The mechanics of natural or synthetic fibrous media is currently undergoing an important development carried on, the one hand, by new experimental and numerical means and on the other hand by the growing needs for characterization and modeling on the application side. In this context, the goal of the CNRS "GDR" Multiscale Mechanics of Fibrous Media - MECAFIB - is to gather french academic and industrial research teams working on this area to reinforce their interactions and to allow scientific issues related to these particular media to be tackled. More precisely, the GDR MECAFIB focuses on the mechanics of flexible fibrous media, characterized by significant relative displacements between fibers, strong non-linearities related both to their contacts and the rheology of their constituents (fibers, fiber bundles, soft matrix). The main objective of the GDR MECAFIB is to develop and/or use tools of experimental, theoretical and numerical mechanics for characterizing and modeling both the architectures and the mechanics of fibrous media. Here are some typical examples among the targeted fibrous systems:

  • Woven, knitted or braided fabrics with synthetic or biosourced fibers, used as ordered fibrous reinforcements in composite materials. Here again, several issues need to be fixed to better predict, for instance during composite forming operations, their mechanical behavior and/or the impregnation and the flow of polymeric resins through them.
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Simulations of the woving of fiber yarns (left) and the stamping of the resulting textile (right)
 
  • Cables and ropes, used for example in tires or to sustains loads.  For these systems, there is is a great challenge to determine the inner geometrical configuration and to predict the mechanical behavior up to failure.
  • Papers and other non-woven fibrous architectures used for printing, packaging, or in chemical engineering processes. Here again, proper tools and methods are required to better characterize and model their disordered microstructures (anisotropy, porosity, specific surface...) and their complex thermo-hygro-mechanical behavior.
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Crack progagation in a paper sheet (synchrotron X-ray tomography)
 
  • Gels and other concentrated colloidal fiber suspensions, used for comsetic products, inks, paintings, or to produce nanopapers, nanocomposites, aerogels... The rheology of these systems is complex and closely linked with to flow-induced re-organization of their fibrous networks, which is in turn altered by the mechanics of both nanofibers and their strerical, colloidal and hydrodynamical interactions. 
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AFM micrograph of cellulose nanofribils (left) and corresponding hydrogel (inset) and foam (right) produced by freeze drying (synchrotron X-ray microtomography)
 
  • Biosourced, synthetic or mineral wools, used for their interesting thermal and acoustical properties, which still need to be better understood and controlled.
  • Soft living tissues, such as blood vessels, ligaments, skin, vocal folds... These media are made of entangled and wavy networks of collagen and elastin fibers playing leading roles on their highly non-linear and quasi-reversible mechanical behavior.
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Network of collagen fibers in human aorta before and after equi-biaxial tension (left, confocal microscopy). Muscle and collagen fibers in vocal folds (right, synchrotron X-ray tomography)
 
  • Soft biomaterials, e.g. woven, knitted, braided fabrics as well as electrospinned or other fibrous materials used for (endo)protheses and scaffolds and designed with complex biomometic and biocompatibiliy constraints.
 
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Left and center: predicted pore size distribution (left) and deformation of a polymeric braided scaffold for knee ligaments (finite element simulation). 3D view of a self-entangled Nitinol filament (X-ray microtomography) with microstructure and mechanical behavior close to cancelous bones.