Publications

2017

• Bifurcation tracking by Harmonic Balance Method for performance tuning of nonlinear dynamical systems
  
  • Xie Lihan
  • Baguet Sébastien
  • Prabel Benoit
  • Dufour Régis
  Mechanical Systems and Signal Processing, Elsevier, 2017, 88, pp.445-461. The aim of this paper is to provide an efficient frequency-domain method for bifurcation analysis of nonlinear dynamical systems. The proposed method consists in directly tracking the bifurcation points when a system parameter such as the excitation or nonlinearity level is varied. To this end, a so-called extended system comprising the equation of motion and an additional equation characterizing the bifurcation of interest is solved by means of the Harmonic Balance Method coupled with an arc-length continuation technique. In particular, an original extended system for the detection and tracking of Neimark-Sacker (secondary Hopf) bifurcations is introduced. By applying the methodology to a nonlinear energy sink and to a rotor-stator rubbing system, it is shown that the bifurcation tracking can be used to efficiently compute the boundaries of stability and/or dynamical regimes, i.e., safe operating zones. (10.1016/j.ymssp.2016.09.037)
  DOI : 10.1016/j.ymssp.2016.09.037
• Stress and flux reconstruction in Biot's poro-elasticity problem with application to a posteriori error analysis
  
  • Riedlbeck Rita
  • Di Pietro Daniele
  • Ern Alexandre
  • Granet Sylvie
  • Kazymyrenko Kyrylo
  Computers & Mathematics with Applications, Elsevier, 2017, 73 (7), pp.1593–1610. We derive equilibrated reconstructions of the Darcy velocity and of the total stress ten-sor for Biot's poro-elasticity problem. Both reconstructions are obtained from mixed finite element solutions of local Neumann problems posed over patches of elements around mesh vertices. The Darcy velocity is reconstructed using Raviart–Thomas finite elements and the stress tensor using Arnold–Winther finite elements so that the reconstructed stress tensor is symmetric. Both reconstructions have continuous normal component across mesh interfaces. Using these reconstructions, we derive a posteriori error estimators for Biot's poro-elasticity problem, and we devise an adaptive space-time algorithm driven by these estimators. The algorithm is illustrated on test cases with analytical solution, on the quarter five-spot problem , and on an industrial test case simulating the excavation of two galleries. (10.1016/j.camwa.2017.02.005)
  DOI : 10.1016/j.camwa.2017.02.005
• Fretting wear of a nitrided 316L/304L contact subject to in-phase normal force fluctuation in dry and lithium-boron solution: An R P -friction energy wear approach
  
  • Marc E.
  • Fouvry S.
  • Graton O.
  • Phalippou C.
  • Maitournam Habibou
  Wear, Elsevier, 2017, 376-377, pp.690 - 704. (10.1016/j.wear.2017.01.075)
  DOI : 10.1016/j.wear.2017.01.075
• A new multi-frequency approach based on Padé approximants for the treatment of transient dynamics problems with the variational theory of complex rays
  
  • Rouzaud Christophe
  • Gatuingt Fabrice
  • Hervé Guillaume
  • Dorival Olivier
  Journal of Sound and Vibration, Elsevier, 2017, 392, pp.170-186. Frequency-based methods were set up in order to circumvent the limits of classical finite element methods in fast dynamic simulations due to discretizations. In this approach the dynamic loading was shifted in the frequency domain by FFT, then treated by the Variational Theory of Complex Rays, and then the time response was reconstructed through an IFFT. This strategy proved to be very efficient due to the CPU VTCR very low cost. However in the case of a large loading spectrum this frequency-by-frequency approach could seriously degrade the computational performances of the strategy. This paper addresses this point by proposing the use of Padé approximants in order to limit the number of frequencies at which the response should be calculated. Padé approximation is applied to the overall VTCR system based on its frequency dependency. Finally, as simulations on a simple academic case and on a civil engineering structure show, this method is found to be very efficient for interpolating the frequency response functions of a complex structure. This is a key point to preserve the efficiency of the complete VTCR strategy for transient dynamic problems. (10.1016/j.jsv.2016.12.026)
  DOI : 10.1016/j.jsv.2016.12.026
• Fluid-solid-electric energy transport along piezoelectric flags
  
  • Xia Yifan
  • Doaré Olivier
  • Michelin Sébastien
  Revue Européenne de Mécanique Numérique/European Journal of Computational Mechanics, Hermès / Paris : Lavoisier, 2017. The fluid–solid–electric dynamics of a flexible plate covered by interconnected piezoelectric patches in an axial steady flow are investigated using numerical simulations based on a reduced-order model of the fluid loading for slender structures. Beyond a critical flow velocity, the fluid–solid instability results in large amplitude flapping of the structure. Short piezoelectric patches positioned continuously along the plate convert its local deformation into electrical currents that are used within a single internal electrical network acting as an electric generator for the external output circuit. The relative role of the internal and external impedance on the energy harvesting of the system is presented and analysed in the light of a full modelling of the electric and mechanical energy exchanges and transport along the structure. (10.1080/17797179.2017.1306827)
  DOI : 10.1080/17797179.2017.1306827
• Flow energy harvesting with piezoelectric plates
  
  • Doaré Olivier
  • Michelin Sébastien
  • Pineirua Miguel
  • Xia Yifan
  , 2017. Le flottement de plaques flexibles dans un écoulement axial a pour origine une instabilité classique en interaction fluide-structure. Cette instabilité a pour conséquence des vibrations auto-entretenues de grande amplitude, il s'agit donc d'un mécanisme intéressant de transfert d'énergie d'un écoulement une structure. En y adjoignant un mécanisme de couplage électromécanique, nous pouvons ainsi convertir l'énergie cinétique d'un écoulement en énergie électrique. Une des pistes envisagées est d'exploiter le couplage piézoélectrique en considérant des drapeaux couverts par les matériaux piézoélectriques. Dans cette présentation, afin d'évaluer la pertinence de tels systèmes, nous tenterons de déterminer sous quelles conditions et pour quelles géométries l'efficacité de récupération d'énergie peut être maximisée. Des approches à la fois théoriques/numériques et expérimentales seront présentées, et différents phénomènes clefs pour l'efficacité seront mis en évidence : déstabilisation par ajout d'amortissement, synchronisation mécanique/électrique, résonance, accrochage.
• Investigation on fatigue behaviors of NiTi polycrystalline strips under stress-controlled tension via in-situ macro-band observation
  
  • Zheng Lin
  • He Y. J.
  • Moumni Ziad
  International Journal of Plasticity, Elsevier, 2017, 90, pp.116 - 145. (10.1016/j.ijplas.2016.12.008)
  DOI : 10.1016/j.ijplas.2016.12.008
• Matériaux et structures anélastiques
  
  • Maitournam Habibou
  , 2017. Les travaux de recherche de Habibou Maitournam portent sur la modélisation des comportements thermomécaniques et asymptotiques des structures anélastiques sous chargements cycliques, la prévision de leur tenue à la fatigue ainsi que la modélisation de procédés. Ses travaux sont largement utilisés par les industries automobiles et ferroviaires. Il est professeur à l’ENSTA ParisTech et professeur associé à l’École polytechnique. Cet ouvrage s’adresse principalement aux élèves des grandes écoles scientifiques ainsi qu’aux étudiants des universités suivant une voie spécialisée en mécanique des matériaux et des structures. L’objectif de cet ouvrage est de donner tous les éléments théoriques nécessaires à la mise en œuvre d’une démarche de détermination de la durée de vie des structures sous chargement cyclique (thermodynamique, comportement cyclique, théorie de l’adaptation et fatigue). En effet, de plus en plus de structures mécaniques, qu’elles soient aéronautiques, automobiles ou ferroviaires, travaillent hors de leur domaine de comportement linéaire, leur dimensionnement optimal nécessite une bonne maîtrise de leurs états thermomécaniques issus de la fabrication et de l’évolution de ceux-ci sous des chargements complexes, de service ou accidentels. Le comportement anélastique des matériaux et des structures sous chargements transitoires et cycliques est étudié en vue de la compréhension des principaux modes de ruine. Il est illustré par des nombreux exemples. Questions et thématiques abordées : 1. Que devient l’énergie fournie à un système ? L’énergie dans tous ses états : énergétique et thermodynamique. 2. Comment construit-on des modèles de comportement anélastique des matériaux ? Thermoélasticité, élastoplasticité, et viscoplasticité. 3. Comment mettre en œuvre numériquement ces modèles pour calculer des structures ? 4. Que reste-il quand la sollicitation disparaît ? Contraintes résiduelles : origine, méthodes de détermination. 5. Comment répond la structure sollicitée cycliquement ? S’adapte-t-elle ou « craque »-t-elle ? Structures sous chargements cycliques : état asymptotique : adaptation, accommodation, rochet ; théorie de l’adaptation : applications aux poutres et aux structures tridimensionnelles. 6. En pratique, il arrive que la structure fatigue... Introduction à la fatigue des structures. C’est une vision unitaire du comportement des matériaux et des structures (comportement mécanique et fatigue) sous l’angle dissipatif qui est exposée. L’angle énergétique avec le rôle clé de la dissipation et le formalisme « standard généralisé » sont mis en valeur. Des mises en œuvre simples permettent une compréhension de la théorie et des exercices adaptés détaillent son application.
• An acoustic-convective splitting-based approach for the Kapila two-phase flow model
  
  • ten Eikelder M. F. P.
  • Daude Frédéric
  • Koren Barry
  • Tijsseling Arris S.
  Journal of Computational Physics, Elsevier, 2017, 331, pp.188-208. In this paper we propose a new acoustic-convective splitting-based numerical scheme for the Kapila five-equation two-phase flow model. The splitting operator decouples the acoustic waves and convective waves. The resulting two submodels are alternately numerically solved to approximate the solution of the entire model. The Lagrangian form of the acoustic submodel is numerically solved using an HLLC-type Riemann solver whereas the convective part is approximated with an upwind scheme. The result is a simple method which allows for a general equation of state. Numerical computations are performed for standard two-phase shock tube problems. A comparison is made with a non-splitting approach. The results are in good agreement with reference results and exact solutions. (10.1016/j.jcp.2016.11.031)
  DOI : 10.1016/j.jcp.2016.11.031
• Experimental Analysis of a Tuned Mass Damper with Eddy Currents Damping Effect
  
  • Lo Feudo Stefania
  • Allani Anissa
  • Cumunel Gwendal
  • Argoul Pierre
  • Maceri Franco
  • Bruno Domenico
  , 2017, 8, pp.235-248. A Tuned Mass Damper (TMD) is a structural passive control device fixed on a structure and composed of a linear oscillator which natural frequency is tuned to that of the structure, or to the dominant resonance frequency. In this paper, an experimental TMD with adjustable stiffness and eddy current damping is proposed. The first step is to check if the dynamical properties of the proposed TMD are constant during the dynamic test and for different values of stiffness and damping. Therefore, the instantaneous modal parameters are evaluated by applying the continuous wavelet transform on the experimental data. Then, the TMD is set with optimal parameters and used to control vibrations of a frame scale model. The structure response with and without the TMD is evaluated from the experimental measurements in case of a shock applied to the top floor. (10.1007/978-3-319-48884-4_13)
  DOI : 10.1007/978-3-319-48884-4_13
• Spatial coherency analysis of seismic ground motions from a rock site dense array implemented during the Kefalonia 2014 aftershock sequence
  
  • Svay Angkeara
  • Perron Vincent
  • Imtiaz Afifa
  • Irmela Zentner
  • Cottereau Régis
  • Clouteau Didier
  • Bard Pierre Yves
  • Hollender F.
  • Lopez-Caballero Fernando
  Earthquake Engineering and Structural Dynamics, Wiley, 2017, 46 (12), pp.1895-1917. The objective of studies presented in this paper is to analyse the spatial incoherency of seismic ground motions using signals from a velocimeter dense array located on a rock site, recording the aftershock sequence of the two M6 Kefalonia earthquakes that occurred in January/February 2014 (Kefalonia island, Greece). The analyses are carried out with both horizontal and vertical components of velocigrams for small separation distances of stations (<100 m). The coherencies of seismic ground motions identified from strong motion windows are compared with those identified from coda parts of signals. It is realized that there is no significant difference between the coherencies estimated from those two parts of signals. The influence of earthquake event number on the result of coherencies and the dispersions of coherencies estimated from different earthquake events are presented. Finally, coherencies estimated from the dense array are compared with several coherency models proposed and widely used in the literature. The possibility of modifying some parameters of those existing coherency models to fit with in situ coherencies are discussed and presented. (10.1002/eqe.2881)
  DOI : 10.1002/eqe.2881
• Mixed DEM/FEM modeling of advanced damage in reinforced concrete structures.
  
  • Potapov S.
  • Masurel A.
  • Marin Philippe Maurice
  • Daudeville L.
  Journal of Engineering Mechanics - ASCE, American Society of Civil Engineers, 2017, 143 (2), pp.04016110. (10.1061/(asce)em.1943-7889.0001173)
  DOI : 10.1061/(asce)em.1943-7889.0001173
• An integration technique for 3D curved cracks and branched discontinuities within the eXtended Finite Element Method
  
  • Paul Bertrand
  • Ndeffo Marcel
  • Massin Patrick
  • Moes Nicolas
  Finite Elements in Analysis and Design, Elsevier, 2017, 123, pp.19-50. In this paper, we present a robust procedure for the integration of functions discontinuous across arbitrary curved interfaces defined by means of level set functions for an application to linear and quadratic eXtended Finite Elements. It includes the possibility to have branching discontinuities between the different sub-domains. For the volume integration, integration subcells are built from the approximation mesh, in order to obtain an accurate approximation of the sub-domains. The set of subcells we get constitutes the integration mesh, which can also be used by the visualization tools. Then, we extract the faces of these integration subcells that coincide with the sub-domain boundaries, allowing us to perform surface integrations on the sub-domain boundaries. When combined with the eXtended Finite Element Method (XFEM) optimal convergence rates are obtained with curved geometries for both linear and quadratic elements. (10.1016/j.finel.2016.09.002)
  DOI : 10.1016/j.finel.2016.09.002
• Influence of a hysteretic damper on the flutter instability
  
  • Malher Arnaud
  • Doaré Olivier
  • Touzé Cyril
  Journal of Fluids and Structures, Elsevier, 2017, 68, pp.356 - 369. The influence of a hysteretic damper on the airfoil flutter instability is investigated. In particular, its effect on the post-critical limit cycle oscillations (LCOs) is emphasized. For that purpose, an aeroelastic model including large amplitude motions and dynamic stall phenomenon, is considered for a rigid flat plate having two degrees of freedom in pitch and plunge motions. The hysteretic behaviour is modeled thanks to a generalized Bouc-Wen formulation. A parametric study of aeroelastic as well as hysteresis model parameters, allows one to draw a complete picture of the bifurcation scenario, highlighting the capacity of the hysteretic damper in precluding the occurrence of stall. The special case of shape memory alloy (SMA) springs is then used numerically and experimentally for controlling the flutter oscillations of a flat plate. The study reveals the ability of the SMA springs to drastically reduce the amplitudes of the LCOs caused by the flutter instability. (10.1016/j.jfluidstructs.2016.11.001)
  DOI : 10.1016/j.jfluidstructs.2016.11.001
• 3D characterization and modeling of low cycle fatigue damage mechanisms at high temperature in a cast aluminum alloy
  
  • Dézécot Sébastien
  • Maurel Vincent
  • Buffière Jean-Yves
  • Szmytka Fabien
  • Köster Alain
  Acta Materialia, Elsevier, 2017, 123, pp.24-34. Synchrotron X-ray tomography was used to monitor damage evolution in three dimensions during in situ Low Cycle Fatigue (LCF) tests at high temperature (250℃) for an industrial material. The studied material is an AlSi7Cu3Mg aluminum alloy (close to ASTM A319) produced by Lost Foam Casting (LFC), a process which generates coarse microstructures but is nevertheless used for engine parts by the automotive industry. The volume analysis (3D images) has shown that cracks are extremely sensitive to microstructural features: coarse pores and hard particles of the eutectic regions are critical regarding respectively the main crack initiation and the crack growth. Finite Elements (FE) simulations, performed on meshes directly generated from 3D volumes and containing only pores, have revealed that mechanical fields also play a major role on the crack behavior. Initiation sites corresponded to areas of maximum inelastic strain while the crack path was globally correlated to high stress triaxiality and inelastic strain fields. (10.1016/j.actamat.2016.10.028)
  DOI : 10.1016/j.actamat.2016.10.028
• Virtual hybrid test control of sinuous crack
  
  • Jailin Clément
  • Carpiuc Andreea
  • Kazymyrenko Kyrylo
  • Poncelet Martin
  • Leclerc Hugo
  • Hild François
  • Roux Stéphane
  Journal of the Mechanics and Physics of Solids, Elsevier, 2017, 102, pp.239 - 256. The present study aims at proposing a new generation of experimental protocol for analysing crack propagation in quasi brittle materials. The boundary conditions are controlled in real-time to conform to a predefined crack path. Servo-control is achieved through a full-field measurement technique to determine the pre-set fracture path and a simple predictor model based on linear elastic fracture mechanics to prescribe the boundary conditions on the fly so that the actual crack path follows at best the predefined trajec-tory. The final goal is to identify, for instance, non-local damage models involving internal lengths. The validation of this novel procedure is performed via a virtual test-case based on an enriched damage model with an internal length scale, a prior chosen sinusoidal crack path and a concrete sample. Notwithstanding the fact that the predictor model selected for monitoring the test is a highly simplified picture of the targeted constitutive law, the proposed protocol exhibits a much improved sensitivity to the sought parameters such as internal lengths as assessed from the comparison with other available experimental tests. (10.1016/j.jmps.2017.03.001)
  DOI : 10.1016/j.jmps.2017.03.001
• A complex mixed-mode crack propagation test performed with a 6-axis testing machine and full-field measurements propagation
  
  • Carpiuc-Prisacari A.
  • Poncelet M.
  • Kazymyrenko K.
  • Leclerc Hugo
  • Hild François
  Engineering Fracture Mechanics, Elsevier, 2017, 176, pp.1-22. A new type of mixed mode crack propagation test is proposed. A single crack is initiated and propagates in a stable way up to complete failure. A combination of tensile, shear and in-plane rotation performed by a 6-axis testing machine is prescribed. The rotation creates a tension/compression gradient in the sample ensuring the stability, while the shear direction is closely related to the orientation of the crack and the tensile load is responsible for the actual propagation. The experiment is performed in an interactive manner, namely, depending on the crack tip position estimated by Digital Image Correlation (DIC) during the test, the loading is changed to bifurcate the crack. The displacements of the sample surfaces are assessed using multiple DIC measurements and displacement sensors. The displacement fields on each face of the sample give access to the crack pattern, and also to the actual boundary conditions that are crucial for a faithful numerical analysis of the test. Last, the 6 load components are recorded enabling for a complete description of the 3D mechanical behavior of the specimen. (10.1016/j.engfracmech.2017.01.013)
  DOI : 10.1016/j.engfracmech.2017.01.013
• Improvement of the acoustic black hole effect by using energy transfer due to geometric nonlinearity
  
  • Denis Vivien
  • Pelat Adrien
  • Touzé Cyril
  • Gautier François
  International Journal of Non-Linear Mechanics, Elsevier, 2017, 94, pp.134-145. Acoustic Black Hole effect (ABH) is a passive vibration damping technique without added mass based on flexural waves properties in thin structures with variable thickness. A common implementation is a plate edge where the thickness is locally reduced with a power law profile and covered with a viscoelastic layer. The plate displacement in the small thickness region is large and easily exceeds the plate thickness. This is the origin of geometric nonlinearity which can generate couplings between linear eigenmodes of the structure and induce energy transfer between low and high frequency regimes. This phenomenon may be used to increase the efficiency of the ABH treatment in the low frequency regime where it is usually inefficient. An experimental investigation evidenced that usual ABH implementation gives rise to measurable geometric nonlinearity and typical nonlinear phenomena. In particular, strongly nonlinear regime and wave turbulence are reported. The nonlinear ABH beam is then modeled as a von Kármán plate with variable thickness. The model is solved numerically by using a modal method combined with an energy-conserving time integration scheme. The effects of both the thickness profile and the damping layer are then investigated in order to improve the damping properties of an ABH beam. It is found that a compromise between the two effects can lead to an important gain of efficiency in the low frequency range. (10.1016/j.ijnonlinmec.2016.11.012)
  DOI : 10.1016/j.ijnonlinmec.2016.11.012
• CARPIUC Benchmark: Crack Advance, Reorientation, Propagation and Initiation Under Complex loadings
  
  • Carpiuc Andreea
  • Poncelet M.
  • Réthoré Julien
  • Roux S.
  , 2017. A series of experiments has been performed to build a benchmark for the numerical modeling of mixed mode crack propagation in concrete. Two tests are selected so that the propagation is almost always stable although the material is quasi-fragile. Moreover the variation of mode mixity enables the study of the reorientation of the crack, as well as more complex phenomena such as branching or link-up. To control stability and mode mixity, the loading is imposed with a 6-axis testing machine while the crack propagation is assessed by full-field measurement. In this paper, a description of the experimental setup is provided as well as numerical simulation results illustrating the sensitivity to boundary conditions and geometry. Links to data needed to perform numerical simulations of these benchmark experiments are given, together with references to publications giving full descriptions of the protocol and experiment results. (10.1186/s40323-018-0115-6)
  DOI : 10.1186/s40323-018-0115-6
• An algebraic expansion of the potential theory for predicting dynamic stability limit of in-line cylinder arrangement under single-phase fluid cross-flow
  
  • Benaouicha Mustapha
  • Baj Franck
  • Longatte Elisabeth
  Journal of Fluids and Structures, Elsevier, 2017, 72, pp.80 - 95. Flow-induced vibration in square cylinder arrangement under viscous fluid incompressible cross-flow is investigated in the present work. The purpose is to contribute to better mod-eling and understanding external fluid loads exerted on long thin cylinders inducing flow perturbations. Due to high flow confinement, thin cylinders may be subjected to strong vibrations, which may lead to dynamic instability development. A theoretical approach is developed to determine a stability criterion of the dynamical system. The influence of geometric, mechanical and flow parameters such as reduced velocity and pitch ratio is investigated. The proposed model is derived from the potential flow theory and enhanced through an algebraic phase lag model in order to predict the critical limit of the reduced velocity for a square cylinder arrangement submitted to an external in-line cross flow. A theoretical formulation of the total damping, including added damping in still fluid, the damping due to fluid flow and the damping derived from the phase shift between the fluid load and the tube displacement, is expressed. A function depending on fluid and structure parameters, such as reduced velocity, pitch ratio and Scruton number is thus obtained. It is shown that this function provides a prediction of the dynamic stability limit of the system for several ranges of the major parameters to be considered. The results are compared to experimental reference solutions and to those provided by other theoretical models. This work proposes a consistent original model based on a potential flow theory enriched by using an algebraic formulation based on standard physical assumptions from literature. The major advantage of this model is due to the fact that it is in the same time robust and very user-friendly from a computational point of view thanks to the potential framework. In order to describe fluid and solid dynamics in the domain, terms coming from the potential flow theory are estimated by using a finite element method and complementary terms acting on damping are obtained through an algebraic formulation. Therefore this is a convenient way to propose a hybrid numerical / algebraic model for predicting dynamic instability limit in cylinder arrangements. (10.1016/j.jfluidstructs.2017.04.004)
  DOI : 10.1016/j.jfluidstructs.2017.04.004
• A modal-based approach to the nonlinear vibration of strings against a unilateral obstacle: Simulations and experiments in the pointwise case
  
  • Issanchou Clara
  • Bilbao Stefan
  • Le Carrou Jean-Loic
  • Touzé Cyril
  • Doaré Olivier
  Journal of Sound and Vibration, Elsevier, 2017, 393, pp.229-251. This article is concerned with the vibration of a stiff linear string in the presence of a rigid obstacle. A numerical method for unilateral and arbitrary-shaped obstacles is developed, based on a modal approach in order to take into account the frequency dependence of losses in strings. The contact force of the barrier interaction is treated using a penalty approach, while a conservative scheme is derived for time integration, in order to ensure long-term numerical stability. In this way, the linear behaviour of the string when not in contact with the barrier can be controlled via a mode by mode fitting, so that the model is particularly well suited for comparisons with experiments. An experimental configuration is used with a point obstacle either centered or near an extremity of the string. In this latter case, such a pointwise obstruction approximates the end condition found in the tanpura, an Indian stringed instrument. The second polarisation of the string is also analysed and included in the model. Numerical results are compared against experiments, showing good accuracy over a long time scale. (10.1016/j.jsv.2016.12.025)
  DOI : 10.1016/j.jsv.2016.12.025
• Comparison between experimental and numerical results of mixed-mode crack propagation in concrete: Influence of boundary conditions choice
  
  • Carpiuc-Prisacari A.
  • Poncelet M.
  • Kazymyrenko K.
  • Hild François
  • Leclerc Hugo
  Cement and Concrete Research, Elsevier, 2017, 100, pp.329--340. no abstract (10.1016/j.cemconres.2017.05.003)
  DOI : 10.1016/j.cemconres.2017.05.003
• Characterization of transport and water retention properties of damaged Callovo-Oxfordian claystone
  
  • M'Jahad Sofia
  • Davy Catherine A.
  • Skoczylas Frédéric
  • Talandier Jean
  The Geology Society of London, Lyell Collection, 2017, 443, pp.159-177. In the context of the underground storage of radioactive waste, the aim of this experimental study is to characterize the effect of damage on transport and water retention properties of Callovo-Oxfordian (COx) argillite. The originality of the study is to simultaneously investigate the pore-size distribution, water retention, the dry, effective and relative gas permeability, and the gas breakthrough pressure (GBP) of damaged COx argillite. These different properties are all relevant to characterizing the fluid transport ability of COx argillite. Results show that the damage has a significant impact on the properties of the COx argillite. It induces a decrease in its water retention capacity and GBP, and it increases its gas permeability and apparent porosity available to water owing to the creation of micro-cracks. Another objective is to show which of these properties is the most suitable to detect early damage states in COx argillite, with a potential use being to identify them in situ. GBP appears to be the best ‘detector’ of damage because of its sensitivity to damage even under high confinement pressures. Gas permeability could be a good indicator of damage, as it increases significantly (one or several orders of magnitude) after the damage. Finally, the water permeability curve is a poor indicator of COx argillite damage. (10.1144/SP443.23)
  DOI : 10.1144/SP443.23
• Flutter Control of a Two-Degrees-of-Freedom Airfoil Using a Nonlinear Tuned Vibration Absorber
  
  • Malher Arnaud
  • Touzé Cyril
  • Doaré Olivier
  • Habib Giuseppe
  • Kerschen Gaëtan
  Journal of Computational and Nonlinear Dynamics, American Society of Mechanical Engineers (ASME), 2017, 12 (5), pp.051016. The influence of a Nonlinear Tuned Vibration Absorber (NLTVA) on the airfoil flutter is investigated. In particular, its effect on the instability threshold and the potential subcriticality of the bifurcation is analyzed. For that purpose, the airfoil is modeled using the classical pitch and plunge aeroelastic model together with a linear approach for the aerodynamic loads. Large amplitude motions of the airfoil are taken into account with nonlinear restoring forces for the pitch and plunge degrees of freedom. The two cases of a hardening and a softening spring behavior are investigated. The influence of each NLTVA parameter is studied and an optimum tuning of these parameters is found. The study reveals the ability of the NLTVA to shift the instability, avoid its possible subcriticality and reduce the LCOs amplitude. (10.1115/1.4036420)
  DOI : 10.1115/1.4036420