Publications

2024

• Modeling and Estimation of Pulmonary Poromechanics : towards a Robust High-Fidelity Digital Twin Approach for Idiopathic Pulmonary Fibrosis
  
  • Peyraut Alice
  , 2024. Idiopathic Pulmonary Fibrosis (IPF) is a disease with an extremely severe prognosis, which directly affects the lung parenchyma, and whose mechanisms of appearance and progression remain poorly understood. The objective of this thesis work is to improve the understanding of IPF by coupling biomechanical modeling and biomedical image processing.Firstly, a review of the literature relating to IPF as well as current pulmonary models was conducted. Particular emphasis is placed on the analysis of the mechanisms that could explain the evolution of this pathology. Notably, the hypothesis of a close link between mechanics, and in particular stress concentrations, and the progression of fibrosis has been formulated in the literature.The first axis of this work focuses on improving the pulmonary poromechanical model developed in the M3DISIM team, by integrating gravity and removing contact with the rib cage. Including gravity in the model indeed allows to reproduce physiological heterogeneities of constraints and deformations during breathing, absent in the model without gravity, and also allows to take into account the orientation (e.g., pronation or supination) of the patient. The contact with the rib cage, unstable and numerically expensive, has been replaced by a pleural pressure field constrained to verify the global equilibrium, modeling all the forces applied on the outside of the lung. In addition, the identification of the parameters of a model is a crucial step for its personalization. Nevertheless, many methods exist, each with its own advantages and drawbacks in terms of robustness and cost. This study therefore proposes a method for quantifying the robustness to noise and model errors for various identification methods. In particular, a new formulation of the Equilibrium Gap Method (EGM) in large transformations is proposed. It is shown that the EGM, which is a direct method and therefore naturally quite unstable, when coupled with a regularization by equilibrium gap of the motion tracking problem, allows a robust estimation of the parameters.The third axis of this study focuses on the quantification of uncertainties on the identification of the parameters of the pulmonary poromechanical model from clinical images. The identifiability of the parameters, as well as their robustness to model and measurement errors, are analyzed in order to determine the best parameterization of the identification problem. The influence of the dataset used as input on the quality of the estimation is also evaluated.Finally, the last axis focuses on the application of the digital twin approach to longitudinal datasets of ten patients with IPF. For each patient, two images, one at the end-exhalation and the other at the end-inhalation, are provided at three different moments of the evolution of the disease. The identification of biomarkers likely to contribute to the explanation of the evolution of the disease is explored, in particular by studying the correlation between certain quantities of interest and the progression of fibrosis.This work constitutes an advance, in terms of modeling and personalization, of the digital twin of the lung developed by the M3DISIM team. It improves the physiology of the model, its numerical reliability, and quantifies the uncertainties related to measurement noise and model errors on the calculated biomarkers. These advances pave the way for promising clinical applications and provide initial results to better understand the evolution of Pulmonary Fibrosis.
• Exploring In-process lasering to alter microstructure and mechanical response of additive manufactured Ti-6Al-4V
  
  • Abdesselam Kouider
  , 2024. This thesis aims at (i) studying the impact of in-process laser heat treatments (LHTs) on microstructure evolution during laser directed energy deposition (LDED) of Ti-6Al-4V, and (ii) correlate this knowledge with an analysis of the as-built microstructure to understand the impact of LHTs on the mechanical response. Three samples were manufactured using a single-track bidirectional printing strategy with a laser operating at 300 W: (i) a reference sample (NHT) that did not undergo LHTs, and the other two subjected to LHTs at (ii) 100 W (LHT100) and (iii) 300 W (LHT300), respectively, after each layer deposition without powder addition. Operando X-ray diffraction (XRD) with Rietveld refinement allowed evaluating the impact of LHTs on hcp, bcc and liquid phases during and after building. Results revealed a strong evolution due to β → α′ and α′/α → β phase transformations occurring during printing and LHTs. Liquid phase was no longer identifiable after the addition of the 4th layer above the layer of interest (say L0). Adding more than 10 layers above L0 did not affect hcp and bcc phase content. Final hcp (∼97%) and bcc (∼3%) phase fractions revealed similar contents between samples, indicating that LHTs did not generate significant changes. A fast thermomechanical model was used to understand the contributions of thermal, elastic and phase transformation strains to the transient lattice strain evolution, and to estimate temperature from the predicted thermal strains. Comparisons betweenexperimentally estimated (by incorrectly assuming that all lattice strains are thermal strains, as is typically done in literature) and numerically computed temperatures showed a maximum difference of ∼64% made when phase transformation and elastic strains are neglected, further enhancing the crucial role of numerical modeling for accurate temperature estimation. Understanding temperature evolution during Ti-6Al-4V LDED will enable targeting LHTs conditions, to initiate α′ decomposition and microstructure coarsening (e.g., αd and β phase growth), thus affecting mechanical properties and helping to improve the strength/ductility trade-off of AM Ti-6Al-4V. Finally, the impact of LHTs on microstructure alteration and mechanical response of as-built samples was assessed by evaluating the contribution of each microstructural feature and internal strains to the mechanical response (along building direction (BD)and printing direction (PD)). Results revealed that all samples exhibit the same Young’s moduli, indicating that printing and LHTs resulted in at least a transversely isotropic response in the planeformed by BD and PD. LHT100 demonstrated a better strength/ductility trade-off compared to NHT. Meanwhile, LHT300, weaker in strength than NHT and LHT100, showed a significant improvement in ductility and toughness. Synchrotron XRD and electron microscopy demonstrated a minor contribution of β phase fraction, internal lattice strains, grain sizes, geometrically necessary dislocation densities,and texture to variations in mechanical response. The main contributions arose from the differences in diffusive αd (soft) and metastable α′ (hard) between samples. The occurrence of massive α was also observed in all samples, which content was higher in LHT100 (∼6.7%) but its proportion was found to be an order of magnitude lower than α′ and αd. This research highlights the potential of LHTs in engineering the microstructure of LDED Ti-6Al-4V during printing while either improving the strength/ductility trade-off or ductility and toughness without the need for additional heat treatments outside an AM machine. In this regard, LHTs can be further explored as potential replacements for traditional post-process heat treatments, such as annealing, to locally tune the microstructure in the bulk of the material.
• Compared Influence of a Lubricant on Mode I and Mode II Fatigue Crack Growth Kinetics in a Gear Steel
  
  • Doquet Véronique
  • Zaid Maël
  • Bonnand Vincent
  • Pacou Didier
  • Chiaruttini Vincent
  • Depouhon Pierre
  Fatigue and Fracture of Engineering Materials and Structures, Wiley-Blackwell, 2024, 48 (3), pp.1137-1150. The influence of a helicopter gearbox lubricant on Mode I or Mode II fatigue crack growth in 16NCD13 steel was characterized through tests performed on single-edge notched tensile samples loaded in tension–compression and on cruciform samples submitted to reversed shear plus static biaxial compression, respectively. In Mode I, the lubricant reduced the growth rate at low ΔKI and increased the threshold , while in Mode II, it accelerated crack growth at low ΔKIIeffective, which was not only due to a reduction in crack face friction. The upward convective flow of lubricant carrying debris exuding from the crack, a modification in oil aspect and properties, and chemical analyses near the crack front suggest that a temperature-induced degradation of the lubricant leads to a corrosive attack of the metal, which accelerates crack growth. A tribologically transformed structure is observed along the lips of cracks grown in Mode II with normal compression in oil. (10.1111/ffe.14541)
  DOI : 10.1111/ffe.14541
• Topological optimization of shells with isogeometric analysis
  
  • Hübner Scherer Fernando
  , 2024. This manuscript presents CAD-compatible optimization methods focusing on Reissner-Mindlin shells within the isogeometric analysis (IGA) paradigm. The main contribution is a novel framework for topological shape optimization of curved, non-conforming multi-patch and trimmed thick shells subjected to external loads.This approach integrates the level set method (LSM) with a diffuse interface, a Hadamard shape derivative, and multi-patch IGA into a gradient descent algorithm, enabling the systematic capture of shape evolution. This integration allows for direct manipulation of CAD-compatible geometries and analysis techniques, ultimately yielding results as a CAD surface.The method is applied to two optimization scenarios:(1) Compliance and volume minimization.(2) Stress-Based Optimization. A general cost function is proposed that combines two strategies. First, the p-norm of the von Mises stress approximates the maximum stress in the domain, providing a robust and effective means of reducing stress globally by accounting for contributions from all regions. Secondly, a local penalization of the stresses is implemented to prevent failure, fatigue, and plastification in the material phase, ensuring that the von Mises stress remains below the yield stress.The novelty of this approach lies in modeling the level set function as a NURBS surface, parameterizing complex three-dimensional shapes from a 2D parameter domain. This allows for the identification of the optimal material distribution within the mid-surface of the shell.The material is modeled under a small strain assumption in linear elasticity using a Reissner-Mindlin kinematic shell model in plane stress.The effectiveness of our approach is demonstrated on several curved non-conforming and trimmed multi-patch geometries in 3D.
• A finite strain viscoelastic model with damage and tension–compression asymmetry considerations for solid propellants
  
  • Gouhier F.
  • Diani J.
  • Vandenbroucke A.
  Mechanics of Materials, Elsevier, 2024, 199, pp.105152. A short survey on the experimental testing of solid propellants has highlighted finite strain responses that are temperature-dependent, viscoelastic with damage, and exhibit tension/compression asymmetry. Consequently, a finite strain viscoelastic model that satisfies the principles of thermodynamics has been developed. This model is based on the common multiplicative decomposition of the deformation gradient into elastic and viscous components, with considerations for damage and asymmetry. The model has been tested against three sets of data from the literature, carefully selected to represent the various characteristics of solid propellants. The model accurately reproduces uniaxial tension responses at different strain rates and temperatures, with the capability to account for superimposed hydrostatic pressure. Notably, these satisfactory representations require only five fitting parameters, in addition to the typical identification of polymer linear viscoelasticity and timetemperature superposition. Finally, an attempt to reproduce both tension and compression tests conducted independently on the same material underscores the need to account for tension-compression asymmetry, as defined in the proposed constitutive equations. This finding advocates for new tests, such as compression following tension and vice versa. (10.1016/j.mechmat.2024.105152)
  DOI : 10.1016/j.mechmat.2024.105152
• Mechanical properties of stromal striae, and their impact on corneal tissue behavior
  
  • Wu Qian
  • Giraudet Chloé
  • Allain Jean-Marc
  Journal of the mechanical behavior of biomedical materials, Elsevier, 2024, 160, pp.106770. Cornea is an essential element of our eye. The refractive power of the cornea is closely related to its shape, which depends on the balance between its mechanical properties and the intraocular pressure. However, in keratoconus, the shape of the cornea is altered, and the mechanical properties (i.e., elastic modulus and viscosity) are reduced. These alterations have been associated with the development of striae within the cornea. Recently, such striae have been observed in healthy corneas as well, but with slightly different shapes. Our study investigated the mechanical role of these striae. To this end, we performed an inflation test under Optical Coherence Tomography: tomographic volumes were acquired in the central zone of eleven human corneas during an inflation test. Striae planes were extracted from the segmented images, and principal deformation maps were obtained by Digital Volume Correlation (DVC). We observe that the pattern of the striae does not change with pressure, even far above physiological pressure. Maximum principal strains are co-localized with the striae and are oriented perpendicular to the striae. We also observe that principal deformations on the striae increase with depth in the cornea. Our results show that striae lead to greater deformability in the direction perpendicular to the striae, especially in the posterior part of the cornea where they are the most visible. This supports the idea that the striae are undulations in the cornea collagenous microstructure, which are progressively unfolded under loading. They decrease the global stiffness of the cornea, in particular in the posterior part, and thus may help in accommodating deformations. (10.1016/j.jmbbm.2024.106770)
  DOI : 10.1016/j.jmbbm.2024.106770
• Modélisation du comportement visco-hyperélastique endommageable de matériaux propergols
  
  • Gouhier Florian
  , 2024. Couramment utilisés par l’industrie aérospatiale du fait de leurs excellentes propriétés énergétiques, les matériaux propergols solides ont néanmoins un comportement mécanique complexe qui peut impacter leur rendement énergétique. En effet, l’apparition d’endommagement par décohésion charge/matrice induit l'apparition de microcavités qui peuvent coalescer et créer des fissures, ce qui s’avèrerait critique dans l'optique d'assurer une combustion optimale. L’échelle macroscopique à laquelle doit se faire le calcul des chargements réels nécessite donc la définition d’une loi de comportement macroscopique prenant correctement en compte le comportement viscoélastique endommageable de ces matériaux afin d’assurer la tenue en service sur une échelle de temps longs des moteurs propergols.L’objectif de la thèse est alors de proposer une telle loi de comportement, basée sur un formalisme de type milieux continus, en grandes déformations avec prise en compte de l’endommagement. Pour ce faire, les propriétés caractéristiques des matériaux propergols solides ont été identifiées à partir des résultats expérimentaux de la littérature. De cette analyse a découlé la proposition d’une loi viscoélastique en grandes déformations, thermodynamiquement admissible, avec endommagement isotrope et prise en compte de l’effet d’une pression hydrostatique venant retarder l’apparition de cavités. Cette loi, écrite dans le cadre classique de la décomposition multiplicative du gradient de déformation, a été définie en suivant un protocole d’identification des paramètres afin d’assurer sa validation par une comparaison avec divers essais menés sur les matériaux propergols. Enfin, une implémentation numérique du modèle dans le code éléments finis Abaqus, à l’aide de la définition d’une UMAT, a permis d’étendre l’utilisation du modèle aux cas de chargements non uniformes.
• Effect of active cooling on the formation of IN718 microstructures in directed energy deposition additive manufacturing
  
  • Bréhier Michèle
  • Weisz-Patrault Daniel
  • Tournier Christophe
  Rapid Prototyping Journal, Emerald, 2024, 31 (4), pp.685-696. Purpose -This paper focuses on laser metal powder directed energy deposition, which is used to repair parts or manufacture high-performance components. Fine and equiaxed microstructures are often targeted because of their homogeneous mechanical properties. However, doing so can only be done by either adjusting process parameters or using external actuators that necessitate additional equipment. This paper presents a method that circumvents these issues by using only the powder spray nozzle and inerting gas when the laser is switched off to actively cool the part without additional equipment. Design/methodology:approach -Single-bead IN718 thin walls were produced with a unidirectional strategy, taking advantage of the return path to actively cool the part. Six different sets of parameters were chosen to cover the operating range of laser power and machine scanning speed. Findings -Analysis of the EBSD maps of the walls highlights the impact of this active cooling strategy on the microstructure. A fine, untextured microstructure was observed, regardless of process parameters, which enables optimization of process parameters to maximize productivity instead of being conditioned by the targeted fine-equiaxed microstructure. The grain size obtained can be further refined by increasing the scanning speed of the actively cooled parts. Originality -An informed choice of off-production nozzle trajectories would enable reaching a homogeneous microstructure independently of process parameters. (10.1108/RPJ-04-2024-0184)
  DOI : 10.1108/RPJ-04-2024-0184
• Linear viscoelasticity of anisotropic carbon fibers reinforced thermoplastics: from micromechanics to dynamic torsion experiments
  
  • Merlette Thomas
  • Diani Julie
  Composites Part B: Engineering, Elsevier, 2024, pp.111931. <div><p>The link between experimental characterization and the constitutive behavior of an anisotropic linear viscoelastic unidirectional carbon fiber-reinforced thermoplastic composite is explored using micromechanics modeling. Dynamic torsion tests were conducted at 1 Hz over a wide temperature range, from the glassy to the rubbery states of the polymeric matrix, on both the pure matrix and the composite, for various cutting angles relative to the fibers. A two-step modeling procedure in the frequency domain is presented to predict and validate the effective behavior of the composite. The first step involves FFT-based homogenization, which maps the microstructure and constituent behaviors to effective transversely isotropic viscoelastic properties. The second step consists of finite element simulations using the effective behavior calculated from homogenization as input to replicate the experiments. A comparison between experimental results and model predictions across the entire temperature range is performed. The modeling predictions show good accuracy at low temperatures, where the matrix is in the glassy state. At high temperatures, where the matrix is in the rubbery state, the predicted behavior becomes too soft. As the phase contrast increases and the ratio of matrix bulk modulus to shear modulus rises significantly, the impact of fiber arrangement on the effective properties becomes more pronounced.</p></div> (10.1016/j.compositesb.2024.111931)
  DOI : 10.1016/j.compositesb.2024.111931
• Fast mesoscopic model of plasticity in polycrystals to compute probabilistic S-N curves in high cycle fatigue
  
  • Echerradi Insaf
  • Weisz-Patrault Daniel
  • Peigney Michaël
  , 2024. High cycle fatigue in polycrystals is mostly governed by deterministic laws such as crystal plasticity, but also depends on probabilistic properties, such as random defects and crystallographic and morphological textures, which result in significant scatter of fatigue lifetime at the macroscopic scale. Thus, modeling fatigue phenomena so that the probabilistic density function of failure is anticipated, would be useful especially for very high cycle fatigue involving up to 10^9 cycles. To do so, the grain structure with crystal orientations should be considered in full field computations, which usually involve prohibitive computation cost therefore hindering numerical exploration of statistical distribution of fatigue failures. This paper therefore consists in developing a very fast full field mesoscopic model of polycrystals subjected to crystal plasticity during cyclic loading based on energy minimization techniques. As a result, the uniform plastic slip in each grain is obtained in the form of a relatively simple recursive formula, which guarantees short computation time even for very high cycle fatigue. The proposed approach has been validated against a classical crystal plasticity finite element model in 2D, and satisfying agreement is observed. In addition the model has be applied in combination with classical fatigue criteria to rapidly compute the fatigue lifetime and then derive probabilistic S-N curves, hence creating a substantial link between crystallographic and morphological textures on the one hand, and fatigue lifetime estimations on the other hand.
• A comparison of finite strain viscoelastic models based on the multiplicative decomposition
  
  • Gouhier F.
  • Diani J.
  European Journal of Mechanics - A/Solids, Elsevier, 2024, 108, pp.105424. The constitutive equations of several finite strain viscoelastic models, based on the multiplicative decomposition of the deformation gradient tensor and written in a thermodynamically consistent framework, are reviewed to demonstrate their similarities and differences. The proposed analysis shows that dissipation formulations, which may appear different, are similar when formulated in the same configuration, allowing the definition of a unified general model. Then, the general model 's ability to reproduce the main features of the behavior of rubbers is explored. First, by comparing its responses to the ones of finite linear viscoelastic models commonly implemented in commercial finite element codes. Cases of monotonic uniaxial tension and simple shear, relaxation, and sinusoidal simple shear are considered. Second, by confronting a classic generalized Maxwell rheological scheme to a Zener one with a non-constant viscosity and exploring the relevance of both options within the general model 's constitutive equations. (10.1016/j.euromechsol.2024.105424)
  DOI : 10.1016/j.euromechsol.2024.105424
• Uniform boundary stabilization of a high-order finite element space discretization of the 1-d wave equation
  
  • Delaunay Tiphaine
  • Imperiale Sébastien
  • Moireau Philippe
  Numerische Mathematik, Springer Verlag, 2024. The objective of this work is to propose and analyze numerical schemes for solving boundary control problems or data assimilation problems by observers for wave propagation problems. The efficiency of the considered control or data assimilation strategy relies on the exponentially stable character of the underlying system. Therefore, the aim of our work is to propose a discretization process that allows preserving the exponential stability at the discrete level when using high-order spectral finite element approximation. The main idea is to add a stabilizing term to the wave equation that dampens the spurious oscillatory components of the solutions. This term is based on a discrete multiplier analysis that gives us the exponential stability of the semi-discrete problem at any order without affecting the approximation properties. (10.1007/s00211-024-01440-9)
  DOI : 10.1007/s00211-024-01440-9
• On Microstructure Development During Laser Melting and Resolidification: an Experimentally Validated Simulation Study
  
  • Chadwick Alexander F
  • Santos Macías Juan Guillermo
  • Samaei Arash
  • Wagner Gregory
  • Upadhyay Manas V
  • Voorhees Peter W
  , 2024. Integrating experiment and simulation provides invaluable insights into the critical parameters that determine the microstructure of alloys produced by additive manufacturing. Here, the grain structure formation due to solidification during single pass laser scans (mimicking bead-on-plate single tracks) on a 316L stainless steel is studied in situ inside a scanning electron microscope that is directly integrated with a continuous-wave laser. The grain size distribution before melting is used as an initial condition in a coupled phase-field/thermal multiphysics modeling framework. The predicted resolidified microstructures are found to agree favorably with those observed experimentally for multiple laser powers and scan velocities, indicating the validity of the overall model. Grain morphology is analyzed quantitatively, and the top surfaces are compared between the experiments and simulations. Analysis of the three-dimensional grain shapes predicted by the simulations shows that the length of the major axis of the resolidified grains is sensitive to laser power and scan speeds, while the length of the minor axis is not. Furthermore, the preferential alignment of the major axes of the grains depends on the melt pool geometry.
• Analyse des retours d'expérience en clientèle par des méthodes de traitement automatique du langage naturel pour identifier les modes de défaillance
  
  • Edeline Gwenaël
  , 2024. Les méthodes d'intelligence artificielle (IA), notamment le traitement automatique du langage (NLP), offrent des possibilités révolutionnaires pour l'analyse des retours d'incidents en clientèle, qui permettent en particulier d'évaluer la fiabilité réelle d'un système en clientèle et de faire une projection de fiabilité à partir de l'identification préalable d'une loi de Weibull sur les incidents. Le présent article détaillera un outil d'IA développé pour attribuer automatiquement un mode de défaillance à chaque retour client, en exploitant des techniques de NLP et de modélisation par Machine Learning (ML). L'approche proposée de prétraitement des données et de classification des retours clients sera décrite. Les résultats obtenus démontreront l'efficacité de notre approche pour faciliter le travail des ingénieurs FMDS et fournir un traitement des réclamations clients précis et rapide.
• Stress-based topological shape optimization for thick shells using the level set method and trimmed non-conforming multi-patch isogeometric analysis
  
  • Hübner Scherer Fernando
  • Zarroug Malek
  • Naceur Hakim
  • Constantinescu Andrei
  Structural and Multidisciplinary Optimization, Springer Verlag, 2024, 67 (10), pp.177. This paper introduces a novel method for optimal shape design of thick shells. We consider shells based on the Reissner-Mindlin theory, with the assumption of linear elastic material behavior. The goal is to find the optimal material distribution within the shell's mid-surface. This is achieved using a cost function that minimizes the volume while considering stressbased constraints, with the material distribution represented by a level set function. The evolution of the shape is driven by the gradient of the cost function within the framework of a Hamilton-Jacobi equation. Both the level set and the displacement fields are described using computer aided design compatible tools, within the framework of isogeometric analysis. This allows for precise definition of the optimal shape and straightforward export of the resulting design to commercial software for manufacturing. Furthermore, the proposed method handles complex, non-conforming multi-patch geometries thanks to an augmented Lagrangian formulation. The latter guarantees strong compatibility with real-world engineering applications. The effectiveness of the method is demonstrated through its application to various three-dimensional multi-patch geometries under different loading conditions. (10.1007/s00158-024-03892-x)
  DOI : 10.1007/s00158-024-03892-x
• Digital twins for chronic lung diseases
  
  • Gonsard Apolline
  • Genet Martin
  • Drummond David
  European Respiratory Review, European Respiratory Society, 2024, 33 (174), pp.240159. Digital twins have recently emerged in healthcare. They combine advances in cyber–physical systems, modelling and computation techniques, and enable a bidirectional flow of information between the physical and virtual entities. In respiratory medicine, progress in connected devices and artificial intelligence make it technically possible to obtain digital twins that allow real-time visualisation of a patient's respiratory health. Advances in respiratory system modelling also enable the development of digital twins that could be used to predict the effectiveness of different therapeutic approaches for a patient. For researchers, digital twins could lead to a better understanding of the gene–environment–time interactions involved in the development of chronic respiratory diseases. For clinicians and patients, they could facilitate personalised and timely medicine, by enabling therapeutic adaptations specific to each patient and early detection of disease progression. The objective of this review is to allow the reader to explore the concept of digital twins, their feasibility in respiratory medicine, their potential benefits and the challenges to their implementation. (10.1183/16000617.0159-2024)
  DOI : 10.1183/16000617.0159-2024
• Kalman-based estimation of loading conditions from ultrasonic guided wave measurements
  
  • Dalmora Andre Luiz
  • Imperiale Alexandre
  • Imperiale Sébastien
  • Moireau Philippe
  Inverse Problems, IOP Publishing, 2024, 40, pp.115009 (44 p.). Ultrasonic guided wave-based Structural Health Monitoring (SHM) of structures can be perturbed by Environmental and Operations Conditions (EOCs) that alter wave propagation. In this work, we present an estimation procedure to reconstruct an EOC-free baseline of the structure suitable for SHM from the only available Ultrasonic guided wave measurements. Our approach is model-based, i.e. we use a precise modeling of the wave propagation altered by structure loading conditions. This model is coupled with the acquired data through a data assimilation procedure to estimate the deformation caused by the unknown loading conditions. From a methodological point of view, our approach is original since we have proposed an iterated Reduced-Order Unscented Kalman strategy, which we justify as an alternative to a Levenberg-Marquardt strategy for minimizing the non quadratic least-squares estimation criteria. Therefore, from a data assimilation perspective, we provide a quasi-sequential strategy that can valuably replace more classical variational approaches. Indeed, our resulting algorithm proves to be computationally very effective, allowing us to successfully apply our strategy to realistic 3D industrial SHM configurations. (10.1088/1361-6420/ad7e4b)
  DOI : 10.1088/1361-6420/ad7e4b
• Topology optimization of curved thick shells using level set method and non-conforming multi-patch isogeometric analysis
  
  • Hübner Scherer Fernando
  • Zarroug Malek
  • Naceur Hakim
  • Constantinescu Andrei
  Computer Methods in Applied Mechanics and Engineering, Elsevier, 2024, 430, pp.117205. We present a novel framework for topological shape optimization of curved non-conforming multi-patch and trimmed thick-shells subjected to external loads. Our method integrates the level set method (LSM) with a diffuse interface, a Hadamard shape derivative, and multi- patch isogeometric analysis (IGA) into a gradient descent algorithm to systematically capture the evolution of the shape. This integration enables us to directly manipulate CAD-compatible geometries and analysis techniques and to obtain the results as a CAD surface. The novelty lies in the utilization of multi-patch IGA models based on NURBS functions, which allows us to simultaneously maximize the stiffness and minimize the volume of the shell by searching for an optimal material distribution within its middle surface. The material is modeled under a small strain assumption in linear elasticity using a Reissner–Mindlin kinematic shell model in plane stress. The effectiveness of our approach is demonstrated on several curved conforming and non-conforming multi-patch geometries in 3D. (10.1016/j.cma.2024.117205)
  DOI : 10.1016/j.cma.2024.117205
• Upscaling transformation plasticity using full field fast Fourier transform simulations of polycrystals undergoing phase transformations under applied loads
  
  • Nambiyankulam-Hussain Shahul-Hameed
  • Weisz-Patrault Daniel
  • Appolaire Benoît
  • Denis Sabine
  • Settefrati Amico
  , 2024. Transformation plasticity has been intensively studied because of its significant impact on various industrial fabrication and forming processes. The widely used analytical macroscopic models are based on idealized microstructures and strong assumptions. Such models predict linear (or weakly non-linear) dependence between the transformation plastic strain rate and the applied load, whereas experimental evidence shows that this dependence becomes highly non-linear when the applied stress becomes non-negligible with respect to the macroscopic yield stress. Such a non-linear response is not fully understood especially for phase transformations arising at high temperatures for which the product phase is often softer than the parent phase, and involving visco-plastic behavior.<p>Therefore to overcome this difficulty, the first key contribution of this paper is to exhibit the detailed mechanisms leading to transformation plasticity in steels undergoing austenite to ferrite phase transformation at high temperature and to explain the non-linear dependence between the transformation plastic strain and the applied load. To do so, full-field simulations of visco-plastic polycrystalline aggregates undergoing phase transformations under applied load are performed. In addition, the second key contribution consists in upscaling the outcomes obtained at the scale of the polycrystal into a macroscopic statistical model, that can be used for large simulations of industrial processes. To do so, a database of computations with various initial microstructures, grain shape distributions, and applied loads have been performed, and used to derive the macroscopic statistical model. Of course, to create such a database, a relatively short computation time should be obtained for the full-field simulations, which is achieved by using a fast Fourier transform-based algorithm.
• A fictitious domain method with enhanced interfacial mass conservation for immersed FSI with thin-walled solids
  
  • Corti Daniele
  • Diaz Jérôme
  • Vidrascu Marina
  • Chapelle Dominique
  • Moireau Philippe
  • Fernández Miguel Angel
  , 2024. In this paper, we extend the low-order fictitious domain method with enhanced mass conservation presented in [ESAIM: Math. Model. Numer. Anal., 58(1):303-333, 2024] to the case of coupling with immersed thin-walled solids. Both surface and 3D-shell models are considered for the description of the solid, including contact between solids. For both models, the interface coupling is enforced on the mid-surface of the shell using a stabilized Lagrange multiplier formulation. Numerical examples in both two and three dimensions illustrate the effectiveness of the method, including its successful application to the simulation of aortic heart valve dynamics.
• Dispersion and ellipticity of Rayleigh waves in a soil substrate supporting resonant beams and plates
  
  • Marigo Jean-Jacques
  • Pham Kim
  • Maurel Agnès
  • Guenneau Sébastien
  Physical Review B, American Physical Society, 2024, 110 (9), pp.094110. The behavior of surface waves in a soil supporting an array of beams in three dimensions, or an array of plates in two dimensions, with compressional and flexural resonances is examined both theoretically and numerically. Our findings demonstrate that Love waves, characterized by displacements perpendicular to the sagittal plane, can propagate even without a homogeneous guiding layer, owing to the influence of flexural resonances in beams. Within the sagittal plane, hybridized Rayleigh waves exhibit a dispersion that is notably altered by the presence of the array, with their properties emerging from the interaction between flexural and compressional resonances. Notably, we uncover the coexistence of two Rayleigh waves with distinct wave numbers within specific frequency ranges, corresponding to prograde and retrograde motions. Additionally, both waves significantly amplify ground motion, either horizontally or vertically. Similar physics, yet quantitatively different, is demonstrated in the case of plate arrays. (10.1103/PhysRevB.110.094110)
  DOI : 10.1103/PhysRevB.110.094110
• A finite deformation theory of dislocation thermomechanics
  
  • Lima-Chaves Gabriel Dante
  • Acharya Amit
  • Upadhyay Manas V
  , 2024. A geometrically nonlinear theory for field dislocation thermomechanics based entirely on measurable state variables is proposed. Instead of starting from an ordering-dependent multiplicative decomposition of the total deformation gradient tensor, the additive decomposition of the velocity gradient into elastic, plastic and thermal distortion rates is obtained as a natural consequence of the conservation of the Burgers vector. Based on this equation, the theory consistently captures the contribution of transient heterogeneous temperature fields on the evolution of the (polar) dislocation density. The governing equations of the model are obtained from the conservation of Burgers vector, mass, linear and angular momenta, and the First Law. The Second Law is used to deduce the thermodynamical driving forces for dislocation velocity. An evolution equation for temperature is obtained from the First Law and the Helmholtz free energy density, which is taken as a function of the following measurable quantities: elastic distortion, temperature and the dislocation density (the theory allows prescribing additional measurable quantities as internal state variables if needed). Furthermore, the theory allows one to compute the Taylor-Quinney factor, which is material and strain rate dependent. Accounting for the polar dislocation density as a state variable in the Helmholtz free energy of the system allows for temperature solutions in the form of dispersive waves with finite propagation speed, despite using Fourier's law of heat conduction as the constitutive assumption for the heat flux vector.
• On the thermomechanics of field dislocations
  
  • Lima Chaves Gabriel
  , 2024. This thesis investigates the coupling between dislocation evolution and heat conduction in continuum bodies through a theoretical and numerical approach. The main objectives are twofold: (i) to develop a finite deformation theory of thermomechanics of field (i.e. continuously represented) dislocations that account for the interplay between dislocation activity and temperature evolution, while considering only observable fields; (ii) to propose a geometrical linearisation of the finite deformation theory showing that it is similar to the small deformation thermal field dislocation mechanics (TFDM) theory proposed in Upadhyay,J. Mech. Phys. Solids, 145 (2020) 104150, and numerically implement the latter using the finite element (FE) approach to study temperature evolution during dislocation transport.The fundamental aspects of dislocation modelling are reviewed, highlighting the different approaches that have commonly been used to study dislocation-based plasticity in crystals. After identifying the current limitations of the state of the art, a theory with a novel kinematics for thermo-elastoplastic problems based on dislocation mechanics in a finite deformation framework within a transient heterogeneous temperature field is proposed. The theory does not require the specification of a global reference configuration, whence we do not make use of a multiplicative decomposition of the deformation gradient into elastic, plastic, and thermal parts. Instead, considering only observable state variables, we show that the kinematics based on the conservation of Burgers vector is sufficient to yield the commonly-accepted additive decomposition of the velocity gradient into elastic, plastic, and thermal distortion rates. Accounting for the polar dislocation density as a state variable in the Helmholtz free energy of the system, using the first and second laws of thermodynamics, we obtain a new structure of the temperature evolution equation, which allows for solutions in the form of dispersive waves with finite propagation speed without a second derivative of the temperature field in time.The developed theory is shown to reduce, when geometrically linearised, to the small-strain TFDM theory previously proposed. Then, the focus is turned to the latter, and the variational forms of its partial differential equations (PDEs) are presented. Using an open-source library designed to solve PDEs with the FE method, the variational forms are implemented in a staggered algorithm. The implementation is verified against an analytical solution for the temperature field generated by a moving dislocation, and excellent agreement is obtained. Some of the TFDM capabilities are then explored in examples of the heat generated by single edge/screw dislocation, dislocation annihilation, and dislocation loop expansion, which provide a clear understanding of the transient thermoelastic and plastic heat sources involved in each case.The present research advances the field of continuum dislocation modelling by proposing a novel theoretical framework, as well as the numerical implementation of its linearised version. This work serves as a basis for understanding the evolution of dislocation structures during different thermomechanical processes, such as metal additive manufacturing, welding, quenching, etc., which would ultimately contribute to better controlling the mechanical properties of manufactured parts. Future work would include an extension of the numerical implementation to the general finite-deformation theory proposed, as well as an upscaling of the latter to account for the role of statistically stored dislocations in classical problems of plasticity.
• Using Novel Printed Piezoelectric Sensors for Monitoring the Health of a Composite Foreign Object Damage Panel
  
  • Paunikar Shweta
  • Rébillat Marc
  , 2024. This research focuses on the structural health monitoring (SHM) of a foreign object damage (FOD) composite panel substructure of an aircraft engine fan blade equipped with an architecture array of novel screen printed piezoelectric sensors and is being carried out within the purview of the MORPHO – H2020 project. The state of the art printing technology ensures that architecture network of printed sensor is not only non-intrusive and lightweight but can also be printed during the manufacturing process before the structure goes into service. The FOD panel in this work is made of 3D woven composite, measuring approximately 800 mm x 350 mm, with a stainless-steel leading edge bonded to one of the longer edges and hosts a network of 5 arrays of 5 printed sensors each. The printed sensors can potentially be used in multiple ways to analyse the health of the host structure. Since the fabrication process of the sensors is an on-going research, first the electromechanical behaviour of the sensors is analysed with the help of impedance measurements. It is observed that the printing process ensures repeatability. Secondly, the performance of the printed sensors in case of impact loading is discussed here, as bird impact is one of the leading causes of engine fan blade failure. The impact response measured by the printed sensors is studied to detect the impact location on the FOD panel. Next, the ability of the printed sensors to sense ultrasonic guided wave responses generated by standard ceramic piezoelectric disc actuators is demonstrated. Finally, the health of these printed sensors upon undergoing multi-load multi-cycle bending tests is also discussed here. The ultimate goal of this project is to create diverse diagnostic and prognostic techniques for estimating the remaining lifespan and Structural Health Monitoring (SHM) of the FOD panel based on the range of measurements gathered using the printed sensors.
• Modeling-based Radial Pressure Waveform Reconstruction Using Photoplethysmography Signals
  
  • Diaz Jérôme
  • Kimmig François
  • Vallée Fabrice
  • Le Gall Arthur
  • Kirszenblat Romain
  • Willemet Marie
  • Moireau Philippe
  , 2024, 51. <div><p>This study introduces a model linking photoplethysmography (PPG) dynamics to radial pressure waveform (RPW), which could be integrated into digital twins, that enables the reconstruction of RPW from PPG measurements using pulse pressure extrema. Built upon existing literature and supervised symbolic regression on anesthesia data, the model was validated on 581 continuous 10 seconds subsequences from 24 patients. Calibration through an unscented Kalman filter ensured patient-specific accuracy, yielding an averaged Pearson correlation coefficient of 0.955 for the reconstructed signal. The model's ordinary differential equation (ODE) with three parameters showed consistency with existing models. The stable, identifiable parameters underscore the model's robustness. The proposed model gives some insights into the physiology hidden behind the PPG and paves the way for RPW reconstruction using non-invasive measurements.</p></div> (10.22489/CinC.2024.332)
  DOI : 10.22489/CinC.2024.332