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Experimental Assessment of Strain Gradient Plasticity

Published online by Cambridge University Press:  21 March 2011

Monica M. Barney ,
Geoffrey H. Campbell ,
James S. Stölken ,
Adam J. Schwartz ,
Jürgen M. Plitzko ,
Wayne E. King  and
John W. Morris Jr.
Monica M. Barney
Affiliation:
Chemistry and Materials Science Directorate, University of California, Lawrence Livermore National Laboratory P.O. Box 808, Livermore, CA 94550, U.S.A.
Geoffrey H. Campbell
Affiliation:
Chemistry and Materials Science Directorate, University of California, Lawrence Livermore National Laboratory P.O. Box 808, Livermore, CA 94550, U.S.A.
James S. Stölken
Affiliation:
Chemistry and Materials Science Directorate, University of California, Lawrence Livermore National Laboratory P.O. Box 808, Livermore, CA 94550, U.S.A.
Adam J. Schwartz
Affiliation:
Chemistry and Materials Science Directorate, University of California, Lawrence Livermore National Laboratory P.O. Box 808, Livermore, CA 94550, U.S.A.
Jürgen M. Plitzko
Affiliation:
Chemistry and Materials Science Directorate, University of California, Lawrence Livermore National Laboratory P.O. Box 808, Livermore, CA 94550, U.S.A.
Wayne E. King
Affiliation:
Chemistry and Materials Science Directorate, University of California, Lawrence Livermore National Laboratory P.O. Box 808, Livermore, CA 94550, U.S.A.
John W. Morris Jr.
Affiliation:
Chemistry and Materials Science Directorate, University of California, Lawrence Livermore National Laboratory P.O. Box 808, Livermore, CA 94550, U.S.A. Materials Sciences Division, Ernest Orlando Lawrence Berkeley National Laboratory, One Cyclotron Road, MS 66-200, Berkeley, CA 94720, U.S.A.
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Abstract

Classical plasticity theories generally assume that the stress at a point is a function of strain at that point only. However, when gradients in strain become significant, this localization assumption is no longer valid. These conventional models fail to display a ‘size effect’. This effect is seen experimentally when the scale of the phenomenon of interest is on the order of several microns. Under these conditions, strain gradients are of a significant magnitude as compared to the overall strain and must be considered for models to accurately capture observed phenomena.

The mechanics community has been actively involved in the development of strain gradient theories for many years. Recently, interest in this area has been rekindled and several new approaches have appeared in the literature. Two different approaches are currently being evaluated. One approach considers strain gradients as internal variables that do not introduce work conjugate higher order stresses. Another approach considers the strain gradients as internal degrees of freedom that requires work conjugate higher order stresses. Experiments are being performed to determine which approach models material behavior accurately with the least amount of complexity. A key difference between the two models considered here is the nature of the assumed boundary conditions at material interfaces. Therefore, we are investigating the deformation behavior of aluminum/sapphire interfaces loaded under simple shear. Samples are fabricated using ultra-high vacuum diffusion bonding. To determine the lattice rotations near the boundary, we are examining the samples with both electron backscatter diffraction methods (EBSD) in the scanning electron microscope and with a variety of diffraction techniques in the transmission electron microscope. The experimentally found boundary conditions shall be subsequently used to determine whether the simpler internal variable model is adequately descriptive or if the greater complexity associated with the internal degree of freedom approach is warranted.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 653: Symposium Z – Multiscale Modeling of Materials-2000 , 2000 , Z8.6.1
Copyright
Copyright © Materials Research Society 2001

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References

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