Prédiction de la pénétration dans une dalle en béton d'un missile rigide par la méthode aux éléments discrets

Un modèle numérique 3D utilisant la méthode des éléments discrets a été développé pour prédire la profondeur de pénétration d'un missile impactant une dalle en béton armé. Le modèle a été calibré sur un essai d'impact de référence impliquant un missile à nez plat. Une fois le modèle calibré, des simulations numériques ont été réalisés en faisant varier seulement la forme du nez du missile. Les résultats numériques sont comparés avec les résultats expérimentaux réalisés par CEA-EDF et la loi de prédiction de Li. La bonne prédiction de la profondeur de pénétration par le modèle numérique est confirmée par les observations issues des essais expérimentaux

Discrete Element Modeling of a Subduction Zone with a Seafloor Irregularity and its Impact on the Seismic Cycle

peer reviewedSeafloor irregularities influence rupture behavior along the subducting slab and in the overriding plate, thus affecting earthquake cycles. Whether seafloor irregularities increase the likelihood of large earthquakes in a subduction zone remains contested, partially due to focus put either on fault development or on rupture pattern. Here, we simulate a subducting slab with a seafloor irregularity and the resulting deformation pattern of the overriding plate using the discrete element method. Our simulations illustrate the rupture along three major fault systems: megathrust, splay and backthrust faults. Our results show different rupture dimensions of earthquake events varying from tens to ca. 140 km. Our results suggest that the recurrence interval of megathrust events with rupture length of ca. 100 km is ca. 140 years, which is overall comparable to the paleoseismic records at the Mentawai area of the Sumatran zone. We further propose the coseismic slip amounts decrease and interseismic slip amounts increase from the surface downwards gradually. We conclude that the presence of seafloor irregularities significantly affects rupture events along the slab as well as fault patterns in the overriding plate

Modélisation du comportement dynamique du béton par la méthode des éléments discrets

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Discrete Element Modeling of Permeability Evolution During Progressive Failure of a Low-Permeable Rock Under Triaxial Compression

International audienceUnderstanding permeability evolution caused by the nucleation, propagation and coalescence of cracks enables to better assess fluid migration in the vicinity of underground excavations, boreholes or reservoirs. In this study, we propose a three-dimensional approach combining a bonded particle model and a dual-permeability pore network model to investigate the crack permeability behavior of low-permeable rocks. First, we verify the performances of the numerical scheme by comparing its predictions to analytical permeability solutions for microcracked and fractured porous samples respectively. Then, we simulate a triaxial compression test on an argillaceous rock sample with periodic permeability measurements. The model is able to reproduce the stressstrain-permeability evolution observed experimentally, from the early stage of microcracking up to the residual post-failure state: i) permeability does not change significantly before reaching the crack damage threshold, ii) permeability increases by several orders of magnitude after failure due to the appearance of a discrete shear band across the sample. The good agreement between the numerical results and the experimental observations confirms the relevance of the proposed approach to simulate the crack permeability behavior of low permeable rocks during their progressive failure. Based on this result, we simulate triaxial compression tests under different confining pressures to propose relationships between post-failure permeability and residual mean stress

Strength characterization of rock masses, using a coupled DEM-DFN model

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Influence of the reinforcement on penetration and perforation of concrete targets

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Incrementally non-linear plasticity applied to rock joint modelling

International audienceRock joint constitutive modelling is discussed through two new rock joint constitutive relations and a discrete numerical model. Regarding the constitutive relations, we emphasise the number of " tensorial zones " , i.e. domains of constitutive incremental linearity, they involve: four zones for the first (called " quadrilinear "), and an infinite number for the second one (called " incrementally nonlinear "). Using these formulations, a large class of loading paths can be considered. Hardening through shearing and relations between the normal and tangential directions of the joint (e.g., dilatancy), can be described. Their predictive abilities are checked. Plastic features are included even if the relations are defined outside of the elasto-plastic formalism. These relations obey hence the physical evidences as the plastic limit criterion and flow rule. The flow rule is nonassociated, and the corresponding link with the nonsymmetry of the constitutive matrix is examined. Comparisons between the two relations and the discrete numerical model, i.e. a direct numerical simulation which is fundamentally different, are also discussed within the context of infilled rock joints

Penetration prediction of missiles with different nose shapes by the discrete element numerical approach

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Rigid obstacle impacted by a supercritical cohesive granular flow using a 3D discrete element model

International audienceThis study examines the drag coefficient of an obstacle impacted by a 3D cohesive granular flow using a discrete element model. A specific numerical setup is used to carry out reproducible and controlled normal impact simulations, in which the upstream flow properties are fully controlled parameters. The micromechanical contact model involves the physical properties of friction, normal elastic-plastic repulsion, dissipation, and a normal cohesion factor that induces bulk cohesion in the granular assembly. The effect of cohesion on the obstacle load is investigated through a micro-scale analysis. We show that increasing the cohesion leads to an increase of the obstacle drag, through a densification of the contact network, which enhances the transmission of contact forces to the obstacle. This experiment is extended to a wide range of supercritical flows, with Froude numbers between 1.5 and 11.2. The resulting drag coefficient curves are represented as power law functions of the Froude number. We then demonstrate the dependency of the power law exponent on the ratio between inertia and gravitational forces. Our results suggest that the assessment of drag coefficient critical values by conventional avalanche protection guidelines could be improved by a mechanical consideration of cohesion for certain snow types

Material stability analysis of rock joints

International audienceFor prediction of rockfalls, the failure of rock joints is studied. Considering these failures as constitutive instabilities, a second‐order work criterion is used because it explains all divergence instabilities (flutter instabilities are excluded). The bifurcation domain and the loading directions of instabilities, which fulfill the criterion, are determined for any piecewise linear constitutive relation. The instability of rock joints appears to be ruled by coupling features of the behavior (e.g., dilatancy). Depending on the loading parameters, instabilities can lead to failure, even before the plastic limit criterion. Results for two given constitutive relations illustrate the approach. Some given loading paths are especially considered. Constant volume (undrained) shear and τ‐constant paths are stable or not depending on the link between the deviatoric stress and strain along undrained paths, as found for soils. Some unstable loading paths are illustrated. Along these paths, failure before the plastic limit criterion is possible. The corresponding failure rules are determined