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Energy considerations regarding yield points during indentation

Published online by Cambridge University Press:  31 January 2011

D. F. Bahr*
Affiliation:
Mechanical and Materials Engineering, Washington State University, Pullman, Washington 99164–2920
D. E. Wilson
Affiliation:
Mechanical and Materials Engineering, Washington State University, Pullman, Washington 99164–2920
D. A. Crowson
Affiliation:
Nanomechanics Research Laboratory, Hysitron Inc., Minneapolis, Minnesota 55439
*
a)Address all correspondence to this author. e-mail: bahr@mme.wsu.edu
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Abstract

Two experiments that probe the nature of the rapid transition from elastic to plastic deformation are described. The load, and therefore stress, at which this yield point occurs is shown to be relatively independent of temperature in an iron alloy. When stresses lower than those required to generate a yield point during loading are applied for times between seconds and minutes, yielding occurs while the sample is under an applied stress. The time to generate a yield point increases as the applied stress is decreased. The possibilities of dislocation glide loop nucleation, double kink nucleation, and dislocation breakaway from pinning points are examined. Only glide loop nucleation appears to match the experimental observations. Criteria based on the stress-volume requirements of glide loop nucleation and the stress field underneath an indenter are presented which qualitatively describe the experimental data.

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Copyright
Copyright © Materials Research Society 1999

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