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SUMMARY:Compressive behaviour of long-fibre composites: a multi-scale appr
 oach
DTSTART:20160422T121500
DTEND:20160422T131500
DTSTAMP:20260924T095039Z
UID:9b86c2a2c5d8c484715a4fe0a372eefddcc1f037a2c81bd36157d6ba
CATEGORIES:Conferences - Seminars
DESCRIPTION:Prof. Dr Olivier Allix\, LMT-Cachan / Institut Universitaire d
 e France\nThe intensive use of Carbon Fibres Reinforced Plastics in aerona
 utics implies to master the prediction of the behaviour of composite up to
  final failure and if one consider energy absorption even further. The so-
 called virtual testing approach supports this goal and relies on the use o
 f robust models keeping the key physical mechanisms into account.\nAn impo
 rtant aspect of the response of composite is compression\, which involve a
  particular mode of deterioration the kinking of fibres. In dynamics it ca
 n lead to a large amount of dissipated energy thanks to the fragmentation 
 of the whole structure. Thanks to many works the physics of formation of k
 inking is today relatively well understood at the scale of the fibres\, th
 e one of the energy dissipated in the process far less. Moreover\, its mod
 elling at the meso-scale and its interaction with delamination is still a 
 challenging issue.\nPreliminary studies focus on quasi-static loadings of 
 small samples. A micro model of a representative unit cell incorporating c
 arbon fibres in an epoxy matrix has been developed to account for the main
  degradation mechanisms associated to kinking. It is based on Fleck & Budi
 ansky’s kinking theory [1]. This micro model has been used to extract th
 e most important characteristics (strength\, dissipated energy\, kink band
  size) [2-3] and the associated scattering mainly due to the statistical w
 aviness of the fibres. From that point on\, a ply-scale model has been imp
 roved to account for compressive loadings [4]. The chosen representative v
 olume element relies on the fragment size at the micro scale. An approxima
 te potential form has been proposed and the associated state and evolution
  laws are identified using an energy equivalence principle between the sca
 les – and models. The kink band size plays the role of a localization li
 miter. This constitutive law is parameterized by the fibre waviness angle 
 and is able to represent material and geometrical nonlinearities under mul
 ti-axial loadings.\nThis work can be divided in three parts. The first one
  describes the kinking micro model and the main associated results. The se
 cond part focuses on the construction of a homogenized constitutive law at
  the meso-scale. The third part features an application of the strategy to
  the modelling of the degradation of holed plates in compression. For this
  purpose\, the meso-scale model has been implemented in the virtual materi
 al model proposed in [5]. This hybrid description strategy allows the inte
 raction between the micro buckling mechanism (kinking) and other classical
  degradation mechanisms\, such as delamination and transverse cracking [6]
 \, to take place for any configuration. The discussion of the relevance of
  the approach using qualitative comparisons between simulation [7] and exp
 eriments from the literature [8-9] will be discussed.\n[1] B. Budiansky an
 d N. A. Fleck\, N. Compressive failure of fibre composites. Journal of the
  Mechanics and Physics of Solids\, 41(1):183-211\, 1993.\n[2] J.M. Guimard
 \, O. Allix\, N. Pechnik\, and P. Thévenet. Energetic analysis of fragmen
 tation mechanisms and dynamic delamination modelling in {CFRP} composites.
  Computers and Structures\, 87(15):1022-1032\, 2009.\n[3] N. Feld\, O. All
 ix\, E. Baranger\, and J.M. Guimard. Micro-mechanical prediction of UD lam
 inates behavior under combined compression up to failure: influence of mat
 rix degradation. Journal of Composite Materials\, 45(22):2317-2333\, 2011.
 \n[4] N. Feld\, O. Allix\, E. Baranger\, and J. M. Guimard. A micromechani
 cs-based mesomodel for unidirectional laminates in compression up to failu
 re. Journal of Composite Materials\, 46(23):2893-2909\, 2012.\n[5] P. Lade
 vèze\, G. Lubineau\, and D. Violeau. A computational damage micromodel of
  laminated composites. International Journal of Fracture\, 137(1):139-150\
 , 2006.\n[6] C. S. Yerramalli and A. M. Waas. A failure criterion for fibe
 r reinforced polymer composites under combined compression-torsion loading
 . International journal of solids and structures\, 40(5):1139-1164\, 2003.
 \n[7] Allix\, O.\, Feld\, N.\, Baranger\, E.\, Guimard\, J.M.\, Ha-Minh\, 
 C. The compressive behaviour of composites including fiber kinking: modell
 ing across the scales. Meccanica. Vol 49. Num 11. Pages 2571-2586. 2014\n[
 8] Soutis C\, Fleck NA (1990) Static compression failyre of 943 carbon fib
 re T800/924C composite plate with a single hole. 944\, J Compos Mater 24:5
 36–558\n[9] Lee J\, Soutis C (2008) Measuring the notched compressive st
 rength of composite laminates: specimen size effects.  Compos Sci Technol
  68:2359–2366\nBio : Olivier Allix is Professor (of Exceptional class) a
 t the Ecole Normale Supérieure de Cachan and previous director of LMT-Cac
 han and is member of the prestigious Institut Universitaire de France. Oli
 vier Allix has worked intensively in connection with Airbus and other comp
 anies on the modelling of the mechanical behaviour of composites and the d
 evelopement of multiscale strategies to deal with those complex material a
 nd structures. He recently proposed non intrusive computational methods to
  easily implemnt those techniques into commercial packages. Olivier Allix 
 serves as member of 12 editorial boards of international journals. He orga
 nized the Fourth European Conference on Computational Mechanics in Paris i
 n 2010 with more than 2000 participants and is an Euromech and IACM fellow
 .
LOCATION:GCB330 http://plan.epfl.ch/?lang=fr&room=GCB330
STATUS:CONFIRMED
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