JIAYIN (KAY) LU 卢嘉茵
Applied Mathematician & Computational Artist & Freelance Photographer
Multi-scale Modeling of the Bulk Metallic Glasses (BMGs)
Fall 2021 -Present
Advisor: Prof. Christopher Rycroft
Collaborators: Bin Xu, Zhao Wu, Michael Falk, Franz Bamer, Michael Shields
Status: Close to finish. We expect to publish our findings in late 2023 / early 2024.
Bulk metallic glasses (BMGs) are a category of amorphous materials renowned for their outstanding physical and mechanical characteristics, including remarkable strength, exceptional toughness, and high fatigue resistance. Although BMGs excel over traditional crystalline metals in numerous aspects, they can experience catastrophic failure in a notably brittle manner. Consequently, extensive research efforts have been dedicated to investigating their plastic deformation behaviors. The ultimate goal is to enhance our ability to predict material failure accurately, a critical step toward harnessing their full potential in various engineering applications.
Figure: χ is a state variable representing the disorderliness of the system. Higher χ corresponds to larger plastic deformations.
(a)-(c) Coarse-grained view of two example MD simulations of a 400,000-atom system.
(a) The initial χ field of the MD simulations.
(b) In one simulation, a horizontal SB formed.
(c) In another simulation, a vertical SB formed.
(d)-(f) Two example simulations using the stochastic multi-scale model.
(d) Both simulations used the same initial χ fields;
(e) One simulation led to the formation of a horizontal shear band (SB);
(f) Another simulation evolved into the formation of a vertical SB.
Working with my advisor Prof. Christopher Rycroft, Prof. Michael Falk and his group at Johns-Hopkins University, and Prof. Franz Bamer and his group at RWTH Aachen University, I have developed a multi-scale model to study plastic deformation behaviors of BMGs.
Our collaborators developed a mesoscopic model to describe the plastic deformation behaviors of a representative element (RE) with a size of 4,000 atoms. They used a large data-set harvested from Molecular Dynamics (MD) simulations, and built a statistical model, that stochastically describes when and how much plastic deformation happens for the RE under simple shear.
In my work, I incorporated the mesoscopic, data-driven and stochastic model into the macroscopic continuum model [1]. The original continuum plasticity model is less realistic, since it is deterministic and can not simulate the stochastic plastic deformation behaviors of the materials. I switched out the original plasticity model, and replaced it with the mesoscopic model. I use the mesoscopic model to describe local plastic deformations for the continuum model, by resolving the differences in scales of the two models in physically reasonable ways.
Previously, researchers have to use MD simulations to obtain realistic plastic deformation behaviors of BMGs. However, MD simulates interactions at the atomistic level, and therefore, is too expensive to be used for systems of large sizes. With the multi-scale model, we can now simulate BMGs of large system sizes thanks to the continuum framework, and the simulations will have realistic and stochastic plastic deformations due to the mesoscopic data-driven model. An example is shown in the figure.
Reference
[1] Chris H. Rycroft, Yi Sui, and Eran Bouchbinder. An eulerian projection method for quasi-static elastoplasticity. Journal of Computational Physics, 300:136–166, 2015.