PROMETAF

Programmable metainterfaces for friction control

This project was funded by ANR through Grant ANR-18-CE08-0011

Project summary

Although the optimization of the devices involving functional contacts would enable significant energy savings, at the beginning of the project, there was no established method to prepare an interface with pre-defined frictional properties. The aim of PROMETAF has been to propose a simple and generic surface design strategy to obtain such interfaces.

The idea has been to build surfaces with a deterministic texture, by placing model asperities, one by one, on a deformable substrate. By tuning the shape and altitude of each individual asperity, we have been piloting the macroscopic behaviour of the interface, while targeting unprecedented frictional properties. In practice we have explored various types of interfaces giving access to various pre-defined, non-linear friction laws, some of which connecting working conditions usually considered incompatible.

This newly accessible toolbox is expected to be useful to advance the state-of-the-art, both by questioning the usual approach to friction control through homogeneous surface coatings, and by extending the range of applications of metamaterials to friction.

To validate a new interface design, the following three main methods are used.

First, we identify the relevant multi-asperity model, based on a preliminary calibration of the tribological behavior of a single microcontact. The model is then inverted, to predict the list of geometrical descriptors of all individual asperities (radii of curvature, altitudes) that is expected to provide the desired macroscale frictional behavior. In this project, we used analytical inversions.

Second, we fabricate an elastomer substrate according to surface topography prescribed by the inversion. We prepare an aluminum mold decorated by an array of spherical holes with the prescribed individual depths, and use it to obtain a polydimethylsiloxane (PDMS) substrate with the negative topography: an array of spherical asperities.

Third, we form a contact between the textured PDMS and a smooth glass substrate, and perform mechanical tests in order to measure the friction law of the interface (friction force vs normal force). The experimental friction law is finally compared quantitatively to the desired one.

Using the above methods, we validated various original interface designs. Those include: (i) interfaces whose friction laws passes through three operating points usually considered as incompatible, (ii) interfaces whose friction coefficient can be tuned on-demand and (iii) interfaces featuring two different friction coefficients according to the range of normal force applied to the contact.

Illustration of the design strategy

Flowchart of the design strategy. Upper sketch: single microcontact submitted to a normal force p and a friction force f. Lower sketch: metainterface submitted to normal and friction forces, P and F. Black ellipses: real contact regions.

Outputs of the project

Publication in peer-reviewed international journals

[1] E. Delplanque, A. Aymard, D. Dalmas, J. Scheibert. Solving curing-protocol-dependent shape errors in PDMS replication. Journal of Micromechanics and Microengineering 32, 045006 (2022) (link, pdf)

Oral communications in international conferences

[1] J. Scheibert. Approche modèle en tribologie : application aux contacts élastomères secs. Journées Internationales Francophones de Tribologie 2021. Distanciel. Invited conference

[2] A. Aymard. Friction law of model asperity-based rough elastomer contacts. Contact Mechanics International Symposium 2022, Chexbres, Switzerland

[3] J. Scheibert. Shear-induced contact morphology changes in rough elastomer interfaces. Contact Mechanics International Symposium 2022, Chexbres, Switzerland. Invited conference

[4] A. Aymard. Design and realization of metasurfaces with tunable friction law. 7^th World Tribology Congress, Lyon, France

[5] J. Scheibert. Creating soft interfaces with pre-defined static friction forces. 9^th International Tribology Congress, 2023, Fukuoka, Japan. Invited conference

Oral communications in national conferences

[1] A. Aymard. Realisation of surfaces with controlled friction laws. 17èmes Journées de la Matière Condensée 2021, Rennes, France

[2] E. Delplanque. Résolution des erreurs de forme dépendantes du protocole de durcissement, lors de la réplication par du PDMS. Journée 50 ans du groupe français des polymères, 2021, Lyon, France (poster)

[3] J. Scheibert. Frictional metainterfaces. Journée « Soft metamaterials » du GDR MEPHY, 2023, Paris, France