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go to next speaker imageJean-François Molinari
Director, Computational Solid Mechanics Laboratory (LSMS), Professeur, École Polytechnique Fédérale De Lausanne (EPFL)

Jean-François Molinari is currently an Associate Professor of structural mechanics at the School of Architecture, Civil and Environmental Engineering (ENAC) and Associate Research Professor in Mechanical Engineering at the Johns Hopkins University. He earned a bachelor's degree in mechanical engineering at the University of Technology of Compiègne in 1997. He then continued his studies at the California Institute of Technology, where in 2001 he completed a doctorate in aeronautics with a specialty in applied mathematics. From 2000 to 2005, he was an assistant professor in the Department of Mechanical Engineering at Johns Hopkins University. In 2005, he was appointed as a professor at the /École Normale Supérieure/ in Cachan (France), and since 2006 has also been a part-time professor at the /École Polytechnique/ in Paris.

His major contributions are in the area of numerical modeling of complex materials systems (metallic, ceramic, concrete and composite). Specifically, he has developed and improved models for the propagation of cohesive fractures that provide a better understanding of the phenomena of cracking and fragmentation on different scales. In particular, he is studying the influence of micro and nanostructural defects on the behavior and performance of structures that include new materials. He has also developed research in the area of contact mechanics and seeks to understand the microscopic origins of friction and wear.

Abstract: Numerical Modelling of Nanotribology Nanotechnology is a new frontier in research, and as with any new domain, new tools must be developed. As surface to volume ratios become large, engineering at the nanoscale will be dominated by surface science. While for a long time considered a traditional discipline of Mechanical Engineering, Contact Mechanics is prone to exciting developments. The study of Contact Mechanics at nanoscales, i.e. nanotribology, needs to fully account for adhesive forces, third body interactions and deformation mechanisms at contacting asperities. Understanding these factors as well as evolutions in the morphology of contact areas has the potential of explaining the origin of frictional forces and wear. This fundamental understanding is needed to guide us in the design of tailored-made lubricants and surface morphologies.

Be they at the macroscopic or nano scale, tribological problems are particularly difficult to comprehend. Different physical mechanisms (which include for instance environment, plastic deformation, third body interactions, phase transformations, recrystallisation) interact at disparate length scales. It is therefore not surprising that contact sciences have been primarily driven by careful experimental investigations. Nonetheless, as experiments go down in size and as computational power expands, numerical simulations become increasingly relevant to experimental work.

We begin the presentation with simulation results at the continuum scale. Finite-element calculations are conducted for normal and sliding contact of rough solids. The surfaces are modelled with self-affine fractals. In accordance to theory and experimental work, we observe a linear dependence between applied load and the real contact area, for both elastic and elasto-plastic solids. However, we contrast our results with prior theoretical models which do not explicitly take into account interactions between asperities. In the second part of the presentation, we review key atomistic (MD) simulations results from the literature. We highlight the limitations of a purely continuum approach and motivate the development of a multiscale framework, in which MD is directly coupled to finite elements. We present preliminary 3D simulation results of rough on rough sliding and give a road map for efficient parallel scaling of the simulation capability.


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