Adhesion and Edge Effects in Contact Mechanics of Third-Body Particles and Their Impact on Particle Transport and Friction Properties

• Applicant: Dr.-Ing. Qiang Li
• Subject Area: Mechanics
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 465596821

The “third body” essentially determines all processes in a tribological contact. Understanding the dynamics of the third body is one of the central problems of tribology, which is still insufficiently studied to date - due to the high complexity of the processes occurring in tribological contacts. The aim of the present project is to explore the aspects of the third body that are related to the dynamics of the particles in the gap between two contact partners. For this purpose, a system of two base bodies with rough surfaces with trapped particles is investigated. A complete contact problem is solved for the particles, in which the exact geometry of the contact, the quasi-static relative sliding of the base bodies as well as adhesion and friction in the contact of the particles with the base bodies are taken into account. Even if the base bodies and the particles are elastic, friction and adhesion introduce nonlinearity into the system. Friction and adhesion introduce processes into the system that are similar to plastic flow (friction) and cracking (adhesion). Thus, the model system remains relatively simple, but captures the most important qualitative processes in the contact, including plasticity and fracture phenomena and particle transport. The simplifications are necessary in order to be able to use the main calculation tool - the Fast Fourier Transform-assisted boundary element method (FFT-BEM). In the framework of the project, two methodological problems of the FFT-BEM are addressed: Firstly, implementation of the handling of the simultaneous effects of adhesion and friction. Two approaches are being pursued: an approach based on the consideration of explicit adhesive potentials and the concept of boundary friction in adhesive contact, developed in 2020 with the participation of the applicant. On the other hand, contacts with sharp edges are considered and the combined friction and adhesive interactions are also implemented. The methods developed are then used to simulate particles in the gap, with a focus on the macroscopic friction properties and transport properties. During transport, the "diffusion-like" movement of the particles in the direction perpendicular to the sliding direction is examined, as well as the effect of the macroscopic curvature of the bodies and the proximity of the edge of the contact area on the directional creep of particles towards or away from the edge of the contact. Parametric studies are carried out for the macroscopic coefficient of friction as well as the transport parameters (including diffusion and creep coefficients) with the aim of determining the most important controlling “master parameters” for friction and transport properties.

• DFG Programme: Research Grants