Breakloose suppression in minimal friction models

TL;DR

This paper investigates how the breakloose friction peak at the onset of sliding is suppressed in nanoscale contacts, revealing multiple mechanisms involving system size, temperature, and loading geometry across different minimal friction models.

Contribution

It demonstrates that suppression of breakloose friction can arise from diverse mechanisms, challenging the idea of a single underlying cause and highlighting the roles of elasticity, pinning, and contact architecture.

Findings

Suppression mechanisms vary with system size, temperature, and loading geometry.

Elastic stress redistribution delays sliding in end-driven models.

Spring stiffness controls slip synchronization in uniformly driven models.

Abstract

Breakloose friction, the transient force peak at the onset of sliding, is often pronounced in nanoscale contacts but weak or absent in macroscopic systems. Although this behavior is commonly associated with rupture fronts and process-zone effects, how the stiction peak is controlled by system size, temperature, driving rate, and loading geometry, and what mechanisms underlie its emergence or suppression, remains incompletely understood. Here we investigate this problem using three minimal friction models with distinct loading geometries: a multi-particle Prandtl-Tomlinson system with independently driven particles, an end-driven Frenkel-Kontorova chain with elastic stress transmission along the interface, and a uniformly driven FK chain in which each site is coupled locally to the driving stage. We show that similar macroscopic suppression of breakloose friction can arise from fundamentally different mechanisms. In multi-particle PT systems, increasing system size or temperature promotes statistical dephasing of local depinning events, smoothing the global response. In end-driven FK chains, internal elasticity redistributes stress along the interface, delaying sliding onset and, together with higher temperature or slower driving, enabling progressive relaxation during loading. In uniformly-driven FK chains, the stiffness of the driving springs controls the synchronization of slip events and thereby the character of the sliding response. These results demonstrate that the presence or absence of a breakloose peak does not uniquely identify a single physical mechanism, but instead reflects the interplay of local pinning, elastic coupling, and contact architecture.