Publications

2022

• Dissimilar Al6061 to Al7075 friction stir welds : processing, static and fatigue properties
  
  • Dimov Nicolas
  , 2022. Friction Stir Welding (FSW) is a solid state (without fusion) welding technique involving no filler material. Patented for the first time in 1991 by The Welding Institute (Cambridge, UK), it consists in the mixing of the material of two parts to be assembled by plastic deformation. Friction StirWelding allows homogeneous or bi-material joints with a small decrease in the mechanical properties (compared to conventional assembly processes) as well as an excellent repeatability. This technology does not use consumables and is adaptable to conventional CNC machines. Numerous industrial examples using FSW on these alloys exist. Nevertheless, questions still remain regarding some mechanical properties of aluminium assemblies, particularly in the case of fatigue of so called dissimilar joints (welds containing multiple aluminium alloys). After a brief introduction on the process in and of itself and a wide range of industrial applications, majors results from the literature regarding mechanical and microstructural properties of aluminium FSW joints are presented. A particular attention is devoted to the impact of process parameters on previously described properties. A chapter first describes the methodology used to establish a process window for AA6061/AA7075: welds quality control and thermal aspects are described as well. It is then followed by the characterization of said joints (similar and dissimilar) by various means: optical microscopy, Vicker hardness measurements and tensile testing using Digital Image Correlation (DIC). Links between these properties and process parameters used in the manufacturing of the joints are established. A tensile test carried out inside a scanning electron microscope is presented in order to analyze local plastic deformation distribution inside the stir zone of a dissimilar joint. Finally, fatigue testing is carried out on some samples and relationships are established between thermal input during welding as well as stir zone morphology and fatigue life properties. Exploratory aluminium and titanium friction stir welds are presented and characterized in the appendix.
• Optimisation de formes de structures viscoélastiques sous sollicitations dynamiques
  
  • Joubert Antoni
  , 2022. Cette thèse porte sur l'optimisation de formes de structures en vibration exploitant les propriétés amortissantes des polymères. Un sujet aux enjeux importants puisque ces matériaux sont au cœur d'une grande partie des applications industrielles actuelles. L'objectif principal de ce travail est d'augmenter significativement les capacités d'amortissement de structures viscoélastiques homogènes en vibration libre, en s'appuyant sur des techniques de recherche du design optimal.L'optimisation paramétrique de l'épaisseur d'une poutre et d'une plaque, satisfaisant respectivement les hypothèses d'Euler-Bernoulli et de Kirchhoff-Love, est tout d'abord considérée. Cette étude est suivie de l'optimisation couplée de l'épaisseur et de la forme d'une plaque, satisfaisant les hypothèses de Kirchhoff-Love ou de Reissner-Mindlin, par la méthode de variation de frontière d'Hadamard.Enfin, une généralisation de ces problèmes est proposée à travers l'optimisation topologique de structures viscoélastiques 3D par la méthode level-set et appliquée au cas de la semelle de chaussure de course dans un cadre industriel. Le matériau viscoélastique linéaire isotrope est modélisé par un modèle classique de Maxwell généralisé, représentant le comportement de polymères réalistes de façon satisfaisante. Le gradient des fonctions objectifs est établi par une approche adjointe. L'optimisation est réalisée par un algorithme de descente de gradient et les modèles mécaniques sont évalués par la méthode des éléments finis.Les designs optimisés montrent un gain de performance significatif. Les résultats numériques indiquent également que les designs optimaux, ainsi que leur propriétés d'amortissement, dépendent fortement des paramètres matériaux.
• Modeling and inverse problems in hemodynamics : towards augmented cardiovascular monitoring
  
  • Manganotti Jessica
  , 2022. This project is at the interface between biomechanics and applied mathematics in a clinical context. More precisely, the clinical background is general anesthesia, which is a high-risk procedure as it can induce an unphysiological circulatory behavior. For this reason a close monitoring of the cardiovascular status of the patient near the heart is crucial. However, this requires invasive measurements that are not always available and therefore anesthesiologists usually rely on peripheral measurements, for example the radial pressure. The objective of this work is to provide, by means of a blood flow model coupled with a cardiac model and of data assimilation techniques, a strategy to estimate the cardiovascular state by using these distal measurements. We start from a one-dimensional blood flow model that is able to reproduce the wave propagation phenomena that affect the arterial circulation. The model relies on a novel discrete energy-preserving formulation which allows for a numerically stable coupling with a previously proposed reduced-order model of the left ventricle. This coupled model is able to simulate, given an atrial pressure, physiological results and is extended to take into account the pathway that links the cardiac outlet to the measurements site. Then, an important part of the work is dedicated to the construction and analysis of inverse problem strategies that, once applied on the blood flow model, allows to estimate central cardiovascular markers from the distal measurements of pressure. It is based on an iterative 4D-variational approach that relies on an approximated Gauss-Newton method, suitable for the solution of optimal control problems applied on non-linear formulations. The inverse problem is analyzed in its linearized version around a steady state, which corresponds to the first step of the iterative procedure. Our inversion strategy, allows us to reproduce the input flow and pressure and show promising results when real clinical data are involved.
• Characteristic features of salt-cavern behavior
  
  • Gordeliy Elizaveta
  • Berest Pierre
  , 2022. The behavior of an idealized spherical cavern leached out from a salt formation can be described by a first-order integro-differential equation when the Poisson’s ratio is 0.5. Three constitutive laws are considered: Norton-Hoff (N-H), Munson-Dawson (M-D) and Marketos-Spiers (M-S). The parameters of the M-D law can be fitted against both short- and long-term field data. It is shown that, following a pressure change, a “geometrical” transient evolution of the cavern volume is observed even when the constitutive law includes no “rheological” transient behavior (N-H, M-S). Following a large pressure increase, geometrical reverse creep and onset of tensile effective stresses at the cavern wall are observed. In a cavern subject to cyclic pressure, volume loss rate is faster than in a cavern where the average cycle pressure is applied. The loss rate is not extremely sensitive to cycle period; it is much faster when the M-D law (rather than the N-H law) is adopted. The M-S law, which accounts for the effect of pressure solution creep at low deviatoric stresses (in addition to dislocation creep), predicts a higher volume-loss rate (than the N-H law) when caverns are more shallow. A simple solution of the leaching problem (in which cavern radius is a function of time) can be found.
• On the structural origin of the anisotropy in the myocardium: Multiscale modeling and analysis
  
  • Tueni Nicole
  • Allain Jean-Marc
  • Genet Martin
  Journal of the mechanical behavior of biomedical materials, Elsevier, 2022, 138, pp.105600. Due to structural heterogeneities within the tissue, the myocardium displays an orthotropic material behavior. However, the link between the microstructure and the macroscopic mechanical properties is still not fully established. In particular, if it is admitted that the cardiomyocyte organization induces a transversely isotropic symmetry, the relative role in the observed orthotropic symmetry of cardiomyocyte orientation variation and perimysium collagen "sheetlet" structure, two mechanisms occurring at different scales, is still a matter of debate. In order to shed light on this question, we designed a multiscale model of the myocardium, bridging the cell, sheetlet and tissue scales. More precisely, we compared the macroscopic anisotropy obtained by homogenization of different mesostructures consisting in cardiomyocytes and extracellular collageneous layers, also taking into account the variation of cardiomyocyte and sheetlet orientations on the macroscale, to available experimental data. This study confirms the importance of sheetlets layers in assuring the tissue's anisotropic response, as cardiomyocytes-only mesostructures cannot reproduce the observed anisotropy. Moreover, our model shows the existence of a size effect in the myocardial tissue shear properties, which will require further experimental analysis.
• Statistically equivalent surrogate material models: Impact of random imperfections on the elasto-plastic response
  
  • Khristenko Ustim
  • Constantinescu Andrei
  • Le Tallec Patrick
  • Wohlmuth Barbara
  Computer Methods in Applied Mechanics and Engineering, Elsevier, 2022, 402, pp.115278. Manufactured materials usually contain random imperfections due to the fabrication process, e.g., the 3D-printing, casting, etc. These imperfections affect significantly the effective material properties and result in uncertainties in the mechanical response. Numerical analysis of the effects of the imperfections and the uncertainty quantification (UQ) can be often done by use of digital stochastic surrogate material models. In this work, we present a new flexible class of surrogate models depending on a small number of parameters and a calibration strategy ensuring that the constructed model fits to the available observation data, with special focus on two-phase materials. The surrogate models are constructed as the level-set of a linear combination of an intensity field representing the topological shape and a Gaussian perturbation representing the imperfections, allowing for fast sampling strategies. The mathematical design parameters of the model are related to physical ones and thus easy to interpret. The calibration of the model parameters is performed using progressive batching sub-sampled quasi-Newton minimization, using a designed distance measure between the synthetic samples and the data. Then, employing a fast sampling algorithm, an arbitrary number of synthetic samples can be generated to use in Monte Carlo type methods for prediction of effective material properties. In particular, we illustrate the method in application to UQ of the elasto-plastic response of an imperfect octet-truss lattice which plays an important role in additive manufacturing. To this end, we study the effective material properties of the lattice unit cell under elasto-plastic deformations and investigate the sensitivity of the effective Young’s modulus to the imperfections. (10.1016/j.cma.2022.115278)
  DOI : 10.1016/j.cma.2022.115278
• Measure of the hygroscopic expansion of human dentin
  
  • Gharbi Hakim
  • Wenlong Wang
  • Giraudet Chloé
  • Allain Jean-Marc
  • Vennat Elsa
  , 2022. Background: Direct dental restoration implies a drying of the dentin substrate. This drying may induce significant strain in the dentin, affecting the bonding efficiency of the restoration. Objective: We measure the dilatation of dentine under changes of relative humidity as well as the impact of humidity on dentin elastic properties. This investigates the role of relative humidity variation during dental surgery on restoration lifetime. Methods: We have coupled an environmental chamber to control both temperature and humidity on the sample, with an optical microscope to measure precisely the strain on the sample surface, after a quantification of the measurement noise. This set-up is used on carefully prepared samples placed on a compression device to measure the elastic parameters. Results: Dentin dilates when the relative humidity increases, with a coefficient of hygroscopic expansion of typically 6.10-3 %.(%RH)-1. This dilatation occurs in about ten minutes. Young modulus and Poisson’s ratio are not modified by the variation of relative humidity. Conclusions: Hygroscopic expansion is an order of magnitude larger than thermal expansion during dental surgery: around 0.3% with respect to 0.03%. These levels are low with respect to dental rupture, but may induce a significant decrease of the life-expectancy of a restoration.
• Dimensional reduction of a poromechanical cardiac model for myocardial perfusion studies
  
  • Chabiniok Radomír
  • Burtschell Bruno
  • Chapelle Dominique
  • Moireau Philippe
  Applications in Engineering Science, 2022, 12, pp.100121. In this paper, we adapt a previously developed poromechanical formulation to model the perfusion of myocardium during a cardiac cycle. First, a complete model is derived in 3D. Then, we perform a dimensional reduction under the assumption of spherical symmetry and propose a numerical algorithm that enables us to perform simulations of the myocardial perfusion throughout the cardiac cycle. These simulations illustrate the use of the proposed model to represent various physiological and pathological scenarios, specifically the vasodilation in the coronary network (to reproduce the standard clinical assessment of myocardial perfusion and perfusion reserve), the stenosis of a large coronary artery, an increased vascular resistance in the microcirculation (microvascular disease) and the consequences of inotropic activation (increased myocardial contractility) particularly at the level of the systolic flow impediment. Our results show that the model gives promising qualitative reproductions of complex physiological phenomena. This paves the way for future quantitative studies using clinical or experimental data. (10.1016/j.apples.2022.100121)
  DOI : 10.1016/j.apples.2022.100121
• Rheology of partially molten plagioclase containing wetting silica-rich anhydrous melt
  
  • Dimanov Alexandre
  Geophysical Journal International, Oxford University Press (OUP), 2022, 231 (2), pp.770-785. Abstract This work explores the effects of melt chemistry on diffusion controlled creep of partially molten labradorite plagioclase (An50) at anhydrous conditions. Using sol-gel and hot pressing techniques we produced: (1) nominally melt-free samples, with <1 vol. per cent residual glass confined solely to multiple-grain junctions; (2) two types of partially molten samples, containing respectively ∼1 and ∼5 vol. per cent silica-rich partial melts, wetting numerous grain boundaries by thin (<10 nm) amorphous films. Energy dispersive X-ray analysis showed that the amorphous phases of the latter materials contained ∼85 and 95 wt. per cent SiO2, thus representing different polymerization degrees. Infrared spectroscopy showed that the initial traces of water (∼0.05 wt. per cent) were dried out by annealing in air above 1100 °C. Uniaxial creep tests performed at temperatures and flow stresses ranging, respectively, between 1100–1250 °C and 3–60 MPa showed dominantly linear viscous flow, with a strong grain size dependence indicating grain boundary diffusion control. Counter-intuitively strength and activation energy increased with the content of melts. However, for the sample suite silica content covaries with melt proportion, and thus our results suggest that the kinetics of grain boundary diffusion controlled creep strongly depends on melt chemistry. Instead of acting as shortcut for diffusion, thin films of highly viscous amorphous phases may in turn considerably hinder grain boundary transport properties. (10.1093/gji/ggac218)
  DOI : 10.1093/gji/ggac218
• Thermo-mechanical Coil Cooling Model to Tackle Shape and Mechanical Properties Issues after Hot Rolling of Steel Sheets
  
  • Weisz-Patrault Daniel
  • Legrand Nicolas
  • Deka M
  • Magnana M
  • Cooke C
  • Ehrhardt Bertram
  • Jimenez Stéphane
  • Jacolot Ronan
  , 2022. The goal is to better understand the strip shape and hardness variability issues that appear after hot rolling on two distinct high strength steel grades A and B. These issues strongly affect the yield loss of the two grades and are mainly due to late austenite transformation in the coil during its heterogeneous cooling in the coil yard after mandrel removal. To tackle these problems, an existing thermo-mechanical coil cooling model is calibrated on the two grades using industrial temperature measurements of the coils taken with infrared cameras (to tune the coil cooling temperature model) and using laboratory dilatometric tests to tune the phase transformation kinetics model of each grade. The infrared cameras reveal a difference of cooling kinetics between the two grades attributed to a difference of phase transformation kinetics: one grade is mainly coil transforming (grade A) while the other is rather run out table transforming (grade B). This difference was confirmed by the TTT and CCT diagrams established on the two grades with the laboratory dilatometric tests. Furthermore, the calibrated coil cooling model clearly shows that the slow kinetics of coil cooling after mandrel removal depends not only on material parameters, boundary conditions, coil geometry and phase transformation kinetics but also on the heterogeneous contact pressure between laps in the radial direction of the coil. Once calibrated, the model is used to compare the two grades and analyse several new rolling practices to mitigate the issues. Finally the industrial evaluations of some of these new practices are presented together with the yield benefits.
• Influence de la vitesse de scan sur la microstructure de murs fins en IN718, produits par dépôt sous énergie concentrée
  
  • Bréhier Michèle
  • Weisz-Patrault Daniel
  • Tournier Christophe
  , 2022.
• Varying thin filament activation in the framework of the Huxley'57 model
  
  • Kimmig François
  • Caruel Matthieu
  • Chapelle Dominique
  International Journal for Numerical Methods in Biomedical Engineering, John Wiley and Sons, 2022. Muscle contraction is triggered by the activation of the actin sites of the thin filament by calcium ions. It results that the thin filament activation level varies over time. Moreover, this activation process is also used as a regulation mechanism of the developed force. Our objective is to build a model of varying actin site activation level within the classical Huxley'57 two-state framework. This new model is obtained as an enhancement of a previously proposed formulation of the varying thick filament activation within the same framework [1]. We assume that the state of an actin site depends on whether it is activated and whether it forms a cross-bridge with the associated myosin head, which results in four possible states. The transitions between the actin site states are controlled by the global actin sites activation level and the dynamics of these transitions is coupled with the attachment-detachment process. A preliminary calibration of the model with experimental twitch contraction data obtained at varying sarcomere lengths is performed. (10.1002/cnm.3655)
  DOI : 10.1002/cnm.3655
• L-PBF and DED processing of a Ni-based superalloy
  
  • Thomas M
  • Charkaluk Eric
  • Solas Denis
  • Szmytka Fabien
  • Locq Didier
  • Morel Ariel
  • Hubert Olivier
  • Muller Nicolas
  • Tournier Christophe
  , 2022. Different additive manufacturing (AM) technologies such as L-PBF and DED do become really attractive for both repair and 3D part manufacturing. In particular, extensive work is in progress for the non-weldable nickel-based superalloys which tend to exhibit cracks due to residual stresses build-up during AM thermal cycles. Within the framework of the project FAPS conducted at Université Paris-Saclay, the present investigation will highlight the processing conditions and build-up strategy that produce crack-free specimens for alloy AD730®. The latter was developed by Aubert & Duval for cast&wrought gas turbine applications. In this work, a comparison between such conventional processing and AM will be provided in terms of mechanical performance. The results clearly show an anisotropic behaviour related to the sharp crystallographic texture induced by the epitaxial grain growth. The results will be discussed, with a perspective analysis of maturity for this AM processedmaterial, the process robustness, the potential technological developments and application prospects.
• Blowout Prediction on a Salt Cavern Selected for a Hydrogen Storage Pilot
  
  • Djizanne Hippolyte
  • Murillo Rueda Carlos
  • Brouard Benoit
  • Bérest Pierre
  • Hévin Grégoire
  Energies, MDPI, 2022, 15 (20), pp.7755. To prevent climate change, Europe and the world must shift to low-carbon and renewable energies. Hydrogen, as an energy vector, provides viable solutions for replacing polluting and carbon-emitting fossil fuels. Gaseous hydrogen can be stored underground and coupled with existing natural gas pipe networks. Salt cavern storage is the best suited technology to meet the challenges of new energy systems. Hydrogen storage caverns are currently operated in the UK and Texas. A preliminary risk analysis dedicated to underground hydrogen salt caverns highlighted the importance of containment losses (leaks) and the formation of gas clouds following blowouts, whose ignition may generate dangerous phenomena such as jet fires, unconfined vapor cloud explosions (UVCEs), or flashfires. A blowout is not a frequent accident in gas storage caverns. A safety valve is often set at a 30 m depth below ground level; it is automatically triggered following a pressure drop at the wellhead. Nevertheless, a blowout remains to be one of the significant accidental scenarios likely to occur during hydrogen underground storage in salt caverns. In this paper, we present modelling the subterraneous and aerial parts of a blowout on an EZ53 salt cavern fully filled with hydrogen. (10.3390/en15207755)
  DOI : 10.3390/en15207755
• Multiphysics simulation of electric motors with an application to stators
  
  • Hanappier N.
  • Charkaluk Eric
  • Triantafyllidis N.
  International Journal of Solids and Structures, Elsevier, 2022, 253, pp.111406. The development of a new generation of more efficient electric motors leads to designs with higher stresses, currents and electromagnetic fields. To improve on the prevailing existing methodology for the concurrent calculation of electromagnetic and mechanical fields in electric motors, the authors recently presented in Hanappier et al. (2021a) a multiphysics formulation of the problem using the direct (current configuration) approach of continuum mechanics together with analytical solutions of idealized motor problems. However, due to the complex geometry of a typical electric motor and the nonlinearity of the coupled (magneto-mechanical) constitutive laws, numerical solutions of the governing equations are required. To this end, a Lagrangian (reference configuration) variational principle is proposed for the eddy current approximation that properly retrieves the Maxwell stresses and is consistent with its direct approach counterpart. Based on this variational principle, a numerical (FEM) approach is proposed. It is next applied to an idealized (cylindrical) stator, where an analytical solution can be found for the linear magnetization regime, thus providing firstly an independent code verification and then an assessment of the influence of the stator's nonlinear magnetic response. The approach is subsequently used to tackle a realistic geometry stator with two pole pairs under a three-phase current for two different cases: loosely or tightly packed conducting wires to calculate the corresponding magnetic, stress and strain fields. (10.1016/j.ijsolstr.2021.111406)
  DOI : 10.1016/j.ijsolstr.2021.111406
• Fatigue crack growth in bearing steel under cyclic mode II + static biaxial compression
  
  • Zaid Mael
  • Bonnand Vincent
  • Doquet Véronique
  • Chiaruttini Vincent
  • Pacou Didier
  • Depouhon Pierre
  International Journal of Fatigue, Elsevier, 2022, 163, pp.107074. Mode II fatigue crack growth under reversed shear and static biaxial compression was investigated in two bearing steels. Many aborted branches, quasi-orthogonal to the main crack, were observed along the crack face. The compressive stress parallel to the main crack hindered the growth of these branches and favored coplanar mode II crack growth. The crack face sliding displacement profiles measured by DIC were used to derive ΔKII,eff, at the main crack tip, using elastic-plastic FE simulations with crack face friction, by an inverse method. Frictioncorrected crack growth kinetics were obtained for mode II crack growth in both steels. (10.1016/j.ijfatigue.2022.107074)
  DOI : 10.1016/j.ijfatigue.2022.107074
• Méthodes mathématiques et numériques pour des problèmes de propagation d’ondes double échelles
  
  • Imperiale Sébastien
  , 2022.
• Modelling and Simulation of the Magnetostriction Effect in a Magneto-sensitive Material
  
  • Saouli N.
  • Dammak H.
  • Hayoun M.
  • Bodelot L.
  , 2022.
• Analysis and fast modelling of microstructures in duplex stainless steel formed by directed energy deposition additive manufacturing
  
  • Edwards Alexander
  • Weisz-Patrault Daniel
  • Charkaluk Eric
  , 2022. Superduplex stainless steels have seen increasing use in past decades in applications that require both excellent mechanical properties and corrosion resistance. The properties of duplex steels depend strongly on their thermal history, which can produce a wide range of austenite to ferrite ratios; whereas optimal properties generally require near 50-50 ferrite-austenite duplex microstructures. Additive manufacturing processes involve large thermal gradients as new material is melted on top of already printed material, and thermal history depends on process parameters. As the equilibrium phase ratio depends strongly on temperature, the result is a wide range of reported phase ratios, ranging from negligible fractions of austenite to greater than 60 %. So it is important to understand and predict how the phase ratio depends on process parameters. We assesses the microstructures in single-bead-thickness walls of SAF 2507 superduplex stainless steel printed using constant process parameters, using the laser metal powder directed energy deposition (LMPDED) additive manufacturing technique. Post-printing microstructural analysis revealed a gradient of austenite phase fraction as a function of distance from the build platform. This data reveals the relation between the thermal history and solid-solid phase transformation of ferrite to austenite during the fabrication process. The thermal history of each position in the wall was modelled by a previous fast numerical simulation (that has been improved in this contribution), and a fast diffusion controlled solid-solid phase transformations model based on semi-analytical methods has been developed. Numerical results for the phase ratios are in reasonable agreement with experimental observations. The proposed simulations strategy is sufficiently fast to enable to adjust the process parameters to achieve a targeted distribution of phase ratio in order to facilitate additive manufacturing of super duplex stainless steels, and a temperature control strategy of the build platform has been proposed on this basis to reach almost uniform near 50-50 phase ratios.
• Insights into the viscohyperelastic response of soft magnetorheological elastomers: Competition of macrostructural versus microstructural players
  
  • Lucarini S.
  • Moreno-Mateos M.A.
  • Danas K.
  • Garcia-Gonzalez D.
  International Journal of Solids and Structures, Elsevier, 2022, pp.111981. Magnetorheological elastomers (MREs) are multifunctional composites that consist of an elastomeric matrix filled with magnetic particles. These materials respond to an external magnetic field by mechanically deforming and/or changing their magnetorheological properties. Such a multi-physical response has made them extraordinary candidates for a wide variety of applications in soft robotics and bioengineering. However, there are still some gaps of knowledge that prevent the optimal design and application of these MREs. In this regard, the effect of viscoelastic mechanisms remains elusive from a microstructural perspective. To the best of the authors’ knowledge, this work provides for the first time a numerical homogenization analysis for various magneto-active microstructures accounting for viscous deformation mechanisms. To this end, we propose an incremental variational formulation that incorporates viscoelasticity via internal variables, which is properly modified to deal with the continuity of Maxwell stresses. The proposed framework is applied to study the magneto-mechanical couplings in extremely soft MREs (stiffness 10 kPa). Such soft matrix promotes microstructural rearrangements while transmitting internal forces leading to macrostructural synergistic responses. The constitutive parameters are calibrated with experimental tests. The numerical results are accompanied with original magnetostriction tests considering different sample geometries and confined magneto-mechanical tests, reporting the macroscopic response. The results obtained in this work suggest that the effective magneto-mechanical response of the MRE is the outcome of a competition between macrostructural and local microstructural responses, where viscous mechanisms play a relevant role. (10.1016/j.ijsolstr.2022.111981)
  DOI : 10.1016/j.ijsolstr.2022.111981
• Estimation of regional pulmonary compliance in idiopathic pulmonary fibrosis based on personalized lung poromechanical modeling
  
  • Patte Cécile
  • Brillet Pierre-Yves
  • Fetita Catalin
  • Bernaudin Jean Francois
  • Gille Thomas
  • Nunes Hilario
  • Chapelle Dominique
  • Genet Martin
  Journal of Biomechanical Engineering, American Society of Mechanical Engineers, 2022, 144 (9), pp.091008:1-091008:14. Pulmonary function is tightly linked to the lung mechanical behavior, especially large deforma-tion during breathing. Interstitial lung diseases, such as Idiopathic Pulmonary Fibrosis (IPF), havean impact on the pulmonary mechanics and consequently alter lung function. However, IPF re-mains poorly understood, poorly diagnosed and poorly treated. Currently, the mechanical impactof such diseases is assessed by pressure-volume curves, giving only global information. We de-veloped a poromechanical model of the lung that can be personalized to a patient based on routineclinical data. The personalization pipeline uses clinical data, mainly CT-images at two time stepsand involves the formulation of an inverse problem to estimate regional compliances. The estima-tion problem can be formulated both in terms of “effective”, i.e., without considering the mixtureporosity, or “rescaled”, i.e., where the first-order effect of the porosity has been taken into account,compliances. Regional compliances are estimated for one control subject and three IPF patients,allowing to quantify the IPF-induced tissue stiffening. This personalized model could be used in theclinic as an objective and quantitative tool for IPF diagnosis. (10.1115/1.4054106)
  DOI : 10.1115/1.4054106
• Asymptotic derivation of a higher-order one-dimensional model for tape springs
  
  • Kumar Arun
  • Audoly Basile
  • Lestringant Claire
  , 2022. We derive a one-dimensional model for tape springs. The derivation starts from nonlinear thin-shell theory and uses a dimension reduction technique that combines a centerline-based parameterization of the tape-spring mid-surface with the assumption that the strain varies slowly along the length of the tape spring. The one-dimensional model is effectively a higherorder rod model: at leading order, the strain energy depends on the extensional, bending and twisting strains and is consistent with classical results from the literature; the two following orders are novel and capture the dependence of the strain energy on the strain gradients. The cross-sectional displacements are solved as part of the dimension reduction process, making the one-dimensional model asymptotically exact. We expect that the model will accurately and efficiently capture the deformations and instabilities in tape springs, including those involving highly localized deformations.
• Analyse multi-échelle du comportement des carbonates poreux sous chargement triaxial
  
  • Doré-Ossipyan Catherine
  • Sulem Jean
  • Bornert Michel
  • Dimanov Alexandre
  • Aimedieu Patrick
  • de Greef Vincent
  , 2022, pp.12 p. Sous conditions triaxiales, on observe souvent dans les roches carbonatées poreuses la formation de bandes de déformation. Dans le cas du carbonate de Saint Maximin, une étude précédente menée sur des échantillons de 40 mm de diamètre a montré que leur localisation est gouvernée par l’hétérogénéité de porosité locale. Un dispositif triaxial insérable dans un tomographe permet d’analyser ce phénomène de localisation en continu à une plus petite échelle (diamètre 15 mm). On décrit ici ce protocole expérimental permettant d’analyser le comportement d’une roche à microstructure complexe. Un premier essai sur un échantillon très poreux montre que la nucléation des bandes est toujours contrôlée par la porosité locale, mais les modes de déformation diffèrent entre la méso et la micro-échelle.
• Etude expérimentale et modélisation de la fissuration d’un polymère thermoplastique
  
  • Coq Arnaud
  • Diani Julie
  • Brach Stella
  , 2022.
• Thermal analysis and shrinkage characterization of the photopolymers for DLP additive manufacturing processes
  
  • Sekmen Kubra
  • Rehbein Thomas
  • Johlitz Michael
  • Lion Alexander
  • Constantinescu Andrei
  Continuum Mechanics and Thermodynamics, Springer Verlag, 2022. This paper proposes an experimental investigation of a commercial photopolymer resin followed by material modelling and manufacturing system characterization. We focus on the effect of the degree of cure and temperature on the material properties of the photopolymer materials. UV curing properties of the liquid resin are assessed with the thickness measurement by optical tomography. Besides, the specific heat capacity is determined for the almost completely cured and uncured samples with DSC measurements. Photo-DSC experiments are performed to investigate the curing reaction and modelling of the evolution of the degree of cure depending on the light intensity and temperature. In addition, chemical shrinkage behaviour is captured as function of the degree of cure by the high-precision balance setup. As a result of our experimental studies, model equations are proposed to describe the material behaviour. (10.1007/s00161-022-01137-0)
  DOI : 10.1007/s00161-022-01137-0