Velocity-Independent Dry Friction on Mica: Realization of Ideal Amontons-Coulomb Friction

The Amontons-Coulomb friction law assumes that the frictional force between materials is independent of sliding velocity. However, as Coulomb noted, this is a rough approximation, and a second-order dependence of friction on the logarithm of sliding velocity is incorporated in a commonly used "rate- and state-dependent" friction representation. Here, we conduct shear experiments on mica, a layer-structured mineral, at temperatures ranging from 22 to 200 °C and under normal stress of 100 MPa. The friction coefficient clearly depends on the logarithmic sliding velocity at 22 °C, but rate sensitivity decreases with increasing temperature until at 200 °C, the friction coefficient is independent of sliding velocity. Our findings could initiate the development of velocity-independent frictional materials, realizing the ideal Amontons-Coulomb friction.