In the framework of reducing energy losses and of improving eco-efficiency, the Lumiere project aims to better understand and model the mechanisms governing the mixed lubrication regime with the objective of a more accurate estimate of the lifetime and friction losses of the lubricated components. Among the many facets of this problem, the impact of wear particles and their interactions with the lubricating fluid and the surfaces will be more particularly studied: by in situ observations on dedicated test benches and by the method of discrete elements (DEM) coupled with a lubrication model. The results will then be integrated into a multiscale tool allowing simulations at the component level. The work will be carried out by the Pprime Institute, specialized in the study and simulation of lubrication in collaboration with the LaMCoS, recognized for its skills in the experimental study of tribology and the LMGC, expert in the simulation of contact and wear by DEM.

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 fusion welding processes, metallic materials of dissimilar type, nature or properties are joined in order to develop a single part with new functionalities. However, during the cooling process, the solidification stage leads to the development of particular material defects inside the weld bead depending from process parameters [Wel01, Kou02]. A thin liquid metal layer may persist between grains and dendrite arms in the coherent grain structure which endure large thermal stresses. This phenomenon promotes the development of hot cracking defects. Similarly, at the same ending solidification stage, the formation of intermetallic brittle phases is commonly observed induced by the complex nature of segregation phenomena. These specific welding defects have to be carefully monitored regarding the expected high level of reliability, mechanical strength and fatigue life intended by industries. This control is particularly evident considering the safety of welded equipment in automotive, aircraft or energy industries. The development of defects is also made worse with the recent use of advanced materials, innovative processes or complex geometries. These defects and theirs consequences are barriers to the efficiency of welding processes to meet future expectations of industries. The NEMESIS project aims to deliver a generalized approach to remove these barriers through the use of virtual materials in a collaborative partnership balanced between modelling, experimentation and valorization. The NEMESIS project will first propose a reliable modelling of grain growth development in welding and associate defect occurrences considering the complex physical phenomena taking place during the whole fusion process. In-situ experimental observations on test benches will investigate grain growth and hot cracking mechanisms (ICB, LMGC) to analyse local criteria leading to defects development. Simultaneously grain structure and associated defects will be modelled in a multi-physics approach (ARMINES-CEMEF) based on the Cellular Automaton-Finite Element (CAFE) approach. Modelling of grain growth at the mesoscopic scale will be coupled with the resolution of the conservation equations at the macroscopic scale in a multiscale approach taking into account thermomechanical, solute and fluid flow evolutions. The CAFE tool will offer the possibility to develop realistic virtual microstructure similar to the ones observed by industries. In addition, the current ultrasonic Non Destructive Testing (NDT) used to detect, localize and estimate welding defects will benefit from this project. Indeed the simulated microstructure and defect morphology obtained from the numerical simulation of welding will be used as input of the ultrasonic inspection simulation codes: the CIVA Software (CEA LIST) and the ATHENA Code (EDF R&D). Defect echoes will be simulated on the numerical material also considering ultrasonic interactions with grains which has large consequence on NDT performances. The effects of the weld microstructure and cracks morphology position, shape or orientation on the inspection reliability will be investigated. Influences of intermetallic phases on ultrasonic interaction will also be a point of interest. The model validation will be conducted on steel grades in industrial configurations. Thus the solidification microstructure and hot cracking formation in welded equipment will be investigated. Nuclear power plant (EDF R&D) and development of brittle phase on automotive steels strengthened with manganese (ArcelorMittal) will be considered. Softwares modelling welding processes (TRANSWELD) and control of defects (CIVA, ATHENA) will benefit from this research and promote the outcomes of NEMESIS. This project corresponds to a significant breakthrough in the mastering and control of arc welding defects through the use of virtual materials and an undeniable technological advance in the mastery of welding processes as a response to industrial needs.

Plant residues are an abundant source of renewable matter, but require targeted dissociation at the tissue scale for the design of high-quality products. This is a huge scientific challenge that crucially depends on the variety of the compositions and histological structures of plant tissues as well as the complex physics of grinding, involving the poorly-understood flow of breakable particles of various shapes and properties. The ambition of this project is to elaborate a generic multiscale approach for realistic modeling of plant comminution accounting for both cellular and granular microstructures of plant residues. This bottom-up approach will proceed from the mechanical and physicochemical interactions at the scale of the relevant constituents (cells, envelopes, organs...) to model intercellular dissociation with the goal of developing single-particle fracture laws that will be validated experimentally and included in dynamic simulations of a large number of particles at the process scale. The methodology that we propose is based on state-of-the art computational (Peridynamics, Discrete Elements) and experimental (histology, multispectral imaging, tomography, milling) approaches. It will be organized in three work packages dealing with 1) Mechanics of fracture at the cell/tissue scales, 2) Fracture behavior at the scale of a single plant residue particle, and 3) Fragmentation process of plant material. The consortium is composed of three partners with complementary expertise, involving early-career and confirmed researchers. The project will benefit from the longstanding experience with tissue characterization methods and grinding of vegetal powders in Montpellier and X-ray and neutron imaging in Grenoble. The originality of PlantCom lies in its multiscale and cross-disciplinary nature, bridging powder process with fracture mechanics and the rheology of granular materials, to elaborate a physics-based toolkit for plant comminution.

In the field of cultural heritage, various data describe the state of the monument (survey data and scientific imaging, mappings of degradations, photographic collections, historical archives, analysis documents, coring, etc.). For the difficulty to collect, compare, analyze and validate data prior to restoration, this project aims to mobilize various disciplines (architecture, conservation, mechanics, informatics) to define a prototype of chain for the processing of information (including metrics and spatial analysis of surfaces, geometric models of structures, heterogeneous documentary sources, etc.). The objective is to design and develop an open and extensible software platform for the capitalization and the management of knowledge that enhances the comprehension and analysis of degradation phenomena affecting historic buildings. This project belongs to a highly multidisciplinary approach, and aims to support, in a rational way, the set of technical features (leaning on the "technological blocks" already developed by the consortium partners). Moreover, it aims to integrate them within a methodological reflection related to scientific questions raised by real objects of study. In terms of computational modeling, this project presents two innovative aspects: on one side, the idea of ??linking (and of bringing near) the phase of acquisition of spatial data to the one of data analysis and interpretation, on the other side, the ambition to develop analysis supports (morphology of the building, surface state, structural behavior) interconnected in a system conceived for the semantic characterization, based on mechanisms of distribution / spread (multiscale and multi-projection) of concepts structured according to an ontology specific to cultural heritage domain.