Publications

2019

• Design of multi-layer materials using inverse homogenization and a level set method
  
  • Nika Grigor
  • Constantinescu Andrei
  Computer Methods in Applied Mechanics and Engineering, Elsevier, 2019, 346, pp.388-409. This work is concerned with the micro-architecture of multi-layer material that globally exhibits desired mechanical properties, for instance a negative apparent Poisson ratio. We use inverse homogenization, the level set method, and the shape derivative in the sense of Hadamard to identify material regions and track boundary changes within the context of the smoothed interface. The level set method and the shape derivative obtained in the smoothed interface context allows to capture, within the unit cell, the optimal micro-geometry. We test the algorithm by computing several multi-layer auxetic micro-structures. The multi-layer approach has the added benefit that contact during movement of adjacent \branches" of the micro-structure can be avoided in order to increase its capacity to withstand larger stresses. (10.1016/j.cma.2018.11.029)
  DOI : 10.1016/j.cma.2018.11.029
• Enhanced resonance of sparse arrays of Helmholtz resonators—Application to perfect absorption
  
  • Maurel Agnès
  • Mercier Jean-François
  • Pham Trung Kien
  • Marigo J.-J
  • Ourir Abdelwaheb
  Journal of the Acoustical Society of America, Acoustical Society of America, 2019, 145 (4), pp.2552-2560. We inspect the influence of the spacing on the resonance of a periodic arrangement of Helmholtz resonators. An effective problem is used which captures accurately the properties of the resonant array within a large range of frequency, and whose simplified version leaves us with an impedance condition. It is shown that the strength of the resonance is enhanced when the array becomes sparser. This degree of freedom on the radiative damping is of particular interest since it does not affect the resonance frequency nor the damping due to losses within each resonator; besides, it does not affect the total thickness of the array. We show that it can be used for the design of a perfect absorbing walls. (10.1121/1.5098948)
  DOI : 10.1121/1.5098948
• Strain localization in ductile shear zones: This is a crystal plasticity's world, but it wouldn't be nothing without a micro-cracking or a sliding grain
  
  • Dimanov Alexandre
  • Bornert Michel
  • Raphanel Jean
  • Héripré Eva
  • Gharbi Hakim
  • Ababacar Gaye
  • Bourcier Mathieu
  • Ludwig Wolfgang
  • King Andrew
  , 2019. Strain localization in ductile shear zones: This is a crystal plasticity’s world, but it wouldn’t be nothing without a micro-cracking or a sliding grain Localization of ductile strain in rocks results in development of mylonites, which microstructures always display the signatures of several different micro-mechanisms operating at the grain and aggregate scales. Intense crystal plasticity and dynamic recrystallization coexist with micro-cracking, grain boundary migration and sliding, ductile cavitation and failure, diffusive and solution mass transfer along interfaces. Their chronology of activation, their interactions and their respective quantitative roles in the development of the localization process are still unclear. Therefore, a simple inference of the overall mylonitic rheology on the basis of one or another of the latter mechanisms seems illusory. In order to clarify the interplay of mechanisms at the onset of ductile deformation, we performed multi-scale full mechanical field investigations of the ductile deformation of coarse grained synthetic rock salt at room and high temperatures. We applied in situ optical (OM) and scanning electron microscopy (SEM) and X-ray micro-tomography (MCT) during uniaxial compression up to 10 % shortening. Digital surface image and digital volume correlation (DIC and DVC) techniques allowed characterizing and quantifying the multiscale organization of 2D and 3D full strain fields. The same localization patterns are observed in 2 and 3D: the macroscopic shear bands appearing at the sample scale refine into mesoscopic localization bands at the aggregate microstructure scale. The highest resolution investigations clearly demonstrate that the latter result from the concomitant and co-operative interplay between dominant crystal slip plasticity (CSP) and minor but necessary interfacial mechanisms, such as grain boundary sliding (GBS), migration, micro-cracking and cavitation. The quantitative analysis of the interfacial mechanism activity evidence only a modest contribution of less than 10 % to the overall strain, but without the latter development of ductile localization could not occur. The interfacial mechanisms (as GBS) are absolutely necessary to accommodate for the plastic strain incompatibilities among neighboring grains, related to the intrinsic anisotropy of CSP. To conclude, the coupling of CSP and interfacial mechanisms is immediate, right at the onset of ductile deformation. Our major conclusion is that during ductile localization in rocks CSP and GBS act as co-operative mechanisms due to the pronounced plastic anisotropy of minerals. At the beginning CSP appears to be the principal strain mechanism, but GBS happens to be best necessary and supporting one. We further suggest for mylonite development that once grain size reduction and phase mixing had occurred, GBS may become the principal actor, allowing for dominant Newtonian rheology and enhancement of localization.
• On adhesive theories in multilayered interfaces, with particular regard to "surface force apparatus" geometry
  
  • Tricarico Michele
  • Papangelo Antonio
  • Constantinescu Andrei
  • Ciavarella Michele
  Facta Universitatis, Series: Mechanical Engineering, 2019, 17 (1), pp.95. Adhesion is a key factor in many tribological processes, especially wear. We generalize a recent formulation for the indentation of a multilayered material using an efficient integral transform method, to the case of adhesion, using a simple energetic transformation in the JKR regime. Then, we specialize the study for the geometry of the Surface Force Apparatus, which consists of two thin layers on a substrate, where the intermediate layer is softer than the other two. We find the pull-off force under "force control" (i.e. for "soft" loading systems), as well as under "displacement control" (i.e. for "rigid" systems), as a function of the geometrical thicknesses and material properties ratios, and the method is fully implemented in a fast Mathematica code, available to the public. (10.22190/FUME190118011T)
  DOI : 10.22190/FUME190118011T
• Combination of Traction Assays and Multiphoton Imaging to Quantify Skin Biomechanics
  
  • Bancelin Stéphane
  • Lynch Barbara
  • Bonod-Bidaud Christelle
  • Dokládal Petr
  • Ruggiero Florence
  • Allain Jean-Marc
  • Schanne-Klein Marie-Claire
  , 2019, 1944, pp.145-155. An important issue in tissue biomechanics is to decipher the relationship between the mechanical behavior at macroscopic scale and the organization of the collagen fiber network at microscopic scale. Here, we present a protocol to combine traction assays with multiphoton microscopy in ex vivo murine skin. This multiscale approach provides simultaneously the stress/stretch response of a skin biopsy and the collagen reorganization in the dermis by use of second harmonic generation (SHG) signals and appropriate image processing. (10.1007/978-1-4939-9095-5_11)
  DOI : 10.1007/978-1-4939-9095-5_11
• Programmable higher-order Euler buckling modes in hierarchical beams
  
  • Tarantino M.G. G
  • Danas K.
  International Journal of Solids and Structures, Elsevier, 2019. We present a numerical-aided experimental study on the buckling of hierarchical beams comprising multiple self-similar modules. Each module consists of multiple elemental beams and is arranged in series to form the hierarchical beam. We show, through a combination of experiments and computations, that these beams exhibit stable and realizable higher-order buckling modes. By contrast to the canonical Euler buckling problem, such modes emerge naturally in the proposed self-similar beams since they correspond to almost identical critical loads. By harnessing the imperfection sensitivity of the hierarchical structures, we 3D-print weakly imperfect polymer samples with a small geometric imperfection corresponding to the desired eigenmode. We subsequently carry out uniaxial compression experiments and show in practice that higher-order patterns can be triggered selectively upon buckling. Moreover, these patterns are preserved in the post-bifurcation regime in many cases and are reversible upon load release. The ability to trigger higher-order buckling modes is found to depend on two main geometrical parameters which lead to scale coupling. Those are the slenderness of the macroscopic hierarchical beam and the slenderness of the lower-scale elemental beam. With increasing slenderness of the hierarchical beam, we observe a significant softening in the overall stress-strain response and patterns exhibiting curvature lo-calization in the post-bifurcation regime. The numerical finite-strain simulations carried out in the present study are found to be in very good agreement with the experiments and are used to quantify further the observed curvature localization in the hierarchical beams. The present study and the obtained results are geometric in nature and thus can be extended to different scales and hierarchies ad infinitum. (10.1016/j.ijsolstr.2019.03.009)
  DOI : 10.1016/j.ijsolstr.2019.03.009
• A fully equilibrated microsphere model with damage for rubberlike materials
  
  • Diani J.
  • Le Tallec Patrick
  Journal of the Mechanics and Physics of Solids, Elsevier, 2019, 124, pp.702-713. A non-affine microsphere model for rubberlike materials is proposed, based on a local minimization of the network free energy under a maximal advance path constraint. It accounts for any chain weight distribution and for damage such as Mullins softening observed in filled rubber materials. The non-affine equal-force model is compared to the common affine model and a hybrid equal-force model from the literature, when considering the isotropic hyperelastic behavior without damage of rubber materials presenting chains of various lengths. The non-affine model shows an improved deformability compared to the affine model limited by the maximal extension of the shorter chains and a significantly softer behavior. Possible damage is introduced by increasing the chain lengths according to the submitted maximal chain traction force. Each chain are impacted independently resulting in a directional softening that introduces the evolution of the stress-free configuration that needs to be assessed over the loadings. The model was successfully tested on the cyclic uniaxial tension stretch-stress responses of carbon-black filled styrene butadiene rubbers that were well fitted with three parameters only. (10.1016/j.jmps.2018.11.021)
  DOI : 10.1016/j.jmps.2018.11.021
• Functionality of Disorder in Muscle Mechanics
  
  • Borja da Rocha Hudson
  • Truskinovsky Lev
  Physical Review Letters, American Physical Society, 2019, 122 (8), pp.088103. A salient feature of skeletal muscles is their ability to take up an applied slack in a microsecond timescale. Behind this fast adaptation is a collective folding in a bundle of elastically interacting bistable elements. Since this interaction has a long-range character, the behavior of the system in force and length controlled ensembles is different; in particular, it can have two distinct order-disorder–type critical points. We show that the account of the disregistry between myosin and actin filaments places the elementary force-producing units of skeletal muscles close to both such critical points. The ensuing “double criticality” contributes to the system’s ability to perform robustly and suggests that the disregistry is functional. (10.1103/PhysRevLett.122.088103)
  DOI : 10.1103/PhysRevLett.122.088103
• Equilibrium unzipping at finite temperature
  
  • Borja da Rocha Hudson
  • Truskinovsky Lev
  Archive of Applied Mechanics, Springer Verlag, 2019, 89 (3), pp.535-544. We study thermally activated unzipping, which is modeled as a debonding process. The system is modeled as a parallel bundle of elastically interacting breakable units loaded through a series spring. Using equilibrium statistical mechanics, we compute the reversible response of this mechanical system under quasi-static driving. Depending on the stiffness of the series spring, the system exhibits either ductile behavior, characterized by noncoopera-tive debonding, or brittle behavior, with a highly correlated detachment of the whole bundle. We show that the ductile to brittle transition is of the second order and that it can also be controlled by temperature. (10.1007/s00419-018-1485-4)
  DOI : 10.1007/s00419-018-1485-4
• Medical images registration with finite elements and mechanical regularization
  
  • Genet Martin
  , 2019.
• Validation of Finite Element Image Registration-based Cardiac Strain Estimation from Magnetic Resonance Images
  
  • Berberoglu Ezgi
  • Stoeck Christian T
  • Moireau Philippe
  • Kozerke Sebastian
  • Genet Martin
  , 2019. Accurate assessment of regional and global function of the heart is an important readout for the diagnosis and routine evaluation of cardiac patients. Indeed, recent clinical and experimental studies suggest that compared to global metrics, regional measures of function could allow for more accurate diagnosis and early intervention for many cardiac diseases. Although global strain measures derived from tagged magnetic resonance (MR) imaging have been shown to be reproducible for the majority of image registration techniques, the measurement of regional heterogeneity of strain is less robust. Moreover, radial strain is underestimated with the current techniques even globally. Finite element (FE)-based techniques offer a mechanistic approach for the regularization of the ill-posed registration problem. This paper presents the validation of a recently proposed FE-based image registration method with mechanical regularization named equilibrated warping. For this purpose, synthetic 3D-tagged MR images are generated from a reference biomechanical model of the left ventricle (LV). The performance of the registration algorithm is consequently tested on the images with different signal-to-noise ratios (SNRs), revealing the robustness of the method. (10.1002/pamm.201900418)
  DOI : 10.1002/pamm.201900418
• Force-induced repolarization of an active crawler
  
  • Recho Pierre
  • Putelat Thibaut
  • Truskinovsky Lev
  New Journal of Physics, Institute of Physics: Open Access Journals, 2019, 21. We develop a quantitative model of mechanical repolarization in a contraction-driven gel layer mimicking a crawling cell. We show that the force-velocity relations for such active crawlers exhibit multi-valuedness and hysteresis under both force and velocity control. The model predicts steady oscillations of cells attached to an elastic environment and offers a selfconsistent mechanical explanation for all experimentally observed outcomes of cell collision tests. (10.1088/1367-2630/ab05fd)
  DOI : 10.1088/1367-2630/ab05fd
• Analysis and calibration of a linear model for structured cell populations with unidirectional motion : Application to the morphogenesis of ovarian follicles
  
  • Clément Frédérique
  • Robin Frédérique
  • Yvinec Romain
  SIAM Journal on Applied Mathematics, Society for Industrial and Applied Mathematics, 2019, 79 (1), pp.207-229. We analyze a multi-type age dependent model for cell populations subject to unidirectional motion, in both a stochastic and deterministic framework. Cells are distributed into successive layers; they may divide and move irreversibly from one layer to the next. We adapt results on the large-time convergence of PDE systems and branching processes to our context, where the Perron-Frobenius or Krein-Rutman theorem cannot be applied. We derive explicit analytical formulas for the asymptotic cell number moments, and the stable age distribution. We illustrate these results numerically and we apply them to the study of the morphodynamics of ovarian follicles. We prove the structural parameter identifiability of our model in the case of age independent division rates. Using a set of experimental biological data, we estimate the model parameters to fit the changes in the cell numbers in each layer during the early stages of follicle development. (10.1137/17M1161336)
  DOI : 10.1137/17M1161336
• Representative volume elements for the simulation of isotropic composites highly filled with monosized spheres
  
  • de Francqueville Foucault
  • Gilormini Pierre
  • Diani Julie
  International Journal of Solids and Structures, Elsevier, 2019, 158, pp.277-286. A method is proposed for generating reliable representative volume elements (RVEs) that allows reducing the statistical analysis required for the simulation of the mechanical behavior of isotropic composites highly filled with monosized spheres. The method combines (i) an algorithm inspired from molecular dynamics and associated with an analytical equation of state, and (ii) a geometrical analysis using the two-point correlation function and a nearest-neighbor distribution function. A restrictive selection process is defined, which leads to microstructures reasonably close to randomness and isotropy. The pertinence of the proposed generation and selection of RVEs is confirmed by the simulation of their elastic behavior with the nite element method. In particular, it is shown how the selection procedure allows reducing the computational e ort required to reach reliable elastic moduli by operating on a limited number of suitable RVEs. The results are in good agreement with the generalized self-consistent model and with original experimental data obtained on a composite where an acrylate matrix was reinforced by sifted glass beads. (10.1016/j.ijsolstr.2018.09.013)
  DOI : 10.1016/j.ijsolstr.2018.09.013
• Prediction of irradiation hardening Reactor Pressure Vessel steels: Multiscale modeling of crystal plasticity
  
  • Monnet G
  • Vincent Ludovic
  • Gelebart Lionel
  Journal of Nuclear Materials, Elsevier, 2019, 514, pp.128-138. (10.1016/j.jnucmat.2018.11.028)
  DOI : 10.1016/j.jnucmat.2018.11.028
• Mathematical modelling and numerical simulation of elastic wave propagation in soft tissues with application to cardiac elastography
  
  • Caforio Federica
  , 2019. This PhD thesis concerns the mathematical modelling and numerical simulation of impulsive Acoustic Radiation Force (ARF)-driven Shear Wave Elastography (SWE) imaging in a prestressed soft tissue, with a specific reference to the cardiac setting. The first part of the manuscript deals with the mathematical modelling of the ARF, the resulting shear wave propagation, and the characterisation of the shear wave velocity in a general constitutive law for the myocardial tissue. We also show some applications to the extraction of fibre orientation in the myocardium and the detection of “synthetic pathologies”. One of the main contributions of this work is the derivation of an original mathematical model of the ARF. In more detail, starting from an accurate biomechanical model of the heart, and based on asymptotic analysis, we infer the governing equation of the pressure and the shear wave field remotely induced by the ARF, and we compute an analytical expression of the source term responsible for the generation of shear waves from an acoustic pressure pulse. In the second part of the PhD thesis, we propose efficient numerical tools for a realistic numerical simulation of an SWE experiment in a nearly-incompressible, pre-stressed, fibered soft tissue. The spatial discretisation is based on high-order Spectral Finite Elements (HO-SEM). Concerning the time discretisation, we propose a novel method adapted to incompressible elasticity. In particular, only the terms travelling at infinite velocity, associated with the incompressibility constraint, are treated implicitly by solving a scalar Poisson problem at each time step of the algorithm. Furthermore, we provide a novel matrix-free, high-order, fast method to solve the Poisson problem, based on the use of the Discrete Fourier Transform. (10.70675/8ce7577bz4987z450ezae38z677139df5191)
  DOI : 10.70675/8ce7577bz4987z450ezae38z677139df5191
• Identification d’un modèle orthotrope viscoplastique de comportement de l’alliage aéronautique Ti-6Al-4V
  
  • Ruiz de Sotto Miguel
  • Doquet Véronique
  • Longère Patrice
  • Papasidero Jessica
  , 2019.
• Critical strain energy release rate for rubbers: single edge notch tension versus pure shear tests
  
  • Roucou David
  • Diani Julie
  • Brieu Mathias
  • Mbiakop-Ngassa Armel
  International Journal of Fracture, Springer Verlag, 2019.
• Gradient damage models coupled with plasticity and their application to dynamic fragmentation
  
  • Fischer Arthur Geromel
  • Marigo Jean-Jacques
  , 2019, pp.chapter 3, pp. 95-141. This chapter explains the development of the so‐called "gradient damage models" and their extension to ductile materials and dynamic loading. It presents the construction of gradient damage models for brittle softening materials based on the principle of minimum energy. The chapter discusses the main hypothesis and the need for regularization. It then briefly discusses the von Mises plasticity criterion and how to take it into account. The chapter briefly discusses the numerical implementation and shows a few examples and results using the FEniCS library and an industrial code. It considers the case of small strains theory and an isotropic material. The chapter reviews variational approach used to describe damage evolution for a quasi‐static loading. It expresses that the evolution of the plasticity minimizes the energy. The chapter concerns the study of the fragmentation of a cylinder under a strong internal pressure. (10.1002/9781119579311.ch3)
  DOI : 10.1002/9781119579311.ch3
• Influence of as-cast spherulites on the fracture toughness of a Zr 55 Cu 30 Al 10 Ni 5 bulk metallic glass
  
  • Hin S.
  • Bernard C.
  • Doquet V.
  • Yokoyama Y.
  • Magueresse A.
  • Keryvin V.
  Materials Science and Engineering: A, Elsevier, 2019, A 740-741, pp.137-147. (10.1016/j.msea.2018.10.061)
  DOI : 10.1016/j.msea.2018.10.061
• Monitoring dynamic collagen reorganization during skin stretching with fast polarization‐resolved second harmonic generation imaging
  
  • Ducourthial Guillaume
  • Affagard Jean‐sébastien
  • Schmeltz Margaux
  • Solinas Xavier
  • Lopez‐poncelas Maeva
  • Bonod‐bidaud Christelle
  • Rubio‐amador Ruth
  • Ruggiero Florence
  • Allain Jean-Marc
  • Beaurepaire Emmanuel
  • Schanne-Klein Marie-Claire
  Journal of Biophotonics, Wiley, 2019, 12 (5), pp.e201800336. The mechanical properties of biological tissues are strongly correlated to the specific distribution of their collagen fibers. Monitoring the dynamic reorganization of the collagen network during mechanical stretching is however a technical challenge because it requires mapping orientation of collagen fibers in a thick and deforming sample. In this work, a fast polarization-resolved SHG microscope is implemented to map collagen orientation during mechanical assays. This system is based on line-to-line switching of polarization using an electro-optical modulator and works in epidetection geometry. After proper calibration, it successfully highlights the collagen dynamic alignment along the traction direction in ex vivo murine skin dermis. This microstructure reorganization is quantified by the entropy of the collagen orientation distribution as a function of the stretch ratio. It exhibits a linear behavior, whose slope is measured with a good accuracy. This approach can be generalized to probe a variety of dynamic processes in thick tissues. (10.1002/jbio.201800336)
  DOI : 10.1002/jbio.201800336
• Role of medical reaction in management of inappropriate ventricular arrhythmia diagnosis: the inappropriate Therapy and HOme monitoRiNg (THORN) registry
  
  • Perrin Tilman
  • Boveda Serge
  • Defaye Pascal
  • Rosier Arnaud
  • Sadoul Nicolas
  • Bordachar Pierre
  • Klug Didier
  • Ritter Philippe
  • Belhameche Mohamed
  • Babuty Dominique
  • Mansourati Jacques
  • Lazarus Arnaud
  • Deharo Pierre
  EP-Europace, Oxford University Press (OUP), 2019, 21 (4), pp.607-615. (10.1093/europace/euy284)
  DOI : 10.1093/europace/euy284
• Analysis and numerical simulation of an inverse problem for a structured cell population dynamics model
  
  • Clément Frédérique
  • Laroche Béatrice
  • Robin Frédérique
  Mathematical Biosciences and Engineering, AIMS Press, 2019, 16 (4), pp.3018-3046. In this work, we study a multiscale inverse problem associated with a multi-type model for age structured cell populations. In the single type case, the model is a McKendrick-VonFoerster like equation with a mitosis-dependent death rate and potential migration at birth. In the multi-type case, the migration term results in an unidirectional motion from one type to the next, so that the boundary condition at age 0 contains an additional extrinsic contribution from the previous type. We consider the inverse problem of retrieving microscopic information (the division rates and migration proportions) from the knowledge of macroscopic information (total number of cells per layer), given the initial condition. We first show the well-posedness of the inverse problem in the single type case using a Fredholm integral equation derived from the characteristic curves, and we use a constructive approach to obtain the lattice division rate, considering either a synchronized or non-synchronized initial condition. We take advantage of the unidirectional motion to decompose the whole model into nested submodels corresponding to self-renewal equations with an additional extrinstic contribution. We again derive a Fredholm integral equation for each submodel and deduce the well-posedness of the multi-type inverse problem. In each situation, we illustrate numerically our theoretical results. (10.3934/mbe.2019150)
  DOI : 10.3934/mbe.2019150
• Front shape similarity measure for data-driven simulations of wildland fire spread based on state estimation: Application to the RxCADRE field-scale experiment
  
  • Zhang Cong
  • Collin Annabelle
  • Moireau Philippe
  • Trouvé Arnaud
  • Rochoux Mélanie C.
  Proceedings of the Combustion Institute, Elsevier, 2019, 37 (3), pp.4201-4209. Data-driven wildfire spread modeling is emerging as a cornerstone for forecasting real-time fire behavior using thermal-infrared imaging data. One key challenge in data assimilation lies in the design of an adequate measure to represent the discrepancies between observed and simulated firelines (or "fronts"). A first approach consists in adopting a Lagrangian description of the flame front and in computing a Euclidean distance between simulated and observed fronts by pairing each observed marker with its closest neighbor along the simulated front. However, this front marker registration approach is difficult to generalize to complex front topology that can occur when fire propagation conditions are highly heterogeneous due to topography, biomass fuel and micrometeorology. To overcome this issue, we investigate in this paper an object-oriented approach derived from the Chan-Vese contour fitting functional used in image processing. The burning area is treated as a moving object that can undergo shape deformations and topological changes. We combine this non-Euclidean measure with a state estimation approach (a Luenberger observer) to perform simulations of the time-evolving fire front location driven by discrete observations of the fireline. We apply this object-oriented data assimilation method to the three-hectare RxCADRE S5 field-scale experiment. We demonstrate that this method provides more accurate forecast of fireline propagation than if either the fire spread model or the observations were taken separately. Results show that when the observation frequency becomes lower than 1/60 s −1 , the forecast performance of data assimilation is improved compared to simply extrapolating observation data. This highlights the need of a physics-based forward model to forecast flame front propagation. We also demonstrate that the front shape similarity measure is suitable for both Eulerian and Lagrangian-type front-tracking solvers and thereby can provide a unified framework to track moving structures such as flame front position and topology in combustion problems. (10.1016/j.proci.2018.07.112)
  DOI : 10.1016/j.proci.2018.07.112
• Aggregate-driven reconfigurations of carbon nanotubes in thin networks under strain: in-situ characterization
  
  • Bodelot Laurence
  • Pavic Luka
  • Hallais Simon
  • Charliac Jérôme
  • Lebental Bérengère
  Scientific Reports, Nature Publishing Group, 2019, pp.11p. This work focuses on the in-situ characterization of multi-walled carbon nanotube (CNT) motions in thin random networks under strain. Many fine-grain models have been devised to account for CNT motions in carbon nanotube networks (CNN). However, the validation of these models relies on mesoscopic or macroscopic data with very little experimental validation of the physical mechanisms actually arising at the CNT scale. In the present paper, we use in-situ scanning electron microscopy imaging and high resolution digital image correlation to uncover prominent mechanisms of CNT motions in CNNs under strain. Results show that thin and sparse CNNs feature stronger strain heterogeneities than thicker and denser ones. It is attributed to the complex motions of individual CNTs connected to aggregates within thin and sparse CNNs. While the aggregates exhibit a collective homogeneous deformation, individual CNTs connecting them are observed to fold, unwind or buckle, seemingly to accommodate the motion of these aggregates. In addition, looser aggregates feature internal reconfgurations via cell closing, similar to foam materials. Overall, this suggests that models describing thin and sparse CNN deformation should integrate multiphase behaviour (with various densities of aggregates in addition to individual CNTs), heterogeneity across surface, as well as imperfect substrate adhesion. (10.1038/s41598-019-41989-2)
  DOI : 10.1038/s41598-019-41989-2