Wednesday 2:00 PM

March 2, 2022

Room: 253A

Location: Anaheim Convention Center

Line defects known as dislocations are the carriers of plastic deformation in crystalline materials. Because of the computational limitations of discrete dislocation simulations, the evolution of mesoscale plasticity is often studied using continuum dislocation dynamics (CDD) theories. In this presentation, we contemplate the approximations made by two common CDD models: the vector-density theory assumes the underlying dislocations to be parallel to the continuum vector-density, while higher-order models rely on parallel dislocations having equal curvature. This paper numerically evaluates these postulates by means of local probability density functions for orientations and curvatures. To do this, we introduce a partition of the material sample into sub-volumes, and examine statistical measures of the dislocation distribution within each sub-volume. It is found that the probability functions are concentrated around the directions of the mean fields (vector-density and curvature density). In particular, this validates the vector-density approach for suitably small scales.

Crystal Plasticity models are increasingly used in engineering applications to obtain microstructure-sensitive mechanical response of polycrystalline materials. These models require a proper consideration of the single crystal deformation mechanisms, a representative description of the microstructure, and an appropriate scheme to connect the microstates with the macroscopic response. The latter can be based on homogenization, which relies on a statistical description of the microstructure, or on full-field solutions, which requires a spatial description of the microstructure. Full-field Fast Fourier Transform (FFT)-based methods are attractive due their relative higher efficiency and direct use of voxelized microstructural images. In this talk, we will report recent progress on FFT-based polycrystal plasticity, with emphasis in novel implementations for advanced constitutive regimes, including large-strain elasto-visco-plasticity, strain-gradient plasticity, field dislocation mechanics, and dynamic deformation regimes including inertia, along with integration with emerging 3-D characterization methods in Experimental Mechanics.

Dislocation dynamics simulations are very useful in advancing our knowledge on plastic deformation at the intragranular level. Recent advances in non-destructive space/time-resolved characterization techniques e.g., dark-field X-ray microscopy, open the possibility of comparing and validating dislocation dynamics simulation predictions. However, the fine temporal-resolution required to run most dislocation dynamics models often prevents a one-to-one comparison with experiments running at time scales that are several orders of magnitude higher than those achievable by simulations.Bearing this challenge in mind, we have developed a time-explicit Runge-Kutta Discontinuous Galerkin Finite Element (RKDG-FE) scheme to solve the Field Dislocation Mechanics (FDM) problem. FDM is a continuum theory that rigorously (mathematically and thermo-mechanically) connects dislocation transport and interactions to the static/dynamic response of single/poly-crystals. By implementing FDM numerically with RKDG-FE, we show that it is possible to model transport and interaction of individual dislocations at experimental time scales while keeping a “compact dislocation core”.

Titanium alloys are superior structural materials based on high specific strength, fracture toughness, and have potential as armor in defense applications. Our method to understand Ti-6Al-4V as armor material is to computationally model dislocation motion and microstructural evolution of a dual-phase lamellar alloy under a varied parametric space consisting of beta phase volume fraction, grain size, loading orientation, and strain rate, ultimately considering ballistic strain rate conditions such as dε/dt ≥ 100 s