Strain Soliton Activated Gliding for Length Invariant Friction

In the prevailing paradigm of tribology, a long filament in a bundle is asymptotically confined by friction, which rises and theoretically diverges with the filament length. Here, we provide an analytical solution that the stress at the trailing end can nonlinearly penetrate into the bulk region to neatly form strain solitons, which then propagate with no energy cost to activate the gliding motion of the slider and, thus, a length invariant friction. Such a motion is demonstrated by coarse-grained simulations in carbon nanotubes under both quasi-static and dynamic loading conditions. We also derive that the ratio of intrinsic elasticity and interfacial stiffness dictate the scope of the length invariant frictional regime and transitions to smooth sliding or stick-slip regimes. These findings not only align with previous experimental observation but also enrich the fundamental knowledge of ubiquitous frictional sliding in both natural and artificial systems.