20/04/2017 – J. Scheibert – Evolution of real contact area under shear and the value of static friction
Séminaire régulier IUSTI – 20 avr. 2017 – 11h salle 250
Evolution of real contact area under shear and the value of static friction
Julien Scheibert – LTDS, Lyon
The frictional properties of a rough contact interface are controlled by its area of real contact, the dynamical variations of which underlie our modern understanding of the ubiquitous rate-and-state friction law. In particular, the real contact area is proportional to the normal load, slowly increases at rest through aging, and drops at slip inception. In this seminar, based on direct measurements on various contacts involving elastomers or human fingertips, I will show that the real contact area also decreases under shear, with reductions as large as 30%, starting well before macroscopic sliding. All data are captured by a single reduction law enabling excellent predictions of the static friction force. In elastomers, the area reduction rate of individual contacts obeys a scaling law valid from micrometer-sized junctions in rough contacts to millimeter sized smooth sphere/plane contacts. Those results are expected to motivate first-order improvements of current contact mechanics models and prompt reinterpretation of the rate-and-state parameters.