Seminar on Evading the strength-ductility trade-off in steels through gradient microstructures

25 Apr 2023 02.00 PM - 03.00 PM MAE Meeting Room B (Blk N3-02b-65) Current Students, Public

Prof Yujie Wei

Director

 State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences

This seminar will be chaired by Prof Zhou Kun.

Seminar Abstract

The outmost surface of engineering materials typically faces the most severe risk of damage. When such boundary conditions are given, employment of graded structures is desired to enhance the reliability of the structure in an economic way. In this discussion, we present experimental observation and simulation results on how gradient twins and gradient phases change the deformation and stress partition in TWIP steels and stainless steel. The mechanisms accounting for the exceptional mechanical properties were investigated at the microscopic level. In TWIP steel, it is found that the switch of twin or phase transformation systems at the sub-grain level and the formation of hierarchical microstructures are responsible for the strengthening and toughening of the material. For stainless steel deforming at different temperature, our investigation show that a set of cylindrical steel samples acquire a graded mixture of hard martensitic and soft austenitic phases through pre-torsion at low temperature, which results in an optimal stress partition in the material—the hard martensitic structures showing a positive density gradient from core to edge carry higher stress near the edge, while the soft austenitic phase showing a negative density gradient from core to edge serves to retain substantial tensile ductility.

Speaker’s Biography​

Dr. Yujie Wei received his B.S. degree in mechanics from Beijing University in 1997, a M.S. degree in solid mechanics from Institute of Mechanics, Chinese Academy of Sciences in 2000, and a PhD degree in applied mechanics from Massachusetts Institute of Technology in 2006. After two years of post-doc experience at Brown University, he joined the University of Alabama as an assistant professor. In 2012, he joined the Institute of Mechanics, Chinese Academy of Sciences and has been a professor there since then.

Dr. Wei’s research interest is about the strength of solids and their plastic deformation mechanisms, with a focus to build-up the relationship between macroscopic mechanical properties and microscale structures of materials. He is also interested in employing advanced computational techniques and big data for structural healthy analysis of large-scale complex systems like high speed trains. Dr. Wei has published multiple papers, as a leading author and/or the corresponding author, in journals like Nature, Nature Materials, Nature Communications, PNAS, PRL, Nano Letters, J Mech Phys Solids, Adv Mater, Acta Mater and so on. He is a recipient of NSFC Outstanding Young Investigator Award (Year 2014).  

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