Publications

2016

• FIRST STEPS IN THE DEVELOPMENT OF AN EULERIAN FIXED-GRID POSTULATION FOR TWO-PHASE FLOW-INDUCED VIBRATION NUMERICAL MODELING
  
  • Longatte E.
  • Benguigui William
  • Mimouni Stéphane
  , 2016.
• Effects of confinment in the buckling of a flexible plate in axial flow: experimental and numerical study
  
  • Adjiman Julie
  • Doaré Olivier
  • Moussou Pierre
  • de Buretel de Chassey Nicolas
  , 2016. Static instability of flexible structures forced by a parallel flow, a.k.a. divergence, has been the subject of a relatively small amount of studies, unlike flutter. In order to prepare future studies of the collective behaviour of several slender structures coupled by the fluid in axial flow, the canonical case of a flat flexible plate clamped at both ends is investigated numerically and experimentally. The onset of divergence is determined throughout a series of calculation of the fluid forces generated by a prescribed deformation of the plate. Using the Galerkin method, these fluid forces are expanded in the basis of the natural modes; they exactly balance the mechanical forces when the fluid velocity reaches the instability threshold. The instability velocity can be determined by an eigenvalue calculation involving the fluid force expansion and the modal stiffnesses of the plate. Comparisons are provided with 2D analytical calculations and with an experiment performed with a 0.3m×0.03m mylar plate at Reynolds numbers varying between 10 4 and 10 5. A fair agreement is observed between the 3D potential calculation and the experiments, whereas the 2D analytical solution underestimates the instability velocity.
• Contribution à la simulation du comportement des enceintes de confinement de centrales nucléaires
  
  • Jason Ludovic
  , 2016. Ce document présente une synthèse des travaux réalisés sur la simulation du comportement des enceintes de confinement de centrales nucléaires à double paroi en béton armé et précontraint. Il s’intéresse au comportement mécanique à plusieurs échelles, celle de la structure industrielle pour laquelle il est délicat d’obtenir des résultats précis sur la fissuration (ouverture notamment) et l’échelle des structures métriques pour lesquelles il devient possible d’introduire des modélisations plus raffinées (liaison acier-béton, représentation des hétérogénéités géométriques, lois de comportement). Ces travaux s’appuient dès que possible sur un triptyque associant modélisation, simulation et essais. Un nouveau modèle de liaison acier-béton, basé sur un élément joint, est en particulier développé. Sa calibration et son domaine de validité, par rapport à l’hypothèse classique de « liaison parfaite », sont discutés. Une méthode de condensation statique adaptative est présentée, qui vise à passer de l’échelle de l’enceinte vers celle de Volumes Structurels Représentatifs. La problématique des enceintes de confinement étant très fortement liée à celle de l’étanchéité des structures en béton armé et donc des transferts à travers une paroi en béton, deux approches sont comparées. La première est basée sur une approche hydro – mécanique chaînée. Elle tend à démontrer que, dans le contexte particulier des enceintes de confinement, l’endommagement mécanique n’a d’impact sur le débit sortant que lorsque la fissure devient traversante. Dans cette situation, une méthode pour les transferts localisés est évaluée aboutissant à la définition d’une ouverture de fissure équivalente.
• Modelling strategies of prestressing tendons and reinforcement bars in concrete structures
  
  • Llau Antoine
  • Jason Ludovic
  • Dufour Frederic
  • Baroth Julien
  , 2016. This contribution presents an original approach to improve the modeling of steel rebars and prestressing tendons in concrete structures at a reduced cost. Classical 1D meshes and models typically used for civil engineering applications tend to provoke strain localization due to the geometrical singularity and are thus unable to reproduce local mechanical effects. Complete 3D models can be applied in some cases, however their accuracy at the local scale comes at the cost of engineering work on the meshes, especially for complex structures. The 1D-3D model presented in this contribution generates an equivalent volume for the steel bars, based on existing 1D models. Its 3D stiffness and stress state are computed, and then condensed on its interface with the concrete. The condensed degree of freedom are then linked to the surrounding concrete elements by kinematic relations. The presented approach is validated on different representative cases, and is able to predict the 3D effects of the bars and tendons at the local scale. In particular it provides the representativeness and mesh stability of a full 3D model, without the need for a complex mesh.
• Crack opening estimate in reinforced concrete walls using a steel–concrete bond model
  
  • Mang Chetra
  • Jason Ludovic
  • Davenne Luc
  Archives of civil and mechanical engineering, Springer, 2016, 16 (3), pp.422--436. This paper presents the application of a new steel-concrete bond model on a reinforced concrete shear wall, experimentally tested during the French National Project CEOS.FR. The proposed results include both global (evolution of the force as a function of the displacement for example) and local results (crack opening and spacing). A new post-processing method to compute these local properties even in a case of a complex crack pattern (oriented cracks for example) is proposed. It is based on the change in the sign of the bond slip between steel and concrete. The simulated results are in a good agreement with the experiment and validate the developments. Finally, the interest of including a specific steel-concrete bond model in the finite element simulation is highlighted, compared to classical "no-slip" relation. (10.1016/j.acme.2016.02.001)
  DOI : 10.1016/j.acme.2016.02.001
• On constitutive models of finite elasticity with possible zero apparent Poisson's ratio
  
  • Nedjar Boumediene
  International Journal of Solids and Structures, Elsevier, 2016, 91, pp.72-77. The idea in this paper is to build a class of constitutive equations for highly compressible isotropic materials that, among others, are capable to describe a zero apparent Poisson’s ratio in the whole finite strain range, not only for moderate straining. This remarkable property is, for instance, observed in many soft materials with micro-structures such as sponges and polymeric foams with high porosities. It would then be suitable to describe their behavior within a macroscopic modeling framework. More specifically, herein by means of elementary considerations, we deduce adequate forms of strain-energy functions that are a priori decomposed into purely volumetric and volume-preserving parts. A class of compressible hyperelastic materials of the general Odgen type is obtained. It can consequently be specialized, for instance, to neo-Hookean, Mooney–Rivlin, and Varga’s model types as well. Furthermore, for the elastic parameters, a connection with the limiting case of linear elasticity is made whenever possible, in particular with the classical Poisson’s ratio, and with the bulk to shear moduli ratio. (10.1016/j.ijsolstr.2016.04.026)
  DOI : 10.1016/j.ijsolstr.2016.04.026
• An approach to model the mechanical behavior of transversely isotropic materials
  
  • Mahjoub M.
  • Rouabhi A.
  • Tijani M.
  • Granet S.
  International Journal for Numerical and Analytical Methods in Geomechanics, Wiley, 2016, 40 (6), pp.942 - 961. The present work proposes an approach to adapt existing isotropic models to transversely isotropic materials. The main idea is to introduce equivalence relations between the real material and a fictitious isotropic one on which one can take all the advantages of the well-established isotropic theory. Two applications of this approach are presented here: a failure criterion and a damage model that takes into account the load-induced anisotropy. In both cases, theoretical predictions are in agreement with the experimental data. In the present paper, the developed approach is applied to sedimentary rock materials; nevertheless, it can be generalized to any material that exhibits transverse isotropy. (10.1002/nag.2469)
  DOI : 10.1002/nag.2469
• Méthode modale mixte pour le contact unilatéral corde / obstacle : application au chevalet de la tampoura
  
  • Issanchou Clara
  • Bilbao Stefan
  • Doaré Olivier
  • Le Carrou Jean-Loic
  • Touzé Cyril
  , 2016. Les contacts entre une corde vibrante et un obstacle rigide sont fréquemment rencontrés dans divers instruments de musique (bassé electrique, contrebasse, sitar, tampoura...), ce qui donne lieù a des sonorités riches et variées. Dans la littérature , ceprobì eme est l'objet d'´ etudes analytiques, numériques et, dans une moindre mesure, expérimentales. Dans cetté etude, on présente une nouvelle méthode numérique permettant de calculer en temps les déplacements d'une corde, ´ eventuellement raide et amortie, en présence d'un obstacle unilatéral de forme quelconque. Le mod ele est dit modal mixte car les opérateurs numériques sont issus d'une description modale du syst eme mais exprimés dans l'espace physique. La force de contact est régularisée et un schéma conservatif en temps est mis en oeuvre. Cette méthode implique un nombre de modes egal au nombre de points de discrétisation spatiale, et permet de prendre en compte finement les fréquences propres et les amortissements réels d'une corde. Des résultats numériques sont confrontés a des mesures expérimentales dans le cas d'un obstacle ponctuel. Celui-ci est placé soit au milieu de la corde, soit tr es proche de l'une de ses extrémités , cettedernì ere configuration correspondant a une approximation d'un chevalet de tampoura.
• Effet des non linéarités géométriques sur l'amortissement par effet trou noir
  
  • Denis Vivien
  • Pelat Adrien
  • Gautier François
  • Touzé Cyril
  , 2016. L'effet Trou Noir Acoustique (TN) est une technique passive d'amortissement de vibrations sans ajout de masse fondée sur les propriétés des ondes de flexion dans des structures minces d'épaisseur variable. La mise en œuvre habituelle consiste en une plaque avec une extrémité profilée selon une loi exponentielle, recouverte d'un film viscoélastique. L'inhomogénéité de la structure conduit a une baisse de la célérité et une augmentation de l'amplitude des ondes de flexion, ce qui a pour conséquence une dissipation d'énergie efficace quand un film amortissant est placé dans la zone de faible épaisseur. L'amplitude des ondes a l'extrémité peut facilement atteindre l'ordre de grandeur de l'épaisseur de la plaque, ce qui est une source de non-linéarités géométriques. Ces non-linéarités peuvent avoir pour conséquences des couplages entre les modes de vibration de la structure, et induire un transfert d'énergie des basses fréquences vers les hautes fréquences. Ce phénomène de transfert d'énergie peut être exploité pour augmenter l'efficacité du traitement dans le domaine des basses fréquences pour lequel le trou noir est peu efficace. Une expérience montre que la terminaison TN se comporte de manière non linéaire et permet un couplage entre modes. Un régime fortement non-linéaire peut également être observé, qui est associé au phénomène de turbulence d'ondes. Une modélisation d'une poutre TN comme une plaque de von Kármán d'épaisseur variable et une résolution du problème par une méthode modale permet de confirmer les effets observés dans l' expérience et d'analyser plus finement ces résultats .
• Couplage d'un modèle de source aéroacoustique et d'un code d'équation parabolique pour la propagation du bruit des éoliennes a grande distance
  
  • Cotté Benjamin
  • Tian Y
  , 2016, pp.665-671. Dans cette étude, nous proposons de coupler un modèle de source basé sur la théorie d'Amiet et un code d'équation parabolique afin de modéliser la propagation du bruit des éoliennes dans une atmosphère inhomogène. Deux mécanismes de génération de bruit large bande sont considérés, à savoir le bruit de bord de fuite et le bruit d'impact de turbulence. Nous prenons en compte l'effet du cisaillement du vent et de la turbulence atmosphérique a l'aide de la théorie de la similitude de Monin-Obukhov. La méthode de couplage est tout d'abord validée par comparaison avec un modèle analytique pour la propagation au-dessus d'un sol d' impédance finie. On analyse ensuite l'influence des effets de réfraction pour différentes directions de propagation, afin de mettre en évidence la modification du spectre lié à l'effet de sol et la présence d'une zone d'ombre.
• Numerical modeling of liquefaction-induced failure of geostructures subjected to earthquakes
  
  • Rapti Ioanna
  , 2016. The increasing importance of performance-based earthquake engineering analysis points out the necessity to assess quantitatively the risk of liquefaction. In this extreme scenario of soil liquefaction, devastating consequences are observed, e.g. excessive settlements, lateral spreading and slope instability. The present PhD thesis discusses the global dynamic response and interaction of an earth structure-foundation system, so as to determine quantitatively the collapse mechanism due to foundation's soil liquefaction. As shear band generation is a potential earthquake-induced failure mode in such structures, the FE mesh dependency of results of dynamic analyses is thoroughly investigated and an existing regularization method is evaluated. The open-source FE software developed by EDF R&D, called Code_Aster, is used for the numerical simulations, while soil behavior is represented by the ECP constitutive model, developed at CentraleSupélec. Starting from a simplified model of 1D SH wave propagation in a soil column with coupled hydromechanical nonlinear behavior, the effect of seismic hazard and soil's permeability on liquefaction is assessed. Input ground motion is a key component for soil liquefaction apparition, as long duration of mainshock can lead to important nonlinearity and extended soil liquefaction. Moreover, when a variation of permeability as function of liquefaction state is considered, changes in the dissipation phase of excess pore water pressure and material behavior are observed, which do not follow a single trend. The effect of a regularization method with enhanced kinematics approach, called first gradient of dilation model, on 1D SH wave propagation is studied through an analytical solution. Deficiencies of the use of this regularization method are observed and discussed, e.g. spurious waves apparition in the soil's seismic response. Next, a 2D embankment-type model is simulated and its dynamic response is evaluated in dry, fully drained and coupled hydromechanical conditions. Two criteria are used to define the onset of the structure's collapse. The second order work is used to describe the local instability at specific instants of the ground motion, while the estimation of a local safety factor is proposed by calculating soil's residual strength. Concerning the failure mode, the effect of excess pore water pressure is of great importance, as an otherwise stable structure-foundation system in dry and fully drained conditions becomes unstable during coupled analysis. Finally, a levee-foundation system is simulated and the influence of soil's permeability, depth of the liquefiable layer, as well as, characteristics of input ground motion on the liquefaction-induced failure is evaluated. For the current levee model, its induced damage level (i.e. settlements and deformations) is strongly related to both liquefaction apparition and dissipation of excess pore water pressure on the foundation. A circular collapse surface is generated inside the liquefied region and extends towards the crest in both sides of the levee. Even so, when the liquefied layer is situated in depth, no effect on the levee response is found. This research work can be considered as a reference case study for seismic assessment of embankment-type structures subjected to earthquake and provides a high-performance computational framework accessible to engineers.
• On estimation of internal state by an optimal control approach for elastoplastic material
  
  • Stolz Claude
  Discrete and Continuous Dynamical Systems - Series A, American Institute of Mathematical Sciences, 2016, 9 (2), pp.599-611. After a general formulation of the evolution of an elastoplastic body using duality based on the constitutive behaviour, some classes of inverse problems (estimation of the internal state, determination of an unknown history, ...) for such materials are investigated. A general formulation based on optimal control is proposed, the control variables are related to the internal state. In each class of inverse problem, the solution is obtained by introducing a adjoin state and a suitable cost function. (10.3934/dcdss.2016014)
  DOI : 10.3934/dcdss.2016014
• Comparison of two hot tearing criteria in numerical modelling of arc welding of stainless steel AISI 321
  
  • Bellet Michel
  • Qiu Gonghao
  • Carpreau Jean-Michel
  Journal of Materials Processing Technology, Elsevier, 2016, 230, pp.143-152. Two hot cracking criteria have been tested: the RDG criterion, based on the prediction of liquid cavitation as a precursor of crack formation, and a strain-based solid mechanics criterion. Both criteria have been implemented in a finite element thermo-mechanical simulation of gas tungsten arc welding. After comparison with experimental results obtained in a test campaign on stainless steel AISI 321, both criteria have shown good ability to predict crack occurrence. Yet, the best response in terms of cracking prediction was obtained with the strain-based solid mechanics criterion. (10.1016/j.jmatprotec.2015.11.002)
  DOI : 10.1016/j.jmatprotec.2015.11.002
• On a concept of directional damage gradient in transversely isotropic materials
  
  • Nedjar Boumediene
  International Journal of Solids and Structures, Elsevier, 2016 (88-89), pp.56-67. Of interest in this paper is the description of damage evolution in anisotropic materials where it is mainly observed that damage is in general strongly influenced by the anisotropy itself. More specifically, transversely isotropic materials such as unidirectional fibre-reinforced composites and sedimentary rocks are under focus. The approach we use is based on continuum damage mechanics where the damage gradient quantity is involved. In this work, this latter is oriented toward privileged directions where damage will most probably propagate. This task is accomplished by adopting the integrity-basis formulation where the directional damage gradient is embedded and, otherwise, allows for a neat decomposition of the material response into directional, transverse, and pure shear contributions. This offers an appealing framework where damage characterization can be easily formulated. Damage can be chosen to be governed by transverse strains, by in-plane pure shear strains, or by both of them. One can then speak, respectively, of a mode-I, mode-II, or mixed I/II damage mechanisms if use is made of the terminology adopted in fracture mechanics. On the numerical side, an algorithmic design is proposed for an easy implementation within the context of the finite element method. A set of numerical examples is then presented to explore qualitatively the potential of the proposed framework. (10.1016/j.ijsolstr.2016.03.026)
  DOI : 10.1016/j.ijsolstr.2016.03.026
• Méthode EFS condensée pour l’analyse des structures sous incertitudes
  
  • Llau Antoine
  • Baroth Julien
  • Jason Ludovic
  • Dufour Frederic
  , 2016. Cette communication présente une méthode d’éléments finis stochastiques condensée, permettant de calculer des approximations des lois de probabilité des grandeurs d’intérêt d’une structure. Cette technique couple une méthode de condensation adaptative (extension de la technique de la condensation statique de Guyan) à un algorithme de collocation stochastique pour l’analyse de problèmes de mécanique non linéaire sous incertitudes. La méthode de collocation stochastique condensée proposée réduit la dimension des problèmes déterministes non linéaires utilisés pour créer un méta-modèle de la réponse mécanique du système. Elle tire parti des spécificités du calcul EFS, en créant un second méta-modèle pour calculer les grandeurs nécessaires à la condensation adaptative, telles que les matrices de rigidité réduites. La méthode de collocation stochastique condensée est appliquée à l’analyse d’une poutre en béton sollicitée en flexion. Les résultats obtenus par la méthode d’EFS condensée sont comparés à une méthode EFS de l’état de l’art. La méthode proposée permet d’obtenir des résultats similaires à la collocation stochastique classique pour une charge de calcul moindre.
• 2D coupled HM-XFEM modeling with cohesive zone model and applications to fluid-driven fracture network
  
  • Faivre M
  • Paul Bertrand
  • Golfier Fabrice
  • Giot Richard
  • Massin Patrick
  • Colombo D
  Engineering Fracture Mechanics, Elsevier, 2016, 159, pp.115-143. The present work focuses on a new numerical model for the fully coupled hydro-mechanical analysis of groundwater flows through poroelastic saturated media. In particular, the presence and eventual propagation of fluid-driven fractures is accounted for within a non-regularized cohesive zone model. In this paper, the fracture propagation is considered as a reactivation process: the fracture already exists and evolves (i.e. opens or closes) on a pre-defined path initially constrained. The Talon-Curnier constitutive law is considered for the fracture interfaces and its expression has been adapted to the hydro-mechanical coupling related to the fracture evolution. The fluid pressure inside the fracture is governed by the lubrication equation. The momentum-stress balance equations involving fluid flow and deformation of the solid porous matrix are derived within the framework of the generalized Biot theory. The extended finite element method (XFEM) is preferred to a standard finite element spatial discretization in order to easily handle the presence and evolution of dis-continuities in the porous medium. A set of four Lagrange multipliers is introduced to prevent spurious oscillations of the numerical solution at the interface. Comparisons between numerical results and theoretical solution assess the validity of the model presented in this paper. In addition, the hydro-mechanical interactions between neighboring fractures and the effects of the permeability of the porous medium are investigated. We also demonstrate the capability of our model to handle non-planar fracture paths. (10.1016/j.engfracmech.2016.03.029)
  DOI : 10.1016/j.engfracmech.2016.03.029
• Stochastic fluid structure interaction of a flat plate facing a uniform flow
  
  • Cadot Olivier
  , 2016, Proceedings of 3rd International Conference on Violent Flows 2016. An experiment of a flat rectangular plate facing a uniform flow at Re=264000 shows the importance on the base pressure loading of the asymmetric static modes of the turbulent wake. The plate is free to rotate around its small symmetry axis. For plates with aspect ratio <6, the angular position exhibits strong random discontinuities between steady states of large non zero angles. The steady states have long time durations, more than one order of magnitude larger than the convective timescale. The discontinuities, comparable to violent and unexpected events are due to strong fluid forces associated with the drastic global change of the three dimensional wake, mainly the switching between static asymmetric modes.
• Fluid force and symmetry breaking modes of a 3D bluff body with a base cavity
  
  • Evrard Antoine
  • Cadot Olivier
  • Herbert V
  • Ricot D
  • Vigneron R
  • Délery J
  Journal of Fluids and Structures, Elsevier, 2016, 61, pp.99-114. A cavity at the base of the squareback Ahmed model at Re 4 × 10 5 is able to reduce the base suction by 18% and the drag coefficient by 9%, while the geometry at the separation remains unaffected. Instantaneous pressure measurements at the body base, fluid force measurements and wake velocity measurements are investigated varying the cavity depth from 0 to 35% of the base height. Due to the reflectional symmetry of the rectangular base, there are two Reflectional Symmetry Breaking (RSB) mirror modes present in the natural wake that switch from one to the other randomly in accordance with the recent findings of Grandemange et al. (2013b). It is shown that these modes exhibit an energetic 3D static vortex system close to the base of the body. A sufficiently deep cavity is able to stabilize the wake toward a symmetry preserved wake, thus suppressing the RSB modes and leading to a weaker elliptical toric recirculation. The stabilization can be modelled with a Langevin equation. The plausible mechanism for drag reduction with the base cavity is based on the interaction of the static 3D vortex system of the RSB modes with the base and their suppression by stabilization. There are some strong evidences that this mechanism may be generalized to axisym-metric bodies with base cavity. (10.1016/j.jfluidstructs.2015.12.001)
  DOI : 10.1016/j.jfluidstructs.2015.12.001
• Variational formulation and stability analysis of a three dimensional superelastic model for shape memory alloys
  
  • Alessi Roberto
  • Pham Kim
  Journal of the Mechanics and Physics of Solids, Elsevier, 2016, 87, pp.150-176. (10.1016/j.jmps.2015.11.006)
  DOI : 10.1016/j.jmps.2015.11.006
• Time-domain damping models in structural acoustics using digital filtering
  
  • Parret-Fréaud Augustin
  • Cotté Benjamin
  • Chaigne Antoine
  Mechanical Systems and Signal Processing, Elsevier, 2016, 68-69, pp.587-607. This paper describes a new approach in order to formulate well-posed time-domain damping models able to represent various frequency domain profiles of damping properties. The novelty of this approach is to represent the behavior law of a given material directly in a discrete-time framework as a digital filter, which is synthesized for each material from a discrete set of frequency-domain data such as complex modulus through an optimization process. A key point is the addition of specific constraints to this process in order to guarantee stability, causality and verification of thermodynamics second law when transposing the resulting discrete-time behavior law into the time domain. Thus, this method offers a framework which is particularly suitable for time-domain simulations in structural dynamics and acoustics for a wide range of materials (polymers, wood, foam, etc.), allowing to control and even reduce the distortion effects induced by time-discretization schemes on the frequency response of continuous-time behavior laws. (10.1016/j.ymssp.2015.08.005)
  DOI : 10.1016/j.ymssp.2015.08.005
• Experimental database with full field measurements for mixed-mode crack propagation in concrete: comparison between experimental and numerical results
  
  • Carpiuc Andreea
  • Jailin Clément
  • Poncelet M.
  • Kyrylo K.
  • Hild François
  , 2016. no abstract
• A simple turbulent two-fluid model
  
  • Hérard Jean-Marc
  • Lochon Hippolyte
  Comptes Rendus. Mécanique, Académie des sciences (Paris), 2016, 344 (11-12), pp.776-783. We present in this paper a simple turbulent two-phase flow model using the two-fluid approach. The model, that relies on the classical ensemble averaging, allows the computation of unsteady flows including shock waves, rarefaction waves and contact discontinuities. It requires the definition of adequate source terms and interfacial quantities. The hyperbolic turbulent two-fluid model is such that unique jump conditions hold within each field. Closure laws for the interfacial velocity and the interfacial pressure comply with a physically relevant entropy inequality. Moreover, source terms that account for mass, momentum and energy in-terfacial transfer are in agreement with the entropy inequality. Particular attention is also given to the jump conditions when assuming a perfect gas equation of state within each phase ; this enables to recover expected bounds on the mean density through shock waves. (10.1016/j.crme.2016.10.010)
  DOI : 10.1016/j.crme.2016.10.010
• Feedback control of bimodal wake dynamics
  
  • Li Ruying
  • Barros Diogo
  • Borée Jacques
  • Cadot Olivier
  • Noack Bernd R.
  • Cordier Laurent
  Experiments in Fluids, Springer Verlag (Germany), 2016, 57, pp.158. Feedback control is applied to symmetrize the bimodal dynamics of a turbulent blunt body wake. The flow is actuated with two lateral slit jets and monitored with pressure sensors at the rear surface. The physics-based controller is inferred from preliminary open-loop tests and is capable of symmetrizing the wake. A slight pressure recovery is achieved due to the net balance between the favourable effect of wake symmetrization and adverse effect of shear layer mixing and vortex shedding amplification (10.1007/s00348-016-2245-2)
  DOI : 10.1007/s00348-016-2245-2
• Gradient damage modeling of brittle fracture in an explicit dynamics context
  
  • Li Tianyi
  • Marigo Jean-Jacques
  • Guilbaud Daniel
  • Potapov Serguei
  International Journal for Numerical Methods in Engineering, Wiley, 2016. In this contribution we propose a dynamic gradient damage model as a phase-field approach for studying brutal fracture phenomena in quasi-brittle materials under impact-type loading conditions. Several existing approaches to account for the tension-compression asymmetry of fracture behavior of materials are reviewed. A better understanding of these models is provided through a uniaxial traction experiment. We then give an efficient numerical implementation of the model in an explicit dynamics context. Simulations results obtained with parallel computing are discussed both from a computational and physical point of view. Different damage constitutive laws and tension-compression asymmetry formulations are compared with respect to their aptitude to approximate brittle fracture. (10.1002/nme.5262)
  DOI : 10.1002/nme.5262
• Gradient damage models and their use in brittle fracture
  
  • Marigo Jean-Jacques
  • Maurini Corrado
  • Pham Kim
  , 2016. The paper is devoted to gradient damage models which allow us to describe all the process of degradation of a body including the nucleation of cracks and their propagation. The construction of such model follows the variational approach to fracture and proceeds into two stages: (i) definition of the energy; (ii) formulation of the damage evolution problem. The total energy of the body is defined in terms of the state variables which are the displacement field and the damage field in the case of quasi-brittle materials. That energy contains in particular gradient damage terms in order to avoid too strong damage localizations. The formulation of the damage evolution problem is then based on the concepts of irreversibility, stability and energy balance. That allows us to construct homogeneous as well as localized damage solutions in a closed form and to illustrate the concepts of loss of stability, of scale effects, of damage localization, and of structural failure. Moreover, the variational formulation leads to a natural numerical method based on an alternate minimization algorithm. Several numerical examples illustrate the ability of this approach to account for all the process of fracture including a 3D thermal shock problem where the crack evolution is very complex.