Phononic dynamics in sliding friction

Friction is generated due to the relative motion between two contacting objects, involving a multitude of atoms in the dissipation of translational kinetic energy. Current models often simplify the scenario of two objects in relative motion by depicting it as an elastic object excited by either a moving rigid body or an external force. Such approaches overlook the many-body nature inherent in friction systems and are insufficient in accounting for certain essential characteristics of friction. Here, we propose a parameter-free phononic dynamics model derived from the atomistic Green's function method, which includes all-atomic interactions in the friction process. Our model demonstrates that the phonon spectrum induced by friction exhibits narrow peaks around the washboard frequency and its harmonics, a phenomenon consistent with experimental observations. Furthermore, our model elucidates the mechanisms by which friction excites phonons and how these nonequilibrium phonons contribute to energy dissipation. Under the framework of phononic dynamics, the spring-stiffness-dependent, velocity-strengthening and velocity-weakening friction can be quantitatively explained without any assumptions.