BEGIN:VCALENDAR VERSION:2.0 PRODID:-//Memento EPFL// BEGIN:VEVENT SUMMARY:MEchanics GAthering -MEGA- Seminar: Talk1 - The density of interac ting quasi-localised modes in amorphous solids\; Talk2 - How inertia can f acilitate friction\; Talk3 - Sudden failure in amorphous materials during quasistatic loading DTSTART:20181122T161500 DTEND:20181122T173000 DTSTAMP:20260510T032027Z UID:58a753bc411333355d91a7cb3a1c7457d5f1775369f2353e5ec31b94 CATEGORIES:Conferences - Seminars DESCRIPTION: Wencheng Ji\, Tom de Geus\, Marko Popovic\, PCSL\, EPFL\n The density of interacting quasi-localised modes in amorphous solids by W encheng Ji\, PCSL\, EPFL\nAbstract Amorphous solids are very common mate rials in our daily life\, such as glass\, toothpaste\, mayonnaise\, coffee foam\, and soya beans. Unlike crystals\, amorphous solids do not present topological defects due to their lack of long-range order. Instead they di splay excitations where a group of particles can rearrange. These essentia lly local excitations lead to a dipolar change of stress in the medium\, w hich can effectively couple them. One physical quantity related to the loc al low-energy excitations is a quasi-localized mode whose density follows D(ω)~ω4 [2-3] in glass different from Debye theory\, where ω is the vi brational frequency of the quasi-localized modes.\nHere\, we provide a the ory for the density of quasi-localized modes for classical systems at zero temperature\, which takes their interactions into account and clarifies t heir relationship with shear transformations [4-5]. We confirm this relati onship by using the molecular dynamics simulations of quasi-statically she ared glasses. \n[1] ArXiv prepring arXiv:1806.01561.\n[2] V. Gurevuch\, D . Parshin\, and H. Schober\, Physical Review B 67\, 094203 (2003).\n[3] E. Lerner\, G. During\, and E. Bouchbinder\, Physical Review Letters 117\, 0 35501 (2016).\n[4] A. Argon\, Acta Mettalurgica 27\, 47 (1979).\n[5] J. Li n and M. Wyart\, Physical Review X 6\, 011005 (2016).\n\nHow inertia can f acilitate friction by Tom de Geus\, PCSL\, EPFL\nAbstract We study the nucleation of slip between two sliding  solids\, whereby we focus on a me soscopic level where the disorder\, introduced by the surface roughness\, matters. It is at this scale that we can study how different contacts inte ract through the bulk’s elasticity. A result of this interaction is that the detachment of one asperity can trigger that of other contacts in its vicinity. An interesting question is if such collective effects organise i nto depinning-like avalanches. Vice versa this system allows the clarifica tion of the debated roled of inertia on an avalanche-like response [1-3]. We argue that\, due to the presence of rare weak sites\, the response is s mooth in the thermodynamic limit. At the same time we find this mechanism not to be efficient\, leading to a stick-sliip response in finite systems. \n[1] D.S. Fisher\, K. Dahmen\, S. Ramanathan\, Y. Ben-Zion\, PRL 78(25)\, 4885-4888 (1997).\n[2] J.M. Schwarz\, D.S. Fisher\, PRE\, 67(2)\, 021603 (2003).\n[3] K. Karimi\, E.E. Ferrero\, J.-L. Barrat\, PRE\, 95(1)\, 01300 3 (2017).\n\nSudden failure in amorphous materials during quasistatic load ing by Marko Popovic\, PCSL\, EPFL\nAbstract The response of amorphous materials to an applied strain can be continuous\, or instead display a ma croscopic stress drop when a shear band nucleates. Such discontinuous resp onse can be observed if the initial configuration is very stable. We study theoretically how such brittleness emerges in athermal\, quasi-statically driven\, materials as their initial stability is increased. We show that this emergence is well reproduced by elasto-plastic models and is predicte d by a mean field approximation\, where it corresponds to a continuous tra nsition. In mean field\, failure can be forecasted from the avalanche stat istics. We show that this is not the case for very brittle materials in fi nite dimensions due to rare weak regions where a shear band nucleates. We build an analogy with fracture mechanics predicting that their critical nu cleation radius follows ac~(Σ- Σb)-2  where Σ is the stress a shear b and can carry.\n  LOCATION:MED 2 2423 https://plan.epfl.ch/?room=MED22423 STATUS:CONFIRMED END:VEVENT END:VCALENDAR