October 22, 2024

Understanding Strain Hardening of Face-Centered Cubic Metals using Dislocation Dynamics

In this MSE Seminar, Professor Wei Cai will present recent findings from dislocation dynamics simulations of how single crystal copper deforms under different loading orientations.
2:00pm - 3:00pm

Speaker

Wei Cai

Department of Mechanical Engineering, Stanford University

About This Talk

Understanding plasticity and strength of crystalline materials in terms of the physics of microscopic defects has been a long-standing goal of materials research. Over the last two decades, much effort has been placed on the prediction of stress-strain curve of single crystals through large-scale dislocation dynamics (DD) simulations. If successful, DD can thus provide a quantitative link, which has been lacking to date, between dislocation physics at the atomistic scale and crystal plasticity at the continuum scale. Cai reports on the latest findings from DD simulations of uniaxial deformation of single crystal Cu along more than 100 loading orientations. These DD simulations generate a large amount of data on the dislocation microstructure evolution based on which physics-based constitutive relations can be constructed systematically. The dislocation networks are found to have a much more complex structure than previously expected, in the sense that most nodes (where three dislocation lines meet) are not recognizable from the conventional picture of binary junction formation. The dislocation link length on every slip system is found to obey a distribution describable by the sum of two exponentials. We also report the first direct comparison between DD simulations and Kolsky bar experiments for single crystal Cu under [001] and [011] orientations under identical loading conditions (strain rate ~ 104 s-1). Such a comparison is essential in establishing the fundamental premise of dislocation-based theory of crystal plasticity. Cai will present the insights gained from these comparisons, including the importance of jogs on dislocation mobility.

Biography

Wei Cai received his B.S. degree in optoelectronic engineering from Huazhong University of Science and Technology, China, in 1995, and his PhD in nuclear engineering from MIT in 2001. He was a Lawrence Postdoctoral Fellow at the Lawrence Livermore National Laboratory from 2001 to 2004. He is currently a professor in the Department of Mechanical Engineering at Stanford University. He received the Presidential Early Career Award for Scientists and Engineers in 2004, and the American Society of Mechanical Engineers Hughes Young Investigator Award in 2013. His research interests include dislocation dynamics and metal plasticity, atomistic simulations of deformation mechanisms at the nanoscale, and metal 3D printing. He is co-author of 150-plus journal publications, a book “Computer Simulations of Dislocations” (2006), and an undergraduate-graduate textbook, “Imperfections in Crystalline Solids” (2016).

About the MSE Seminar Series

The Materials Science and Engineering (MSE) Seminar Series features distinguished speakers from leading institutions, offering a platform for sharing groundbreaking research, innovative ideas, and entrepreneurial experiences. Held multiple times each semester, these seminars bring global perspectives world to MIT’s materials research community, exposing students, faculty, and postdocs to cutting-edge concepts and valuable networking opportunities.