arXiv subjects

D. Dalmas

Publications and source records attributed to D. Dalmas.

5 recordsLinked to original sources

arXiv2026

Automated Discovery of Metainterfaces with Tailored Friction Laws

Providing dry solid contacts with on-demand macroscale frictional behaviour remains a formidable challenge in tribology, haptics or robotics. Metainterfaces created from surfaces with engineered asperity-based topographies can achieve such friction control. However, only few friction behaviours were demonstrated because suitable topographies were identified based on human intuition. Here, we introduce a numerical-optimisation-based inverse design framework to automatically discover new metainterfaces satisfying specified relationships between friction and normal forces (friction law). To illustrate the framework's versatility, we first expand the range of achievable friction coefficients at a constant material pair; we next unlock power-law friction laws with arbitrary exponents between 2/3 and 1.35; we then achieve bilinear laws with a smaller slope in the second segment than in the first. We validate relevant cases experimentally. By enabling systematic exploration of large parameter spaces, not limited to topography but potentially incorporating the individual asperities' bulk material or surface physicochemistry, our automated framework offers design solutions for any physically possible friction law. It also provides new insights into the elusive relationship between local interfacial properties and macroscopic friction.

physics.class-ph↗

arXiv2023

Adhesion in soft contacts is minimum beyond a critical shear displacement

The most direct measurement of adhesion is the pull-off force, i.e. the tensile force necessary to separate two solids in contact. For a given interface, it depends on various experimental parameters, including separation speed, contact age and maximum loading force. Here, using smooth contacts between elastomer spheres and rigid plates, we show that the pull-off force also varies if the contact is sheared prior to separation. For shear displacements below a critical valueabout 10% of that necessary to yield gross sliding, the pull-off force steadily decreases as shear increases. For larger shear, the pull-off force remains constant, at a residual value 10%--15% of its initial value. Combining force measurements and in situ imaging, we show how the unloading path leading to contact separation is modified by the initial shear. In particular, we find that the residual pull-off force prevails if the contact reaches full sliding during unloading. Based on those observations, a first modeling attempt of the critical shear displacement is proposed,involving a competition between jump instability and transition to sliding. Overall, those results offer new insights into the interplay between adhesion and friction, provide new constraints on adhesion measurements and challenge existing adhesive models. They will be useful wherever soft contacts undergo both normal and shear stresses, including tire grip, soft robotics, haptics and animal locomotion.

cond-mat.soft↗

arXiv2020

Finite deformations govern the anisotropic shear-induced area reduction of soft elastic contacts

Solid contacts involving soft materials are important in mechanical engineering or biomechanics. Experimentally, such contacts have been shown to shrink significantly under shear, an effect which is usually explained using adhesion models. Here we show that quantitative agreement with recent high-load experiments can be obtained, with no adjustable parameter, using a non-adhesive model, provided that finite deformations are taken into account. Analysis of the model uncovers the basic mechanisms underlying shear-induced area reduction, local contact lifting being the dominant one. We confirm experimentally the relevance of all those mechanisms, by tracking the shear-induced evolution of tracers inserted close to the surface of a smooth elastomer sphere in contact with a smooth glass plate. Our results suggest that finite deformations are an alternative to adhesion, when interpreting a variety of sheared contact experiments involving soft materials.

cond-mat.soft↗

arXiv2005

The mechanics of glass and functionalised glass surfaces

Glass is highly sensitive to surface flaws generated by contact. Surface cracks threaten both its mechanical strength and visual aspect. Recent trends in glass functionalisation by grafting or coating lend an even more prominent role to the surface. For these reasons, the glass surface mechanics, which couples surface physico-chemistry with mechanical response, must be considered in details to optimize glass processing and products. We review a few recent advances in the field of glass surface mechanics, with special emphasis on the local ductility of silicate glasses and the mechanical stability of films and coatings.

cond-mat.mtrl-sci↗

arXiv2003

Crack fronts and damage in glass at the nanometer scale

We have studied the low speed fracture regime for different glassy materials with variable but controlled length scales of heterogeneity in a carefully mastered surrounding atmosphere. By using optical and atomic force microscopy (AFM) techniques we tracked in real-time the crack tip propagation at the nanometer scale on a wide velocity range (mm/s - pm/s and below). The influence of the heterogeneities on this velocity is presented and discussed. Our experiments reveal also -for the first time- that the crack progresses through nucleation, growth and coalescence of nanometric damage cavities within the amorphous phase. This may explain the large fluctuations observed in the crack tip velocities for the smallest values. This behaviour is very similar to what is involved, at the micrometric scale, in ductile fracture. The only difference is very likely due to the related length scales (nanometric instead of micrometric). Consequences of such a nano-ductile fracture mode observed at a temperature far below the glass transition temperature in glass is finally discussed.

cond-mat↗