Publications

2025

• Silicon-Based Microscale Multistable Metamaterials: Microfabrication and Characterization
  
  • Bronstein E.
  • Ilssar D.
  • Kannan Vignesh
  • Kochmann D.M.
  Experimental Mechanics, Society for Experimental Mechanics, 2025. Abstract Background The design space of multistable reconfigurable metamaterials, typically constructed of bistable unit cells, is virtually limitless; yet, many existing fabrication methods suffer from low spatial resolution or limited build volumes. This limits scalability and the construction of complex architectures composed of numerous building blocks. Microfabrication on silicon wafers overcomes these limitations, offering a scalable manufacturing route for architectures with large numbers of unit cells on a single wafer. Actuating and measuring the unstable response of microscale bistable structures is not trivial, calling for the development of specialized experimental tools. Objective (i) A scalable microfabrication protocol for creating multistable metamaterials composed of unprecedented numbers of bistable unit cells. (ii) An experimental method for actuating microscale bistable structures and characterizing their mechanical response to quasistatic loading in situ . Methods We employ microfabrication to realize free-standing, silicon-based, wafer-scale multistable metamaterials using photolithography, deep reactive ion etching, and vapor hydrogen fluoride etching, along with an experimental setup leveraging a micro-needle, a position-sensing detector, and in-situ full-field imaging for actuation and characterization. Results Bistable structures with a range of design parameters, along with various multistable chains comprising 5, 10, and 100 unit cells, have been successfully microfabricated on a single wafer. The non-monotonic force-displacement relations, characteristic of bistable structures, have been measured, linking structural design to mechanical behavior through experiments. Conclusions The established framework enables the creation and characterization of unit cells with tunable multistability, admitting closed-loop feedback between structural design, microfabrication, and characterization. This lays the foundation for metamaterial architectures with diverse functionality. (10.1007/s11340-025-01258-y)
  DOI : 10.1007/s11340-025-01258-y
• Réseaux de neurones pour accélérer la simulation thermo-mécanique des solides à comportement irréversible
  
  • Lesueur Louis
  , 2025. Une large classe de problèmes non linéaires, comme ceux rencontrés en élastoplasticité à grandes transformations, nécessite traditionnellement des simulations coûteuses par éléments finis pour obtenir des solutions approchées. Cette thèse explore l’utilisation des réseaux de neurones, parmi les dernières avancées en apprentissage automatique, comme modèles de substitution aux méthodes par éléments finis. Elle se concentre spécifiquement sur le cas de l’élastoplasticité à grandes transformations. Ces modèles permettent de réduire significativement les temps et les ressources de calcul, tout en rendant possible la simulation en temps réel. Ce travail ouvre ainsi la voie à des applications concrètes, notamment dans des domaines comme la fabrication additive. (10.70675/e9edbfffz81cdz4e4dza4eez9bd681eef286)
  DOI : 10.70675/e9edbfffz81cdz4e4dza4eez9bd681eef286
• Imaging-based multi-scale investigation on inter- and intra-granular deformation, damage, and healing micro-mechanisms of natural salt rock
  
  • Li Xinjie
  , 2025. The deformation, damage, and healing mechanisms of salt rock, an optimal medium forl arge-scale underground hydrogen storage, are studied through in-situ experiments. Two coarse-grainedand one fine-grained natural salt rocks, as well as are-synthetic salt rock, are first tested under uniaxial conditions combined with optical and SEM-based observation. Local strain maps computed with DIC reveal strong strain localization on the grain bounda-ries for natural salt rocks. Deformation related to CSPand GBS is quantified separately by computing and segmenting the strain field through phase partition,revealing the co-existence of both mechanisms fromthe onset of plasticity and their stable contributions to the overall deformation. A third mechanism, intra-granular cracking, is also observed and is shown to be necessary to accommodate the accumulated deformation when the combined action of CSP and GBSis not sufficient. Secondly, the research is extendedto triaxial conditions on the fine-grained natural salt sample. The initiation and evolution of micro-cracksare followed with X-ray CT, as well as the operation of the dissolution-precipitation mechanism that modifies the morphology of interfaces. A comprehensive comparison between natural salts and synthetic salts indicates a higher level of activation of grain boundaries for natural salts. Finally, a healing test under confinement and in the presence of brine is conducted on apre-ruptured fine-grained natural salt sample, allowing the partial sealing of micro-cracks and grain growth in stress-free regions, promoted by fluid-assisted mass transfer, to be observed via tomography imaging. (10.70675/7ca37fc0z4ef8z48aezb214z37fa8cee1d7a)
  DOI : 10.70675/7ca37fc0z4ef8z48aezb214z37fa8cee1d7a
• 3D finite element investigation of hyperelastic foam behavior. I. Voronoi closed-cell microstructures
  
  • Merlette Thomas C
  • Diani Julie
  Mechanics of Materials, Elsevier, 2025, pp.105566. <div><p>The mechanical behavior of isotropic, elastomeric, Classical Voronoi closedcell foams is investigated numerically using 3D finite element simulations under finite-strain uniaxial compression, and infinitesimal-strain shear and hydrostatic loading conditions. Foam microstructures with porosities ranging from 77% to 95% and narrow pore volume distributions were generated by subtracting irregular polyhedra, obtained from Voronoi tessellations of well dispersed seed points, from a cubic matrix. Severe finite-strain uniaxial compression, up to 95% nominal strain, was simulated using the Abaqus/Explicit solver. Parametric studies revealed that the compressive response of the foams scales proportionally with the factor (1 -c) 2 , where c denotes the porosity. Moreover, at high porosities (typically 90%), the influence of the base polymer's hyperelasticity reduces to its initial shear modulus µ 0 , since the matrix undergoes only limited strain, whereas the effect of the polymer's large-strain behavior becomes significant at lower porosities (typically 77%). As a result, all stress-strain curves collapse onto a single master curve when the stress is normalized by µ 0 (1 -c) 2 . The effect of internal gas pressure within the closed cells was also assessed numerically and compared against experimental data, validating the simple analytical model proposed by Gibson and Ashby (1997). At small strains, the shear modulus is accurately predicted by the Differential Hollow Sphere Assemblage (DHSA) originally developed for spherical voids. However, the same model was found to overestimate the bulk modulus, and a phenomenological correction is therefore proposed to enable rapid and more accurate estimation of this quantity.</p></div> (10.1016/j.mechmat.2025.105566)
  DOI : 10.1016/j.mechmat.2025.105566
• A general UMAT for finite-strain viscoelasticity with damage
  
  • Gouhier Florian
  • Diani Julie
  Finite Elements in Analysis and Design, Elsevier, 2025, 252, pp.104468. A UMAT for general finite-strain viscoelastic materials exhibiting strain softening and temperature dependence is presented and shared. The model builds on the thermodynamically consistent formulation of Reese and Govindjee (1998), extended to support a general deviatoric strain energy function depending on the invariants I1 and I2, as well as isotropic damage mechanisms affecting both deviatoric and hydrostatic responses. The paper first outlines the modeling assumptions and describes the numerical implementa- tion, including modifications for the flexible incorporation of general strain energy functions, compatibility with hybrid finite elements, and the structure of the UMAT subroutine. The implementation is validated through a series of uniaxial and shear benchmark tests under various loading conditions. Finally, a structural simulation involving the cyclic torsion of a slender rectangular bar confirms the correct implementation of the consistent tangent modulus. The proposed UMAT is versatile and applicable to a broad class of materials, including quasi-incompressible rubbers exhibiting Mullins softening and solid propellants undergoing volumetric damage due to matrix-filler debonding. (10.1016/j.finel.2025.104468)
  DOI : 10.1016/j.finel.2025.104468
• Residual stress control in large-format additive manufacturing of polylactic acid via a digital twin and in-operando imaging
  
  • Viano Rafaël
  • Demont Léo
  • Margerit Pierre
  • Mesnil Romain
  • Caron Jean-François
  • Weisz-Patrault Daniel
  Materials & Design, Elsevier, 2025, 260, pp.114870. Polymer-based Large Format Additive Manufacturing (LFAM) is an extrusion-based technology that deposits large-diameter polymer beads using a robotic arm-mounted nozzle. However, slow cooling rates and heat accumulation generate technical challenges, including significant deformation that requires nozzle path adjustments and the buildup of residual stresses from thermo-chemical shrinkage that may cause debonding. This study integrates two fast modeling approaches, ScanFast (thermal) and QuadWire (mechanical), to reduce the number of degrees of freedom compared to conventional methods while maintaining accuracy. A computationally efficient digital twin of the process is developed and validated experimentally on a thin wall printed with polylactic acid. Anisotropic material properties are characterized, and in-operando temperature and displacement fields are measured using infrared thermography and backward Digital Image Correlation. The results show correlation coefficients greater than 0.80 between experimental and numerical data. The validated digital twin is then applied to assess the influence of process parameters on three key aspects: (i) the number of layers above the glass transition temperature, (ii) residual stress development, and (iii) positional offset between the nozzle and the structure. The proposed approach provides an efficient tool to optimize process parameters and nozzle trajectories, thereby enhancing the quality and manufacturability of LFAM-produced parts. (10.1016/j.matdes.2025.114870)
  DOI : 10.1016/j.matdes.2025.114870
• PlastiNN: a Neural Network architecture for Finite Strain Elastoplasticity
  
  • Lesueur L
  • Thorin Anders
  • Weisz-Patrault Daniel
  , 2025. <div><p>Fields such as materials science (metal forming, forging, additive manufacturing) and automotive engineering (crash simulations) can involve finite strain elastoplastic simulations. These simulations are traditionally carried out using computationally intensive</p></div> (10.57745/HQJMYA)
  DOI : 10.57745/HQJMYA
• Stress dependence of the chemical potential of lithium in a silicon electrode
  
  • Le Anh Tuan
  • Bruant Xavier
  • Phung Ngoc Tram
  • Ozanam Francois
  • Rosso Michel
  • Guin Laurent
  Journal of the Mechanics and Physics of Solids, Elsevier, 2025. We report operando measurements and concurrent modeling of the stress dependence of the chemical potential of lithium in a silicon electrode. An experimental study is carried out on hydrogenated amorphous silicon thin films in which the electrode stress state is modified operando during electrochemical lithiation and delithiation by applying an external mechanical load. During galvanostatic cycling, the electrode is periodically subjected to a tensile strain, inducing stress variations that are reflected in voltage changes. The measured stress-induced voltage changes are interpreted using a well-established chemomechanical model of lithium insertion in silicon. Comparison of voltage measurements with model predictions allows us to determine the concentration-dependent Young's modulus (from 29 GPa to 26 GPa with increasing lithium content) and some of the viscoplastic parameters of lithiated silicon. The calibrated model shows good predictive capability when applied to lithiation cycles performed at a C-rate different from that of the calibration cycle. However, it shows limitations in explaining voltage changes under delithiation. These results show that thermodynamically-consistent chemomechanical models of lithiation not only adequately describe the effect of lithium insertion and deinsertion on stress, as already shown in the literature, but also capture the reverse effect of stress on lithium insertion. In this respect, this work opens up new perspectives for the quantitative validation and calibration of existing diffusion-deformation theories, notably by highlighting their possible limitations. (10.1016/j.jmps.2025.106421)
  DOI : 10.1016/j.jmps.2025.106421
• INCOMPATIBLITY-GOVERNED DEFORMATIONS: TOWARDS A NEW MODEL OF SMALL-STRAIN ELASTOPLASTICITY
  
  • Amstutz Samuel
  • Le Thien-Nga
  • van Goethem Nicolas
  , 2025. <div><p>We describe a novel formalism for elasto-plastic deformations based on the strain incompatibility, to model an elastic solid filled with dislocations, hence subject to plastic deformations, at the macroscopic scale and under a time-discrete quasi-static framework. The main kinematical descriptor is the strain tensor E, that we define from a mesoscopic analysis. The associated state equations, as derived from a virtual work approach, are second-gradient in E, because they explicitly incorporate the incompatibility inc E, and are linear. Due to the introduction of an internal variable θ and a dissipation potential, related to the motion of dislocations, the overall problem is variational and nonlinear. It is numerically solved by alternating minimization with respect to (E, θ). Numerical simulations are performed to assess both loading-unloading and evolutionary problems on some simple two-dimensional geometries. Elaborating on previous works by the authors, the present contribution is an in-depth description of an alternative approach to elasto-plastic deformations, grounded on firm mathematical basis, and consolidated by numerical results. By nature, this approach is multi-scale, therefore opening the way to a comprehensive study of strain incompatibility, dislocations and plasticity as a complex interaction of multiscale phenomena, of which hardening is only an archetypal example.</p></div>
• Dynamic behavior of anisotropic polystyrene foams
  
  • Iaccarino Paolo
  • Eisenhardt Philipp
  • Auricchio Ferdinando
  • Di Maio Ernesto
  • Constantinescu Andrei
  Continuum Mechanics and Thermodynamics, Springer Verlag, 2025, 38 (1), pp.1. Microstructural anisotropy plays a crucial role in determining the qualitative and quantitative mechanical properties of polymer foams. Moreover, their behavior at high strain rates remains an open question due to the limited studies on the topic, which poses a limit in the design of impact absorbing foam-made components (e.g., helmets). In this work we study the influence of microstructural anisotropy on the dynamic behavior of transversely isotropic closed cells polystyrene foams. We first produce isodensity foams with different degrees of microstructural anisotropy by using the gas foaming technique. We characterize the microstructure of the cells of the produced polystyrene foams by analyzing 2D images of the microstructure and computing the statistics of the shape indicators of the cells. We then characterize their dynamical behavior on split Hopkinson pressure bars at an average strain rate of 835 s-1. Dynamic results are compared with quasistatic ones and confirm similar findings to the literature. We report a different strain rate sensitivity for the different foams. In particular, a higher sensitivity for foams when cells are aligned with the loading direction. Therefore, the strain rate sensitivity of the foam can be associated with the microstructural distribution of cell and the strain rate sensitivity of the base material. (10.1007/s00161-025-01433-5)
  DOI : 10.1007/s00161-025-01433-5
• Interfacial homogenization of a periodically corrugated surface in linear elasticity
  
  • Singh Vivek
  • Pham Kim
  • Fischer Arthur Geromel
  • Danas Kostas
  Journal of the Mechanics and Physics of Solids, Elsevier, 2025, 207, pp.106420. This work presents a homogenization framework for modeling the mechanical behavior of three-dimensional linear elastic bodies with a periodically corrugated surface subjected to Dirichlet boundary conditions. The surface microstructure is assumed to be invariant along one spatial direction and periodic along the other. By combining asymptotic homogenization with matched asymptotic expansions near the surface corrugations, we derive an effective interface constitutive model that replaces the corrugated surface and the Dirichlet boundary condition with a flat boundary governed by a mixed (Robin-type) boundary condition. This boundary condition involves a second-order effective tensor, computed from elementary problems set on a representative periodic unit cell, hence allowing to account for the effect of the microstructure on the macroscopic response. We prove the symmetry and positive definiteness of the effective tensor and establish a uniqueness result of the effective problem. The model is assessed by comparison with 2D and 3D full-field simulations, demonstrating excellent agreement in both global and local responses. In particular, a cost-efficient post-processing strategy is proposed to reconstruct the local fields near the corrugations by use of a simple periodic unit cell, providing access to fine-scale information without the need for full-resolution computations. (10.1016/j.jmps.2025.106420)
  DOI : 10.1016/j.jmps.2025.106420
• Investigating the uniaxial compressive mechanics of graded polymer foams via in-situ synchrotron X-ray microtomography
  
  • Iaccarino Paolo
  • Miele Lorenzo
  • Okumko Victor
  • Scheel Mario
  • Weitkamp Timm
  • Proudhon Henry
  • Auricchio Ferdinando
  • Di Maio Ernesto
  • Constantinescu Andrei
  , 2025. Graded polymer foams are emerging as transformative materials for structural applications, outperforming uniform foams due to their spatially tailored density and microstructural features. However, harnessing their full potential requires a deep understanding of how their macroscopic mechanical behavior relates to their complex microstructure evolution. In this study, we elucidate the uniaxial compressive response of graded foams using in-situ synchrotron X-ray microtomography, complemented by comparative experiments on uniform foams of varying densities. Our findings reveal that graded foams exhibit both qualitatively and quantitatively distinct mechanical behavior, driven by unique microscale deformation mechanisms. We evaluate and discuss their superior energy absorption performance and demonstrate how the density profile evolves under increasing macroscopic strain. Notably, the graded architecture enables precise control over the localization and progression of densification bands, offering unprecedented design flexibility for advanced structural applications. (10.31224/5674)
  DOI : 10.31224/5674
• A new Surrogate Microstructure Generator for Porous Materials with Applications to the Buffer Layer of TRISO Nuclear Fuel Particles
  
  • Eisenhardt Philipp
  • Khristenko Ustim
  • Wohlmuth Barbara
  • Constantinescu Andrei
  , 2025. We present a surrogate material model for generating microstructure samples reproducing the morphology of the real material. The generator is based on Gaussian random fields, with a Matérn kernel and a topological support field defined through ellipsoidal inclusions clustered by a random walk algorithm. We identify the surrogate model parameters by minimizing misfits in a list of statistical and geometrical descriptors of the material microstructure. To demonstrate the effectiveness of the method for porous nuclear materials, we apply the generator to the buffer layer of Tristructural Isotropic Nuclear Fuel (TRISO) particles. This part has been shown to be failure sensitive part of TRISO nuclear fuel and our generator is optimized with respect to a dataset of FIB-SEM tomography across the buffer layer thickness. We evaluate the performance by applying mechanical modeling with problems of linear elastic homogenization and linear elastic brittle fracture material properties and comparing the behaviour of the dataset microstructure and the surrogate microstructure. This shows good agreement between the dataset microstructure and the generated microstructures over a large range of porosities. (10.48550/arXiv.2506.15874)
  DOI : 10.48550/arXiv.2506.15874
• Fully explicit numerical scheme for linearized wave propagation in nearly-incompressible soft hyperelastic solids
  
  • Merlini Giulia
  • Allain Jean-Marc
  • Imperiale Sébastien
  Wave Motion, Elsevier, 2025, 139, pp.103594. The numerical approximation of wave propagation problems in nearly or pure incompressible solids faces several challenges such as locking and stability constraints. In this work we propose a stabilized Leapfrog scheme based on the use of Chebyshev polynomials to relax the stability condition, which is strongly limited by the enforcement of incompressibility. The scheme is fully explicit, second order accurate and energy-preserving. For the space discretization we use a mixed formulation with high-order spectral elements and mass-lumping. A strategy is proposed for an efficient and accurate computation of the pressure contribution with a new definition of the discrete Grad-div operator. Finally, we consider linear wave propagation problems in nearly-incompressible hyperelastic solids subject to static preload. (10.1016/j.wavemoti.2025.103594)
  DOI : 10.1016/j.wavemoti.2025.103594
• Formation mechanism and microstructural characteristics of a body-centered cubic phase in 3D printed 316L–CuCrZr multi-material structures, combining laser powder bed fusion with foils
  
  • Jamili A.M.
  • Basu I.
  • Cayron C.
  • van Petegem S.
  • Jhabvala J.
  • Grundy A. Nicholas
  • Weisz-Patrault Daniel
  • Nohava J.
  • Ozsoy A.
  • Casati N.
  • Löffler Jörg
  • Logé R.E.
  Scripta Materialia, Elsevier, 2025, 268, pp.116844. Additive manufacturing of 316L/CuCrZr multi-material metallic structures has recently attracted significant attention, due to the ideal combination of structural and thermal/electrical properties. In this work, a unique multi-phase microstructure was produced with a hybrid laser-powder bed fusion (L-PBF) process combining 316L steel thin foils and CuCrZr powders. In-situ XRD, together with EDS and EBSD measurements, revealed the formation of two distinct Cu- and Fe-rich FCC phases that co-exist with an Fe-rich BCC phase. From the observed phase morphologies and using thermodynamic calculations, the formation mechanism of the BCC phase is proposed to result from the miscibility gap of the phase diagram, elemental diffusion, and fluid dynamics within the melt pool. The control of the BCC phase content in additive manufacturing is anticipated to be critical for designing complex FCC+BCC “composite” microstructures that can impart substantial strengthening to L-PBF multi-material 316L/Cu structures. (10.1016/j.scriptamat.2025.116844)
  DOI : 10.1016/j.scriptamat.2025.116844
• Fatigue Performance of Cemented Aeolian Sands: Linking Material Structural Characteristics to Long-Term Subgrade Durability
  
  • Darsanj Solmaz
  • Tabrizi Mehrdad Emami
  • Constantinescu Andrei
  Transportation Geotechnics, Elsevier, 2025, pp.101757. In arid and semi-arid regions, subgrades often consist of loose aeolian sands with insufficient bearing capacity, making effective stabilization essential. Among various techniques, soil–cement columns present a viable solution; however, their long-term performance under cyclic loading is frequently neglected in design considerations. This study investigated the fatigue behavior of cement-treated aeolian sands, representative of soil–cement column materials, subjected to uniaxial cyclic compressive loading, focusing on the effects of cement content and dry density. Cylindrical specimens were prepared with cement contents of 2%, 3%, and 4% (by dry weight) and two dry densities corresponding to relative densities of 10% and 70% in uncemented sand. Cyclic tests were conducted under sinusoidal loading with stress levels ranging from 70% to 98% of the monotonic strength. Fatigue life as well as axial strains were measured, while Scanning Electron Microscopy (SEM) was employed to examine the microstructural features. The results demonstrated that increasing both cement content and density significantly enhances fatigue life. Microstructural analyses revealed that, beyond the quantity of bonds, the spatial distribution and morphology of interparticle bonds critically influence fatigue resistance. Additionally, the evolution and accumulation of dissipated energy were found to be closely associated with fatigue life and applied stress levels. A predictive model was proposed based on total cumulative dissipated energy and the porosity/cement index, providing a practical tool for assessing the durability of stabilized sands. These findings contribute to a deeper understanding of fatigue mechanisms in cemented aeolian sands and support the design of more resilient subgrades in dry regions. (10.1016/j.trgeo.2025.101757)
  DOI : 10.1016/j.trgeo.2025.101757
• Metallurgically-driven thermomechanical analysis of multiple side-to-side laser melting on a 316L substrate
  
  • Li Zixuan
  • Bellet Michel
  • Gandin Charles-André
  • Upadhyay Manas Vijay
  • Zhang Yancheng
  Additive Manufacturing, Elsevier, 2025, 112, pp.104991. In additive manufacturing, the solidification grain structure has a significant influence on the properties of as-built material. In this context, the solidifi-cation grain structure and internal stress evolution during laser scanning of polycrystalline 316L stainless steel are simulated. A strongly coupled crystal viscoplasticity model is developed and integrated with a cellular automaton finite element (CAFE) approach to accurately capture grain structure and stress evolution, where the CAFE model is validated based on a literature experiment. The crystal viscoplasticity model is calibrated using stress-strain curves of annealed 316L from experiments considering small thermo-elasto-viscoplastic (TEVP) deformations. The resolution algorithm dynamically couples heat transfer, melting and solidification simulations while concurrently computing stress and strain evolution within the grain structure. Four scanning strategies are simulated using the coupled CAFE-crystal viscoplas-ticity approach, capturing stress evolution during grain growth. This enables the simultaneous thermo-viscoplastic modeling in the mushy zone and TEVP modeling in the solid, providing insights into stress evolution and grain orientation over a large domain. The melting-solidification process involves variations in compression and tension, leading to stress concentration within neighboring grains with significant orientation differences, extending along elongated grains. A framework for multiscale process-structure-mechanical investigation is established based on microscale stress evolution in additive manufacturing. (10.1016/j.addma.2025.104991)
  DOI : 10.1016/j.addma.2025.104991
• Synchrotron 4D X‐Ray Computed Tomography of a Porous Limestone: Influence of Porosity on Deformation Mechanisms at Multiple Scales
  
  • Doré-Ossipyan C.
  • Quacquarelli A.
  • Bornert Michel
  • Sulem J.
  • Dimanov Alexandre
  Journal of Geophysical Research : Solid Earth, American Geophysical Union, 2025, 130 (10), pp.e2025JB031620. This study investigates the relationship between deformation mechanisms and heterogeneity of porosity of a porous carbonate rock across several scales. The Saint Maximin limestone (SML), characterized by centimeter‐scale alternations of dense and porous zones, serves as a model rock to examine the evolution of deformation modes. Cylindrical samples of 8 mm in diameter, extracted from both the dense and porous zones of the SML, were tested in axisymmetric triaxial conditions with in situ synchrotron imaging. High‐resolution 3D strain fields and porosity maps were derived from synchrotron images to assess local‐scale correlations. The results demonstrate that initial porosity exerts a primary control on strain patterns, spanning from the microscale to the centimeter scale. Under brittle conditions, deformation localizes into bands, predominantly accommodated within the more porous regions, while the denser zones remain largely unaffected. At intermediate confining pressures, heterogeneity induces a transitional behavior where diffuse and localized deformation coexist. In ductile conditions, multiple small compactant bands progressively saturate the sample, leading to porosity homogenization. (10.1029/2025JB031620)
  DOI : 10.1029/2025JB031620
• Hard magnetorheological foams : experiments, modeling and applications in haptic sensing
  
  • Lin Zehui
  , 2025. Hard magnetorheological elastomers (h-MREs) in general are two-phase composite materials consisting of hard magnetic particles that are embedded in an otherwise soft elastomer matrix. In turn, this work proposes a family of novel mechanically-soft and magnetically-hard magnetorheological foams that, upon deformation, lead to robust and measurable magnetic flux changes in their surroundings. This allows to infer qualitatively and even quantitatively the imposed deformation and, eventually from that, an estimation of the stiffness and average stress on the sample even in complex loading scenarios involving combinations of uniform or nonuniform compression/tension with superposed shearing in different directions.At first, we analyze experimentally, numerically and theoretically the purely magnetic response of h-MRE foams with variable particle and porositycontent. The fabrication and experimental measurement of the remanent magnetic flux of h-MRE foams are discussed in detail. We find that at lower particle content, the foam comprises closed-cell porosity, with the voids having a variable size and ellipsoidal shape. As the particle content in the matrix increases, the voids become smaller in size and more spherical in shape, while the porosity decreases. We show experimentally that theremanent magnetic flux is entirely independent of the shape and orientation of the voids. Image-based morphological analysis of the h-MRE foam microstructure subsequently allows to reconstruct numerically unit-cells that share the same statistics as those of the experimental foams. These unit-cells are used to construct an explicit theoretical model with magnetic dissipation. We show that the remanent magnetization is a linear functionof the overall particle volume fraction in the foam. The model is further used to scale up the analysis and solve the experimental boundary value problem of a permanently magnetized h-MRE cube, and the numerical estimates show excellent agreement with the experiments. The numerical model is shown to match available analytical solutions for the remanent magnetic flux of parallelepiped magnets.Subsequently, the magneto-mechanical response of isotropic h-MRE foams is explored through a novel and complete theoretical, numerical and experimental framework. The fabrication process of h-MRE foams is slightly modified to obtain both isotropic mechanical and magnetic responses, with the resulting voids having rather polygonal and spherical shapes. This, in turn, allows to simplify substantially the rather complex compressible magneto-mechanical response of these materials. In particular, we provide a combined experimental protocol coupled with analytical solution of the boundary value problem corresponding to the experimental setup and a fully explicit homogenization-based model with only a very small number of material parameters requiring calibration. After calibration and numerical implementation, the proposed model is assessed with the experimental results obtained under different particle volume fractions and compression types, showing sufficient accuracy without requiring recalibration. Furthermore, we show that these permanently magnetized foams provide versatile sensing capabilities without the need for an externally-applied magnetic field by taking advantage of the pore closure/opening and the resulting effective change in apparent magnetization saturation, but also of the specimen shape changes involved in such large deformation processes.The complete experimental, theoretical and numerical framework on finite strain and compressible magneto-elasticity for h-MRE foams presented in this work allows to measure and predict coupled magneto-mechanical properties of such materials with different particle volume fractions. Thus, this framework provides an efficient tool to predict material behavior and design sensing devices by h-MRE foams. (10.70675/bb6cbae7z0b72z48eczb504z9f281ba9a07c)
  DOI : 10.70675/bb6cbae7z0b72z48eczb504z9f281ba9a07c
• Modèles 1D enrichis pour la fabrication additive : construction thermodynamique et applications multi-matériaux
  
  • Viano Rafaël
  , 2025. Ce travail propose un cadre original de modélisation mécanique basé sur des modèles~1D à cinématique enrichie pour la fabrication additive par dépose de cordon. Les modèles développés sont des modèles multifils construits à l’aide d’une méthode de construction axiomatique, s’appuyant sur le principe des puissances virtuelles et le cadre thermodynamique des matériaux standards généralisés. L’approche de modélisation s’appuie sur la géométrie caractéristique des pièces issues de la fabrication additive, construites par superposition de cordons élancés. La section étant très réduite par rapport à la longueur, la discrétisation numérique est contrainte par l’épaisseur du cordon. Les modèles proposés exploitent cet élancement non comme une limite, mais comme un levier pour réduire le nombre de degrés de liberté et accélérer le calcul mécanique. Bien que géométriquement simples du fait de leur nature unidimensionnelle, ils permettent de représenter des efforts tels que la traction-compression ou le cisaillement, induisant des déformations complexes de la section du cordon. La construction des modèles, comprenant la définition des grandeurs généralisées, l’établissement des équations d’équilibre, de diffusion de la chaleur et du comportement des matériaux, est présentée dans un premier temps. Le modèle mécanique nommé QuadWire est ensuite utilisé dans une stratégie de couplage faible avec le modèle thermique ScanFast pour simuler différents procédés de fabrication additive métallique et polymère. Une validation expérimentale du modèle est ensuite réalisée à l’aide de mesures in-situ. Enfin, il est utilisé comme outil de conception, dans le cadre de procédés de fabrication additive grande échelle à base de polymère et de béton, pour réduire l'instabilité structurelle, les contraintes résiduelles et ajuster la trajectoire et le parcours d'impression. Ces applications démontrent la capacité du modèle a être utilisé comme outil de conception, de dimensionnement et de contrôle du procédé. (10.70675/58563d91z8882z41bcz8733z6db040a4d252)
  DOI : 10.70675/58563d91z8882z41bcz8733z6db040a4d252
• Microstructure Evolution and Deformation Mechanisms in Additively Manufactured 316L Stainless Steel
  
  • Barkia Bassem
  • Vallet Maxime
  • Tanguy Alexandre
  • Auger Thierry
  • Héripré Eva
  , 2025. We investigate the evolution of deformation mechanisms and dislocation structures in 316L stainless steel produced by directed energy deposition (DED) across different strain levels. We show that the deformation mechanisms are strongly influenced by the initial dual-scale cellular structure. At low to moderate strains, plasticity is accommodated primarily by dislocation slip within the cell interiors and the formation of micro-bands. At higher strains, plastic deformation is primarily controlled by mechanical nano-twinning initiated through the overlap of stacking fault ribbons. Unlike conventionally processed 316L, the additively manufactured alloy exhibits an almost linear increase in dislocation density throughout the full range of plastic deformation. The retained cellular architecture impedes dislocation motion, contributing to the material’s high ductility. Finally, a clear correlation between work-hardening rate and deformation modes confirms the atypical plastic behavior of AM 316L, providing valuable insights for the development of large-scale predictive plasticity models for these steels.
• Approche variationnelle de l'homogénéisation d'ordre supérieur
  
  • Thbaut Manon
  , 2025. Il est pratique de décrire les matériaux possédant une microstructure à l'aide de propriétés effectives homogènes. Lorsque le rapport η entre la taille de la microstructure et celle de la structure est très petit, des modèles effectifs peuvent être obtenus en appliquant une procédure d'homogénéisation. L'homogénéisation asymptotique, qui repose sur un développement des champs mécaniques en puissances du rapport η, est particulièrement adaptée pour traiter les microstructures périodiques. A l'ordre dominant, on retrouve les résultats de l'homogénéisation classique i.e. un milieu effectif de Cauchy. Les ordres suivants produisent des corrections qui dépendent des gradients de la déformation. Contrairement aux approches phénoménologiques, l'homogénéisation asymptotique permet d'identifier rigoureusement la solution microscopique associée au comportement effectif. De plus, les corrections d'ordre supérieur permettent d'améliorer la précision du modèle en tenant compte d'effets d'échelle. Ces effets sont significatifs lorsque le rapport d'échelle η n'est pas suffisamment petit ou en présence de raideurs microscopiques contrastées.Les corrections d'ordre supérieur issues de l'homogénéisation sont correctes en volume mais négligent des effets de bords, ce qui peut dégrader la qualité des prédictions. De plus, dans ces modèles d'ordre supérieur, l'ordre de l'équation d'équilibre est augmenté et de nouvelles conditions aux limites sont nécessaires. En mécanique des milieux continus, les conditions aux limites sont souvent obtenues en minimisant l'énergie du système. Pour les modèles d'ordre supérieur une telle énergie n'est pas disponible, ce qui rend l'identification de conditions aux limites particulièrement difficile.L'obtention d'une telle énergie présente plusieurs difficultés. D'abord, la raideur à gradient apparaissant dans ces modèles peut être non positive. En tronquant brutalement l'énergie de volume, on obtient donc une densité d'énergie élastique non positive. Cette propriété est très malvenue car elle conduit à des problèmes aux limites mal posés. Ensuite, afin de garantir la précision du modèle, il faut tenir compte de l'énergie générée par les couches limites. Celle-ci produit des termes de bord dans l'énergie qui peuvent, à leur tour, être non positifs.Dans ce travail, on aborde ces limitations et on identifie une telle énergie en 1D. On procède en deux étapes. D'abord, on combine homogénéisation asymptotique dans le volume et analyse des couches limites afin d'établir une approximation formelle de l'énergie microscopique, que l'on appelle pseudo-énergie. Cette pseudo-énergie contient un terme de volume et un terme de bord qui sont précis jusqu'à l'ordre η². De plus, on montre que les tractions d'ordre supérieur entrant dans le terme de bord vérifient des conditions de compatibilité garantissant que la pseudo-énergie puisse être rendue stationnaire ordre par ordre (perturbativement). À titre d'exemple, on traite un réseau de ressorts 1D avec second voisins. On prouve que les prédictions de ce modèle perturbatif sont asymptotiques à l'ordre η².Ensuite, on propose une nouvelle procédure qui transforme une telle pseudo-énergie en une énergie tronquée, dont la positivité est restaurée. Cette méthode s'appuie sur deux ingrédients. D'abord, on rétablit la positivité aux bords en transférant l'élasticité de bord dans un terme fantôme qui peut, par construction, être ignoré. Puis, on rétablit la positivité dans le volume en utilisant une troncature inspirée de la décomposition de Cholesky. L'énergie ainsi obtenue est positive et produit un problème aux limites bien posé. C'est l'énergie d'un milieu à gradients, formulée en termes d'une déformation généralisée. On montre, sur l'exemple des ressorts, que les prédictions de ce modèle coïncident avec celles du modèle perturbatif.Enfin, on étend notre étude en établissant la pseudo-énergie d'un stratifié continu. Dans ce cas, les raideurs aux bords sont calculées numériquement. (10.70675/8fdcdf09zfdffz4614z89ffza8c700f20cde)
  DOI : 10.70675/8fdcdf09zfdffz4614z89ffza8c700f20cde
• Asymptotic Analysis of a class of abstract stiff wave propagation problems
  
  • Imperiale Sébastien
  Multiscale Modeling and Simulation: A SIAM Interdisciplinary Journal, Society for Industrial and Applied Mathematics, 2025, 23 (3), pp.1389-1416. This work addresses the mathematical analysis, by means of asymptotic analysis, of a class of linear wave propagation problems with singular stiff terms represented by a single small parameter. This abstract setting is defined using linear operators in Hilbert spaces. In this setting, we show, under some assumptions on the structure of the wave propagation problems, weak and strong convergence of solutions with respect to the small parameter towards the solution of a well-defined limit problem. Applications in nearly incompressible elastodynamics, elastic waves in thin plates, piezoelectricity, and homogenization are presented. (10.1137/24M1679458)
  DOI : 10.1137/24M1679458
• Mathematical analysis of an observer for solving inverse source wave problem
  
  • Delaunay Tiphaine
  • Imperiale Sébastien
  • Moireau Philippe
  Inverse Problems and Imaging, AIMS American Institute of Mathematical Sciences, 2025. The objective of this work is to propose a method using observers to estimate a source term of a wave equation from internal measurements in a subdomain. The first part of the work consists in proving an identifiability result from classical observability conditions for wave equations. We show that the source reconstruction is an ill-posed inverse problem of degree 1 or 2 depending on the measurements type. This inverse problem is solved using observers -- a sequential strategy -- that is proven to be equivalent to a minimization of a cost functional with Tikhonov regularization. (10.3934/ipi.2025043)
  DOI : 10.3934/ipi.2025043
• Thermo-rheologically complex polymers: multiaxial constitutive modeling, numerical implementation and experimental validation
  
  • Iaccarino Paolo
  • Di Maio Ernesto
  • Constantinescu Andrei
  • Auricchio Ferdinando
  Polymer Testing, Elsevier, 2025, 150, pp.108937. We propose a simple multiaxial linear viscoelastic constitutive model to describe the behavior of thermo- rheologically complex polymers in both the time and frequency domains. The numerical implementation is discussed along with the parameter identification procedure. In particular, we propose a modification of the parameter identification procedure proposed by Jalocha et al. (2015) introducing a regularization step, enabling robust handling of large experimental datasets. We perform an extensive experimental investigation, including calorimetry analysis, as well as tensile, shear, and torsion frequency sweep, creep, and stress- relaxation experiments, and results are benchmarked against existing literature. The frequency-temperature superposition principle is applied to the experimental data using horizontal and vertical shift functions, explicitly integrated into the constitutive model framework. The calibration of the constitutive model is performed in the frequency domain, while the validation is performed in the time domain, demonstrating the accuracy and reliability of the model in multiple experimental domains. Finally, model predictions are reported in the frequency domain for different temperatures. (10.1016/j.polymertesting.2025.108937)
  DOI : 10.1016/j.polymertesting.2025.108937