Publications

2016

• Damage Investigation in A319 Aluminium Alloy by X-ray Tomography and Digital Volume Correlation during In Situ High-Temperature Fatigue Tests
  
  • Dahdah Nora
  • Limodin Nathalie
  • El Bartali Ahmed
  • Witz Jean-Francois
  • Seghir Rian
  • Charkaluk Eric
  • Buffiere Jean-Yves
  Strain, Wiley-Blackwell, 2016, 52 (4), pp.324-335. The aim of this work is to analyse the strain field heterogeneity in an aluminium alloy subjected to low-cycle fatigue at high temperature. In the cylinder heads produced by a lost-foam casting process, the microstructure of the studied alloy consists hard intermetallic phases and large gas and microshrinkage pores. In order to study the influence of this complex 3D microstructure on fatigue crack initiation and propagation at 250 °C, an experimental protocol using laboratory and synchrotron tomography, finite element simulation and a new digital volume correlation platform have been used. The results showed the role of pores in the crack nucleation and highlighted the importance of hard phases in the crack propagation, thanks to the resolution on the DVC measurement. (10.1111/str.12193)
  DOI : 10.1111/str.12193
• Graphitization and amorphization of textured carbon using high-energy nanosecond laser pulses
  
  • Loisel Loïc
  • Châtelet Marc
  • Giudicelli Guillaume
  • Lebihain Mathias
  • Yang Yi
  • Cojocaru Costel-Sorin
  • Constantinescu Andrei
  • Tay Beng Kang
  • Lebental Bérengère
  Carbon, Elsevier, 2016, 105, pp.227-232. Laser pulses can effectively induce local structural changes and modify the physical properties of carbon allotropes. So far, only graphitization has been demonstrated using low laser energies (≤1 J/cm2). The novelty of this paper is a result of laser-induced amorphization of a highly anisotropic carbon allotrope by using high energy (1.5–15.4 J/cm2) 5 ns, 532 nm Nd-YAG laser pulses. Moreover, cycling phase change, between an amorphous and a crystalline phase, is also obtained by adjusting the pulse energy. However, cycling ability is restricted to a few cycles as a consequence of laser-induced surface damages caused by both high temperatures during and high thermal gradients during and after laser exposure. The occurrence of graphitization or amorphization depends on the amount of solid crystalline seeds during solidification from the melt, which is controlled by the post-pulse temperature of the carbon surface. This study uncovers new applications of carbon allotropes, such as optically-controlled reversible phase-change memories. (10.1016/j.carbon.2016.04.026)
  DOI : 10.1016/j.carbon.2016.04.026
• The viscous curtain: General formulation and finite-element solution for the stability of flowing viscous sheets
  
  • Perdigou C
  • Audoly Basile
  Journal of the Mechanics and Physics of Solids, Elsevier, 2016, 96, pp.291 - 311. The stability of thin viscous sheets has been studied so far in the special case where the base flow possesses a direction of invariance: the linear stability is then governed by an ordinary di↵erential equation. We propose a mathematical formulation and a numerical method of solution that are applicable to the linear stability analysis of viscous sheets possessing no particular symmetry. The linear stability problem is formulated as a non-Hermitian eigenvalue problem in a 2D domain and is solved numerically using the finite-element method. Specifically, we consider the case of a viscous sheet in an open flow, which falls in a bath of fluid; the sheet is mildly stretched by gravity and the flow can become unstable by 'curtain' modes. The growth rates of these modes are calculated as a function of the fluid parameters and of the geometry, and a phase diagram is obtained. A transition is reported between a buckling mode (static bifurcation) and an oscillatory mode (Hopf bifurcation). The effect of surface tension is discussed. (10.1016/j.jmps.2016.07.015)
  DOI : 10.1016/j.jmps.2016.07.015
• Fatigue and corrosion-fatigue in Cr-Mo steel in biaxial tension
  
  • Gaur Vidit
  , 2016. The clip connectors used to join the riser tubes for offshore oil drilling undergo cyclic loading due to sea waves. 90% of the service life is spent in the “connected mode” with a high mean stress and 10% in the “disconnected mode” with a lower mean stress. Finite element computations revealed in-phase biaxial tension in the critical areas of the clip connector along with high mean stresses. Thus, both the mean stress effect and the biaxiality effect need to be addressed for proper design of these structures. However, most of the multiaxial fatigue criteria are based on tension-torsion fatigue data and do not discriminate the influence of biaxial tension from that of a mean stress. This study investigates separately these two effects.For investigating the mean stress effect, uniaxial fatigue tests were run on Cr-Mo steel with various R ratios (σmin/σmax). The fatigue lives, as well as the slope of the S-N curves were found to decrease with increasing R, and the endurance limit to follow Gerber’s parabola. At low R ratios and thus relatively high stress ranges, fatigue cracks initiated from the surface, while for high R ratios, and thus low stress ranges, cracks initiated from internal or surface-cutting defects. This transition was analyzed based on elastic-plastic computations of stress-strain fields around the defects. The threshold for internal fatigue crack growth from defects was found to be quite low and independent from the R ratio. This was attributed to a nearly closure-free propagation.To investigate the effect of positive stress biaxiality, combined cyclic tension and internal pressure tests with various proportions of each loading were run on tubular specimens, at fixed R ratio (0.25). Moderate stress biaxialities (B= 0.25 and 0.5) had a beneficial effect on fatigue lives, attributed mainly to a retardation of crack initiation, while equibiaxial tension had a slightly detrimental effect, attributed to a “pseudo size effect” (higher probability for an incipient crack to grow along two possible planes, compared to a single one).Intergranular facets associated with temper and H2 embrittlement were observed on the fracture surfaces. The evolutions of their surface fraction with ΔK and load biaxiality suggested a possible reduction in crack growth rate at moderate biaxialities, but the detrimental effect of equibiaxial tension could not be explained in terms of crack growth rate.Several popular fatigue criteria failed to describe all fatigue data. Endurance criteria that include a linear mean stress term or contain a hydrostatic tension term fail to predict the variations of the endurance limit of this material with the R ratio and biaxiality ratio. Thus, a new fatigue criterion based on Gerber’s parabola was proposed. It captured the evolution of the endurance limit under the combined effects of positive mean stress and biaxiality.Similar tests were run to investigate the influence of salt water (3.5% NaCl) on fatigue lives under two types of test conditions: 1) free corrosion and 2) cathodic protection.In free corrosion, salt water strongly reduced the fatigue lives and suppressed the endurance limit. This was due to the formation of corrosion pits that favor early, multiple crack initiations. The detrimental effect of salt water was not enhanced by equibiaxial tension, which did not modify the size and density of corrosion pits. Fatigue lives in uniaxial and biaxial tension were nearly the same, although the crack growth mechanism was different: transgranular brittle decohesion in uniaxial loading and mostly intergranular in biaxial tension.Cathodic protection cancelled the detrimental effect of salt water for all biaxialities, in spite of a clear enhancement of H-induced embrittlement of the grain boundaries. The fracture surfaces were nearly fully intergranular, irrespective of load biaxialities, while in air the proportion of intergranular fracture was less than 45%.
• Homogenization models for thin rigid structured surfaces and films
  
  • Marigo Jean-Jacques
  • Maurel Agnès
  Journal of the Acoustical Society of America, Acoustical Society of America, 2016, 140 (1), pp.260-273. A homogenization method for thin microstructured surfaces and films is presented. In both cases, sound hard materials are considered, associated with Neumann boundary conditions and the wave equation in the time domain is examined. For a structured surface, a boundary condition is obtained on an equivalent flat wall, which links the acoustic velocity to its normal and tangential derivatives (of the Myers type). For a structured film, jump conditions are obtained for the acoustic pressure and the normal velocity across an equivalent interface (of the Ventcels type). This interface homog-enization is based on a matched asymptotic expansion technique, and differs slightly from the classical homogenization, which is known to fail for small structuration thicknesses. In order to get insight into what causes this failure, a two-step homogenization is proposed, mixing classical ho-mogenization and matched asymptotic expansion. Results of the two homogenizations are analyzed in light of the associated elementary problems, which correspond to problems of fluid mechanics, namely, potential flows around rigid obstacles. (10.1121/1.4954756)
  DOI : 10.1121/1.4954756
• Simultaneous microstructural and mechanical characterization of human corneas at increasing pressure
  
  • Benoit Aurélie
  • Latour Gaël
  • Marie-Claire Schanne-Klein
  • Allain Jean-Marc
  Journal of the mechanical behavior of biomedical materials, Elsevier, 2016, 60, pp.93-105. The cornea, through its shape, is the main contributor to the eye׳s focusing power. Pathological alterations of the cornea strongly affect the eye power. To improve treatments, complex biomechanical models have been developed based on the architecture and mechanical properties of the collagen network in the stroma, the main layer of the cornea. However, direct investigations of the structure of the stroma, as well as its link to the mechanical response, remained limited. We propose here an original set up, associating nonlinear optical imaging and mechanical testing. By using polarization resolved Second Harmonic signals, we simultaneously quantified micrometer (orientation of the collagen lamellae) and nanometer (local disorder within lamellae) scale corneal organization. We showed that the organization of the lamellae changes along the stroma thickness. Then, we measured simultaneously the deformation on the epithelial side of the cornea and the reorientation of the collagen lamellae for increasing intraocular pressure levels, from physiological ones to pathological ones. We showed that the observed deformation is not correlated to initial orientation, but to the reorganization of the lamellae in the stroma. Our results, by providing a direct multi-scale observation, will be useful for the development of more accurate biomechanical model (10.1016/j.jmbbm.2015.12.031)
  DOI : 10.1016/j.jmbbm.2015.12.031
• Structural, morphological and electrical properties of Cu2ZnSn1-xSixS4 (x = 0.8, x = 1) for solar-cells applications
  
  • Hamdi M.
  • Oueslati A.
  • Lafond A.
  • Guillot-Deudon C.
  • Hlel F.
  Journal of Alloys and Compounds, Elsevier, 2016, 674, pp.73 - 81. (10.1016/j.jallcom.2016.02.219)
  DOI : 10.1016/j.jallcom.2016.02.219
• Quantification of biventricular myocardial strain from magnetic resonance images of pulmonary hypertensive patients using hyperelastic warping
  
  • Xi Ce
  • Zhao Xiaodan
  • Zhong Liang
  • Genet Martin
  • Lee Chuan
  , 2016. Pulmonary hypertension (PH) is a disease resulting from restricted flow in the pulmonary arterial circulation. This results in an increase in pulmonary vascular resistance. Left untreated, the disease leads to right ventricular (RV) failure, which is the most common cause of death in PH patients. The quantification of RV function is important for clinical management of PH patients, with clinical studies showing that the RV function is a major determinant of the functional capacity and prognosis in PH patients. Recent studies have demonstrated that the RV strain is associated with the RV function, and is a potentially useful prognostic marker in PH patients. Compared to quantifying strain in the left ventricle (LV), which can be approximated by a truncated ellipsoid, the in vivo quantitative assessment of the strain in the RV is challenging because of its complex geometry and thin wall. Here, we describe the application of a hyperelastic warping technique for quantifying RV strain in PH patients using regular CINE-MR images, which has the potential to overcome these challenges.
• Atomistically derived cohesive zone model of intergranular fracture in polycrystalline graphene
  
  • Guin Laurent
  • Raphanel Jean L
  • Kysar Jeffrey W
  Journal of Applied Physics, American Institute of Physics, 2016, 119 (24), pp.245107. Pristine single crystal graphene is the strongest known two-dimensional material, and its nonlinear anisotropic mechanical properties are well understood from the atomic length scale up to a continuum description. However, experiments indicate that grain boundaries in the polycrystalline form reduce the mechanical behavior of polycrystalline graphene. Herein, we perform atomistic-scale molecular dynamics simulations of the deformation and fracture of graphene grain boundaries and express the results as continuum cohesive zone models (CZMs) that embed notions of the grain boundary ultimate strength and fracture toughness. To facilitate energy balance, we employ a new methodology that simulates a quasi-static controlled crack propagation which renders the kinetic energy contribution to the total energy negligible. We verify good agreement between Griffith’s critical energy release rate and the work of separation of the CZM, and we note that the energy of crack edges and fracture toughness differs by about 35%, which is attributed to the phenomenon of bond trapping. This justifies the implementation of the CZM within the context of the finite element method (FEM). To enhance computational efficiency in the FEM implementation, we discuss the use of scaled traction-separation laws (TSLs) for larger element sizes. As a final result, we have established that the failure characteristics of pristine graphene and high tilt angle bicrystals differ by less than 10%. This result suggests that one could use a unique or a few typical TSLs as a good approximation for the CZMs associated with the mechanical simulations of the polycrystalline graphene. (10.1063/1.4954682)
  DOI : 10.1063/1.4954682
• Couplage de techniques de microscopies électroniques, mesures de champs et calculs pour l’étude de l'influence des paramètres microstructuraux sur l’amorçage de fissures en corrosion sous contrainte.
  
  • Chaumun E.
  • Heripré E.
  • Sennour M.
  • Duhamel C.
  • Guerre C.
  • de Curières I.
  • Crépin J.
  , 2016.
• Output error minimizing back and forth nudging method for initial state recovery
  
  • Aalto Atte
  Systems and Control Letters, Elsevier, 2016, 94, pp.111-117. We show that for linear dynamical systems with skew-adjoint generators, the initial state estimate given by the back and forth nudging method with colocated feedback, converges to the minimizer of the discrepancy between the measured and simulated outputs — given that the observer gains are chosen suitably and the system is exactly observable. If the system's generator A is essentially skew-adjoint and dissipative (with not too much dissipation), the colocated feedback has to be corrected by the operator e^{At}e^{A*t} in order to obtain such convergence. In some special cases, a feasible approximation for this operator can be found analytically. The case with wave equation with constant dissipation will be demonstrated. (10.1016/j.sysconle.2016.06.002)
  DOI : 10.1016/j.sysconle.2016.06.002
• Construction and analysis of an adapted spectral finite element method to convective acoustic equations
  
  • Hüppe Andreas
  • Cohen Gary
  • Imperiale Sebastien
  • Kaltenbacher Manfred
  Communications in Computational Physics, Global Science Press, 2016. The paper addresses the construction of a non spurious mixed spectral finite element (FE) method to problems in the field of computational aeroacous-tics. Based on a computational scheme for the conservation equations of linear acoustics, the extension towards convected wave propagation is investigated. In aeroacoustic applications, the mean flow effects can have a significant impact on the generated sound field even for smaller Mach numbers. For those convec-tive terms, the initial spectral FE discretization leads to non-physical, spurious solutions. Therefore, a regularization procedure is proposed and qualitatively investigated by means of discrete eigenvalues analysis of the discrete operator in space. A study of convergence and an application of the proposed scheme to simulate the flow induced sound generation in the process of human phonation underlines stability and validity. (10.4208/cicp.250515.161115a)
  DOI : 10.4208/cicp.250515.161115a
• Determination of a fatigue crack growth law and the influence of the local plasticity by using Digital Image Correlation
  
  • Hosdez Jerome
  • Witz Jean-Francois
  • Limodin Nathalie
  • Najjar Denis
  • Charkaluk Eric
  , 2016.
• Evolution of the Skin Microstructural Organization During a Mechanical Assay
  
  • Lynch Barbara
  • Bancelin Stéphane
  • Bonod Bidaud Christelle
  • Marie-Claire Schanne-Klein
  • Allain Jean-Marc
  , 2016, 6, pp.45-52. Skin is a complex multi-layered tissue, consisting of three main parts: the epidermis, the dermis and the hypodermis. The dermis is responsible for most of the complex mechanical properties of skin, such as viscoelasticity, non-linearity and anisotropy. At the microscopic level the dermis consists for the greater part of extracellular matrix, compounded mainly of collagen fibers forming an orderless network. The mechanical properties of skin have been studied in the past, but their exact link with the microscopic organization is still an open question. The goal of our study is to measure the evolution of the microstructure during a mechanical assay and to improve existing mechanical models of skin with relevant parameters identified at the microscopic level. We perform uniaxial tensile test on ex vivo mouse skin. The mechanical tests are performed in situ under a second harmonic generation microscope. This allows us to determine quantitatively and simultaneously the mechanical response and the microstructural reorganization of the tissue. This technique can be used to better understand the link between pathological alterations of collagen synthesis, fibers organization, and alteration of the biomechanical properties of skin, as in the Ehlers-Danlos syndrome (EDS). (10.1007/978-3-319-41351-8_7)
  DOI : 10.1007/978-3-319-41351-8_7
• Delayed Feedback Control Method For Calculating Space-Time Periodic Solutions Of Viscoelastic Problems
  
  • Le Tallec Patrick
  • Khristenko Ustim
  , 2016, 3. We are interested in fast techniques for calculating a periodic solution to viscoelastic evolution problems with a space-time periodic condition of ”rolling” type. Such a solution is usually computed as an asymptotic limit of the initial value problem with arbitrary initial data. We want to invent a control method, accelerating the convergence. The main idea is to modify our problem by introducing a feedback control term, based on a periodicity error, in order to accelerate the convergence to the desired periodic solution of the problem. First, an abstract evolution problem has been studied. From the analytic solution of the modified (controlled) problem, an efficient control has been found, optimizing the spectrum of the problem. The proposed control term can be mechanically interpreted, and its efficiency increases with the relaxation time. In order to confirm numerically the theoretical results, a finite element simulation has been carried out on a full 2D model for a steady rolling of a viscoelastic tyre with periodic sculpture. It has demonstrated that the controlled solution converges indeed faster than the non-controlled one, and that the efficiency of the method increases with the problem’s relaxation time, that is when the memory of the underlying problem is large.
• Statistical mechanics of the Huxley-Simmons model
  
  • Caruel M.
  • Truskinovsky L.
  Physical Review E, American Physical Society (APS), 2016, 93 (6), pp.062407. The chemomechanical model of Huxley and Simmons (HS) [A. F. Huxley and R. M. Simmons, Nature 233, 533 (1971)] provides a paradigmatic description of mechanically induced collective conformational changes relevant in a variety of biological contexts, from muscles power-stroke and hair cell gating to integrin binding and hairpin unzipping. We develop a statistical mechanical perspective on the HS model by exploiting a formal analogy with a paramagnetic Ising model. We first study the equilibrium HS model with a finite number of elements and compute explicitly its mechanical and thermal properties. To model kinetics, we derive a master equation and solve it for several loading protocols. The developed formalism is applicable to a broad range of allosteric systems with mean-field interactions. (10.1103/PhysRevE.93.062407)
  DOI : 10.1103/PhysRevE.93.062407
• A shakedown analysis of high cycle fatigue of shape memory alloys
  
  • Auricchio Ferdinando
  • Constantinescu Andrei
  • Menna Costantino
  • Scalet Giulia
  International Journal of Fatigue, Elsevier, 2016, 87, pp.112-123. Shape memory alloys (SMAs) are exploited in several innovative applications, experiencing up to millions of cycles, and thus requiring a fully understanding of material fatigue and fracture resistance. However, experimental and methodological descriptions of SMA cyclic response are still incomplete. Accordingly, the present paper aims to investigate the cyclic response of SMAs under macroscopic elastic shakedown and to propose a criterion for the high cycle fatigue of SMAs. A multiaxial criterion based on a multiscale analysis of the phase transformation between austenite and martensite and using the rigorous framework of standard generalized materials is proposed. The criterion is an extension of the Dang Van high cycle fatigue criterion to SMAs. The criterion is applied to uniaxial experimental data taken from the literature. It distinguishes run out from failure tests in the infinite lifetime regime. The sound structure of the underlying concepts permits a novel insight into the development of a general multiaxial failure criterion for SMA materials. (10.1016/j.ijfatigue.2016.01.017)
  DOI : 10.1016/j.ijfatigue.2016.01.017
• Thermographie infrarouge et analyse expérimentale en génie mécanique
  
  • Luong Minh Phong
  Techniques de l'Ingénieur, Techniques de l'ingénieur, 2016. Dans un contexte de développement durable, le génie mécanique est confronté à des problèmes pratiques liés aux processus irréversibles et dissipatifs, responsables du vieillissement, de l'endommagement, de la dégradation, de la fatigue et de la rupture des matériaux et structures sous charges. La thermographie infrarouge proposée en analyse expérimentale offre une technique non destructive, sans contact, utilisable en temps réel permettant de tester des hypothèses de dimensionnement. Les résultats exposent les avantages de la thermographie infrarouge différentielle et montrent qu'une interprétation réaliste des phénomènes thermomécaniques détectés conduit à des applications innovantes et variées dans l'étude de la performance mécanique des matériaux et des structures dans leur environnement. (10.51257/a-v1-r2745)
  DOI : 10.51257/a-v1-r2745
• Effect of biaxial cyclic tension on the fatigue life and damage mechanisms of Cr–Mo steel
  
  • Gaur Vidit
  • Doquet Véronique
  • Persent Emmanuel
  • Roguet Eléonore
  International Journal of Fatigue, Elsevier, 2016, 87, pp.124-131. Combined cyclic tension and internal pressure tests with various proportions of each loading were run on a 2.5%Cr–1%Mo steel to investigate the effect of positive stress biaxiality on fatigue lives and damage mechanisms. While moderate stress biaxiality had a beneficial effect on fatigue lives, attributed mainly to a retardation of crack initiation, equibiaxial tension had a slightly detrimental effect, attributed to a ‘‘pseudo size effect”. Intergranular facets associated with temper and hydrogen embrittlement were observed on the fracture surfaces. The evolutions of their surface fraction with DK and load biaxiality suggested a possible reduction in crack growth rate at moderate biaxialities. Several popular multiaxial fatigue criteria failed to describe all fatigue data. Thus, a new fatigue criterion based on Gerber’s parabola has been proposed. It captures the evolution of the endurance limit under the combined effects of a positive mean stress and positive biaxiality. (10.1016/j.ijfatigue.2016.01.021)
  DOI : 10.1016/j.ijfatigue.2016.01.021
• Characterization of the acoustical directivity of a speaker on a sound bar enclosure, a comparison between measurements, boundary element method and a spheroidal analytical model
  
  • Roggerone Vincent
  • Boutillon Xavier
  • Corteel Etienne
  , 2016. The directivity of loudspeakers mounted on a sound bar with a slender shape is analyzed. Measurements are compared to results obtained with a boundary element method. A good agreement is obtained in the low-mid frequency range. In order to reduce the computing time, a spheroidal analytical model based on a geometrical approximation of the sound-bar is also considered. This approximation holds up to a certain frequency. The spheroid shape produces a more regular sound field pattern.
• Numerical simulation of electrocardiograms for full cardiac cycles in healthy and pathological conditions
  
  • Schenone Elisa
  • Collin Annabelle
  • Gerbeau Jean-Frédéric
  International Journal for Numerical Methods in Biomedical Engineering, John Wiley and Sons, 2016, 32 (5). This work is dedicated to the simulation of full cycles of the electrical activity of the heart and the corresponding body surface potential. The model is based on a realistic torso and heart anatomy, including ventricles and atria. One of the specificities of our approach is to model the atria as a surface, which is the kind of data typically provided by medical imaging for thin volumes. The bidomain equations are considered in their usual formulation in the ventricles, and in a surface formulation on the atria. Two ionic models are used: the Courtemanche-Ramirez-Nattel model on the atria, and the " Minimal model for human Ventricular action potentials " (MV) by Bueno-Orovio, Cherry and Fenton in the ventricles. The heart is weakly coupled to the torso by a Robin boundary condition based on a resistor-capacitor transmission condition. Various ECGs are simulated in healthy and pathological conditions (left and right bundle branch blocks, Bachmann's bundle block, Wolff-Parkinson-White syndrome). To assess the numerical ECGs, we use several qualitative and quantitative criteria found in the medical literature. Our simulator can also be used to generate the signals measured by a vest of electrodes. This capability is illustrated at the end of the article. (10.1002/cnm.2744)
  DOI : 10.1002/cnm.2744
• A virtual sizing tool for mitral valve annuloplasty
  
  • Rausch Manuel K.
  • Zöllner Alexander M.
  • Genet Martin
  • Baillargeon Brian
  • Bothe Wolfgang
  • Kuhl Ellen
  International Journal for Numerical Methods in Biomedical Engineering, John Wiley and Sons, 2016. Functional mitral regurgitation, a backward leakage of the mitral valve, is a result of left ventricular growth and mitral annular dilatation. Its gold standard treatment is mitral annuloplasty, the surgical reduction in mitral annular area through the implantation of annuloplasty rings. Recurrent regurgitation rates may, however , be as high as 30% and more. While the degree of annular downsizing has been linked to improved long-term outcomes, too aggressive downsizing increases the risk of ring dehiscences and significantly impairs repair durability. Here, we prototype a virtual sizing tool to quantify changes in annular dimensions , surgically induced tissue strains, mitral annular stretches, and suture forces in response to mitral annuloplasty. We create a computational model of dilated cardiomyopathy onto which we virtually implant annuloplasty rings of different sizes. Our simulations confirm the common intuition that smaller rings are more invasive to the surrounding tissue, induce higher strains, and require larger suture forces than larger rings: The total suture force was 2.2 N for a 24-mm ring, 1.9 N for a 28-mm ring, and 0.8 N for a 32-mm ring. Our model predicts the highest risk of dehiscence in the septal and postero–lateral annulus where suture forces are maximal. These regions co-localize with regional peaks in myocardial strain and annular stretch. Our study illustrates the potential of realistic predictive simulations in cardiac surgery to identify areas at risk for dehiscence, guide the selection of ring size and shape, rationalize the design of smart annu-loplasty rings and, ultimately, improve long-term outcomes after surgical mitral annuloplasty. (10.1002/cnm.2788)
  DOI : 10.1002/cnm.2788
• A autonomous, wireless carbon nanotube strain sensor embedded in concrete for crack monitoring
  
  • Michelis Fulvio
  • Bodelot Laurence
  • Laheurte Jean-Marc
  • Zaki Fadi
  • Bonnassieux Yvan
  • Lebental Bérengère
  , 2016, pp.14p. We describe the prototyping of a battery-powered, RFID-enabled carbon nanotube strain sensor for concrete strain and crack monitoring. A series of 10 prototypes has been embedded in a real structure. After a year it is still providing valuable information on the state of the structure. The final volume of the embedded module is 43cm3, the lowest volume reported to date in the field of embedded monitoring of concrete.
• Solution-Processed p-Dopant as Interlayer in Polymer Solar Cells
  
  • Guillain F.
  • Endres J.
  • Bourgeois L.
  • Kahn A.
  • Vignau L.
  • Wantz Guillaume
  ACS Applied Materials & Interfaces, Washington, D.C. : American Chemical Society, 2016, 8 (14), pp.9262 - 9267. (10.1021/acsami.6b00356)
  DOI : 10.1021/acsami.6b00356
• An incremental variational formulation for the prediction of the effective work-hardening behavior and field statistics of elasto-(visco)plastic composites
  
  • Boudet Julien
  • Auslender François
  • Bornert Michel
  • Lapusta Yuri
  International Journal of Solids and Structures, Elsevier, 2016, 83, pp.90–113. A new nonlinear and variational homogenization procedure that incorporates the fluctuations of the plastic strains within the phases is proposed to assess the local and effective responses of elasto-(visco)plastic composites with local work-hardening. The formulation is an extension of the EIV approach of Lahellec and Suquet (2007a) initially proposed for elasto-viscoplastic composites without both threshold and hardening. This extension relies both on an appropriate linearization of the stored-energy function which accounts for the isotropic and kinematic hardening and an incorporation of the elastic unloading. The accuracy of the approach is then assessed by comparisons with reference numerical solutions and other nonlinear homogenization schemes of the literature carried out on both porous elasto-plastic materials and several reinforced elasto-(visco)plastic composites subjected to cyclic proportional loadings. (10.1016/j.ijsolstr.2016.01.003)
  DOI : 10.1016/j.ijsolstr.2016.01.003