Author
K.S. Kumar
Other affiliations: Martin Marietta Materials, Inc., Massachusetts Institute of Technology
Bio: K.S. Kumar is an academic researcher from Brown University. The author has contributed to research in topics: Microstructure & Strain rate. The author has an hindex of 32, co-authored 104 publications receiving 5270 citations. Previous affiliations of K.S. Kumar include Martin Marietta Materials, Inc. & Massachusetts Institute of Technology.
Topics: Microstructure, Strain rate, Alloy, Deformation (engineering), Creep
Papers published on a yearly basis
Papers
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TL;DR: In this article, the authors present an overview of the mechanical properties of nanocrystalline metals and alloys with the objective of assessing recent advances in the experimental and computational studies of deformation, damage evolution, fracture and fatigue, and highlighting opportunities for further research.
1,811 citations
TL;DR: In this article, the mechanisms of deformation and damage evolution in electrodeposited, fully dense, nanocrystalline Ni with an average grain size of ~30 nm and a narrow grain size distribution were investigated by recourse to (i) tensile tests performed in situ in the transmission electron microscope and (ii) microscopic observations made at high resolution following ex situ deformation induced by compression, rolling and nanoindentation.
689 citations
TL;DR: In this article, nanoindentation and uniaxial compression of focused ion beam-milled cylindrical micropillars (1-2 μm diameter) were conducted on as-received and pre-strained specimens.
255 citations
TL;DR: In this article, the effect of prior stretching on the identity of strengthening phases in various aging conditions was examined, and the results showed that overaging of the stretched material produced streaks and spots of lower intensity than in the unstretched material.
154 citations
TL;DR: In this article, the authors measured the evolution of intermetallic volume, stress, and whisker density in Sn and Pb-Sn alloy layers on Cu to study the fundamental mechanisms controlling whisker formation.
Abstract: We have simultaneously measured the evolution of intermetallic volume, stress, and whisker density in Sn and Pb–Sn alloy layers on Cu to study the fundamental mechanisms controlling whisker formation. For pure Sn, the stress becomes increasingly compressive and then saturates, corresponding to a plastically deformed region spreading away from the growing intermetallic particles. Whisker nucleation begins after the stress saturates. Pb–Sn layers have similar intermetallic growth kinetics but the resulting stress and whisker density are much less. Measurements after sputtering demonstrate the important role of the surface oxide in inhibiting stress relaxation.
121 citations
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TL;DR: The mechanical properties of nanocrystalline materials are reviewed in this paper, with emphasis on their constitutive response and on the fundamental physical mechanisms, including the deviation from the Hall-Petch slope and possible negative slope, the effect of porosity, the difference between tensile and compressive strength, the limited ductility, the tendency for shear localization, fatigue and creep responses.
3,828 citations
TL;DR: In this article, the Hall-Petch relation is discussed separately for the yield stress of polycrystalline metals and for the flow stress of deformed metals for a grain size range from about 20 nm to hundreds of micrometers.
2,043 citations
TL;DR: An approach to optimize strength and ductility is outlined by identifying three essential structural characteristics for boundaries: coherency with surrounding matrix, thermal and mechanical stability, and smallest feature size finer than 100 nanometers.
Abstract: [Lu, K.; Lu, L.] Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, Shenyang 110016, Peoples R China. [Lu, L.; Suresh, S.] MIT, Sch Engn, Cambridge, MA 02139 USA.;Lu, K (reprint author), Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, Shenyang 110016, Peoples R China;lu@imr.ac.cn ssuresh@mit.edu
1,812 citations
TL;DR: In this article, the authors present an overview of the mechanical properties of nanocrystalline metals and alloys with the objective of assessing recent advances in the experimental and computational studies of deformation, damage evolution, fracture and fatigue, and highlighting opportunities for further research.
1,811 citations
TL;DR: In this paper, a review of continuum-based variational formulations for describing the elastic-plastic deformation of anisotropic heterogeneous crystalline matter is presented and compared with experiments.
1,573 citations