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Critical configurations for dislocation nucleation from crack tips

Xu, G. and Argon, A. S. and Ortiz, M. (1997) Critical configurations for dislocation nucleation from crack tips. Philosophical Magazine A, 75 (2). pp. 341-367. ISSN 0141-8610. doi:10.1080/01418619708205146.

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In the present paper, we analyse several activation configurations of embryonic dislocations nucleated from the tip of a cleavage crack. The activation configurations include nucleation on inclined planes, on oblique planes and on cleavage ledges and are treated within the classical framework of Peierls. A variational boundary integral method with an interplanar tension-shear potential developed earlier is used to solve for the saddle-point configurations of embryonic dislocation loops and their associated energies. Based on the assumption that the brittle-to-ductile transition in cleavage fracture is a nucleation-controlled process (as is expected to be the case in bcc transition metals such as α-Fe) the results of the calculations are used to estimate the brittle-to-ductile transition temperatures. It is concluded that only dislocation nucleation on cleavage ledges furnishes realistic values of the transition temperature. The homogeneous nucleation of dislocations on either inclined or oblique planes requires transition temperatures well above the melting point. This implies that nucleation of dislocations from a crack tip in intrinsically brittle crystals is only possible at local crack front heterogeneities such as cleavage ledges, and that the homogeneous nucleation of dislocations from a straight crack front is not possible. This conclusion is supported by the experimental observation that dislocation nucleation from a crack tip is a rare event which occurs preferentially at heterogeneities.

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Ortiz, M.0000-0001-5877-4824
Additional Information:© 1997 Taylor & Francis Ltd. [Received 25 January 1996 and accepted in revised form 16 June 1996] This research was supported by the Office of Naval Research (ONR) under Contract No. N00014-92-J-4022, with an additional supplement for the present simulation for which we are grateful to Dr R. Barsoum of that agency. M.O. gratefully acknowledges support from the ONR under Contract No. N00014-90-J1758. We acknowledge 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. Moreover, we acknowledge support from the Army Research Office under a Supplementary Equipment Grant No. P-33768-MA-RIP for purchases of computer equipment used in this work. The computations were carried out in the facilities of the Mechanics of Materials group at Massachusetts Institute of Technology, and those of the Solid Mechanics group at Brown University.
Funding AgencyGrant Number
Office of Naval Research (ONR)N00014-92-J-4022
Office of Naval Research (ONR)N00014-90-J1758
Army Research Office (ARO)P-33768-MA-RIP
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ID Code:83877
Deposited By: Lydia Suarez
Deposited On:13 Dec 2017 18:23
Last Modified:15 Nov 2021 20:14

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