Archive 4 December 2018

PhD Defence : Carolina Baruffi

PhD Defence : Carolina Baruffi

Carolina Baruffi will defend her Phd thesis entitled “Application of an Overdamped Langevin Dynamics to the study of microstructural evolutions in crystalline materials” on Monday, December 17 at 2 pm. Her defence will take place at the ONERA Centre in Châtillon (29 avenue de la division Leclerc) – Contensou room.

Application of an Overdamped Langevin Dynamics to the study of microstructural evolutions in crystalline materials

The macroscopic properties of metals and metalLIC alloys are highly dependent on their microstructure. Numerical modeling is a very powerful instrument for understanding its evolution under given thermomechanical conditions. The need to understand the processes at the microscopic scale that drive phenomena such as crystal plasticity, recrystallization and phase transformations, led to a growing interest in atomistic modeling techniques such as Molecular Dynamics. This approach takes into account the discrete nature of matter and thus automatically incorporates all the processes acting on the atomic scale. However, it has strong limitations in terms of accessible time and space scales. In particular, the presence of high frequency vibrations (phonons) requires the use of integration time steps of the order of the femtosecond, which limits the time scale observed to a few nanoseconds.



This thesis deals with the problematic of the time scale limit. In order to get rid of phonons, we propose the use of an overdamped Langevin dynamics. The first order in time nature of the equations used in the model implies that vibrations are not explicitly represented. Their effect in the system evolution is integrated in the stochastic noise term. To our knowledge, it is the first time that the overdamped Langevin dynamics has been applied in this context. Consequently, the main objective of this thesis has been studying the potentialities of this method by applying it to two phenomena that characterize the microstructural evolution in metals: grain boundary migration and phase transformations.

Key words: atomistic simulations, Langevin dynamics, grain boundary, phase transition

PhD Defence : Hocine Lebbad

PhD Defence : Hocine Lebbad

Mr Hocine Lebbad will defend his Phd thesis entitled “Modeling the growth of Widmanstätten structures using the phase field method” on Tuesday, December 12 at 2 pm. His defence will take place at the ONERA Centre in Châtillon (29 avenue de la division Leclerc) – Contensou room.