Geometrically-Compatible Dislocation Pattern and Simulations of Plastic Deformations in Crystalline and Amorphous Materials
“Geometrically-Compatible Dislocation Pattern and Simulations of Plastic Deformations in Crystalline and Amorphous Materials”
14.12.2018, 10:30 - 11:30 + 14:00 - 16:00
17.12.2018, 09:30 - 11:30 + 14:00 - 16:00
Prof. Shaofan Li
Department of Civil and Environmental Engineering
The University of California-Berkeley
In this talk, we present two recent major developments on atomistic-informed multiscale simulations of plastic deformation in crystalline and amorphous solids. In the first part of the talk, we shall discuss a recently developed multiscale dislocation pattern dynamics called Multiscale Crystal Defect Dynamics (MCDD), in which we put forth a novel concept of Geometrically-consistent dislocation pattern. Based on this notion and higher order Cauchy-Born rule, we have developed a systematic approach that uses the generic geometrically-compatible dislocation pattern in crystals to establish a multiscale crystal plasticity formulation, or an atomistic-informed crystal plasticity. The main novelties of MCDD-based crystal plasticity are: (1) We have discovered a multiscale quasi-crystal patterns to represent geometrically-necessary dislocation pattern distribution, which is related to the original crystal structure, and (2) We adopt a fourth-order (four scales) Cauchy-Born rule-based strain gradient theory to model constitutive behaviors of various dislocation patterns and crystal defects, and we can simulate single crystal plasticity at sub-micro level or even higher levels. MCDD theory is an atomistic-informed macroscale or multiscale modeling theory that does not require any empirical formalism in the material theory. In the second part of this talk we shall introduce a recent development of the Multiscale Shear-Transformation-Zone (STZ) theory that can simulate plastic deformation in amorphous solids. In the multiscale STZ theory, we developed a concept of the representative sampling cell (RS-cell) to extend the notion of the unit cell in crystalline materials to amorphous solids. Moreover, we have developed a coarse-grained Parrinello-Rahman molecular mechanics-based Cauchy-Born rule, and by combining it with the RS-cells, we have successfully simulated plastic deformations in a Lennard-Jones binary solid, a benchmark amorphous solid, at macroscale including the yield stress, flow stress, the Bauschinger effect, and plasticity under cyclic loadings, etc. at macroscale level without any empirical material parameters.