Nicolas Fillot
Simulation of particles detachments

Trying to model the detachment of particle during friction between two bodies, we built simulations of a cohesive granular material sliding along a rigid plate, on which we apply a normal force. Granules from the granular material can be detached if locally the forces are strong enough to break the bounds between granules. Because of the periodic boundary of our simulations, the granules can not leave the contact, and a kind of equilibrium can be observed, where, after a first phase of degradation, no degradation takes place and enough "free" particles (called third body particles) are produced inside the contact to accommodate the speed, to support the pressure, and to fully separate the (first) bodies in contact. It is shown with these simulations that this equilibrium depends both on the mechanical conditions (sliding speed, normal pressure) and on the third body properties (cohesion, energy dissipation). In a second part of the talk, it was discussed about the way we could model the granular "degradable" material. A first approach was to apply only normal interactions between grain (repulsion, adhesion, damping). This simple approach already provide the results discussed before. A new way to build the material was to consider "stuck spheres" (inspired by the work of Delenne presented in a previous MIDI session) where spheres share a point of hangs, in which we apply normal and tangential forces and a rolling couple. The bound is broken when the forces or couples exchanged exceed a critical threshold.

This model gives better results mechanically since the broken bounds are mainly located near the rubbing surface.

References
  1. Godet, M., 1984, "The Third body Approach : A Mechanical View of Wear", Wear, 100, pp. 437-452.
  2. Godet, M., 1990, "Third Bodies in Tribology", Wear, 136, pp. 29-45.
  3. Berthier, Y., 1995, "Maurice Godet's Third Body", 22nd Leeds Lyon Symposium on Tribology, Elsevier Tribology series 31, pp. 21-30.
  4. Iordanoff, I., Seve, B., Berthier, Y., 2002, "Solid Third Body Analysis Using a Discrete Approach : Influence of Adhesion and Particle Size on the Macroscopic Behavior of the Contact", ASME Journal of Tribology 124, pp. 530-538.
  5. Fillot, N., Iordanoff, I., Berthier, Y., 2002, "Stable Contact and Degradation of Materials : A Model for Third Body Source Flow", Proc. 6th Austrib International Tribology Conference, G.W. Stachowiak, eds., Perth, Vol. 2, pp. 709-716.
  6. Fillot, N., Iordanoff, I. , Berthier, Y., "A granular dynamic model for the degradation of materials", submitted to ASME Journal of Tribology.
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