For that reason, the study of elementary plasticity mechanisms is essential to understand the mechanical properties of solids.
On the other hand, this study allows one to increase our knowledge of the behaviour of crystals at the nanoscopic scale, in connection with other aspects of the physics of solids ("ab initio calculations").
The study of the elementary mechanisms of plasticity includes a combination of the following approaches :
- Choice of model materials adapted to the problems to be solved. These are pure metals, or simple alloys, in which the interesting mechanisms can be isolated. For instance, the study of dislocations in pure iron, and in iron alloys, allow one to better understand the mechanical properties of steels.
- Extensive use of in situ experiments. This original technique, where micro-samples are strained in a transmission electron microscope, is a speciality of our lab. It allows one to observe in real time the motion of crystalline defects, under stress, between -170°C and 1200°C, with a resolution of the order of one nanometre.(vidéos)
- Multiscale approach. The properties of crystalline defects (dislocations) are studied at various complementary scales : nanoscopic (dislocation core structures), microscopic (groups of interacting dislocations), mesoscopic (heterogeneous aspects of deformation, interactions between dislocations and a microstructure), and macroscopic (mechanical tests). The integration of all these results allows one make a link between atomic positions in the core of dislocations and some mechanical properties.
- Modelling. Multiscale modelling is performed on the basis of physical mechanisms rather than phenomenological equations.
Present research activities :
- Modelling of the core of dislocations in titanium
- Simulation of plasticity mechanisms
- Diffusion in the core of dislocations
- Dislocations in quasicrystals
- Plasticity by climb and osmotic forces
- Dislocation mechanisms in iron and iron alloys
- Kinetics of dislocations in silicon
- Shape memory alloys
- Fatigue mechanisms in silicon