第170回構材ゼミ Dr. Laurent Pizzagalli, Director of Research, Institut Pprime, CNRS - Université de Poitiers, Poitiers, France 2025.04.14 開催報告

2025年4月14日、Dr. Laurent Pizzagalliによるご講演が第170回構材ゼミとして開催されました。

Mechanical properties of nanoparticles:
A tale of high strength, shape and size dependence and uncommon plasticity mechanisms.
Dr. Laurent Pizzagalli, Director of Research, Institut Pprime, CNRS -Université de Poitiers, Poitiers, France

Abstract of seminar:
Mechanical properties of materials with dimensions ranging from a few tens of nanometers to about one micron have been largely investigated during the last decades, with the now well-attested fact that the strength tends to increase as dimensions decrease. Fundamental reasons are the reduced defects density and the increasing dominance of surfaces at small scales, which hinder certain plasticity mechanisms and favor others usually inoperative at low stresses. What is less known is how mechanical properties change at smaller scales. For example, the few experiments available do not allow us to assess whether the strength continues to increase or whether it saturates below a given size. Another open question is the influence of the shape of nano-objects like nanoparticles on the mechanical properties.  
In order to obtain additional information, we have performed molecular dynamics calculations of the compression of nanoparticles made of various materials like aluminum, tungsten, silicon, and silicon carbide. Since the reliability of interatomic potentials becomes questionable in such high strain states, atomic interactions are calculated using DFT for the smallest sizes. In this seminar, I will present a summary of these investigations. Several aspects will be discussed such as the limit of the strength increase and the influence of the nanoparticle shape, in relation with the activation of unusual plasticity mechanisms. I will also show how and why we determine strength values larger than the ideal bulk strength in certain conditions.

A short biography of the speaker:
Laurent Pizzagalli received his PhD in Physics of Materials from the University of Strasbourg (France) in 1997. He undertook post-doctoral research in Basel (Switzerland), then in Livermore (USA), following which he joined the CNRS as a permanent researcher, at Institut Pprime (Poitiers, France), in 2000. During his career, he spent long research stays in Toulouse (France), Reykjavik (Iceland), and Modena (Italy).
He is specialized in numerical simulations at the atomic scale, using electronic structure calculation methods like DFT and tight-binding, and molecular dynamics, which he uses to study defects in materials, with a specific focus on mechanical properties and irradiation. He has authored or co-authored 129 publications, a few book chapters, as well as giving ~270 presentations.