Projects
Project description
Very sticky rough surfaces separate in an intermittent fashion: parts of the contacting area break off. These instabilities lead to adhesion hysteresis and friction and may play a role in contact charging. My simulations of contact mechanics complement the experimental investigations of Qiwei Hu and Ravi Divakar to correlate mechanics and charge transfer at the microscale.
Project outcome
Because of the fractal nature of surface roughness, understanding how a soft, sticky solid detaches from a rough surface is a challenge: bumps at the milimeter scale have smaller bumps on top of them, which in turn are covered by even smaller bumps. This happens all the way down to the atomic scale.
The first challenge is to measure surface roughness over all scales, which my experimental collaborators in the university of Pittsburgh recently started. My work on scale-dependent roughness parameters and the web service „contact.engineering“ helps them and other researchers of the community to statistically analyze and interprete such measurements.
The second challenge is to quantitatively account for this roughness in a theoretical model. I developed an efficient crack perturbation model to describe the contact of soft spheres against rough surfaces. The model is only valid for very soft sphere that can fully conform to the counter surface, but its computational efficiency allows to resolve all lengthscales that affect stickiness. My model shows that soft contacts are stickier when broken than when made because the roughness triggers elastic instabilities that dissipate energy as the contact perimeter moves.
Future work could compare the pattern of instabilities predicted by the crack front model with measurements of surface charge patterns. This could provide hints as to whether jumps during the detachment of the surfaces promote the separation of triboelectric charges.
Supervisor and dissertation
Prof. Dr. Lars Pastewka
Antoine Sanner completed his dissertation in March 2023.
Dissertation: How surface roughness affects adhesion
Current position
Postdoctoral researcher in Prof. David Kammer’s group for Computational Mechanics of Building Materials in the Institute for Building Materials at ETH Zurich. The research is about investigating how elastomers and gels break by simulating the network of polymer chains.