Vibration-Induced Sliding of Friction Interfaces by Activating Nonlinear Resonance

In contrast to friction-induced vibration (e.g., brake squeal), vibration-induced friction is comparatively under-studied despite its potential for transformative engineering technologies. For instance, vibrations can induce a temporary change of friction within slip-joints and provide the means to (dis)connect wind turbine towers without any fasteners, or re-straighten buildings after earthquakes without any damage. To investigate this possibility, the present study examines how frictional interfaces that are initially stuck together can subsequently be triggered to slide upon an externally introduced excitation. The cases considered are characterized by high initial friction, and a low or insufficient preload force provided in the sliding (x) direction. Numerical models of a 2-DOF system are used to investigate the stick-slip process with one DOF in each of the sliding (x) and excitation (x/y/z) directions. Initial results indicate that nonlinear resonance may be exploited to trigger sliding, even when excitation and preload forces are well below the static friction threshold. Sliding velocity averaged over the long-run results in a constant velocity despite the presence of stick-slip in each cycle. For x/y-excitations, vibration patterns include sliding with one/two-stops per cycle, and failure to slide in ‘dead zones’ around subharmonic frequencies. Excitation in z-direction exhibited sliding with/without separation of contact surfaces, along with the associated jump phenomenon. The relative efficacy of excitation in different directions is dependent on both the level of preload and excitation. Simple equations are produced to calculate the frequency of excitation marking the transition between each sliding pattern. Ongoing analyses aim to elucidate these mechanisms further.