Thursday, 11 March 2021

Speaker: Dr. Lucas Frérot

Johns Hopkins University, Baltimore, USA

Roles of Roughness in Tribology

Abstract

Roughness is an inevitable part of virtually all tribological systems, and often dominates the frictional [1] and wear [2,3] responses of solid interfaces. The present seminar aims to picture selected effects of roughness on wear of elastoplastic materials and on the friction response of fatty acid coatings. We first discuss the development of an efficient numerical method for the modeling of elastic-plastic rough contact. Because self-affine surfaces have no separation of scales, very fine meshes at the contact interface are necessary. Fourier-based boundary integral approaches have proved superior to FEM in elastic contact, but are not appropriate for plastic constitutive modeling. We therefore develop a Fourier-based volume integral method [4] which performs about 200 times faster than FEM in elastic-plastic contact [5]. This new high-performance method allows the investigation of the impact of plasticity on the wear of ductile materials. We discuss in particular how plasticity can increase the likelihood of crack nucleation in the vicinity of contacts [6]. We also discuss the role of roughness in frictional systems composed of self-assembled monolayers of stearic acid molecules. This fatty acid compound is often used in applications where reduced friction is necessary. The experimental works of Dr. Juliette Cayer-Barrioz and her group [7] have shown that these friction layers exhibit rate-and-state frictional properties: the dynamic friction force depends on the sliding velocity, the static friction force depends on the resting time of the interface, and the interface has a memory length-scale characteristic of rate-and-state friction. We will show with nano-scale molecular dynamics that roughness plays a fundamental role in the emergence of these features.



Biography

Dr. Lucas Frérot is a postdoctoral fellow at Johns Hopkins University, currently working with professors J. Al-Awady and V. Nguyen, previously with professor Mark Robbins before his passing. Dr. Frérot recieved his PhD in 2020 under the supervision of prof. Jean-François Molinari and Dr. Guillaume Anciaux at École Polytechnique Fédérale de Lausanne. His PhD work on numerical methods and modeling of rough contact and wear was awarded with the EPFL Outstanding PhD Thesis Distinction in Civil and Environmental Engineering. Dr. Frérot holds a Master of Science degree in civil engineering (2015). Dr. Frérot’s work revolves around modeling tribological phenomena, such as friction and wear, at rough contact interfaces. His current work aims to uncover rate-dependencies of nano-scale wear mechanisms in polymer glasses, for which he was awarded a Swiss National Science Foundation fellowship, as well as to identify the underlying physics of rate-and-state friction in self-assembled monolayers of fatty acids. This latter work is the fruit of a collaboration with an experimental group led by Dr. Cayer-Barrioz of École Centrale Lyon.

References

Notes

by Arnaud Coq and Bertrand Leturcq

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