Publications

2017

• Parametric study of flow-induced vibrations in cylinder arrays under single-phase fluid cross flows using POD-ROM
  
  • Longatte Elisabeth
  • Liberge Erwan
  • Pomarede Marie
  • Sigrist Jean-François
  • Hamdouni Aziz
  Journal of Fluids and Structures, Elsevier, 2017, 78, pp.314-330. Modeling numerically Flow-Induced Vibrations in heat exchangers at a microscopic scalerequires high computational resources and time which are still unreachable. Thereforemodel reduction is investigated in the present work in order to address the issue ofsimulation computational time reduction. In the framework of POD-Galerkin projectionmethods, the purpose is to propose optimal a posteriori reduction strategies enabling errorcontrol on approximation as well as Reduced-Order Model (ROM) interpolation to dealwith sensitivity analysis of solutions to parameter perturbations. A multi-phase fluid–solidPOD-Galerkin-based method is proposed for modeling flows and vibrations in cylinderarrangements under single-phase fluid cross-flows. Moreover a single-POD basis method isevaluated in the context of ROM interpolation. This work is a first step in the developmentof robust ROM describing fluid and solid dynamics in the presence of turbulence, heattransfer effects and large magnitude structure displacements and deformations (10.1016/j.jfluidstructs.2017.12.011)
  DOI : 10.1016/j.jfluidstructs.2017.12.011
• Contrôle sismique des structures
  
  • Vu Duc-Chuan
  , 2017. Cette thèse est motivée par diverses questions qui se posent quant à l’utilisation de l’isolation sismique dans l’industrie nucléaire. À la différence de la grande majorité des travaux antérieurs sur l’isolation sismique en générale et l’isolation mixte en particulier, qui portent principalement leur intérêt sur la réponse de la structure isolée (déplacements relatifs, accélérations maximales des étages, etc.), une grande partie de ce travail est consacrée au comportement des équipements, par le biais de l’étude des spectres de plancher. L’objectif principal est de diminuer la déformation des isolateurs sans amplification de la réponse des modes supérieurs, qui peut apparaître sous certaines conditions et qui peut être une source de sollicitation des équipements. Pour ce faire, des alternatives aux appuis parasismiques couramment utilisés sont explorées. Il s’agit des combinaisons d’un appui à faible amortissement avec un élément de Maxwell (isolateur de relaxation) ou avec un amortisseur hydraulique semi-actif (système d’isolation mixte). L’élément de Maxwell se comportant comme un amortisseur à basse fréquence et un ressort de faible rigidité à haute fréquence permet de satisfaire l’objectif souhaité. En ce qui concerne les systèmes d’isolation mixtes, trois techniques de contrôle semi-actif sont proposées. Afin d’améliorer la performance du contrôle, une attention particulière a été donné à la prise en compte de l’excitation sismique et des caractéristiques de l’amortisseur lors de la conception du contrôleur est focalisée. Les analyses numériques confirment l'efficacité de ces systèmes. En vue de l’utilisation de ces méthodes pour de structures réelles, certains aspects pratiques comme, par exemple, l’observation du système, les effets de la réduction du modèle utilisé par le contrôleur ou du temps de retard sur la performance du contrôle, ainsi que le contrôle d’un ensemble de plusieurs dispositifs semi-actifs redondant, sont, également, abordés. (10.70675/0ad965b5z6721z45b0z9e12z671fdd86ecc2)
  DOI : 10.70675/0ad965b5z6721z45b0z9e12z671fdd86ecc2
• A new preconditioner update strategy for the solution of sequences of linear systems in structural mechanics: application to saddle point problems in elasticity
  
  • Mercier Sylvain
  • Gratton Serge
  • Tardieu Nicolas
  • Vasseur Xavier
  Computational Mechanics, Springer Verlag, 2017, 60 (6), pp.969-982. Many applications in structural mechanics require the numerical solution of sequences of linear systems typically issued from a finite element discretization of the governing equations on fine meshes. The method of Lagrange multipliers is often used to take into account mechanical constraints. The resulting matrices then exhibit a saddle point structure and the iterative solution of such preconditioned linear systems is considered as challenging. A popular strategy is then to combine preconditioning and deflation to yield an efficient method.We propose an alternative that is applicable to the general case and not only to matrices with a saddle point structure. In this approach, we consider to update an existing algebraic or application-based preconditioner, using specific available information exploiting the knowledge of an approximate invariant subspace or of matrix-vector products. The resulting preconditioner has the form of a limited memory quasi-Newton matrix and requires a small number of linearly independent vectors. Numerical experiments performed on three large-scale applications in elasticity highlight the relevance of the new approach. We show that the proposed method outperforms the deflation method when considering sequences of linear systems with varying matrices. (10.1007/s00466-017-1450-z)
  DOI : 10.1007/s00466-017-1450-z
• Correction to: Comparison between thick level set (TLS) and cohesive zone models
  
  • Gómez Andrés Parrilla
  • Moës Nicolas
  • Stolz Claude
  Advanced Modeling and Simulation in Engineering Sciences, Springer, 2017, 4 (1). (10.1186/s40323-017-0091-2)
  DOI : 10.1186/s40323-017-0091-2
• On the construction of approximation space to model discontinuities and cracks with linear and quadratic extended finite elements
  
  • Ndeffo Marcel
  • Massin Patrick
  • Moës Nicolas
  • Martin Alexandre
  • Gopalakrishnan Srikanth
  Advanced Modeling and Simulation in Engineering Sciences, Springer, 2017, 4 (1), pp.6. This paper presents a robust enrichment strategy to model weak and strong discontinuities as well as cracks for industrial applications. First, numerical issues encountered with popular extended finite element approximation spaces are pointed out. Then, the paper gives indications on how to circumvent those issues. The very originality of the paper relies on questioning the theoretical approximation spaces with respect to numerical results and to modify accordingly their design. The relationship between the new design and the previous designs is clearly established, in order to highlight the very small implementation cost of the modifications exposed here. Hence with minimal additional computational cost, gains in accuracy can be significant as shown later in the paper. (10.1186/s40323-017-0090-3)
  DOI : 10.1186/s40323-017-0090-3
• Fatigue resistance of branching phase-transformation fronts in pseudoelastic NiTi polycrystalline strips
  
  • Zhang Shaobin
  • He Y. J.
  International Journal of Solids and Structures, Elsevier, 2017. (10.1016/j.ijsolstr.2017.11.023)
  DOI : 10.1016/j.ijsolstr.2017.11.023
• Piano acoustics : string’s double polarisation and piano source identification
  
  • Tan Jin Jack
  , 2017. The objective of this thesis is to improve the understanding of the acoustics of the piano in the context of physically-based sound synthesis. The manuscript is decomposed in three parts, the first two being devoted to the undertsanding of the origin of the double polarisation in piano string, while the third one is dedicated to the identification of sound sources of a complete piano.In the first part, the geometric (large-amplitude) nonlinearity is studied in order to understand if the nonlinear coupling can transfer energy to an initially non excited polarisation, thus leading to the double polarisation phenomenon. A multiple-scaleanalysis is conducted on a Kirchhoff-Carrier string model with fixed boundary conditions at both ends. Each polarisation is restrained to its fundamental mode, leading to two oscillors having nearly equal eigenfrequencies, and thus presenting a 1:1 internal resonance. The existence condition and stability criteria for double polarisation to occur are obtained and validated numerically based on the complete Kirchhoff-Carrier equations, as well as a more enriched third-order string model. Experiments are carried out on a monochord setup where the natural polarisation angles of the string, detuning between the two polarisations and its nonlinear behaviour are observed and identified.The second part is devoted to the string/bridge coupling. The degrees of freedom of the string are coupled to the bridge whose translational and rotational motions are respresented by a set of oscillators. The eigenfrequencies of various coupled systems are analysed. Numerical schemes are proposed and implemented where the string is solved via high-order finite-element method while the lumped bridge is solved analytically and coupled to the string by Lagrange multipliers. Experimentally, the string is strung over a bridge in a zig-zag configuration and excited vertically and horizontally. In both cases, double polarisation and double decay are observed and similar results are also obtained qualitatively in numerical models.The last part is devoted to a quantitative description of the vibroacoustic sources of a Bösendorfer 280VC-9 piano via operational transfer path analysis. The contribution of the soundboard, inner and outer rim, iron frame and lid are investigated in the frequency domain. It is found out that the soundboard is the primary contributor but the iron frame and the lid also play a significant role, especially at high frequencies. (10.70675/2544db64z0e8cz45c1z97a4z683809211344)
  DOI : 10.70675/2544db64z0e8cz45c1z97a4z683809211344
• Digital image correlation & Fracture mechanics: Brittle Fracture of Ceramics and Refractories
  
  • Bouterf Amine
  • Carpiuc-Prisacari A.
  • Hild François
  • Poncelet Martin
  • Roux Stéphane
  , 2017.
• Exploring damage kinetics in short glass fibre reinforced thermoplastics
  
  • Nouri Hedi
  • Guessasma Sofiane
  • Roger Frédéric
  • Ayadi Abderrahmane
  • Maitournam Habibou
  Composite Structures, Elsevier, 2017, 180, pp.63 - 74. In situ SEM tensile tests are performed to shed more light on the onset and damage evolution in the shell layer of a short glass fibre reinforced polyamide 6.6 (SGFRP) composite obtained by injection moulding. Damage mechanisms are studied in three different loading directions including 0 degrees, 45 degrees and 90 degrees with respect to the mould flow direction (MFD). The development of damage is monitored until total failure at different scales of observation. Qualitative results indicate that the orientation of tensile specimens with respect to the mould direction determines to a large extent the nature of involved damage mechanisms. Interfacial damage is by far the leading damage mechanism. Quantitative investigation further indicates multi-stage damage kinetics, which demonstrates an asymmetric behaviour with respect to sample orientation. One to two main directions of damage growth are identified as responsible for the failure properties of the studied composite depending on sample orientation. (10.1016/j.compstruct.2017.07.096)
  DOI : 10.1016/j.compstruct.2017.07.096
• Toward an integrated seismic risk assessment for nuclear safety improving current French methodologies through the SINAPS@ research project
  
  • Berge-Thierry Catherine
  • Svay Angkeara
  • Laurendeau Aurore
  • Chartier Thomas
  • Perron Vincent
  • Guyonnet-Benaize Cédric
  • Kishta Ejona
  • Cottereau Régis
  • Lopez-Caballero Fernando
  • Hollender Fabrice
  • Richard Benjamin
  • Ragueneau Frédéric
  • Voldoire François
  • Banci Fabien
  • Zentner Irmela
  • Moussallam Nadim
  • Lancieri Maria
  • Bard Pierre-Yves
  • Grange Stéphane
  • Erlicher Silvano
  • Kotronis Panagiotis
  • Le Maoult Alain
  • Nicolas Marc
  • Régnier Julie
  • Bonilla Fabian
  • Theodoulidis Nikolaos
  Nuclear Engineering and Design, Elsevier, 2017, 323, pp.185-201. The Tohoku earthquake and associated tsunami in March 2011 caused a severe nuclear accident at the Fukushima Daiichi Nuclear Power Plant, where level 7 (International Atomic Energy Agency (IAEA) – INES scale) meltdown at three reactors occurred. The underestimation of the seismic and tsunami hazards has been recognized and the seismic margins assessment of the nuclear plants remains a priority for the whole nuclear community. In this framework a five-year research project called SINAPS@ (Earthquake and Nuclear Installations: Ensuring and Sustaining Safety) is currently on-going in France. A reliable estimate of seismic margins is possible only if all uncertainties, epistemic and aleatory, are effectively identified, quantified and integrated in the seismic risk analysis. SINAPS@ brings together a multidisciplinary community of researchers and engineers from the academic and the nuclear world. SINAPS@ aims at exploring the uncertainties associated to databases, physical processes and methods used at each stage of seismic hazard, site effects, soil and structure interaction, structural and nuclear components vulnerability assessments, in a safety approach: the main objective is ultimately to identify the sources of potential seismic margins resulting from assumptions or when selecting the seismic design level or the design strategy. The whole project is built around an “integrating” work package enabling to test state-of-the-art practices and to challenge new methodologies for seismic risk assessment: the real case of Kashiwazaki-Kariwa Japanese nuclear plant, shocked by the severe earthquake in 2007 provided a rich dataset which will be used to compare with the predictions. The present paper proposes for each step of the seismic risk analysis a review of the state of practice in France in the nuclear field and then precise the objectives and research strategy of SINAPS@ to overcome identified limitations or weaknesses. Scientific issues are illustrated through preliminary results of the project. (10.1016/j.nucengdes.2016.07.004)
  DOI : 10.1016/j.nucengdes.2016.07.004
• On the capability of the Thick Level Set (TLS) damage model to fit experimental data of size and shape effects
  
  • Parrilla Gómez Andrés
  • Moes Nicolas
  • Stolz Claude
  • Grégoire David
  • Pijaudier-Cabot Gilles
  Engineering Fracture Mechanics, Elsevier, 2017, 184, pp.75-87. Size and shape effects are important issues in predicting the global response of concrete structures. Small-scale tests performed in laboratory to determine the material properties are not enough to simulate large-scale structures. Many models are used to extrapolatesmall scale results to large scale simulations, but only few are able to recover size and shape effects. Recently a model of graded damage (TLS) has been proposed and comparison with cohesive zone models shows that this new model contains a new degree of freedom,the length of transition between totally damaged material and undamaged zone (ie the process zone size). In this paper, the capability of the model (TLS) to represent size and shape effects for two recently published experimental campaigns is studied. (10.1016/j.engfracmech.2017.07.014)
  DOI : 10.1016/j.engfracmech.2017.07.014
• Settling velocity and preferential concentration of heavy particles under two-way coupling effects in homogeneous turbulence
  
  • Monchaux R.
  • Dejoan A
  Physical Review Fluids, American Physical Society, 2017. The settling velocity of inertial particles falling in homogeneous turbulence is investigated by making use of Direct Numerical Simulation (DNS) at moderate Reynolds number that include momentum exchange between both phases (two-way coupling approach). Effects of particle volume fraction, particle inertia and gravity are presented for flow and particle parameters similar to the experiments of Aliseda et al. [1]. A good agreement is obtained between the DNS and the experiments for the settling velocity statistics, when overall averaged but as well when conditioned on the local particle concentration. Both DNS and experiments show that the settling velocity further increases with increasing volume fraction and local concentration. At the considered particle loading the effects of two-way coupling is negligible on the mean statistics of turbulence. Nevertheless , the DNS results show that fluid quantities are locally altered by the particles. In particular, the conditional average on the local particle concentration of the slip-velocity shows that the main contribution to the settling enhancement results from the increase of the fluid velocity surrounding the particles along the gravitational direction induced by the collective particle back-reaction force. Particles and the surrounding fluid are observed to fall together, which in turn results in an amplification of the sampling of particles in the downward fluid motion. Effects of two-way coupling on preferential concentration are also reported. Increase of both volume fraction and gravity is shown to lower preferential concentration of small inertia particles while a reverse tendency is observed for large inertia particles. This behavior is found to be related to an attenuation of the centrifuge effects and to an increase of particle accumulation along gravity direction, as particle loading and gravity become large.
• Updated VOFIRE algorithm for fast fluid–structure transient dynamics with multi-component stiffened gas flows implementing anti-dissipation on unstructured grids
  
  • Faucher Vincent
  • Bulik Michal
  • Galon Pascal
  Journal of Fluids and Structures, Elsevier, 2017, 74, pp.64-89. The present paper is dedicated to the simulation of fast transient phenomena involving multi-component flows with fluid–structure interaction and ALE grid motion, where the fluid interfaces are tracked using the VOFIRE anti-dissipative scheme for unstructured meshes. It introduces an extension of the existing scheme in EUROPLEXUS software, written for liquid–gas flows only, to handle a combination of stiffened gases as equations of state for the fluid components, thus increasing its genericity and overcoming some limitations, at the cost of significantly modifying its implementation. The proposed methodology is proven to achieve its goals through validation examples with fluid only, such as the sloshing of a liquid in a decelerated tank or a gas–gas interaction with Richtmyer–Meshkov instability. Two large scale three-dimensional examples with full fluid–structure interaction are then provided to fully demonstrate the capabilities and the robustness of the complete proposed computational framework. (10.1016/j.jfluidstructs.2017.07.001)
  DOI : 10.1016/j.jfluidstructs.2017.07.001
• Computation of fast depressurization of water using a two-fluid model: revisiting Bilicki modelling of mass transfer
  
  • Lochon Hippolyte
  • Daude Frédéric
  • Galon Pascal
  • Hérard Jean-Marc
  Computers and Fluids, Elsevier, 2017, 156, pp.162-174. This paper is devoted to the computation of the fast depressurization of water using a two-fluid model. Such application, which is extensively studied in the nuclear field, involves many interactions between two phenomena, the mass transfer and the propagation of pressure waves. A simple but physically-based modelling of the mass transfer for the depressurization of water is proposed, which relies on the work of Bilicki & Kestin [4] in the homogeneous frame. Four different experiments have been chosen to assess the proposed model. Three of them study the depressurisation of hot water in a pressurized pipe. The comparison between converged numerical results and the experimental data shows a good agreement and demonstrates the ability of the two-fluid-model to capture the proper mass transfer for a wide range of thermodynamical conditions. The last test-case is the HDR experiment which considers the depressurization of a full-scale vessel under the hypothesis of a Loss Of Coolant Accident. The results of an ALE computation show the ability of the proposed model to retrieve experimental data in both structure and fluid. (10.1016/j.compfluid.2017.07.008)
  DOI : 10.1016/j.compfluid.2017.07.008
• A one dimensional variational model of superelasticity for shape memory alloys
  
  • Pham Kim
  Vietnam Journal of Mechanics, Viện Hàn Lâm Khoa học và Công nghệ Việt Nam, 2017, 39 (3), pp.275-301. (10.15625/0866-7136/10750)
  DOI : 10.15625/0866-7136/10750
• Constitutive Modeling of the Thermomechanical and Cyclic Behavior of Shape Memory Alloys in Finite Deformations
  
  • Wang Jun
  , 2017. Shape Memory Alloys (SMAs) are a class of smart materials that possess two salient features known as pseudoelasticity (PE) and shape memory effect(SME). In industrial applications, SMA structures are typically subjected to complex service conditions, such as large deformations, thermomechanically coupled boundaries and loadings, and cyclic loadings. The reliability and durability analysis of these SMA structures requires a good understanding of constitutive behavior in SMAs. To this end, this work develops a comprehensive constitutive modeling approach to investigate thermomechanical and cyclic behavior of SMAs in fi nite deformations. The work is generally divided into three steps. First, to improve accuracy of SMA model infinite deformation regime, the ZM model proposed by Zaki and Moumni (2007b) is extended within a fi nite-strain thermodynamic framework. Moreover, the transformation strain is decomposed into phase transformation and martensite reorientation components to capture multi-axial non-proportional response. Secondly, in addition to the fi nite deformation, thermomechanical coupling effect is taken into account by developing a new fi nite-strain thermomechanical constitutive model. A more straightforward approach is obtained by using the fi nite Hencky strain. This model incorporates three important thermomechanical characteristics, namely the coexistence effect between austenite and two distinct martensite variants, the variation with temperature of hysteresis size, and the smooth transition at initiation and completion of phase transformation. Finally, with a view to studying SMA behavior under cyclic loading, the model developed in the second step is generalized to describe cyclic pseudoelasticity of polycrystalline SMAs. The generalized model captures four fundamental characteristics related to the cyclic behavior of SMAs: large accumulated residual strain, degeneration of pseudoelasticity and hysteresis loop, rate dependence, and evolution of phase transformation from abrupt to smooth transition. Numerical implementation of these models are realized by introducing proper integration algorithms. Finite element simulations, including orthodontic archwire, helical and torsion spring actuators, are carried out using the proposed models. The future directions of this work mainly involve plasticity and fatigue analysis of SMA structures. (10.70675/9e5b75bfz9141z4172z955dzbb78e1b8a45d)
  DOI : 10.70675/9e5b75bfz9141z4172z955dzbb78e1b8a45d
• Nouvelles approches de l'endommagement
  
  • Stolz Claude
  , 2017.
• Phase-field simulation of interactive mixed-mode fracture tests on cement mortar with full-field displacement boundary conditions
  
  • Wu T.
  • Carpiuc-Prisacari A.
  • Poncelet Martin
  • de Lorenzis L.
  Engineering Fracture Mechanics, Elsevier, 2017, 182, pp.658 - 688. Phase-field modeling is an elegant approach to simulate complicated fracture processes, including crack initiation, propagation, merging and branching in a unified framework without the need for ad-hoc criteria and on a fixed mesh. These capabilities can only be fully validated through the comparison with experiments featuring crack development histories and patterns of sufficient complexity. As opposed to conventional mixed-mode fracture tests with predefined loading, interactive tests with multiaxial loading which are controlled during the propagation of the cracks can create more complex and stable crack propagation patterns. Moreover, the development of measurement techniques such as digital image correlation (DIC) provides the possibility to quantitatively characterize the full-field kinematics during the tests. In this work, full-field displacements measured by DIC during interactive mixed-mode fracture tests on cement mortar specimens are adopted as boundary conditions for phase-field numerical simulations. Qualitative and quantitative comparisons are illustrated, demonstrating the capability of the phase-field approach to predict complex mixed-mode fracture phenomena in cement mortar and suggesting possible further developments. (10.1016/j.engfracmech.2017.06.014)
  DOI : 10.1016/j.engfracmech.2017.06.014
• PWR effect on crack initiation under equi-biaxial loading development of the experiment
  
  • Dhahri Hager
  • Gourdin Cédric
  • Perez Grégory
  • Courtin Stéphane
  • Le Roux Jean‐Christophe
  • Maitournam Habibou
  , 2017. The lifetime extension of the nuclear power stations is considered as an energy challenge worldwide. That is why, the risk analysis and the study of various effects of different factors that could potentially represent a hazard to a safe long term operation are necessary. These structures, often of great dimensions, are subjected during their life to complex loading combining varying mechanical loads, multiaxial, with non-zero mean values associated with temperature fluctuations and also PWR environment.The methodology for fatigue dimensions of the Pressurized Water Reactor components (PWR) (ASME, RCC-M, KTA, ) is based on the use of design curves established from test carried out in air at 20DC on smooth specimens by integrating safety coefficient that covers the dispersion of tests associated with the effects of structures.To formally integrate these effects, some international codes have already proposed and suggested a modification of the austenitic stainless steels fatigue curve combined with a calculation of an environmental penalty factor, namely Fen, which has to be multiplied by the usual fatigue usage factor.The aim of this paper is to present a new device FABIME2E developed in the LISN in collaboration with EDF and AREVA. These new tests allow quantifying accurately the effect of PWR environment on semi-structure specimen. This new device combines the structural effect like equi-biaxiality and mean strain and the environmental penalty effect with the use of PWR environment during the fatigue tests.
• PWR Effect on Crack Initiation Under Equi-biaxial Loading: First tests with a particular fatigue device
  
  • Dhahri Hager
  • Gourdin Cédric
  • Perez Gregory
  • Courtin Stéphan
  • Le Roux Jean-Christophe
  • Maitournam Habibou
  , 2017. The lifetime extension of the nuclear power stations is considered as an energy challenge worldwide. That is why, the risk analysis and the study of various effects of different factors that could potentially represent a hazard to a safe long term operation are necessary. These structures, often of great dimensions, are subjected during their life to complex loading combining varying mechanical loads, multiaxial, with non-zero mean values associated with temperature fluctuations and also PWR environment. The methodology for fatigue dimensions of the Pressurized Water Reactor components (PWR) (ASME, RCC-M, KTA, ...) is based on the use of design curves established from test carried out in air at 20°C on smooth specimens by integrating safety coefficient that covers the dispersion of tests associated with the effects of structures. In the framework of fatigue design rules upgrading (RCC-M, RCC-MRx), the uniaxial reference fatigue curve was altered by taking into account effects like: Multiaxiality, Mean stress or strain, Surface roughness (polished or ground), Scale effect, Loading History. In addition to this effect, Environmentally Assisted Fatigue is also receiving nowadays an increased level of attention. In order to take into account the effects of these aggravating factors, two experimental device are developed at LISN with same specimen geometry: The first device (FABIME2) is to determinate the effect of equi-biaxiality and mean strain/ stress on the fatigue behavior of 316L and 304L-CLI austenitic stainless steel. A second and a new device (FABIME2E) based on FABIME2 is developed to study the impact of the environmental effect in the biaxial fatigue. The first results obtained with this new test stand FABIME2E of biaxial fatigue in the PWR environment will be presented. Their numerical interpretations using the engineering methods, provide answers to the different aggravating effects of fatigue in the components of nuclear reactors.
• MODELING HEART TISSUE AS A MICROMORPHIC MEDIUM: A NUMERICAL INVESTIGATION
  
  • Thurieau Nicolas
  • Jehl Jean-Philippe
  • Njiwa Richard Kouitat
  • Tran Nguyen
  • Maureira Pablo
  Journal of Mechanics in Medicine and Biology, World Scientific Publishing, 2017, 17 (05). (10.1142/S0219519417500786)
  DOI : 10.1142/S0219519417500786
• Crack nucleation in variational phase-field models of brittle fracture
  
  • Tanne Erwan
  • Li Tianyi
  • Bourdin Blaise
  • Marigo J.-J
  • Maurini Corrado
  , 2017. Phase-field models, sometimes refered to as gradient damage or smeared crack models, are widely used methods for the numerical simulation of crack propagation in brittle materials. Theoretical results and numerical evidences show that they can predict the propagation of a pre-existing crack according to Griffith' criterion. For a one-dimensional problem, it has been shown that they can predict nucleation upon a critical stress, provided that regularization parameter be identified with the material's internal or characteristic length. In this article, we draw on numerical simulations to study crack nucleation in commonly encountered geometries for which closed-form solutions are not available. We use U-and V-notches to show that the nucleation load varies smoothly from that predicted by a strength criterion to that of a toughness criterion, when the strength of the stress concentration or singularity varies. We present validation and verifications numerical simulations for both types of geometries. We consider the problem of an elliptic cavity in an infinite or elongated domain to show that variational phase field models properly account for structural and material size effects. We conclude that variational phase-field models can accurately predict crack nucleation through energy minimization in a nonlinear damage model instead of introducing ad-hoc criteria.
• Fluid damping in fuel assemblies
  
  • Moussou Pierre
  • Guilloux Adrien
  • Boccaccio Eric
  • Ricciardi Guillaume
  , 2017, pp.PVP2017-65664, V004T04A048. Damping is known to be a major parameter in the seismic design of nuclear facilities. Of special interest is the case of fuel assemblies in PWR plants, which, unlike other components, are submitted to axial flows: it has been known since the late 80s that their frequency response to lateral excitations was largely dependent on the flow velocity, and the issue raised by this observation is to determine a consistent fluid force model which could be used in seismic design. In the scientific literature, the standard model of fluid forces exerted upon an oscillating slender body was originally derived by Lighthill, and it involves a lift coefficient which, up to a reference frame shift, describes the force generated by a small angle of inclination of the body axis against the flow direction. Recent works by Divaret et al. have provided a value of this lift coefficient equal to 0.11 for a single cylinder, and to 0.18 for a square array of 5 by 8 cylinders, the Reynolds numbers being in the range of 104. Sticking to the idea that the damping stems from the local angle of inclination of the structure against the flow direction, the present study revisits recent tests performed in the Hermes test rig of CEA Cadarache, where a fuel assembly was submitted to incipient flow velocities varying from 1.5 to 5m.s−1, and to a lateral force exerted upon the middle grid, generating displacements in the ranges of a few mm and of a few Hz. Under the assumption that the fuel assembly behaves in an approximately linear manner and that it undergoes harmonic deformations close to its first natural mode shape, the dissipative fluid force can be expressed by an adequate combination of the hydraulic cylinder force and of the structure displacements. A lift coefficient equal to 0.3–0.4 is obtained with this procedure, which stands for the overall fuel bundle, rods and grids included. (10.1115/PVP2017-65664)
  DOI : 10.1115/PVP2017-65664
• Flutter suppression using a magnetic vibration absorber
  
  • Malher Arnaud
  • Amandolese Xavier
  • Touzé Cyril
  • Doaré Olivier
  • Habib Giuseppe
  • Kerschen Gaëtan
  , 2017.
• PROBABILISTIC THERMOMECHANICAL FATIGUE CRITERIA FOR SPHEROIDAL GRAPHITE CAST-IRONS
  
  • Szmytka Fabien
  • Charkaluk E.
  • Constantinescu A.
  , 2017. This paper proposes a method to establish and identify a probability density function characterizing the low-cycle fatigue lifetime for a cast-iron between 300 and 600°C. The method is initiated with a quantitative analysis of the microstructure of the material, which provides the initial probability distribution of graphite particles size. After identifying a given probability density function of particles, one can transport it into a lifetime probability density function using a growth law involving a macroscopic measure of the inelastic loading over a cycle. Several parameters of the growth law are finally estimated from a given set of fatigue experiments on specimens providing a criterion enabling a very satisfying matching between computed and experimental lifetime.