The role of free surfaces on the formation of prismatic dislocation loops

Munday, Lynn; Crone, Joshua C.; Knap, Jaroslaw

doi:10.1016/j.scriptamat.2015.03.009

Cited by 15 publications

(26 citation statements)

References 19 publications

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“…7b, where the stress concentrations increase the resolved shear stress by only 5-10% in most of the simulation domain. While these results suggest that including the effects due to stress concentrations are not significant in determining the strength of voids as obstacles to dislocation glide, we note that stress concentrations have been shown to play an important role in controlling dislocation evolution around voids such as dislocation nucleation [32,33] and cross-slip [26].…”

Section: Stress Concentrationsmentioning

confidence: 62%

“…The image stress is then superimposed with the stress field due to the dislocations in an infinite body [23]. Conservation of the Burgers vector is assured by the introduction of virtual segments [25,20] extending from the surface-piercing dislocations to the center of the void [26] (c.f Fig. 1).…”

Section: Simulation Proceduresmentioning

confidence: 99%

“…When using numerical methods to compute the image stress field, it has been shown that high resolution is required to capture the large stress gradients as dislocations approach the surface [20,30,31,26]. We first examine the convergence in s c with respect to FEM element size.…”

Section: Mesh Convergencementioning

confidence: 99%

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Capturing the effects of free surfaces on void strengthening with dislocation dynamics

2015

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a b s t r a c tVoid strengthening in crystalline materials refers to the increase in yield stress due to the impediment of dislocation motion by voids. Dislocation dynamics (DD) is a modeling method well suited to capture the physics, length scales, and time scales associated with void strengthening. However, previous DD simulation of dislocation-void interactions have been unable to accurately account for the strong image forces acting on the dislocation due to the void's free surface. In this article, we employ a finite-element-based DD method to determine the obstacle strength of voids, defined as the critical resolved shear stress for a dislocation to glide past an array of voids. Our results demonstrate that the attractive image forces between the dislocation and free surface significantly reduce the obstacle strength of voids. Effects of surface mobility and stress concentrations around the void are also explored and are shown to have minimal effect on the critical stress. Finally, a new model relating void size and spacing to obstacle strength is proposed.

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Section: Stress Concentrationsmentioning

confidence: 62%

Section: Simulation Proceduresmentioning

confidence: 99%

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Capturing the effects of free surfaces on void strengthening with dislocation dynamics

2015

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“…This type of PDL 15 generation is favored under high strain rate loading where several dislocations are simultaneously nucleated on different glide planes around a defect. Still, such a mechanism may also be active at low strain rates if cross-slip of a nucleated dislocation is suppressed by energy barriers [5,6] or free surface effects [7].…”

Section: Introductionmentioning

confidence: 99%

“…The reduction in active dislocation sources for small voids is likely to cause void growth to transition from multiplication of existing dislocations to dislocation nucleation for voids below 500 nm [15]. For voids on the order of 50 nm, three-dimensional DD simulations have shown that locally activated modes of dislocation motion, including dislocation cross-slip and nucleation, are 50 indispensable for PDL generation [7]. These DD simulations have also drawn attention to the importance of void image stresses for cross-slip in PDL formation at low pressures.…”

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confidence: 99%

Prismatic and helical dislocation loop generation from defects

2016

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Plastic deformation induced by stress concentrations near crystal defects occurs through the generation of prismatic dislocation loops (PDL). The production of PDLs leads to void growth and particle decoherence. In this work we use dislocation dynamics simulations to characterize two mechanisms for PDL formation. The first mechanism corresponds to a classical model of PDL generation from dislocation nucleation. The second mechanism considers PDL generation through cross-slip of a screw dislocation intersecting the particle. We systematically study the effect of the crystal lattice and defect type on PDL generation for both mechanisms as a function of pressure. The simulations show image stresses produced by the dislocation's interaction with the free surface of a void suppresses PDL generation. The highest PDL generation rates are found for a dislocation nucleated from a void in a body-centered cubic lattice. Our simulations also show helical coiling of screw dislocations produces a continuous emission of PDLs without the need for dislocation nucleation at pressures as low as 1.0 GPa.(DD) simulations. DD simulations are capable of accurately capturing the motion of dislocations in the vicinity of large stress gradients due to material heterogeneities [13]. Two-and threedimensional DD simulations excluding cross-slip have been used to capture the later stages of void growth through multiplication of dislocations in the crystal [14,15]. In these simulations, the number of dislocation sources in the vicinity of a void activated by its stress concentration 45 increases with the void size. This observation may indicate higher void growth rates for large voids. The reduction in active dislocation sources for small voids is likely to cause void growth to transition from multiplication of existing dislocations to dislocation nucleation for voids below 500 nm [15]. For voids on the order of 50 nm, three-dimensional DD simulations have shown that locally activated modes of dislocation motion, including dislocation cross-slip and nucleation, are 50 indispensable for PDL generation [7]. These DD simulations have also drawn attention to the importance of void image stresses for cross-slip in PDL formation at low pressures. Dislocation cross-slip at free surfaces has also been shown in three-dimensional DD simulations to be an important generator of dislocation sources available for dislocation multiplication [6,16,17].The formation of PDLs through cross-slip is largely dependent on the crystal lattice which 55 determines both the number of secondary glide planes available for cross-slip and their orientation relative to one another. Here, we consider PDL formation in face-centered cubic (fcc), body-centered cubic (bcc), and hexagonal close-packed (hcp) lattices. In atomistic simulations of hydrostatically loaded voids, the availability of cross-slip planes leads to the formation of foursided rhombus PDLs in fcc lattices [3] and hexagonal or triangular PDLs in bcc lattices [18, 4]. 140

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Line Dislocation Dynamics Simulations with Complex Physics

Sills¹,

Aubry²

2018

Handbook of Materials Modeling

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The role of free surfaces on the formation of prismatic dislocation loops

Cited by 15 publications

References 19 publications

Capturing the effects of free surfaces on void strengthening with dislocation dynamics

Capturing the effects of free surfaces on void strengthening with dislocation dynamics

Prismatic and helical dislocation loop generation from defects

Line Dislocation Dynamics Simulations with Complex Physics

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