Mercredi 4 novembre 2026 à 11h00 ; salle 357 , IUSTI
Abstract: Cohesion in complex mechanical assemblies emerges from diverse physical origins, in which contact mechanics between constituents and cooperative effects are intertwined. In this talk, I will present experimental studies of two paradigmatic cases in which macroscopic cohesion can be traced back i) to frictional forces and ii) to polymer-mediated adhesion.
In the first part, I will discuss stick-slip dynamics in an assembly made of two interleaved blocks of paper sheets [1], whose exceptional resistance to detachment is due to a friction amplification phenomenon. The analysis focuses on the dynamic regime that follows the onset of detachment when the two blocks are pulled apart in a traction machine. Mechanical testing synchronized with sample imaging allows us to relate typical stick slip observables (peak forces, oscillation amplitudes) and the effective stiffness of the system to the mobility of the sheets across the assembly. The dependence of these observables on the degree of entanglement of the blocks is captured by combining a friction amplification model with a minimal spring-slider model. Remarkably, the effective stiffness of the system is governed by the tensile response of a subset of sheets located in an internal shell of the assembly, which is subjected to particularly high normal compression.
In the second part, I will give an overview of an ongoing experimental study on cohesive granular materials made of glass particles coated with polyborosiloxane (PBS), a crosslinked polymer with remarkable adhesive properties. The study aims to link the bulk rheology of PBS to grain-grain adhesion, and in turn to the macroscopic mechanical response of granular aggregates. It focuses in particular on how these properties depend on the physicochemical composition of PBS, notably the crosslinker concentration.
[1]: A. Plati, F. Restagno, C. Poulard, «Stick-slip dynamics in an interleaved system with self-amplified friction», Tribology International 255, 112355 (2026). (https://arxiv.org/abs/2602.14935)