  In 1958, Ernest Rabinowicz suggested a simple criterion distinguishing the
regimes of plastic smoothing and formation of wear particles in a contact of
homogeneous sliding bodies. However, he did not consider any detailed mechanism
of either plastic smoothing or debris formation. In a recent paper in Nature
Communications, Molinari et al. have confirmed the criterion using explicit
mesoparticle simulation. The work of Molinari's group provides a strong support
to the general concept of Rabinowicz which is based on the consideration of
competition of plastic deformation and fracture. It is interesting to apply
this concept to more general configurations than those considered by Rabinowicz
and Molinari's group. An important case is a system having a very soft surface
layer. In the present paper, the analysis similar to that of Rabinowicz is
applied to materials with soft layer. It is shown that in this case, too, both
cases of plastic deformation and debris formation may occur. It would be
interesting to verify this prediction by explicit meso-particle simulations
similar to those of Molinari's group.
