SUMMARY A connectivity of scale in terms of numbers of dislocations emitted at a point source and their average spacing has been established for both nanoindenters and crack tips. Determination of the numbers of parallel slip bands have been indirectly and in some cases directly observed allowing estimates of the number of dislocations per slip band. This gives a crude estimate for the back stress on the source which is surprisingly even much greater for sharp indenter tips than a crack tip. For the same two orders of magnitude displacement scale examined (10–1000 nm), this agreement gives some reason to believe that a consistent length scale is controlling the plastic deformation process. What we have learned with such small scale deformation processes leads to a refined brittle-to-ductile transition model via the Rice-Thomson and Lin-Thomson formalism. This is then easily modified for the hydrogen embrittlement process where either a cleavage plane, a grain boundary or a bi-material thin film interface is degraded. The key here is a length scale dictated by the closest approach of the last dislocation emitted in a shielding array. ACKNOWLEDGMENTS This research was supported by the Office of Naval Research under Grant N00014-91-J-1998. REFERENCES 1. Gerberich, W.W., Tymiak, N.I., Horstemeyer, M. and Baskes, M. (2001) ``Interpretation of Indentation Size Effects,” submitted to J. Appl. Mech. 2. Tymiak, N.I., Kramer, D.E., Bahr, D.F., Wyrobek, T.J. and Gerberich, W.W. (2001) “Plastic Strain and Strain Gradients at Very Small Indentation Depths,” Acta Mater. 49, in press. 3. Volinksy, A.A., Moody, N.R., Adhihetty, I. and Gerberich, W.W. (2001) “Interfacial Toughness Measurements of Thin Metal Films,” submitted to Acta Mater. 4. Katz, Y., Tymiak, N.I. and Gerberich, W.W. (2001) “Nanomechanical Probes as New Approaches to Hydrogen/Deformation Interaction Studies,” Engng. Fract. Mech., in press. 5. Gerberich, W.W. (2001) “Scaling Fracture Resistance in Thin Films,” submitted to ICF10. 6. Zhuk, A.V., Evans, A.G. and Hutchinson, J.W. (1998) J. Mater. Res. 13, No. 2 , 3555. 7. Zielinski, W., Lii, M.J., Marsh, P.G., Huang, H. and Gerberich, W.W. (1992) Acta Metall. Mater. 40 Parts I, II, III on pages 1861, 2873, 2883; Huang, H. and Gerberich, W.W., (1994) Acta Metall. Mater. 42 No. 3, 639; Gerberich, W.W., Volinsky, A.A. and Tymiak, N.I. (2000) MRS Symp. Vol. 594, 351. 8. Rice, J.R. and Thomson, R. (1974) Phil. Mag. 29, 73. 9. Lin, I.H. and Thomson, R. (1986) Acta Metall. 34, 187. 10. Gerberich, W.W., Lilleodden, E.T., Foecke, T.J. and Wyrobek, J.T. (1995), In Micromechanics of Advanced Materials, Chu, S.N.G., et al. (Eds.), TMS, Warrendale, PA, p. 29. 11. Harvey, S., Huang, H., Venkataraman, S., Zielinski, W. and Gerberich, W.W. (1993), J. Materials Research 8 No. 6, 1291, ibid. p. 1300. 12. Gerberich, W.W., Nelson, J.C., Lilleodden, E.T., Anderson, P. and Wyrobek, J.T. (1996) Acta Materialia 44, No. 9, 3585. 13. Hull, D. (1975) Introduction to Dislocations, 2nd Ed., Pergamon Press, Oxford, p. 224. 14. Chen, X. and Gerberich, W.W. (1991) Metall. Trans. A 22A, 59. 15. Qian, C.-Fu and Li, J.C.M. (1996) Mechanics of Materials 24, 11.
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