Intitulé de l'offre : PhD candidate on the design of metainterfaces with on-demand friction and adhesion (M/F) (H/F)
Référence : UMR5513-JULSCH-004
Nombre de Postes : 1
Lieu de travail : ECULLY
Date de publication : mardi 30 janvier 2024
Type de contrat : CDD Doctorant/Contrat doctoral
Durée du contrat : 36 mois
Date de début de la thèse : 1 avril 2024
Quotité de travail : Temps complet
Rémunération : 2 135,00 € gross monthly
Section(s) CN : Material and structural engineering, solid mechanics, biomechanics, acoustics
Description du sujet de thèse
My sneakers slip on the gym floor! I can't open my jam jar! So many everyday actions become difficult when the level of friction is inadequate.
Beyond these minor inconveniences, any system where friction is poorly optimized generates energy waste, malfunctions and premature wear of parts in contact. The costs associated with these inconveniences amount to several percent of global GDP! This is why becoming capable of creating solid contacts with a level of friction on demand is considered a grail in tribology, the science of contact interfaces .
The aim of this thesis is precisely to design and produce contact interfaces whose friction response, among other properties, optimally meets prior specifications.
There are currently two types of solutions for controlling friction between two solids. Firstly, since friction is deemed to be a characteristic of a pair of materials, the aim is to select the ideal pair for a given application. However, the most suitable materials for their tribological properties are not necessarily the most suitable for their other properties, such as thermal or electrical. Secondly, texture, i.e. micro-roughness, can be added to the surface of solids to modify the frictional behavior of the interface. However, the link between the texture's properties and its effect on friction is still poorly understood, often requiring a long and costly preliminary phase of experimental identification of the appropriate texture.
It is precisely this latter scientific challenge that has just been overcome at LTDS. We have developed a method enabling us to produce, on the first try, an interface with a coefficient of friction defined as a prior specification . To achieve this, we simplified the surface roughness to a network of small spherical asperities. Under these conditions, the tribological response of the interface becomes easy to model. This model can then be used to determine how high each of these asperities must be to give the interface the desired frictional behavior.
We have experimentally validated this design method, using the example of contact between glass and an elastomer. Not only were we able to obtain different target coefficients of friction, without changing the materials in contact, but we were also able to obtain contacts with two different coefficients of friction, depending on the level of compression exerted on the solids. This type of behavior does not exist in nature. This is why these tailor-made interfaces are referred to as metainterfaces, in reference to the broader field of metamaterials .
The ambition of this experimental thesis is to push back the current limits of these metainterfaces, with three objectives:
- firstly, to greatly expand the domain of accessible behavior laws, by diversifying the shapes of asperities. The design method will be extended to ellipsoidal asperities, with eccentricities and orientations chosen according to the desired tribological response. This significant increase in the number of design degrees of freedom will be accompanied by the development of advanced optimization methods in a partner laboratory.
- secondly, it will be necessary to tackle multi-objectives specifications, for example by simultaneously optimizing friction and adhesion at the same interface. Here again, specific optimization methods will be an invaluable tool.
- thirdly, we will need to miniaturize asperities, so as to get closer to the sizes that manufacturers dream of for their applications. To achieve this, we will rely on a partner platform specialized in femtosecond laser surface texturing.
Very operationally, to achieve these objectives, the candidate will first have to familiarize himself/herself with them through an in-depth bibliographical phase. This will be followed by further development of (i) surface preparation processes, (ii) experimental tools for mechanical characterization of tribological interfaces (friction, contact area, adhesion, stiffness, etc.) and (iii) analysis of experimental data, including image analysis. The candidate should also be able to use numerical optimization tools developed by our partners.
As can be seen, this thesis is characterized by advanced experimental aspects, interaction with numerical and technological partners, fundamental scientific challenges but also clear applied perspectives.
Beyond the thesis manuscript and final defense, the deliverables of this project will be scientific articles, patents and conference presentations.
 A. Vakis, V. Tastrebov, J. Scheibert, et al. Modeling and simulation in tribology across scales: An overview. Tribology International 125, 169 (2018)
 A. Aymard, E. Delplanque, D. Dalmas, J. Scheibert. Designing metainterfaces with specified friction laws. Science 383, 200 (2024)
 M. Kadic, T. Bückmann, R. Schittny, M. Wegener, Metamaterials beyond electromagnetism. Reports on Progress in Physics 76, 126501 (2013)
Contexte de travail
The thesis will be attached to the Mechanics, Energetics, Civil Engineering and Acoustics (MEGA) Doctoral School. The work will be carried out mainly at the Tribology and Dynamics Laboratory (LTDS), on the campus of the Ecole Centrale de Lyon (ECL), near Lyon. Occasional travel to our partners and conferences is to be expected.
The PhD student will have access to all LTDS shared tools for the preparation and characterization of surfaces and interfaces. The PhD student will also have privileged access to an elastomer sample preparation room, and above all to a world-class tribometer developed in-house. This tribometer enables us to stimulate and measure the mechanical response of an interface with five degrees of freedom, while observing in situ the evolution of real contact zones between the two solids.
This thesis work is part of a larger project (DESTRIER project), funded by the Institut Carnot Ingénierie@Lyon. In addition to LTDS, it involves:
- the LAMCOS laboratory at INSA-Lyon, where a one-year postdoc will work on developing the numerical optimization tools that will ultimately be used for the thesis
- the MANUTECH-USD laser texturing platform in Saint-Etienne, where miniaturized textures will be produced.
The candidate will be part of a research group including other PhD students working on related subjects and using the same experimental tools. Where necessary, he/she will interact with three researchers and an engineer. The candidate will also be involved in discussions with industries interested in monitoring our innovations.
The position is located in an area covered by the protection of scientific and technical potential (PPST), and therefore requires, in accordance with regulations, that your arrival be authorized by the competent authority at the french Ministry of Research.
Le poste se situe dans un secteur relevant de la protection du potentiel scientifique et technique (PPST), et nécessite donc, conformément à la réglementation, que votre arrivée soit autorisée par l'autorité compétente du MESR.
Contraintes et risques
Constraints and risks are mainly related to experiments. The candidate will have to conform to the general safety rules of the laboratory, and the rules specific to the use of the experimental equipment necessary to his work. These tools will only be accessible after appropriate training.
It should be noted that mechanical measurements will be carried out in a clean room, to avoid contamination of samples by dust. Working in a cleanroom requires specific equipment (gowns, masks, gloves, overshoes, etc.).
The risks associated with working at a computer workstation must also be taken into account.
The candidate should have a master's degree in experimental physics or experimental mechanics and/or an engineering degree. The position requires a sound knowledge of solid mechanics and materials, particularly soft materials. The following specific skills are not required but will be a plus:
- Practical experience with elastomers (material of choice for the textured surfaces planned)
- Practical experience in micromachining
- Practical experience in image analysis
- Practical experience of numerical tools in mechanics (ideally Abaqus)
- Ability to develop or modify an experimental set-up
Proficiency in at least one programming language (ideally Matlab) is required.
Good command of English is required. At least 3 months' experience in a non-French-speaking country is highly desirable.
Excellent writing skills.
Demonstrated ability to manage scientific projects (through internships, for example).
Ability to work in an international, multidisciplinary team.
A high degree of autonomy, proven organizational skills and good accountability are expected.
Candidates must be able to demonstrate a high level of critical thinking, scientific argumentation and initiative.
The application must include :
- a detailed CV
- if possible, two references (people likely to be contacted)
- a one-page cover letter (not repeating the CV)
- a one-page summary of your Master's thesis or dissertation
- grades from Master 1 and 2 or engineering school.