Ifsttar PhD subject

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Title : Constitutive laws for icy regoliths : from Mars to Saturn moons

Main host Laboratory - Referent Advisor MAST - GPEM  -  ARTONI Riccardo      tél. : +33 240845616

Director of the main host Laboratory RICHARD Patrick  -

PhD Speciality Physique; Sciences de la terre

Axis of the performance contract 2 - COP2017 - More efficient and resilient infrastructure

Main location Nantes

Doctoral affiliation UNIVERSITE DE NANTES

PhD school EGAAL - Ecologie, Géosciences, Agronomie et Alimentation

Planned PhD supervisor ARTONI Riccardo  -  Université Gustave Eiffel  -  MAST - GPEM

Planned financing Contrat doctoral  - Ifsttar

Abstract

In finely sized granular materials, i.e. powders, an important phenomenon is interparticle cohesion which may be due to, for example, Van der Waals forces [Andreotti et al. 2013]. Due to such cohesion, powders have a peculiar mechanical behavior, allowing to stabilize loose packings, which can however collapse under load. Ice powders at low temperature belongs to this class of materials : the understanding of its rheology is important for several industrial applications (temperature control during mixing of granular pastes or granulation, innovative sandblasting technologies, …). Moreover, this kind of cohesive granular material is ubiquitous at the surface of several bodies in the solar system, and determines the physical properties of the soil in such bodies. An outstanding example is Enceladus, a small Saturn moon, where jets and deposition of finely grained ice from the south pole have been observed [Porco et al. 2006, Jaumann et al., 2008 ; Taffin et al. 2012], but another example is Mars, where ice powder avalanches have been observed near the north pole [Russel et al., 2008].

The study of the rheology of ice powders at low and very low temperatures will allow to better understand and predict the behavior of such cohesive materials in order to, on one hand, optimize processes involving them and, on the other hand, understand the geophysics of the surface of icy bodies in our solar system. With respect to the latter, the research aims at understanding surface processes, but also anticipate the technical constraints for the landing and digging systems for future in-situ missions [Konstantinidis et al. 2018]. Two in situ missions are currently being developed by NASA, a first towards Titan (Dragonfly Mission), a second towards Europa (Europa Lander Mission). Anticipating the properties of these icy soils is essential to minimize the technical problems that future missions may encounter.

In this context, the objective of this thesis is to develop knowledge on the mechanical behavior of granular materials made of ice powder through the implementation of discrete numerical simulations involving cohesive grains, and cold room experiments. The ultimate goal is to understand the stability of the material in relation to surface flows (avalanches), impact (landing), and drilling. This project is the result of a collaboration between IFSTTAR's GPEM laboratory (Aggregates and Materials Processing) and the LPG (Laboratory of Planetology and Geodynamics, University of Nantes & CNRS), which aims to combine the expertise of the GPEM on the rheology of granular materials and its applications to that of LPG on the characterization of the surface-interior interactions in icy bodies.

From an experimental point of view, a technique for manufacturing ice powders with a controlled size distribution will be developed. The powders will be characterized with a powder shear cell (for example, a Brookfield Powder Flow Tester), which will be adapted to the temperature constraints of the experiments, and installed in the cold room of the LPG. This tool will make it possible to characterize the yield locus [Molerus 1975] according to the consolidation stress, the size distribution, the shape of the particles, their composition (presence of rock powder). The parameters obtained (effective coefficient of friction, cohesion, critical state density) will give rise to a quantification of the powder flowability (with reference to the flow triggering) and will provide a data set to validate the discrete element simulations. The experiments will initially be conducted at temperatures of -30 / -20 ° C, accessible in the cold room of the LPG, which are relevant for industrial and Martian applications. Subsequently, the installation of a cooling system will be evaluated, to reach lower temperatures, potentially up to 80 K representative of the surface of the moons of Saturn.

The numerical activity will consist in the development of a discrete model reproducing the properties of the powders in question. To do this, a model of interparticle cohesive force built by considering the nature of the materials (polydispersity, multicomponent) and interactions (electrostatic forces, van der Waals, ...) will be integrated into a DEM code developed by the GPEM laboratory. At first, simulations to replicate the shear cell experiments will be used to validate the model and adjust the parameters of the interaction models. Once validated, the numerical model will be used to simulate complex flow conditions such as (1) destabilization of a slope, inspired by avalanche problems and (2) body impact, inspired by impact problems or localized compression and (3) drilling using different techniques (percussion vs. rotation).
This thesis is part of the GRIM project carried out by IFSTTAR and LPG, funded by region Pays de la Loire in the framework of the call "Paris scientifiques en Pays de la Loire", which supports emerging, fundamental and transdisciplinary subjects.

The results will be disseminated in international peer-reviewed journals (physics journals, the granular materials community, planetary sciences). At least two articles should be submitted before the end of the thesis. It is also envisaged that the PhD student will present his work at thematic conferences (eg Powders and Grains 2021, Partec 2022, Congress AGU 2022, EPSC2021).

Applicants must hold a Master's degree in physics, mechanics, earth sciences, or equivalent. They must be motivated by approaches coupling experiences with numerical simulations.

Keywords : cohesive granular materials; rheology; stability; ice powder; icy bodies of the solar system

Main host Laboratory - Referent Advisor	MAST - GPEM - ARTONI Riccardo tél. : +33 240845616
Director of the main host Laboratory	RICHARD Patrick -
PhD Speciality	Physique; Sciences de la terre
Axis of the performance contract	2 - COP2017 - More efficient and resilient infrastructure
Main location	Nantes
Doctoral affiliation	UNIVERSITE DE NANTES
PhD school	EGAAL - Ecologie, Géosciences, Agronomie et Alimentation
Planned PhD supervisor	ARTONI Riccardo - Université Gustave Eiffel - MAST - GPEM
Planned financing	Contrat doctoral - Ifsttar
Abstract In finely sized granular materials, i.e. powders, an important phenomenon is interparticle cohesion which may be due to, for example, Van der Waals forces [Andreotti et al. 2013]. Due to such cohesion, powders have a peculiar mechanical behavior, allowing to stabilize loose packings, which can however collapse under load. Ice powders at low temperature belongs to this class of materials : the understanding of its rheology is important for several industrial applications (temperature control during mixing of granular pastes or granulation, innovative sandblasting technologies, …). Moreover, this kind of cohesive granular material is ubiquitous at the surface of several bodies in the solar system, and determines the physical properties of the soil in such bodies. An outstanding example is Enceladus, a small Saturn moon, where jets and deposition of finely grained ice from the south pole have been observed [Porco et al. 2006, Jaumann et al., 2008 ; Taffin et al. 2012], but another example is Mars, where ice powder avalanches have been observed near the north pole [Russel et al., 2008]. The study of the rheology of ice powders at low and very low temperatures will allow to better understand and predict the behavior of such cohesive materials in order to, on one hand, optimize processes involving them and, on the other hand, understand the geophysics of the surface of icy bodies in our solar system. With respect to the latter, the research aims at understanding surface processes, but also anticipate the technical constraints for the landing and digging systems for future in-situ missions [Konstantinidis et al. 2018]. Two in situ missions are currently being developed by NASA, a first towards Titan (Dragonfly Mission), a second towards Europa (Europa Lander Mission). Anticipating the properties of these icy soils is essential to minimize the technical problems that future missions may encounter. In this context, the objective of this thesis is to develop knowledge on the mechanical behavior of granular materials made of ice powder through the implementation of discrete numerical simulations involving cohesive grains, and cold room experiments. The ultimate goal is to understand the stability of the material in relation to surface flows (avalanches), impact (landing), and drilling. This project is the result of a collaboration between IFSTTAR's GPEM laboratory (Aggregates and Materials Processing) and the LPG (Laboratory of Planetology and Geodynamics, University of Nantes & CNRS), which aims to combine the expertise of the GPEM on the rheology of granular materials and its applications to that of LPG on the characterization of the surface-interior interactions in icy bodies. From an experimental point of view, a technique for manufacturing ice powders with a controlled size distribution will be developed. The powders will be characterized with a powder shear cell (for example, a Brookfield Powder Flow Tester), which will be adapted to the temperature constraints of the experiments, and installed in the cold room of the LPG. This tool will make it possible to characterize the yield locus [Molerus 1975] according to the consolidation stress, the size distribution, the shape of the particles, their composition (presence of rock powder). The parameters obtained (effective coefficient of friction, cohesion, critical state density) will give rise to a quantification of the powder flowability (with reference to the flow triggering) and will provide a data set to validate the discrete element simulations. The experiments will initially be conducted at temperatures of -30 / -20 ° C, accessible in the cold room of the LPG, which are relevant for industrial and Martian applications. Subsequently, the installation of a cooling system will be evaluated, to reach lower temperatures, potentially up to 80 K representative of the surface of the moons of Saturn. The numerical activity will consist in the development of a discrete model reproducing the properties of the powders in question. To do this, a model of interparticle cohesive force built by considering the nature of the materials (polydispersity, multicomponent) and interactions (electrostatic forces, van der Waals, ...) will be integrated into a DEM code developed by the GPEM laboratory. At first, simulations to replicate the shear cell experiments will be used to validate the model and adjust the parameters of the interaction models. Once validated, the numerical model will be used to simulate complex flow conditions such as (1) destabilization of a slope, inspired by avalanche problems and (2) body impact, inspired by impact problems or localized compression and (3) drilling using different techniques (percussion vs. rotation). This thesis is part of the GRIM project carried out by IFSTTAR and LPG, funded by region Pays de la Loire in the framework of the call "Paris scientifiques en Pays de la Loire", which supports emerging, fundamental and transdisciplinary subjects. The results will be disseminated in international peer-reviewed journals (physics journals, the granular materials community, planetary sciences). At least two articles should be submitted before the end of the thesis. It is also envisaged that the PhD student will present his work at thematic conferences (eg Powders and Grains 2021, Partec 2022, Congress AGU 2022, EPSC2021). Applicants must hold a Master's degree in physics, mechanics, earth sciences, or equivalent. They must be motivated by approaches coupling experiences with numerical simulations.
Keywords :	cohesive granular materials; rheology; stability; ice powder; icy bodies of the solar system

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