Multiscale Modeling of Dislocation Mechanisms in Nanoscale Multilayered Composites
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1130-W13-01
Multiscale Modeling of Dislocation Mechanisms in Nanoscale Multilayered Composites Firas Akasheh1, Hussein M. Zbib2, Sreekanth Akarapu2, Cory Overman2, and David Bahr2 Tuskegee University, Tuskegee, AL 36088, U.S.A. 2 Washington State University, Pullman, WA 99164-2920, U.S.A.
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ABSTRACT It is well known that the mechanical behavior of nanoscale multilayered composites is strongly governed by single dislocation mechanisms and dislocation-interface interactions. Such interactions are complex and multiscale in nature. In this work, two such significant effects are modeled within the dislocation dynamics-continuum plasticity framework: elastic properties mismatch (Koehler image forces) and interface shearing in the case of weak interfaces. The superposition principle is used to introduce the stress fields due to both effects solved for by finite elements. The validation of both methodologies is presented. Furthermore, it was found that the layer-confined threading stress of a dislocation in hair-pin configuration increases if the layer is surrounded by layers made of a stiffer material and that this strengthening effect grows more significant as the layer thickness decreases. The observation made through molecular dynamics, that weak interfaces act as dislocation sinks, was also captured with our approach. A dislocation is attracted to the interface independent of its sign or character. Also the force increases sharply as the dislocation approaches the interface. These findings agree with published molecular dynamics simulations and dislocation-based equilibrium models of this type of interaction. INTRODUCTION Nanoscale metallic multilayered (NMM) composites have been shown to exhibit ultra high strength on the order of GPa, much higher (3-5 times) than the value predicted by the ruleof mixtures. As shown by the work of several researchers, dislocation interactions such as pileups and cell structure formation, which are dominant at the micro and bulk scales, are not possible at the nanoscale due to the restrictions imposed by confinement in nano-thick layers. Instead a deformation regime exists which is dominated by single dislocation interactions, anisotropic effect, heterogeneity effects (image forces), interface properties, and the nature of dislocation-interface interactions. In this work we present a multiscale dislocation dynamics (DD)-continuum modeling approach to model two of such effects: image forces due to elastic property mismatch and interface shearing in the case of weak interfaces. The fact that most strengthening mechanisms in NMM composites are multiscale in nature imposes a challenge to modeling. For example, through molecular dynamics (MD) simulations, Hoagland et al [1] found out that due to their weak resistance to shearing, incoherent interfaces can be sheared by a dislocation approaching the interface which in turn leads to the absorption of the dislocation by the interface and its consequent core spreading and trapping within the interface. Capturing the effect of this fundamenta
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