ME Seminar - Dislocation climb models from atomistic scheme to dislocation dynamics and its related phase field model coupling with self-climb

Guest Speaker: Prof. NIU Xiaohua

School of Mathematics and Statistics
Xiamen University of Technology

Prof. NIU received her Bachelor degree from Central China Normal University in 2000, Master degree from Zhejiang University in 2005, and PhD degree from the Hong Kong University of Science and Technology in 2017. She is an associate professor at School of Mathematics and Statistics, Xiamen University of Technology. Her research interests include multi-scale modeling and computation in materials science, phase field models, dislocation dynamics and machine learning. She has been responsible for a Youth Fund Project from the National Natural Science Foundation of China and a General Project from the Natural Science Foundation of Fujian Province. Recently the main papers published in Journal of the Mechanics and Physics of Solid, International Journal of Plasticity, Journal of Computational and Applied Mathematics, Communications in Mathematical Sciences etc.

In this talk, I will present a mesoscopic dislocation dynamics model for vacancy-assisted dislocation climb by upscalings from a stochastic model on the atomistic scale. The effects of the vacancy diffusion microscopic mechanisms are incorporated by a Robin boundary condition near the dislocations for the bulk diffusion equation and a new contribution in the dislocation climb velocity due to vacancy pipe diffusion driven by the stress variation along the dislocation. Based on this model, a phase field model for the motion of prismatic dislocation loops by both climb and self-climb is developed. The model is set up in a Cahn- Hilliard/Allen-Cahn framework with incorporation of the climb force on dislocations. Asymptotic analysis shows that the proposed phase field model gives the dislocation climb and self-climb velocity accurately in the sharp interface limit. Numerical simulations of evolution, translation, coalescence and repelling of prismatic loops by self-climb show excellent agreement with discrete dislocation dynamics simulation results and the experimental observation. The simulation results with and without self-climb contribution show the big difference for the prismatic dislocation loops in the evolution time and the pattern.