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In classical solids mechanics, when analyzing the mechanical behavior of materials, a fundamental underlying assumption is generally made : properties and behaviors are assumed to be constant, or to evolve smoothly, through space and time when considering scales larger than a so-called representative volume element (RVE). This way, simple (averaged) relationships can be proposed between stresses and strains, and an important goal of modern mechanics is to link small scale properties (within the RVE) to the macroscopic behavior, in a procedure called homogenization.
However, over the last decades, it became clear that for various problems (fracture, faulting, plastic deformation,..) and materials (heterogeneous materials, granular media, geophysical objects,..), homogenization is irrelevant as the considered systems and processes are characterized by fluctuations and instabilities of all sizes, up to the size of the finite system itself. In this case, the different space and time scales are related through emergent scaling laws, without characteristic scales, defining the concept of complexity in solid mechanics. A paradigmic example is the celebrated Gutenberg-Richter distribution of earthquake energies.
The backbone of my research is centered on the analysis of this complexity, from collective dislocations dynamics during plastic deformation of crystalline materials, to the large scale brittle deformation of the sea ice cover or of the Earth’s crust. This is done through laboratory experiments, analysis of geophysical data, numerical simulations, and theoretical modeling, importing concepts and tools recently developed in statistical physics to the fields of solid mechanics, material science, and geophysics.
In material science, with my colleagues and students, we have shown that, at least for some materials, plastic deformation occurs through intermittent strain bursts, power law distributed in size and energy, organized in a fractal pattern, and clustered in time with mainshocks triggering aftershocks, much like Earthquakes at geophysical scales. More recently, I focused on the failure of heterogeneous materials and media under compression and shear, showing that this macroscopic failure from an “intact” state can be considered as a critical phase transition with precursors and emergent scaling laws. This novel interpretation of failure has fundamental consequences in terms of failure’s prediction or size effects on strength.
In geophysics, large fluctuations, instabilities and scaling are ubiquitous, from crustal brittle deformation (earthquakes) to the kinematics of the sea ice cover, from landslides to cliff’s collapse. Over the last years, I focused on the mechanics and kinematics of the Arctic sea ice cover. We have shown that sea ice drift and deformation are characterized by space and time scaling laws, signatures of the its brittle rheology at odds with the continuous, viscous-like description of sea ice rheology in climate models. As sea ice isolates the ocean from the atmosphere, it largely controls exchanges of heat and momentum between these two fluids, and so plays a fundamental role on climate. This stresses the need for a new mechanical modeling framework. In addition, we have shown that both Arctic sea ice mechanics, drift and deformation evolve in a spectacular way over the last decades, with important consequences in terms of sea ice mass balance, hence on climate in the northern latitudes.
Shifting my research interests from the cryosphere to Solid Earth’s geophysics, my objective will be an experimental and theoretical analysis of the fundamentals of shear faulting, using conceptual as well as methodological tools recently developed in the statistical physics of disordered media.