Referee : 

Frédéric Dau

Members :
Jean-Luc Barou, Cathy Froustey, Jérémie Girardot, Sandra Guérard, Ivan Iordanoff, Jean Benoît Kopp, Jonathan Merzeau, Etienne Prulière, Philippe Viot

DIR (Dynamic Impact Rupture) research team focuses dynamic behavior of homogeneous (metallic and polymer materials) and heterogeneous materials (cellular and composite materials but also tow and fabrics are mainly adressed) under severe loadings (shock, impact) and consecutive fatigue-impact , impact-fatigue.

Velocities adressed vary from several m/s (< 10-20 m/s for low velocity impact) to 300 m/s and over for balistic applications.

Analyzing and understanding of physical mechanisms involved at different scales (from micro to macro scales), their characterization and effects on material behavior are the roots of the team motivations.

Both experimental and numerical investigations and developments are conducted.

The scientific expertises for the team are : 

• studying of dynamic fracture for brittle and hyper-brittle materials ;
• applying the discrete modelling to impact and dynamic loadings on divided materials ;
• developing multi-scales numerical methods to link local and global effects ;
• analysing the geometrical and material variabilities  at different scales ;
• building consitituve law including a strain rate effect for architectured materials ;
• understanding dynamics phemenon occuring on manufacturing processes ;

studying the consecutive loading fatigue/impact and impact/fatigue 

Observation d’un impact d’une gélatine sur un assemblage de sphères creuses (vitesse = 50 m/s)

Referee : 
Nicolas Saintier

Members:
Christophe Bois, Charles Brugger, M. Elmay, Thierry Palin-Luc, Nicolas Saintier, Jean-Christophe Wahl

The FMS research group aims at the fundamental understanding and multiscale modeling of the fatigue behavior of materials and structures under cyclic loading. The team has a strong expertise in the field of complex mechanical loadings (multiaxiality, variable amplitude loading) on a large variety of materials (alloys, elastomers, polymers, composites). The main research axes are the following :

• Microstructure-process-fatigue interactions : the objectives are to better understand the effect of microstructural features on the fatigue behavior (volume and surface defects, texture, phases, materials with gradients). We are focussing on aaditive manufacturing, casting, laser shot peening and stamping.
• Very high cycle fatigue : numerous structures experience fatigue lifes far beyond the usual endurance limit range (10⁸ to 1010 cycles)
• Fatigue of composite materials : actual work deal with short fiber reinforced materials and continuous fibers composites. In situ fatigue damage evaluation (particularlly tomography)  and physically based modeling are under focus. 
• Environnemental effets : actual works deal with the evaluation and understanding of  synergetic effects in fatigue-corrosion with the development of original experimental setups and methods.

Research works combine state of the art experimental technics and original methodologies together with microstructure based multiscale modeling to reach a deep understanding of fatigue damage processes. The team also devellops scale transition methodologies in order to ensure their applicabilty at the structural level  ensuring a strong degree of industrial partnership, 80 % of our activity being supported by industry.

Fatigue crack initiation in short fiber reinforced composites as observed by micro-tomography

Referee : 
Isabelle Aubert

Members :
Isabelle Aubert, Olivier Devos, Jérémy Guitard, Jean-Marc Olive, Monique Puiggali et Marie Touzet-Cortina

The research interests of the Mechanics-Corrosion-Hydrogen team concern the coupled effects of the aggressive media, the mechanical stresses and the microstructure on the durability of metallic materials.

Degradation modes are the following:

• Localized corrosion
• Stress corrosion
• Fatigue corrosion
• Hydrogen Embrittlement

A multi-scale approach (from nanoscopic to macroscopic scale) is used to improve understanding of the observed phenomena. It is based on the use of a variety of experimental technics as well as numerical modelling and simulations

Experimental technics : 

• Mechanical tests (static, cyclic with low frequency) in aqueous media with tensile and micro tensile machines for slow strain rate tests.
• In situ video microscopy associated with displacement field identification
• Electrochemical technics at macroscopic scale, mesoscopic scale (millimetric electrochemical cells…) and microscopic scale (scanning electrochemical microscopy SECM, local electrochemical impedance spectroscopy LEIS…).
• In-situ and ex-situ atomic force microscopy AFM (in aqueous media associated with microtensile machine). SKFM mode measurements on the AFM.

In partnership with the platform PLACAMAT : 

• Physico-chemical analyses of the surfaces: EDX analyses, AUGER, GDOES
• Microscopy observations (SEM, TEM)
• EBSD
• Tomography

Numerical simulation and model :

• Crack propagation in polycrystalline microstructure
• Elastoplasticity and hydrogen diffusion coupling
• Effect of the grain boundary segregation on the diffusion of hydrogen

 Materials: carbon steel, stainless steel, nickel base alloys, aluminum alloys, metallic coatings

Characterization and finite element model at the microstructure scale of the intergranular stress corrosion cracking

Referee :

Yves Chemisky

Members:

Anita Catapano, Yves Chemisky, Frédéric Dau, Sandra Guerard, Etienne Prulière

The thematic group 3MAH (Multiscale Modelling and Behaviour of Heterogeneous Materials) is interested in the analysis of heterogeneous materials (cellular, composite, architectural, biological), which require the implementation of modelling tools and advanced characterisation techniques.
The study of these materials requires :

• a fine characterization of the physical mechanisms operating at microscopic (or even nanoscopic) scales
• analysis of these mechanisms and understanding their relationship with the mechanical behaviour of the material and its performance (service life, functionalities)
• observe and model the kinetics of these mechanisms and their links with the evolution of the material's microstructure at different scales
• to numerically simulate the observed phenomena to better understand the behaviour of the material during complex solicitations
• use optimized numerical strategies to simulate the behavior of structures by adopting a multi-scale modeling approach
• to combine numerical and experimental results in order to establish process-microstructure-behaviour relationships of heterogeneous materials

These actions are at the basis of the investigations and developments, both experimental and numerical, carried out within the 3MAH research group. The 3MAH team is also particularly interested in the use of Artificial Intelligence tools in order to simulate the complex, non-linear behaviour of architectural materials.
 The main research axes of the group focus more specifically on :

• The generation of numerical microstructures representing heterogeneous materials (architectural, composite, cellular, granular structures)
• The formulation of complex, multi-physical behavioural laws integrating coupled behaviours (damage, plasticity, viscoelasticity, phase transformation)
• The definition of optimized and reduced numerical methods adapted to the multi-scale simulation of structures. These methods integrate algorithms inspired by Artificial Intelligence (neural network, perceptron, learning).
• The development of numerical methods of multi-scale coupling allowing the dialogue between local and global effects;
• The development of behavioural laws taking into account the speed effects applied to architectural materials;
• helping to understand the dynamic phenomena in several manufacturing processes.

    The 3MAH team also develops software solutions. An open-source library, dedicated to the numerical simulation of the thermomechanical behaviour of heterogeneous materials, integrating multi-scale methods is available here:
https://simcoon.github.io/