Quasi-fluid nano-layers at the interface between rubbing bodies: simulations by movable cellular automata

Most of technical surfaces show roughness on different space scales. When pressed against each other, they initially come into contact only in small number of micro-contacts. Our aim was to study the processes occurring in a single micro-contact between two rubbing bodies. The solids were simulated in the frame of the method of movable cellular automata (MCA). The main finding of our simulations is formation of a boundary layer where intensive plastic deformation and mixing processes occur. The boundary layer is well localized and does not spread to deeper layers. We investigated how the thickness of the boundary layer and the friction force stemming from the processes in this layer do depend on parameters of material and loading. To this end, all the parameters involved in the numerical model have been varied and the average friction coefficient as well as thickness of the layer determined for each set of parameter. We found that at velocities much smaller than velocity of sound and normal pressures much smaller than the yield stress, the thickness of the quasi-fluid layer is proportional to effective viscosity of the medium and the friction coefficient does depend only on two dimensionless parameters: κ1=ρv2E/σ02 and κ2=PE/σ02.