arXiv subjects

Hadrien Rattez

Publications and source records attributed to Hadrien Rattez.

9 recordsLinked to original sources

arXiv2025

Predicting cement microstructure and mechanical properties in hydrating cement paste with a Phase-Field model

Predicting the evolving microstructure of hydrating cement is essential for understanding and modeling its mechanical property development. Physics-based continuum approaches offer a rigorous framework for capturing the thermodynamics of dissolution and precipitation processes at the microstructural scale. In this work, we present an adapted Phase-Field (PF) model for cement hydration that resolves key physical inconsistencies in existing PF formulations by introducing a revised free-energy potential and distinct equilibrium constants for clinker dissolution and hydrate precipitation. The resulting PF framework reproduces microstructural evolution, yielding realistic porosity levels and continuous phase boundaries in close agreement with experimental observations. The predicted hydrated microstructures are subsequently used in a computational homogenization scheme to evaluate the elastic response of the material. The PF-derived mechanical properties show good agreement with experimental trends, supporting the ability of the proposed framework to consistently link hydration chemistry, microstructure formation, and the resulting mechanical response.

cond-mat.mtrl-sci↗

arXiv2024

Importance of precipitation on the slowdown of creep behaviour induced by pressure-solution

Pressure-solution is a chemo-mechanical process, involving dissolution at grain/asperity contacts and precipitation away from them. It induces a compaction in time of rocks and sediments. The present study investigates numerically the impact of precipitation on the slowdown of creep behavior induced by pressure-solution. A recently published framework, called the Phase-Field Discrete Element Model, is carefully calibrated against existing indentation experiments and validated for other rate-limiting scenarios. It is shown that when precipitation is relatively slow, the slowdown of pressure-solution is due to a chemical mechanism (accumulation of solute concentration within the pore space), whereas, at fast precipitation, the slowdown is due to a mechanical mechanism (stress reduction at the contact).

cond-mat.mtrl-sci↗

arXiv2024

Stress state evolution of a cemented granular material subjected to bond dissolution by Discrete Element Modeling

Rock weathering is a common phenomenon in most engineering applications, such as underground storage or geothermal energy. This work offers a discrete element modelization of the problem considering cohesive granular material and debonding effect. Oedometer conditions are applied during the weathering and the evolution of the coefficient of lateral earth pressure, a proxy of the state of stress, is tracked. Especially, the influence of the degree of cementation, the confining pressure, the initial value of k0 and the history of load are investigated. It has been emphasized that the granular media aims to reach an attractor configuration. And the grain reorganization occurring is divided into two main phenomena: the collapse of the unstable chain forces (stable only thanks to the cementation) and the softening of the grains.

cond-mat.mtrl-sci↗

arXiv2023

Frictional weakening of a granular sheared layer due to viscous rolling revealed by Discrete Element Modeling

Considering a 3D sheared granular layer modeled with discrete elements, it is well known the rolling resistance significantly influences the mechanical behavior. Even if the rolling resistance role has been deeply investigated as it is commonly used to represent the the roughness of the grains and the interparticle locking, the role of rolling viscous damping coefficient has been largely overlooked so far. This parameter is rarely used or only to dissipate the energy and to converge numerically. This paper revisits the physical role of those coefficients with a parametric study of the rolling friction and the rolling damping for a sheared layer at different shear speeds and different confinement pressures. It has been observed that the damping coefficient induces a frictional weakening. Hence, competition between the rolling resistance and the rolling damping occurs. Angular resistance aims to avoid grains rolling, decreasing the difference between the angular velocities of grains. Whereas, angular damping acts in the opposite, avoiding a change in the difference between the angular velocities of grains. In consequence, grains keep rolling and the sample strength decreases. This effect must be considered to not overestimate the frictional response of a granular layer.

physics.geo-ph↗

arXiv2023

A Phase-Field Discrete Element Method to study chemo-mechanical coupling in granular materials

This paper presents an extension of the discrete element method using a phase-field formulation to incorporate grain shape and its evolution. The introduction of a phase variable enables an effective representation of grain geometry and facilitates the application of physical laws, such as chemo-mechanical couplings, for modeling shape changes. These physical laws are solved numerically using the finite element method coupled in a staggered scheme to the discrete element model. The efficacy of the proposed Phase-Field Discrete Element Model (PFDEM) is demonstrated through its ability to accurately capture the real grain shape in a material subjected to dissolution only and compute the stress evolution. It is then applied to model the phenomenon of pressure solution involving dissolution and precipitation in granular materials at the microscale and enables to reproduce the creep response observed experimentally. This framework contributes to the enhanced understanding and simulation of complex behaviors in granular materials and sedimentary rocks for many geological processes like diagenesis or earthquake nucleation.

cond-mat.mtrl-sci↗

arXiv2021

Morphometric description of strength and degradation in porous media

The influence of the microstructural geometry on the behavior of porous media is widely recognized, particularly in geomaterials, but also in biomaterials and engineered materials. Recent advances in imaging techniques, such as X-ray microcomputed tomography, and in modeling make it possible to capture the exact morphometry of the microstructure with high precision. However, most existing continuum theories only partially account for the morphometry. We propose here a unifying approach to link the strength of porous materials with the necessary and sufficient microstructural information, using Minkowski functionals, as per Hadwiger's theorem. A morphometric strength law is inferred from synthetic microstructures with a wide range of porosities and heterogeneities, through qualitative 2D phase-field simulations. Namely, the damage is modeled at the microstructural level by tracking the solid-pore interfaces under mechanical loading. The strength is found to be best described by an exponential function of the morphometers, thus generalizing early works on metals and ceramics. We then show that the predictiveness of this relationship extends to real porous media, including rocks and bones.

cond-mat.soft↗

arXiv2020

Strain localization regularization and patterns formation in rate-dependent plastic materials with multiphysics coupling

Strain localization is an instability phenomenon occurring in deformable solid materials which undergo dissipative deformation mechanisms. Such instability is characterized by the localization of the displacement or velocity fields in a zone of finite thickness and is generally associated with the failure of materials. In several fields of material engineering and natural sciences, estimating the thickness of localized deformation is required to make accurate predictions of the evolution of the physical properties within localized strain regions and of the material strength. In this context, scientists and engineers often rely on numerical modeling techniques to study strain localization in solid materials. However, classical continuum theory for elasto-plastic materials fails at estimating strain localization thicknesses due to the lack of an internal length in the model constitutive laws. In this study, we investigate at which conditions multiphysics coupling enables to regularize the problem of strain localization using rate-dependent plasticity. We show that coupling the constitutive laws for deformation to a single generic diffusion-reaction equation representing a dissipative state variable can be sufficient to regularize the ill-posed problem under some conditions on the softening parameters in the plastic potential. We demonstrate in these cases how rate-dependent plasticity and multiphysics coupling can lead to material instabilities depicting one or several internal length scales controlled by the physical parameters resulting in the formation of regular or erratic patterns. As we consider a general form of the equations, the results presented in this study can be applied to a large panel of examples in the material engineering and geosciences communities.

physics.geo-ph↗

arXiv2019

Contact phase-field modeling for chemo-mechanical degradation processes. Part I: Theoretical foundations

As phase-field modeling (PFM) is booming across various disciplines and has been proven fitted for numerically modeling interfacial problems, we aim at taking a step back to revisit its fundamental validity, in the light of non-equilibrium thermodynamics. For that, a general contact thermodynamics (CT) framework is derived from contact geometry, based on the maximum dissipation principle (MaxDP), thus extending Gibbs' seminal geometrical representation of thermostatics. Combining CT and micro-force balance, the gradient flow equation usually derived for PFM from the variational formulation can be written as generalized relaxation equations. The obtained viscous Allen-Cahn equation allows both the PFM kinematic degrees of freedom, the order parameter and its gradient, to be fully dissipative. The model is also extended to a double PFM, in order to include chemo-mechanical coupling, corresponding respectively to endothermic and exothermic processes and thus leading to a phase change bidirectionality. This contact PFM (CPFM) will be applied in the second part of this work to irregular microstructures like geomaterials, valid for porous media in general, with a focus on pressure solution.

cond-mat.stat-mech↗

arXiv2019

Contact phase-field modeling for chemo-mechanical degradation processes. Part II: Numerical applications with focus on pressure solution

The microstructural geometry (MG) of materials has a significant influence on their macroscopic response, all the more when the process is essentially microscopic as for microstructural degradation processes. However, the MG tends to be approximated by ideal spherical packings with constitutive description of the microstructural contacts. Interfaces tracking models like phase-field modeling (PFM) are promising candidates to capture the microstructures dynamics. Contact PFM (CPFM) enables to include catalyzing/inhibiting (CI) effects, accelerating/delaying equilibrium, such as temperature or the presence of certain constituents. To emphasize the influence of geometry and CI effects, we study numerically the chemo-mechanical response of digitalized geomaterials at the grain scale. An application to pressure solution creep (PSC) shows the importance of the MG and how the influence of temperature and clay can be taken into account without explicit modeling. As already inferred in previous works on PSC, the lack of MG considerations could be the reason why a unique description of PSC is missing. A simple reason could be that PSC is directly dependent on the strain concentration, which is directly dependent on the MG. This is our motivation here to investigate and suggest the influence of the MG on a degradation process like PSC.

physics.geo-ph↗