A numerical method based on Fast Fourier Transforms to compute the thermoelastic response of heterogeneous materials is presented and validated by comparison with analytical solutions of the Eshelby inclusion problem. Spherical and cylindrical, homogeneous and inhomogeneous inclusion configurations are used to validate the results of the proposed spectral method. Dependencies of the numerical solutions on homogeneity, geometry and resolution are also explored, and the differences with respect to known analytical solutions are quantified and discussed. In the case of homogeneous inclusions, the proposed numerical method is direct, i.e. does not require iteration. Using enough resolution, the micromechanical fields predicted for these simple geometries are shown to be in good agreement with the analytical results. The specific way in which inclusions are voxelized is also explored, and its effect on local fields near interfaces is assessed.

Electron backscatter diffraction analysis was employed to compute the closest orientation relationship and the distribution of intervariant boundary character in a lath martensitic microstructure. The misorientations were close to the Kurdjumov-Sachs orientation relationship. The intervariant crystallographic plane distribution exhibited a relatively high anisotropy with a tendency for the lath interfaces to terminate on (110) planes. This results from the crystallographic constraints associated with the shear transformation rather than a low energy interface configuration. The lath martensite habit plane was determined to be mostly (110) or near (110). The relative populations of boundaries with [111] and [110] misorientations were greater than other high index misorientations, mostly characterized as (110) symmetric tilt and (110) twist boundary types, respectively. Analysis with homology metrics of the connectivity in the lath martensitic microstructure revealed the connectivity dominated by population of misorientation angle and boundary plane type. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

A micro-tensile test system equipped with in situ monitoring of the in-plane displacements of a surface and an electron backscattered diffraction-based serial-sectioning technique were used to study the deformation (up to 2.4 pct axial plastic strain in tension) of a polycrystalline nickel micro-specimen. The experimental data include the global engineering stress-engineering strain curve, the local mesoscopic in-plane displacement and strain fields, the three-dimensional microstructure of the micro-specimen reconstructed after the tensile test, and the kernel-average misorientation distribution. The crystal plasticity finite element method using elasto-viscoplastic constitutive formulations was used to simulate the global and local deformation responses of the micro-specimen. Three different boundary conditions (BCs) were applied in simulation in order to study the effects of the lateral displacement (perpendicular to the loading direction) of the top and bottom faces of the specimen gage section. The simulation results were compared to the experimental results. The comparison between experiment and simulation results is discussed, based upon their implications for understanding the deformation of micro-specimens and the causes associated with uncertainties embedded in both experimental and numerical approaches. Also, the sensitivity of BCs to near-field and far-field responses of the micro-specimen was systematically studied. Results show that the experimental methodology used in the present study allows for limited but meaningful comparisons to crystal plasticity finite element simulations of the micro-specimen under the small plastic deformation.

Abstract Low-symmetry crystals and polycrystals have anisotropic mechanical properties which, given better understanding of their deformation modes, could lead to development of next generation materials. Understanding how grains in a bulk polycrystal interact will guide and improve material modeling. Here, we show that tensile twins, in hexagonal close-packed metals, form where the macroscopic stress does not generate appropriate shear stress and vice versa. We use non-destructive high-energy X-ray diffraction microscopy to map local crystal orientations in three dimensions in a series of tensile strain states in a zirconium polycrystal. Twins and intragranular orientation variations are observed and it is found that deformation-induced rotations in neighboring grains are spatially correlated with many twins. We conclude that deformation twinning involves complex multigrain interactions which must be included in polycrystal plasticity models.