Static strain aging, a phenomenon caused by diffusion of solute atoms to dislocations, is an important contributor to the strength of substitutional alloys. Accurate modeling of this complex process requires both atomic spatial resolution and diffusional time scales, which is very challenging to achieve with commonly used atomistic computational methods. In this paper, we use the recently developed "diffusive molecular dynamics" (DMD) method that is capable of describing the kinetics of the solute segregation process at the atomic level while operating on diffusive time scales in a computationally efficient way. We study static strain aging in the Al-Mg system and calculate the depinning shear stress between edge and screw dislocations and their solute atmospheres formed for various waiting times with different solute content and for a range of temperatures. A simple phenomenological model is also proposed that describes the observed behavior of the critical shear stress as a function of segregation level.
Enabled by the technique of objective molecular dynamics, we reveal the unusual mechanics exhibited by nanoscale twisted graphene nanoribbons containing up to seven layers. Unlike in a linear-elastic plate, we find that the deformation practically does not contain contributions associated with in-plane shearing but largely with inhomogeneous stretching and compression of the constituent layers. The whole twisted structure undergoes shortening when no axial force is applied, while the constituent layers store various strain energies, depending on their location. We capture this behavior with a simple model and show that the deviations from the plate model are increasing with the number of layers and width of the ribbon. Our results are especially relevant for the experimental efforts of measuring graphene's shear modulus.
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