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Nucleation of dislocations from crack tips under mixed modes of loading: Implications for brittle against ductile behaviour of crystals

Xu, G. and Argon, A. S. and Ortiz, M. (1995) Nucleation of dislocations from crack tips under mixed modes of loading: Implications for brittle against ductile behaviour of crystals. Philosophical Magazine A, 72 (2). pp. 415-451. ISSN 0141-8610. doi:10.1080/01418619508239933.

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The variational boundary integral method of Xu and Ortiz is taken as a basis for studying dislocation nucleation from atomically sharp cracks under combined mode I-mode II loading. The tension-shear potential of Rice et al. is extended to allow for skewness in the shear resistance curve and to account for the surface production resistance which accompanies ledge formation. The calculated unstable equilibrium configurations of the incipient dislocations and the dependence of the associated activation energies on crack tip energy release rate are found to differ from the Rice-Beltz perturbation solution and the Schöck-Püschl more approximate solution. Simulations of dislocation nucleation on inclined slip planes reveal that, while tension softening facilitates nucleation, surface production resistance impedes it. The extent to which these two effects influence critical conditions for dislocation nucleation is quantified. The calculations suggest that homogeneous dislocation nucleation on inclined planes is not favoured for materials with all but the lowest of unstable stacking-energy-to-surface-energy ratios. This emphasizes the importance of heterogeneous dislocation nucleation and nucleation on oblique slip planes on which free surface production should play a much weaker role. The implications of these findings on the nucleation-controlled brittle-ductile transition in cleavage fracture are discussed.

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Ortiz, M.0000-0001-5877-4824
Additional Information:© 1995 Taylor & Francis. [Received 7 October 1994 and accepted 21 January 1995] This research was supported by the Office of Naval Research (ONR) under Contract No. N00014-92-J-4022. M.O. gratefully acknowledges support from the ONR under Contract No. N00014-90-J-1758. We acknowledge a number of fruitful discussions with Professor J. R. Rice and Professor E. Kaxiras of Harvard University and Dr R. Thomson of the National Institute of Standards and Technology. The computations were carried out with the facilities of the Mechanics of Materials group at the Massuchusetts Institute of Technology and those of the Solid Mechanics group at Brown University. Moreover, G.X. gratefully acknowledges also the earlier guidance of Professor R. J. Clifton of Brown University on fracture on the atomic scale.
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Office of Naval Research (ONR)N00014-92-J-4022
Office of Naval Research (ONR)N00014-90-J-1758
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ID Code:83900
Deposited By: Lydia Suarez
Deposited On:15 Dec 2017 00:54
Last Modified:15 Nov 2021 20:15

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