Journal
ACTA MATERIALIA
Volume 61, Issue 5, Pages 1469-1477Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.actamat.2012.11.023
Keywords
Discrete dislocation dynamics; Plastic deformation; Hardening; Strengthening mechanism; Scale effects
Funding
- NSF Materials Research Science and Engineering Center on Micro and Nanomechanics of Materials at Brown University [DMR-0520651]
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The operation of a single Frank Read (FR) source in the presence of a spatial stress gradient is studied using 3D discrete-dislocation dynamics (DDD) simulations and analytic models. Under a sufficiently large stress gradient, the FR source shows a new stable configuration controlled by the low-stress region of the graded stress field. Successive emissions from the source generate a growing dislocation pile-up that exerts an increasing back stress on the source, leading to hardening. The operation of the FR source in the gradient field can be well-approximated by a single critical stress at a unique critical location, allowing for the development of an analytic model of the source operation. These results are applied to rationalize the size-scaling of strength measured in simulations of single-crystal beam bending using DDD and in experiments on bending of single:crystal cantilever beams. This work demonstrates that size effects in plasticity emerge naturally from the mechanics of dislocation sources operating within a stress gradient, and in this case the relevant material length scale is the length of the FR source. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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