The French territory presents many old historical constructions classified as building open to the public (ERP). However, this architectural heritage in masonry is fragile regarding the fire risk as the disaster that occurred on April 15 at Notre-Dame Cathedral in Paris. After a fire, the heritage value of these ERP implies that, if a doubt of structural stability exists, the question of their demolition is generally ruled out, unlike contemporary constructions without architectural value. Moreover, when these buildings are classified as Historic Monuments (HM), they must be restored and, or at least be rebuilt as it was. In any case, the question of the structure stability subjected to fire remains. However, today, knowledge and tools to assess the post-fire structural stability of a masonry building are still missing. The DEMMEFI project proposes to respond to this problem by carrying out a post-fire structural assessment methodology for complex 3D masonry structures. This methodology will first be applied to a common span of the nave of Notre-Dame cathedral and then generalized to similar masonry historic buildings with high heritage value. The methodology developed will be based on the combined and optimized use of the two main existing numerical methods: the finite element method (FEM) and the discrete element method (DEM). A so-called hybrid FEM-DEM method will be proposed in order to combine the advantages of the FEM and DEM methods in order to simulate the mechanical behavior of masonry material. The problem of mechanical stability subjected to fire action (during fire and post-fire) will be provided by a thermo-mechanical characterization of equivalent materials (limestone and lime mortar) and assemblies. Moreover, an estimation of the spatio-temporal fire action on the vault extrados will be studied. The modeling strategy will be based on a multi-scale approach using the hybrid method from the material to the structure. Finally, the relevance of stability indicators in terms of limit thrusts, limit displacements or limit stresses will be studied for each type of sub-structure of the cathedral in order to propose practical verification methods contributing to the structural assessment of these complex heterogeneous structures.

In the last past years, Additive Manufacturing (AM) processes have been intensively developed leading to a revolution in many industrial sectors. These processes offer the possibility of developing parts of complex geometry and high mechanical strength, with short manufacturing times and with important raw material saving. However, conventional metallic AM processes suffer from the prohibitive cost of raw materials, in a powder form, and low deposition rates, increasing manufacturing times and limiting the dimensions of the produced parts. In this context, the MACCADAM project aims to promote the industrialization of a new arc-metal additive manufacturing process derived from welding and based on the deposition of successive layers of a metallic wire melted with an electric arc. This original process differs from other traditional AM processes by allowing high material deposit rates and the use of low cost and easy to use massive products. MACCADAM proposes to solve several issues that still limit the use and diffusion of this innovative process. The aim of this project is to : 1) identify potential applications of this new process based on a comparative analysis of the respective characteristics of the arc-metal process and the other AM processes; 2) identify the process parameters (electric parameters, protective gas, layer stacking strategy ...) leading to optimal geometrical characteristics and limiting the distortions due to residual stresses, for two materials chosen for their industrial interest (316L stainless steel and TA6V titanium alloy); 3) carry out a microstructural and fatigue resistance characterization of the materials in order to assess the parts mechanical properties according to the manufacturing parameters set; 4) model the solidification process of the deposits in order to predict the microstructures and associated mechanical behavior with numerical simulations. MACCADAM gathers academic and industrial partners specialized in the fields of additive manufacturing processes (LMGC, Poly-Shape), materials characterization (ICA, LGP, LMGC) as well as modeling and numerical simulation of forming and manufacturing processes of metallic materials (CEMEF). Ultimately, MACCADAM intends to promote the diffusion of this new process in the industrial world, within a controlled framework, to guarantee the production of high performance parts at a reduced cost.

The demonstration of safety and the extension of the lifetime of complex industrial devices (nuclear...) are based on the periodic non-destructive testing (NDT) of welded parts. When there are thick welds (30 to 70 mm), in austenitic stainless steel, the ultrasonic method for defect detection is the only one possible. It is however complex because the heterogeneous and anisotropic nature of these thick multi-pass welds induces strong perturbations in the propagation of the acoustic beam which distort the diagnostic. The best (non-destructive) solution to overcome this difficulty is obtained by modelling the ultrasonic propagation, but this requires the detailed description of the real crystalline structure of the weld. The current 2D weld models, except LMA’s work, provide either a simplified description of the crystallographic growth, based on a symmetry assumption, or a more realistic description, but at the cost of high instrumentation and computation time. Moreover, no model exists for a weld made in position, when the solidification is also governed by gravity. The objective of the project is to produce a realistic 3D model for welds made with GTAW process in all positions, from minimalist input data (those given by the DMOS) and with a calculation speed compatible with industrial needs. Gravity induces inclinations of the texture not only in the direction perpendicular to the weld, but also in the welding direction. The transition from 2D to 3D is therefore not a simple evolution or adaptation of MINA 2D, because the gap is very important. The study will be progressive: some mock-ups will be manufactured for a narrow chamfer (U-type) which allow a stacking of a single pass per layer, and open chamfer (V-type) geometry, in vertical-up and horizontal groove welding position. Specific instrumentations (embedded camera, optical microscopy, EBSD) will help us to understand the solidification kinetics and the grain growth, and then to create the model, the challenge being linked to the various length scales present (weld, grain, dendrite). The objective is to determine a link between the pool shape (gravity, welding energy, ...), the thermal gradient (part temperature, chamfer, preheating, ...), and the crystal growth (crystal competition, ...). The orientation of the grains will be ultimately calculated from information voluntarily restricted to the welding notebook which describes the welding procedure (geometry of the chamfer, sequence of passes, etc.), to be in adequacy with the industrial practice, which cannot afford to instrument each welding carried out in a complex way. The micrographs simulated by the model will be compared to the real micrographs and will thus allow to validate it. A second validation will also be sought by comparing the ultrasonic propagation predictions obtained by associating the MINA 3D model with a 3D ultrasound propagation model, with experimental data. The prediction of the deviations and divisions of the ultrasonic beam will then be mastered, bringing a significant improvement of the ultrasonic testing. The MINA 3D project perfectly fits with the research axis B.4. One innovation concerns the increase in knowledge of the material, but the main innovation is in the application, and therefore in the consequent improvement of the potential of NDT by ultrasound. The 6 partners of the project are the best French specialists in the field and used to work together.

In the context of demolition programs which are growing rapidly, particularly in the framework of major urban projects, ECOREB (Eco construction with concrete recycling) aims at dealing with recycling issues in the field of construction waste for the future sustainable city. Among the building wastes, only a part of concrete from demolition is currently recycled, mainly for road construction. Recovery of all of these materials as components for the production of recycled concrete is now opening up new environmental, economical and technological prospects but needs to overcome scientific and technological brakes. Reuse of recycled aggregates from demolition / deconstruction can limit the extraction of raw materials and thus contribute to the preservation of natural aggregates. It deals thus primarily with environmental issues. The use of recycled aggregates for the development of new concrete is part of a commitment to sustainable development, partly due to expectations of the “Grenelle de l’Environnement” in France and European regulations. Note also that waste management of building is also a growing market. ECOREB is an industrial research complementary to the National Project RECYBETON. It proposes overcoming fears about the use of recycled aggregates from concrete in the building industry to produce new concretes, using largely experimental results. ECOREB aims, also, at developing new tools dedicated to the study of the water demand due to the presence of cement mortar embedded to aggregates. Moreover ECOREB will make possible the characterization of the interfaces quality between (1) the new concrete and the recycled aggregate and (2) the recycled mortar and the natural aggregate. It also aims at providing a tool for predicting recycled concretes characteristics and especially their behavior under external stresses (mechanical loads, snow, corrosive atmospheres, ...) and under internal stresses (shrinkage, change in humidity or heat of concrete hydration ) and to establish empirical relationships between mechanical parameters and indicators of sustainability in relation to the microstructure which depends on water demand. To achieve these objectives the scientific program is divided into three technical tasks that interact and complement each other. The first "Water and recycled materials" provide recommendations on the formulation of concrete made from recycled materials, the curing of young concrete and the plastic shrinkage phenomenon as well as the associated cracking. The second "Study of mechanical behavior of recycled concrete under static, cyclic, creep and relaxation loadings" will characterize the mechanical behavior of recycled concrete and establish empirical models incorporating microstructural effects. These models will be used by building industry actors to predict the lifetime of the recycled concrete. The third task "durability" will evaluate the freeze / thaw resistance and long-term behavior of concrete recycled regarding to corrosion, chlorides migration and steel corrosion risk. Durability indicators will be assessed. Water and curing effects will be treated. Results of ECOREB will lead to a breakthrough on the reuse of demolished concrete as components of new concrete and, ultimately, to a way in which the use of recycled aggregates in concrete will become part of everyday practices.

A key element of the biomechanical design of trees is their ability to generate large mechanical stresses in wood at the stem periphery. This function is necessary for the tree to control the orientation of its axes, and therefore to grow in height, maintain its branches at an optimal angle or achieve adaptive reorientations. This "maturation stress" appears in wood fibres at the end of the formation of their secondary cell wall, but the underlying biophysical process is still unknown. Understanding the mechanism of maturation stress generation is a question of paramount importance in tree physiology, with important technological outcomes regarding wood processing and also for biomimetic inspiration in material design. As this research needs to integrate knowledge from plant biology, chemistry, physics and mechanics, the project will be supported by three complementary partners, with excellent expertises on tree biomechanics, micromechanics, wood diversity, tree physiology and molecular biology. This partnership will be complemented with a large network of French and international laboratories covering extra-competences needed for the project. Two plant models are chosen, poplar will represent the species developing a specific unlignified gelatinous layer (G-layer) like most temperate species and simarouba will represent non-G-layer species like two third of tropical species. Whereas most researches have been concentrated on G-layer species, our project is a pioneer in the study of the maturation stress mechanisms in non-G-layer species. The strategy relies on i) the determination of both the structural organisation and the mechanical behaviour of wood constituents along the sequence of cell maturation from the cambium to the mature wood and ii) the identification of associated molecular triggers allowing these changes. The observations performed at different scales (macromolecular constituents, cell-wall layer, macroscopic wood), will feed a micro-biomechanical model that will be developed to test the consistency between hypothetic mechanisms and observations made at each level. The research plan is organised in 5 tasks (Molecular triggers, Cellulose and matrix organisation and behaviour, Cell-wall behaviour, Micro-mechanical modelling, Hypotheses testing) designed to solve this old question that still remains enigmatic.