Experimental and numerical analysis of frictional contact scenarios: from macro stick–slip to continuous sliding

This work is an in-depth analysis of frictional phenomena including macroscopic stick–slip and mode coupling instabilities, which can occur at different scales ranging from earthquakes to vibrational issues in machining processes. The paper presents a comparison between experimental observations of frictional macroscopic behaviours reproduced in a dedicated laboratory set-up and numerical simulations, obtained by transient finite element simulations able to reproduce the contact dynamics. The explicit finite element code PLASTD has been used to perform numerical transient analysis of two elastic bodies in frictional contact. On the other hand an experimental set-up has been used to investigate the macroscopic response of two blocks of polycarbonate in relative motion, highlighting how the contact frictional behaviour is affected by the imposed boundary conditions. Time evolution of global contact forces has been investigated; macroscopic stick–slip, modal instability behaviours and the transition to continuous sliding as a function of the system parameters have been observed. The frequency and time analysis of experimental phenomena exhibits a good agreement with numerical results obtained through transient contact simulations. The numerical analysis allows for explaining the interaction between local contact behaviour and system dynamics, which is at the origin of the different frictional scenarios. Maps of the instability scenarios are drawn as a function of boundary conditions or system parameters.