Validity of the One-Dimensional Limp Model for Porous Media

A straightforward criterion for determining the validity ofthe limp model validity for porous materials is addressed here. The limp model is an “equivalent fluid” model which gives a better description of porous behavior than the well known “rigid frame” model. It is derived from the poroelastic Biot model, assuming that the frame has no bulk stiffness. A criterion is proposed for identifying the porous materials for which the limp model can be used. It relies on a new parameter, the Frame Stiffness Influence FSI, based on porous material properties. The critical values of FSI under which the limp model can be used are determined using 1D analytical modeling for a specific boundary set: radiation of a vibrating plate covered by a porous layer.

How reproducible are methods to measure the dynamic viscoelastic properties of poroelastic media?

There is a considerable number of research publications on the acoustical properties of porous media with an elastic frame. A simple search through the Web of Science™ (last accessed 21 March 2018) suggests that there are at least 819 publications which deal with the acoustics of poroelastic media. A majority of these researches require accurate knowledge of the elastic properties over a broad frequency range. However, the accuracy of the measurement of the dynamic elastic properties of poroelastic media has been a contentious issue. The novelty of this paper is that it studies the reproducibility of some popular experimental methods which are used routinely to measure the key elastic properties such as the dynamic Young's modulus, loss factor and Poisson ratio of poroelastic media. In this paper, fourteen independent sets of laboratory measurements were performed on specimens of the same porous materials. The results from these measurements suggest that the reproducibility of this type of experimental method is poor. This work can be helpful to suggest improvements which can be developed to harmonize the way the elastic properties of poroelastic media are measured worldwide

Validity of the One-Dimensional Limp Model for Porous Media

A straightforward criterion for determining the validity ofthe limp model validity for porous materials is addressed here. The limp model is an “equivalent fluid” model which gives a better description of porous behavior than the well known “rigid frame” model. It is derived from the poroelastic Biot model, assuming that the frame has no bulk stiffness. A criterion is proposed for identifying the porous materials for which the limp model can be used. It relies on a new parameter, the Frame Stiffness Influence FSI, based on porous material properties. The critical values of FSI under which the limp model can be used are determined using 1D analytical modeling for a specific boundary set: radiation of a vibrating plate covered by a porous layer.

Etude de peptides amyloïdogéniques dérivés de la tropoélastine humaine par simulations numériques

Ce travail de thèse porte sur l étude de peptides dérivés de la tropoélastine par simulations de dynamique moléculaire en solvant explicite. Ces peptides sont issus des exons 7, 28 et 30 et possèdent une séquence consensus XGGZG (X, Z = Valine, Leucine) identifiée expérimentalement comme responsable de la formation d assemblages supramoléculaire ayant des propriétés amyloïdes. Nous montrons tout d abord que le motif minimal XGGZG et (XGGZG) adoptent un grand nombre de coudes quel que soit la permutation entre valine et leucine et que localement les résidus non glycine présentent une conformation de type polyproline II dans des proportions significatives. L étude des répétitions (XGGZG)3 fait apparaître des structures allant du feuillet b antiparallèle pour (VGGVG)3 à de l hélice a et 310 pour (LGGLG)3. Les répétitions (VGGLG) 3 et (LGGVG)3 donnent pour leur part à la fois des structures comportant de faibles proportions d hélices ou de feuillets. Des résultats équivalents sont obtenus sur les exons 28 et 30 entiers, ainsi que sur le peptide comprenant les 17 premier résidus de l exon 30. La création d un plancher poly(VGGVG) de brins b virtuellement infini nous permet de montrer qu en sa présence, des peptides VGGVG peuvent s organiser parallèlement ou perpendiculairement à ce dernier. Enfin, es simulations préliminaires distinctes ont été menées afin d évaluer le rôle du cholestérol dans les phénomènes d agrégation ou dynamiques des peptides dérivés de la tropélastine. Des études de l effet biologique des peptides ont été débutées et sont une perspectives intéressantes de ce travail.This work deals with the study of tropoelastin-derived peptides by molecular dynamics simulations in explicit solvent. These peptides are identified in exons 7, 28 and 30 possess a consensus sequence XGGZG (X, Z = Valine, Leucine) described experimentally as responsible for the formation of supramolecular assemblies with amyloid properties. We first show that the minimal motif XGGZG and (XGGZG) adopt a large number of turns, independently of the permutation of valine and leucine residues. Locally, non-glycine residues exhibit polyproline-II conformation in significant proportions. The study of (XGGZG)3 show that it gives rise to structure form antiparallel b sheets for (VGGVG)3 to a and 310 helices for (LGGLG)3. (VGGLG)3 and (LGGVG)3 sequences give rise to both structures in small proportions. Equivalent results are obtained on the entire exons 28 and 30, and the peptide including the first 17 residues of exon 30. The construction of a poly(VGGVG) plan with virtually infinite b strand allows us to show that in contact with it, VGGVG peptides can organize parallel or perpendicularly to the plan. Finally, separate preliminary simulations were conducted to evaluate the role of cholesterol in the phenomena of aggregation and dynamics to tropoelastin-derived peptides. Studies of the biological effect of these peptides were initiated and are an interesting perspective of this work.REIMS-BU Sciences (514542101) / SudocSudocFranceF

On the contact law of open-cell poro-granular materials

International audienceThe contact stiffness between a poro-elastic spherical grain, made out of an open-cell foam, and a plane is studied with the aim of determining the contact law, and in particular verifying if the Hertz interaction potential, originally derived in the frame of continuum mechanics, holds. The contact law is studied experimentally by compressing a half-sphere of melamine foam into a rigid flat surface, and numerically by mean of a finite element model where the porous half-sphere is modeled by irregular tetrakaidecahedral cells. Both approaches reveal two regimes, at low and at high deformations in respect to the size of the cells. Above a cutoff value of the indentation, larger than the ligament length, a Hertzian interaction is observed. The latter is reliably described in terms of the radii of curvature of the contacting bodies and the effective elasticity of the foam structure. Below the cutoff, at the microscale, a more complex trend emerges because of the discrete nature of the foam and in particular the small number of ligaments in contact with the plane, which is function of the sphere radius at the macroscale and the cells shape at the mesoscale. Such microscopic features are akin to a surface roughness between continuous materials. These findings have practical implications to accurately describe the mechanical response of poro-granular media, used for instance in sound and vibration insulation