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Transition from static to kinetic friction : insights from numerical experiments
The contact between macroscopic rough solids is made of many micrometric asperities in contact. Under increasing shear force, each microcontact deforms, reaches its breaking threshold, and triggers a local micro-slip event. In some conditions, such an event can destabilize neighbouring microcontacts and a collective micro-slip front propagates across the interface at speeds close to that of sound in the material. Gross sliding of the solids only begins when the front has spanned the whole interface. This scenario has emerged recently from a series of pioneering experiments [1], many aspects of which are still unexplained. Here, I will present recent numerical efforts towards a better understanding of the transition from stuck to sliding interfaces.
I will first show that 2D models incorporating all boundary conditions used in experiments are required to successfully predict the triggering force and propagation length of precursors to sliding motion (Fig.). Surprisingly, this good agreement is obtained even with the minimalistic Amontons-Coulomb friction law [2,3]. In contrast, I will then show that realistic propagation speeds of micro-slip fronts are spontaneously reproduced only using more complex friction laws involving an intrinsic time scale. I will use this model to identify the sufficient physical mechanism at the origin of so-called slow fronts, discovered recently [1].
[1] S.M. Rubinstein et al., Nature (2004) ; O. Ben-David et al., Science (2010)
[2] D.S. Amundsen et al., Tribol. Lett. 45, 357-369 (2012)
[3] J. Trømborg et al., Phys. Rev. Lett. 107, 074301 (2011)
