PhD in experimental and numerical physics/mechanics of contacts under complex loading (M/W)

22 Sep 2023
Job Information

Organisation/Company

CNRS

Department

Laboratoire de tribologie et dynamique des systèmes

Research Field

Engineering » Materials engineering
Physics » Acoustics

Researcher Profile

First Stage Researcher (R1)

Country

France

Application Deadline

12 Oct 2023 – 23:59 (UTC)

Type of Contract

Temporary

Job Status

Full-time

Hours Per Week

35

Offer Starting Date

1 Dec 2023

Is the job funded through the EU Research Framework Programme?

Not funded by an EU programme

Is the Job related to staff position within a Research Infrastructure?

No

Offer Description

-The PhD thesis will be attached to the Ecole Doctorale Mécanique, Energétique, Génie Civile et Acoustique (MEGA). The student will work within a multidisciplinary team of the LTDS including two supervisors (physicists) and on engineers in surface sciences. The work will include an important experimental component: preparation / physico-chemical characterization of samples, their mechanical and optical characterization. It will also involve processing and analyzing a large amount of data. Finally, the doctoral student will have to synthesize these results, place them in the context of international literature and use them to write articles for international scientific journals. The work also includes participation in national or international congresses.

The PhD work will be part of a broader collaborative project (acronym CLOSER) between two teams of the Laboratoire de Tribologie et Dynamique des Systèmes (LTDS) funded by the French National Agency for Research (ANR).
Contacts involving elastomers combine strong friction and strong adhesion, two hysteretic effects making their sliding transition very dependent on the loading history. The monotonic and unidirectional loadings conditions generally used to characterize friction of elastomers are therefore not sufficiently representative of applications (tires, seals, haptic devices), where loadings conditions are very complex (multiaxial, vibratory). In this project, a consortium of experimenters and modelers will try to reach a complete understanding of the elementary mechanisms at the origin of the resistance to friction of elastomeric contacts under arbitrarily complex loading histories in order to go beyond the simplistic methods (simple shear) usually used in the literature. Through quantitative comparison between measurements and simulations of the contact’s strain field, we expect to unravel the respective roles of the various elementary mechanisms at the origin of the transition to sliding in contacts under realistic loading of increasing complexity.
To achieve this ambitious goal, we will apply a wide range of different loading sequences on elastomer contacts, both in carefully controlled experiments and in relevant numerical simulations. Those measurements will be used to challenge the state-of-the-art models of the onset of sliding of elastomer contacts, recently developed in the consortium [J. Lengiewicz, et al. J. Mech. Phys. Solids 143, 104056 (2020)], in order to account simultaneously, for the first time at the local scale, for friction, adhesion and elastic non-linearities of elastomers.
While the numerical simulations will be carried out in parallel by another PhD student, the realization et analyses of the experiments are the focus of the present PhD project. In recent years, the consortium developed an internationally recognized expertise in the contact mechanics of sheared elastomer contacts. Under increasing shear, those contacts undergo important changes in the average contact pressure and in the micro-contact morphology, even under constant normal loading [R. Sahli et al. PNAS 115, 471 (2018); J. Lengiewicz, et al. J. Mech. Phys. Solids 143, 104056 (2020)]. For this new project, our main research hypothesis is that the relevant loading history is essentially encoded into the current contact’s strain field, i.e., the local pressure/shear deformation state of the elastomer at the very interface. To test this hypothesis, we propose three sets of shear experiments on model interfaces with increasing loading complexity which will allow, in addition to normal and tangential macroscopic forces, to measure during shear both the strain field and the evolution of the real contact area. These last two quantities will be obtained thanks to an advanced analysis of in-situ contact images using particle tracking [J. Lengiewicz, et al. J.Mech. Phys. Solids 143, 104056 (2020)] or digital image correlation (DIC) [A. Prevost et al. Eur. Phys. J.E 36, 17 (2013)]. In the first set of experiments, we will keep the usual condition of constant normal loading and investigate the contact behavior under complex quasi-static in-plane displacements (change in the direction of motion). In the second one, we will investigate the role of superimposed normal load variations. In the last set, by varying systematically the driving velocity, we will test the influence of the visco-elastic properties of our elastomer and also investigate the stability of an interface submitted to additional vibrations.
Our strategy will rely on carrying out sliding experiments on carefully designed PDMS samples with various properties and topographies (single/multi-asperities and/or rough surfaces) with a new, worldclass opto-mechanical device, recently developed in the LTDS-TPCDI team. This device enables contact loading through five simultaneous and independent degrees of freedom (three displacements, possibly additionally vibrated at high frequency, and two rotations) [Guibert ey al. Rev. Sci. Instrum. 92, 085002 (2021)] and allows simultaneous high-resolution monitoring of all three forces and three moments at the contact interface. Finally, it enables high-resolution in-situ visualization of the contact area, giving access to in-operando, full-field measurements of the real contact area and of the tangential displacement.

Requirements

Research Field

Engineering

Education Level

PhD or equivalent

Research Field

Physics

Education Level

PhD or equivalent

Languages

FRENCH

Level

Basic

Research Field

Engineering » Materials engineering

Years of Research Experience

None

Research Field

Physics » Acoustics

Years of Research Experience

None

Additional Information
Additional comments

The candidate must hold a master’s degree and / or an engineering degree in experimental/numerical physics or mechanics. The position requires solid knowledge in continuum solids mechanics, in particular for elastomers. The following specific skills are not required but will be a plus:
– Practical experience in Tribology and in particular in Contact mechanics
– Practical experience with elastomers
– Practical experience in image analysis
– Ability to develop or modify an experimental device
A good command of at least one programming language (ideally Matlab) is necessary. A good command of English is required. Experience of at least 3 months in a non-French speaking country is highly desirable. Candidates must demonstrate excellent writing skills, and have demonstrated (internships for example) their ability to lead a scientific project. They should be able to work in an international and multidisciplinary team. A great deal of autonomy, a proven organizational capacity and a good capacity to report are expected. Candidates must show a high level of critical thinking, ease in scientific argumentation and the ability to take initiative. Applications should include a detailed CV; if possible two references (people likely to be contacted); a one-page cover letter; a one-page summary of the master’s thesis or end of study thesis; Master 1 or 2 or engineering school grades).

Website for additional job details

https://emploi.cnrs.fr/Offres/Doctorant/UMR5513-DAVDAL-005/Default.aspx

Work Location(s)

Number of offers available

1

Company/Institute

Laboratoire de tribologie et dynamique des systèmes

Country

France

City

ECULLY

Where to apply

Website

https://emploi.cnrs.fr/Candidat/Offre/UMR5513-DAVDAL-005/Candidater.aspx

Contact

City

ECULLY

Website

http://ltds.ec-lyon.fr

STATUS: EXPIRED