose of this work is an in-depth analysis of physical phenomena occurring at the contact interface and at the origin of the macroscopic stick-slip instability, which can occur at different scale ranging from earthquakes to vibrational issues in machining processes . This paper presents a comparison between numerical results, obtained by transient finite element simulations able to reproduce contact dynamics, and experimental observations of global contact behavior in a laboratory set-up. The explicit finite element code PLASTD has been used to perform numerical transient analysis of two elastic bodies during sliding evolution. On the other hand an experimental set-up has been utilized to investigate the frictional macroscopic behavior of two blocks of polycarbonate in relative motion. Time evolution of global contact forces has been investigated and stick-slip regime and its transition to continuous sliding in function of system parameters has been observed. The frequency and time analysis of experimentally stick–slip phenomena exhibit good agreement with numerical results obtained through transient contact simulations. While the numerical simulations allow for the understanding of the physical phenomena and investigating the coupling between local and global dynamics, the experimental results allow for validating the numerical simulations.