CE08 - Matériaux métalliques et inorganiques et procédés associés

Programmable metasurfaces for friction control – Prometaf

Programmable metasurfaces for friction control

Despite centuries of research, the friction of dry macroscopic contact interfaces remains imperfectly understood and thus poorly mastered. Although the optimization of the devices involving functional contacts would enable significant energy savings, there is currently no established method to prepare an interface with pre-defined frictional properties. The aim of PROMETAF is precisely to propose a simple, generic, ground-breaking surface design strategy to obtain such interfaces.

Designing metasurfaces with controlled contact and friction behaviour

The idea is to build deterministic metasurfaces by placing model asperities, one by one, on a deformable substrate. By tuning the shape, size, altitude, bulk material and surface coating of each asperity, as well as the substrate structure, we will pilot de macroscopic behaviour of the interface to obtain unprecedented frictional properties. In practice we will develop an ambitious set of four tools:<br />(i) interfaces with a pre-defined, highly non-linear friction law, connecting various, usually incompatible, working conditions<br />(ii) programmable interfaces, each sample enabling, through preliminary tuning of a static substrate deformation, selection of any desired friction law out of a full family of accessible laws<br />(iii) metasurfaces which, contrary to all natural surfaces, have a decreasing friction force when the confining pressure on the interface increases<br />(iv) active surfaces the topography of which can be varied using remotely controlled actuators, thus enabling real-time tuning of the friction force, without changing the external loading.

The design of metasurfaces is based on a series of analytical and numerical tools: asperity-based statistical models are adapted to describe the relationship between surface properties and emerging frictional behaviour. In practice, we perform inversions with a friction law as input and arrays of asperity properties (height, radius, in-plane location) as outputs.
Once the design is proposed, actual surfaces are prepared in four steps: (i) preparation of an aluminum mold via micro-milling, (ii) filling with an elastomer melt, (iii) curing of the elastomer and (iv) demolding.
Those surfaces are then tested in a dedicated opto-mechanical tribometer, enabling precise force measurements and in-situ imaging of the contact interface.
Eventually, signal and image analysis enable quantitative comparison with the expected behaviour.

So far, we have:
(i) developed the protocols for the production of reproducible rubber samples with the desired topographical features.
(ii) worked out the inversion procedure for interfaces featuring two-branched non-linear friction laws
(iii) created the corresponding surfaces
(iv) tested them with the tribometer
The agreement is satisfactory, validating this first example of application of our design strategy (tool A).

There no focus so far.
We will in the future continue exploring the various proposed tools (tools B to D), starting with tool B.

None so far.

Despite centuries of research, the friction of dry macroscopic contact interfaces remains imperfectly understood and thus poorly mastered. Although the optimization of the devices involving functional contacts would enable significant energy savings, there is currently no established method to prepare an interface with pre-defined frictional properties. The aim of PROMETAF is precisely to propose a simple, generic, ground-breaking surface design strategy to obtain such interfaces.

The idea is to build deterministic metasurfaces by placing model asperities, one by one, on a deformable substrate. By tuning the shape, size, altitude, bulk material and surface coating of each asperity, as well as the substrate structure, we will pilot de macroscopic behaviour of the interface to obtain unprecedented frictional properties. In practice we will develop an ambitious set of four tools:

(i) interfaces with a pre-defined, highly non-linear friction law, connecting various, usually incompatible, working conditions
(ii) programmable interfaces, each sample enabling, through preliminary tuning of a static substrate deformation, selection of any desired friction law out of a full family of accessible laws
(iii) metasurfaces which, contrary to all natural surfaces, have a decreasing friction force when the confining pressure on the interface increases
(iv) active surfaces the topography of which can be varied using remotely controlled actuators, thus enabling real-time tuning of the friction force, without changing the external loading.

This newly accessible toolbox will be useful to advance the state-of-the-art, both by questioning the paradigm of a single, monotonous friction law for a given interface, and by extending the range of applications of metamaterials to friction.

The proposed methodology intimately couples experiments, theory and simulations, to reach a deep understanding of each of the developed tools. After a step of theoretical/numerical design, the most promising metasurfaces will be prepared using an original combination of micro-machining, additive fabrication and surface coating. Their frictional behaviour (force, contact area, etc.) will then be characterized, using acutting edge opto-mechanical device recently developed by PROMETAF team members, and finally compared quantitatively to theoretical/numerical predictions.

The project is led by an internationally recognized young researcher with extensive experience in dry friction, both at the micro- and macroscale. He and his international, multi-disciplinary team already master all the necessary skills to reach PROMETAF’s objectives. The success of the project will be ensured by a detailed task-based organisation in which the main risks and the associated fallback solutions have been carefully identified. So, despite the novelty and ambition of PROMETAF, the success rate is deemed very high.

The project’s results are expected to impact not only the scientific community, in mechanical engineering, physics and geoscience, but also various industries, in particular in the fields of robotics and virtual reality. The past effort of the team to (i) publish in the leading scientific journals in mechanics and physics, as well as in high-impact multidisciplinary journals, and (ii) to organise international scientific events, will be continued here to ensure the maximal exposure of the project’s results.

For the coordinator, managing PROMETAF will be a unique opportunity to (i) take increased responsibilities and consolidate his team and (ii) develop a research direction which is not only new for him, but also for the international scientific community, thus strengthening his international recognition as a major expert in the field of friction.

Project coordination

Julien Scheibert (Laboratoire de Tribologie et Dynamique des Systèmes)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

LTDS Laboratoire de Tribologie et Dynamique des Systèmes

Help of the ANR 274,710 euros
Beginning and duration of the scientific project: March 2019 - 48 Months

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