In the context of the Cigéo project, the French National Radioactive Waste Management Agency (Andra) is studying the behaviour of a deep geological facility for radioactive waste deposit in the ...Callovo-Oxfordian (COx) claystone. The assessment of durability of this project requires the prediction of irreversible strain over a large time scale. The mechanical interaction of the host rock and the concrete support of tunnels must be investigated to ensure the long-term sustainability of the structure. The instantaneous and time-dependent behaviour of the claystone-concrete interface is experimentally investigated with direct shear tests and long-duration shear tests of a few months. The mechanical and structural state of the claystone which is affected after interaction with concrete reflects to the response of the claystone-concrete interface, and thus different types of COx claystone-concrete interfaces are tested. The delayed deformation of the interface is found to be linked to the level of the normal loading and the loading history, while a different response of the interface was observed from the short- and long-duration tests, indicating a possible progressive modification of interface under long-duration loadings.
Stress-based nonlocal damage model Giry, Cédric; Dufour, Frédéric; Mazars, Jacky
International journal of solids and structures,
12/2011, Letnik:
48, Številka:
25
Journal Article
Recenzirano
Odprti dostop
Progressive microcracking in brittle or quasi-brittle materials, as described by damage models, presents a softening behavior that in turn requires the use of regularization methods in order to ...maintain objective results. Such regularization methods, which describe interactions between points, provide some general properties (including objectivity and the non-alteration of a uniform field) as well as drawbacks (damage initiation, free boundary).
A modification of the nonlocal integral regularization method that takes the stress state into account is proposed in this contribution. The orientation and intensity of nonlocal interactions are modified in accordance with the stress state. The fundamental framework of the original nonlocal method has been retained, making it possible to maintain the method’s advantages. The modification is introduced through the weight function, which in this modified version depends not only on the distance between two points (as for the original model) but also on the stress state at the remote point.
The efficiency of this novel approach is illustrated using several examples. The proposed modification improves the numerical solution of problems observed in numerical simulations involving regularization techniques. Damage initiation and propagation in mode I as well as shear band formation are analyzed herein.
Modal analysis, aiming at estimating modal characteristics such as natural frequencies and mode shapes, is fundamental for studying the dynamic behaviours of a structure. This paper presents a modal ...analysis of an arch dam using three different techniques. The reference one is based on the statistical analysis of the ambient vibration data collected from the dam crest. The two other approaches are both numerical but with different methods (fluid‐element and Westergaard) for the modelling of the reservoir and its interactions with the dam. By applying the three techniques to the studied dam and comparing their results, it is demonstrated that: (1) analysing the ambient vibration data through an operational modal analysis method is able to extract the dam modal characteristics; (2) the fluid‐element method is effective for arch dams since the first 10 natural frequencies can be accurately predicted once the material parameters are calibrated on the first three modes; and (3) the Westergaard method, a technique with only additional masses, produces significantly under‐estimated frequencies for the first few modes if same parameters are used as the fluid‐element method; the underestimation can be corrected for several modes by using a higher stiffness parameter but the required value is unrealistic for the case study. Furthermore, a modified Westergaard method is introduced in this paper by using a reduced added‐mass coefficient. This method, once the coefficient is calibrated on the 1st mode, is able to well predict the partially coupled modes as illustrated with the case study of the Saint‐Guérin dam.
Understanding the migration of high-temperature fluids through the porous medium of cement-based materials has a pivotal role in many engineering applications. The space and time evolution of the ...free water content and the crack network in these materials creates a complex migration process. In this work, we experimentally investigate water vapour migration in pre-cracked porous media of dry and saturated initial saturation states. Besides studying the mean temperature and pressure evolution, we quantify the rapid spatial distribution of the condensed water operando through high-speed neutron radiography. The associated physical phenomena for the condensed water migration into the porous media is reported one order of magnitude stronger in the dry sample. Combined features of neutron and x-ray tomographies enable the 3D quantification of condensed water distribution. This unique data set aims to provide a novel database for the multi-physics modelling of two-phase fluid flow in cracked media for varying initial saturation.
•A new EVP constitutive equation coupling the bingham and maxwell models is presented.•Computations have been performed using the FEMLIP method.•Elasticity and plasticity have an influence on flow ...morphology.•The fore-aft asymmetry is due to elasticity.•Elastic effects decrease as plastic effects become stronger.
This numerical study investigates the creeping flow of an elasto-viscoplastic fluid around a plate perpendicular to the flow direction. The analysis is performed with the Finite Element Method with Lagrangian Integration Points (FEMLIP). This numerical method is able to simulate large deformations problems and to describe yielded and unyielded regions by precisely accounting for elastic stresses. An elasto-viscoplastic model coupling the Bingham and the Maxwell constitutive equations is used. The influences of plasticity and elasticity on kinematic and stress fields are discussed. The influence of elasticity on the fore-aft asymmetry of the flow morphology is shown and quantified. The size and shape of the yielded and unyielded regions around the obstacle are also quantified. Finally, far and local stress fields as well as the drag coefficient are quantified as a function of the plastic and elastic contributions.
The present paper describes a numerical study of force fluctuations experienced by a boundary wall subjected to a granular flow on two distinct systems, namely a lid-driven cavity and an immersed ...wall system. Though the two systems exhibit different time-averaged dynamics, the force fluctuations experienced by the boundary wall show robust features in terms of the shapes of the probability density distributions and auto-correlation functions, under a wide range of boundary confinement pressure and shearing velocity imparted to the granular flow at the top of the system. This study identifies the key link between the grain-wall force fluctuations and the μ(I)–rheology while moving from quasistatic to inertial regime.
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•Vapor penetration in cracked concrete probed with fast neutron radiography.•Full-field analysis revealed moisture clogging and discontinuous moisture fronts.•Moisture accumulation ...was found to precede sudden jumps in moisture profiles.•Pressure driven moisture speed is 4 times the speed of capillary absorption.
This paper presents, for the first time, full-field dynamic measurements of vapour injection and condensation within a fractured concrete, observed in-operando by means of rapid neutron radiography (acquisition rate of 30 Hz with 87 μm pixel size). Time-dependant moisture evolution is analysed in terms of equivalent water thickness measurements. We observe that movement of condensed moisture along and transversely to the crack plane is non-monotonic in both space and time, exhibiting occasional sub-second jumps.
The Franklin igneous event (ca. 718 Ma) emplaced basalts and mafic intrusions across Arctic Laurentia just prior to the onset of the ca. 717–661 Ma Sturtian Snowball Earth event. Given the close ...association in time between these two events, it has been widely argued that the Franklin event contributed to the initiation of global glaciation. However, a lack of accurate high-precision geochronology has hampered establishing the timeframe of Franklin magmatism and discerning its precise temporal and possible causative relationship to glaciation. Here we present new high-precision U-Pb CA-ID TIMS zircon ages for two dykes and two sills from Baffin Island, Canada, and Avannaata, northwestern Greenland, related to the Franklin event. Combined with field relationships showing that the dykes crosscut the sills, these four dates indicate magmatic activity over 1.10±0.74 Myr at ca. 718 Ma, immediately prior to Sturtian glaciation, which we estimate to have initiated at 717.19 +0.26/−0.33 Ma. Our results are consistent with recent high precision U-Pb CA-ID TIMS age estimates for the Franklin magmatic activity in the central and western parts of the province. Combining our new dates with the other high precision CA-ID-TIMS ages yields a duration for the Franklin event of 2.14±0.75 Myr which is shorter than the previous estimates but somewhat longer than that for typical Phanerozoic large igneous events.
•We present new U-Pb zircon ages on four Franklin dykes and sills in Canada and Greenland.•These ages indicate short-lived Franklin magmatism at ca. 718 Ma.•Franklin magmatism immediately precedes the ca. 717 Ma onset of the Sturtian Snowball Earth.•Weathering of flood basalts contributed to the onset of global glaciation.
This article aims to discuss and complete the avalanche representations of the failure process of quasi-brittle materials. Paper was used as a model material. We proposed an original method to ...determine avalanches extracted directly from the force drops in the post-peak regime of experimental force–displacement curves. We studied the avalanche distributions on notched and unnotched samples, taking into account the measurement noise. From these experimental tests, two regimes in the avalanche distribution were observed during the propagation of a macrocrack, in particular with a well-defined power law at small scale, that was consistent with other avalanche distributions based on other methods and other materials in literature. A single regime power-law distributed was found for a diffuse damage (without a significant macrocrack propagation) using the Mazars’ damage model. Our results showed that the post-peak regime of tensile curves contained the statistical signature of the propagation of a macrocrack during the rupture of paper.
The prediction of large concrete structures behaviour such as bridges, dams and nuclear containment buildings (NCB) is a vital issue regarding the evaluation of the durability, safety and effect on ...the surrounding environment. In this work, experimental and numerical estimations of the saturation ratio profiles in the VeRCoRs NCB mock-up structure are presented, and their blind comparison is discussed. Non-destructive testing (NDT) based capacitive measurements are processed to quantify the saturation ratio experimentally. Then, a weakly coupled thermo-hydric (TH) finite element model is presented within the serviceability state of VeRCoRs for the numerical counterpart. The uncertainty in the capacitive measurements and the constitutive parameters of the numerical model are highlighted as coming from the following three sources: (a) the natural randomness of the material properties and physical processes, (b) the limited knowledge of some input parameters in the mathematical model either obtained experimentally at the specimen scale and (c) empirically derived in the exploitation of the physical process. The influence of the uncertainty in the saturation ratio estimations is presented by error bars experimentally and is addressed by a stochastic finite element (SFE) study in the numerical work. Accounting for uncertainties in NDT and SFE measurements, the mean values of saturation ratio (reported in %) profile are forecasted up to 40% and 34% respectively, with standard deviation for both in the range of 3.5–4.5% in magnitude.
•Estimation of the in-situ saturation ratio in the VeRCoRs nuclear containment buildings (NCB) structure using non-destructive capacitive measurements•Suggestion of a weakly coupled Thermo-Hydric (TH) modelling strategy of large concrete structures’ behaviour.•Use of realistic in-situ TH boundary conditions around an operating NCB.•Analysis of the effects of spatial and temporal variation of TH boundaries on concrete saturation ratio in NCBs.•Uncertainty quantification of the TH model parameters by surrogate model-based probabilistic sensitivity analysis.
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