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(80) Production(s) de GEORGE M.
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On the effect of local sample slope during modulus measurements by contact-resonance atomic force microscopy
Auteur(s): Heinze K., Arnould Olivier, Delenne Jean-Yves, Lullien-Pellerin V., Ramonda M., George M.
(Article) Publié:
Ultramicroscopy, vol. 194 p.78 - 88 (2018)
Texte intégral en Openaccess :
Ref HAL: hal-01869770_v1
DOI: 10.1016/j.ultramic.2018.07.009
WoS: 000450281700010
Exporter : BibTex | endNote
1 Citation
Résumé: Contact-resonance atomic force microscopy (CR-AFM) is of great interest and very valuable for a deeper understanding of the mechanics of biological materials with moduli of at least a few GPa. However, sample surfaces can present a high topography range with significant slopes, where the local angle can be as large as ± 50°. The non-trivial correlation between surface slope and CR-frequency hinders a straightforward interpretation of CR-AFM indentation modulus measurements on such samples. We aim to demonstrate the significant influence of the surface slope on the CR-frequency that is caused by the local angle between sample surface and the AFM cantilever and present a practical method to correct the measurements. Based on existing analytical models of the effect of the AFM set-up's intrinsic cantilever tilt on CR-frequencies, we compute the non-linear variation of the first two (eigen)modes CR-frequency for a large range of surface angles. The computations are confirmed by CR-AFM experiments performed on a curved surface. Finally, the model is applied to directly correct contact modulus measurements on a durum wheat starch granule as an exemplary sample.
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Les plastiques se biodégradent-ils en mer ?
Auteur(s): Gaillard T., George M., Gastaldi Emmanuelle, Ghiglione Jean François, Dussud Claire, Salomez Mélanie, Fabre P.
Conference: 6èmes journées scientifiques du LabeX NUMEV (Montpellier, FR, 2017-11-13)
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In situ AFM investigation of slow crack propagation mechanisms in a glassy polymer
Auteur(s): George M., Nziakou Y. K., Goerke S., Genix A.-C., Bresson Bruno, Roux Stéphane, Delacroix H., Halary J.-L., Ciccotti M.
(Article) Publié:
Journal Of The Mechanics And Physics Of Solids, vol. 112 p.109-125 (2018)
Texte intégral en Openaccess :
Ref HAL: hal-01656192_v1
DOI: 10.1016/j.jmps.2017.11.019
WoS: 000426536400006
Exporter : BibTex | endNote
2 Citations
Résumé: A novel experimental technique based on in situ AFM monitoring of the mechanisms of damage and the strain fields associated to the slow steady-state propagation of a fracture in glassy polymers is presented. This micron-scale investigation is complemented by optical measurements of the sample deformation up to the millimetric macroscopic scale of the sample in order to assess the proper crack driving conditions. These multi-scale observations provide important insights towards the modeling of the fracture toughness of glassy polymers and its relationship with the macromolecular structure and non-linear rheological properties. This novel technique is first tested on a standard PMMA thermoplastic in order to both evaluate its performance and the richness of this new kind of observations. Although the fracture propagation in PMMA is well known to proceed through crazing in the bulk of the samples, our observations provide a clear description and quantitative evaluation of a change of fracture mechanism towards shear yielding fracture accompanied by local necking close to the free surface of the sample, which can be explained by the local change of stress triaxiality. Moreover , this primary surface necking mechanism is shown to be accompanied by a network of secondary grooves that can be related to surface crazes propagating towards the interior of the sample. This overall scenario is validated by post-mortem fractographic investigations by scanning electron microscopy.
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Numerical modeling of the tensile strength of a biological granular aggregate: Effect of the particle size distribution
Auteur(s): Heinze K., Frank Xavier, Lullien-Pellerin Valerie, George M., Radjai Farhang, Delenne Jean-Yves
Conference: International workshop on Powders and Grains (Montpellier, FR, 2017-07-03)
Actes de conférence: EPJ Web of Conferences, vol. 140 p. (2017)
Texte intégral en Openaccess :
Ref HAL: hal-01539472_v1
DOI: 10.1051/epjconf/201714008013
Exporter : BibTex | endNote
Résumé: Wheat grains can be considered as a natural cemented granular material. They are milled under highforces to produce food products such as flour. The major part of the grain is the so-called starchy endosperm.It contains stiff starch granules, which show a multi-modal size distribution, and a softer protein matrix thatsurrounds the granules. Experimental milling studies and numerical simulations are going hand in hand tobetter understand the fragmentation behavior of this biological material and to improve milling performance.We present a numerical study of the effect of granule size distribution on the strength of such a cementedgranular material. Samples of bi-modal starch granule size distribution were created and submitted to uniaxialtension, using a peridynamics method. We show that, when compared to the effects of starch-protein interfaceadhesion and voids, the granule size distribution has a limited effect on the samples’ yield stress.
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