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SUMMARY:MEchanics GAthering -MEGA- Seminar: Talk 1 - Why do surgeons sleep
  better with plasticity in their knots? Talk 2 - Snap buckling of bi-stabl
 e beams under magnetic actuation
DTSTART:20211202T161500
DTEND:20211202T173000
DTSTAMP:20260510T165052Z
UID:09b559158e37636b0695db3c1b044a7303800f80570d218c8bce5744
CATEGORIES:Conferences - Seminars
DESCRIPTION:Paul Johanns & Arefeh Abbasi (fleXLab\, EPFL)\nTalk 1: Why 
 do surgeons sleep better with plasticity in their knots? by Paul Johanns
  (fleXLab\, EPFL)\n\nAbstract Surgery\, rooted etymologically in “hand
  work”\, is a craftsmanship\; high-quality suturing requires optimal man
 ual skills reached only after years of experience. Knots are a suture’s 
 weakest link and their failure can be disastrous. While monofilaments (ver
 sus braided ones) have the advantage of lower infection risks\, they are m
 ore challenging to ensure mechanical safety. Preventing failure of surgica
 l knots in monofilaments requires for the applied tension to lie within a 
 precise range\; under-tension yields insufficient plastic deformation\, wi
 th the elastic energy stored in bending serving as an unravelling driver\,
  while filament rupture can result from over-tension. We perform an invest
 igation on the operational and safety limits of surgical knots\, highlight
 ing the previously overlooked but crucial effect of plastic deformation. W
 e analyze the sutures produced by an experienced surgeon and in a model sy
 stem to characterize the relevant range of applied tensions and geometric 
 features\, through mechanical testing and X-ray tomographic imaging. Our e
 xperiments combined with FEM simulations enable us to rationalize the prim
 ary ingredients dictating the mechanical performance of surgical knots.\n\
 nSupported by the Fonds National de la Recherche\, Luxembourg 12439430.\n\
 nBio Paul Johanns got his B.Sc. and M.Sc. both in Mechanical Engineering 
 from ETH Zurich. He performed his Master Thesis at Caltech working on tens
 egrity-inspired structures for impact protection. Here\, he developed a st
 rong interest for the mechanics of slender structures before joining EPFL
 ’s fleXLab as a Ph.D. student in 2018. His research focuses on the funda
 mental understanding of the topological influence on the mechanics of comp
 lex knots.\n\nTalk 2: Snap buckling of bi-stable beams under magnetic actu
 ation\, by Arefeh Abbasi (fleXLab\, EPFL)\n\nAbstract We investigate t
 he mechanics of bi-stable\, hard-magnetic\, elastic beams under magnetic
  actuation\, combining precision model experiments\, 3D finite elem
 ent modeling (FEM)\, and a reduced-order centerline-based theoretical mode
 l. In the experiments\, a beam is fabricated using a hard magneto-rheolo
 gical elastomer (hard-MRE) magnetized such that the beam contains two segm
 ents with antiparallel magnetization along the beam centerline but otherwi
 se identical mechanical properties. The beam is initially pre-loaded into 
 a curved\, bi-stable configuration by fixing its end-to-end shorten
 ing. Then\, under the application of an external uniform magnetic field\, 
 the beam can be made to snap\, reversibly\, between its two stable states.
  First\, we experimentally characterize the critical field strength for th
 e onset of snapping for different levels of end-to-end shortening. We p
 erform 3D FEM simulations\, which adopt an exiting continuum theory for
  hard-MREs. In the FEM\, the RIKS method is used to analyze high
 -order deformation modes and the corresponding energy states of the beam d
 uring snapping. In parallel\, a reduced-order centerline-based beam theo
 ry is developed to rationalize the observed magneto-elastic response
 . The validity of the theory and simulations is established by their exce
 llent quantitative agreement with experiments. Finally\, we consider the c
 ase of combined mechanical (point indentation) and magnetic loading. We
  examine how the applied field affects the bi-stability and quantify the 
 maximum load-bearing capacity of the beam under indentation. Our work prov
 ides a set of predictive tools for the rational design of one-dimensional\
 , bi-stable\, magneto-elastic structural elements\, which could potentiall
 y form the basis of a novel class of functional mechanisms.\n\nBio Arefeh
  Abbasi got his B.Sc. and M.Sc. both in Mechanical Engineering from Shiraz
  University\, Iran. She developed a strong interest for the mechanics of s
 lender structures before joining EPFL’s fleXLab as a Ph.D. student in 20
 19. Her research focuses on the snap buckling of magneto-active structures
  for designing functional devices.\n\n 
LOCATION:MED 0 1418 https://plan.epfl.ch/?room==MED%200%201418 https://epf
 l.zoom.us/j/67873367071?pwd=b0NEeWY2MFJqNGUzUitJV256YSt6QT09
STATUS:CONFIRMED
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