Grain-resolved statistical analysis of in-situ strain fields with combined image correlation and orientation mapping

Metallic polycrystals, the common form of engineering materials, are complex composites of anisotropic grains. For these materials, there is an intense drive to form high-fidelity crystal-plasticity models that build the mechanical response from the grain scales since such models can represent multiple microstructures of the same material without the need for repetitive experimentation. Historically, bulk diffraction has been the primary experimental method in validating these models. More recently, however, the real space method of digital image correlation (DIC) has been implemented with in-situ microscopy, generating immense data sets of high statistical significance and resolution, potentially offering a multi-scale validation of such models. This thesis features an area-scanning, high-resolution DIC variant with optical microscopy that has nominal 1 $\mu$m data spacing and thousands of grains field coverage, conducted in-situ with fine load intervals. The distinguishing feature of the current effort, however, is to form and incorporate a grain mask that will allow singling out strain fields of individual grains and their subzones. As critically, grain orientations are also predetermined over identical fields by electron back scatter diffraction. A basic material is opted in this study, high-purity FCC nickel, though its large anisotropy ratio (2.5) is opted for high strain heterogeneity among grains that will be the subject of a statistical analysis. The goals of the study are two fold, associated with elastic and plastic strains. The first part explores the measurement of elastic strains, which DIC is typically not sufficiently sensitive for, by improving accuracy with over-the-grain averaging. The measurement of grain-averaged elastic strain through partial unloads is then used to offer a technique for grain-averaged stress estimation. The second part explores the statistical trends in the plastic strain accommodation of grains with differing orientation and sizes.