  Wear is well known for causing material loss in a sliding interface.
Available macroscopic approaches are bound to empirical fitting parameters,
which range several orders of magnitude. Major advances in tribology have
recently been achieved via Molecular Dynamics, although its use is strongly
limited by computational cost. Here, we propose a study of the physical
processes that lead to wear at the scale of the surface roughness, where
adhesive junctions are formed between the asperities on the surface of the
materials. Using a brittle formulation of the variational phase-field approach
to fracture, we demonstrate that the failure mechanisms of an adhesive junction
can be linked to its geometry. By imposing specific couplings between the
damage and the elastic energy, we further investigate the triggering processes
underlying each failure mechanism. We show that a large debris formation is
mostly triggered by tensile stresses while shear stresses lead to small or no
particle formation. We also study groups of junctions and discuss how
microcontact interactions can be favored in some geometries to form
macro-particles. This leads us to propose a classification in terms of
macroscopic wear rate. Although based on a continuum approach, our phase-field
calculations are able to effectively capture the failure of adhesive junctions,
as observed through discrete Molecular Dynamics simulations.
