Publications

2024

• Impact of Continuous Scanning Speed Variation on Microstructure in LMP-DED Additive Manufacturing
  
  • Bréhier Michèle
  • Tournier Christophe
  • Weisz-Patrault Daniel
  , 2024. This paper deals with additive manufacturing, which enables parts with complex geometries to be produced layer by layer. For specific geometries, such as bent parts, it is necessary to vary the bead size within or between layers by modifying process parameters, such as scanning speed. However, it has been shown in the literature that modifying process parameters leads to changes in the microstructure. This paper inspects the impact of continuous variation in scanning speed on the microstructure produced with the LMP-DED additive manufacturing process. An experimental study was carried out on single-bead Inconel 718 thin walls. Scanning speed varied linearly along each bead so that at a given position in the wall, the scanning speed was the same throughout the height of the wall. An EBSD analysis of the microstructure was carried out over a length of about 20 mm for a speed variation ranging from 1125mm/min to 1875mm/min. A continuous variation in microstructure was observed from one end of the sample to the other, passing from a mix of columnar and equiaxed grains with no textured structure to large, highly textured columnar grains. These results show that it is possible to intentionally and continuously vary the microstructure of a part along its length by choosing the proper parameters and strategy. This work is preliminary to the microstructure control of a complex part.
• Shrinkage characterization and compensation for 3DPC
  
  • Viano Rafaël
  • Margerit Pierre
  • Mesnil Romain
  • Weisz-Patrault Daniel
  • Caron Jean-François
  , 2024. 3D concrete printing is an additive manufacturing process in which elongated beads are assembled in layers to form 3D parts. In cementitious materials, water evaporation as well as the setting of the material results in a volumetric shrinkage of the printed structures. This imposed shrinkage strain, commonly refereed to as eigenstrain, is the source of residual progressive stress evolution within the printed parts. Consequently, the accumulation of stress during fabrication and drying may induce cracks, buckling, and surface defects in the final product. Evaluating and modeling the effect of shrinkage on the printed beads is therefore essential to optimize the machine path and process parameters in order to mitigate such issues and guarantee the integrity of the printed parts. In particular, this paper focuses on the development of a compensation strategy such that the final geometry correctly approximates the target geometry. The proposed approach relies on the experimental characterization of the displacement field and hence the total strain by using Digital Image Correlation performed on in-situ imaging of the process. The history of the eigenstrain strain (i.e., shrinkage) has been measured on flat rectangular thin-walled walls, and then used in a mechanical model as an imposed strain. Resulting geometrical distortions have been validated against experiments. On this basis, a simple compensation strategy is proposed consisting in correcting the initial machine path by the opposite of the computed distortions when the structure is subjected to shrinkage. Several examples on various part geometries are presented and discussed. A fast one-dimensional mechanical model named QuadWire proposed recently is being used for numerical simulations, as the final objective is to create large database to train neural network algorithms in order to apply this compensation strategy in realtime during the printing process.
• Development of a Mechaplastronic approach for optimizing hydrogen tank composites with in-situ Structural Health Monitoring (SHM).
  
  • Shirinbayan Mohammadali
  • Rébillat Marc
  • Fitoussi Joseph
  • Mechbal Nazih
  , 2024. sustainable environments. Hydrogen, as a vector of energy, offers a high energy density and produces only water when used in fuel cells, making it an environmentally friendly alternative to fossil fuels. Hydrogen storage in gaseous form is typically achieved in type IV composite tanks. These tanks feature a thermosetting matrix, usually an epoxy reinforced with carbon fibers, which provides mechanical strength. Additionally, a polymer liner, onto which the composite is deposited via filament winding, ensures the hydrogen barrier function. A metal base is incorporated to facilitate the introduction of hydrogen into the tank. Type V hydrogen tanks are made from thermoplastic polymers and consist of a monolithic structure including an internal layer of unfilled polymer and a multilayer composite external layer made of the same thermoplastic matrix reinforced with continuous carbon fibres. The interface between the composite and the liner is thus assumed to be perfect. These tanks will be subjected to the different types of thermomechanical loads as type IV tanks: nominal pressure of 700 bars, burst pressure of 1750 bars, temperature ranging from -60°C to 85°C, fill-drain cycles, shocks, and impacts (figure 1). However, in terms of service life, the difficulty of damage detection and measurement and monitoring of physical quantities within composite structures still requires the development of specific and reliable technological tools and methods, such as the integration of sensors into the composite structure. The interest in integrating such a function lies in the potential for in-situ health monitoring of the structure from its implementation (Process Health Monitoring - PHM) to its service life (Structural Health Monitoring - SHM). Mastering this technology in all its aspects could significantly reduce maintenance costs and ensure better durability while optimizing the manufacturing process. The integration of sensors into hydrogen storage structures is essential to advancing the use of hydrogen as an energy carrier in transportation. Integrated sensors can provide an easy and effective means to monitor manufacturing quality and mechanical performance of the tanks during their service life. Indeed, these sensors contribute to several essential functions of so-called "smart tanks" currently in development. However, the integration of sensors is complex and poses several challenges such as type of sensors, the methodology of integration of the sensors. To overcome these challenges, the proposed methodology aims to establish a structured approach for selecting and/or optimizing the Process-Material-Sensor (PMS) trio to ensure the reliability of the mechanical and electronic functions integrated within hydrogen tanks. The proposed approach involves combining an experimental method with a numerical one. Additionally, it leverages cross-disciplinary skills, including: • The characterization and modeling of the Mechanical behavior of materials and the optimization of tank performance. • The processes involved in the manufacturing of hydrogen tanks (plastics engineering). • The integration and use of sensors, particularly the analysis of electronic signals to correlate with the assessment of the tank's degradation state. In this paper the development of a highly transversal global approach that called Mechaplastronic has been proposed. Indeed, it can be considered that optimizing the integration of sensors within a tank involves studying different types of intrusiveness: A) Intrusiveness of the Fabrication Process on Electronic Functions: Firstly, when sensors are integrated within the materials or at their interfaces, they must be compatible with the fabrication process of the structure (Automated Fiber Placement (AFP) / Filament Winding). Therefore, it is necessary to study the impact of the process on the operating mechanisms of the sensors and the reliability of its electrical and magnetic properties. This involves optimizing the process parameters and the choice of materials. B) Mutual Intrusiveness of Electronic and Mechanical Functions: The presence of sensors creates interfaces and stress concentrations that can weaken the structures. Therefore, it is important to study the effect of the presence of sensors on the mechanical properties of the structural materials (especially the composite). Conversely, the various thermomechanical stresses endured by the structure can affect the operation of the sensors. The proposed methodology, aiming to control the different potential intrusiveness and their interactions within a hydrogen tank, can be schematized as illustrated in figure 2. Thus, this study aims to enhance the understanding of the performance of critical areas in H2 tanks. The entirety of this study's results, along with the understanding of the phenomena involved, particularly damage, constitutes an important experimental and numerical foundation.
• Effective boundary conditions for second-order homogenization
  
  • Thbaut Manon
  • Audoly Basile
  • Lestringant Claire
  Journal of the Mechanics and Physics of Solids, Elsevier, 2024, 190, pp.105707. Using matched asymptotic expansions, we derive an equivalent bar model for a periodic, one-dimensional lattice made up of linear elastic springs connecting both nearest and next-nearest neighbors. We obtain a strain-gradient model with effective boundary conditions accounting for the boundary layers forming at the endpoints. It is accurate to second order in the scale separation parameter $\varepsilon \ll 1$, as shown by a comparison with the solution to the discrete lattice problem. The homogenized modulus associated with the gradient effect (gradient stiffness) is found negative, as is often the case in second-order homogenization. Negative gradient stiffnesses are widely viewed as paradoxical as they can induce short-wavelength oscillations in the homogenized solution. In the one-dimensional lattice, the asymptotically correct boundary conditions are shown to suppress the oscillations, thereby restoring consistency. By contrast, most of the existing work on second-order homogenization makes use of postulated boundary conditions which, we argue, not only ruin the order of the approximation but are also the root cause of the undesirable oscillations. (10.1016/j.jmps.2024.105707)
  DOI : 10.1016/j.jmps.2024.105707
• A Clinical‐Grade Partially Decellularized Matrix for Tracheal Replacement: Validation In Vitro and In Vivo in a Porcine Model
  
  • Arakelian Lousineh
  • Léger Maëlys
  • Kellouche Sabrina
  • Agniel Rémy
  • Bruneval Patrick
  • Allain Jean-Marc
  • Caputo Valentino
  • Gendron Nicolas
  • Gozlan Romane
  • Bargui Rezlene
  • Vigouroux Augustin
  • Sansac Caroline
  • Jarraya Mohamed
  • Denoyelle Françoise
  • Larghero Jérôme
  • Thierry Briac
  Advanced Biology, Wiley, 2024, 8 (12), pp.2400208. The management of extensive tracheal resection followed by circumferential replacement remains a surgical challenge. Numerous techniques are proposed with mixed results. Partial decellularization of the trachea with the removal of the mucosal and submucosal cells is a promising method, reducing immunogenicity while preserving the biomechanical properties of the final matrix. Despite many research protocols and proofs of concept, no standardized clinical grade protocol is described. Furthermore, local and systemic biointegration mechanisms of decellularized trachea are not well known. Therefore, in a translational research perspective, this work set up a partial tracheal decellularization protocol in line with Cell and Tissue Products regulations . Extensive characterization of the final product is performed in vitro and in vivo. The results show that the Partially Decellularized Trachea (PDT) is cell‐free in the mucosa and submucosa, while the cartilage structure is preserved, maintaining the biomechanical properties of the trachea. When implanted in the muscle in vivo for 28 days, no systemic inflammation is observed, and locally, the PDT shows an excellent biointegration and vascularization. No signs of graft rejection are observed. These encouraging results confirmed the efficacy of the clinical grade PDT production protocol, which is an important step for future clinical applications. (10.1002/adbi.202400208)
  DOI : 10.1002/adbi.202400208
• Spatial heterogeneity of aliphatic compounds and their link with phyllosilicates as a result of aqueous alteration of ryugu samples
  
  • Dionnet Zelia
  • Djouadi Z.
  • Brunetto R.
  • Aléon-Toppani A.
  • Nakamura T
  • Rubino Stefano
  • Delaye L
  • Caron L
  • Baklouti Donia
  • Lantz Cateline
  • Mivumbi O
  • Borondics F
  • Héripré E
  • Troadec D.
  • Tsuchiyama A
  • Matsuno J
  • Matsumoto M
  • Morita T
  • Kikuiri M
  • Amano K
  • Kagawa E
  • Yurimoto H
  • Noguchi T
  • Okazaki R
  • Yabuta H
  • Naraoka H
  • Sakamoto K
  • Tachibana S
  • Watanabe S
  • Tsuda Y
  , 2024.
• A model of mechanical loading of the lungs including gravity and a balancing heterogeneous pleural pressure
  
  • Peyraut Alice
  • Genet Martin
  Biomechanics and Modeling in Mechanobiology, Springer Verlag, 2024, 23 (6), pp.1933-1962. Recent years have seen the development of multiple in silico lung models, notably with the aim of improving patient care for pulmonary diseases. These models vary in complexity, and typically only consider the implementation of pleural pressure, a depression that keeps the lungs inflated. Gravity, often considered negligible compared to pleural pressure, has been largely overlooked, also due to the complexity of formulating physiological boundary conditions to counterbalance it. However, gravity is known to affect pulmonary functions, such as ventilation. In this study, we incorporated gravity into a recent lung poromechanical model. To do so, in addition to the gravitational body force, we proposed novel boundary conditions consisting in a heterogeneous pleural pressure field constrained to counterbalance gravity to reach global equilibrium of applied forces. We assessed the impact of gravity on the global and local behavior of the model, including the pressure-volume response and porosity field. Our findings reveal that gravity, despite being small, influences lung response. Specifically, the inclusion of gravity in our model led to the emergence of heterogeneities in deformation and stress distribution, compatible with in vivo imaging data. This could provide valuable insights for predicting the progression of certain pulmonary diseases by correlating areas subjected to higher deformation and stresses with disease evolution patterns. (10.1007/s10237-024-01876-w)
  DOI : 10.1007/s10237-024-01876-w
• Silicon mediated twin formation in laser direct energy deposited 316L stainless steel
  
  • Chen Kewei
  • Santos Macías Juan Guillermo
  • Isac Nathalie
  • Vallet Maxime
  • Cornet Louis
  • Upadhyay Manas V
  , 2024. Microstructures of two laser direct energy deposited 316L stainless steel samples printed using the same additive manufacturing parameters and primarily differing in their Si content, 2.2wt% (316L-Si) and 0.73wt% (316L), were studied. A larger length fraction of Σ3 twin boundaries (~23% of all boundaries in austenite) was observed in 316L-Si than in 316L (~2%). The twin-related domains in 316L-Si are attributed to two mechanisms: (i) icosahedral short-range order-mediated nucleation in the melt based on observation of grain clusters sharing a common <110> fivefold symmetry axis, and (ii) massive transformation from ferrite to austenite, confirmed by the presence of refined grains, absence of solidification cells and jagged boundaries between austenite grains. For the same printing parameters, massive transformation occurs in 316L-Si due to a higher equivalent chromium to equivalent nickel ratio (1.73) than in 316L (1.46). Thus, twin boundary fractions in additively manufactured 316L can be increased via Si addition.
• Uterine healing after cesarean, Development of a rabbit model
  
  • Debras Elodie
  • Maudot Constance
  • Allain Jean-Marc
  • Pierangelo Angelo
  • Courilleau A.
  • Rivière Julie
  • Dahirel Michèle
  • Richard Christophe
  • Gelin Valerie
  • Morin Gwendoline
  • Capmas Perrine
  • Chavatte-Palmer Pascale
  , 2024.
• QuadWire: An extended one dimensional model for efficient mechanical simulations of bead-based additive manufacturing processes
  
  • Preumont Laurane
  • Viano Rafaël
  • Weisz-Patrault Daniel
  • Margerit Pierre
  • Allaire Grégoire
  Computer Methods in Applied Mechanics and Engineering, Elsevier, 2024, 427, pp.117010. This paper presents the basis of a new mechanical model named QuadWire dedicated to efficient simulations of bead-based additive manufacturing processes in which elongated beads undergoing significant cooling and eigenstrain are assembled to form 3D parts. The key contribution is to use a multi-particular approach containing 4 particles per material point to develop an extended 1D model capable of capturing complex 3D mechanical states, while significantly reducing computation time with respect to conventional approaches. Indeed, 3D models usually require at least 3 to 4 elements across the bead section, which results in fine discretization along the tangential direction to avoid conditioning issues, and therefore very fine mesh of the entire 3D part. In the QuadWire model, the bead height and thickness are internal dimensions, enabling a significantly coarser mesh along the tangential direction. Thus, although the QuadWire has 12 degrees of freedom per material point instead of 3 for classical models, the total number of degrees of freedom is reduced by several orders of magnitude for large parts. The proposed model is classically developed within the framework of the principle of virtual power and standard generalized hyperelastic media (i.e finite strain theory), which necessitates a thermodynamic analysis. Furthermore, the proposed approach includes native and manageable kinematic constraints between successive beads so that the stress state properly evolves during fabrication. Finite element analysis is used for numerical implementation under infinitesimal strain assumption for the sake of simplicity, and the QuadWire stiffness parameters are optimized so that the mechanical response fit conventional 3D approaches. To validate and demonstrate the capabilities of the proposed strategy, the evolution of displacements and stresses in fused deposition modeling of polylactide is simulated. (10.1016/j.cma.2024.117010)
  DOI : 10.1016/j.cma.2024.117010
• Spatial Heterogeneity of the Mechanical Properties in Photo-Curable Polymers
  
  • Sekmen Kübra
  • Constantinescu Andrei
  , 2024. Digital light processing (DLP) is one of the main additive manufacturing (AM) techniques that robustly builds 3D objects in a layer-by-layer fashion, via simultaneous in-plane photopolymerization. During the DLP 3D printing process, various sources of UV light heterogeneities can lead to variations in the final chemical, thermal, and mechanical properties in an unpredictable manner, depending on the specific printing conditions used. The small thickness of the printed layers imposes continuous UV light exposure to the previously printed layers. Moreover, in the printing plane, the UV light projected by micromirrors creates heterogeneous exposure at the level of each printed pixel. These phenomena induce uncontrolled photopolymerization resulting in a heterogeneous printed product. The layer-wise heterogeneity of UV curing, material properties, and shrinkage polymerization strain leads to the formation of surface wrinkles (see [1,2]). The wrinkle patterns can be explained by the following mechanism: the stiffer top layer tends to excessively relax stresses by introducing an out-of- plane strain through buckling. The presence of nanoscale wrinkles is a signature of excessive stresses and is a precursor of critical cracks and variations in the dimensions of parts, which are frequently reported for DLP 3D printing products. The presentation will discuss the previous topics based on experimental measurements and observations obtained with SEM and AFM microscopy.
• Porous materials : constitutive modeling and computational issues
  
  • Xenos Sokratis
  , 2024. This work is concerned with the development, calibration, and numerical implementation of a novel fully explicit isotropic, rate-independent, elasto-plastic model for porous metallic materials. The microstructure is assumed to consist of a random, with uniform probability, distribution of randomly oriented spheroidal voids of the same shape. The proposed model is based on earlier homogenization estimates that use a Linear Comparison Composite (LCC) theory. The resulting expressions exhibit the simplicity of the well known Gurson model and, thus, its numerical implementation in a finite element code is straightforward. To assess the accuracy of the analytical model, we carry out detailed finite-strain, three-dimensional finite element (FE) simulations ofrepresentative volume elements (RVEs) with the corresponding microstructures. Properparameter calibration of the model leads to fairly accurate agreement of the analytical predictions with the corresponding FE average stresses and porosity evolution. We show, both analytically and numerically, that the initial aspect ratio of the voids has a significant effect on the homogenized effective response of the porous material leading to extremely soft responses for flat oblate voids (e.g., aspect ratio less than 0.5) especially at high stress triaxialities.Next, we examine the computational issues related to the numerical implementation of rate-independent constitutive models that lead to softening behavior. It is shown analytically that elastic-plastic models based on ``local'' continuum formulations that do not incorporate a characteristic length scale may lead to loss of ellipticity of the governing partial differential equations (PDEs) and mesh-dependent numerical solutions. To remedy the associated numerical problems, we propose an implicit non-local version of the porous model developed in this work which is based on the introductionof a non-local porosity variable determined from the solution of an additional PDE. We show both analytically and numerically that the regularized version of the model allows for preservation of the elliptic properties of the governing equations yielding mesh-independent, converged solutions in the post-bifurcation regime. The bifurcation point (i.e., strain-to-localization) is found to be highly dependent on the micro-void's shape, with very flat voids (e.g., aspect ratio less than 0.3) leading to lower localization strains. The material length introduced by the non-local formulation is found tohave minimal effect on the predicted bifurcation point, only affecting the post-bifurcation gradient of the macroscopic stress-strain curve and the size of the highly strained zone in the structure.In the last part of this study, both the local and the non-local versions of the model are efficiently implemented in a commercial finite element code (ABAQUS). The models are used for the numerical solution of boundary value problems (BVPs) related to forming and ductile fracture processes under both quasi-static and dynamic conditions. In particular, the industrially relevant problems of Hole expansion (HET) and Charpy impact (CVN) test, the cup-and-cone fracture phenomenon as well as ductile fracture of a specimen with complex geometry and comparison with corresponding experimentalresults are analyzed in detail. Numerical predictions in all cases indicate that ductility is an increasing function of the void shape parameter and materials comprising flat oblate voids of low aspect ratio exhibit early macroscopic crack initiation and propagation compared to materials with spherical/almost spherical voids. Finally, the model's capability to reproduce experimental results with sufficient accuracy suggests that it can be utilized to provide predictions with only a small amount of parameters that may be calibrated from either micromechanics calculations or experimental data.
• Elastic Instability behind Brittle Fracture
  
  • Riccobelli D.
  • Ciarletta P.
  • Vitale G.
  • Maurini C.
  • Truskinovsky L.
  Physical Review Letters, American Physical Society, 2024, 132 (24), pp.248202. We argue that nucleation of brittle cracks in initially flawless soft elastic solids is preceded by a nonlinear elastic instability, which cannot be captured without accounting for geometrical precise description of finite elastic deformation. As a prototypical problem we consider a homogeneous elastic body subjected to tension and assume that it is weakened by the presence of a free surface which then serves as a site of crack nucleation. We show that in this maximally simplified setting, brittle fracture emerges from a symmetry breaking elastic instability activated by softening and involving large elastic rotations. The implied bifurcation of the homogeneous elastic equilibrium is highly unconventional for nonlinear elasticity as it exhibits an extraordinary sensitivity to geometry, reminiscent of the transition to turbulence in fluids. We trace the post-bifurcational development of this instability beyond the limits of applicability of scale free continuum elasticity and use a phase-field approach to capture the scale dependent sub-continuum strain localization, signaling the formation of actual cracks. (10.1103/PhysRevLett.132.248202)
  DOI : 10.1103/PhysRevLett.132.248202
• Multi-scale approaches to tire grip on wet roads
  
  • de Lorenzo Oliveira Matheus
  , 2024. This research presents the development of a nuanced contact model to analyze tire-road interactions, focusing on the complex interplay of tire tread patterns, road surface profiles, and the viscoelastic properties of rubber. The study integrates experimental, modeling, and numerical efforts, highlighting the challenges of addressing tribological contacts across multiple scales.Experimentally, viscoelastic behavior of industrial filled rubber mixes are explored through dynamic mechanical analysis and uniaxial tests, uncovering crucial non-linear effects regarding strain magnitude and strain rate sensitivity. Those aspects served as basis for the development and calibration of a finite non-linear viscoelastic material model, verified within a Finite Element environment against semi-analytical cases. This model facilitates the exploration of hysteresis-induced deformations in simplified landing-sliding contact experiments, aimed at minimizing adhesive contributions and temperature effects, leveraging both non-linear and classical viscoelastic models.Ultimately, a multi-scale frictional contact model is proposed capturing geometrical features of the ground and a non-linear viscoelastic material with complex geometry, yielding a reasonable correlation with experimental observations and capturing essential deformation trends within the sculpture.
• Génération de trajectoires en fabrication additive par projection de poudre pour contrôler la géométrie et la microstructure
  
  • Bréhier Michèle
  • Weisz-Patrault Daniel
  • Tournier Christophe
  , 2024. La fabrication additive est devenue un procédé très répandu ces dernières années en raison de sa capacité à produire des pièces de formes complexes. Cependant, malgré son utilisation généralisée, le contrôle des propriétés mécaniques des pièces métalliques fabriquées reste un défi majeur. Ces propriétés sont liées à la microstructure des pièces, laquelle dépend des paramètres du procédé et des stratégies de fabrication. Connaissant l’influence de certains de ces paramètres sur la microstructure, il est envisageable d’obtenir des microstructures différentes au sein d’une même pièce. Cela nécessite de modifier les paramètres pendant le procédé. Or, jouer sur des paramètres comme la vitesse de scan et la puissance du laser, n’aura pas seulement pour conséquence de modifier la microstructure, mais aura aussi un impact sur la morphologie des cordons déposés. Dans cette article, une méthode de calcul de trajectoires de fabrication additive est proposée pour garantir la modulation des paramètres au sein d’une même couche. Ainsi pour un ensemble de paramétries correspondant à des microstructures souhaitées dans différentes zones de la pièce, une trajectoire est calculée en 3 axes ou en 5 axes. Après avoir présenté la méthode de calcul, celle-ci est appliquée à un cas particulier constitué d’un mur fin mono cordon. La vitesse de scan de la buse diffère entre les deux zones extrêmes du mur de manière linéaire dans la zone de transition.
• Comparison of Mode I fracture toughness of an elastic and an elastoplastic methyl methacrylate polymer as measured by SENB and DCDC tests
  
  • Coq Arnaud
  • Diani Julie
  Engineering Fracture Mechanics, Elsevier, 2024, 306, pp.110237. An elastic and an elastoplastic methyl methacrylate polymer, both in the glassy state, have been submitted to mode I fracture characterization with two different tests, the single edge notch bending (SENB) and the double cleavage drilled compression (DCDC) tests. The elastic material toughness was simply assessed by the linear elastic fracture mechanics analysis. For the elastoplastic material, the $J$-integral was computed when the strain fields were available. Moreover, numerical analyses were carried out using finite element simulations with a phase-field damage approach, providing comparison when the $J$-integral had been calculated and estimate otherwise, of the critical energy release rate. For each material, as well as for each test, the values of the critical energy release rate that have been estimated here, are in good agreement with the literature. More interestingly, for the same material, both tests provide with very different estimates of this material parameter, leaving engineers uncertain on which test to choose to asses the material toughness in crack opening mode. (10.1016/j.engfracmech.2024.110237)
  DOI : 10.1016/j.engfracmech.2024.110237
• Sur la réponse intergranulaire pendant le traitement laser de l’acier inoxydable obtenu via fabrication additive : une étude de simulation thermomécanique
  
  • Mohanan Nikhil
  , 2024. Les contraintes résiduelles générées au cours du procédé de fabrication additive (FA) jouent un rôle non négligeable dans la réponse mécanique et la durabilité des pièces fabriquées. Comprendre comment les contraintes inter-granulaires et les déformation plastiques sont formées et évoluent lors d’un chauffage laser localisé est indispensable pour une optimisation des paramètres du procédé de fabrication afin d’obtenir des microstructures ayant une réponse mécanique souhaitée.Au cours d’une récente étude utilisant un nouveau dispositif combinant un laser continu avec un microscope électronique à balayage (L-MEB), une série de traitements lasers localisés, à passe unique, ont été effectuées sur un acier inoxydable 316L obtenu via FA. Les analyses microstructurales détaillées de cette étude ont permis de mettre en évidence un affinement des cellules intra-granulaires riche en Chrome et Molybdène (Cr-Mo), la formation de bandes de désorientation et, de dislocation géométriquement nécessaires au sein de la zone traitée au laser.Ce travail se focalise sur l’utilisation des données et analyses microstructurales acquises lors des expériences L-MEB mentionnées précédemment pour guider le développement d’un modèle polycristallin thermo-élasto-viscoplastique par éléments finis (TEVP-FE ) dans le cadre de petites déformations. Le développement du modèle TEVP-FE permet d’étudier l’évolution des contraintes inter-granulaires et des déformations plastiques au cours des traitements lasers. La nouveauté de cette étude réside dans la comparaison directe du modèle avec les mesures obtenues expérimentalement en surface de l’acier inoxydable 316L. Pour ce faire, des simulations de traitement laser ont été réalisées avec une approximation EBSD 2D de microstructure colonnaire extrudée.L’analyse des résultats à révéler que pour 93% des grains de la zone soumise au traitement par laser; le tenseur de densité de dislocation polaires (Nye) moyenné sur la surface supérieure de chaque grains, prédit se situe à un facteur deux (supérieur ou inférieur) du tenseur expérimental.Des recherches complémentaires ont permis d’étudier l’origine des contraintes résiduelle locales et des déformations plastiques. Sur la surface traitée au laser, la composante normale moyenne de contrainte résiduelle et la déformation plastique le long de la direction de balayage atteignent respectivement ~1.7 GPa et 0.04. De plus, la contribution de l’anisotropie élastique, de l’hétérogénéité plastique ainsi que l’effet de l’affinement des cellules de micro ségrégation Cr-Mo après les balayages laser ont également étés étudiés.Dans la continuité de l’approximation 2D de la microstructure, une étude comparative a été conduite. L’objectif a été d’évaluer les performances de l’approximation par rapport à une microstructure en 3D générée par des simulations séquentielles dynamiques des fluides couplés à une modélisation par champs de phases. Cette comparaison à révéler une concordance entre les prédictions 2D et 3D au niveau de la distribution de la moyenne des contraintes résiduelles et des déformations plastique, au niveau de la surface des grains.
• Un modèle micro-poro-mécanique du parenchyme pulmonaire
  
  • Genet Martin
  • Manoochehr Tayebi Mahdi
  • Bel Brunon Aline
  , 2024. Pour mieux comprendre le lien entre le comportement macroscopique du parenchymepulmonaire et ses caractéristiques géométriques et mécaniques microscopiques, nous avons développé un modèle micromécanique (à l'échelle alvéolaire) et étudié sa réponse globale (en termes de contrainte/déformation moyenne ainsi que de pression/porosité) à diverses sollicitations (contrainte moyenne, déformation ou pression). Nous avons également comparé sa réponse globale à celle d'un modèle poromécanique macroscopique (à l'échelle tissulaire) que nous avons récemment proposé pour le parenchyme pulmonaire.
• Quantification d'incertitudes pour la modélisation pulmonaire personnalisée
  
  • Peyraut Alice
  • Genet Martin
  , 2024. Le développement d’un modèle in-silico personnalisé de poumons pourrait permettre d’améliorer la prise en charge de différentes maladies, e.g. la fibrose pulmonaire idiopathique, en définissant des biomarqueurs obtenus en fusionnant modèles physiques et données cliniques. Une étape importante de la personnalisation est l’identification des paramètres de comportement et de chargement du modèle. Afin de quantifier la fiabilité de l’estimation, nous proposons dans ce travail une approche statistique, qui consiste à appliquer le processus d’identification sur des donnée synthétiques bruitées et biaisées.
• Modèle 1D enrichi pour le calcul mécanique rapide : approche multiparticulaire appliquée à la fabrication additive par dépôt de cordon
  
  • Preumont Laurane
  • Viano Rafaël
  • Weisz-Patrault Daniel
  • Margerit Pierre
  • Allaire Grégoire
  , 2024. Une nouvelle approche multiparticulaire (i.e., plusieurs champs de vitesse par point de matière) est présentée pour l’analyse mécanique des procédés de fabrication additive par dépôt de cordons. En effet, le modèle que nous proposons est un fil enrichi à quatre particules par point de matière permettant un maillage plus grossier dans la direction tangente du cordon, ce qui permet de réduire significativement le coût calculatoire. Le fondement théorique du modèle est rappelé brièvement et ses performances numériques (discrétisation aux éléments finis) sont comparées à un modèle 3D classique. Enfin, une étude paramétrique est proposée pour démontrer la pertinence et l’utilité de notre approche. Ce modèle mécanique rapide permet d’envisager des boucles d’optimisation sur des paramètres procédé tels que la vitesse de balayage et la puissance du laser.
• Optimisation topologique des coques épaisses avec la méthode level set en analyse isogéometrique multi-patches
  
  • Hubner Scherer Fernando
  • Zarroug Malek
  • Naceur Hakim
  • Constantinescu Andrei
  , 2024. Nous présentons un cadre d’optimisation topologique pour les coques épaisses en utilisant la méthode level set (LSM) couplée à l’analyse isogéométrique multi-patches (IGA). La description paramétrique de l’IGA permet d’extraire les géométries optimisées en format CAO. L’optimisation vise à trouver la distribution de matière dans la surface moyenne de la coque qui maximise la rigidité de la structure tout en minimisant son volume. L’approche est validée sur plusieurs exemples de coques 3D, suivant un modèle de Reisnner-Mindlin en élasticité linéaire.
• Réduction de modèles en dynamique non-linéaire pour la simulation de structures soumises à une famille de chargements
  
  • Daby-Seesaram Alexandre
  • Fau Amélie
  • Charbonnel Pierre-Étienne
  • Néron David
  , 2024. Cet article propose une stratégie multi-query utilisant l’information calculée lors de pre- mières simulations pour accélérer les calculs suivants. Cette stratégie repose sur le caractère non-incré- mental de la méthode LATIN en proposant une initialisation judicieuse du solveur non-linéaire. Afin de tirer au mieux parti de la redondance entre les simulations, cette méthode s’appuie sur une technique de réduction de modèles. Enfin, cette méthode a été dotée d’un cadre multi-fidélité lors de son application à la prédiction de probabilité de défaillance de structures soumises à des chargements incertains.
• Bayesian Identification of Surrogate Microstructure Generators
  
  • Eisenhardt Philipp
  • Khristenko Ustim
  • Wohlmuth Barbara
  • Constantinescu Andrei
  , 2024. The generation of heterogeneous microstructures using surrogate models plays an important role in order to quantify the resultant material properties given only limited specimen. Using Gaussian Random Fields, material microstructure realizations can be obtained through a surrogate model from which new realizations can quickly be generated. The given paper explores the opportunities of identifying the surrogate model parameters using Bayesian Inference. The use of stochastic methods enables the future application to uncertainty propagation, for example in the area of reliability analysis.
• Intergranular stress and plastic strain formation during laser scanning of an additively manufactured stainless steel: an experimentally-driven thermomechanical simulation study
  
  • Mohanan Nikhil
  • Macías Juan Guillermo Santos
  • Bleyer Jérémy
  • Helfer Thomas
  • Upadhyay Manas
  Materialia, Elsevier, 2024, 34, pp.102082. A novel experiment-driven modelling and simulation approach is proposed to study the formation of intergranular stresses and plastic strains during laser scanning of additively manufactured 316L stainless steel. Recently, laser scanning experiments were performed using a unique coupling between a continuous-wave laser and a scanning electron microscope. These experiments form the basis for the development of a thermo-elasto-viscoplastic polycrystal model endowed with the minimum necessary physics of the problem in order to facilitate simulating sufficiently large domains to obtain reasonable stress magnitudes. The case of a single laser line scan performed in vacuum is analyzed in detail. Polar dislocation density magnitudes and distribution predicted from the simulation are compared with those measured experimentally. Results reveal that for 93% of the grains in the lasered zone, a statistical measure of the predicted polar dislocation density (Nye’s) tensor lies within a factor of 2 (higher or lower) of the experimental one; this result sets a benchmark for future experiment-simulation comparisons. Subsequent investigation studies the origin of the local residual stresses and plastic strains. On the lasered surface, the grain surface-averaged normal residual stress component and plastic strain component along the scan direction reaches a value and 0.04, respectively. The contribution of elastic anisotropy, plastic heterogeneity and strengthening due to microstructure refinement after laser scanning on the formation of stresses and plastic strains is studied in detail. (10.1016/j.mtla.2024.102082)
  DOI : 10.1016/j.mtla.2024.102082
• On the influence of secondary branches on crack propagation in Rolling Contact Fatigue
  
  • Zaid Mael
  • Doquet V.
  • Chiaruttini Vincent
  • Depouhon Pierre
  • Bonnand Vincent
  • Pacou Didier
  International Journal of Fatigue, Elsevier, 2024, 182, pp.Article 108211. Gear and bearing failures are most often caused by rolling contact fatigue (RCF). Understanding the growth of a main surface-initiated crack into the depth of the piece, as well as the growth of subsurface-initiated branches towards the surface is necessary, in order to improve fatigue life prediction and reduce fatigue damage repair or component replacements before catastrophic failure. The purpose of this work is to analyze, based on 3D finite element simulations, the initiation and mode I growth of secondary branches in a case hardened gear, their influence on the main crack growth in mode II, and the competition between mode I and mode II crack growth. The residual stress field issued by the case hardening is taken into account and its role is analyzed. The reasons why branch cracks develop only from the upper main crack face and why only those initiated when the main crack is still shallow can reach the surface, inducing spalling are explained. (10.1016/j.ijfatigue.2024.108211)
  DOI : 10.1016/j.ijfatigue.2024.108211