Séminaire

Saint-Martin-d'Hères - Domaine universitaire

Constitutive modelling is a core subject in the field of computational geotechnics, as the quality of
predictions made by finite element simulations depends on the quality of the constitutive model
used. For many students, constitutive modelling is perceived as an abstract and 'hard to grasp'
topic in engineering education. The aim of the project ’Animating Soil Models’ is to improve the
understanding of constitutive modelling through animations and interactive figures. Topics
visualised include yield surfaces, stress invariants, critical state soil mechanics and some related
models such as the Modified Cam Clay model and hypoplasticity. The visualisations are available
on the SoilModels.com platform under the open CC BY license, making them freely available as
educational resources. The animations certainly do not replace the study of equations,
calculations or reading books. However, they can facilitate the teaching and understanding of
concepts related to constitutive modelling.

• En savoir plus sur Gertraud Medicus

Saint-Martin-d'Hères - Domaine universitaire

The energy industry is transitioning towards a future with lower carbon footprint. Many countries
and companies have pledged to achieve zero-greenhouse gas emissions by 2050. Three major
areas that can contribute to these objectives while providing energy security are (1) natural gas
from unconventional formations, (2) carbon capture utilization and storage, and (2) deep
geothermal energy. This talk will present recent advances in these three areas focused on studies
done by the presenter. The contents help understand how to to securely develop unconventional
formations, reduce risks in carbon dioxide geological utilization and storage, and deploy safely and
effectively geothermal energy. Examples include (1) optimizing fracture geometry, reducing sharp
decline rates and enabling enhanced recovery for unconventionals, (2) maintaining high injection
rates, optimizing pore space use, and averting fault reactivation or losing seal integrity for carbon
geological storage, and last, lowering uncertainties and improving design of multistage hydraulic
fracture and closed loop wells, maximizing power output, and limiting potential induced
seismicity for geothermal energy. Last the presentation will include the presenter’s experience on
sharing freely geomechanics concepts and courses through github and youtube for the worldwide
geomechanics community.

• En savoir plus sur Nicolas Espinoza

Saint-Martin-d'Hères - Domaine universitaire

Predicting the maximum load that a (quasi-)brittle specimen can sustain, along with determining the correct crack path, is a crucial scientific and practical challenge. A natural approach to address this problem is to identify appropriate criteria. Strength and toughness criteria are well-suited for simple specimens with either no defects or an existing crack. However, when defects are present, the criteria become more complex and require more sophisticated approaches. Over the last few decades, numerous models have demonstrated their ability to predict both critical loads and crack paths effectively. Some of these models include the Thick Level Set (TLS) models (Moës et al., 2011; Zghal et al., 2018), Phase Field damage models (Miehe et al., 2010; Wu, 2017), Peridynamics (Diehl et al., 2022; Jafarzadeh et al., 2024), and more recently, the Lip Field damage model (Chevaugeon & Moës, 2022; Moës et al., 2022) ...

Phase Field damage model has been widely adopted over the past few decades, and it primarily builds on the foundational work of Ambrosio and Tortorelli (Ambrosio & Tortorelli, 1990). The excitement for this method within the mechanics community surged following the publication of Miehe’s influential work (Miehe et al., 2010). More recently, Wu proposed a unified formulation of the Phase Field model (Wu, 2017), enabling the treatment of different Phase Field versions, such as PF-AT1, PF-AT2, and PF-CZM ... This lecture will present a critical analysis of the Phase Field damage model. The first part will be dedicated to the PFDam tool, developed in the LEME laboratory on the FEniCS open-source computing platform. Then, various Phase Field damage models and resolution strategies will be compared within a quasi-static framework. In the final part, some preliminary results will be discussed from the extension of the PFDam tool to dynamic scenarios.

Faure, Y., Bayart, E. Experimental evidence of seismic ruptures initiated by aseismic slip.
Nat Commun 15, 8217 (2024). https://doi.org/10.1038/s41467-024-52492-2

• En savoir plus sur Elsa Bayart

Saint-Martin-d'Hères - Domaine universitaire

Predicting the maximum load that a (quasi-)brittle specimen can sustain, along with determining the correct crack path, is a crucial scientific and practical challenge. A natural approach to address this problem is to identify appropriate criteria. Strength and toughness criteria are well-suited for simple specimens with either no defects or an existing crack. However, when defects are present, the criteria become more complex and require more sophisticated approaches. Over the last few decades, numerous models have demonstrated their ability to predict both critical loads and crack paths effectively. Some of these models include the Thick Level Set (TLS) models (Moës et al., 2011; Zghal et al., 2018), Phase Field damage models (Miehe et al., 2010; Wu, 2017), Peridynamics (Diehl et al., 2022; Jafarzadeh et al., 2024), and more recently, the Lip Field damage model (Chevaugeon & Moës, 2022; Moës et al., 2022) ...

Phase Field damage model has been widely adopted over the past few decades, and it primarily builds on the foundational work of Ambrosio and Tortorelli (Ambrosio & Tortorelli, 1990). The excitement for this method within the mechanics community surged following the publication of Miehe’s influential work (Miehe et al., 2010). More recently, Wu proposed a unified formulation of the Phase Field model (Wu, 2017), enabling the treatment of different Phase Field versions, such as PF-AT1, PF-AT2, and PF-CZM ... This lecture will present a critical analysis of the Phase Field damage model. The first part will be dedicated to the PFDam tool, developed in the LEME laboratory on the FEniCS open-source computing platform. Then, various Phase Field damage models and resolution strategies will be compared within a quasi-static framework. In the final part, some preliminary results will be discussed from the extension of the PFDam tool to dynamic scenarios.

• En savoir plus sur Jihed Zghal

Saint-Martin-d'Hères - Domaine universitaire

The sodium salt of carboxymethylcellulose (NaCMC) is a water-soluble derivative of cellulose, which is broadly used for industrial applications such as food, pharmaceuticals, paints, etc., and serves as a thickener and water retention. The properties of NaCMC can be exquisitely tuned via their degree of substitution (DS), which corresponds to the average number of carboxymethyl groups per repeating glucose unit and varies between 0 and 3. Highly substituted polymers, i.e., for DS >1, are hydrophilic and disperse easily in water, yielding rheological features typical of polyelectrolyte solutions. In contrast, weakly substituted polymers, i.e., for DS<0.9, contain hydrophobic regions, which favor interchain aggregation and the formation of so-called ``fringed micelles'' yielding thixotropic and even gel-like properties at high enough concentrations. Here we show that gelation of NaCMC solution can be induced by lowering the pH, which decreases the charge density along the CMC chain and promotes the formation of multichain aggregates.

• En savoir plus sur Thibaut Divoux

Saint-Martin-d'Hères - Domaine universitaire

The lecture focuses on the use of advanced centrifuge modeling to enhance the understanding of offshore structures behavior. The example chosen is the torpedo pile used to anchor FPSO platforms in marine clay soils in deep water environment. The presentation compares the performance of vertical and inclined torpedo anchors, as well as torpedo clusters with varying spacing. The results of vertical pullout tests are also compared with API recommendations.

• En savoir plus sur Márcio de Souza Soares de Almeida

Saint-Martin-d'Hères - Domaine universitaire

The lecture focuses on the use of advanced physical modeling to enhance the understanding of offshore structure behavior. The example chosen is the monopile foundations for wind farms. The results of monotonic loading tests are presented and measured p-y curves are compared with API recommendations. In addition, the results of 100.000 cyclic loading tests are shown, with emphasis on the variation of stiffness and natural frequency with the number of cycles.

• En savoir plus sur Maria Cascão Ferreira de Almeida

Charged polymers or polyelectrolytes (PEs) are ubiquitous. The conformations
of highly charged PEs are influenced by a combination of factors, including
long-range electrostatic interactions, solvent quality, temperature, counterion
valency, and dielect ric constant of the solvent. In this seminar, we will discuss
the impact of attractive neutral crowders on the conformations of a single,
similarly charged PE in the presence of oppositely charged counterions. Us-
ing extensive molecular dynamics simulations utilizing generic coarse-grained
bead–spring models, we identify three distinct phases: (1) the CCI phase
(Charged Collapsed due to Intra-polymer interactions), which corresponds to a
collapsed state primarily driven by the condensation of counterions; (2) the CE
phase (Charged Extended), characterized by an extended conformation of the
polymer due to repulsive electrostatic interactions within the PE; and (3) the
CCB phase (Charged Collapsed due to Bridging interactions), representing a
secondary collapsed state primarily induced by the presence of attractive bridg-
ing crowders, with a substantial number of crowders located within the col-
lapsed conformation. By identifying the phase transitions among these phases,
we obtain the phase diagram in the PE charge density and polymer–crowder
interaction phase space for monovalent, divalent, and trivalent counterions. Our simulations reveal that the interaction with
crowders can induce collapse, despite the presence of strong repulsive electrostatic interactions, and can replace condensed coun-
terions to facilitate a direct transition from the CCI and CE phases to the CCB phase.

• En savoir plus sur Kamal Tripathi

Bio-cementation soil improvement methods are alternatives to invasive, carbon-intensive stabilisation techniques. These methods, which include microbially induced carbonate precipitation (MICP) and enzyme induced carbonate precipitation (EICP), use biogeochemical processes to drive carbonate precipitation and cement soil grains, thereby improving the material mechanical performance. Sands treated by bio-cementation methods typically exhibit an improvement in strength and stiffness, yet often with variable magnitudes, even at equal calcium carbonate contents. The variation in the mechanical performance of bio-cemented sands impedes the practical applications of MICP/ EICP, while it is poorly understood. In this presentation, we are going to understand the mechanical behaviour of bio-cemented sands, particularly the uncertainty or variation of the mechanical performance, from the microscopic point of view by using the discrete element method (DEM).

• En savoir plus sur Zhang Aoxi

Molecular dynamics simulations are ubiquitous in materials science, from drug discovery to design of advanced structural nanocomposites. Owing to the high-resolution of these simulations taking place at the atomic scale, predictions give access to data often complementary to experiments; be it characterisation of the nanostructure or even sophisticated instrumentation. I will begin the talk introducing the fundamentals of setting up molecular models and dynamics simulations to investigate the mechanics of materials. I will illustrate these aspects focusing on the collagen, the structural protein of choice in the human body and more largely the animal kingdom. I will present our recent investigations on the influence of hydration on the assembly of collagen microfibrils and the complex water dynamics within, trying to draw conclusions on the mechanical properties of the biopolymer.

While being quite popular, molecular dynamics simulations have several limitations (force field precision, ergodicity). Among these, the spectrum of spatiotemporal scales integrated within a simulation is extremely limited. This is particularly problematic when mechanical properties are of interest, as these emerge from the combination of scales ranging from the nanoscale (chemistry) to the macroscale (processing, testing). Unlike real-life experiments, all scales cannot be resolved simultaneously using computer simulations. I will give an overview of the existing multiscale simulation strategies: from rather cheap hierarchical to expensive concurrent approaches. I will illustrate their applicability with examples from my past research on the fracture of concrete under seismic loading and the dynamic behaviour of impacted shells of epoxy-graphene nanocomposites.

• En savoir plus sur Maxime Vassaux