Pierre Bésuelle

A novel type of damageable cohesive law is presented for paired particle interactions in a DEM granular arrangement. It is designed in the spirit of a mixed breakage criterion for solid cohesion interaction, which can be implemented in parallel to a granular-frictional contact law. The evolution of damage at the contact level can be be easily modulated to enable a progressive transition from an initially linear elastic response to a loss of cohesion, by using a single parameter χ *. In a straightforward numerical implementation, the effect of this contact model is presented for a 3D periodic boundary condition DEM code. The results from a series of simulations show that, for a constant peak resistance of the cohesion, a more progressive damage result in an increase of the peak stress in a particle assembly, as well as a continuous transition in the stiffness of the stress-strain response around the peak stress.

The Callovo-Oxfordian claystone is a material with notoriously complex hydro-mechanical behaviour. Combined neutron and x-ray tomography modalities are used for the first time to characterise the dynamics of water absorption in this material by comparing material deformation as well as water arrival. Exploiting recent work on multimodal registration, neutron, and x-ray datasets are registered pairwise into a common coordinate system, meaning that a vector-valued field (i.e., neutron and x-ray reconstructed values) is available for each timestep, essentially making this a 5D dataset. The ability to cross-plot each field into a joint histogram (an inherent input into the registration) allows an improved identification of mineral phases in this complex material. Material deformation obtained from the application of Digital Volume Correlation on the x-ray timeseries data is locally compared to changes in water content available from the neutrons, opening the way toward a quantitative description of the hydro-mechanics of this process.

In this work, we present an isogeometric (IGA) finite element implementation for hydro–mechanical coupled problems within the framework of (small–strain) second gradient plasticity. Higher-order continuity across elements is one of the interesting properties of IGA basis functions that allows a straightforward implementation of second gradient formulations, which restores objectivity when strain localization occurs. As compared to traditional implementation of second gradient poromechanics, the proposed approach results in a decrease of the total number of degrees of freedom required for a given discretization density, and thus in a higher computational efficiency. Smoothness of the approximating functions is another desirable feature of IGA which mitigates significantly the requirements for minimum time steps in transient poromechanics problems. A serie of biaxial tests on a fully saturated porous media are simulated in order to demonstrate the capabilities of the enriched hydro–mechanical second gradient formulation using IGA, as well as showing effective regularization of the localization patterns.