Date: Thursday, March 12th 2015
Time: 12:00 pm to 1:00 pm
Location: JHU Homewood Campus, Hackerman Hall B-17
Speaker: Prof. George Z. Voyiadjis
Boyd Professor, Chair & Bingham C. Stewart
Distinguished Professor of Engineering
Department of Civil & Environmental Engineering
Director for Center for GeoInformatics C4G
Patrick F. Taylor Hall, Room 3508-B
Louisiana State University
Baton Rogue, LA 70803
USA
Title:
Thermo/Mechanical Length Scales in Metals from Gradient Plasticity and Molecular Dynamics Studies of Nano-indentation
Abstract:
Strain gradient plasticity (SGP) is used to predict size effects in the deformation behavior of metals at the micron and submicron scale and it is appropriate for problems involving small dimensions. Size dependency of the mechanical properties is a consequence of increase in strain gradients inherent in small localized zones which lead to geometrically necessarily dislocations that cause additional strengthening. The current SGP theories do not give sound interpretations of the size effects if a definite and fixed length scale parameter is used and variable length scale which changes with the deformation of the microstructure that depends on dislocation evolution, temperature, and rate effects in addition to the grain size is required to address the real behavior of the materials. Moreover, the observed indentation size effect cannot be well explained by the SGP theories.
The correlation of the data obtained from MD and SGP simulations of nano-indentation is used to guide the process of identification of characteristic thermo/mechanical length scales in metals. The research studies aim at developing fundamental understanding of critical issues such as: i) the role of characteristic length scales, temperature, and microstructural features (grain size, grain boundaries, texture, etc.) on the yield and flow stresses of nanomaterials, ii) the enabling knowledge of grain boundary engineering aimed at achieving microstructures with desired properties, and iii) advancing the multiscale and physical-based theoretical and computational models to capture the observed mechanical response and scale-dependent characteristics.
About the Speaker:
George Z. Voyiadjis is the Boyd Professor at the Louisiana State University, in the Department of Civil and Environmental Engineering. Voyiadjis is a Foreign Member of the Polish Academy of Sciences. He is the recipient of the 2008 Nathan M. Newmark Medal of the American Society of Civil Engineers and the 2012 Khan International Medal for outstanding life-long Contribution to the field of Plasticity. Voyiadjis’ primary research interest is in plasticity and damage mechanics of metals, metal matrix composites, polymers and ceramics with emphasis on the theoretical modeling, numerical simulation of material behavior, and experimental correlation. Research activities of particular interest encompass macro-mechanical and micro-mechanical constitutive modeling, experimental procedures for quantification of crack densities, inelastic behavior, thermal effects, interfaces, damage, failure, fracture, impact, and numerical modeling. He has two patents, over 260 referred journal articles and 17 books (10 as editor) to his credit. He gave over 350 presentations as plenary, keynote and invited speaker as well as other talks. Over fifty graduate students (30 Ph. D.) completed their degrees under his direction. He has also supervised numerous postdoctoral associates. Voyiadjis has been extremely successful in securing more than $15.0 million in research funds as a principal investigator from the National Science Foundation, the Department of Defense, the Air Force Office of Scientific Research, the Department of Transportation, and major companies such as IBM and Martin Marietta.
Faculty Host:Prof. Somnath Ghosh, 203 Latrobe, 410-516-7833, [email protected]
For more information, please contact Khairul Bariah Abd Majid, 410-516-5033, [email protected]