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Tribology of Polymers: from Atomistic to Continuum Scales

Applicant Frérot Lucas
Number 191720
Funding scheme Early Postdoc.Mobility
Research institution Whiting School of Engineering Department of Computer Science Johns Hopkins University
Institution of higher education Institution abroad - IACH
Main discipline Mechanical Engineering
Start/End 01.02.2020 - 31.07.2021
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All Disciplines (3)

Mechanical Engineering
Material Sciences
Condensed Matter Physics

Keywords (5)

wear; molecular dynamics; up-scaling; polymers; contact

Lay Summary (French)

L'usure des matériaux est un phénomène qui affecte tous les systèmes mécaniques. Entre autres, elle est à l'origine des émissions de particules fines, elle dicte la durée de vie des prothèses médicales et influence les propriétés des failles tectoniques. Malgré son omniprésence et son impact sur la société, il n'existe pas encore de moyen de prédire les propriétés d'usure d'un système mécanique donné. L'étude de l'usure s'appuie nécessairement sur des données empiriques collectées au plus proche du système d'intérêt. Cette collecte de données est souvent difficile voire impossible. De plus, si des conditions changent (humidité, matériaux, etc.), de nouvelles données doivent être collectées, limitant ainsi la capacité de prédiction. Ce projet contribue à l'établissement d'un lien entre les connaissances de l'usure à l'échelle microscopique et les échelles macroscopiques afin d'établir des modèles prédictifs d'usure.
Lay summary
Les difficultés de prédiction de l'usure des matériaux sont dues à sa nature multi-physique (combinant contact, adhésion, rupture, etc.) et multi-échelle. En effet, les surfaces en frottement sont toujours rugueuses à petite échelle. Et bien que certains phénomènes liés à l'usure soient bien compris à l'échelle microscopique, la façon dont ils interagissent avec la rugosité est encore inconnue et empêche l'élaboration de modèles macroscopiques prédictifs.

Ce projet de recherche à pour objectif de palier à ce problème avec comme matériaux d'étude les polymères. Ces derniers se prêtent aux simulations par dynamique moléculaire, et la première étape de se projet est d'approfondir les connaissances sur les mécanismes d'usure à l'échelle microscopique, en particulier l'usure par transfert plastique. Les modèles ainsi construits serviront ensuite à informer une approche de simulation de contact entre surfaces rugueuses qui établira la liaison entre les échelles microscopique et macroscopique.

Tout les outils et les codes développés durant ce projet seront publiés sous licence libre, et les publications issues des résultats seront disponibles en open-access.
Direct link to Lay Summary Last update: 10.12.2019

Responsible applicant and co-applicants


Tamaas: a library for elastic-plastic contact of periodic rough surfaces
Frérot Lucas, Anciaux Guillaume, Rey Valentine, Pham-Ba Son, Molinari Jean-François (2020), Tamaas: a library for elastic-plastic contact of periodic rough surfaces, in Journal of Open Source Software, 5(51), 2121.


Group / person Country
Types of collaboration
Juliette Cayer-Barrioz / LTDS / École Centrale de Lyon France (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
Jaafar El-Awady / Department of Mechanical Engineering / JHU United States of America (North America)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
Vicky Nguyen / Department of Mechanical Engineering / JHU United States of America (North America)
- in-depth/constructive exchanges on approaches, methods or results

Associated projects

Number Title Start Funding scheme
162569 Contact mechanics of rough surfaces 01.10.2015 Project funding


Both natural and man-made mechanical systems are subjected to wear of materials, from the nano-scale geartrains of nanoelectromechanical systems, to common engineering systems like car tires or medical prostheses, all the way to kilometer-scale geological faults. The impact of wear on the economy of a developed country isestimated as 1% of the GDP [1], in addition to potential environmental risks from particle emissions. Because wearis an interfacial phenomenon that combines different physical aspects, (e.g. mechanics, adhesion, friction), ourability to control it is limited by an empirical understanding built in the second half of the 20th century that hasno predictive capacity [2]. The investigation of wear in a given system relies on gathering experimental data asclose to the operating conditions as possible, which is expensive in most cases and sometimes impossible. Recentadvancements in nano-tribology have however made significant breakthroughs, among them the discovery of acritical length-scale governing the formation of adhesive wear particles in brittle materials [3]. However, knowledgeof ductile wear mechanisms is still lacking, and there is currently no transfer of the nano-scale understanding ofwear to the macro-scale, which hinders predictive capacity.The current research proposal aims to address these two issues. It focuses in particular on the study of wear inpolymers, as they possess ductile failure mechanisms and few relevant scales (as opposed to the metal-like modelmaterials used in nano-scale wear modeling [4]). We will use molecular dynamics simulations of polymers toquantify the ductile mode of adhesive wear and identify rate effects in the wear process, both of which have beenoverlooked in recent wear models. We will also examine the nano-scale wear process for contact of realistic roughasperities, as opposed to the hemispherical geometries used in the past. Finally, in order to up-scale our findings atthe small-scale to macroscopic sizes, we will develop a statistical approach using rough-surface elastoviscoplasticcontact models adjusted for the modeling of polymer constitutive behavior. Physics-based laws for the wearing ofpolymer asperities will be used to understand the global evolution of the statistics of a rough surface.To tackle these scientific challenges, we propose two work packages articulated around the two central aspectsof this research proposal: the atomistic modeling of local asperity wear in polymers and the up-scaling of the localmodel to multi-asperity self-affine rough surface contact at the continuum scale. The former will make use of theopen-source molecular dynamics software LAMMPS, with interatomic potentials for polymer chains that allowscission [5] so as to be able to represent the detachment of a wear particle. The latter will rely on the open-sourceperiodic contact library Tamaas which can efficiently solve elastoplastic rough contact problems.The research proposed here will further the understanding of ductile wear mechanisms, and in particularpolymer wear, which may have a broad impact on the additive manufacturing industry with the advent of polymer3D printing techniques nowadays used in medicine, aerospace, etc., as well as on the experimental investigationof friction, which often uses polymers such as poly(methyl methacrylate). It will also provide sound tools andrationale for the future up-scaling of nano-scale findings to the macroscopic scales.---[1] Tzanakis, I. et al. Future perspectives on sustainable tribology. Renewable and Sustainable Energy Reviews 16, 4126-4140 (2012).[2] Meng, H. C. & Ludema, K. C. Wear models and predictive equations: their form and content. Wear 181, 443-457 (1995).[3] Aghababaei, R., Warner, D. H. & Molinari, J.-F. Critical length scale controls adhesive wear mechanisms. Nat Commun 7, 11816 (2016).[4] Aghababaei, R., Brink, T. & Molinari, J.-F. Asperity-Level Origins of Transition from Mild to Severe Wear. Phys. Rev. Lett. 120, 186105 (2018).[5] Ge, T., Grest, G. S. & Robbins, M. O. Tensile Fracture of Welded Polymer Interfaces: Miscibility, Entanglements, and Crazing. Macromolecules 47, 6982-6989 (2014).