COMPLAS 2025

Keynote

Viscoelastic Contact Hysteresis with Green’s Function Molecular Dynamics: Methods and Insights

  • Müser, Martin (Saarland University)

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The adhesive hysteresis of soft elastomers with sticky counterfaces can have various origins, particularly when the true contact is not a singly connected domain but is instead fragmented into small patches due to microscale roughness. One potential mechanism for adhesive hysteresis, which remains active during quasi-static loading, is that less energy is gained during microscale jump-into-contact instabilities than is lost when breaking contact patches during retraction. This talk will address such situations while highlighting both the need for and the challenges associated with modeling short-range adhesion, particularly in viscoelastic solids. Special attention will be given to how viscoelasticity enhances the described multi-contact hysteresis and why saddle points and valleys in the topography, rather than asperity peaks, require particular focus. To investigate these effects, we compare the simulated and experimentally measured time evolution of the interfacial force and real contact area between a soft elastomer and a rigid, flat punch with small-scale, single-sinusoidal roughness. To this end, we extend the Green’s function molecular dynamics method and apply recently developed imaging techniques to elucidate the rate- and preload-dependence of the pull-off process. Our results reveal that hysteresis is significantly enhanced when the saddle points of the topography come into contact—a process that is, however, impeded by viscoelastic forces and may require sufficiently large preloads. [1] C. Müller and M. H. Müser, How short-range adhesion slows down crack closure and contact formation, J. Chem. Phys. 159, 234705 (20023) [2] C. Müller, M. Samri, R. Hensek, E. Arzt, and M. H. Müser, Revealing the coaction of viscous and multistability hysteresis in an adhesive, nominally flat punch: A combined numerical and experimental study, J. Mech. Phys. Solids 174, 105260 (2023) [3] A. Wang and M. H. Müser, Is there more than one stickiness criterion? Friction 11, 1027 (2022).