Accueil >
Production scientifique
(5) Production(s) de l'année 2018


Inertial shear flow of assemblies of frictionless polygons: Rheology and microstructure
Auteur(s): Azema E., Radjai F., Roux JeanNoël
(Article) Publié:
European Physical Journal E, vol. 41 p. (2018)
Ref HAL: hal01675180_v1
DOI: 10.1140/epje/i2018116089
Exporter : BibTex  endNote
Résumé: Motivated by the understanding of shape effects in granular materials, we numerically investigate the macroscopic and microstructural properties of anisotropic dense assemblies of frictionless polydisperse rigid pentagons in shear flow, and compare them with similar systems of disks. Once subjected to large cumulative shear strains their rheology and microstructure are investigated in uniform steady states, depending on inertial number I, which ranges from the quasistatic limit (I ∼ 10 −5) to 0.2. In the quasistatic limit both systems are devoid of Reynolds dilatancy, i.e., flow at their random close packing density. Both macroscopic friction angle ϕ, an increasing function of I, and solid fraction ν, a decreasing function of I, are larger with pentagons than with disks at small I, but the differences decline for larger I and, remarkably , nearly vanish for I ∼ 0.2. Under growing I, the depletion of contact networks is considerably slower with pentagons, in which increasingly anisotropic, but still wellconnected forcetransmitting structures are maintained throughout the studied range. Whereas contact anisotropy and force anisotropy contribute nearly equally to the shear strength in disk assemblies, the latter effect dominates with pentagons at small I, while the former takes over for I of the order of 10 −2. The size of clusters of grains in sidetoside contact, typically comprising more than 10 pentagons in the quasistatic limit, very gradually decreases for growing I.




Experimental evaluation of transverse friction between fibers
Auteur(s): Gassara Houssem Eddine, Barbier Gérald, WagnerKocher C., Sinoimeri Artan, Pumo Besnik
(Article) Publié:
Tribology International, vol. 119 p.112  122 (2018)
Ref HAL: hal01668780_v1
DOI: 10.1016/j.triboint.2017.10.035
Exporter : BibTex  endNote
Résumé: The mechanical behavior of fibrous assemblies, particularly the transverse behavior of fiber yarns and multifilament strands depends, inter alia, on the fibertofiber contact and sliding. All studies on inter fiber friction presented in the literature focus on cases where the relative inter fiber motion occurs either in longitudinaltolongitudinal or longitudinaltotransverse direction. The transversetotransverse inter fiber friction plays an important role as far as the mechanical transverse behavior of fiber yarns and multifilament strands are concerned. In order to evaluate the case named here ‘transverse friction, the present study proposes an original method and an associated model analyzing the transversal component of friction between two oblique crossing fibers. A relatively simple and original statistical approach has also been developed to evaluate the confidence interval of friction coefficient. The first results show a relative stability of the transverse friction. This coefficient is also significantly inferior to the longitudinal one.




Elastic characterization of wood by Resonant Ultrasound Spectroscopy (RUS): a comprehensive study
Auteur(s): Longo Roberto, Laux Didier, Pagano S., Delaunay Thomas, Le Clézio Emmanuel, Arnould O.
(Article) Publié:
Wood Science And Technology, vol. p. (2018)
Ref HAL: hal01674610_v1
DOI: 10.1007/s002260170980z
Exporter : BibTex  endNote
Résumé: The main principle of Resonant Ultrasound Spectroscopy (RUS) measurement method is to excite a sample and to deduce its elastic constants from its free mechanical resonant frequencies. The goal of this paper is to propose an application of RUS in the case of wood cubic samples by: (1) using frequencies and mode shapes (or vibration patterns) of the free resonant modes in an iterative numerical procedure to solve the inverse problem for identifying components of the stiffness tensor of the sample’s material, (2) finding the limits and optimizing the robustness of the identification procedure in the case of wood and (3) applying it to a large density range of wood samples. Specific continuous waves have been used as excitation signal in order to experimentally determine the free resonant frequencies and mode shapes of the sample in a faster way by means of Scanning Doppler Vibrometer measurements. Afterward, the stiffness tensor was derived by solving iteratively an inverse problem. The gain of using the mode shapes in the inverse identification procedure is demonstrated to be particularly necessary for wood, especially for pairing each measured frequency with its corresponding theoretically predicted one, as viscoelastic damping causes the resonant peaks to overlap and/or disappear. A sensitivity analysis of each elastic constant on the measured resonant frequencies has thus been performed. It shows that, in its current state of development, not all of the elastic constants can be identified robustly and a modified identification procedure is thus proposed. This modified procedure has been applied successfully to wood samples with a large density range, including softwood and hardwood, and particularly nonhomogeneous wood species or with specific anatomical features.




Viscoelastic modeling of wood in the process of formation to clarify the hygrothermal recovery behavior of tension wood
Auteur(s): Capron Marie, Bardet S., Sujan K.C., MatsuoUeda Miyuki, Yamamoto H.
(Article) Publié:
Journal Of Materials Science, vol. 53 p.14871496 (2018)
Ref HAL: hal01662538_v1
DOI: 10.1007/s1085301715739
Exporter : BibTex  endNote
Résumé: To explain the hygrothermal recovery (HTR) behavior of tension wood (TW) from the physical and chemical point of view in relation to the time, species and microfibril angle, a theoretical discussion using an analytical onedimensional viscoelastic modeling was made. The chosen model includes an elastic element, a deformation mechanism and two viscoelastic elements called also as Kelvin–Voigt model. In this analysis, a topdown approach between the model and the experimental data was introduced to find the realistic parameters for the model. It enables us to fit the model to the HTR experimental data for three wood species: konara oak (Quercus serrata Murray), urihada maple (Acer rufinerve Siebold et Zucc.) and keyaki wood (Zelkova serrata Makino). The fitted experimental data show that the two compliances of the two viscoelastic elements are the most important parameters that explain the evolution of TW longitudinal strain during the thermal treatment.




Relaxation of nonconvex unbounded integrals with general growth conditions in Cheeger–Sobolev spaces
Auteur(s): Anza Hafsa O., Mandallena JeanPhilippe
(Article) Publié:
Bulletin Des Sciences Mathématiques, vol. 142 p.4993 (2018)
Ref HAL: hal01662240_v1
Exporter : BibTex  endNote
Résumé: We study relaxation of nonconvex integrals of the calculus of variations in the setting of Cheeger–Sobolev spaces when the integrand does not have polynomial growth and can take infinite values.

