Structural materials are consistent with the French national priorities, concerning the transportation systems improvements, energy consumption reduction and environment. This axis will strongly benefit from the Le Bourget Techno-Centre development, the latter being focused on aeronautics. This project will include industrials such as EADS and Eurocopter, able to federate many small companies, the ASTech competitiveness pole, others actors from the economical world (territorial collectivities, Air France Industry, Dassault services,....), and from research and education (University Paris 13, SUPMECA, in the future University Paris Diderot...). Because of more and more demanding performances, structural materials need to be studied under various thermomechanical loading conditions and environments : mechanical, physical and chemical characteristics need to be measured, sometimes simultaneously ; the modeling of their coupled properties must be developed ; and some efforts should also be put on the control of elaboration or transformation processes. Consequently, all the aspects concerning material science are present, from the elaboration to the evaluation of the life time and recycling processes, through modeling and development of characterization tools. The fact that these complementary steps can be coordinated within a single LABEX and treated simultaneously is certainly a condition of fast progress. We project to concentrate our efforts on 3 main subjects based on existing competences.

1. Microstructure optimization for enhanced mechanical properties

This axis mainly developed in LSPM will focus on 3 sub-topics :

• Multi-scale investigation and modelling of the behaviour of materials in plasticity, damage and fracture. The advanced methodologies present mainly in LSPM include original experimental techniques (in situ mechanical testing combined within SEM, large strain mechanical tests and strain field measurements, high resolution X-Ray diffraction and complex modeling procedures (mean field or full field micromechanical modeling, polycrystalline FE methods, damage modeling based on second gradient approaches, microstructural evolutions during recrystallization, .... They can be applied to the study of all heterogeneous materials like metals, composites, ceramics, elastomers, since they allow to take into account the microstructural organization of composing phases. The aim of these researches is to improve the prediction and optimization of behaviour and life time of the investigated materials. The developed models will also be tested and validated on other types of materials, studied in the LABEX, such as thin films developed for their magnetic properties.

• Development of nanostructured structural materials, from nanopowders, based on the use and development of a unique transformation plateform present in LSPM, and comprising very
  high pressure devices and severe deformation techniques. This unique set will allow to further develop metallic alloys or composites with ultrafine grains with improved coupled properties, or multiphase alloys with exceptional mechanical properties simultaneous ductility and strength), and to develop new crystalline phases, whose properties can be a priori estimated with the models presented above. This part should greatly benefit from the collaboration with other teams of the LABEX involved in elaboration and characterization of nanopowders. Also, the HP Plateform will be used to elaborate other kinds of materials, such as e.g. biomaterial.

• Development of advanced transformation processes and the control of the resulting properties of materials and structures. Based on the methodology developed at LSPM in the field of thermomechanical treatments (around an asymmetrical rolling mill) we plan to re-visit (EADS and ASTech labeled projects) some other metal forming processes such as flowforming, or warm extrusion. These processes, which are considered as ecological alternatives to machining, need to be associated with an extensive study of the produced mechanical and microstructural characteristics at each step of the process to optimize the final properties and to develop an "environmentally friendly design" approach (thickness and weight reduction, ...).

Surface treatments, tribology and physico-mechanical examinations for integrity control

Although a lot of research projects inside the LABEX are concerned with surface problems (elaboration of thin films, functionalization of surfaces for various applications, ... ), the mechanical properties of these surfaces are rarely examined. LISMMA from SUP-MECA possesses a unique plateform of tribological devices, which allows simulating a wide variety of contact modes and that are used with associated models, to investigate and improve the mechanical properties of surfaces of materials and systems. This platform will be used, in connection with the expertise of ITODYS in functionalization, of LSPM in the physical characterization of thin films, and of MSC for some " thin " complex systems, to develop 3 main themes :

• Development of graded materials and nanostructured coatings, in order to optimize the overall mechanical properties of materials or mechanical parts. LSPM will be involved in this axis for the development of new elaboration processes and of associated mechanical models. One of the main application domains for this axis is the aeronautics industry (the main materials being the Ti alloys and/or some composite materials) and this is why EADS is highly interested by this part of the SEAM LABEX project ;
• "Multifunctionnalization" of surfaces, will combine the expertise of the mechanics in term of control of mechanical properties and the expert thermoplastic polymers) ; this axis can lead to the development and to the validation (through the use of models and mechanical characterization) of new multi-materials or new assembly techniques, which will have some potential applications for ecological constructions ;
• Materials and wetting phenomena. In order to control the elaboration of coatings (and to get uniform or patterned surfaces) from particles, nanoparticles, liquid polymers,.. on solid or flexible substrates, the physical mechanisms active during solidification processes must be thoroughly understood ; this is e.g. what is investigated in MSC for the elaboration of glass sheets (Collaboration with Saint-Gobain) with some controlled experiments and development of analytical models. This type of study will be developed for other applications and completed by the characterization of the final tribological and mechanical properties.

Advanced structural materials and coupled properties

Finely architectured materials for structural or/and functional applications : based on the existence of high level platforms concerning the elaboration, the transformation, the characterization of various materials, coupled with some expertise in multiscale modelling, it becomes naturally consistent to develop even more widely the design of new multifunctional materials and their validation through modeling ; some examples already exist within the LABEX such as the elaboration of ultrahard materials (LSPM), permanent magnets from Co nanowires (ITODYS and MSC), hybrid materials composed of soft components (foams, sprays, polymers) and inorganics components (nanoparticles, polyometallic or alkooxydes, ...) (MSC), multiferroic materials (LSPM), ..... In this field, only the imagination of the researchers can limit the extent of their work ; up to now, the efforts are mainly put on the elaboration and modeling steps. By adding some contributions on the characterization side, the LABEX will become more and more convincing in the development of industrial collaborations.

Functionalized structural materials

For all these structural materials which are asked to become " smarter ", and to resist to more and more severe environments, it becomes also essential investigating their coupled properties as well as the interaction between a given material and it environment. In the field of multi-scale modelling, some coupled properties (mechanical and thermal, magnetic, electrical,....) have already been successfully predicted in LSPM for a wide variety of materials. Some teams in MSC work on the development of porous materials that present a good capacity of reducing the vibrations or the sounds and that can be incorporated into structural materials for constructions or aeronautic applications. Also, the investigation of the behaviour of materials under severe environment (corrosion, high temperatures, Hydrogen embrittlement) is already treated in LSPM which both developed original equipments. More recently, LSPM got involved in this research and developed some FE modeling. In the context of a developing aeronautic technocenter in Le Bourget, all skills are thus gathered inside this LABEX to make significant progresses in the development of smart structural materials (with combined properties) and systems (including their surfaces), capable of resisting in extreme environments. LISMMA from SUP-MECA will be associated to a number of researches.