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系列学术讲座之三――美国田纳西大学、橡树岭国家实验室,E. P. George

 

国家重点实验室学术讲座

SKL-AMM Seminar

 

题目/TitleRecent developments in understanding size effects in crystalline materials: micro-pillar

compression and nanoindentation

报告人/SpeakerE. P. George

报告人工作单位/Affiliation美国田纳西大学、橡树岭国家实验室

日期/Date201067日,June 7 (Monday), 2010

时间/Time 10:00 ? 11:30 AM

联系人/Contact吕昭平教授,luzp@ustb.edu.cn

报告地点/Location:北京科技大学主楼 353,  353 Main Building, USTB

 

报告摘要/Abstract

Interesting size effects are observed when an internal material length scale (e.g., dislocation spacing) becomes comparable to a geometric length scale (e.g., volume of material tested). In this talk I will discuss how these size effects were investigated in single crystals using two complementary techniques, micropillar compression and spherical nanoindentation. Dislocation spacing can be systematically controlled by pre-straining, and the geometric length scale by varying the pillar size/indenter radius. In both cases, yield strengths approach theoretical values when the probed volume is small, and bulk values when the probed volume is large. The transition between these two extremes is stochastic and depends on factors such as the distribution of dislocations and their pinning strengths. A simple statistical model consisting of a distribution of dislocations with different pinning strengths interacting with the applied stress was developed and shown to be consistent with the experimental results including the measured dislocation densities.

 

 

作者简介/Speaker’s short biography

 

Prof. E. P. George is a Distinguished Research Staff Member and Group Leader of the Alloying Behavior and Design Group in the Metals and Ceramics Division. He also has a joint faculty appointment as Professor of Materials Science and Engineering at the University of Tennessee. He has more than 20 years of experience in physical metallurgy and mechanical behavior and has authored more than 150 technical publications including several review articles, a book chapter, and threeencyclopedia articles. His papers are highly cited in the literature: in 1995 ISI ranked him eighth in the world among authors publishing high-impact papers in materials science and ngineering. His primary research interest is understanding the relationship between microstructure at different length scales and mechanical properties. He has expertise in the use of Auger electron

spectroscopy to study effects of interface chemistry on mechanical behavior. He has made seminal contributions to the understanding of brittle fracture and its causes (both intrinsic and extrinsic) in Ni3Al and FeAl, the role of vacancies in causing anomalous strengthening in FeAl, and innovative processing to achieve well-controlled microstructures at multiple length scales. For his contributions he has received numerous awards including the Humboldt Prize from Germany, the Sustained Outstanding Research Award from DOE-BES, and two Best Paper Awards.