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

Abstract

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.

Edge dislocations bowing out from a row of collinear obstacles in Al

“…(2) is known to overestimate the critical stress because of a number of significant simplifications in the model [20], which is also demonstrated in our simulations in that the critical stresses for an isolated pair of obstacles surprisingly agree with Eq. (2) which assumes an infinite array of obstacles.…”

“…In dislocation/precipitate interactions, Bacon et al [17] included three precipitates in one simulation supercell with PBCs to represent an infinite row. Crone et al [20] found that introducing additional voids beyond three doesn't show a significant influence on the critical depinning stress in dislocation/void interactions. Studies of a dislocation passing a random array of obstacles have been pursued using line tension models [21][22][23] and DD simulations [24].…”

“…2(c), at τ zy III ). For each critical event, the stress τ c k = τ zy k − Δτ zy (k = I, II,or III) is taken as the critical shear stress [41] and the segment shape at the end of an energy minimization subject to τ c k is recorded as the critical dislocation configuration [20]. In particular for the critical event III, in the case of n = 1, we found that (1) as each element has a larger number of atoms, τ zy III becomes smaller, (2) the relative coarsegraining error of τ zy III for 2197 atoms per element is approximately 9.5%, with respect to the fully resolved atomistic simulation.…”

On the role of initial void geometry in plastic deformation of metallic thin films: A molecular dynamics study

“…Voids, frequently introduced during manufacturing, processing, or irradiation, play a significant role in mechanical properties of metals by altering the microstructure and influencing dislocation motion [1][2][3]. Dislocationvoid interactions are important mechanisms of the strain hardening in which a higher applied shear stress is required for dislocations to bypass even nmsized voids [4].…”

The effects of initial void and dislocation on the onset of plasticity in copper single crystals

“…Although a void is generally considered to be the activated location for dislocation nucleation that promotes the incipient plasticity, the obstacle strength of voids was defined by evaluating the critical stress for a dislocation to glide past an array of voids. 16 Coincidentally, the depinning stress of an edge dislocation from a void in copper was also evaluated by the molecular dynamics (MD) simulation, 17 which contains less artificial criteria or parameters in the modeling of dislocation activities. To perform a multiscale model-based simulation, the atomic-scale study is a key component for which there is a lack of understanding.…”