Publications

2017

• Fatigue models for life prediction of structures under multiaxial loading with variation in time and space.
  
  • Ma Zepeng
  , 2017. The aim of this work is to propose a multi-scale approach to energy-based fatigue, which can estimate lifetimes associated with variable multidimensional loading. The foundation of the approach is to assume that the energy dissipated on a small scale governs the fatigue behavior. Each material point is associated to a stochastic distribution of weak points that are likely to plasticize and contribute to the dissipation of energy without affecting global macroscopic stresses. This amounts to adopting Dang Van's paradigm of high cycle fatigue. The structure is supposed to be elastic (or adapted) on a macroscopic scale. In addition, we adopt on the mesoscopic scale an elastoplastic behavior with a dependence of the plastic load function not only of the deviatoric part of the stresses, but also of the hydrostatic part. Linear kinematic hardening is also considered under the assumption of an associated plasticity. Instead of using the number of cycles as an incremental variable, the concept of temporal evolution of the load is adopted for a precise follow-up of the history of the actual loading. The effect of mean stress is taken into account in the mesoscopic yield function; a law of nonlinear accumulation of damage is also considered in the model. Fatigue life is then determined using a phenomenological law based on mesoscopic energy dissipation from the plastic accommodative cycle. The first part of the work focused on a proposal for a fatigue model with a simpler implementation gradient than the previous models.
• Variational phase-field models from brittle to ductile fracture : nucleation and propagation
  
  • Tanne Erwan
  , 2017. Phase-field models, sometimes referred to as gradient damage, 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’s criterion. For a one- dimensional problem, it has been shown that they can predict nucleation upon a critical stress, provided that the regularization parameter is identified with the material’s internal characteristic length.In this work, 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 the one predicted by a strength criterion to the one of a toughness criterion when the strength of the stress concentration or singularity varies. We present validation and verification of 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.In a second movement, this model is extended to hydraulic fracturing. We present a validation of the model by simulating a single fracture in a large domain subject to a control amount of fluid. Then we study an infinite network of pressurized parallel cracks. Results show that the stimulation of a single fracture is the best energy minimizer compared to multi-fracking case. The last example focuses on fracturing stability regimes using linear elastic fracture mechanics for pressure driven fractures in an experimental geometry used in petroleum industry which replicates a situation encountered downhole with a borehole called burst experiment.The last part of this work focuses on ductile fracture by coupling phase-field models with perfect plasticity. Based on the variational structure of the problem we give a numerical implementation of the coupled model for parallel computing. Simulation results of a mild notch specimens are in agreement with the phenomenology of ductile fracture such that nucleation and propagation commonly reported in the literature.
• Carbon nanotube sensor array for water monitoring with conjugated polymers
  
  • Lebental Bérengère
  • Benda Robert
  • Bodelot Laurence
  • Florea Ileana
  • Godumala Mallesham
  • Gusarov Boris
  • Gutierrez Alfredo
  • Loisel Loic
  • Merliot Erick
  • Ramachandran Sasikumar
  • Zhang Xin Yang
  • Zucchi Gaël
  , 2017, pp.18p. In the field of water quality monitoring, there is an increasing demand for compact, low cost multiparameter water monitoring probes. The goal of the H2020 Proteus project (www.proteus-sensor.eu) is to meet this demand: based on the use of a set of novel conjugated polymers (FR1753131) functionalizing non-covalently multi-walled carbon nanotubes, we herein demonstrate the simultaneous monitoring of pH, chlorine, chloride and calcium ions with a single heavily minaturized sensor chip. The principle of sensing is based on the resistance variations of the functionnalized carbon nanotube network (deposited by ink-jet printing) upon changing chemical concentrations in water. In this paper, we present the functionalization strategy, from polymer design to proof of CNT functionnalization to CNT-polymer interaction modeling. Then we show the fabrication process and study the sensor array response, both in the lab and along field deployments. The measurements clearly show selectivity between the different CNT-polymers sensors, for instance pH sensitivity enhancement by a factor of 10 compared with the other devices with one of our polymers tuned with a urea-derivative. For field testing, the sensor chips are integrated into a 250cm3 pre-industrial sensor nodes and tested for several weeks in Sense-City 40m water loop. We demonstrate the first scale one deployment of arrayed carbon nanotubes chemical sensors, for instance showing demonstrating the capability to monitor active chlorine (HClO) or pH in real time in the field.
• In-situ investigation of local motion mechanisms in carbon nanotubes strain sensors
  
  • Bodelot Laurence
  • Charliac Jérôme
  • Hallais Simon
  • Lebental Bérengère
  • Pavic Luka
  • Tanguy Alexandre
  , 2017, pp.26p. In this work, we focus on percolating carbon nanotubes (CNT) networks deposited by inkjet printing on ethylene tetrafluoroethylene (EFTE) substrates. It was demonstrated that such devices constitute highly reproducible flexible strain sensors, whose resistance grows linearly with a gage factor close to 1 up to 600 µµ [1]. In the prospect of developing a physically-based model describing the resistance variation of these sensors under strain, the local motion mechanisms arising at the CNT network scale need to be understood. To this end, a setup was developed in order to observe CNT networks deposited on ETFE substrates submitted to tensile strains inside a scanning electron microscope (SEM). SEM images of CNT networks are thus obtained at different strain levels and processed by digital image correlation. This gives access to the strain fields developing at the scale of CNT networks and highlights local motion mechanisms arising within such networks when strained.
• How aging impacts skin biomechanics: a multiscale study in mice
  
  • Lynch Barbara
  • Bonod-Bidaud Christelle
  • Ducourthial Guillaume
  • Affagard Jean-Sébastien
  • Bancelin Stéphane
  • Psilodimitrakopoulos Sotiris
  • Ruggiero Florence
  • Allain Jean-Marc
  • Schanne-Klein Marie-Claire
  Scientific Reports, Nature Publishing Group, 2017, 7 (1). Skin aging is a complex process that strongly affects the mechanical behavior of skin. This study aims at deciphering the relationship between age-related changes in dermis mechanical behavior and the underlying changes in dermis microstructure. To that end, we use multiphoton microscopy to monitor the reorganization of dermal collagen during mechanical traction assays in ex vivo skin from young and old mice. The simultaneous variations of a full set of mechanical and microstructural parameters are analyzed in the framework of a multiscale mechanical interpretation. They show consistent results for wild-type mice as well as for genetically-modified mice with modified collagen V synthesis. We mainly observe an increase of the tangent modulus and a lengthening of the heel region in old murine skin from all strains, which is attributed to two different origins that may act together: (i) increased cross-linking of collagen fibers and (ii) loss of water due to proteoglycans deterioration, which impedes inner sliding within these fibers. In contrast, the microstructure reorganization upon stretching shows no age-related difference, which can be attributed to opposite effects of the decrease of collagen content and of the increase of collagen cross-linking in old mice. Aging is a complex process that affects the function of all organs and tissues and most often has an irreversible impact on their mechanical behavior. The most visible effects of aging are observed in skin and have been extensively studied for medical and cosmetic purposes. The three skin layers are affected both structurally and functionally. However, aging primary impacts the mechanical integrity of the dermis. At macroscopic scale, the mechanical behavior of aged dermis shows an increased stiffness and a decreased ability to recoil 1–3. At lower scales, a complex multi-parameters process eventually results in a decrease of collagen and elastin contents due to an imbalance between matrix proteins synthesis and degradation by matrix metalloproteinases, an increase of collagen cross-linking, a deterioration of proteoglycans and a subsequent loss of water 4–9. However, the link between these microstructural modifications and the mechanical changes has so far been inferred rather than experimentally demonstrated due to the technical issues encountered when trying to obtain multiscale data. Collagens are the main component of the dermis and other connective tissues 7,10. Fibril-forming collagens assemble into striated fibrils, the diameter and three-dimensional organization of which are tissue-specific. They form multiprotein networks with other matrix proteins such as the elastin fibers and non-fibrillar matrix (pro-teoglycans, glycoaminoglycans…) that determine the mechanical behavior of dermis and other collagen-rich tissues 11–18. Collagen fibers are usually heterotypic structures. In dermis, they are made of type I, III and V col-lagens. Type V collagen is a minor component that acts as a regulatory fibril-forming collagen 19,20. As such, it plays an important role in the pathogenesis of the classical Ehlers-Danlos (EDS) syndrome. This rare connective tissue disease illustrates the close link between collagen microstructure and tissue mechanics since it is caused by mutations in collagen V genes, while being primary characterized by skin hyperextensibility 19–21. Moreover, EDS patients show a prematurely aged skin, which illustrates the close link between collagen microstructure and skin aging. (10.1038/s41598-017-13150-4)
  DOI : 10.1038/s41598-017-13150-4
• Influence of the neck shape for Helmholtz resonators
  
  • Mercier Jean-François
  • Marigo Jean-Jacques
  • Maurel Agnès
  Journal of the Acoustical Society of America, Acoustical Society of America, 2017, 142 (6), pp.3703 - 3714. The resonance of a Helmholtz resonator is studied with a focus on the influence of the neck shape. This is done using a homogenization approach developed for an array of resonators, and the resonance of an array is discussed when compared to that of a single resonator. The homogenization makes a parameter ℬ appear which determines unambiguously the resonance frequency of any neck. As expected, this parameter depends on the length and on the minimum opening of the neck, and it is shown to depend also on the surface of air inside the neck. Once these three geometrical parameters are known, ℬ has an additional but weak dependence on the neck shape, with explicit bounds. (10.1121/1.5017735)
  DOI : 10.1121/1.5017735
• A sequential pre-cracking procedure to measure the mode-I fracture toughness of ultra pure bulk metallic glasses
  
  • Bernard Cédric
  • Keryvin Vincent
  • Doquet Véronique
  • Hin Sovanara
  • Yokoyama Yoshihiko
  Scripta Materialia, Elsevier, 2017, 141, pp.58-61. A dedicated fatigue pre-cracking method, performed successively under mode II and mode I, has been set up to initiate and propagate a crack close to the notch plane, which is particularly difficult to achieve using pure mode I loading on some ultra pure bulk metallic glasses, free from oxygen contamination. This method, was applied to a pure Zr55Cu30Al10Ni5 (at.%) amorphous alloy, and allowed successful pre-cracking and reliable measurement of the apparent mode I fracture toughness. (10.1016/j.scriptamat.2017.07.027)
  DOI : 10.1016/j.scriptamat.2017.07.027
• Cases, causes and classifications of craters above salt caverns
  
  • Bérest Pierre
  International Journal of Rock Mechanics and Mining Sciences, Pergamon and Elsevier, 2017, 100, pp.318-329. Based on the description of a dozen of cases, this paper suggests a categorization of craters formed above brine-production caverns for “piston” and “hourglass” types. The deliberate creation of three craters in Lorraine (France) above the Keuper salt formation is described first. After the cavern roof reaches the top of the salt formation, stoping takes place. A rigid cylinder of rock (a piston) drops abruptly in the cavern, experiencing no deformation and creating vertical crater edges. In the same mining district, a room-and-pillar panel collapsed abruptly in 1873. Multiple pieces of evidence have proven that, here again, no deformation occurred in the cylinder that dropped into the mine. These examples prove that cavern drop is more abrupt when the cavern is filled partly with air, as less brine must be evacuated from the cavern during collapse. The Haoud Berkaoui (Algeria) and Bereznikovsky (Russia) craters also belong to the piston type; less information is available. The main features of the piston mechanism can be captured by a simple model: failure takes place when vertical shear forces along the cylinder edge, plus cavern internal pressure, are not able to balance cylinder weight. This model suggests that the contour of the crater must be a circle and that collapse is easier when the ratio between cavern radius and cavern depth is larger. This may explain why no example of a collapse above a hydrocarbon storage cavern is known: in most cases, this ratio is very small. Three sinkholes formed above salt caverns leached out from the Hutchinson salt formation in Kansas (USA) epitomize the hourglass type. Here, again, stoping occurs until the cavern roof reaches loose sediments at shallow depth. A sinkhole grows when sediments flow to a central hole to fill the cavern underneath, generating an upward flow of brine to the sinkhole. Such a phenomenon also can occur in a salt dome. At Bayou Choctaw (Louisiana, USA) a brine cavern rose through the caprock, allowing loose shallow sediments to flow to the cavern. At Bayou Corne (near Napoleonville in the same state), a cavern was within a short distance from the flank of a dome; a 1500-m-deep breach was created, and loose sediments in the dome sheath, accumulated during geological times, filled the cavern—a process that lasted more than one year and created a sinkhole at ground level. In both cases (piston and hourglass) lakes form in the crater and gravity-driven waves are observed. Sinkhole creation can be prevented when the distance between the cavern roof and the salt top (or dome flanks) is large enough and when the ratio between cavern radius and cavern depth is small enough. (10.1016/j.ijrmms.2017.10.025)
  DOI : 10.1016/j.ijrmms.2017.10.025
• Velocity–pressure loops for continuous assessment of ventricular afterload: influence of pressure measurement site
  
  • Joachim Jona
  • Vallée Fabrice
  • Mateo Joaquim
  • Le Gall Arthur
  • Lenck Stéphanie
  • Millasseau Sandrine
  • Houdart Emmanuel
  • Mebazaa Alexandre
  • Gayat Etienne
  Journal of Clinical Monitoring and Computing, Springer Verlag, 2017, pp.1-8. VPloop, the graphical representation of pressure versus velocity, and its characteristic angles, GALA and β, can be used to monitor cardiac afterload during anesthesia. Ideally VPloop should be measured from pressure and velocity obtained at the same arterial location but standard of care usually provide either radial or femoral pressure waveforms. The purpose of this study was to look at the influence of arterial sites and the use of a transfer function (TF) on VPloop and its related angles. Invasive pressure signals were recorded in 25 patients undergoing neuroradiology intervention under general anesthesia with transesophageal flow velocity monitoring. Pressures were recorded in the descending thoracic aorta, abdominal aorta, femoral and radial arteries. We compared GALA and β from VPloops generated from each location and in high and low risk patients. GALA was similar in the central locations (55°[49–63], 52°[47–61] and 54°[45–62] from descending thoracic to femoral artery, median[interquartile], p = 0.10), while there was a difference in β angle (16°[4–27] to 8°[3–15], p < 0.0001). GALA and β obtained from radial waveforms were different (39°[31–47] compared to 46°[36–54] and 6°[2–14] compared to 16°[4–27] for GALA and β angles respectively, p < 0.001) which was corrected by the use of a TF (45°[32–55] and 17°[5–28], p = ns). GALA and β are underestimated when measured with a radial catheter. Using pressure waveforms from femoral locations alters VPloops, GALA and β in a smaller extend. The use of a TF on radial pressure allows to correctly plot VPloops and their characteristic angles for routine clinical use. (10.1007/s10877-017-0082-3)
  DOI : 10.1007/s10877-017-0082-3
• Elastic Anisotropy Reversal During Brittle Creep in Shale
  
  • Geng Zhi
  • Bonnelye Audrey
  • Chen Mian
  • Jin Yan
  • Dick Pierre
  • David Christian
  • Fang Xin
  • Schubnel Alexandre
  Geophysical Research Letters, American Geophysical Union, 2017, 44 (21). We conducted two brittle creep experiments on shale samples under upper crustal conditions (confining pressure of 80 MPa at 26°C and 75°C). We deformed the samples to failure, with bedding oriented perpendicular to the maximum compressive stress direction, using the stress-stepping methodology. In both experiments, the failure stress was ~64% higher than the short-term peak strength. Throughout each differential stress step, ultrasonic wave velocities initially decreased and then gradually increased with deformation/time. The magnitude of these variations depends both on the direction of measurement with respect to the bedding and the temperature, and it is largest for velocities measured parallel to the bedding and at high temperature. Elastic wave anisotropy was completely reversed at 75°C, following a limited amount of axial strain (~0.6%). Scanning electron microscope investigation confirmed evidence of a time-dependent pressure solution, localized compaction, crack sealing/healing, and mineral rotation. Our observations reveal that elastic anisotropy can evolve rapidly in both time and space, which has implications on the stress state and its rotation near fault zones. (10.1002/2017GL074555)
  DOI : 10.1002/2017GL074555
• Magnetic Resonance Imaging of the Heart and Large Vessels -- Survey of methods and new perspectives
  
  • Chabiniok Radomir
  • Súkupová Lucie
  • Kautznerová Dana
  • Tintěra Jaroslav
  Česká radiologie, Česká lékařská společnost, 2017, 71 (4), pp.279-290. Early cardiac magnetic resonance imaging (CMR) scans were of inferior quality. A sig- ni cant improvement in image quality was achieved a er introducing the segmented acquisition of the k-space synchronized with patient’s ECG, performed either in breath hold or free breathing. CMR is now used widely in the clinical setting for assessment of cardiac chamber volumes, global and regional cardiac contraction, morphology and tissue charac- terization. In ammatory or post- myocardial infarction changes involve sequences which can appreciate myocardial edema or the use of late post-gadolinium contrast enhancement (LGE) to visualise di use or focal scar. Other applications include the assessment of valvular stenosis or regurgitation by means of ow me- asurement through a de ned ori ce and rst pass myocardial perfusion to assess ischemia. Last but not least, CMR is increasingly used for the assessment of congenital heart diseases, in which CMR o ers objective and directly com- parable measures during serial examinations, without any radiation exposure.
• Application de la tomographie à rayons X à la caractérisation de la microstructure et des mécanismes d'endommagement d'un alliage AlSi7Cu3
  
  • Wang Long
  • Dahdah Nora
  • Limodin Nathalie
  • El Bartali Ahmed
  • Witz Jean-Francois
  • Buffiere Jean-Yves
  • Balloy David
  • Tandjaoui Amina
  • Quaegebeur Philippe
  • Charkaluk Eric
  , 2017, pp.91.
• Coupled variational formulations of linear elasticity and the DPG methodology
  
  • Fuentes Federico
  • Keith Brendan
  • Demkowicz Leszek
  • Le Tallec Patrick
  Journal of Computational Physics, Elsevier, 2017, 348, pp.715 - 731. This article presents a general approach akin to domain-decomposition methods to solve a single linear PDE, but where each subdomain of a partitioned domain is associated to a distinct variational formulation coming from a mutually well-posed family of broken variational formulations of the original PDE. It can be exploited to solve challenging problems in a variety of physical scenarios where stability or a particular mode of convergence is desired in a part of the domain. The linear elasticity equations are solved in this work, but the approach can be applied to other equations as well. The broken variational formulations, which are essentially extensions of more standard formulations, are characterized by the presence of mesh-dependent broken test spaces and interface trial variables at the boundaries of the elements of the mesh. This allows necessary information to be naturally transmitted between adjacent subdomains, resulting in coupled variational formulations which are then proved to be globally well-posed. They are solved numerically using the DPG methodology, which is especially crafted to produce stable discretizations of broken formulations. Finally, expected convergence rates are verified in two different and illustrative examples. (10.1016/j.jcp.2017.07.051)
  DOI : 10.1016/j.jcp.2017.07.051
• A general result for the magnetoelastic response of isotropic suspensions of iron and ferrofluid particles in rubber, with applications to spherical and cylindrical specimens
  
  • Lefèvre Victor
  • Danas Kostas
  • Lopez-Pamies Oscar
  Journal of the Mechanics and Physics of Solids, Elsevier, 2017, 107, pp.343 - 364. This paper puts forth an approximate solution for the effective free-energy function describing the ho-mogenized (or macroscopic) magnetoelastic response of magnetorheological elastomers comprised of non-Gaussian rubbers filled with isotropic suspensions of either iron or ferrofluid particles. The solution is general in that it applies to N = 2 and 3 space dimensions and any arbitrary (non-percolative) isotropic suspension of filler particles. By construction, it is exact in the limit of small deformations and moderate magnetic fields. For finite deformations and finite magnetic fields, its accuracy is demonstrated by means of direct comparisons with full-field simulations for two prominent cases: (i) isotropic suspensions of circular particles and (ii) isotropic suspensions of spherical particles. With the combined objectives of demonstrating the possible benefits of using ferrofluid particles in lieu of the more conventional iron particles as fillers and gaining insight into recent experimental results, the proposed homogenization-based constitutive model is deployed to generate numerical solutions for boundary-value problems of both fundamental and practical significance: those consisting of magnetorheological elas-tomer specimens of spherical and cylindrical shape that are immersed in air and subjected to a remotely applied uniform magnetic field. It is found that magnetorheological elastomers filled with ferrofluid particles can exhibit magnetostrictive capabilities far superior to those of magnetorheological elastomers filled with iron particles. The results also reveal that the deformation and magnetic fields are highly heterogenous within the specimens and strongly dependent on the shape of these, specially for magnetorheological elas-tomers filled with iron particles. From an applications perspective, this evidence makes it plain that attempts at designing magnetrostrictive devices based on magnetorheological elastomers need to be approached, in general, as structural problems, and not simply as materials design problems. (10.1016/j.jmps.2017.06.017)
  DOI : 10.1016/j.jmps.2017.06.017
• Veno-Arterial-ECMO in the Intensive Care Unit:From Technical Aspects to Clinical Practice
  
  • Le Gall Arthur
  • Follin Arnaud
  • Cholley Bernard
  • Mantz Jean
  • Aissaoui Nadia
  • Pirracchio Romain
  Anaesthesia Critical Care & Pain Medicine, Elsevier Masson, 2017, pp.1-43. The use of Veno-Arterial ExtraCorporeal Membrane Oxygenation (VA-ECMO) as a salvage therapy in cardiogenic shock is becoming of current practice. While VA-ECMO is potentially a life-saving technique, results are sometimes mitigated, emphasizing the need for selecting the right indication in the right patient. This relies upon a clear definition of the individual therapeutic project, including the potential for recovery as well as the possible complications associated with VA-ECMO. To maximize the benefits of VA-ECMO, the basics of extracorporeal circulation should be perfectly understood since VA-ECMO can sometimes be detrimental. Hence, to be successful, VA-ECMO should be used by teams with sufficient experience and initiated after a thorough multidisciplinary discussion considering patient’s medical history, pathology as well the anticipated evolution of the disease. (10.1016/j.accpm.2017.08.007)
  DOI : 10.1016/j.accpm.2017.08.007
• Harnessing Photochemical Shrinkage in Direct Laser Writing for Shape Morphing of Polymer Sheets
  
  • Bauhofer Anton
  • Krödel Sebastian
  • Rys Jan
  • Bilal Osama R.
  • Constantinescu Andrei
  • Daraio Chiara
  Advanced Materials, Wiley-VCH Verlag, 2017, 29 (42). Structures that change their shape in response to external stimuli unfold possibilities for more efficient and versatile production of 3D objects. Direct laser writing (DLW) is a technique based on two-photon polymerization that allows the fabrication of microstructures with complex 3D geometries. Here, it is shown that polymerization shrinkage in DLW can be utilized to create structures with locally controllable residual stresses that enable programmable, self-bending behavior. To demonstrate this concept, planar and 3D-structured sheets are preprogrammed to evolve into bio-inspired shapes (lotus flowers and shark skins). The fundamental mechanisms that control the self-bending behavior are identified and tested with microscale experiments. Based on the findings, an analytical model is introduced to quantitatively predict bending curvatures of the fabricated sheets. The proposed method enables simple fabrication of objects with complex geometries and precisely controllable shape morphing potential, while drastically reducing the required fabrication times for producing 3D, hierarchical microstructures over large areas in the order of square centimeters. (10.1002/adma.201703024)
  DOI : 10.1002/adma.201703024
• Comparison of Systolic Period Duration using Aortic Flow or Pressure Based Methods in Anesthetized Patients
  
  • Le Gall Arthur
  • Laurin Alexandre
  • Vallée Fabrice
  • Chemla Denis
  , 2017. It has been shown that Systolic Period Duration (SPD) measured with trans-esophageal echocardiography (TEE) is significantly shorter compared to measurements made with radial arterial pressure waveform. This difference could be interpreted in terms of arterial pressure amplification , a mechanism by which arterial pressure waveform is transformed alongside the arterial tree. This amplification is closely related to cardiac afterload as it shares common determinants, like arterial stiffness, pulse wave velocity, or aortic reflection waves. In turn, afterload estimated partly using arterial pressure amplification is useful during general anesthesia (GA) to evaluate detrimental or beneficial effects of vasopressors given to combat hypotensions. Despite TEE measurements comport some impracticalities, trans-esophageal Doppler (TE Doppler) is routinely used for cardiac output monitoring. The goal of this paper was to compare SPD measured with TE Doppler and with arterial pressure at the same location. A secondary goal was to describe a novel dicrotic notch identification algorithm that uses the interspace between the pressure waveform and the straight line going from the systolic peak of one beat to the foot of the subsequent beat. Twenty three patients undergoing GA for neurointerventional procedures were included. Central pressure was obtained by fluid filled radiologic guidewire connected to a pressure transducer. Flow velocity waveform was obtained using TE Doppler probe inserted in the esophagus after induction of GA. Pressure and flow velocity measurements were recorded simultaneously when the tip of the pressure catheter was placed in front of the Doppler probe, in the descending Aorta. SPD measured from Flow velocity waveform was significantly shorter than from Pressure waveform (343 ± 46 ms vs 415 ± 54 ms; p < 0.001). Flow velocity and Pressure waveform methods are not interchangeable. To measure SPD consistently at different locations, a consistent algorithm should be used, such as automated identification of dicrotic notch.
• The p−n junction under nonuniform strains: general theory and application to photovoltaics
  
  • Guin Laurent
  • Jabbour Michel
  • Triantafyllidis Nicolas
  Journal of the Mechanics and Physics of Solids, Elsevier, 2017, 110, pp.54 - 79. It is well known that mechanical strains influence the electronic properties of semiconductor devices. Modeling the fully coupled mechanical, electrical, and electronic responses of semiconductors is therefore essential for predicting the effects of mechanical loading on their overall electronic response. In the first part of this paper, we develop a general continuum model that couples the mechanical, electrical, and electronic responses of a finitely deformable semiconductor. The proposed model accounts for the dependence of the band edge energies, densities of states, and electronic mobilities on strain. The governing equations are derived from the basic principles of the thermomechanics of electromagnetic continua undergoing electronic transport. In particular, we find that there exists electronically induced strains that can exceed their electromagnetic (Maxwell) counterparts by an order of magnitude. In the second part, motivated by applications that involve the bending of a photovoltaic cell, we use asymptotic methods to compute the current–voltage characteristic of a p − n junction under nonuniform strains. We find that, for a typical monocrystalline silicon solar cell, the changes in dark current are significant, i.e., of the order of 20% for strains of 0.2%. (10.1016/j.jmps.2017.09.004)
  DOI : 10.1016/j.jmps.2017.09.004
• Association Between Mutation Size and Cardiac Involvement in Myotonic Dystrophy Type 1
  
  • Wahbi Karim
  • Chong-Nguyen Caroline
  • Algalarrondo Vincent
  • Becane Henri Marc
  • Arnaud Pauline
  • Furling Denis
  • Lazarus Arnaud
  • Bassez Guillaume
  • Behin Anthony
  • Payssoil Abdallah
  • Laforet Pascal
  • Stojkovic Tanya
  • Eymard Bruno
  • Duboc Denis
  , 2017. Introduction: In Myotonic Dystrophy type 1, the association between mutation size (CTG expansion) and the severity of cardiac involvement is controversial. Methods: We selected 855 patients with myotonic dystrophy type 1 (women, 51%; median age, 37 years), with genetic testing performed at the moment of their initial cardiac evaluation, out of 1014 patients included in the Mvotonic Dvstrophy Type 1-Heart Registry between January 2000 and December 2015. We studied the association between CTG expansion size and other baseline characteristics and (1) cardiac involvement at baseline and (2) the incidence of death, sudden death, and other cardiac adverse events. Results: At initial presentation, the median CTG expansion size was 530 (interquartile range, 300-830). In multivariate analysis, larger expansions were associated with the presence at baseline of conduction defects on the ECG and left ventricular systolic dysfunction. In a median 11.5 years of followup period, 210 patients died (25%), including 32 suddenly(4%). Supraventricular arrhythmias developed over lifetime in 166 patients (19%). sustained ventricular tachyarrhythmias in 17 (2%), and permanent pacemakers were implanted in 181 (21% ). In Cox regression analyses, larger CTG expansions were significantly associated with (1) total death, sudden dealth and pacemaker implantation in a model, including CTG expansion size, age, sex, diabetes mellius, and (2) all end points except sudden death in a model including all baseline characteristics. Discussion: The size of the CTG expansion in the blood of myoionic dystrophy type 1 patients is associated with total and sudden deaths, conduction defects, left ventricular dysfunction, and supraventricular arrhythmias.
• On-board Decision Making Platform for Structural Health Monitoring
  
  • Barthes Cécile
  • Rebillat Marc
  • Mosalam Khalid
  • Mechbal Nazih
  , 2017, pp.1-8. The ability to monitor the health of complex structures such as aeronautic or civil engineering structures in real time is becoming increasingly important. This process is referred to as structural health monitoring (SHM) and relies on onboard platforms comprising sensors, computational units, communication resources, and sometimes actuators. Many of such platforms have been developed within the last years but there is still a lack of structuration and knowledge exchange regarding the software and hardware architectures of such platforms. The aim of the present paper is to introduce an open hardware and open software platform dedicated to SHM within the fields of aeronautics and civil engineering. The platform presented here will be made available in an open hardware and open source framework to allow SHM researchers to run concurrent detection, localization, classification or quantification algorithms using simple interpreted languages such as Python.
• Multiphase model for transformation induced plasticity Extended Leblond's model
  
  • Weisz-Patrault Daniel
  Journal of the Mechanics and Physics of Solids, Elsevier, 2017. Transformation induced plasticity (TRIP) classically refers to plastic strains observed during phase transitions that occur under mechanical loads (that can be lower than the yield stress). A theoretical approach based on homogenization is proposed to deal with multiphase changes and to extend the validity of the well known and widely used model proposed by Leblond, J.-B., De-vaux, J., and Devaux, J. (1989). Mathematical modelling of transformation plasticity in steels i: case of ideal-plastic phases. International journal of plasticity, 5(6):551–572. The approach is similar, but several product phases are considered instead of one and several assumptions have been released. Thus, besides the generalization for several phases, one can mention three main improvements in the calculation of the local equivalent plastic strain: the deviatoric part of the phase transformation is taken into account, both parent and product phases are elastic-plastic with linear isotropic hardening and the applied stress is considered. Results show that classical issues of singularities arising in the Leblond's model (corrected by ad hoc numerical functions or thresholding) are solved in this contribution excepted when the applied equivalent stress reaches the yield stress. Indeed, in this situation the parent phase is entirely plastic as soon as the phase transformation begins and the same singularity as in the Leblond's model arises. A physical explanation of the cutoff function is introduced in order to regularize the singularity. Furthermore, experiments extracted from the literature dealing with multiphase transitions and multiaxial loads are compared with the original Leblond's model and the proposed extended version. For the extended version, very good agreement is observed without any fitting procedures (i.e., material parameters are extracted from other dedicated experiments) and for the original version results are more qualitative.
• Multiphase model for transformation induced plasticity. Extended Leblond’s model
  
  • Weisz-Patrault Daniel
  Journal of the Mechanics and Physics of Solids, Elsevier, 2017, 106, pp.152 - 175. Transformation induced plasticity (TRIP) classically refers to plastic strains observed during phase transitions that occur under mechanical loads (that can be lower than the yield stress). A theoretical approach based on homogenization is proposed to deal with multiphase changes and to extend the validity of the well known and widely used model proposed by Leblond, J.-B., De-vaux, J., and Devaux, J. (1989). Mathematical modelling of transformation plasticity in steels i: case of ideal-plastic phases. International journal of plasticity, 5(6):551–572. The approach is similar, but several product phases are considered instead of one and several assumptions have been released. Thus, besides the generalization for several phases, one can mention three main improvements in the calculation of the local equivalent plastic strain: the deviatoric part of the phase transformation is taken into account, both parent and product phases are elastic-plastic with linear isotropic hardening and the applied stress is considered. Results show that classical issues of singularities arising in the Leblond's model (corrected by ad hoc numerical functions or thresholding) are solved in this contribution excepted when the applied equivalent stress reaches the yield stress. Indeed, in this situation the parent phase is entirely plastic as soon as the phase transformation begins and the same singularity as in the Leblond's model arises. A physical explanation of the cutoff function is introduced in order to regularize the singularity. Furthermore, experiments extracted from the literature dealing with multiphase transitions and multiaxial loads are compared with the original Leblond's model and the proposed extended version. For the extended version, very good agreement is observed without any fitting procedures (i.e., material parameters are extracted from other dedicated experiments) and for the original version results are more qualitative. (10.1016/j.jmps.2017.05.019)
  DOI : 10.1016/j.jmps.2017.05.019
• Stress relaxation in polymeric microlattice materials
  
  • Krödel Sebastian
  • Li Lichen
  • Constantinescu Andrei
  • Daraio Chiara
  Materials & Design, Elsevier, 2017, 130, pp.433-441. Breakthroughs in fabrication techniques enabled the creation of microlattice materials, which are assembled from truss-like elements on the micro-scale. The mechanical properties of these materials can be controlled varying the geometry of their microstructure. Here, we study the effect of topology and effective density on the visco-elastic properties of microlattices fabricated by direct laser writing. We perform micro scale relaxation experiments using capacitive force sensing in compression. The experimental results are analyzed using a generalized Maxwell model and the viscoelastic properties are studied in terms of density scaling laws. We develop a finite element model that allows extracting the bulk polymer viscoelastic properties. The experimental results show that the stiffness of lattice materials can be adjusted independently from the loss factor in a wide range of frequencies. We find that the loss factor dramatically increases with applied strain due to the onset of nonlinear dissipation mechanism such as buckling and plasticity. We show that at effective densities around 50% the energy dissipation per cycle in a microlattice outperforms the dissipation in the bulk, giving rise to a "less is more" effect. The present research defines a first step in the application of microlattice materials in vibration absorption. (10.1016/j.matdes.2017.05.060)
  DOI : 10.1016/j.matdes.2017.05.060
• Energetic approach coupled with analytic solutions for the evaluation of residual stress.
  
  • Weisz-Patrault Daniel
  , 2017. This paper is part of a more general mixed analytical/numerical strategy aiming at computing residual stresses of metallic strips after coiling process. Multiphase transitions and transformation induced plasticity occur during coil cooling. Thus, each layer of coil is subjected to an overall eigenstrain that can be sufficient to generate macroscopic plastic deformations. For each layer, a solution of the problem of an elastic-plastic hollow cylinder undergoing an arbitrary eigenstrain is derived. Mathematical developments relies on the linear inhomogeneous Navier equation by dealing with plasticity through the introduction of a deviatoric unknown plastic strain. An analytical solution is obtained in the form of series expansion, for any trial plastic strain. Then, an energetic principle enables to determine the plastic strain chosen as a solution of the problem. Practically, a numerical optimization procedure is performed directly on coefficients of the plastic strain series expansion.
• Energetic approach coupled with analytic solutions for the evaluation of residual stress
  
  • Weisz-Patrault D.
  , 2017. This paper is part of a more general mixed analytical/numerical strategy aiming at computing residual stresses of metallic strips after coiling process. Multiphase transitions and transformation induced plasticity occur during coil cooling. Thus, each layer of coil is subjected to an overall eigenstrain that can be sufficient to generate macroscopic plastic deformations. For each layer, a solution of the problem of an elastic-plastic hollow cylinder undergoing an arbitrary eigenstrain is derived. Mathematical developments relies on the linear inhomogeneous Navier equation by dealing with plasticity through the introduction of a deviatoric unknown plastic strain. An analytical solution is obtained in the form of series expansion, for any trial plastic strain. Then, an energetic principle enables to determine the plastic strain chosen as a solution of the problem. Practically, a numerical optimization procedure is performed directly on coefficients of the plastic strain series expansion.