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Jamming, plasticité et défaillance des matériaux
(44) Production(s) de l'année 2018
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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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Roughness of oxide glass subcritical fracture surfaces
Auteur(s): Pallares Gael, Lechenault F., George M., Bouchaud Elisabeth, Ottina Cédric, Rountree Cindy L., Ciccotti Matteo
(Article) Publié:
Journal Of The American Ceramic Society, vol. 101 p.1279-1288 (2018)
Texte intégral en Openaccess : 
Ref HAL: hal-01633422_v1
Ref Arxiv: 1711.05040
DOI: 10.1111/jace.15262
WoS: 000419096700032
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
Résumé: An original setup combining a very stable loading stage, an atomic force microscope and an environmental chamber, allows to obtain very stable sub-critical fracture propagation in oxide glasses under controlled environment, and subsequently to finely characterize the nanometric roughness properties of the crack surfaces. The analysis of the surface roughness is conducted both in terms of the classical root mean square roughness to compare with the literature, and in terms of more physically adequate indicators related to the self-affine nature of the fracture surfaces. Due to the comparable nanometric scale of the surface roughness, the AFM tip size and the instrumental noise, a special care is devoted to the statistical evaluation of the metrologic properties. The 2 roughness amplitude of several oxide glasses was shown to decrease as a function of the stress intensity factor, to be quite insensitive to the relative humidity and to increase with the degree of heterogeneity of the glass. The results are discussed in terms of several modeling arguments concerning the coupling between crack propagation, material's heterogeneity, crack tip plastic deformation and water diffusion at the crack tip. A synthetic new model is presented combining the predictions of a model by Wiederhorn et al. [1] on the effect of the material's heterogeneity on the crack tip stresses with the self-affine nature of the fracture surfaces.
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