PhD opportunity: Multiscale investigation of ductile-to-brittle transition in snow

Dear colleagues,

We are looking for a candidate to apply for a PhD opportunity about Multiscale investigation of ductile-to-brittle transition in snow (see below for details). This PhD will be supervised by M. Montagnat, P. Hagenmuller et G. Chambon and will take place in collaboration between Institut des Géosciences de l’Environnement (CNRS, Univ. Grenoble Alpes), Centre d’Etude de la Neige (CNRM MétéoFrance) and ETNA research unit (IRSTEA, Univ. Grenoble Alpes). Applications must be done on this site, before June 3rd.

Please contact Maurine Montagnat (maurine.montagnat@univ-grenoble-alpes.fr) before application or for more information

Details of the subject: Snow is a complex material whose microstructure is subjected to rapid evolutions under natural conditions, via metamorphism processes and grain sintering. Advancing the knowledge on the mechanical behavior of this material is required for numerous applications ranging from avalanche forecasting, to modelling the evolution of seasonal snowpack and polar firn, or to predicting efforts induced by the snowpack on infrastructures and buildings. The  mechanical properties and deformation regime of snow strongly depend on the applied loading rate. This rate-dependent character is generally interpreted as resulting from a competition between: (1) grain bond damage and rupture processes, and (2) healing and strengthening of these bonds through sintering. At the ductile to brittle transition, which occurs for strain rates on the order of 10-4 – 10-3 s-1, different sintering mechanisms, associated to a multiplicity of characteristic times, can be identified. Additional internal time scales can also arise from the elastoviscoplastic properties of ice. The activation and relative influence of these different mechanisms are likely to strongly depend on temperature conditions as well as on the considered snow microstructure (e.g., rounded versus faceted grains). However, existing data regarding the evolution of the loading rate for ductile-to-brittle transition as a function of these parameters, are scarce and inconclusive. Moreover, attempts at directly observing the micromechanisms at play in the ductile and fragile deformation regimes, remain extremely rare.

The aim of this PhD work is to study deformation mechanisms in snow at the brittle to ductile transition, and in particular, the role of microstructure and its evolution. The experimental work will consist in mechanical tests in a cold lab with a sample characterization pre- and post-deformation by means of X-ray microtomography. In parallel, numerical simulations of the mechanical behavior will be conducted through the use of Discrete Element Approaches.

The Phd candidate will have to show a strong interest for experimental work, with a background in physics and/or in mechanics of materials. The main skill required is curiosity and motivation for working with a multidisciplinary research team.

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