New constraints on energy consumption impose a strong research effort in order to develop new materials, less energy-consuming during their production, energy-saving during their use, and more efficient in recycling processes. The incorporation of air into conventional materials appears to be a simple and efficient answer to these new constraints, in every stage of the material life, from the production stage to its use as thermal insulation material in buildings. This proposal concerns issues for aerated materials known as Particulate Aerated Materials (PAM), elaborated from granular pastes, such as cementitious and plaster pastes. The potential of development of these MAP is huge, especially in the field of the thermal renovation of buildings, because contrary to the nowadays used organic foams, these materials are incombustible and can be directly produced on construction site. Nevertheless, in order to increase their thermal performance at a level comparable to that of organic foams, important research effort must be undertaken in order to increase as much as possible the fraction of incorporated air, and so increase the energy benefits which we have just recalled. So, from slightly aerated materials, they are called to become foamy materials. This transition is under way in building materials companies, but it is nowadays hindered by several major scientific challenges that must be overcome to develop this class of new materials in an optimum way. This proposal aims at overcoming a decisive stage in the understanding and the development of the existing PAM. We like to elaborate model systems for which it is possible to control finely all parameters influencing their properties. These systems will allow us to study in a parametric manner the properties of solidified and non-solidified PAM. The most ambitious objective is to develop one or several functions of industrial interest (thermal, acoustical) without degrading the mechanical resistance of the material. The morphological evolution of these systems between the instant of their generation and their hardening, which poses serious difficulties in their elaboration nowadays, will be also studied to resolve the numerous issues encountered for this class of materials. This multidisciplinary proposal gathers academic and industrial partners with supplementary competences, covering all theoretical and experimental aspects in physics and chemical physics of cellular materials, in mechanics, in heat science and in acoustics. Dedicated work will be simultaneously devoted to model systems, allowing for a complete experimental study to be undertaken on problems of industrial interest, as well as a rigorous comparison of results obtained with theoretical predictions – also developed as part of this proposal. The optimization of industrial materials, such as foamed concrete, is also planned.

This proposal is concerned with the development of novel methodologies (including identification and validation strategies), stochastic representations and numerical methods in stochastic micromechanical modeling of nonlinear microstructures and imperfect interfaces. For the sake of feasibility, the applications will specifically focus on the modeling of hyperelastic microstructures and materials exhibiting surface effects and containing nano-inhomogeneities (such as nanoreinforcements and nanopores). For the case of nonlinear microstructures, the project aims at developing relevant probabilistic models for quantities of interests at both the microscale and mesoscale. The consideration of the latter turns out to be especially suitable for random nonlinear microstructures (such as living tissues) for which the scale separation, which is usually assumed in nonlinear homogenization, cannot be stated. Random variable and random field models for strain-energy functions will be constructed by invoking the maximum entropy principle and propagated through stochastic nonlinear homogenization techniques. A complete methodology for identifying the proposed representations will be further introduced and validated on a simulated database. Concerning the imperfect interface modeling, one may note that surface effects are usually taken into account by retaining an interface model (such as the widely used membrane-type model) involving several assumptions such as those related to the mechanical description of the membrane. Such arbitrary choices certainly generate model uncertainties which may be critical while propagated to coarsest scales and which may therefore penalize the predictive capabilities of the associated multiscale approaches. In this project, we propose to tackle the issue of model uncertainties in multiscale analysis of random microstructures with nano-heterogeneities by constructing nonparametric probabilistic representations for the homogenized properties. A complementary aspect is the construction of robust random generators, able to simulate random variables taking their values in given subspaces defined by inequality constraints and non-Gaussian random fields. Whereas such random fields can typically be generated making use of point-wise polynomial chaos expansions, the preservation of the statistical dependence is hardly achievable with the currently available techniques. In this proposal, we will subsequently address the construction of new random generators relying on the definition of families of Itô stochastic differential equations. Such generators are intended to depend on a limited number of parameters (independent of the probabilistic dimension), for which tuning guidelines will be provided. The proposed models will clearly go a step beyond what is currently done in deterministic mechanics for such materials and the expected results are in the forefront of the ongoing developments within the scopes of uncertainty quantification and material science. In addition, it worth pointing out that such theoretical derivations are absolutely required in order to support the current new developments of 3D-fields measurements and image processing at the microscale of complex materials.

This project is devoted to the low-frequency (LF) vibration analysis of dynamical structures having a high modal density in the LF band. The increasing complexity of dynamical structures in many industrial fields (automotive, aerospace…) induces an increase of the LF modal density and requires new predictive and efficient tools for the analysis of their complex dynamical behavior. The frequency spectrum of such structures is characterized by the presence of well separated global elastic modes which are coupled with a large number of local elastic modes in this LF band. Therefore, the classical modal analysis, which is known to be efficient for the case of well-separated resonances is no longer adapted in the investigated case. Furthermore, the global elastic modes cannot easily be separated from the local elastic modes. Indeed, due to the coupling between global elastic modes and local elastic modes, the deformations related to global elastic modes include some local contributions. In the same way, the deformations related to local elastic modes include global contributions. Thus, there are no efficient method which can be used to select the global elastic modes and the local elastic modes. In addition, although the Reduced-Order Model (ROM) must be constructed with respect to the global elastic modes, it must have the capability to predict correctly the dynamical behavior of the structure in this LF range. Since there are local elastic modes in the LF range, a part of the mechanical energy is transferred from the global elastic modes to the local elastic modes. These local modes store this energy and then induce an apparent damping at the resonances associated with the global elastic modes. There are three objectives in this project: (1) the first objective concerns the construction of a robust ROM by using a basis which is constituted of global modes and which is able to take into account the effects of the local displacements. To achieve this objective we propose to use a recent method which allows the extraction of a basis of global displacements and a basis of local displacements by solving two separated eigenvalue problems. The reduced modeling of the local contributions is the main issue for which this project aims to provide a solution. (2) The second objective is to construct ROMs in the context of slender complex dynamical structures which are characterized by a high modal density of local elastic modes in the LF band. Usually, the industry uses equivalent beam models (for which the validity is generally limited to the first resonances) to analyze this type of structure. We propose here to directly extract beam-like vectors in order to construct a ROM, which remains predictive in a large frequency domain. (3) The third objective concerns the dynamical analysis of non-linear structures (large deformations). The use of the modal analysis method to reduce the non-linear equations is prohibitive when the modal density is too high. We propose here to construct a ROM by using a global displacement basis and if needed by taking into account the effect of the local displacements. These three objectives would be achieved through: - Theoretical developments. - Experimental validations on a simple structure. - Several industrial applications. Concerning the final phase, the first industrial application concerns the construction of an efficient ROM of an automotive vehicle in collaboration with PSA Peugeot-Citroën. The second one concerns an application for the fuel assembly of a Pressurized Water Reactor in collaboration with EDF R&D. These researches aim at removing methodological locks and at providing non-intrusive methods directly usable by the involved engineers.

Vision and other light-based signaling processes are ubiquitous in Nature. Among all the molecular mechanisms responsible for light emission (eg fluorescence, phosphorescence …), chemiluminescence and its corresponding process in living organisms, bioluminescence, are interesting because of their molecular origin: chemical energy converted to light. It is noteworthy that the emitted light is a signature of the underlying chemical reaction. Hence bioluminescence has inspired the development of many analytical toolboxes in biomedical applications (eg imaging) using analogues of typical light emitters (fireflies, beetles, jellyfishes, ...) Because these analogues exhibit photochemical properties similar to their natural counterparts (luminophores), they usually emit blue and green colors, i.e. synthetic yellow or red light emitters remain scarce. The design of bio-inspired light emitters requires a deeper understanding of the factors responsible at the molecular level for the tuning of the emitted color. As exemplified by the design of Green Fluorescent Protein (GFP, 2008 Nobel Prize in Chemistry)-like systems with optimum photophysical properties, it is of paramount importance to deeply understand the interactions between the light-active species and their protein binding pocket. Similar achievement is needed for the development of bioluminescence-based highly sensitive analytical techniques in environmental, medical, food analysis to cite just a few. The BIOLUM project aims to combine state-of-the-art theoretical and experimental fundamental researches to assess the effect of two major color tuning factors: 1) the luminophore + protein structures and interactions, 2) pH. Crossing the informations accumulated for both native and modified luciferin luminophores in the paradigmatic firefly luciferase enzyme, we envision an improved picture of the mechanisms at work in color modulation, with focus on 1) structures of native and modified luciferins in the luciferase binding pocket, 2) relevant photochemical steps in light emission, 3) key proton transfers between oxyluciferin (denoting the very last luciferin structure before light emission) and various donors and acceptors and 4) amino acids of the protein binding pocket that are crucial to control light emission color. Finally, the gained knowledge will help to suggest new directions for the rational design of man-taylored chemi- and bio-luminescent systems with selected colors.

The subject of this project is the 3D printing (SLS) of PA12/glass beads composite for applications in aerospace industry. The SLS process uses laser sintering of composite powder with polymer matrix containing glass beads. One of the limiting points of polymers composites for their use in aerospace systems is their durability, and more specifically their resistance to failure due to fatigue cracking. The objective of this project will focus on the study of finished products obtained by SLS of composites powders and their resistance to cracking. The objectives of this work are to understand failure mechanisms in these highly heterogeneous materials at two scales, the scale of the microsctructure and the scale of the workpiece, by combining experimental characterization of cracks networks by mechanical testing, 3D imaging by X-rays laboratory microtomography image analysis, and numerical simulations. The identified microstructural damage models will be used to construct a crack propagation model at the scale of the workpieces, and will account for specificities related to the material and the process: the highly heterogeneous nature of the microstructure and its strong anisotropy due to the layered structure obtained by SLS. Then, it will be used to optimize the process parameters and the shapes of products in the design step. Up to now, the damage mechanisms in compounds obtained by SLS 3D printing are not very well understood, even less for products obtained from composite powders. The objectives imply several challenges related to the numerical simulation of complex crack networks in highly heterogeneous materials, the detection of micro cracks by 3D imagery imaging within combined with in situ mechanical testing, the modelling of damage and its identification at both micro and macro scales. The mechanical parameters, including the damage ones, will be characterized at the micro and macro scales by approaches combining tomography within microstructures (damage at the interfaces, damage related to the layered structure of the material) or at the scale of the workpiece, and numerical simulations through inverse approaches. The studied material is obtained from composite powder made of a polymer matrix of PA12 and containing glass beads. The powder is then sintered by laser to obtain 3D workpieces by PRISMADD. This project will allow optimizing the process parameters of the 3D process and the geometries of the workpieces with respect to failure criteria and lightweight. A numerical simulation code working able to capture damage mechanisms at both microscopic and macroscopic scales will be developed, based on the phase field method. This technique allows modelling initiation, propagation and merging of complex 3D crack networks in heterogeneous media. The method will be extended to the behaviour related to the material, characterized by a strongly nonlinear anisotropic behaviour. The tasks will consist into: (a) developing an efficient modeling numerical framework for simulating complex networks of cracks in highly heterogeneous microstructures from voxel models such as those arising from X-rays computed micro tomography imaging (XRµCT) and at the scale of the workpieces; (b) manufacturing by SLS 3D printing samples for a set of controlled process parameters; (c) characterize the strength properties of the new manufactured materials, with both macroscopic experimental mechanical testing and imaging at microscale, based on in situ mechanical testing in imaging devices and full-field kinematic measurement techniques, in 2D (optical observation) and in full 3D (XRµCT) ; (d) proposing microstructural and macroscopic damage models, identifying them by the mentioned experiments, and developing simplified multiscale damage models for bridging micro and macro damage; (e) optimizing the process parameters and the geometries of the produced workpieces with respect to the strength resistance of the produced products.