Scratching across ductile regimes of wear: the role of load-bearing area and friction

Ductile wear is highly desirable in manufacturing and machining operations to achieve high finish quality. In such a ductile regime of operation, a characteristic transition from ploughing to cutting is often observed in materials with different mechanical properties. We unveil the origin of this transition through a plastic, debris free model of a tip wearing off a flat surface. The abraded volume depends on the equilibrium depth which is reached once the normal force is balanced by a lifting force during the scratching process. We show that the dependence of the equilibrium depth on the lifting force is highly non-linear and diverges above a threshold force that depends on the hardness, friction and geometry of the tip. The threshold corresponds to a characteristic depth marking the ploughing–cutting transition. When this characteristic depth is below the ductile–brittle depth of cut, ploughing, cutting and brittle modes of operation are all possible. The findings of this model, derived from theoretical considerations, are validated by DEM simulations and literature data from experiments.